corrosion inhibiting mechanism of nitrite ion on the...
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Research ArticleCorrosion Inhibiting Mechanism of Nitrite Ion onthe Passivation of Carbon Steel and Ductile Cast Ironfor Nuclear Power Plants
K T Kim1 H W Kim1 H Y Chang2 B T Lim2 H B Park2 and Y S Kim1
1Materials Research Centre for Energy and Clean Technology School of Materials Science and EngineeringAndong National University 1375 Gyeongdongro Andong 760-749 Republic of Korea2Power Engineering Research Institute KEPCO Engineering amp Construction Company 8 Gumiro Bundang SeongnamGyeonggi 463-870 Republic of Korea
Correspondence should be addressed to Y S Kim yikimanuackr
Received 1 July 2015 Accepted 27 September 2015
Academic Editor Randhir Singh
Copyright copy 2015 K T Kim et alThis is an open access article distributed under theCreative CommonsAttribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
While NaNO2addition can greatly inhibit the corrosion of carbon steel and ductile cast iron in order to improve the similar
corrosion resistance ca 100 times more NaNO2addition is needed for ductile cast iron compared to carbon steel A corrosion and
inhibition mechanism is proposed whereby NO2
minus ion is added to oxidize The NO2
minus ion can be reduced to nitrogen compoundsand these compounds may be absorbed on the surface of graphiteTherefore since nitrite ion needs to oxidize the surface of matrixand needs to passivate the galvanic corroded area and since it is absorbed on the surface of graphite a greater amount of corrosioninhibitor needs to be added to ductile cast iron compared to carbon steel The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semiconductive properties and its resistance is increased the passive current density is
thus decreased and the corrosion rate is then lowered In addition the film is mainly composed of iron oxide due to the oxidationby NO
2
minus ion however regardless of the alloys nitrogen compounds (not nitrite) were detected at the outermost surface but werenot incorporated in the inner oxide
1 Introduction
Since the operation period of nuclear power plants aroundthe world increases each year the degradations in buriedpipes have become an important issue in the nuclear powerindustry Many reports have been carried out on the degra-dation of buried pipes such as the lining damage of buriedpipe for a component cooling seawater system at Hanul 1unit (Korea) 1998 [1] the leakage of buried pipe for a fireprotection system at Hanbit 4 unit (Korea) 2006 [2] andthe cooling water leakage (ca 227m3) at Indian Point 2unit (USA) 2009 [3] In the case of buried pipe its corrosionenvironment differs from that of air-exposure pipe Whilethe interior of the pipe becomes corroded by fluids theoutside undergoes mechanical and chemical damage fromthe soil Also even though leakage occurs in the buried
pipe it is very difficult to determine the reason for theleakage and to fix it timely because of a lack of accessibilityVarious pipes of ca 30sim40 km per unit of nuclear powerplant have been buried and operated and depending on theapplication system and water chemistry they are separatelymaintained as the large diameter pipes and the other pipesLarge diameter pipes are installed to convey the primarycooling seawater system the secondary cooling seawatersystem and the circulating system the cooling water ofwhich is seawater [4 5] About 70 of pipes are PrestressedConcrete steel Cylinder Pipe (PCCP) and Prestressed Con-crete Pipe (PCP) Another pipework has been installed forconveying water for the fire-fighting system which was madeof carbon steel or cast iron [6] The types of damage thatcan occur in buried pipe include leakage fracture blockageand deformation by mechanical impact Secondary damage
Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2015 Article ID 408138 16 pageshttpdxdoiorg1011552015408138
2 Advances in Materials Science and Engineering
Table 1 Chemical compositions of experimental alloys
Alloys Chemical compositions wtC Mn P S Si Cr Cu Mo Ni V Fe
CS 026 086 0014 0005 023 004 0057 0033 0029 0008 balDCI 401 017 0022 0026 153 mdash 0023 0028 0059 0016 balCS carbon steel ASME SA106 GrB DCI ductile cast iron KS D4311
then occurs including general corrosion pitting microbialinduced corrosion scale buildupmultiplication ofmicrobialand fatigue Therefore several corrosion control methodssuch as painting and coating electrical protection and theuse of corrosion inhibitors have been applied [7ndash9] Carbonsteel and cast iron used in a closed cooling system may becorroded In order to control this type of corrosion problemcorrosion inhibitors such as nitrite silicate molybdate andhydrazine have been used among them nitrite is widely usedbecause of its excellent performance
Many reports have been presented on corrosion inhi-bition by nitrite including Fe
2O3formation on steel by
nitrite addition [10] adherent protective oxide on steel [11]correlation of oxygen and nitrite on steel corrosion [12]comparative study of nitrite including various inhibitors onsteel [13ndash15] and inhibition effect of nitrite on steel withtime [16 17] Nitrite as an anodic inhibitor has a tendencyto increase anodic polarization and thus increase corrosionpotential to a noble direction and decrease the corrosioncurrent Since nitrite contains a strong oxidizing power itoxidizes the surface and forms Fe
2O3[18] Formation rate of
protective film due to nitrite is very fast and thus among theseveral corrosion inhibitors nitrite shows good performance[19]
On the other hand ductile cast iron has a very differentmicrostructure to that of carbon steel Spheroidized graphiteforms in the matrix and galvanic corrosion occurs betweenthe matrix and graphite Also cast iron does not have highcorrosion resistance to various corrosion environments andit should be protected by a coating As described abovemany reports have been presented on the corrosion inhibitionof carbon steel but there are few reports on cast ironTherefore in this work corrosion inhibition effects of nitriteon carbon steel and ductile cast iron for nuclear powerplant pipework using chemical and electrochemical methodswere evaluated This work attempts to clarify the corrosioninhibition mechanism between steel and iron by NaNO
2
addition
2 Experimental Procedure
21 Materials and Corrosion Environments Commercial car-bon steel (ASME SA106 GrB) [20] and ductile cast iron (KSD4311) [21] were used in this work and Table 1 shows thechemical composition of the experimental alloys
The test solution was simulated primary cooling waterused in the nuclear power plant The standard solution was16 ppm NaCl and its pH was modified with 1N NaOHsolution and the range of pH 9 plusmn 02 was controlled NaNO
2
as a corrosion inhibitor was added as a ppm order
22 Corrosion Tests
221 Immersion Corrosion Test A specimen was cut to a sizeof 20times 20times 5mmand each surfacewas groundusing 120 SiCpaper Immersion tests were carried out in a stagnant solutioncondition (500mL glass flask) and in a circulating solutionin which test chamber has a dimension of 50 times 100 times 50 cmand the flow rate was 5 Lmin After the immersion tests eachspecimen was cleaned with acetone and alcohol and was thendried the corrosion rate was then determined
222 Electrochemical Tests Specimens were cut to a sizeof 20 times 20mm and after electrical connection they wereepoxy-mounted and the surface was ground using 600SiC paper and coated with epoxy resin except an area of1 cm2 A polarization test was performed using a potentiostat(Gamry DC105) and the reference electrode was a saturatedcalomel electrode and the counter electrode was Pt wire Thetest solution was deaerated using nitrogen gas at the rateof 100mLmin for 30 minutes and the scanning rate was033mVsec In order to measure the AC impedance thespecimens were ground using 2000 SiC paper and thenpolished using a diamond paste (3120583m)The test solution wasthe same as that of the polarization test AC impedance mea-surement was performed using an electrochemical analyzer(Gamry EIS 300) Before measuring passivation was treatedat +400mV(SCE) for carbon steel and 0mV(SCE) for ductilecast iron for 30 minutes AC impedance was measured ata passivation potential from 10 kHz to 001Hz and the ACvoltage amplitude was 10mV Also a Mott-Schottky plot wasprepared to determine the semiconductive properties of thepassive film The specimen preparation was the same as thatfor AC impedance measurement and the DC amplitude was10mV (peak-to-peak) at 1580Hz of the AC frequency [22]The capacitance was measured at the scan rate of 50mVsecfrom +1V(SCE) to minus15 V(SCE)
223 Surface Analysis X-ray photoelectron spectroscopy(XPS K-alpha (Thermo VG UK) Al-K
120572(14866 eV 12 kV
3mA)) was analyzed to determine the chemical state ofseveral species of the passive film The specimen was cutto a size of 20 times 20 times 5mm and then ground with 2000SiC paper and polished with a 3 120583m diamond paste thespecimenwas finally cleaned with alcohol using an ultrasoniccleaner Carbon steel and ductile cast iron were passivatedby immersion for 24 hours in 1000 ppm and 100000 ppmNaNO
2 respectively The depth profile was obtained every
5 seconds by Ar-sputtering Also an Electron Probe MicroAnalyzer (EPMA EPMA-1600 15 KV) was used to identifythe elemental distribution of the passivated surface Optical
Advances in Materials Science and Engineering 3
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Figure 1 Effect of NaNO2addition on corrosion rate in circulating and stagnant simulated cooling water at 25∘C (a) carbon steel and (b)
ductile cast iron
Microscope (OM Zeiss Axiotech 100HD) and SEM-EDS(Tescan Vega II LMU) and a 3Dmicroscope (Zeiss KH-7700)were used
224 Corrosion Simulation In order to determine the differ-ence in galvanic corrosion between the matrix and spheroid-ized graphite of the ductile cast iron computer simulationwas performed using COMSOL Multiphysics software Tafelslopes of anodic and cathodic reactions were used and therate controlling equation applied in this modeling was thesecondary corrosion condition
3 Results and Discussion
31 Effect of Nitrite Concentration Figure 1 shows the effectof NaNO
2addition on corrosion rate in circulating and
stagnant simulated coolingwater in the air at 25∘C In the caseof carbon steel increasing NaNO
2concentration reduced
significantly the corrosion rate of carbon steel When theinhibitor was absent the rates of stagnant and circulatingsolutions were 023 and 048mmyear respectively Also theeffect of nitrite ion was stronger in the circulating solutionthan in the stagnant solution However in the case of ductilecast iron the effect of nitrite addition was similar to that ofcarbon steel but the similar corrosion inhibition of ductilecast iron needs a significant addition of NaNO
2 When the
inhibitor was absent the rates of stagnant and circulatingsolutions were 047 and 084mmyear respectively Eventhough the NaNO
2addition was increased the corrosion
rate of ductile cast iron showed relatively higher values thanthose of carbon steel The corrosion of carbon steel can beinhibited at near 100 ppmNaNO
2addition but the corrosion
of ductile cast iron can be inhibited by an addition of morethan 10000 ppm NaNO
2 Moreover while the corrosion of
carbon steel can be inhibited more readily by the circulation
of the solution the circulation facilitated the corrosion ofductile cast iron
The open circuit potential with immersion time byNaNO
2addition in circulating (solid symbol) and stagnant
(open symbol) simulated cooling water in the air at 25∘Cwas shown in Figure 2 Regardless of the alloys used and thecirculation of solution the open circuit potential of the spec-imen without NaNO
2addition decreased with immersion
time However the open circuit potential of the specimenwith NaNO
2addition increased and its tendency depends
on the alloys In the case of carbon steel an addition of100 ppm NaNO
2increased the open circuit potential and the
circulation stimulated its rate Also in the case of ductile castiron a greater concentration (about 100 times) of NaNO
2is
needed for a similar effect of NaNO2addition
The effect of NaNO2addition on the polarization behav-
ior in deaerated simulated cooling water at 25∘Cwas revealedin Figure 3 the scanning rate was 033mVsWhenNaNO
2is
not added carbon steel and ductile cast iron dissolved readilywithout the passivation by anodic polarization With 10and 100 ppm NaNO
2additions carbon steel revealed active-
passive transition but the passive current density was highand transpassive behavior occurred Ductile cast iron did notshow an active-passive transition until a 10000 ppm NaNO
2
addition From a 1000 ppm NaNO2addition carbon steel
showed excellent passivation behavior but the ductile castiron revealed the best passivation curve from 100000 ppmNaNO
2addition This tendency is coincident with the result
of the immersion test shown in Figure 1Figure 4 shows the corrosion rate due to the NaNO
2
addition obtained from the immersion test (circulationcondition) shown in Figure 1 and the current density wasobtained at +400mV(SCE) as shown in Figure 3 Regardlessof the chemical or electrochemical tests the corrosion ofcarbon steel can be inhibited by a small NaNO
2addition
4 Advances in Materials Science and Engineering
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V(S
CE))
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Figure 2 Open circuit potential with immersion time by nitrite addition in circulating (solid symbol) and stagnant (open symbol) simulatedcooling water at 25∘C (a) carbon steel and (b) ductile cast iron
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Figure 3 Effect of NaNO2addition on polarization behavior in deaerated simulated cooling water at 25∘C (scanning rate 033mVs) (a)
carbon steel and (b) ductile cast iron
(ca 1000 ppm) but the corrosion of ductile cast iron couldbe only inhibited by a significant NaNO
2addition (ca
100000 ppm)That is it was demonstrated that the differencein the NaNO
2addition needed between carbon steel and
ductile cast iron was about 100 times
In order to determine the resistance of the passive filmformed on the surface of carbon steel and ductile cast iron byNaNO
2addition the AC impedance was measured Figure 5
shows the effect of NaNO2addition in Nyquist plot obtained
from AC impedance measurement at +400mV(SCE) for
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(Ac
m2)
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Figure 4 Comparison of (a) corrosion rate (circulation condition) from Figure 1 and (b) current density obtained at +400mV (SCE) ofFigure 3 by NaNO
2addition to simulated cooling water
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Figure 5 Effect of NaNO2addition on Nyquist plot obtained from AC impedance measurement in deaerated simulated cooling water at
25∘C (a) carbon steel at +400mV (SCE) and (b) ductile cast iron at 0V (SCE)
carbon steel and 0V(SCE) for ductile cast iron in deaeratedsimulated cooling water at 25∘C In the case of carbon steel astable passive film could not be formedwith a 10 ppmNaNO
2
addition and very small impedance (156 kohm) was thusshownA 100 ppmNaNO
2addition formed a passive film but
its polarization resistancewas small (1946 kohm)However astable passive film (4425 kohm)was formedwith a 1000 ppmNaNO
2addition In the case of ductile cast iron a stable
passive film (3337 kohm) was formed with a 100000 ppmNaNO
2addition As shown in Figures 1 and 4 the difference
of corrosion inhibition between carbon steel and ductile castiron due to the NaNO
2addition was closely related to the
formation of a stable passive film on the surface
32 Corrosion Inhibition Mechanism of Carbon Steel andDuctile Cast Iron by Nitrite Ion It was revealed that thedifference in the effect of corrosion inhibition due to NaNO
2
addition between carbon steel and ductile cast iron was about100 times through the immersion test and electrochemicaltests as described above As shown in Table 1 the significant
6 Advances in Materials Science and Engineering
50120583m
(a)
50120583m
(b)
(c) (d)
Figure 6 Optical microstructures (a b) and SEM images (c d) (a c) carbon steel and (b d) ductile cast iron
difference in the composition between the two alloys iscarbon content Figure 6 shows optical microstructures andSEM images for carbon steel and ductile cast iron In the caseof carbon steel ferrite and pearlite phases can be observedHowever in the case of ductile cast iron spheroidized phaseswere formed in the ferrite matrix and the spheroidizedphase was shown to be graphite by SEM-EDS analysis Thesepictures show the typical microstructures of carbon steel andductile cast iron
In order to determine the effect of NaNO2addition
on the corrosion morphologies of ductile cast iron afterimmersion the corroded surface was observed The effect ofNaNO
2addition on the surface appearance of ductile cast
iron after the immersion test in simulated cooling water for 3hours at 25∘C was presented in Figure 7 Figure 7(a) showsthe addition of 0 ppm NaNO
2and Figure 7(b) shows the
addition of 10000 ppmNaNO2When noNaNO
2was added
the ductile cast iron was generally corroded on the entiresurface However when 10000 ppm NaNO
2was added (this
addition of which is not sufficient to inhibit corrosion ofductile cast iron as shown in Figures 1 and 3) the iron wascorroded locally near the spheroidized graphite and the cor-roded areas were agglomerated Figure 8 shows the corrosionmorphologies of ductile cast iron in which ductile cast iron
was corroded for 3 hours in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C Figure 8(a) shows the surface
contour using a 3D microscope and local corrosion near thespheroidized graphite was confirmed Figure 8(b) shows anSEM image of the corroded area showing that it was corrodedspherically near the graphite and thenfinally the graphite hadchipped off Also corrosion products and even cracks wereobserved near the chipped-off graphite These figures showthat galvanic corrosion took place in the ductile cast iron Itis well known that graphite is nobler than matrix iron [23]
The galvanic corrosion between graphite and matrixiron was simulated using a COMSOLMultiphysics programAnodic and cathodic Tafel slopes (+108mV and minus206mVresp) were applied to calculate the corrosion behavior of thecorroding and noncorroding areas Figure 9 shows computer3D simulation results of the corrosion propagation of ductilecast iron occurring in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C At the initial stage (0 hour)
the potential difference between graphite (the center) andmatrix (left and right) is shown by the blue and red colorsrespectively By increasing the immersion time the matrixnear the graphite corroded and the corrosion depth wasincreased its depth was greater near the graphite (Thisis the distance effect observed in galvanic corrosion) This
Advances in Materials Science and Engineering 7
50120583m
(a)
50120583m
(b)
Figure 7 Effect of NaNO2addition on surface appearance of ductile cast iron after the immersion test in simulated cooling water for 3 hours
at 25∘C (a) 0 ppm NaNO2and (b) 10000 ppm NaNO
2
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Height 10835120583m
Max 12584120583m
Width 1Width 2
(a) (b)
Figure 8 Corrosion morphologies of ductile cast iron corroded in stagnant simulated cooling water (10000 ppm NaNO2) for 3 hours at
25∘C (a) 3D microscope and (b) SEM image
simulation result differs from that shown in Figure 8(b) Thisdifference could be due to the characteristics of the graphite(However it should be noted that the COMSOLMultiphysicsprogram does not simulate the mechanical damage in gal-vanic corrosion)The crystal structure of graphite is covalentbonded with neighboring atoms in the same layer althoughlayers are van der Waals bonded together [24 25] and thusthe bonding force of graphite is very weak Therefore it isconsidered that the matrix is corroded galvanically and thatthe graphite is protruded and then graphite is peeled off layerby layer because of the weak bonding force of graphite
Figure 10 shows the elemental distribution analyzed usingEPMA on the surface of ductile cast iron passivated in
simulated cooling water (100000 ppm NaNO2) at 25∘C for
72 hours The SEM image clearly shows the microstructureof ductile cast iron Fe was depleted in the graphite area andcarbon was concentrated as spheroidized shapes Also whileoxygen was detected on the entire surface it was particularlyconcentrated on the graphite area and dim spots of nitrogenwere detected Figure 11 shows the elemental distributionanalyzed using EPMA on the surface of ductile cast ironcorroded in simulated cooling water (10000 ppm NaNO
2)
at 25∘C for 72 hours The SEM image shows the locallycorroded morphology as seen in Figure 7(b) Fe was notuniform and this is related to local corrosion However thecarbon distribution was very different to the fully passivated
8 Advances in Materials Science and Engineering
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Figure 9 Surface electrolyte potential (V(SCE) the right vertical color bar) obtained by computer 3D simulation (the unit of 119909- 119910- and119911-axes 120583m) using COSOL Multiphysics on corrosion propagation with immersion time of ductile cast iron occurred in stagnant simulatedcooling water (10000 ppm NaNO
2) at 25∘C (a) 0 hour (b) 24 hours (c) 48 hours (d) 72 hours and (e) 144 hours
surface as shown in Figure 10(c)While spheroidized graphitewas not observed destroyed graphite and its location wereidentified this result provides the evidence that graphite canbe peeled off layer by layer as discussed above Oxygen wasdetected more on the Fe-depleted areas and dim spots ofnitrogenwere detectedThis oxygen comes from the sufficientNaNO
2 It will be discussed below
The depth profile on the passivated surface was obtainedusing XPS to determine the role of nitrite ion on thepassivation of steel and iron Figure 12 shows the depth profileusing XPS on the passive film of carbon steel passivated for24 hours in simulated cooling water (1000 ppm NaNO
2) at
25∘COxygen and nitrogenwere enriched at the outer surfaceand Fe drastically increased with etch time Figures 12(b)and 12(c) show that iron oxide was enriched at the outersurfaceNitrogenwas only detected before sputtering andwasnot detected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surface evenwith the NaNO
2addition to the solution Figure 13 shows
the depth profile using XPS on the passive film of ductilecast iron passivated for 24 hours in simulated cooling water(100000 ppm NaNO
2) at 25∘C Oxygen and nitrogen were
enriched at the outer surface and Fe is drastically increasedwith etch time Figures 13(b) and 13(c) show that iron oxide
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Figure 10 Elemental distribution analyzed by EPMA on the surface of ductile cast iron passivated in simulated cooling water (100000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
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Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
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Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
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405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
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TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
2 Advances in Materials Science and Engineering
Table 1 Chemical compositions of experimental alloys
Alloys Chemical compositions wtC Mn P S Si Cr Cu Mo Ni V Fe
CS 026 086 0014 0005 023 004 0057 0033 0029 0008 balDCI 401 017 0022 0026 153 mdash 0023 0028 0059 0016 balCS carbon steel ASME SA106 GrB DCI ductile cast iron KS D4311
then occurs including general corrosion pitting microbialinduced corrosion scale buildupmultiplication ofmicrobialand fatigue Therefore several corrosion control methodssuch as painting and coating electrical protection and theuse of corrosion inhibitors have been applied [7ndash9] Carbonsteel and cast iron used in a closed cooling system may becorroded In order to control this type of corrosion problemcorrosion inhibitors such as nitrite silicate molybdate andhydrazine have been used among them nitrite is widely usedbecause of its excellent performance
Many reports have been presented on corrosion inhi-bition by nitrite including Fe
2O3formation on steel by
nitrite addition [10] adherent protective oxide on steel [11]correlation of oxygen and nitrite on steel corrosion [12]comparative study of nitrite including various inhibitors onsteel [13ndash15] and inhibition effect of nitrite on steel withtime [16 17] Nitrite as an anodic inhibitor has a tendencyto increase anodic polarization and thus increase corrosionpotential to a noble direction and decrease the corrosioncurrent Since nitrite contains a strong oxidizing power itoxidizes the surface and forms Fe
2O3[18] Formation rate of
protective film due to nitrite is very fast and thus among theseveral corrosion inhibitors nitrite shows good performance[19]
On the other hand ductile cast iron has a very differentmicrostructure to that of carbon steel Spheroidized graphiteforms in the matrix and galvanic corrosion occurs betweenthe matrix and graphite Also cast iron does not have highcorrosion resistance to various corrosion environments andit should be protected by a coating As described abovemany reports have been presented on the corrosion inhibitionof carbon steel but there are few reports on cast ironTherefore in this work corrosion inhibition effects of nitriteon carbon steel and ductile cast iron for nuclear powerplant pipework using chemical and electrochemical methodswere evaluated This work attempts to clarify the corrosioninhibition mechanism between steel and iron by NaNO
2
addition
2 Experimental Procedure
21 Materials and Corrosion Environments Commercial car-bon steel (ASME SA106 GrB) [20] and ductile cast iron (KSD4311) [21] were used in this work and Table 1 shows thechemical composition of the experimental alloys
The test solution was simulated primary cooling waterused in the nuclear power plant The standard solution was16 ppm NaCl and its pH was modified with 1N NaOHsolution and the range of pH 9 plusmn 02 was controlled NaNO
2
as a corrosion inhibitor was added as a ppm order
22 Corrosion Tests
221 Immersion Corrosion Test A specimen was cut to a sizeof 20times 20times 5mmand each surfacewas groundusing 120 SiCpaper Immersion tests were carried out in a stagnant solutioncondition (500mL glass flask) and in a circulating solutionin which test chamber has a dimension of 50 times 100 times 50 cmand the flow rate was 5 Lmin After the immersion tests eachspecimen was cleaned with acetone and alcohol and was thendried the corrosion rate was then determined
222 Electrochemical Tests Specimens were cut to a sizeof 20 times 20mm and after electrical connection they wereepoxy-mounted and the surface was ground using 600SiC paper and coated with epoxy resin except an area of1 cm2 A polarization test was performed using a potentiostat(Gamry DC105) and the reference electrode was a saturatedcalomel electrode and the counter electrode was Pt wire Thetest solution was deaerated using nitrogen gas at the rateof 100mLmin for 30 minutes and the scanning rate was033mVsec In order to measure the AC impedance thespecimens were ground using 2000 SiC paper and thenpolished using a diamond paste (3120583m)The test solution wasthe same as that of the polarization test AC impedance mea-surement was performed using an electrochemical analyzer(Gamry EIS 300) Before measuring passivation was treatedat +400mV(SCE) for carbon steel and 0mV(SCE) for ductilecast iron for 30 minutes AC impedance was measured ata passivation potential from 10 kHz to 001Hz and the ACvoltage amplitude was 10mV Also a Mott-Schottky plot wasprepared to determine the semiconductive properties of thepassive film The specimen preparation was the same as thatfor AC impedance measurement and the DC amplitude was10mV (peak-to-peak) at 1580Hz of the AC frequency [22]The capacitance was measured at the scan rate of 50mVsecfrom +1V(SCE) to minus15 V(SCE)
223 Surface Analysis X-ray photoelectron spectroscopy(XPS K-alpha (Thermo VG UK) Al-K
120572(14866 eV 12 kV
3mA)) was analyzed to determine the chemical state ofseveral species of the passive film The specimen was cutto a size of 20 times 20 times 5mm and then ground with 2000SiC paper and polished with a 3 120583m diamond paste thespecimenwas finally cleaned with alcohol using an ultrasoniccleaner Carbon steel and ductile cast iron were passivatedby immersion for 24 hours in 1000 ppm and 100000 ppmNaNO
2 respectively The depth profile was obtained every
5 seconds by Ar-sputtering Also an Electron Probe MicroAnalyzer (EPMA EPMA-1600 15 KV) was used to identifythe elemental distribution of the passivated surface Optical
Advances in Materials Science and Engineering 3
023
0060 0 0
048
0 0 0 00
02
04
06
08
1
0 10 100 1000 10000
Cor
rosio
n ra
te (m
my
r)
Stagnant solutionCirculating solution
NaNO2 (ppm)
(a)
Stagnant solutionCirculating solution
047
009004 002 0 0 0
084
041
014008 007
001 00
02
04
06
08
1
0 10 100 1000 10000 50000 100000
Cor
rosio
n ra
te (m
my
r)
NaNO2 (ppm)
(b)
Figure 1 Effect of NaNO2addition on corrosion rate in circulating and stagnant simulated cooling water at 25∘C (a) carbon steel and (b)
ductile cast iron
Microscope (OM Zeiss Axiotech 100HD) and SEM-EDS(Tescan Vega II LMU) and a 3Dmicroscope (Zeiss KH-7700)were used
224 Corrosion Simulation In order to determine the differ-ence in galvanic corrosion between the matrix and spheroid-ized graphite of the ductile cast iron computer simulationwas performed using COMSOL Multiphysics software Tafelslopes of anodic and cathodic reactions were used and therate controlling equation applied in this modeling was thesecondary corrosion condition
3 Results and Discussion
31 Effect of Nitrite Concentration Figure 1 shows the effectof NaNO
2addition on corrosion rate in circulating and
stagnant simulated coolingwater in the air at 25∘C In the caseof carbon steel increasing NaNO
2concentration reduced
significantly the corrosion rate of carbon steel When theinhibitor was absent the rates of stagnant and circulatingsolutions were 023 and 048mmyear respectively Also theeffect of nitrite ion was stronger in the circulating solutionthan in the stagnant solution However in the case of ductilecast iron the effect of nitrite addition was similar to that ofcarbon steel but the similar corrosion inhibition of ductilecast iron needs a significant addition of NaNO
2 When the
inhibitor was absent the rates of stagnant and circulatingsolutions were 047 and 084mmyear respectively Eventhough the NaNO
2addition was increased the corrosion
rate of ductile cast iron showed relatively higher values thanthose of carbon steel The corrosion of carbon steel can beinhibited at near 100 ppmNaNO
2addition but the corrosion
of ductile cast iron can be inhibited by an addition of morethan 10000 ppm NaNO
2 Moreover while the corrosion of
carbon steel can be inhibited more readily by the circulation
of the solution the circulation facilitated the corrosion ofductile cast iron
The open circuit potential with immersion time byNaNO
2addition in circulating (solid symbol) and stagnant
(open symbol) simulated cooling water in the air at 25∘Cwas shown in Figure 2 Regardless of the alloys used and thecirculation of solution the open circuit potential of the spec-imen without NaNO
2addition decreased with immersion
time However the open circuit potential of the specimenwith NaNO
2addition increased and its tendency depends
on the alloys In the case of carbon steel an addition of100 ppm NaNO
2increased the open circuit potential and the
circulation stimulated its rate Also in the case of ductile castiron a greater concentration (about 100 times) of NaNO
2is
needed for a similar effect of NaNO2addition
The effect of NaNO2addition on the polarization behav-
ior in deaerated simulated cooling water at 25∘Cwas revealedin Figure 3 the scanning rate was 033mVsWhenNaNO
2is
not added carbon steel and ductile cast iron dissolved readilywithout the passivation by anodic polarization With 10and 100 ppm NaNO
2additions carbon steel revealed active-
passive transition but the passive current density was highand transpassive behavior occurred Ductile cast iron did notshow an active-passive transition until a 10000 ppm NaNO
2
addition From a 1000 ppm NaNO2addition carbon steel
showed excellent passivation behavior but the ductile castiron revealed the best passivation curve from 100000 ppmNaNO
2addition This tendency is coincident with the result
of the immersion test shown in Figure 1Figure 4 shows the corrosion rate due to the NaNO
2
addition obtained from the immersion test (circulationcondition) shown in Figure 1 and the current density wasobtained at +400mV(SCE) as shown in Figure 3 Regardlessof the chemical or electrochemical tests the corrosion ofcarbon steel can be inhibited by a small NaNO
2addition
4 Advances in Materials Science and Engineering
E (m
V(S
CE))
0ppm100ppm1000 ppm10000 ppm
0ppm100ppm1000 ppm10000 ppmCirculating solution Stagnant solution
Time (hour)
minus100
minus200
minus300
minus400
minus500
minus600
minus700
minus800
100
806040200 100
0
(a)
E (m
V(S
CE))
Circulating solution Stagnant solution
Time (hour)
minus100
minus200
minus300
minus400
minus500
minus600
minus700
minus800
100
806040200 100
0
0ppm1000 ppm50000 ppm100000 ppm
0ppm1000 ppm50000 ppm100000 ppm
(b)
Figure 2 Open circuit potential with immersion time by nitrite addition in circulating (solid symbol) and stagnant (open symbol) simulatedcooling water at 25∘C (a) carbon steel and (b) ductile cast iron
minus10 minus8 minus6 minus4 minus2 0minus1000
minus800
minus600
minus400
minus200
0
200
400
600
800
1000
E (m
V(S
CE))
10000ppm1000ppm
100ppm10ppm0ppm
10000ppm
1000ppm
100ppm
10ppm
0ppm
log i (Acm2)
(a)
minus1000
minus800
minus600
minus400
minus200
0
200
400
600
800
1000
E (m
V(S
CE))
minus10 minus8 minus6 minus4 minus2 0log i (Acm2)
100000ppm10000ppm
1000ppm100ppm0ppm
100000ppm
10000ppm
1000ppm
100ppm 0ppm
(b)
Figure 3 Effect of NaNO2addition on polarization behavior in deaerated simulated cooling water at 25∘C (scanning rate 033mVs) (a)
carbon steel and (b) ductile cast iron
(ca 1000 ppm) but the corrosion of ductile cast iron couldbe only inhibited by a significant NaNO
2addition (ca
100000 ppm)That is it was demonstrated that the differencein the NaNO
2addition needed between carbon steel and
ductile cast iron was about 100 times
In order to determine the resistance of the passive filmformed on the surface of carbon steel and ductile cast iron byNaNO
2addition the AC impedance was measured Figure 5
shows the effect of NaNO2addition in Nyquist plot obtained
from AC impedance measurement at +400mV(SCE) for
Advances in Materials Science and Engineering 5
0
1
2
3
4
0 1 2 3 4 5 6
log
corr
osio
n ra
te (120583
my
r)
CSDCI
log C (ppm NaNO2)
(a)
CSDCI
minus7
minus6
minus5
minus4
minus3
minus2
minus1
0 1 2 3 4 5 6
logi
(Ac
m2)
log C (ppm NaNO2)
(b)
Figure 4 Comparison of (a) corrosion rate (circulation condition) from Figure 1 and (b) current density obtained at +400mV (SCE) ofFigure 3 by NaNO
2addition to simulated cooling water
0
50
100
150
200
250
0 100 200 300 400 500
1000ppm100ppm10ppm
Real impedance Zr (kΩ)
Imag
inar
y im
peda
nceZi
(kΩ
)
(a)
0
20
40
60
80
100
120
140
160
180
0 100 200 300 400
100000ppm50000ppm
Real impedance Zr (kΩ)
Imag
inar
y im
peda
nceZi
(kΩ
)
(b)
Figure 5 Effect of NaNO2addition on Nyquist plot obtained from AC impedance measurement in deaerated simulated cooling water at
25∘C (a) carbon steel at +400mV (SCE) and (b) ductile cast iron at 0V (SCE)
carbon steel and 0V(SCE) for ductile cast iron in deaeratedsimulated cooling water at 25∘C In the case of carbon steel astable passive film could not be formedwith a 10 ppmNaNO
2
addition and very small impedance (156 kohm) was thusshownA 100 ppmNaNO
2addition formed a passive film but
its polarization resistancewas small (1946 kohm)However astable passive film (4425 kohm)was formedwith a 1000 ppmNaNO
2addition In the case of ductile cast iron a stable
passive film (3337 kohm) was formed with a 100000 ppmNaNO
2addition As shown in Figures 1 and 4 the difference
of corrosion inhibition between carbon steel and ductile castiron due to the NaNO
2addition was closely related to the
formation of a stable passive film on the surface
32 Corrosion Inhibition Mechanism of Carbon Steel andDuctile Cast Iron by Nitrite Ion It was revealed that thedifference in the effect of corrosion inhibition due to NaNO
2
addition between carbon steel and ductile cast iron was about100 times through the immersion test and electrochemicaltests as described above As shown in Table 1 the significant
6 Advances in Materials Science and Engineering
50120583m
(a)
50120583m
(b)
(c) (d)
Figure 6 Optical microstructures (a b) and SEM images (c d) (a c) carbon steel and (b d) ductile cast iron
difference in the composition between the two alloys iscarbon content Figure 6 shows optical microstructures andSEM images for carbon steel and ductile cast iron In the caseof carbon steel ferrite and pearlite phases can be observedHowever in the case of ductile cast iron spheroidized phaseswere formed in the ferrite matrix and the spheroidizedphase was shown to be graphite by SEM-EDS analysis Thesepictures show the typical microstructures of carbon steel andductile cast iron
In order to determine the effect of NaNO2addition
on the corrosion morphologies of ductile cast iron afterimmersion the corroded surface was observed The effect ofNaNO
2addition on the surface appearance of ductile cast
iron after the immersion test in simulated cooling water for 3hours at 25∘C was presented in Figure 7 Figure 7(a) showsthe addition of 0 ppm NaNO
2and Figure 7(b) shows the
addition of 10000 ppmNaNO2When noNaNO
2was added
the ductile cast iron was generally corroded on the entiresurface However when 10000 ppm NaNO
2was added (this
addition of which is not sufficient to inhibit corrosion ofductile cast iron as shown in Figures 1 and 3) the iron wascorroded locally near the spheroidized graphite and the cor-roded areas were agglomerated Figure 8 shows the corrosionmorphologies of ductile cast iron in which ductile cast iron
was corroded for 3 hours in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C Figure 8(a) shows the surface
contour using a 3D microscope and local corrosion near thespheroidized graphite was confirmed Figure 8(b) shows anSEM image of the corroded area showing that it was corrodedspherically near the graphite and thenfinally the graphite hadchipped off Also corrosion products and even cracks wereobserved near the chipped-off graphite These figures showthat galvanic corrosion took place in the ductile cast iron Itis well known that graphite is nobler than matrix iron [23]
The galvanic corrosion between graphite and matrixiron was simulated using a COMSOLMultiphysics programAnodic and cathodic Tafel slopes (+108mV and minus206mVresp) were applied to calculate the corrosion behavior of thecorroding and noncorroding areas Figure 9 shows computer3D simulation results of the corrosion propagation of ductilecast iron occurring in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C At the initial stage (0 hour)
the potential difference between graphite (the center) andmatrix (left and right) is shown by the blue and red colorsrespectively By increasing the immersion time the matrixnear the graphite corroded and the corrosion depth wasincreased its depth was greater near the graphite (Thisis the distance effect observed in galvanic corrosion) This
Advances in Materials Science and Engineering 7
50120583m
(a)
50120583m
(b)
Figure 7 Effect of NaNO2addition on surface appearance of ductile cast iron after the immersion test in simulated cooling water for 3 hours
at 25∘C (a) 0 ppm NaNO2and (b) 10000 ppm NaNO
2
12584
10067
7550
5034
2517
0000
(120583m
)
111858120583m107115 120583m
Height 10835120583m
Max 12584120583m
Width 1Width 2
(a) (b)
Figure 8 Corrosion morphologies of ductile cast iron corroded in stagnant simulated cooling water (10000 ppm NaNO2) for 3 hours at
25∘C (a) 3D microscope and (b) SEM image
simulation result differs from that shown in Figure 8(b) Thisdifference could be due to the characteristics of the graphite(However it should be noted that the COMSOLMultiphysicsprogram does not simulate the mechanical damage in gal-vanic corrosion)The crystal structure of graphite is covalentbonded with neighboring atoms in the same layer althoughlayers are van der Waals bonded together [24 25] and thusthe bonding force of graphite is very weak Therefore it isconsidered that the matrix is corroded galvanically and thatthe graphite is protruded and then graphite is peeled off layerby layer because of the weak bonding force of graphite
Figure 10 shows the elemental distribution analyzed usingEPMA on the surface of ductile cast iron passivated in
simulated cooling water (100000 ppm NaNO2) at 25∘C for
72 hours The SEM image clearly shows the microstructureof ductile cast iron Fe was depleted in the graphite area andcarbon was concentrated as spheroidized shapes Also whileoxygen was detected on the entire surface it was particularlyconcentrated on the graphite area and dim spots of nitrogenwere detected Figure 11 shows the elemental distributionanalyzed using EPMA on the surface of ductile cast ironcorroded in simulated cooling water (10000 ppm NaNO
2)
at 25∘C for 72 hours The SEM image shows the locallycorroded morphology as seen in Figure 7(b) Fe was notuniform and this is related to local corrosion However thecarbon distribution was very different to the fully passivated
8 Advances in Materials Science and Engineering
10 0 minus100
50
0minus10
10
zx
y
Graphite
055050045040035030(V(SCE))
(120583m)
(120583m
)
(120583m
)
(a)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m
)
(120583m
)
(b)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(c)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m)
(120583m
)
(d)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(e)
Figure 9 Surface electrolyte potential (V(SCE) the right vertical color bar) obtained by computer 3D simulation (the unit of 119909- 119910- and119911-axes 120583m) using COSOL Multiphysics on corrosion propagation with immersion time of ductile cast iron occurred in stagnant simulatedcooling water (10000 ppm NaNO
2) at 25∘C (a) 0 hour (b) 24 hours (c) 48 hours (d) 72 hours and (e) 144 hours
surface as shown in Figure 10(c)While spheroidized graphitewas not observed destroyed graphite and its location wereidentified this result provides the evidence that graphite canbe peeled off layer by layer as discussed above Oxygen wasdetected more on the Fe-depleted areas and dim spots ofnitrogenwere detectedThis oxygen comes from the sufficientNaNO
2 It will be discussed below
The depth profile on the passivated surface was obtainedusing XPS to determine the role of nitrite ion on thepassivation of steel and iron Figure 12 shows the depth profileusing XPS on the passive film of carbon steel passivated for24 hours in simulated cooling water (1000 ppm NaNO
2) at
25∘COxygen and nitrogenwere enriched at the outer surfaceand Fe drastically increased with etch time Figures 12(b)and 12(c) show that iron oxide was enriched at the outersurfaceNitrogenwas only detected before sputtering andwasnot detected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surface evenwith the NaNO
2addition to the solution Figure 13 shows
the depth profile using XPS on the passive film of ductilecast iron passivated for 24 hours in simulated cooling water(100000 ppm NaNO
2) at 25∘C Oxygen and nitrogen were
enriched at the outer surface and Fe is drastically increasedwith etch time Figures 13(b) and 13(c) show that iron oxide
Advances in Materials Science and Engineering 9
24384
42064
30120583m
(a)
523483443
564
362322282
402
241201161
80400
120
30120583m
(b)
339431332872
3656
235020891828
2611
156613051044
5222610
783
30120583m
(c)
928578
100
645750
71
433629
1581
22
30120583m
(d)
928578
100
645750
71
433629
1581
22
30120583m
(e)
Figure 10 Elemental distribution analyzed by EPMA on the surface of ductile cast iron passivated in simulated cooling water (100000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
10 Advances in Materials Science and Engineering
32880
40288
60120583m
(a)
463
431
398
496
333
301
268
366
236
203
171
106
73
41
138
60120583m
(b)
125011541058
1347
865769673
962
577481384
192960
288
60120583m
(c)
315291267
340
219195171
243
14612298
50262
74
60120583m
(d)
928578
100
645750
71
423528
1470
21
60120583m
(e)
Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Advances in Materials Science and Engineering 3
023
0060 0 0
048
0 0 0 00
02
04
06
08
1
0 10 100 1000 10000
Cor
rosio
n ra
te (m
my
r)
Stagnant solutionCirculating solution
NaNO2 (ppm)
(a)
Stagnant solutionCirculating solution
047
009004 002 0 0 0
084
041
014008 007
001 00
02
04
06
08
1
0 10 100 1000 10000 50000 100000
Cor
rosio
n ra
te (m
my
r)
NaNO2 (ppm)
(b)
Figure 1 Effect of NaNO2addition on corrosion rate in circulating and stagnant simulated cooling water at 25∘C (a) carbon steel and (b)
ductile cast iron
Microscope (OM Zeiss Axiotech 100HD) and SEM-EDS(Tescan Vega II LMU) and a 3Dmicroscope (Zeiss KH-7700)were used
224 Corrosion Simulation In order to determine the differ-ence in galvanic corrosion between the matrix and spheroid-ized graphite of the ductile cast iron computer simulationwas performed using COMSOL Multiphysics software Tafelslopes of anodic and cathodic reactions were used and therate controlling equation applied in this modeling was thesecondary corrosion condition
3 Results and Discussion
31 Effect of Nitrite Concentration Figure 1 shows the effectof NaNO
2addition on corrosion rate in circulating and
stagnant simulated coolingwater in the air at 25∘C In the caseof carbon steel increasing NaNO
2concentration reduced
significantly the corrosion rate of carbon steel When theinhibitor was absent the rates of stagnant and circulatingsolutions were 023 and 048mmyear respectively Also theeffect of nitrite ion was stronger in the circulating solutionthan in the stagnant solution However in the case of ductilecast iron the effect of nitrite addition was similar to that ofcarbon steel but the similar corrosion inhibition of ductilecast iron needs a significant addition of NaNO
2 When the
inhibitor was absent the rates of stagnant and circulatingsolutions were 047 and 084mmyear respectively Eventhough the NaNO
2addition was increased the corrosion
rate of ductile cast iron showed relatively higher values thanthose of carbon steel The corrosion of carbon steel can beinhibited at near 100 ppmNaNO
2addition but the corrosion
of ductile cast iron can be inhibited by an addition of morethan 10000 ppm NaNO
2 Moreover while the corrosion of
carbon steel can be inhibited more readily by the circulation
of the solution the circulation facilitated the corrosion ofductile cast iron
The open circuit potential with immersion time byNaNO
2addition in circulating (solid symbol) and stagnant
(open symbol) simulated cooling water in the air at 25∘Cwas shown in Figure 2 Regardless of the alloys used and thecirculation of solution the open circuit potential of the spec-imen without NaNO
2addition decreased with immersion
time However the open circuit potential of the specimenwith NaNO
2addition increased and its tendency depends
on the alloys In the case of carbon steel an addition of100 ppm NaNO
2increased the open circuit potential and the
circulation stimulated its rate Also in the case of ductile castiron a greater concentration (about 100 times) of NaNO
2is
needed for a similar effect of NaNO2addition
The effect of NaNO2addition on the polarization behav-
ior in deaerated simulated cooling water at 25∘Cwas revealedin Figure 3 the scanning rate was 033mVsWhenNaNO
2is
not added carbon steel and ductile cast iron dissolved readilywithout the passivation by anodic polarization With 10and 100 ppm NaNO
2additions carbon steel revealed active-
passive transition but the passive current density was highand transpassive behavior occurred Ductile cast iron did notshow an active-passive transition until a 10000 ppm NaNO
2
addition From a 1000 ppm NaNO2addition carbon steel
showed excellent passivation behavior but the ductile castiron revealed the best passivation curve from 100000 ppmNaNO
2addition This tendency is coincident with the result
of the immersion test shown in Figure 1Figure 4 shows the corrosion rate due to the NaNO
2
addition obtained from the immersion test (circulationcondition) shown in Figure 1 and the current density wasobtained at +400mV(SCE) as shown in Figure 3 Regardlessof the chemical or electrochemical tests the corrosion ofcarbon steel can be inhibited by a small NaNO
2addition
4 Advances in Materials Science and Engineering
E (m
V(S
CE))
0ppm100ppm1000 ppm10000 ppm
0ppm100ppm1000 ppm10000 ppmCirculating solution Stagnant solution
Time (hour)
minus100
minus200
minus300
minus400
minus500
minus600
minus700
minus800
100
806040200 100
0
(a)
E (m
V(S
CE))
Circulating solution Stagnant solution
Time (hour)
minus100
minus200
minus300
minus400
minus500
minus600
minus700
minus800
100
806040200 100
0
0ppm1000 ppm50000 ppm100000 ppm
0ppm1000 ppm50000 ppm100000 ppm
(b)
Figure 2 Open circuit potential with immersion time by nitrite addition in circulating (solid symbol) and stagnant (open symbol) simulatedcooling water at 25∘C (a) carbon steel and (b) ductile cast iron
minus10 minus8 minus6 minus4 minus2 0minus1000
minus800
minus600
minus400
minus200
0
200
400
600
800
1000
E (m
V(S
CE))
10000ppm1000ppm
100ppm10ppm0ppm
10000ppm
1000ppm
100ppm
10ppm
0ppm
log i (Acm2)
(a)
minus1000
minus800
minus600
minus400
minus200
0
200
400
600
800
1000
E (m
V(S
CE))
minus10 minus8 minus6 minus4 minus2 0log i (Acm2)
100000ppm10000ppm
1000ppm100ppm0ppm
100000ppm
10000ppm
1000ppm
100ppm 0ppm
(b)
Figure 3 Effect of NaNO2addition on polarization behavior in deaerated simulated cooling water at 25∘C (scanning rate 033mVs) (a)
carbon steel and (b) ductile cast iron
(ca 1000 ppm) but the corrosion of ductile cast iron couldbe only inhibited by a significant NaNO
2addition (ca
100000 ppm)That is it was demonstrated that the differencein the NaNO
2addition needed between carbon steel and
ductile cast iron was about 100 times
In order to determine the resistance of the passive filmformed on the surface of carbon steel and ductile cast iron byNaNO
2addition the AC impedance was measured Figure 5
shows the effect of NaNO2addition in Nyquist plot obtained
from AC impedance measurement at +400mV(SCE) for
Advances in Materials Science and Engineering 5
0
1
2
3
4
0 1 2 3 4 5 6
log
corr
osio
n ra
te (120583
my
r)
CSDCI
log C (ppm NaNO2)
(a)
CSDCI
minus7
minus6
minus5
minus4
minus3
minus2
minus1
0 1 2 3 4 5 6
logi
(Ac
m2)
log C (ppm NaNO2)
(b)
Figure 4 Comparison of (a) corrosion rate (circulation condition) from Figure 1 and (b) current density obtained at +400mV (SCE) ofFigure 3 by NaNO
2addition to simulated cooling water
0
50
100
150
200
250
0 100 200 300 400 500
1000ppm100ppm10ppm
Real impedance Zr (kΩ)
Imag
inar
y im
peda
nceZi
(kΩ
)
(a)
0
20
40
60
80
100
120
140
160
180
0 100 200 300 400
100000ppm50000ppm
Real impedance Zr (kΩ)
Imag
inar
y im
peda
nceZi
(kΩ
)
(b)
Figure 5 Effect of NaNO2addition on Nyquist plot obtained from AC impedance measurement in deaerated simulated cooling water at
25∘C (a) carbon steel at +400mV (SCE) and (b) ductile cast iron at 0V (SCE)
carbon steel and 0V(SCE) for ductile cast iron in deaeratedsimulated cooling water at 25∘C In the case of carbon steel astable passive film could not be formedwith a 10 ppmNaNO
2
addition and very small impedance (156 kohm) was thusshownA 100 ppmNaNO
2addition formed a passive film but
its polarization resistancewas small (1946 kohm)However astable passive film (4425 kohm)was formedwith a 1000 ppmNaNO
2addition In the case of ductile cast iron a stable
passive film (3337 kohm) was formed with a 100000 ppmNaNO
2addition As shown in Figures 1 and 4 the difference
of corrosion inhibition between carbon steel and ductile castiron due to the NaNO
2addition was closely related to the
formation of a stable passive film on the surface
32 Corrosion Inhibition Mechanism of Carbon Steel andDuctile Cast Iron by Nitrite Ion It was revealed that thedifference in the effect of corrosion inhibition due to NaNO
2
addition between carbon steel and ductile cast iron was about100 times through the immersion test and electrochemicaltests as described above As shown in Table 1 the significant
6 Advances in Materials Science and Engineering
50120583m
(a)
50120583m
(b)
(c) (d)
Figure 6 Optical microstructures (a b) and SEM images (c d) (a c) carbon steel and (b d) ductile cast iron
difference in the composition between the two alloys iscarbon content Figure 6 shows optical microstructures andSEM images for carbon steel and ductile cast iron In the caseof carbon steel ferrite and pearlite phases can be observedHowever in the case of ductile cast iron spheroidized phaseswere formed in the ferrite matrix and the spheroidizedphase was shown to be graphite by SEM-EDS analysis Thesepictures show the typical microstructures of carbon steel andductile cast iron
In order to determine the effect of NaNO2addition
on the corrosion morphologies of ductile cast iron afterimmersion the corroded surface was observed The effect ofNaNO
2addition on the surface appearance of ductile cast
iron after the immersion test in simulated cooling water for 3hours at 25∘C was presented in Figure 7 Figure 7(a) showsthe addition of 0 ppm NaNO
2and Figure 7(b) shows the
addition of 10000 ppmNaNO2When noNaNO
2was added
the ductile cast iron was generally corroded on the entiresurface However when 10000 ppm NaNO
2was added (this
addition of which is not sufficient to inhibit corrosion ofductile cast iron as shown in Figures 1 and 3) the iron wascorroded locally near the spheroidized graphite and the cor-roded areas were agglomerated Figure 8 shows the corrosionmorphologies of ductile cast iron in which ductile cast iron
was corroded for 3 hours in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C Figure 8(a) shows the surface
contour using a 3D microscope and local corrosion near thespheroidized graphite was confirmed Figure 8(b) shows anSEM image of the corroded area showing that it was corrodedspherically near the graphite and thenfinally the graphite hadchipped off Also corrosion products and even cracks wereobserved near the chipped-off graphite These figures showthat galvanic corrosion took place in the ductile cast iron Itis well known that graphite is nobler than matrix iron [23]
The galvanic corrosion between graphite and matrixiron was simulated using a COMSOLMultiphysics programAnodic and cathodic Tafel slopes (+108mV and minus206mVresp) were applied to calculate the corrosion behavior of thecorroding and noncorroding areas Figure 9 shows computer3D simulation results of the corrosion propagation of ductilecast iron occurring in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C At the initial stage (0 hour)
the potential difference between graphite (the center) andmatrix (left and right) is shown by the blue and red colorsrespectively By increasing the immersion time the matrixnear the graphite corroded and the corrosion depth wasincreased its depth was greater near the graphite (Thisis the distance effect observed in galvanic corrosion) This
Advances in Materials Science and Engineering 7
50120583m
(a)
50120583m
(b)
Figure 7 Effect of NaNO2addition on surface appearance of ductile cast iron after the immersion test in simulated cooling water for 3 hours
at 25∘C (a) 0 ppm NaNO2and (b) 10000 ppm NaNO
2
12584
10067
7550
5034
2517
0000
(120583m
)
111858120583m107115 120583m
Height 10835120583m
Max 12584120583m
Width 1Width 2
(a) (b)
Figure 8 Corrosion morphologies of ductile cast iron corroded in stagnant simulated cooling water (10000 ppm NaNO2) for 3 hours at
25∘C (a) 3D microscope and (b) SEM image
simulation result differs from that shown in Figure 8(b) Thisdifference could be due to the characteristics of the graphite(However it should be noted that the COMSOLMultiphysicsprogram does not simulate the mechanical damage in gal-vanic corrosion)The crystal structure of graphite is covalentbonded with neighboring atoms in the same layer althoughlayers are van der Waals bonded together [24 25] and thusthe bonding force of graphite is very weak Therefore it isconsidered that the matrix is corroded galvanically and thatthe graphite is protruded and then graphite is peeled off layerby layer because of the weak bonding force of graphite
Figure 10 shows the elemental distribution analyzed usingEPMA on the surface of ductile cast iron passivated in
simulated cooling water (100000 ppm NaNO2) at 25∘C for
72 hours The SEM image clearly shows the microstructureof ductile cast iron Fe was depleted in the graphite area andcarbon was concentrated as spheroidized shapes Also whileoxygen was detected on the entire surface it was particularlyconcentrated on the graphite area and dim spots of nitrogenwere detected Figure 11 shows the elemental distributionanalyzed using EPMA on the surface of ductile cast ironcorroded in simulated cooling water (10000 ppm NaNO
2)
at 25∘C for 72 hours The SEM image shows the locallycorroded morphology as seen in Figure 7(b) Fe was notuniform and this is related to local corrosion However thecarbon distribution was very different to the fully passivated
8 Advances in Materials Science and Engineering
10 0 minus100
50
0minus10
10
zx
y
Graphite
055050045040035030(V(SCE))
(120583m)
(120583m
)
(120583m
)
(a)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m
)
(120583m
)
(b)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(c)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m)
(120583m
)
(d)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(e)
Figure 9 Surface electrolyte potential (V(SCE) the right vertical color bar) obtained by computer 3D simulation (the unit of 119909- 119910- and119911-axes 120583m) using COSOL Multiphysics on corrosion propagation with immersion time of ductile cast iron occurred in stagnant simulatedcooling water (10000 ppm NaNO
2) at 25∘C (a) 0 hour (b) 24 hours (c) 48 hours (d) 72 hours and (e) 144 hours
surface as shown in Figure 10(c)While spheroidized graphitewas not observed destroyed graphite and its location wereidentified this result provides the evidence that graphite canbe peeled off layer by layer as discussed above Oxygen wasdetected more on the Fe-depleted areas and dim spots ofnitrogenwere detectedThis oxygen comes from the sufficientNaNO
2 It will be discussed below
The depth profile on the passivated surface was obtainedusing XPS to determine the role of nitrite ion on thepassivation of steel and iron Figure 12 shows the depth profileusing XPS on the passive film of carbon steel passivated for24 hours in simulated cooling water (1000 ppm NaNO
2) at
25∘COxygen and nitrogenwere enriched at the outer surfaceand Fe drastically increased with etch time Figures 12(b)and 12(c) show that iron oxide was enriched at the outersurfaceNitrogenwas only detected before sputtering andwasnot detected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surface evenwith the NaNO
2addition to the solution Figure 13 shows
the depth profile using XPS on the passive film of ductilecast iron passivated for 24 hours in simulated cooling water(100000 ppm NaNO
2) at 25∘C Oxygen and nitrogen were
enriched at the outer surface and Fe is drastically increasedwith etch time Figures 13(b) and 13(c) show that iron oxide
Advances in Materials Science and Engineering 9
24384
42064
30120583m
(a)
523483443
564
362322282
402
241201161
80400
120
30120583m
(b)
339431332872
3656
235020891828
2611
156613051044
5222610
783
30120583m
(c)
928578
100
645750
71
433629
1581
22
30120583m
(d)
928578
100
645750
71
433629
1581
22
30120583m
(e)
Figure 10 Elemental distribution analyzed by EPMA on the surface of ductile cast iron passivated in simulated cooling water (100000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
10 Advances in Materials Science and Engineering
32880
40288
60120583m
(a)
463
431
398
496
333
301
268
366
236
203
171
106
73
41
138
60120583m
(b)
125011541058
1347
865769673
962
577481384
192960
288
60120583m
(c)
315291267
340
219195171
243
14612298
50262
74
60120583m
(d)
928578
100
645750
71
423528
1470
21
60120583m
(e)
Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
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CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
4 Advances in Materials Science and Engineering
E (m
V(S
CE))
0ppm100ppm1000 ppm10000 ppm
0ppm100ppm1000 ppm10000 ppmCirculating solution Stagnant solution
Time (hour)
minus100
minus200
minus300
minus400
minus500
minus600
minus700
minus800
100
806040200 100
0
(a)
E (m
V(S
CE))
Circulating solution Stagnant solution
Time (hour)
minus100
minus200
minus300
minus400
minus500
minus600
minus700
minus800
100
806040200 100
0
0ppm1000 ppm50000 ppm100000 ppm
0ppm1000 ppm50000 ppm100000 ppm
(b)
Figure 2 Open circuit potential with immersion time by nitrite addition in circulating (solid symbol) and stagnant (open symbol) simulatedcooling water at 25∘C (a) carbon steel and (b) ductile cast iron
minus10 minus8 minus6 minus4 minus2 0minus1000
minus800
minus600
minus400
minus200
0
200
400
600
800
1000
E (m
V(S
CE))
10000ppm1000ppm
100ppm10ppm0ppm
10000ppm
1000ppm
100ppm
10ppm
0ppm
log i (Acm2)
(a)
minus1000
minus800
minus600
minus400
minus200
0
200
400
600
800
1000
E (m
V(S
CE))
minus10 minus8 minus6 minus4 minus2 0log i (Acm2)
100000ppm10000ppm
1000ppm100ppm0ppm
100000ppm
10000ppm
1000ppm
100ppm 0ppm
(b)
Figure 3 Effect of NaNO2addition on polarization behavior in deaerated simulated cooling water at 25∘C (scanning rate 033mVs) (a)
carbon steel and (b) ductile cast iron
(ca 1000 ppm) but the corrosion of ductile cast iron couldbe only inhibited by a significant NaNO
2addition (ca
100000 ppm)That is it was demonstrated that the differencein the NaNO
2addition needed between carbon steel and
ductile cast iron was about 100 times
In order to determine the resistance of the passive filmformed on the surface of carbon steel and ductile cast iron byNaNO
2addition the AC impedance was measured Figure 5
shows the effect of NaNO2addition in Nyquist plot obtained
from AC impedance measurement at +400mV(SCE) for
Advances in Materials Science and Engineering 5
0
1
2
3
4
0 1 2 3 4 5 6
log
corr
osio
n ra
te (120583
my
r)
CSDCI
log C (ppm NaNO2)
(a)
CSDCI
minus7
minus6
minus5
minus4
minus3
minus2
minus1
0 1 2 3 4 5 6
logi
(Ac
m2)
log C (ppm NaNO2)
(b)
Figure 4 Comparison of (a) corrosion rate (circulation condition) from Figure 1 and (b) current density obtained at +400mV (SCE) ofFigure 3 by NaNO
2addition to simulated cooling water
0
50
100
150
200
250
0 100 200 300 400 500
1000ppm100ppm10ppm
Real impedance Zr (kΩ)
Imag
inar
y im
peda
nceZi
(kΩ
)
(a)
0
20
40
60
80
100
120
140
160
180
0 100 200 300 400
100000ppm50000ppm
Real impedance Zr (kΩ)
Imag
inar
y im
peda
nceZi
(kΩ
)
(b)
Figure 5 Effect of NaNO2addition on Nyquist plot obtained from AC impedance measurement in deaerated simulated cooling water at
25∘C (a) carbon steel at +400mV (SCE) and (b) ductile cast iron at 0V (SCE)
carbon steel and 0V(SCE) for ductile cast iron in deaeratedsimulated cooling water at 25∘C In the case of carbon steel astable passive film could not be formedwith a 10 ppmNaNO
2
addition and very small impedance (156 kohm) was thusshownA 100 ppmNaNO
2addition formed a passive film but
its polarization resistancewas small (1946 kohm)However astable passive film (4425 kohm)was formedwith a 1000 ppmNaNO
2addition In the case of ductile cast iron a stable
passive film (3337 kohm) was formed with a 100000 ppmNaNO
2addition As shown in Figures 1 and 4 the difference
of corrosion inhibition between carbon steel and ductile castiron due to the NaNO
2addition was closely related to the
formation of a stable passive film on the surface
32 Corrosion Inhibition Mechanism of Carbon Steel andDuctile Cast Iron by Nitrite Ion It was revealed that thedifference in the effect of corrosion inhibition due to NaNO
2
addition between carbon steel and ductile cast iron was about100 times through the immersion test and electrochemicaltests as described above As shown in Table 1 the significant
6 Advances in Materials Science and Engineering
50120583m
(a)
50120583m
(b)
(c) (d)
Figure 6 Optical microstructures (a b) and SEM images (c d) (a c) carbon steel and (b d) ductile cast iron
difference in the composition between the two alloys iscarbon content Figure 6 shows optical microstructures andSEM images for carbon steel and ductile cast iron In the caseof carbon steel ferrite and pearlite phases can be observedHowever in the case of ductile cast iron spheroidized phaseswere formed in the ferrite matrix and the spheroidizedphase was shown to be graphite by SEM-EDS analysis Thesepictures show the typical microstructures of carbon steel andductile cast iron
In order to determine the effect of NaNO2addition
on the corrosion morphologies of ductile cast iron afterimmersion the corroded surface was observed The effect ofNaNO
2addition on the surface appearance of ductile cast
iron after the immersion test in simulated cooling water for 3hours at 25∘C was presented in Figure 7 Figure 7(a) showsthe addition of 0 ppm NaNO
2and Figure 7(b) shows the
addition of 10000 ppmNaNO2When noNaNO
2was added
the ductile cast iron was generally corroded on the entiresurface However when 10000 ppm NaNO
2was added (this
addition of which is not sufficient to inhibit corrosion ofductile cast iron as shown in Figures 1 and 3) the iron wascorroded locally near the spheroidized graphite and the cor-roded areas were agglomerated Figure 8 shows the corrosionmorphologies of ductile cast iron in which ductile cast iron
was corroded for 3 hours in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C Figure 8(a) shows the surface
contour using a 3D microscope and local corrosion near thespheroidized graphite was confirmed Figure 8(b) shows anSEM image of the corroded area showing that it was corrodedspherically near the graphite and thenfinally the graphite hadchipped off Also corrosion products and even cracks wereobserved near the chipped-off graphite These figures showthat galvanic corrosion took place in the ductile cast iron Itis well known that graphite is nobler than matrix iron [23]
The galvanic corrosion between graphite and matrixiron was simulated using a COMSOLMultiphysics programAnodic and cathodic Tafel slopes (+108mV and minus206mVresp) were applied to calculate the corrosion behavior of thecorroding and noncorroding areas Figure 9 shows computer3D simulation results of the corrosion propagation of ductilecast iron occurring in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C At the initial stage (0 hour)
the potential difference between graphite (the center) andmatrix (left and right) is shown by the blue and red colorsrespectively By increasing the immersion time the matrixnear the graphite corroded and the corrosion depth wasincreased its depth was greater near the graphite (Thisis the distance effect observed in galvanic corrosion) This
Advances in Materials Science and Engineering 7
50120583m
(a)
50120583m
(b)
Figure 7 Effect of NaNO2addition on surface appearance of ductile cast iron after the immersion test in simulated cooling water for 3 hours
at 25∘C (a) 0 ppm NaNO2and (b) 10000 ppm NaNO
2
12584
10067
7550
5034
2517
0000
(120583m
)
111858120583m107115 120583m
Height 10835120583m
Max 12584120583m
Width 1Width 2
(a) (b)
Figure 8 Corrosion morphologies of ductile cast iron corroded in stagnant simulated cooling water (10000 ppm NaNO2) for 3 hours at
25∘C (a) 3D microscope and (b) SEM image
simulation result differs from that shown in Figure 8(b) Thisdifference could be due to the characteristics of the graphite(However it should be noted that the COMSOLMultiphysicsprogram does not simulate the mechanical damage in gal-vanic corrosion)The crystal structure of graphite is covalentbonded with neighboring atoms in the same layer althoughlayers are van der Waals bonded together [24 25] and thusthe bonding force of graphite is very weak Therefore it isconsidered that the matrix is corroded galvanically and thatthe graphite is protruded and then graphite is peeled off layerby layer because of the weak bonding force of graphite
Figure 10 shows the elemental distribution analyzed usingEPMA on the surface of ductile cast iron passivated in
simulated cooling water (100000 ppm NaNO2) at 25∘C for
72 hours The SEM image clearly shows the microstructureof ductile cast iron Fe was depleted in the graphite area andcarbon was concentrated as spheroidized shapes Also whileoxygen was detected on the entire surface it was particularlyconcentrated on the graphite area and dim spots of nitrogenwere detected Figure 11 shows the elemental distributionanalyzed using EPMA on the surface of ductile cast ironcorroded in simulated cooling water (10000 ppm NaNO
2)
at 25∘C for 72 hours The SEM image shows the locallycorroded morphology as seen in Figure 7(b) Fe was notuniform and this is related to local corrosion However thecarbon distribution was very different to the fully passivated
8 Advances in Materials Science and Engineering
10 0 minus100
50
0minus10
10
zx
y
Graphite
055050045040035030(V(SCE))
(120583m)
(120583m
)
(120583m
)
(a)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m
)
(120583m
)
(b)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(c)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m)
(120583m
)
(d)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(e)
Figure 9 Surface electrolyte potential (V(SCE) the right vertical color bar) obtained by computer 3D simulation (the unit of 119909- 119910- and119911-axes 120583m) using COSOL Multiphysics on corrosion propagation with immersion time of ductile cast iron occurred in stagnant simulatedcooling water (10000 ppm NaNO
2) at 25∘C (a) 0 hour (b) 24 hours (c) 48 hours (d) 72 hours and (e) 144 hours
surface as shown in Figure 10(c)While spheroidized graphitewas not observed destroyed graphite and its location wereidentified this result provides the evidence that graphite canbe peeled off layer by layer as discussed above Oxygen wasdetected more on the Fe-depleted areas and dim spots ofnitrogenwere detectedThis oxygen comes from the sufficientNaNO
2 It will be discussed below
The depth profile on the passivated surface was obtainedusing XPS to determine the role of nitrite ion on thepassivation of steel and iron Figure 12 shows the depth profileusing XPS on the passive film of carbon steel passivated for24 hours in simulated cooling water (1000 ppm NaNO
2) at
25∘COxygen and nitrogenwere enriched at the outer surfaceand Fe drastically increased with etch time Figures 12(b)and 12(c) show that iron oxide was enriched at the outersurfaceNitrogenwas only detected before sputtering andwasnot detected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surface evenwith the NaNO
2addition to the solution Figure 13 shows
the depth profile using XPS on the passive film of ductilecast iron passivated for 24 hours in simulated cooling water(100000 ppm NaNO
2) at 25∘C Oxygen and nitrogen were
enriched at the outer surface and Fe is drastically increasedwith etch time Figures 13(b) and 13(c) show that iron oxide
Advances in Materials Science and Engineering 9
24384
42064
30120583m
(a)
523483443
564
362322282
402
241201161
80400
120
30120583m
(b)
339431332872
3656
235020891828
2611
156613051044
5222610
783
30120583m
(c)
928578
100
645750
71
433629
1581
22
30120583m
(d)
928578
100
645750
71
433629
1581
22
30120583m
(e)
Figure 10 Elemental distribution analyzed by EPMA on the surface of ductile cast iron passivated in simulated cooling water (100000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
10 Advances in Materials Science and Engineering
32880
40288
60120583m
(a)
463
431
398
496
333
301
268
366
236
203
171
106
73
41
138
60120583m
(b)
125011541058
1347
865769673
962
577481384
192960
288
60120583m
(c)
315291267
340
219195171
243
14612298
50262
74
60120583m
(d)
928578
100
645750
71
423528
1470
21
60120583m
(e)
Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
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CompositesJournal of
NanoparticlesJournal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
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NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
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BioMed Research International
MaterialsJournal of
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Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Advances in Materials Science and Engineering 5
0
1
2
3
4
0 1 2 3 4 5 6
log
corr
osio
n ra
te (120583
my
r)
CSDCI
log C (ppm NaNO2)
(a)
CSDCI
minus7
minus6
minus5
minus4
minus3
minus2
minus1
0 1 2 3 4 5 6
logi
(Ac
m2)
log C (ppm NaNO2)
(b)
Figure 4 Comparison of (a) corrosion rate (circulation condition) from Figure 1 and (b) current density obtained at +400mV (SCE) ofFigure 3 by NaNO
2addition to simulated cooling water
0
50
100
150
200
250
0 100 200 300 400 500
1000ppm100ppm10ppm
Real impedance Zr (kΩ)
Imag
inar
y im
peda
nceZi
(kΩ
)
(a)
0
20
40
60
80
100
120
140
160
180
0 100 200 300 400
100000ppm50000ppm
Real impedance Zr (kΩ)
Imag
inar
y im
peda
nceZi
(kΩ
)
(b)
Figure 5 Effect of NaNO2addition on Nyquist plot obtained from AC impedance measurement in deaerated simulated cooling water at
25∘C (a) carbon steel at +400mV (SCE) and (b) ductile cast iron at 0V (SCE)
carbon steel and 0V(SCE) for ductile cast iron in deaeratedsimulated cooling water at 25∘C In the case of carbon steel astable passive film could not be formedwith a 10 ppmNaNO
2
addition and very small impedance (156 kohm) was thusshownA 100 ppmNaNO
2addition formed a passive film but
its polarization resistancewas small (1946 kohm)However astable passive film (4425 kohm)was formedwith a 1000 ppmNaNO
2addition In the case of ductile cast iron a stable
passive film (3337 kohm) was formed with a 100000 ppmNaNO
2addition As shown in Figures 1 and 4 the difference
of corrosion inhibition between carbon steel and ductile castiron due to the NaNO
2addition was closely related to the
formation of a stable passive film on the surface
32 Corrosion Inhibition Mechanism of Carbon Steel andDuctile Cast Iron by Nitrite Ion It was revealed that thedifference in the effect of corrosion inhibition due to NaNO
2
addition between carbon steel and ductile cast iron was about100 times through the immersion test and electrochemicaltests as described above As shown in Table 1 the significant
6 Advances in Materials Science and Engineering
50120583m
(a)
50120583m
(b)
(c) (d)
Figure 6 Optical microstructures (a b) and SEM images (c d) (a c) carbon steel and (b d) ductile cast iron
difference in the composition between the two alloys iscarbon content Figure 6 shows optical microstructures andSEM images for carbon steel and ductile cast iron In the caseof carbon steel ferrite and pearlite phases can be observedHowever in the case of ductile cast iron spheroidized phaseswere formed in the ferrite matrix and the spheroidizedphase was shown to be graphite by SEM-EDS analysis Thesepictures show the typical microstructures of carbon steel andductile cast iron
In order to determine the effect of NaNO2addition
on the corrosion morphologies of ductile cast iron afterimmersion the corroded surface was observed The effect ofNaNO
2addition on the surface appearance of ductile cast
iron after the immersion test in simulated cooling water for 3hours at 25∘C was presented in Figure 7 Figure 7(a) showsthe addition of 0 ppm NaNO
2and Figure 7(b) shows the
addition of 10000 ppmNaNO2When noNaNO
2was added
the ductile cast iron was generally corroded on the entiresurface However when 10000 ppm NaNO
2was added (this
addition of which is not sufficient to inhibit corrosion ofductile cast iron as shown in Figures 1 and 3) the iron wascorroded locally near the spheroidized graphite and the cor-roded areas were agglomerated Figure 8 shows the corrosionmorphologies of ductile cast iron in which ductile cast iron
was corroded for 3 hours in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C Figure 8(a) shows the surface
contour using a 3D microscope and local corrosion near thespheroidized graphite was confirmed Figure 8(b) shows anSEM image of the corroded area showing that it was corrodedspherically near the graphite and thenfinally the graphite hadchipped off Also corrosion products and even cracks wereobserved near the chipped-off graphite These figures showthat galvanic corrosion took place in the ductile cast iron Itis well known that graphite is nobler than matrix iron [23]
The galvanic corrosion between graphite and matrixiron was simulated using a COMSOLMultiphysics programAnodic and cathodic Tafel slopes (+108mV and minus206mVresp) were applied to calculate the corrosion behavior of thecorroding and noncorroding areas Figure 9 shows computer3D simulation results of the corrosion propagation of ductilecast iron occurring in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C At the initial stage (0 hour)
the potential difference between graphite (the center) andmatrix (left and right) is shown by the blue and red colorsrespectively By increasing the immersion time the matrixnear the graphite corroded and the corrosion depth wasincreased its depth was greater near the graphite (Thisis the distance effect observed in galvanic corrosion) This
Advances in Materials Science and Engineering 7
50120583m
(a)
50120583m
(b)
Figure 7 Effect of NaNO2addition on surface appearance of ductile cast iron after the immersion test in simulated cooling water for 3 hours
at 25∘C (a) 0 ppm NaNO2and (b) 10000 ppm NaNO
2
12584
10067
7550
5034
2517
0000
(120583m
)
111858120583m107115 120583m
Height 10835120583m
Max 12584120583m
Width 1Width 2
(a) (b)
Figure 8 Corrosion morphologies of ductile cast iron corroded in stagnant simulated cooling water (10000 ppm NaNO2) for 3 hours at
25∘C (a) 3D microscope and (b) SEM image
simulation result differs from that shown in Figure 8(b) Thisdifference could be due to the characteristics of the graphite(However it should be noted that the COMSOLMultiphysicsprogram does not simulate the mechanical damage in gal-vanic corrosion)The crystal structure of graphite is covalentbonded with neighboring atoms in the same layer althoughlayers are van der Waals bonded together [24 25] and thusthe bonding force of graphite is very weak Therefore it isconsidered that the matrix is corroded galvanically and thatthe graphite is protruded and then graphite is peeled off layerby layer because of the weak bonding force of graphite
Figure 10 shows the elemental distribution analyzed usingEPMA on the surface of ductile cast iron passivated in
simulated cooling water (100000 ppm NaNO2) at 25∘C for
72 hours The SEM image clearly shows the microstructureof ductile cast iron Fe was depleted in the graphite area andcarbon was concentrated as spheroidized shapes Also whileoxygen was detected on the entire surface it was particularlyconcentrated on the graphite area and dim spots of nitrogenwere detected Figure 11 shows the elemental distributionanalyzed using EPMA on the surface of ductile cast ironcorroded in simulated cooling water (10000 ppm NaNO
2)
at 25∘C for 72 hours The SEM image shows the locallycorroded morphology as seen in Figure 7(b) Fe was notuniform and this is related to local corrosion However thecarbon distribution was very different to the fully passivated
8 Advances in Materials Science and Engineering
10 0 minus100
50
0minus10
10
zx
y
Graphite
055050045040035030(V(SCE))
(120583m)
(120583m
)
(120583m
)
(a)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m
)
(120583m
)
(b)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(c)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m)
(120583m
)
(d)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(e)
Figure 9 Surface electrolyte potential (V(SCE) the right vertical color bar) obtained by computer 3D simulation (the unit of 119909- 119910- and119911-axes 120583m) using COSOL Multiphysics on corrosion propagation with immersion time of ductile cast iron occurred in stagnant simulatedcooling water (10000 ppm NaNO
2) at 25∘C (a) 0 hour (b) 24 hours (c) 48 hours (d) 72 hours and (e) 144 hours
surface as shown in Figure 10(c)While spheroidized graphitewas not observed destroyed graphite and its location wereidentified this result provides the evidence that graphite canbe peeled off layer by layer as discussed above Oxygen wasdetected more on the Fe-depleted areas and dim spots ofnitrogenwere detectedThis oxygen comes from the sufficientNaNO
2 It will be discussed below
The depth profile on the passivated surface was obtainedusing XPS to determine the role of nitrite ion on thepassivation of steel and iron Figure 12 shows the depth profileusing XPS on the passive film of carbon steel passivated for24 hours in simulated cooling water (1000 ppm NaNO
2) at
25∘COxygen and nitrogenwere enriched at the outer surfaceand Fe drastically increased with etch time Figures 12(b)and 12(c) show that iron oxide was enriched at the outersurfaceNitrogenwas only detected before sputtering andwasnot detected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surface evenwith the NaNO
2addition to the solution Figure 13 shows
the depth profile using XPS on the passive film of ductilecast iron passivated for 24 hours in simulated cooling water(100000 ppm NaNO
2) at 25∘C Oxygen and nitrogen were
enriched at the outer surface and Fe is drastically increasedwith etch time Figures 13(b) and 13(c) show that iron oxide
Advances in Materials Science and Engineering 9
24384
42064
30120583m
(a)
523483443
564
362322282
402
241201161
80400
120
30120583m
(b)
339431332872
3656
235020891828
2611
156613051044
5222610
783
30120583m
(c)
928578
100
645750
71
433629
1581
22
30120583m
(d)
928578
100
645750
71
433629
1581
22
30120583m
(e)
Figure 10 Elemental distribution analyzed by EPMA on the surface of ductile cast iron passivated in simulated cooling water (100000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
10 Advances in Materials Science and Engineering
32880
40288
60120583m
(a)
463
431
398
496
333
301
268
366
236
203
171
106
73
41
138
60120583m
(b)
125011541058
1347
865769673
962
577481384
192960
288
60120583m
(c)
315291267
340
219195171
243
14612298
50262
74
60120583m
(d)
928578
100
645750
71
423528
1470
21
60120583m
(e)
Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
6 Advances in Materials Science and Engineering
50120583m
(a)
50120583m
(b)
(c) (d)
Figure 6 Optical microstructures (a b) and SEM images (c d) (a c) carbon steel and (b d) ductile cast iron
difference in the composition between the two alloys iscarbon content Figure 6 shows optical microstructures andSEM images for carbon steel and ductile cast iron In the caseof carbon steel ferrite and pearlite phases can be observedHowever in the case of ductile cast iron spheroidized phaseswere formed in the ferrite matrix and the spheroidizedphase was shown to be graphite by SEM-EDS analysis Thesepictures show the typical microstructures of carbon steel andductile cast iron
In order to determine the effect of NaNO2addition
on the corrosion morphologies of ductile cast iron afterimmersion the corroded surface was observed The effect ofNaNO
2addition on the surface appearance of ductile cast
iron after the immersion test in simulated cooling water for 3hours at 25∘C was presented in Figure 7 Figure 7(a) showsthe addition of 0 ppm NaNO
2and Figure 7(b) shows the
addition of 10000 ppmNaNO2When noNaNO
2was added
the ductile cast iron was generally corroded on the entiresurface However when 10000 ppm NaNO
2was added (this
addition of which is not sufficient to inhibit corrosion ofductile cast iron as shown in Figures 1 and 3) the iron wascorroded locally near the spheroidized graphite and the cor-roded areas were agglomerated Figure 8 shows the corrosionmorphologies of ductile cast iron in which ductile cast iron
was corroded for 3 hours in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C Figure 8(a) shows the surface
contour using a 3D microscope and local corrosion near thespheroidized graphite was confirmed Figure 8(b) shows anSEM image of the corroded area showing that it was corrodedspherically near the graphite and thenfinally the graphite hadchipped off Also corrosion products and even cracks wereobserved near the chipped-off graphite These figures showthat galvanic corrosion took place in the ductile cast iron Itis well known that graphite is nobler than matrix iron [23]
The galvanic corrosion between graphite and matrixiron was simulated using a COMSOLMultiphysics programAnodic and cathodic Tafel slopes (+108mV and minus206mVresp) were applied to calculate the corrosion behavior of thecorroding and noncorroding areas Figure 9 shows computer3D simulation results of the corrosion propagation of ductilecast iron occurring in stagnant simulated cooling water(10000 ppm NaNO
2) at 25∘C At the initial stage (0 hour)
the potential difference between graphite (the center) andmatrix (left and right) is shown by the blue and red colorsrespectively By increasing the immersion time the matrixnear the graphite corroded and the corrosion depth wasincreased its depth was greater near the graphite (Thisis the distance effect observed in galvanic corrosion) This
Advances in Materials Science and Engineering 7
50120583m
(a)
50120583m
(b)
Figure 7 Effect of NaNO2addition on surface appearance of ductile cast iron after the immersion test in simulated cooling water for 3 hours
at 25∘C (a) 0 ppm NaNO2and (b) 10000 ppm NaNO
2
12584
10067
7550
5034
2517
0000
(120583m
)
111858120583m107115 120583m
Height 10835120583m
Max 12584120583m
Width 1Width 2
(a) (b)
Figure 8 Corrosion morphologies of ductile cast iron corroded in stagnant simulated cooling water (10000 ppm NaNO2) for 3 hours at
25∘C (a) 3D microscope and (b) SEM image
simulation result differs from that shown in Figure 8(b) Thisdifference could be due to the characteristics of the graphite(However it should be noted that the COMSOLMultiphysicsprogram does not simulate the mechanical damage in gal-vanic corrosion)The crystal structure of graphite is covalentbonded with neighboring atoms in the same layer althoughlayers are van der Waals bonded together [24 25] and thusthe bonding force of graphite is very weak Therefore it isconsidered that the matrix is corroded galvanically and thatthe graphite is protruded and then graphite is peeled off layerby layer because of the weak bonding force of graphite
Figure 10 shows the elemental distribution analyzed usingEPMA on the surface of ductile cast iron passivated in
simulated cooling water (100000 ppm NaNO2) at 25∘C for
72 hours The SEM image clearly shows the microstructureof ductile cast iron Fe was depleted in the graphite area andcarbon was concentrated as spheroidized shapes Also whileoxygen was detected on the entire surface it was particularlyconcentrated on the graphite area and dim spots of nitrogenwere detected Figure 11 shows the elemental distributionanalyzed using EPMA on the surface of ductile cast ironcorroded in simulated cooling water (10000 ppm NaNO
2)
at 25∘C for 72 hours The SEM image shows the locallycorroded morphology as seen in Figure 7(b) Fe was notuniform and this is related to local corrosion However thecarbon distribution was very different to the fully passivated
8 Advances in Materials Science and Engineering
10 0 minus100
50
0minus10
10
zx
y
Graphite
055050045040035030(V(SCE))
(120583m)
(120583m
)
(120583m
)
(a)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m
)
(120583m
)
(b)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(c)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m)
(120583m
)
(d)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(e)
Figure 9 Surface electrolyte potential (V(SCE) the right vertical color bar) obtained by computer 3D simulation (the unit of 119909- 119910- and119911-axes 120583m) using COSOL Multiphysics on corrosion propagation with immersion time of ductile cast iron occurred in stagnant simulatedcooling water (10000 ppm NaNO
2) at 25∘C (a) 0 hour (b) 24 hours (c) 48 hours (d) 72 hours and (e) 144 hours
surface as shown in Figure 10(c)While spheroidized graphitewas not observed destroyed graphite and its location wereidentified this result provides the evidence that graphite canbe peeled off layer by layer as discussed above Oxygen wasdetected more on the Fe-depleted areas and dim spots ofnitrogenwere detectedThis oxygen comes from the sufficientNaNO
2 It will be discussed below
The depth profile on the passivated surface was obtainedusing XPS to determine the role of nitrite ion on thepassivation of steel and iron Figure 12 shows the depth profileusing XPS on the passive film of carbon steel passivated for24 hours in simulated cooling water (1000 ppm NaNO
2) at
25∘COxygen and nitrogenwere enriched at the outer surfaceand Fe drastically increased with etch time Figures 12(b)and 12(c) show that iron oxide was enriched at the outersurfaceNitrogenwas only detected before sputtering andwasnot detected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surface evenwith the NaNO
2addition to the solution Figure 13 shows
the depth profile using XPS on the passive film of ductilecast iron passivated for 24 hours in simulated cooling water(100000 ppm NaNO
2) at 25∘C Oxygen and nitrogen were
enriched at the outer surface and Fe is drastically increasedwith etch time Figures 13(b) and 13(c) show that iron oxide
Advances in Materials Science and Engineering 9
24384
42064
30120583m
(a)
523483443
564
362322282
402
241201161
80400
120
30120583m
(b)
339431332872
3656
235020891828
2611
156613051044
5222610
783
30120583m
(c)
928578
100
645750
71
433629
1581
22
30120583m
(d)
928578
100
645750
71
433629
1581
22
30120583m
(e)
Figure 10 Elemental distribution analyzed by EPMA on the surface of ductile cast iron passivated in simulated cooling water (100000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
10 Advances in Materials Science and Engineering
32880
40288
60120583m
(a)
463
431
398
496
333
301
268
366
236
203
171
106
73
41
138
60120583m
(b)
125011541058
1347
865769673
962
577481384
192960
288
60120583m
(c)
315291267
340
219195171
243
14612298
50262
74
60120583m
(d)
928578
100
645750
71
423528
1470
21
60120583m
(e)
Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Advances in Materials Science and Engineering 7
50120583m
(a)
50120583m
(b)
Figure 7 Effect of NaNO2addition on surface appearance of ductile cast iron after the immersion test in simulated cooling water for 3 hours
at 25∘C (a) 0 ppm NaNO2and (b) 10000 ppm NaNO
2
12584
10067
7550
5034
2517
0000
(120583m
)
111858120583m107115 120583m
Height 10835120583m
Max 12584120583m
Width 1Width 2
(a) (b)
Figure 8 Corrosion morphologies of ductile cast iron corroded in stagnant simulated cooling water (10000 ppm NaNO2) for 3 hours at
25∘C (a) 3D microscope and (b) SEM image
simulation result differs from that shown in Figure 8(b) Thisdifference could be due to the characteristics of the graphite(However it should be noted that the COMSOLMultiphysicsprogram does not simulate the mechanical damage in gal-vanic corrosion)The crystal structure of graphite is covalentbonded with neighboring atoms in the same layer althoughlayers are van der Waals bonded together [24 25] and thusthe bonding force of graphite is very weak Therefore it isconsidered that the matrix is corroded galvanically and thatthe graphite is protruded and then graphite is peeled off layerby layer because of the weak bonding force of graphite
Figure 10 shows the elemental distribution analyzed usingEPMA on the surface of ductile cast iron passivated in
simulated cooling water (100000 ppm NaNO2) at 25∘C for
72 hours The SEM image clearly shows the microstructureof ductile cast iron Fe was depleted in the graphite area andcarbon was concentrated as spheroidized shapes Also whileoxygen was detected on the entire surface it was particularlyconcentrated on the graphite area and dim spots of nitrogenwere detected Figure 11 shows the elemental distributionanalyzed using EPMA on the surface of ductile cast ironcorroded in simulated cooling water (10000 ppm NaNO
2)
at 25∘C for 72 hours The SEM image shows the locallycorroded morphology as seen in Figure 7(b) Fe was notuniform and this is related to local corrosion However thecarbon distribution was very different to the fully passivated
8 Advances in Materials Science and Engineering
10 0 minus100
50
0minus10
10
zx
y
Graphite
055050045040035030(V(SCE))
(120583m)
(120583m
)
(120583m
)
(a)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m
)
(120583m
)
(b)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(c)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m)
(120583m
)
(d)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(e)
Figure 9 Surface electrolyte potential (V(SCE) the right vertical color bar) obtained by computer 3D simulation (the unit of 119909- 119910- and119911-axes 120583m) using COSOL Multiphysics on corrosion propagation with immersion time of ductile cast iron occurred in stagnant simulatedcooling water (10000 ppm NaNO
2) at 25∘C (a) 0 hour (b) 24 hours (c) 48 hours (d) 72 hours and (e) 144 hours
surface as shown in Figure 10(c)While spheroidized graphitewas not observed destroyed graphite and its location wereidentified this result provides the evidence that graphite canbe peeled off layer by layer as discussed above Oxygen wasdetected more on the Fe-depleted areas and dim spots ofnitrogenwere detectedThis oxygen comes from the sufficientNaNO
2 It will be discussed below
The depth profile on the passivated surface was obtainedusing XPS to determine the role of nitrite ion on thepassivation of steel and iron Figure 12 shows the depth profileusing XPS on the passive film of carbon steel passivated for24 hours in simulated cooling water (1000 ppm NaNO
2) at
25∘COxygen and nitrogenwere enriched at the outer surfaceand Fe drastically increased with etch time Figures 12(b)and 12(c) show that iron oxide was enriched at the outersurfaceNitrogenwas only detected before sputtering andwasnot detected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surface evenwith the NaNO
2addition to the solution Figure 13 shows
the depth profile using XPS on the passive film of ductilecast iron passivated for 24 hours in simulated cooling water(100000 ppm NaNO
2) at 25∘C Oxygen and nitrogen were
enriched at the outer surface and Fe is drastically increasedwith etch time Figures 13(b) and 13(c) show that iron oxide
Advances in Materials Science and Engineering 9
24384
42064
30120583m
(a)
523483443
564
362322282
402
241201161
80400
120
30120583m
(b)
339431332872
3656
235020891828
2611
156613051044
5222610
783
30120583m
(c)
928578
100
645750
71
433629
1581
22
30120583m
(d)
928578
100
645750
71
433629
1581
22
30120583m
(e)
Figure 10 Elemental distribution analyzed by EPMA on the surface of ductile cast iron passivated in simulated cooling water (100000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
10 Advances in Materials Science and Engineering
32880
40288
60120583m
(a)
463
431
398
496
333
301
268
366
236
203
171
106
73
41
138
60120583m
(b)
125011541058
1347
865769673
962
577481384
192960
288
60120583m
(c)
315291267
340
219195171
243
14612298
50262
74
60120583m
(d)
928578
100
645750
71
423528
1470
21
60120583m
(e)
Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
8 Advances in Materials Science and Engineering
10 0 minus100
50
0minus10
10
zx
y
Graphite
055050045040035030(V(SCE))
(120583m)
(120583m
)
(120583m
)
(a)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m
)
(120583m
)
(b)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(c)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zx
y
Graphite
(120583m)
(120583m)
(120583m
)
(d)
10 0 minus10
0
50
0minus10
10
055050045040035030(V(SCE))
zxy
Graphite
(120583m)
(120583m
)
(120583m
)
(e)
Figure 9 Surface electrolyte potential (V(SCE) the right vertical color bar) obtained by computer 3D simulation (the unit of 119909- 119910- and119911-axes 120583m) using COSOL Multiphysics on corrosion propagation with immersion time of ductile cast iron occurred in stagnant simulatedcooling water (10000 ppm NaNO
2) at 25∘C (a) 0 hour (b) 24 hours (c) 48 hours (d) 72 hours and (e) 144 hours
surface as shown in Figure 10(c)While spheroidized graphitewas not observed destroyed graphite and its location wereidentified this result provides the evidence that graphite canbe peeled off layer by layer as discussed above Oxygen wasdetected more on the Fe-depleted areas and dim spots ofnitrogenwere detectedThis oxygen comes from the sufficientNaNO
2 It will be discussed below
The depth profile on the passivated surface was obtainedusing XPS to determine the role of nitrite ion on thepassivation of steel and iron Figure 12 shows the depth profileusing XPS on the passive film of carbon steel passivated for24 hours in simulated cooling water (1000 ppm NaNO
2) at
25∘COxygen and nitrogenwere enriched at the outer surfaceand Fe drastically increased with etch time Figures 12(b)and 12(c) show that iron oxide was enriched at the outersurfaceNitrogenwas only detected before sputtering andwasnot detected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surface evenwith the NaNO
2addition to the solution Figure 13 shows
the depth profile using XPS on the passive film of ductilecast iron passivated for 24 hours in simulated cooling water(100000 ppm NaNO
2) at 25∘C Oxygen and nitrogen were
enriched at the outer surface and Fe is drastically increasedwith etch time Figures 13(b) and 13(c) show that iron oxide
Advances in Materials Science and Engineering 9
24384
42064
30120583m
(a)
523483443
564
362322282
402
241201161
80400
120
30120583m
(b)
339431332872
3656
235020891828
2611
156613051044
5222610
783
30120583m
(c)
928578
100
645750
71
433629
1581
22
30120583m
(d)
928578
100
645750
71
433629
1581
22
30120583m
(e)
Figure 10 Elemental distribution analyzed by EPMA on the surface of ductile cast iron passivated in simulated cooling water (100000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
10 Advances in Materials Science and Engineering
32880
40288
60120583m
(a)
463
431
398
496
333
301
268
366
236
203
171
106
73
41
138
60120583m
(b)
125011541058
1347
865769673
962
577481384
192960
288
60120583m
(c)
315291267
340
219195171
243
14612298
50262
74
60120583m
(d)
928578
100
645750
71
423528
1470
21
60120583m
(e)
Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Advances in Materials Science and Engineering 9
24384
42064
30120583m
(a)
523483443
564
362322282
402
241201161
80400
120
30120583m
(b)
339431332872
3656
235020891828
2611
156613051044
5222610
783
30120583m
(c)
928578
100
645750
71
433629
1581
22
30120583m
(d)
928578
100
645750
71
433629
1581
22
30120583m
(e)
Figure 10 Elemental distribution analyzed by EPMA on the surface of ductile cast iron passivated in simulated cooling water (100000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
10 Advances in Materials Science and Engineering
32880
40288
60120583m
(a)
463
431
398
496
333
301
268
366
236
203
171
106
73
41
138
60120583m
(b)
125011541058
1347
865769673
962
577481384
192960
288
60120583m
(c)
315291267
340
219195171
243
14612298
50262
74
60120583m
(d)
928578
100
645750
71
423528
1470
21
60120583m
(e)
Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
10 Advances in Materials Science and Engineering
32880
40288
60120583m
(a)
463
431
398
496
333
301
268
366
236
203
171
106
73
41
138
60120583m
(b)
125011541058
1347
865769673
962
577481384
192960
288
60120583m
(c)
315291267
340
219195171
243
14612298
50262
74
60120583m
(d)
928578
100
645750
71
423528
1470
21
60120583m
(e)
Figure 11 Elemental distribution analyzed by EPMA on the surface of ductile cast iron corroded in simulated cooling water (10000 ppmNaNO
2) at 25∘C for 72 hours (a) SEM image (b) Fe (c) C (d) O and (e) N
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Advances in Materials Science and Engineering 11
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
Con
tent
s (at
)
Etch time (s)
CO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
0 s
110 s
(b)
5255275295315335355370
500
1000
1500
2000
2500
3000
3500
Cou
nts
s
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s110 s
110 s
0 s
(c)
minus30
minus20
minus10
0
10
20
30
396398400402404
Inte
nsity
(cps
)
Binding energy (eV)
0 s5 s20 s40 s
60 s80 s100 s
0 s
100 s
(d)
Figure 12 Depth profile by XPS on passive film of carbon steel passivated for 24 hours in simulated cooling water (1000 ppm NaNO2) at
25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
was enriched at the outer surface Nitrogen was only detectedbefore sputtering and at 10 secondsrsquo etch time and was notdetected at any sputtered depths This provides evidencethat nitrogen is present only on the outermost surfaceeven with the NaNO
2addition to the solution However
nitrogen of passivated ductile cast iron was detected at aslightly deeper depth than that of the passivated carbonsteel This behavior seems to be related to the corrosion andpassivation between graphite and matrix in ductile cast iron
Figure 14 shows the deconvolution of the chemical speciesdetermined by XPS on the surface of (a b c) carbon steelpassivated in 1000 ppm NaNO
2and (a1015840 b1015840 c1015840) ductile cast
iron passivated in 100000 ppm NaNO2 Regardless of the
alloys and sputtering time (0 sec and 10 sec) the passivefilms formed by NaNO
2addition were composed of iron
oxides (Fe2+ and Fe3+) Also nitrogen before sputtering existsas nitrogen compounds including NOminus (4004 3992 eV)NH4
+ (4011 eV) NH3(3986 3998 eV) and NO (3996 eV)
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
12 Advances in Materials Science and Engineering
0
20
40
60
80
100
minus5 0 5 10 15 20 25 30 35 40 45 50
(at
)
Etch time (s)
CSiO
FeN
(a)
0
2000
4000
6000
8000
10000
704706708710712714716
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(b)
0
500
1000
1500
2000
2500
3000
3500
525527529531533535537
Cou
nts
s
Binding energy (eV)
0 s
110 s
0 s5 s20 s40 s
60 s80 s110 s
(c)
minus30
minus20
minus10
0
10
20
30In
tens
ity (c
ps)
Binding energy (eV)
100 s
0 s
0 s5 s20 s40 s
60 s80 s100 s
405 404 403 402 401 400 399 398 397 396
(d)
Figure 13 Depth profile by XPS on passive film of ductile cast iron passivated for 24 hours in simulated cooling water (100000 ppmNaNO2)
at 25∘C (a) depth profile (b) Fe2p detail scan (c) O1s detail scan and (d) N
1s detail scan
[26 27] However it should be noted that the chemical statesof nitrogen on the passivated surface are not easy to identifyby XPS
Therefore as discussed above corrosion and its inhibitionmodel can be proposed as follows Figure 15 shows the corro-sion and inhibition steps of ductile cast iron with nitrite addi-tion When no corrosion inhibitor is used general corrosionand galvanic corrosion occur simultaneously and thus thesurfacemay show relatively uniform corrosion (Figure 15(a))Also when the amount of corrosion inhibitor is insufficient
(eg 10000 NaNO2) some area may be passivated (red
line) and galvanic corrosion can occur finally the iron thenreveals localized corrosion (Figure 15(b)) However whena sufficient corrosion inhibitor (eg 100000 ppm NaNO
2
in Figure 15(c)) is used (even though galvanic corrosionbetween graphite andmatrix has occurred) the entire surfacecan be passivated and thus corrosion can be inhibited Alsoit should be noted that NO
2
minus ion is used to oxidize thematrixand can itself be reduced to nitric oxide this compound canbe absorbed on the surface of graphite and thus the enriched
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Advances in Materials Science and Engineering 13
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+ FeM
10 s
0
100
200
300
400
500
704706708710712714716
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+ Fe2+
FeM
0 s
0
500
1000
1500
2000
2500
704706708710712714
Inte
nsity
(cps
)
Binding energy (eV)
Fe3+
Fe2+ FeM
10 s
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
0
10
20
30
40
397398399400401402
Inte
nsity
(cps
)
Binding energy (eV)
0 s
NOminus
NOminus
NH3
NH3NO
NH4+
(a)
(b)
(c)
(a998400)
(b998400)
(c998400)
Figure 14 Deconvolution of the chemical species determined by XPS on the surface of (a a1015840 c) carbon steel passivated in 1000 ppmNaNO2
and (b b1015840 c1015840) ductile cast iron passivated in 100000 ppm NaNO2 (a) and (a1015840) Fe 2p (b) and (b1015840) Fe 2p and (c) and (c1015840) N 1s
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
14 Advances in Materials Science and Engineering
G G G
G G G
G G G
DCI
DCI
DCI
(a)
DCI
DCI
DCI
G G G
G G G
GG
(b)
DCI
DCI
DCI
G G G
G G G
G G G
(c)
Figure 15 Corrosion and inhibition steps with nitrite addition of ductile cast iron (a) without corrosion inhibitor (b) with insufficientcorrosion inhibitor (10000 ppmNaNO
2) and with sufficient corrosion inhibitor (100000 ppmNaNO
2) (G graphite red line metallic oxide
dot line nitrogen compound)
0
50
100
150
200
minus15 minus1 minus05 0 05 1E (V(SCE))
1000ppm100ppm
Cminus2
()
120583Fminus2cm
4times10
9
(a)
0
50
100
150
minus15 minus1 minus05 0 05 1
100000ppm50000ppm
E (V(SCE))
Cminus2
()
120583Fminus2cm
4times10
9
(b)
Figure 16 Effect of NaNO2addition on Mott-Schottky plot for the passive film formed in deaerated simulated cooling water at 25∘C (a)
carbon steel at +400mV (SCE) and (b) ductile cast iron at 0mV (SCE)
nitrogen compounds could be detected in the EPMA andXPS results Therefore since nitrite ion needs to oxidize thesurface of the matrix and needs to passivate the galvaniccorroded area and since it is absorbed on the surface ofgraphite a larger amount of corrosion inhibitor is needed forductile cast iron than for carbon steel
On the other hand passivated film of various alloysexhibits semiconductive properties [28ndash30] Acquisition ofMott-Schottky plots is a usual way for semiconductor mate-rials electrochemical characterization Mott-Schottky plot(inverse square of space charge layer capacitance 119862sc
minus2versus semiconductor electrode potential 119864) gives dopingdensity by slope of the straight line and flat band potential byintercept [31] A positive slope in the plot indicates theN-typesemiconductive properties Figure 16 shows a Mott-Schottky
plot of the effect of NaNO2addition for the passive film
formed in deaerated simulated coolingwater at 25∘C Regard-less of the alloys the increasing inhibitor concentrationstrengthened the N-type properties Also these plots revealedthe N-type semiconductive properties of the passivated sur-face film due to nitrite addition
4 Conclusions
(1) While NaNO2addition can greatly inhibit the corro-
sion of carbon steel and ductile cast iron in orderto improve the similar corrosion resistance ca 100timesmore NaNO
2addition is needed for ductile cast
iron than for carbon steel A corrosion and inhibitionmechanism is proposed whereby NO
2
minus ion is added
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
Advances in Materials Science and Engineering 15
to oxidize The NO2
minus ion can be reduced to nitrogencompound and this compound may be absorbed onthe surface of graphite Therefore since nitrite ionneeds to oxidize the surface of matrix and needs topassivate the galvanic corroded area and since it isabsorbed on the surface of graphite a greater amountof corrosion inhibitor needs to be added to ductilecast iron than to carbon steel
(2) The passive film of carbon steel and ductile cast ironformed by NaNO
2addition showed N-type semi-
conductive properties and its resistance is increasedthe passive current density is thus decreased and thecorrosion rate is then lowered In addition the filmis mainly composed of iron oxide due to the oxida-tion by NO
2
minus ion however regardless of the alloysnitrogen compounds (not nitrite) were detected at theoutermost surface but were not incorporated in theinner oxide
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
This work was supported by the Nuclear Power CoreTechnology Development Program of the Korea Instituteof Energy Technology Evaluation and Planning (KETEP)granted financial resource from theMinistry of Trade Indus-try amp Energy Republic of Korea (no 20131520000100)
References
[1] Plant Shutdown Caused by the Crack of the Essential ServiceWater System Concrete Pipe Incident Report 7285 Hanul 1Republic of Korea 1998
[2] Firewater Supply Valve Downstream Buried Piping Leakage ofIntake Area Equipment Failure Report 06-Hanbit 4-1 Hanbit4 Republic of Korea 2006
[3] USNRC ldquoGeneric aging lessons learned (GALL) reportrdquo TechRep NUREG-1801 Rev 2 Division of Regulatory ImprovementPrograms 2010
[4] EPRI ldquoNondestructive evaluation guided wave technologydevelopment and nuclear application assessmentrdquo Tech RepEPRI-1015156 2007
[5] EPRI ldquoCondition assessment of large-diameter buried pipingphase 2-vehicle design and constructionrdquo EPRI 1011829 EPRI2005
[6] NRC Inspection Manual ldquoInspection of structures passivecomponents and civil engineering features at nuclear powerplantsrdquo Inspection Procedure 62002 United States NuclearRegulatory Commission (USNRC) 1996
[7] E McCafferty Introduction to Corrosion Science Springer NewYork NY USA 2009
[8] V S Sastri Corrosion Inhibitors Principles and ApplicationsWiley London UK 1998
[9] K NMohana andAM Badiea ldquoEffect of sodiumnitrite-boraxblend on the corrosion rate of low carbon steel in industrial
watermediumrdquoCorrosion Science vol 50 no 10 pp 2939ndash29472008
[10] M Cohen ldquoInhibition of steel corrosion by sodium nitrite inwaterrdquo Journal of the Electrochemical Society vol 93 no 1 pp26ndash39 1948
[11] R Pyke and M Cohen ldquoRate of breakdown and mechanism ofnitrite inhibition of steel corrosionrdquo Journal of the Electrochem-ical Society vol 93 no 3 pp 63ndash78 1948
[12] M Cohen R Pyke and P Marier ldquoThe effect of oxygen oninhibition of corrosion by nitriterdquo Journal ofTheElectrochemicalSociety vol 96 no 4 pp 254ndash261 1949
[13] S M Matsuda and H H Uhlig ldquoEffect of pH sulfates andchlorides on behavior of sodium chromate and nitrite aspassivators for steelrdquo Journal of the Electrochemical Society vol111 no 2 pp 156ndash161 1964
[14] W D Robertson ldquoMolybdate and tungstate as corrosioninhibitors and the mechanism of inhibitionrdquo Journal of theElectrochemical Society vol 98 no 3 pp 94ndash100 1951
[15] M J Pryor and M Cohen ldquoThe inhibition of the corrosion ofiron by some anodic inhibitorsrdquo Journal of the ElectrochemicalSociety vol 100 no 5 pp 203ndash215 1953
[16] S Karim C M Mustafa Md Assaduzzaman and M IslamldquoEffect of nitrite ion on corrosion inhibition of mild steelin simulated cooling waterrdquo Chemical Engineering ResearchBulletin vol 14 pp 87ndash91 2010
[17] Y T Horng and Y L Tsai ldquoAn investigation of mild steel withnitrogen-containing inhibitor in hydrochloric acidrdquo CorrosionScience and Technology vol 2 no 5 pp 233ndash237 2003
[18] L Abosrra M Youseffi and A F Ashour ldquoEffectiveness ofcalcium nitrite in retarding corrosion of steel in concreterdquoInternational Journal of Concrete Structures and Materials vol5 no 1 pp 65ndash73 2011
[19] R Mehra and A Soni ldquoInhibition of corrosion of mild steelby nitrite hydrogen phosphate and molybdate ions in aqueoussolution of sodium chloriderdquo Indian Journal of Engineering ampMaterials Sciences vol 9 no 2 pp 141ndash146 2002
[20] ASME ASME Boiler amp Pressure Vessel Section IImdashPart AlsquoFerrous Materials Specifications (Beginning to SA-450)rsquo ASME2011
[21] KoreanAgency for Technology and StandardsKSD4311 DuctileIron Pipe Korean Agency for Technology and StandardsGyeonggi-do South Korea 2010
[22] D DMacdonald ldquoThe point defect model for the passive staterdquoJournal of the Electrochemical Society vol 139 no 12 pp 3434ndash3449 1992
[23] Y S Kim S J Park and Y R Yoo ldquoGalvanic corrosion behaviorbetween carbon steel bolted GECM(graphite epoxy compositematerial)Al platesrdquo Corrosion Science and Technology vol 12no 1 pp 19ndash33 2013
[24] P Q Dai Z R He W Q Wu and Z Y Mao ldquoMechanicalbehaviour of graphite in fracture of austempered ductile ironrdquoMaterials Science and Technology vol 18 no 9 pp 1052ndash10562002
[25] J R Davis ASM Specialty Handbook Cast Irons ASM Interna-tional Novelty Ohio USA 1996
[26] C D Wagner W H Riggs L E Davis J F Moulder and GE Muilenberg Handbook of X-Ray Photoelectron SpectroscopyPerkin-Elmer 1979
[27] Y S Kim ldquoSynergistic effect of nitrogen and molybdenum onlocalized corrosion of stainless steelrdquo Corrosion Science andTechnology vol 9 no 1 pp 20ndash28 2010
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
BioMed Research International
MaterialsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Nano
materials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal ofNanomaterials
16 Advances in Materials Science and Engineering
[28] H J Jang ldquoStudy on the semiconducting properties of thepassive films formed on Ni-Cr alloys in pH 85 buffer solutionrdquoJournal of Advanced Engineering and Technology vol 2 no 2pp 285ndash289 2009
[29] A Di Paola ldquoSemiconducting properties of passive films onstainless steelsrdquo Electrochimica Acta vol 34 no 2 pp 203ndash2101989
[30] C Sunseri S Piazza and F Di Quarto ldquoPhotocurrent spectro-scopic investigations of passive films on chromiumrdquo Journal ofthe Electrochemical Society vol 137 no 8 pp 2411ndash2417 1990
[31] A S Bondarenko and G A Ragoisha ldquoVariable Mott-Schottky plots acquisition by potentiodynamic electrochemicalimpedance spectroscopyrdquo Journal of Solid State Electrochem-istry vol 9 no 12 pp 845ndash849 2005
Submit your manuscripts athttpwwwhindawicom
ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CorrosionInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Polymer ScienceInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CeramicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CompositesJournal of
NanoparticlesJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
Biomaterials
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
NanoscienceJournal of
TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of
NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
CrystallographyJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CoatingsJournal of
Advances in
Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Smart Materials Research
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MetallurgyJournal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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