251

HL HL HL HL ISSN: 2231 – 3087(print)

http://heteroletters.org ISSN: 2230 – 9632 (Online)

Coden HLEEAI

Vol. 4: (2), 2014, 251-266

CORROSION RESISTANCE OF MILD STEEL IN ACID SOLUTIONS IN THE

PRESENCE OF [4-METHOXY-6-METHYL-PYRIMIDIN-2 YL] PYRIDINE-2 YLM

ETHYLENE- AMINE AS CORROSION INHIBITOR.

Ompal Singh Yadava, Sudershan Kumar

c, Gurmeet kaur

b, Gurmeet Singh

a

aDepartment of Chemistry, University of Delhi, Delhi-110007 bSGTB Khalsa College, University of Delhi, Delhi- 110007

cHindu College, University of Delhi, Delhi- 110007

*E-mail: gurmeet123@yahoo.com

Abstract:

The new Schiff base namely [4-methoxy-6-methyl-pyrimidin-2-yl] pyridine-2-ylm

ethylene- amine (S1) was synthesized and its capability as corrosion inhibitor on the mild steel in

0.5M H2SO4 was investigated by using the conventional potentiodynamic polarization studies,

linear polarization studies (LPR), electrochemical impedance spectroscopy studies (EIS).

Polarisation curves revealed that this compound is a mixed type (cathodic/anodic) inhibitor.

Atomic force microscopy revealed that a protective film was formed on the surface of the

inhibited sample. The adsorption of the inhibitor was found to confirm Langmuir isotherm and

standard adsorption parameters Kads, and ∆G0ads were determined from adsorption isotherms.

Quantum chemical calculations were further applied to reveal the adsorption structure and

explain the experimental results.

Keywords: Mild Steel; EIS; Polarization; Quantum chemical;Acid inhibition.

Introduction: Mild steel has been extensively used in various industries. Sulphuric acid solutions are widely

used for pickling, descaling, acid cleaning, oil well acidizing etc. [1–5]. Because organic

inhibitors act by adsorption on the metal surface, the efficiency of these compounds depends

strongly on their ability to form complexes with the metal [6]. Both π electrons and polar groups

containing nitrogen, oxygen and/or sulphur are fundamental characteristics of this type of

inhibitor. The polar functional groups are usually considered the chelation centre for chemical

adsorption [7, 8]. Schiff base inhibitors have been reported as corrosion inhibitors for steel,

copper and aluminium previously [9–13]. Some research works reveal that the inhibition

efficiency of Schiff bases is much greater than the corresponding amines and aldehydes which

has been attributed to the presence of a -C=N group in the molecules [14–16]. Many methods

like gravimetric estimation, polentiostatic polarisation, EIS, surface analysis and theoretical

quantum chemical studies have been used in this type of work. The theoretical methods and

252

molecular modelling have already become very powerful methods in determining the molecular

structures as well as elucidating electronic properties characterizing reactivity, shape and binding

properties of molecule.

The purpose of the current study is to observe the inhibitory action of Schiff base containing

nitrogen and oxygen as hetero atoms as substituents in their structure for the corrosion of mild

steel in 0.5M H2SO4 solution. Effects of concentrations and molecular structure on the inhibition

efficiencies of newly synthesized Schiff base namely [4-methoxy-6-methyl-pyrimidin-2-yl]

pyridine-2-ylm ethylene- amine, has been studied systematically by LPR, EIS and

potentiodynamic polarization.

Experimental:

Synthesis of the inhibitors: The Schiff base [4-methoxy-6-methyl-pyrimidin-2-yl] pyridine-2-ylm ethylene- amine was

synthesised by refluxing 2-Amino-4-methoxy-6-methyl pyrimidine(0.4388 gm/mol) and

Pyridine -2- aldehyde (0.3378 ml/mol) in 100ml ethanol for 8 hours then the reaction mixture

was cooled and solvent was removed by rota vapour to get the product. The general reaction

and structure of Schiff base (S1) is shown in fig (1). The 1H NMR spectra of product, was shown

in fig 2. 1H NMR (δ ppm, 400 MHz, CD3OD-d6, 298K): 8.7(d, 1H), 8.0 (t,1H), 8.6(t, 1H),

8.1(d,1H), 6.3(s, 1H),5.8(s,1H), 4.0(s,3H),2.3(s,3H) and IR (KBr): C=N is 1615 cm-1.

Electrodes and chemicals:

The working electrodes were prepared from mild steel with chemical composition (wt. %) of: C

(0.16), Si (0.030), P (0.0020), Mn (1.00) Ti (0.001) and balance was Fe. Mild steel cut as

rectangular specimen having 1cm2 areas, soldered with Cu wire for electrical connection and

covered with araldite except one active flat surface which is supposed to be exposed to the

corrosive solution. Before each experiment the electrode was polished with emery papers of

different grades (100, 320, 600 and 1000) and washed with acetone. The corrosive solution

(0.5M H2SO4) was prepared by dilution of analytical (AR grade 98%) H2SO4 with double-

distilled water. The different concentrations of inhibitor employed were prepared in 0.5 M

H2SO4.

Electrochemical Measurement:

Electrochemical experiments were carried out on electrochemical workstation CHI model 760c.

Potentiodynamic polarization, electrochemical impedance spectroscopy and liner polarization

studies were carried out by using three electrode cell assemblies. The working electrode was

mild steel, Pt-elecrode used as counter electrode (CE), and saturated calomel electrode (SCE)

was used as reference electrode. Potentiodynamic polarization curves were obtained with a scan

rate of 0.01Vs-1 in the potential range from-0.9V to + 0.1V, relative to the corrosion potential.

The impedance measurements were carried out at the open circuit potential. The alternating

current frequency range was extended from 100 KHz to 0.1 Hz, with a 5 mV sine wave as the

excitation signals.

Quantum chemical calculation:

Theoretical calculations such as energy of the highest occupied molecular orbital (EHOMO),

energy of the lowest unoccupied molecular orbital (ELUMO), energy gap (∆E) between LUMO

and HOMO and Mullikan charges on the back bone atoms were calculated using Hyper-chem

8.0.

253

100(%))(×

−=

Corr

iCorrCorr

I

IIE

10000 ×

−=

i

i

Icorr

IcorrIcorrEI

Atomic force microscopy:

Atomic force microscopy was used for surface morphology studies. The protective films were

examined with atomic force microscopy (AFM) Nano Surf Scan-2. The topography of the entire

samples for the scanned area of 4 µm × 4 µm (16 µm2) is evaluated for a set point of 20 nN and a

scan speed of 10 mm/s. The three and two-dimensional topography of surface films gave various

roughness parameters of the film.

Result and discussion:

Polarization measurement: Metallic corrosion process by electrochemical kinetics can be characterized by determining

polarization parameters such as corrosion current density (icorr), corrosion potential (Ecorr), Tafel

slopes (βa and βc) and corrosion efficiencies given in table 1. Potentiodynamic polarization

curves for mild steel in 0.5 M H2SO4 with and without different concentrations of synthesised

inhibitor at 298 K are shown in Fig 3. It is clear from the Fig. 3 that anodic and cathodic

reactions of mild steel electrode corrosion were inhibited by the increase in concentration of the

synthesized Schiff base. This result suggests that the addition of the synthesized inhibitor reduces

anodic dissolution and also retards the hydrogen evolution reaction [17]. The inhibition

efficiency, IE% was calculated from this formula.

Where Icorr and Icorr(i) are the corrosion current densities in the

absence and presence of inhibitor. The inhibition of these reactions is more

pronounced with the increasing inhibitor concentration while the corrosion potential values

shifted towards more negative values. It can be seen that in anodic area for potential higher than -

300 mV/SCE, the presence of Schiff base (S1) did not change the current v/s potential

characteristics and inhibitor start to desorb (Fig. 3). This potential can be defined as the

desorption potential. Similar behaviour has been already reported for other organic compounds

[18,19]. The behaviour of inhibitor at potentials greater than -300mV/SCE could be associated

with the significant dissolution of mild steel. This dissolution results in desorption of the

adsorbed film of inhibitor on the surface of the electrode in 0.5M H2SO4 media. In this case

desorption rate of inhibitor is raised more than its adsorption. However, inhibitors influenced

anodic reaction at potentials lower than-300 mV/SCE. This result indicated that the inhibition of

the mild steel corrosion is under cathodic and anodic control, i.e. mixed type. The Ecorr values for

(S1) shift towards more negative side with an increase in the inhibitor concentration. These shifts

can be attributed to the decrease in the rate of the hydrogen evolution reaction on the mild steel

surface caused by the adsorption of the Schiff base to the metal surface [20].

Electrochemical impedance spectroscopy:

Corrosion behaviour of mild steel in 0.5M H2SO4 in the presence and absence of Schiff base

compound has been investigated using CHI 760c electrochemical workstation at 298 K. The

simplest fitting is represented by Randles equivalent circuit (Fig 9), which is a parallel

combination of the charge-transfer resistance (Rct) and the constant phase element (CPE), both in

series with the solution resistance (Rs). The electrochemical impedance spectra data are listed in

table 2. Table 2 indicates that the Rs values are very small compared to the Rct values, and Rct

values increases with the capacitance (Cdl ) values decreases. The inhibition efficiency, IE% was

calculated from this formula.

1

2

254

1

0 )])([ −= n

CPE jYZ ω

1

max0 )( −= n

dl YC ω

inh

ads

inh CK

C+=

1

θ

)5.55ln(0 ×−=∆ adsKRTG

The double layer between the charged metal surface and the solution is measured as an electrical

capacitor. In Fig. 4, the Nyquist plots contain depressed semicircles with the centre under the

real axis. This type of behaviour characteristic for solid electrodes and often referred to

frequency dispersion could be attributed to different physical phenomena such as roughness and

in homogeneities of the solid surfaces, impurities, grain boundaries and distribution of the

surface active sites [21]. Therefore, a constant phase element (CPE) instead of a capacitive

element is used to get a more accurate fit of experimental data set. The impedance function of a

CPE is defined by the mathematical expression given below [22]:

Where Y0 is the magnitude of the CPE, n is the CPE exponent (phase

shift), ω the angular frequency (ω = 2πf, where f is the AC frequency), and j here is the

imaginary unit. When the value of n is 1, the CPE behaves like an ideal double-layer capacitance

(Cdl) [22]. The correction of capacity to its real values is calculated from.

where ωmax is the frequency at which the imaginary part of impedance (-Zi) has a maximum [23].

The adsorption of inhibitor on the electrode surface decreases its electrical capacity as

they displace the water molecules and other ions originally adsorbed on

the surface [24, 25]. The Rct values increased with inhibitor concentrations may

suggest the formation of a protective layer on the electrode surface. This layer makes a barrier

for mass and charge-transfer [26].

Adsorption Isotherm:

The adsorption isotherm gives the evidence on the metal and inhibitor interaction. The

adsorption process depends on inhibitors such as the chemical structures of organic compounds,

the nature and surface charge of metal, the distribution of charge in molecule and the type of

aggressive media. The adsorption isotherm can be explained by substitution process between

inhibitor in the aqueous media, the water molecules associated with the mild steel surface [27]

and adsorption of organic molecule on metal surface. The substitution process represented by

the equilibrium:

Inhsol + xH2Oads ↔ Inhads + xH2O

Where x is the number of water molecules replaced by adsorption of a molecule of the Schiff

base. Some attempts have been made to fit the values of θ to various isotherms including

Langmuir, Frumkin and Temkin isotherm. However, the best fit is obtained from the Langmuir

isotherm. A correlation between θ and inhibitor concentration can be represented as:

where Cinh is the inhibitor concentration, θ is the fraction of total surface covered by the inhibitor

molecules and Kads is the adsorption equilibrium constant. The value of

determined from the plot of Cinh/θ vs. Cinh at Kads, in Table. 3,

constant temperature (Fig - 5) is used to calculate the value of the standard

free energy of adsorption (∆Gads) using the following expression [28]:

∆G0 is the standard free energy of adsorption, R is universal gas

constant and the value 55.5 is the concentration of water solution in moles. The average values of

∆Gads were found as -35.25 for (S1). The negative values of standard free energy of adsorption

indicates spontaneous adsorption of inhibitor on mild steel surface and also the strong interaction

and stability of the adsorbed layer with the steel surface [29, 30]. Commonly the standard free

energy of adsorption values of -20 kJ mol-1 or less negative are associated with an electrostatic

3

4

5

6

7

255

)exp(RT

EAk a−

=

interaction between charged inhibitor molecule and charged metal surface (physical adsorption);

those of - 40 kJ mol-1

or more negative involves charge sharing or transfer from the inhibitor

molecule to the metal surface to form a co-ordinate covalent bond (chemical adsorption) [31].

The values of standard free energy of adsorption are between these two, but modestly closer to -

40 kJ mol-1. Therefore, it can be concluded that the adsorption of inhibitor on the steel surface

takes place through both chemical and physical adsorption namely mixed type with

predominantly chemical one [32].

Effect of temperature:

The effect of temperature on the corrosion rate of mild steel in 0.5 M H2SO4 solution in the

absence and presence of different concentrations of Schiff base was studied at different

temperatures (298–328 K) by potentiodynamic polarization technique. The corrosion rates at

different temperature with different concentration show are in table 1. The apparent activation

energy, Ea of the corrosion reaction was determined using Arrhenius plots. Arrhenius equation

could be written as [33,34]:

where k is the corrosion rate, Ea is the apparent activation energy of the

corrosion reaction, R is the gas constant, T is the absolute temperature and A is the Arrhenius

pre-exponential factor. The apparent activation energy of the corrosion reaction in the presence

and absence of the inhibitor could be determined by plotting ln Icorr against 1/T, which gives a

straight line with a slope allowing the determination of Ea. Fig. 6 shows these plots in the

absence and presence of different concentrations of inhibitor. The calculated values of the

apparent activation corrosion energies in the absence and presence of inhibitor are listed in table

4. The results show that the corrosion rate increases with increase in temperature. The lower

activation energy in the presence of inhibitor has been explained in different ways in the

literature. Some authors [35] showed that at higher temperatures the covered surface by inhibitor

increases. According to other authors [36] the lower activation energy in presence of inhibitor is

indication for its chemisorption. The pre-exponential factor A in the Eq. (7) is related to the

number of active centres or sites [37].

Theoretical study:

The influence on electronic interaction between iron surface and inhibitor is calculated by

quantum chemical parameters. EHOMO, the energy of highest occupied molecular orbital; ELUMO,

the energy of lowest unoccupied molecular orbital shown in fig-7, ∆E the energy of ELUMO -

EHOMO, µ is the dipole moment have been determined for possible relations with the inhibitor

efficiency of the (S1) molecule and listed in Table 5. EHOMO is often associated with the electron

donating ability of a molecule. The negative coefficient of EHOMO also confirms the

physisorption mechanism [38]. This theoretical result is in good agreement with the values of

∆Goads obtained experimentally. The energy of the LUMO is directly related to the electron

affinity and characterizes the susceptibility of the molecule towards attack by nucleophiles. The

lower the values of ELUMO are, the stronger the electron accepting abilities of molecules. The

HOMO and LUMO energies are correlated with present inhibition efficiencies. The present

inhibition efficiencies increase if the molecules have higher HOMO energies and lower LUMO

energies showed table 5 [39]. The number of transferred electrons (∆N) was calculated using the

following equation [40]:

Where χFe and χinh denote the absolute electronegativity of iron and the inhibitor molecule,

respectively; ηFe and ηinh denote the absolute hardness of iron and the inhibitor molecule,

8

2

AI +=χ 10

)(2 inhFe

inhFeNηη

χχ

+

−=∆

256

respectively. These quantities are related to electron affinity (A) and ionization Potential (I) as

follows:

I and A are related in turn to EHOMO and ELUMO as follows:

I = -EHOMO

A = -ELUMO

I and A values calculated using values of χ and η obtained from quantum chemical calculations.

The fraction of electrons transferred from inhibitors to the iron surface was calculated using a

theoretical χ value of 7 eV mol-1 and η value of 0 eV mol

-1 for iron [42]. Lukovit et al. [40]

reported that if ∆N < 3.6, then the inhibition efficiency increased with increasing electron

donating ability at the metal surface. However, in the present study the calculated ∆N value for

(S1) 0.2126. The experimental observation confirms from the above results that (S1) acts as

electron donor and mild steel surface as electron acceptor and hence (S1) may bind to the metal

surface to form inhibitive adsorption layer against corrosion. Total negative charge (TNC) is the

sum of all such negative charges present in the molecule. Higher the TNC value indicates the

presence of potential adsorption centres. Further, TNC/n ratio could be conveniently used to

compare the magnitude of negative charges between two or more molecules [42].

Linear polarization resistance:

The efficiency of corrosion inhibition by (S1) has been assessed with the help of LPR

measurements. LPR data obtained were added to Table 2. The Rp and IE % values obtained from

the LPR measurements are comparable and run parallel with those obtained from the EIS

measurements. The Rp value of (S1) increased with concentration which suggests that the

improvement of adsorption of molecule on the mild steel surface and blocking the active sites

efficiently [43, 25]. The present results showed that the inhibition efficiency of (S1) molecule

increased to 98% using inhibitor of concentration 0.01mol/L. The greater inhibitive authority of

(S1) can be explained by the presence of long π conjugation in both aromatic ring and electron

donating group as well as an iminic (–C =N–) group which are generally assumed to be active

centre of adsorption [44,45]. During the adsorption process, (S1) is expected to replace by much

more water molecules and cover the metal surface more efficiently. In literature, it was also

reported [46] that, in some cases, the imine group is not stable, particularly in acid medium,

where it undergoes hydrolysis, regenerating an amine and an aldehyde. If the hydrolysis takes

place, the efficiency measured is probably due to the presence of this preceding compound.

Atomic force micrographs:

AFM is a powerful technique to investigative the surface morphology studies which has been

recently used to study the influence of inhibitors on the metal/solution interface [47, 48]. Three-

dimensional AFM images and sectional analysis of the mild steel surface in the absence and

presence of 0.01 M [4-methoxy-6-methyl-pyrimidin-2-yl] pyridine-2-ylm ethylene- amine (S1)

are given in Fig.8a–b. It is clearly evident that the surface is more uniform than the surface in the

absence of the inhibitor. The mean roughness of the steel surface in the inhibited solution is 122

nm. The AFM images indicate that the inhibitor molecules are adsorbed on the steel surface and

reduce the corrosion.

2

AI −=η 11

12

13

257

Potential of zero charge and the inhibition mechanism:

All mechanism of corrosion inhibitors explained by adsorption phenomena. The adsorption

mostly depends on the surface charge of the metal, the charge or dipole moment of the inhibitor

molecules and the other ions that are specifically adsorbed on to the metal surface [49]. The

surface charge of the metal is defined by the position of the open circuit potential with respect to

the PZC [50]. The double layer capacitance value depends on the applied DC potential is

graphically denoted in Fig. 10a-b. The values of PZC and EOCP for mild steel in presence and

absence of inhibitor in 0.5M H2SO4 solution are shown in table 6. It can be determined according

to Antropov et al. [51] by comparing the potential of zero charge (PZC) and the corrosion

potential of the metal in the electrolytic medium. As PZC corresponds to a state at which the

surface is free from charges, at the stationary (corrosion) potential the metal surface will be

positively or negatively charged. Hence, it is necessary to have reliable data about PZC. When

mild steel is immersed in acid solution containing (S1), three kinds of species can be adsorbed on

its surface, as described below.

(1) If the metal surface is positively charged with respect to PZC, the SO4 -2 ions will first get

adsorbed on the metal surface. After this first adsorption step, the mild steel surface will become

negatively charged. Hence, the positively charged of (S1) cationic forms will form an

electrostatic bond with the SO4 -2 ions already adsorbed on mild steel surface. Moreover, the

excess positive potential on the electrode surface, Er (Er = Ecorr - Epzc) increases as more inhibitor

molecules adsorbed on it [52].

(2) If the metal surface is negatively charged with respect to PZC, the protonated water

molecules and (S1) cationic forms would be directly adsorbed on the metal surface. With

increasing negative charge on the metal surface, adsorption of (S1) molecules increase and its

concentration in solution would decrease.

(3) When the metal attains the potential at which the surface charge becomes zero, none of the

ions (neither cations nor anions) adsorb on the surface through their ionic centre, and (S1)

molecules may however get physically adsorbed through their planar p orbitals on the metal

surface (with vacant p orbitals).

During the experiments it was observed that the corrosion potential of mild steel in 0.5 M H2SO4

solution with addition of concentration 0.01 mol/L (S1) is -482 mV. So assumed that Er (Er =

Ecorr–Epzc) potential is positive in these cases. From the above result, it follows those anions

(SO4-2 ions) in aqueous sulphuric acid solution first to get adsorbed on the mild steel surface.

After this first adsorption step, the mild steel surface becomes negatively charged. Hence, the

positively charged of (S1) cationic forms has been formed an electrostatic bond with the SO4 -2

ions already adsorbed on mild steel surface [53] Lastly, we assumed that, the large size and high

molecular weight of Schiff base molecule can also contribute towards greater inhibition

efficiency of (S1).

Conclusion:

The adsorption and inhibition effect of the (S1) molecule on the corrosion behaviour of mild

steel in 0.5M H2SO4 solution were studied by using electrochemical methods and theoretical

calculations. The following conclusion have been drawn:

1. In acid solution the inhibition efficiency of newly synthesized (S1) molecule increased with

increase in inhibitor concentration.

2. The percentage inhibition efficiency (IE%) of (S1) molecule obtained from potentiodynamic

polarization curves, EIS and/or LPR are in good agreement with each other.

258

3. The inhibition is accomplished by adsorption of (S1) molecule on the mild steel surface, and

the adsorption is spontaneous and obeys the Langmuir Isotherm.

4. The polarization curves show that the (S1) molecule behave as mixed type inhibitor.

5. EIS indicates that, as the additive concentration is increased the polarization resistance

increases whereas double layer capacitance decreases.

6. Activation energy decreases with the addition of inhibitor. It is shown that the inhibitor is

physically adsorbed.

7. High values of EHOMO indicate that the (S1) molecules have a tendency to donate electrons.

References:

i. I. Ahamad, M.A. Quraishi, Corros. Sci. 51(2009) 2006–2013.

ii. Q.B. Zhang, Y.X. Hua, Electrochim. Acta 54 (2009) 1881–1887.

iii. W. Li, Q. He, C. Pei, B. Hou, Electrochim. Acta 52 (2007) 6386–6394.

iv. R. Solmaz, G. Kardas_, B. Yazıcı, M. Erbil, Prot. Met. 41 (2005) 581– 585.

v. G. Kardas, Mater. Sci. 41 (2005) 337–343.

vi. S.K. Shukla, M.A. Quraishi,Corros. Sci. 51 (2009)1007–1011.

vii. F.S. de Souza, A. Corros. Sci. 51 (2009) 642–649.

viii. N. Soltani, M. Behpour, S.M. Ghoreishi, H. Naeimi, Corros. Sci. 52 (2010) 1351-1361.

ix. G. Schmitt, L. Sobbe, W. Bruckhoff, Corros. Sci. 27 (1987) 1071–1076.

x. K. Emregul, O. Atakol, Mater. Chem. Phys. 83 (2004) 373–379.

xi. M. Behpour, S.M. Ghoreishi, M. Salavati-Niasari, B. Ebrahimi, Mater. Chem.Phys. 107

(2008) 153–157.

xii. G.K. Gomma, M.H. Wahdan, Mater. Chem. Phys. 39 (1995) 209–213.

xiii. U. Aytac, U. Ozmen, M. Kabasakaloglu, Mater. Chem. Phys. 89 (2005) 176–181.

xiv. Y.K. Agrawal, J.D. Talati, M.D. Shah, M.N. Desai, N.K. Shah, Corros. Sci. 46 (2004) 633–651. xv. M. Behpour, S.M. Ghoreishi, N. Soltani, M. Salavati-Niasari, M. Hamadanian, A. Gandomi,

Corros. Sci. 50 (2008) 2172–2181.

xvi. M. Behpour, S.M. Ghoreishi, N. Soltani, M. Salavati-Niasari, Corros. Sci. 51(2009) 1073–1082.

xvii. K.F. Khaled, N. Hackenman, Electrochim. Acta 49 (2004) 485–495.

xviii. F. Bentiss, M. Traisnel, N. Chaibi, B. Mernari, H. Vezin, M. Lagrenee, Corros. Sci.

44(2002) 2271.

xix. Ishtiaque Ahamad a, Rajendra Prasad b, M.A. Quraishi a,* Corrosion Science 52 (2010)

933–942

xx. Kumaravel Mallaiyaa,∗, Rameshkumar Subramaniama, Subramanian Sathyamangalam

Srikandana,S. Gowria, N. Rajasekaranb, A. Selvarajc ,Electrochimica Acta 56

(2011)3857–3863.

xxi. J.R. Macdonald, D.R. Franceschetti, in: J.R. Macdonald (Ed.), Wiley,

NewYork,1987,p39.s

xxii. I. Ahamad, R. Prasad, M.A. Quraishi, Corros. Sci. 52 (2010) 933.

xxiii. C.H. Hsu, F. Mansfeld, Corrosion 57 (2001) 747.

xxiv. E. Machnikova, K.H. Whitmire, N. Hackerman, Electrochim. Acta 53 (2008)6024.

xxv. G. Avci, Mater. Chem. Phys. 112 (2008) 234–238.

xxvi. K.F. Khaled, Mater. Chem. Phys. 112 (2008) 290.

xxvii. M.S. Morad, A.A.O Sarhan, Corros. Sci. 50 (2008) 744.

xxviii. A. Popova, M. Christov, J. Univ. Chem. Technol. Metall. 43 (1) (2008) 37.

xxix. M.J. Bahrami, S.M.A. Hosseini, P. Pilvar, Corros. Sci. 52 (2010) 2793–2803.

xxx. Ali Doner a, Ramazan Solmaz

b, Muzaffer Ozcan

c, Gulfeza Kardas-

a Corrosion Science

259

53(2011)2902-2913.

xxxi. N.O. Obi-Egbedi, I.B. Obot, Corros. Sci. 53(2011) 263–275.

xxxii. X. Li, S. Deng, H. Fu, Corros. Sci. 53 (2011) 302–309.

xxxiii. S.K. Shukla, M.A. Quraishi, Corros. Sci. 51 (2009) 1990–1997.

xxxiv. L. Tang, G. Mu, G. Liu, Corros. Sci. 45 (2003) 2251–2262.

xxxv. M. Behpour, S.M. Ghoreishi, N. Mohammadi, N. Soltani, M. Salavati-

Niasari,Corros.Sci.52(2010)4046-4057.

xxxvi. T. Szauer, A. Brandt, Electrochim. Acta 26 (1981) 1257–1260.

xxxvii. A. Popova, M. Christov, A. Vasilev, Corros. Sci. 49 (2007) 3276–3289.

xxxviii. I.B. Obot, N.O. Obi-Egbedi, Corros. Sci. 52 (2010) 198e204.

xxxix. V.S. Sastri, J.R. Perumareddi, Corrosion 53 (1997) 617–622.

xl. I. Lukovits, E. Kalman, F. Zucchi, Corrosion 57 (2001) 3-8.

xli. I. Ahamad, R. Prasad, M.A. Quraishi, Corros. Sci. 52 (2010) 3033–3041.

xlii. S.E. Nataraja a, T.V. Venkatesha

a, H.C. Tandon

b, Corrosion Science 60 (2012) 214-223

xliii. I. Ahamad, M.A. Quraishi, Corros. Sci. 51 (2009) 2006–2013.

xliv. A. Yurt, A. Balaban, S. Ustun Kandemir, G. Bereket, B. Erk, Mater. Chem. Phys.

85(2004)420-426.

xlv. R.A. Prabhu, T.V. Venkatesha, A.V. Shanbhag, B.M. Praveen, G.M. Kulkarni, R.G.

Kalkhambkar, Mater. Chem. Phys. 108 (2008) 283–289.

xlvi. A. Barbosa da Silva, E. D’Elia, J.A.C.P. Gomes, Corros. Sci. 52 (2010) 788–793.

xlvii. S.A. Umoren, Y. Li, F.H. Wang, Corros. Sci. 52 (2010) 1777–1786.

xlviii. B. Wang, M. Du, J. Zhang, C.J. Gao, Corros. Sci. 53 (2011) 353–361.

xlix. H. Ma, S. Chen, B. Yin, S. Zhao, X. Liu, Corros. Sci. 45 (2003) 867.

l. R. Solmaz, M.E. Mert, G. Kardas, B. Yazici, M. Erbil, Acta Phys. Chem. Sinica 24(7)

(2008) 1185.

li. L.I. Antropov, E.M. Makushin, V.F. Panasenko, Technika, Kiev, 1981. p.182.

lii. A.C. Makrids, N. Hackerman, J. Phys. Chem. 59 (1955) 707–710.

liii. M. Behpour, S.M. Ghoreishi, M. Salavati-Niasari, B. Ebrahimi, Mater. Chem. Phys. 107

(2008) 153–157.

Received on March 2, 2014.

N

N

O N

NN

N

ONH2

N

O

Refflex

Methanol

Fig. 1. Molecular for S1.

260

Fig.2.1H NMR spectra of [4-methoxy-6-methyl-pyrimidin-2-yl] pyridine-2-yl methylene- amine.

261

Fig. 3. Anodic and cathodic polarization curves obtain mild steel at 298 K in 0.5 M H2SO4 in

various concentrations of studied S1.

Fig. 9. Equivalent circuit of the impedance spectra.

262

Fig. 4. Nyquist plots for mild steel in 0.5 M H2SO4 solution in absence and presence of various

concentration of the S1.

Fig.

5.

Langmuir isotherm for adsorption of Schiff base on the mild steel surface.

263

Fig. 6. Plotting ln Icorr (mA/cm2) vs 1/T (K

-1) to calculate the activation energy of corrosion

process in the presence of S1.

Fig.7. Highest occupied molecular orbital (HOMO) surfaces and lowest occupied molecular

orbital(LUMO) for S1.

264

Fig.8. Three dimensional AFM ima

H2SO4 solution in the presence of 0.01 M (S

Fig. 10.The plot of differential capacitance vs. applied electrode potential in (a

containing 0.005 mol /L of the inhibitor solution

solution.

AFM images and sectional analysis of mild steel exposed to 0.5 M

he presence of 0.01 M (S1).

.The plot of differential capacitance vs. applied electrode potential in (a

mol /L of the inhibitor solution of S1 and (b) 0.5M H2SO4 without inhibitor

mild steel exposed to 0.5 M

.The plot of differential capacitance vs. applied electrode potential in (a-b) 0.5M H2SO4

without inhibitor

265

Table.1 Polarization parameters and inhibition efficiency for the corrosion of mild steel in 0.5 M

H2SO4 without and with addition of various concentration of S1.

TempK Conc

mol/L

-

EcorrvsSCE(mV)

bc (mV)/dec ba (mV)/dec Icorr mA/cm-2 IE%

25 blank 465 60.89 71.59 0.008805 -

0.002 479 93.84 109.36 0.0006817 92.25

0.003 492 87.01 104.25 0.0004031 95.42

0.005 479 87.96 109.06 0.0002626 97.01

0.01 482 94.13 126.33 0.00009336 99.10

35 blank 475 52.82 59.24 0.01499 -

0.002 474 76.66 108.82 0.002014 87.21

0.003 486 78.21 93.06 0.001380 91.39

0.005 492 87.88 158.98 0.0003033 97.97

0.01 471 95.92 194.41 0.0002403 98.32

45 blank 481 48.05 50.91 0.01639 -

0.002 490 71.78 89.79 0.004198 74.38

0.003 489 70.64 80.72 0.001816 88.92

0.005 477 89.88 100.20 0.0008560 94.80

0.01 506 88.20 75.42 0.0003339 97.96

55 blank 490 47.05 58.00 0.01823 -

0.002 508 72.32 50.09 0.005509 70.21

0.003 505 70.31 55.03 0.003312 81.92

0.005 513 88.25 49.02 0.001243 92.72

0.01 507 92.04 45.45 0.0004063 97.55

Table 2. Impedance parameters for corrosion of mild steel in 0.5 M H2SO4 in the absence and

presence of different concentration of (S1) with liner polarization.

Conc

mol/L

Rs(Ωcm2) Y0(10

-6Ω

-

1cm

-2)

n Rct(Ωcm2) Cdl(Ωcm

2) IE% Rp(Ωcm

2)

IE%

LPR

Blank 1.2 158 0.750 6.713 1990 - 4 -

0.002 1.1 68 0.780 81.778 428 91.79 50.4 92.09

0.003 1.2 50 0.810 91.036 318 92.62 60.6 93.32

0.005 1.1 23 0.850 162.591 147 96.29 115.1 96.52

0.01 1.0 20 0.867 180.314 132 97.45 211.2 98.10

266

Table(3) Thermodynamic parameters obtained from polarization curves measurement for the

adsorption of S1 in 0.5 M H2SO4 at different Temp.

Table (4) Activation parameters of dissolution reaction of mild steel in 0.5 M H2SO4 solution in

different concentration of S1.

Table (5) Quantum chemical parameters for S1, obtained from AM1 method.

Dipole

moment

-

EHOMO

-

ELUMO

-∆E=EHOMO-

ELUMO

χ η ∆N IE% TNC/n TNC/m

2.885 9.4396 0.9484 8.4912 5.194 4.247 0.2126 97.74 0.151 0.200

Table, 6. Excess charge on mild steel electrode in 0.5M H2SO4 solutions in the presence and

absence of the inhibitor for S1.

medium EOCP (mV/SCE) PZC (mV/SCE) Excess charge

0.5M H2SO4 465 487 +22

0.5M H2SO4

+0.01mol/L of inhibitor

482

502

+20

Temp K (S1)

Kads (K-1) -∆G

0 kJ/mol

328 8,896 35.25

318 11,961 35.44

308 24,937 36.20

298 42,372 36.34

Conc mol/L Ea kJ/mol

(S1)

Blank 243.25

0.002 135.26

0.003 74.15

0.005 28.18

0.01 8.42