inhibition of aluminium corrosion in 1.0m hcl by …downloads.hindawi.com/archive/2017/6975248.pdf10...

Research ArticleInhibition of Aluminium Corrosion in 10M HCl by CaffeineExperimental and DFT Studies

R H B Beda P M Niamien E B Avo Bileacute and A Trokourey

Laboratoire de Chimie Physique Universite Felix Houphouet Boigny 22BP 582 Abidjan 22 Cote drsquoIvoire

Correspondence should be addressed to P M Niamien niamienfryahoofr

Received 19 October 2017 Revised 24 November 2017 Accepted 28 November 2017 Published 24 December 2017

Academic Editor Franck Rabilloud

Copyright copy 2017 R H B Beda et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Aluminium corrosion inhibition in 10M hydrochloric acid solution by caffeine has been studied using mass loss technique andquantum chemical calculations based on DFT The inhibition efficiency was found to increase with increasing concentrationof caffeine but decreases with a rise in temperature The molecule shows the highest inhibition efficiency of 74 at 10minus2M for119879 = 303K The experimental data were used to fit isotherms including Langmuir Temkin Freundlich and El-Awady Thebest fits were obtained with the Langmuir model and the kinetic-thermodynamic adsorption model of El-Awady Howeverit was found that the adsorption parameters suit well with the isotherm of El-Awady which was chosen as the appropriateisotherm To distinguish between physisorption and chemisorption the Dubinin-Radushkevich adsorption model was used Thethermodynamic parameters governing the adsorption of caffeine onto aluminium and that of the metal dissolution were calculatedand discussed DFT study gave further insight into the mechanism of the inhibiting action of caffeine

1 Introduction

Aluminium and its alloys [1 2] are used in many applicationsin industries (aerospace household industries electronic de-vices food industry etc) due to their lowprice high electricalcapacity and their high energy density Though aluminiumhas the ability to form a stable thin oxide film that protectsit from the corrosion phenomenon it undergoes corrosion[3ndash5] when being in contact with aggressive media such ashydrochloric acid

Corrosioncontrol canbeachieved bymanymethods how-ever the use of corrosion inhibitors is actually the mostpractical method used in industries and academic studies Asurvey of the literature reveals [6ndash8] that most of the well-known ecofriendly corrosion inhibitors are organic com-pounds containing nitrogen oxygen sulphur andor120587bondsin their molecular structure Several heterocyclic N S orO containing organic compounds [9ndash12] have been used toprotect aluminium from hydrochloric acid corrosion

Generally localized corrosion [4] can be avoided by theaction of adsorption inhibitors which prevent the adsorptionof aggressive anions or by the formation of a more resistantoxide film on the metal surface

The adsorption of a given organic compound onto ametalsurface is influenced by its chemical structure Therefore theuse of quantum chemical calculations will lead to structuralparameters of the molecule Recently density functional the-ory (DFT) has emerged as a reliable and inexpensive method[13] for predicting the properties of chemical systems Severalpapers [14ndash16] have documented the use of DFT to getinsight into the corrosion inhibition mechanism by organicmolecules

The aim of this paper is to study the behaviour of caffeineagainst the hydrochloric acid corrosion of aluminium usingmass loss method and density functional theory calculations

2 Material and Methods

21 Material

211 Aluminium Specimens The aluminium specimens werein the form of rod measuring 10mm in length and 2mm indiameter they were cut in commercial aluminium of purity995

HindawiAdvances in ChemistryVolume 2017 Article ID 6975248 10 pageshttpsdoiorg10115520176975248

2 Advances in Chemistry

212 Chemicals All chemicals were of analytical grade andwere used without further purification

(i) HCl fromMerck with purity 37(ii) Caffeine (C8H10N4O2) was acquired from Sigma

Aldrich chemicals and solutions of concentrationsrange from 01mM to 10mM were prepared

(iii) Acetone from Sigma Aldrich with purity 995

22 Methods

221 Mass Loss Method The mass loss method [17 18] isprobably the most widely used method of inhibition assess-ment The simplicity and reliability of the measurementoffered bymass lossmethod [19]make the technique form thebaseline method in many corrosion monitoring programs

Prior to the immersion of the specimens in the test solu-tion (50mL) their surfacewas abradedwith different grade ofemery papers (120-180-240-600-1200) tomirror finish rinsedwith acetone washed with bidistilled water and finally driedin a desiccator The mass loss experiments were performedunder total immersion in the acidic solution of 10M (with orwithout caffeine) opened to the airThe temperaturewas con-trolled by a water thermostat After one-hour immersion thespecimens were retrieved from the solution washed with abristle brush under running water in order to remove the cor-rosion product dried in a desiccator and weighed accuratelyThe study was performed in the temperature range of 303Kto 323K and the concentration range of 01mM to 10mMThe tests were repeated three times for each solution andat the same temperature The mean value was then recorded

The corrosion rate (119882) in gsdotcmminus2sdothminus1 was calculated usingthe following equation

119882 = 1198981 minus 1198982119878119905 (1)

where 1198981 is the mass of the sample before immersion in thetest solution 1198982 is the mass after 1 h immersion in the testsolution 119878 is the total surface of the sample and 119905 is theimmersion time The inhibition efficiency IE () was calcu-lated according to the equation below

IE () = 1198820 minus 1198821198820 times 100 (2)

where 1198820 is the corrosion rate in the absence of the testedmolecule and 119882 is the corrosion rate in its presence

222 Quantum Chemistry Calculations The calculationswere performed using the hybrid functional B3LYP a versionof DFT functional that uses Beckersquos three parameter func-tional (B3) with a mixture of HF and DFT exchange termsassociated with the gradient corrected correlation functionalof Lee et al [20] The full geometry optimization was carriedout at B3LYP6-31G (d) level of theory using Gaussian 03W[21]

The calculations were carried out in gas phase to showthe relationship between themolecular descriptors of caffeine

Figure 1 Optimized structure of caffeine by B3LYP6-31G (d)

and its inhibition efficiencyThe optimized minimum energygeometrical configuration of caffeine is given in Figure 1

DFT [22] has been found to be successful in providingtheoretical insights into the chemical reactivity and selec-tivity using chemical concepts such as electronegativity (120594)hardness (120578) softness (119878) electrophilicity index (120596) and localreactivity descriptors including Fukui functions 119891(119903) and thelocal softness 119904(119903)

Density functional theory (DFT) states that changes inelectronic energy 119889119864[120588(119903)] are related to changes in thenumber of electrons 119873 and changes in the external potentialV(119903) felt by the electron distribution (which refers to thenuclear position in chemical systems)

119889119864 [120588 (119903)] = 120583119875119889119873 + int120588 (119903) 119889V (119903) 119889119903 (3)

According to Parr et al [23] the chemical potential 120583119875 islinked with the first derivative of the energy with respect tothe number of electrons and therefore with the negative of theelectronegativity by the following equation

120583119875 = ( 120597119864120597119873)

V(119903)= minus120594 (4)

where 120583119875 is the electronic chemical potential 119864 is the totalenergy 119873 is the number of electrons and V(119903) is the externalpotential of the system

The second partial derivative of the energy with respectto the number of electrons has been defined as hardness (120578)

120578 = ( 12059721198641205971198732)V(119903)

= (120597120583119875120597119873 )V(119903)

(5)

This quantity [24] measures both the stability and the reac-tivity of the molecule

According to Koopmansrsquos theorem [25] the ionizationpotential (119868) and the electron affinity (119860) of the inhibitors arecalculated using the following equations

119868 = minus119864HOMO119860 = minus119864LUMO (6)

The electronegativity (120594) [24] which measures the power ofan atom or group of atoms to attract electrons towards itselfcan then be written as

120594 = 119868 + 1198602 (7)

Advances in Chemistry 3

The chemical hardness (120578) [24] which expresses the resistanceof an atom to charge transfer is estimated using the equationbelow

120578 = 119868 minus 1198602 (8)

The inverse of the hardness known as softness (119878) [24]measures the capacity of an atom or group of atoms to receiveelectrons it is estimated by

119878 = 1120578 = 2

119868 minus 119860 (9)

The fraction of electrons transferred from the inhibitormole-cule to themetallic surface was calculated using the followingequation [26]

Δ119873 = 120594119872 minus 120594inh2 (120578119872 + 120578inh) = 120601119872 minus 120594inh2120578inh (10)

where (120594119872 120578119872) and (120594inh 120578inh) are respectively the elec-tronegativity and hardness of the metal and the inhibitorwhen 120601119872 is the work function In our study the theoreticalvalues of electronegativity 120601Al = 428 eV [27] and hardness120578Al = 0 [26] have been used for aluminium

The global electrophilicity index introduced by Parr et al[28] is given by the equation below

120596 = 12058321198752120578 (11)

This index [28] measures the propensity of chemical speciesto accept electrons A good nucleophile is characterized by alow value of120596whereas a good electrophile is characterized bya high value of 120596

Fukui function [29] is one of the widely used local densityfunctional descriptors to model chemical reactivity and siteselectivity it is defined as the derivative of the electrondensity 120588(119903) with respect to 119873 the total number of electronsin the system at constant external potential V(119903) acting on anelectron due to all the nuclei in the system

119891 (119903) = ( 120597120583119875120597V (119903))119873 = (120597120588 (119903)120597119873 )

V(119903) (12)

The condensed Fukui functions are calculated using Yang andMortier procedure [30] based on a finite difference method

119891+119896 = 119902119896 (119873 + 1) minus 119902119896 (119873) 119891minus119896 = 119902119896 (119873) minus 119902119896 (119873 minus 1) (13)

where 119902119896 is the electronic population of atom 119896 in the mole-cule The functions 119891+119896 and 119891minus119896 are respectively related tonucleophilic and electrophilic attacks

The local softness [31] is defined as

119904120572119896 = 119891120572119896 119878 (120572 = + ou minus) (14)

Themaximum values of relative nucleophilicity index (119904+119896 119904minus119896 )and relative electrophilicity index (119904minus119896 119904+119896 ) are used to definerespectively the probable sites of nucleophilic and elec-trophilic attacks

01020304050607080

IE (

)

T = 303 ＋

T = 308 ＋

T = 318 ＋

T = 323 ＋

T = 313 ＋

2 4 6 8 10 120CＣＨＢ (mM)

Figure 2 Inhibition efficiency of caffeine against aluminium corro-sion in 10M HCl versus concentration for different temperatures

01020304050607080

IE (

)

305 310 315 320 325300T (K)

= 1Ｇ－CＣＨＢ= 5Ｇ－CＣＨＢ

01 Ｇ－CＣＨＢ =


10Ｇ－CＣＨＢ =

Figure 3 Inhibition efficiency of caffeine against aluminium corro-sion in 10M HCl versus temperature for different concentrations

3 Results and Discussion

31 Mass Loss Technique Figures 2 and 3 illustrate the evolu-tion of the inhibition efficiency of caffeine against aluminiumcorrosion in 10M HCl after 1-hour immersion respectivelyfor different concentrations and temperatures

It is clear from these figures that the inhibition efficiencyincreases with increasing concentration of caffeine butdecreases with a rise in temperature The increase in inhibi-tion efficiency with concentration may be due to the adsorp-tion of caffeine onto the aluminium surface through non-bonding electron pairs of nitrogen and oxygen atoms as wellas the 120587-electrons of the aromatic rings The surface of themetal is therefore covered by a protective layer film whichseparates it from its environment Similar observation [32 33]has been reported in the literature

Though the effect of temperature on the inhibited acidndashmetal reaction is complex [34] due to many changes on themetal surface (rapid etching desorption of molecules etc)the decrease in inhibition efficiencywith a rise in temperaturemay probably due to increased rate of desorption of theinhibitor


0 0002 0004 0006 0008 001 0012

T = 303 ＋

T = 308 ＋

T = 318 ＋

T = 323 ＋

T = 313 ＋

CＣＨＢ (mM)

0

0005

001

0015

002

0025

003

CＣＨＢ

Figure 4 Langmuir adsorption plots for aluminium in presence ofcaffeine

311 Adsorption Isotherm It is admitted [35] that the firststep in corrosion inhibition of metals by organic compoundsis their adsorption onto the metal surface This phenomenonis regarded [35] as a quasi-substitution process betweenorganic compounds in the aqueous phase Org(sol) and watermolecules at the metal surface H2O(ads)

Org(sol) + 119909H2O(ads) 999448999471 Org(ads) + 119909H2O(sol) (15)

where 119909 is the size ratio the number of water moleculesreplaced by one inhibitor Information on the interactionbetween the inhibitor and the metal surface can be obtainedusing adsorption isotherms The isotherms are in generalform

119870ads119862inh = 119891 (120579 119909) exp (minus120572120579) (16)

where 119891(120579 119909) is the configurational factor subject to thephysical model and assumptions involved in the derivation ofthe isotherm 120572 is a molecular interaction parameter 119862inhis the inhibitor concentration and 119870ads is the adsorptionconstant

Attempts were made to fit experimental data (120579 and 119862inh)to some classical isotherms including Langmuir El-AwadyFreundlich and Frumkin By far the best fits were obtainedwith the isotherm of Langmuir (1198772 gt 099) and that of El-Awady (1198772 gt 098) In Langmuir isotherm 120579 and 119862inh arerelated by the following equation

119862inh120579 = 1119870ads

+ 119862inh (17)

Figure 4 depicts the plots of 119862inh120579 versus 119862inhThe slopes of the straight lines obtained are higher than

unity for all the temperatures The considerable deviationfrom unity observed may be due to the interactions amongthe adsorbed species on the metal surface It is thereforepertinent to say that the adsorption can bemore appropriatelyrepresented by a modified Langmuir equation the isothermof Villamil et al [36] or that of El-Awady The parameters ofthese isotherms are collected in Table 1

305 310 315 320 325300T (K)

minus10

minus14

minus18

minus22

minus26

minus30

R2 = 09782

ΔG

0 ＞Ｍ

(ＥＧ

ＩＦminus

1)

ΔG0＞Ｍ = 0462T minus 16873

Figure 5 Δ1198660ads versus temperature for aluminium in presence ofcaffeine

The adsorption constants119870ads have been calculated usingthe equations in Table 1 The changes in standard adsorptionfree enthalpy have been calculated using the following equa-tion

Δ1198660ads = minus119877119879 ln (555 times 119870ads) (18)

where119877 is the gas constant119879 is the absolute temperature and555 is the concentration of water (inmol Lminus1) in the solution

In Villamil equation ldquo119899rdquo is a constant introduced to con-sider all the factors not taken into account in the derivationof Langmuir isotherm

The constant119910 in the isotherm of El-Awady is the numberof active sites on the material surface 1119910 less than oneimplies a multilayer adsorption while 1119910 greater than onesuggests that a given inhibitor molecule occupies more thanone active site

It is clear from Table 1 that only the kinetic-thermo-dynamic adsorption isotherm of El-Awady supports well thetrend of decrease in inhibition efficiency (decrease of theadsorption constant with rise of temperature) therefore theappropriate isotherm is that of El-Awady

In order to determine change in standard adsorptionenthalpy Δ1198670ads and change in standard adsorption entropyΔ1198780ads we used the basic equation

Δ1198660ads = Δ1198670ads minus 119879Δ1198780ads (19)

Plotting Δ1198660ads versus temperature gives the two adsorptionparameters (Figure 5) The negative values of Δ1198660ads suggestthat the adsorption of caffeine onto aluminium is sponta-neousThese values range fromminus289 kJmolminus1 tominus19 kJmolminus1indicating [37] both physisorption and chemisorption pro-cesses

Change in standard adsorption enthalpy (Δ1198670ads =minus168 kJmolminus1) is negative showing an exothermic adsorptionprocess and its absolute value is higher than 100 kJmolminus1which is according to the literature [38] not a typical chemis-orption when referring to the values of Δ1198660ads It may beindicative of both physisorption and chemisorption pro-cesses

Change in standard adsorption entropy (Δ1198780ads =minus462 Jmolminus1Kminus1) is negative it may be explained by desorp-tion of the inhibitor species when the temperature increases


Table 1 Parameters of the modified Langmuir adsorption isotherms

Isotherm Equation 119879 (K) 1198772 Slope Intercept 119870ads(times103M)

Δ1198660ads(kJmolminus1)

Villamil et al119862inh120579 = 119899

119870ads+ 119899119862inh

303 0994 13542 00007 2768 minus301308 0999 16943 00005 5648 minus324313 0998 18394 00007 4598 minus323318 0994 19882 00012 3314 minus320323 0995 23771 00014 3962 minus330

El-Awady log( 1205791 minus 120579) = log1198701015840 + 119910 log119862inh

119870ads = 11987010158401119910


Table 2 Parameters of the Dubinin-Radushkevich model

119879 (K) 1198772 119886 (kJminus2mol2) 120579max 119864119898 (kJmolminus1)303 0991 00121 0696 64308 0995 00081 0582 79313 0984 00063 0517 89318 0965 00063 0466 89323 0974 00061 0401 90

Moreover according to the thermodynamic principles sincethe adsorption is an exothermic process it may be accompa-nied by a decrease in entropy

In order to distinguish between physisorption and chem-isorption the isotherm of Dubinin-Radushkevich has beenused This isotherm is characterized [39] by the equationbelow

ln 120579 = ln 120579max minus 1198861205752 (20)

where 120579max is the maximum surface coverage and 120575 is thePolanyi potential which is given by

120575 = 119877119879 ln(1 + 1119862inh

) (21)

In this equation119877 is the perfect gas constant119879 is the absolutetemperature and 119862inh is the concentration of the inhibitorexpressed in g Lminus1 Figure 6 gives the plots of ln 120579 versus 1205752The parameters of this model are in Table 2

The value of the parameter 119886 in (20) leads to the meanadsorption energy 119864119898 for the related temperature Thisenergy is the transfer energy of 1mol of adsorbate from infin-ity (bulk solution) to the surface of the adsorbent 119864119898 isdefined as

119864119898 = 1radic2119886 (22)

In order to determine the range of temperatures for physis-orption and chemisorption we plot 119864119898 versus temperature(Figure 7)

According to the literature [39] the magnitude of 119864119898gives information about the adsorption 119864119898 values less than

40 60 80 100 1200 20

0minus02minus04minus06minus08minus1

minus12minus14minus16minus18minus2

ＦＨ

2 (Ｅ2ＧＩＦminus2)

Figure 6 Dubinin-Radushkevich isotherm in presence of caffeine

305 310 315 320 325300T (K)

141210

86420

Em

(ＥＧＩＦminus

1)

Em = 025T minus 69267

R2 = 09868

Em = minus00106T2 + 67437T minus 10664

R2 = 09839

Figure 7 Adsorption energy versus temperature for caffeine ontoaluminium

8 kJmolminus1 indicate physical adsorption while that higherthan 8 kJmolminus1 suggest chemisorption Using the equation ofthe straight line in Figure 7 we derived the domains where


Table 3 Dissolution parameters of the aluminium in 10M HCl

119862inh (mM) 119864119886 (kJmolminus1) Δ119867lowast119886 (kJmolminus1) Δ119878lowast119886 (Jmolminus1Kminus1)0 779 754 minus343010 788 763 minus31505 906 881 221 970 945 2195 1001 977 31210 1049 1024 450

minus3

minus25

minus2

minus15

minus1

minus05

0

ＦＩＡ(W

)

31 315 32 325 33 335305

103T (＋minus1)

Blank= 1Ｇ－CＣＨＢ

= 5Ｇ－CＣＨＢ




Figure 8 Arrhenius plots for aluminium in 10M HCl at differentconcentrations of caffeine

each type of adsorption is predominant ((119879 lt 3091K forphysisorption) and (119879 gt 3091K for chemisorption)) Thedecrease in 120579max values confirms that the adsorption decreas-es with increasing temperatures

312 Effect of Temperature Todetermine the activation para-meters of the corrosion process the Arrhenius and the transi-tion state equations were used

log119882 = log119860 minus 1198641198862303119877119879

log(119882119879 ) = [log( 119877

alefsymℎ) + Δ119878lowast1198862303119877] minus Δ119867lowast1198862303119877119879(23)

where 119864119886 is the apparent activation energy 119877 is the perfectgas constant 119860 is the frequency factor ℎ is Planckrsquos constantalefsym is the Avogadro number Δ119867lowast119886 is the change in activationenthalpy and Δ119878lowast119886 is the change in activation entropy

Values of apparent activation energy of corrosion (119864119886) foraluminium in HCl in the absence and presence of variousconcentrations of caffeine were determined from the slope oflog119882 versus 1119879 plots (Figure 8)

The values of change in enthalpy (Δ119867lowast119886 ) and change inentropy (Δ119878lowast119886 ) were obtained respectively from the slopesand intercepts of the plots of log(119882119879) versus 1119879 (Figure 9)All these parameters are collected in Table 3

Blank

minus13

minus12

minus11

minus10

minus9

minus8

minus7

minus6

ＦＩＡ(W

T)

31 315 32 325 33 335305

103T (＋minus1)

= 1Ｇ－CＣＨＢ

= 5Ｇ－CＣＨＢ




Figure 9 Transition state plots of aluminium in 10M HCl at dif-ferent concentrations of caffeine

From Table 3 one can notice that 119864119886 and Δ119867lowast119886 vary in thesame wayThis result permitted verifying the known thermo-dynamic relation between the two activation parameters

Δ119867lowast119886 = 119864119886 minus 119877119879 (24)

The activation energies 119864119886 are all positive and those of theinhibited solutions are higher than those of the blank (unin-hibited solution) suggesting [40] a physisorption process ora mix process The positive sign of change in activationenthalpy Δ119867lowast119886 reflects the endothermic nature of the alu-minium dissolution process The values of change in activa-tion enthalpy increase with increasing concentration of caf-feine showing that the dissolution of the aluminiumbecomesmore and more difficult and slow

The change in activation entropy Δ119878lowast119886 increases withincreasing concentration in caffeine indicating that anincrease in disordering takes place on going from the reac-tants to the activated complex This situation could explainthe decrease in the rate of surface coverage

32 Quantum Chemical Approach The quantum chemi-cal parameters of caffeine obtained from the calculationsinclude the energy of the highest occupied molecular orbital(119864HOMO) the energy of the lowest unoccupied molecularorbital (119864LUMO) the energy gap (Δ119864 = 119864LUMO minus 119864HOMO) thedipolemoment120583 and the total energy (TE) Based on frontiermolecular orbital (FMO) the reactivity parameters such asthe ionization energy (119868) the electronic affinity (119860) the globalelectronegativity (120594) the global hardness (120578) the globalsoftness (119878) the fraction of electrons transferred (Δ119873) and


Table 4 Molecular properties of caffeine calculated with B3LYP6-31G (d)

Parameter Value119864HOMO (eV) minus5959119864LUMO (eV) minus0819Δ119864 (eV) 5140119868 (eV) 5959119860 (eV) 0819120594 (eV) 3389120578 (eV) 2570119878 (eVminus1) 0389120583 (Debye) 3835Δ119873 0173120596 (eV) 2234TE (a u) minus6804

the electrophilicity index (120596) were also calculated All theseparameters are listed in Table 4

The HOMO energy [41] is directly related to the ioniza-tion energy and characterizes the tendency of the moleculeto donate electrons to the unoccupied orbitals of metalsOrganic molecules [42] with less negative HOMO values areexpected to have high donation ability and therefore highinhibition efficiencyThe LUMOenergy is another significantreactivity parameter which is related to the electron affinityand characterizes the capacity of a molecule to gain electronfrom a metal The lower the value of the LUMO energythe stronger the electron accepting ability of the molecule[43] In our case caffeine has a high value of HOMO energy(119864HOMO = minus5959 eV) and a low value of 119864LUMO (119864LUMO =minus0819 eV) when compared with values in the literature [1544] So the incomplete filled 3p of aluminium (electronicstructure 1s22s22p63s23p1) could bond with the HOMO ofcaffeine while the filled 3s orbital could interact with itsLUMO

The energy gap (Δ119864 = 119864LUMO minus 119864HOMO) is an importantparameter related to the reactivity of an inhibitor towardsthe adsorption onto a metallic surface Lower values of Δ119864[45] suggest better adsorption and then better inhibitionefficiency In our case (Δ119864 = 5140 eV) can be considered[46ndash48] as a low value when compared with other values inthe literature

The dipolemoment120583 is widely used as a reactivity param-eter it results from the nonuniformdistribution of charges onatoms in the molecule Though many authors state that lowvalues of dipole moment [49] favour accumulation of theinhibitor molecule in the surface layer and therefore higherinhibition efficiency the survey of literature [50 51] revealsseveral irregularities in case of correlation of dipole momentwith inhibitor efficiency So in general [52] there is no signifi-cant relationship between dipole moment values and inhibi-tion efficiencies

The global hardness (120578) and softness (119878) are importantparameters which measure the reactivity and the molecularstability A hard molecule has a large hardness value and

vice versa [53] In our study the hardness of caffeine (120578 =2570 eV) which can be considered as a low value [54] couldexplain the inhibiting properties of caffeine

The number (Δ119873) of electrons transferred is a parameterwhich indicates the tendency of a molecule to donate elec-trons The higher the value of Δ119873 the greater the tendencyof the molecule to donate electrons to the metal In our case(Δ119873 = 0173) the positive sign shows that themolecule coulddonate electrons to the metal

The electrophilicity index (120596) is another importantparameter [55] which measures the propensity of chemicalspecies to accept electrons a high value of electrophilicityindex describes a good electrophile while a small value ofelectrophilicity indicates a good nucleophile In our study120596 = 2234 eV shows that caffeine has a good capacity to acceptelectrons from the metal

TheHOMOand LUMOorbital densities distributions aregiven in Figure 10

In order to ascertain the role of individual atoms in themolecule its local parameters including Mulliken charges119902119873+1 119902119873 and 119902119873minus1 Fukui functions 119891+119896 and 119891minus119896 and localsoftness 119904+119896 and 119904minus119896 were calculated All these parameters arelisted in Table 5

The analysis of Table 5 shows that carbon C (10) is theprobable site for nucleophilic attacks whereas carbon C(14) is the probable site for electrophilic attacks Howeveraccording to the literature [56] the local parameters 119891+119896 119891minus119896 119904+119896 and 119904minus119896 are influenced by the basis sets So it is judicious touse relative indexes such as the relative nucleophilicity (119904+119896119904minus119896 )and the relative electrophilicity (119904minus119896 119904+119896 ) So in our study N(7) which has the highest value of relative nucleophilicityindex 119904+119896 119904minus119896 = 7240 could be the probable nucleophilicattack site whereas C (2) with the highest value of relativeelectrophilicity 119904minus119896 119904+119896 = 3503 could be the probable site ofelectrophilic attack

Figure 10 allows verifying the belonging of each atom 119896to the HOMO or LUMO densities regions in the moleculeFrom all these results one can deduce (Figure 11) a pictorialpresentation of forces acting between caffeine and aluminiumsurface

At low temperatures physical interactions exist betweenthe protonated form of caffeine and chloride ions adsorbedon aluminium surface physisorption is predominant Therise in temperature leads to desorption of the protonatedform of caffeine only the neutral form which is bonded tothe metal allows the inhibition of aluminium corrosion bychemisorption

4 Conclusion

Caffeine was found to act as an effective corrosion inhibitorfor aluminium in 10M HCl The efficiency depends on theconcentration and the temperature The inhibition efficiencyincreases with increasing concentration of the inhibitorbut decreases with rise in temperature The adsorption ofcaffeine onto aluminium obeys the kinetic-thermodynamicadsorption isotherm of El-Awady The negative sign of Δ1198660adssuggests a spontaneous adsorption process The values of


Table 5 Local parameters of Caffeine

Atom 119902119873+1 119902119873 119902119873minus1 119891+119896 119891minus119896 119904+119896 119904minus119896 119904+119896 119904minus119896 119904minus119896 119904+1198961 C 04259 04753 05423 minus00494 minus00670 minus00192 minus00261 07370 135682 C 01933 02179 03044 minus00247 minus00864 minus00096 minus00336 02855 350293 C 05084 06324 06942 minus01240 minus00618 minus00482 minus00240 20059 049854 C 07588 07852 08159 minus00264 minus00307 minus00103 minus00119 08595 116345 C 00637 02199 02809 minus01562 minus00610 minus00608 minus00237 25623 039036 H 00638 01695 02487 minus01058 minus00792 minus00411 minus00308 13351 074907 N minus05530 minus05740 minus05772 00213 00029 00083 00011 72401 013818 N minus05700 minus05900 minus05595 00198 minus00302 00077 minus00117 minus06565 minus152339 N minus04880 minus04840 minus05009 minus00042 00168 minus00016 00065 minus02478 minus4035710 C minus02910 minus03150 minus03382 00239 00235 00093 00091 10177 0982611 H 01754 01982 02316 minus00228 minus00335 minus00089 minus0013 06820 1466312 H 01284 01773 02196 minus00489 minus00423 minus00190 minus00165 11562 0864913 H 01273 01772 02196 minus00499 minus00423 minus00194 minus00165 11787 0848414 C minus03010 minus03220 minus03500 00208 00282 00081 00110 07355 1359715 H 01389 01977 02396 minus00588 minus00420 minus00229 minus00163 14000 0714316 H 01410 01816 02391 minus00407 minus00575 minus00158 minus00224 07072 1414017 H 01690 01816 02391 minus00126 minus00575 minus00049 minus00224 02187 4573418 C minus02960 minus03150 minus03700 00195 00546 00076 00213 03568 2802919 H 01811 01990 02571 minus00179 minus00581 minus00070 minus00226 03081 3246120 H 01049 01991 02301 minus00942 minus00310 minus00366 minus00120 30417 0328821 H 01069 01662 02300 minus00593 minus00638 minus00231 minus00248 09297 1075622 O minus06400 minus05400 minus04402 minus00994 minus01002 minus00387 minus00390 09928 1007223 O minus05990 minus05270 minus04107 minus00728 minus01159 minus00283 minus00451 06276 1593324 N minus05490 minus05110 minus04456 minus00374 minus00657 minus00145 minus00256 05691 17573

(a) (b)

Figure 10 HOMO (a) and LUMO (b) densities of caffeine

Inh neutral form of caffeine Aluminium ion (Ｆ3+) Chloride ion (Ｆminus)

protonated form of caffeine chemisorption

physisorption[]+

Inh Inh[]+ []+ []+ []+ []+ []+

Figure 11 Schematic mechanism of aluminium corrosion inhibition in 10M HCl by caffeine


change in adsorption free enthalpyΔ1198660ads and that of the acti-vation energy 119864119886 indicate the presence of both physisorptionand chemisorption The quantum chemical calculations arein good agreement with experimental results

Conflicts of Interest

The authors declare that they have no conflicts of interest

References

[1] A S Patel V A Panchal G VMudaliar andN K Shah ldquoImpe-dance spectroscopic study of corrosion inhibition of Al-Pureby organic Schiff base in hydrochloric acidrdquo Journal of SaudiChemical Society vol 17 no 1 pp 53ndash59 2013

[2] A M Abdel-Gaber B A Abd-El-Nabey I M Sidahmed AM El-Zayady andM Saadawy ldquoKinetics and thermodynamicsof aluminium dissolution in 10 M sulphuric acid containingchloride ionsrdquoMaterials Chemistry and Physics vol 98 no 2-3pp 291ndash297 2006

[3] S Berrada M Elboujdaini and E Ghali ldquoComportementelectrochimique des alliages drsquoaluminium 2024 ET 7075 dansun milieu salinrdquo Journal of Applied Electrochemistry vol 22 no11 pp 1065ndash1071 1992

[4] Z Szklarska-Smialowska ldquoInsight into the pitting corrosionbehavior of aluminum alloysrdquo Corrosion Science vol 33 no 8pp 1193ndash1202 1992

[5] R Ambat and E S Dwarakadasa ldquoStudies on the influenceof chloride ion and pH on the electrochemical behaviour ofaluminium alloys 8090 and 2014rdquo Journal of Applied Electro-chemistry vol 24 no 9 pp 911ndash916 1994

[6] A Yurt S Ulutas and H Dal ldquoElectrochemical and theoreticalinvestigation on the corrosion of aluminium in acidic solutioncontaining some Schiff basesrdquo Applied Surface Science vol 253no 2 pp 919ndash925 2006

[7] N A Negm N G Kandile E A Badr and M A MohammedldquoGravimetric and electrochemical evaluation of environmen-tally friendly nonionic corrosion inhibitors for carbon steel in1M HClrdquo Corrosion Science vol 65 pp 94ndash103 2012

[8] P Bommersbach C Alemany-Dumont J P Millet and BNormand ldquoFormation and behaviour study of an environment-friendly corrosion inhibitor by electrochemical methodsrdquo Elec-trochimica Acta vol 51 no 6 pp 1076ndash1084 2005

[9] X Li S Deng and H Fu ldquoInhibition by tetradecylpyridiniumbromide of the corrosion of aluminium in hydrochloric acidsolutionrdquo Corrosion Science vol 53 no 4 pp 1529ndash1536 2011

[10] S Safak B Duran A Yurt and G Turkoglu ldquoSchiff bases ascorrosion inhibitor for aluminium in HCl solutionrdquo CorrosionScience vol 54 no 1 pp 251ndash259 2012

[11] R T Loto CA Loto andA P I Popoola ldquoCorrosion inhibitionof thiourea and thiadiazole derivatives a reviewrdquo Journal ofMaterials and Environmental Science vol 3 no 5 pp 885ndash8942012

[12] A S Fouda K Shalabi and N H Mohamed ldquoCorrosioninhibition of Aluminium in Hydrochloric Acid Solutions usingsome chalcone derivativesrdquo International Journal of InnovativeResearch in Science Engineering and Technology vol 3 no 3 pp9861ndash9875 2014

[13] ON Eddy B I Ita N E Ibissi and E E Ebenso ldquoExperimentaland quantum studies on the corrosion inhibition potentials of 2-(2-oxo indolin-3-Ylideneamino) Acetic Acid and indoline-23-Dionerdquo International Journal of Electrochemical Science vol 6pp 1027ndash1044 2011

[14] X Li S Deng and X Xie ldquoExperimental and theoretical studyon corrosion inhibition of oxime compounds for aluminium inHCl solutionrdquo Corrosion Science vol 81 pp 162ndash175 2014

[15] I B Obot and N O Obi-Egbedi ldquoFluconazole as an inhibitorfor aluminium corrosion in 01 M HClrdquo Colloids and SurfacesA Physicochemical and Engineering Aspects vol 330 no 2-3pp 207ndash212 2008

[16] I A Adejoro C U Ibeji and D C Akintayo ldquoQuantum De-scriptors and Corrosion Inhibition Potentials of Amodaquineand Nivaquinerdquo Chemical Sciences Journal vol 08 no 01 2017

[17] A A Khadom A S Yaro and A A H Kadum ldquoCorrosioninhibition by naphthylamine and phenylenediamine for thecorrosion of copper-nickel alloy in hydrochloric acidrdquo Journalof the Taiwan Institute of Chemical Engineers vol 41 no 1 pp122ndash125 2010

[18] A Y Musa A A Khadom A A H Kadhum A B Mohamadand M S Takriff ldquoKinetic behavior of mild steel corrosioninhibition by 4-amino-5-phenyl-4H-124-trizole-3-thiolrdquo Jour-nal of the Taiwan Institute of Chemical Engineers vol 41 no 1pp 126ndash128 2010

[19] A Rahim and J Kassim ldquoRecent Development of VegetalTannins in Corrosion Protection of Iron and Steelrdquo RecentPatents on Materials Sciencee vol 1 no 3 pp 223ndash231 2008

[20] C Lee W Yang and R G Parr ldquoDevelopment of the Colle-Salvetti correlation-energy formula into a functional of theelectron densityrdquo Physical Review B Condensed Matter andMaterials Physics vol 37 no 2 pp 785ndash789 1988

[21] M J Frisch G W Trucks H B Schlegel et al Gaussian03Gaussian Inc Pittsburgh Penn USA 2003

[22] R G Parr andW YangDensity FunctionalTheory of Atoms andMolecules Oxford University Press Oxford UK 1989

[23] R G Parr R A Donnelly M Levy and W E Palke ldquoElectro-negativity the density functional viewpointrdquo The Journal ofChemical Physics vol 68 no 8 pp 3801ndash3807 1977

[24] R G Parr and R G Pearson ldquoAbsolute hardness companionparameter to absolute electronegativityrdquo Journal of theAmericanChemical Society vol 105 no 26 pp 7512ndash7516 1983

[25] T Koopmans ldquoUber die Zuordnung von Wellenfunktionenund Eigenwerten zu den Einzelnen Elektronen Eines AtomsrdquoPhysica A Statistical Mechanics and its Applications vol 1 no1ndash6 pp 104ndash113 1934

[26] R G Pearson ldquoHard and soft acids and bases-the evolution ofa chemical conceptrdquo Coordination Chemistry Reviews vol 100no C pp 403ndash425 1990

[27] A Kokalj and N Kovacevic ldquoOn the consistent use of elec-trophilicity index and HSAB-based electron transfer and itsassociated change of energy parametersrdquo Chemical PhysicsLetters vol 507 no 1-3 pp 181ndash184 2011

[28] R G Parr L V Szentpaly and S Liu ldquoElectrophilicity indexrdquoJournal of the American Chemical Society vol 121 no 9 pp1922ndash1924 1999

[29] K Fukui ldquoRole of frontier orbitals in chemical reactionsrdquoScience vol 218 no 4574 pp 747ndash754 1982

[30] W Yang and W J Mortier ldquoThe use of global and localmolecular parameters for the analysis of the gas-phase basicityof aminesrdquo Journal of the American Chemical Society vol 108no 19 pp 5708ndash5711 1986


[31] W Yang and R G Parr ldquoHardness Softness and the Fukui func-tion in the electronic theory ofmetals and catalysisrdquoProceedingsof the National Academy of Sciences vol 82 no 20 pp 6723ndash6726 1985

[32] I B Obot S A Umoren and N O Obi-Egbedi ldquoCorrosioninhibition and adsorption behaviour for aluminium by extractof Amingeria robusta in HCl solution synergistic effect ofIodide ionsrdquo Journal of Materials and Environmental Sciencevol 2 no 1 pp 60ndash71 2011

[33] K M Manamela L C Murulana M M Kabanda and E EEbenso ldquoAdsorptive and DFT studies of some imidazoliumbased ionic liquids as corrosion inhibitors for zinc in acidicmediumrdquo International Journal of Electrochemical Science vol9 no 6 pp 3029ndash3046 2014

[34] F Bentiss M Lebrini and M Lagrenee ldquoThermodynamiccharacterization of metal dissolution and inhibitor adsorptionprocesses in mild steel25-bis(n-thienyl)-134-thiadiazoleshydrochloric acid systemrdquo Corrosion Science vol 47 no 12 pp2915ndash2931 2005

[35] H Ashassi-Sorkhabi B Shabani B Aligholipour and D Seif-zadeh ldquoThe effect of some Schiff bases on the corrosionof aluminum in hydrochloric acid solutionrdquo Applied SurfaceScience vol 252 no 12 pp 4039ndash4047 2006

[36] R F V Villamil P Corio S M L Agostinho and J C RubimldquoEffect of sodiumdodecylsulfate on copper corrosion in sulfuricacid media in the absence and presence of benzotriazolerdquoJournal of Electroanalytical Chemistry vol 472 no 2 pp 112ndash119 1999

[37] G Moretti F Guidi and G Grion ldquoTryptamine as a green ironcorrosion inhibitor in 05Mdeaerated sulphuric acidrdquoCorrosionScience vol 46 no 2 pp 387ndash403 2004

[38] A K Singh and M A Quraishi ldquoEffect of Cefazolin on thecorrosion of mild steel in HCl solutionrdquo Corrosion Science vol52 no 1 pp 152ndash160 2010

[39] E A Noor ldquoPotential of aqueous extract of Hibiscus sabdariffaleaves for inhibiting the corrosion of aluminum in alkalinesolutionsrdquo Journal of Applied Electrochemistry vol 39 no 9 pp1465ndash1475 2009

[40] S A Umoren I B Obot I E Apkabio and S E Etuk ldquoAdsorp-tion and Corrosion inhibitive properties of Vigna unguiculatain alkaline acidic mediardquo Pigment amp Resin Technology vol 37pp 98ndash105 2000

[41] I A Adejoro D C Akintayo and C U Ibeji ldquoThe Efficiencyof Chloroquine as Corrosion Inhibitor for Aluminium in 1MHCl Solution Experimental and DFT Studyrdquo Jordan Journal ofChemistry vol 11 no 1 pp 38ndash49 2016

[42] A YMusa AAHKadhumA BMohamadAA B Rahomaand H Mesmari ldquoElectrochemical and quantum chemical cal-culations on 44-dimethyloxazolidine-2-thione as inhibitor formild steel corrosion in hydrochloric acidrdquo Journal of MolecularStructure vol 969 no 1ndash3 pp 233ndash237 2010

[43] H Ashassi-Sorkhabi B Shaabani andD Seifzadeh ldquoCorrosioninhibition of mild steel by some schiff base compounds inhydrochloric acidrdquo Applied Surface Science vol 239 no 2 pp154ndash164 2005

[44] N O Eddy H Momoh-Yahaya and E E Oguzie ldquoTheoreticaland experimental studies on the corrosion inhibition potentialsof some purines for aluminum in 01 M HClrdquo Journal ofAdvanced Research vol 6 no 2 pp 203ndash217 2015

[45] Y YanW Li L Cai and BHou ldquoElectrochemical and quantumchemical study of purines as corrosion inhibitors for mild steel

in 1 M HCl solutionrdquo Electrochimica Acta vol 53 no 20 pp5953ndash5960 2008

[46] I B Obot and N O Obi-Egbedi ldquoInhibitory effect and adsorp-tion characteristics of 23-diaminonaphthalene at aluminumhydrochloric acid interface Experimental and theoreticalstudyrdquo Surface Review and Letters vol 15 no 6 pp 903ndash9102008

[47] A Doner R Solmaz M Ozcan and G Kardas ldquoExperimentaland theoretical studies of thiazoles as corrosion inhibitors formild steel in sulphuric acid solutionrdquo Corrosion Science vol 53no 9 pp 2902ndash2913 2011

[48] Y Qiang S Zhang L Guo X Zheng B Xiang and S ChenldquoExperimental and theoretical studies of four allyl imida-zolium-based ionic liquids as green inhibitors for coppercorrosion in sulfuric acidrdquo Corrosion Science vol 119 pp 68ndash78 2017

[49] N Khalil ldquoQuantum chemical approach of corrosion inhibi-tionrdquo Electrochimica Acta vol 48 no 18 pp 2635ndash2640 2003

[50] K F Khaled K Babic-Samardzija and N Hackerman ldquoThe-oretical study of the structural effects of polymethylene amineson corrosion inhibition of iron in acid solutionsrdquoElectrochimicaActa vol 50 no 12 pp 2515ndash2520 2005

[51] G Bereket E Hur and C Ogretir ldquoQuantum chemical studieson some imidazole derivatives as corrosion inhibitors for ironin acidic mediumrdquo Journal of Molecular Structure vol 578 no1ndash3 pp 79ndash88 2002

[52] G Gece ldquoThe use of quantum chemical methods in corrosioninhibitor studiesrdquo Corrosion Science vol 50 no 11 pp 2981ndash2992 2008

[53] N O Obi-Egbedi I B Obot M I El-Khaiary S A Umorenand E E Ebenso ldquoComputational simulation and statisticalanalysis on the relationship between corrosion inhibition effi-ciency andmolecular structure of some phenanthroline deriva-tives onmild steel surfacerdquo International Journal of Electrochem-ical Science vol 6 no 11 pp 5649ndash5675 2011

[54] M A Bedair ldquoThe effect of structure parameters on the cor-rosion inhibition effect of some heterocyclic nitrogen organiccompoundsrdquo Journal of Molecular Liquids vol 219 pp 128ndash1412016

[55] J Saranya P Sounthari K Parameswari and S Chitra ldquoAdsorp-tion and density functional theory on corrosion of mild steel bya quinoxaline derivativerdquoDer Pharma Chemica vol 7 no 8 pp187ndash196 2015

[56] T Arslan F Kandemirli E E Ebenso I Love and H AlemuldquoQuantum chemical studies on the corrosion inhibition of somesulphonamides on mild steel in acidic mediumrdquo CorrosionScience vol 51 no 1 pp 35ndash47 2009

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal ofInternational Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal ofInternational Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


212 Chemicals All chemicals were of analytical grade andwere used without further purification

(i) HCl fromMerck with purity 37(ii) Caffeine (C8H10N4O2) was acquired from Sigma

Aldrich chemicals and solutions of concentrationsrange from 01mM to 10mM were prepared

(iii) Acetone from Sigma Aldrich with purity 995

22 Methods

221 Mass Loss Method The mass loss method [17 18] isprobably the most widely used method of inhibition assess-ment The simplicity and reliability of the measurementoffered bymass lossmethod [19]make the technique form thebaseline method in many corrosion monitoring programs

Prior to the immersion of the specimens in the test solu-tion (50mL) their surfacewas abradedwith different grade ofemery papers (120-180-240-600-1200) tomirror finish rinsedwith acetone washed with bidistilled water and finally driedin a desiccator The mass loss experiments were performedunder total immersion in the acidic solution of 10M (with orwithout caffeine) opened to the airThe temperaturewas con-trolled by a water thermostat After one-hour immersion thespecimens were retrieved from the solution washed with abristle brush under running water in order to remove the cor-rosion product dried in a desiccator and weighed accuratelyThe study was performed in the temperature range of 303Kto 323K and the concentration range of 01mM to 10mMThe tests were repeated three times for each solution andat the same temperature The mean value was then recorded

The corrosion rate (119882) in gsdotcmminus2sdothminus1 was calculated usingthe following equation

119882 = 1198981 minus 1198982119878119905 (1)

where 1198981 is the mass of the sample before immersion in thetest solution 1198982 is the mass after 1 h immersion in the testsolution 119878 is the total surface of the sample and 119905 is theimmersion time The inhibition efficiency IE () was calcu-lated according to the equation below

IE () = 1198820 minus 1198821198820 times 100 (2)

where 1198820 is the corrosion rate in the absence of the testedmolecule and 119882 is the corrosion rate in its presence

222 Quantum Chemistry Calculations The calculationswere performed using the hybrid functional B3LYP a versionof DFT functional that uses Beckersquos three parameter func-tional (B3) with a mixture of HF and DFT exchange termsassociated with the gradient corrected correlation functionalof Lee et al [20] The full geometry optimization was carriedout at B3LYP6-31G (d) level of theory using Gaussian 03W[21]

The calculations were carried out in gas phase to showthe relationship between themolecular descriptors of caffeine

Figure 1 Optimized structure of caffeine by B3LYP6-31G (d)

and its inhibition efficiencyThe optimized minimum energygeometrical configuration of caffeine is given in Figure 1

DFT [22] has been found to be successful in providingtheoretical insights into the chemical reactivity and selec-tivity using chemical concepts such as electronegativity (120594)hardness (120578) softness (119878) electrophilicity index (120596) and localreactivity descriptors including Fukui functions 119891(119903) and thelocal softness 119904(119903)

Density functional theory (DFT) states that changes inelectronic energy 119889119864[120588(119903)] are related to changes in thenumber of electrons 119873 and changes in the external potentialV(119903) felt by the electron distribution (which refers to thenuclear position in chemical systems)

119889119864 [120588 (119903)] = 120583119875119889119873 + int120588 (119903) 119889V (119903) 119889119903 (3)

According to Parr et al [23] the chemical potential 120583119875 islinked with the first derivative of the energy with respect tothe number of electrons and therefore with the negative of theelectronegativity by the following equation

120583119875 = ( 120597119864120597119873)

V(119903)= minus120594 (4)

where 120583119875 is the electronic chemical potential 119864 is the totalenergy 119873 is the number of electrons and V(119903) is the externalpotential of the system

The second partial derivative of the energy with respectto the number of electrons has been defined as hardness (120578)

120578 = ( 12059721198641205971198732)V(119903)

= (120597120583119875120597119873 )V(119903)

(5)

This quantity [24] measures both the stability and the reac-tivity of the molecule

According to Koopmansrsquos theorem [25] the ionizationpotential (119868) and the electron affinity (119860) of the inhibitors arecalculated using the following equations

119868 = minus119864HOMO119860 = minus119864LUMO (6)

The electronegativity (120594) [24] which measures the power ofan atom or group of atoms to attract electrons towards itselfcan then be written as

120594 = 119868 + 1198602 (7)



120578 = 119868 minus 1198602 (8)


119878 = 1120578 = 2

119868 minus 119860 (9)





120596 = 12058321198752120578 (11)



119891 (119903) = ( 120597120583119875120597V (119903))119873 = (120597120588 (119903)120597119873 )

V(119903) (12)





119904120572119896 = 119891120572119896 119878 (120572 = + ou minus) (14)


01020304050607080

IE (

)

T = 303 ＋

T = 308 ＋

T = 318 ＋

T = 323 ＋

T = 313 ＋

2 4 6 8 10 120CＣＨＢ (mM)


01020304050607080

IE (

)

305 310 315 320 325300T (K)











0 0002 0004 0006 0008 001 0012

T = 303 ＋

T = 308 ＋

T = 318 ＋

T = 323 ＋

T = 313 ＋

CＣＨＢ (mM)

0

0005

001

0015

002

0025

003

CＣＨＢ





119870ads119862inh = 119891 (120579 119909) exp (minus120572120579) (16)



119862inh120579 = 1119870ads

+ 119862inh (17)



305 310 315 320 325300T (K)

minus10

minus14

minus18

minus22

minus26

minus30

R2 = 09782

ΔG

0 ＞Ｍ

(ＥＧ

ＩＦminus

1)

ΔG0＞Ｍ = 0462T minus 16873


















119870ads+ 119899119862inh



119870ads = 11987010158401119910






ln 120579 = ln 120579max minus 1198861205752 (20)


120575 = 119877119879 ln(1 + 1119862inh

) (21)



119864119898 = 1radic2119886 (22)



40 60 80 100 1200 20



ＦＨ



305 310 315 320 325300T (K)

141210

86420

Em

(ＥＧＩＦminus

1)

Em = 025T minus 69267

R2 = 09868

Em = minus00106T2 + 67437T minus 10664

R2 = 09839






minus3

minus25

minus2

minus15

minus1

minus05

0

ＦＩＡ(W

)

31 315 32 325 33 335305

103T (＋minus1)


= 5Ｇ－CＣＨＢ







log119882 = log119860 minus 1198641198862303119877119879

log(119882119879 ) = [log( 119877





Blank

minus13

minus12

minus11

minus10

minus9

minus8

minus7

minus6

ＦＩＡ(W

T)

31 315 32 325 33 335305

103T (＋minus1)

= 1Ｇ－CＣＨＢ

= 5Ｇ－CＣＨＢ






Δ119867lowast119886 = 119864119886 minus 119877119879 (24)




















4 Conclusion





(a) (b)




physisorption[]+

Inh Inh[]+ []+ []+ []+ []+ []+






References




































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



120578 = 119868 minus 1198602 (8)


119878 = 1120578 = 2

119868 minus 119860 (9)





120596 = 12058321198752120578 (11)



119891 (119903) = ( 120597120583119875120597V (119903))119873 = (120597120588 (119903)120597119873 )

V(119903) (12)





119904120572119896 = 119891120572119896 119878 (120572 = + ou minus) (14)


01020304050607080

IE (

)

T = 303 ＋

T = 308 ＋

T = 318 ＋

T = 323 ＋

T = 313 ＋

2 4 6 8 10 120CＣＨＢ (mM)


01020304050607080

IE (

)

305 310 315 320 325300T (K)











0 0002 0004 0006 0008 001 0012

T = 303 ＋

T = 308 ＋

T = 318 ＋

T = 323 ＋

T = 313 ＋

CＣＨＢ (mM)

0

0005

001

0015

002

0025

003

CＣＨＢ





119870ads119862inh = 119891 (120579 119909) exp (minus120572120579) (16)



119862inh120579 = 1119870ads

+ 119862inh (17)



305 310 315 320 325300T (K)

minus10

minus14

minus18

minus22

minus26

minus30

R2 = 09782

ΔG

0 ＞Ｍ

(ＥＧ

ＩＦminus

1)

ΔG0＞Ｍ = 0462T minus 16873


















119870ads+ 119899119862inh



119870ads = 11987010158401119910






ln 120579 = ln 120579max minus 1198861205752 (20)


120575 = 119877119879 ln(1 + 1119862inh

) (21)



119864119898 = 1radic2119886 (22)



40 60 80 100 1200 20



ＦＨ



305 310 315 320 325300T (K)

141210

86420

Em

(ＥＧＩＦminus

1)

Em = 025T minus 69267

R2 = 09868

Em = minus00106T2 + 67437T minus 10664

R2 = 09839






minus3

minus25

minus2

minus15

minus1

minus05

0

ＦＩＡ(W

)

31 315 32 325 33 335305

103T (＋minus1)


= 5Ｇ－CＣＨＢ







log119882 = log119860 minus 1198641198862303119877119879

log(119882119879 ) = [log( 119877





Blank

minus13

minus12

minus11

minus10

minus9

minus8

minus7

minus6

ＦＩＡ(W

T)

31 315 32 325 33 335305

103T (＋minus1)

= 1Ｇ－CＣＨＢ

= 5Ｇ－CＣＨＢ






Δ119867lowast119886 = 119864119886 minus 119877119879 (24)




















4 Conclusion





(a) (b)




physisorption[]+

Inh Inh[]+ []+ []+ []+ []+ []+






References




































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 0002 0004 0006 0008 001 0012

T = 303 ＋

T = 308 ＋

T = 318 ＋

T = 323 ＋

T = 313 ＋

CＣＨＢ (mM)

0

0005

001

0015

002

0025

003

CＣＨＢ





119870ads119862inh = 119891 (120579 119909) exp (minus120572120579) (16)



119862inh120579 = 1119870ads

+ 119862inh (17)



305 310 315 320 325300T (K)

minus10

minus14

minus18

minus22

minus26

minus30

R2 = 09782

ΔG

0 ＞Ｍ

(ＥＧ

ＩＦminus

1)

ΔG0＞Ｍ = 0462T minus 16873


















119870ads+ 119899119862inh



119870ads = 11987010158401119910






ln 120579 = ln 120579max minus 1198861205752 (20)


120575 = 119877119879 ln(1 + 1119862inh

) (21)



119864119898 = 1radic2119886 (22)



40 60 80 100 1200 20



ＦＨ



305 310 315 320 325300T (K)

141210

86420

Em

(ＥＧＩＦminus

1)

Em = 025T minus 69267

R2 = 09868

Em = minus00106T2 + 67437T minus 10664

R2 = 09839






minus3

minus25

minus2

minus15

minus1

minus05

0

ＦＩＡ(W

)

31 315 32 325 33 335305

103T (＋minus1)


= 5Ｇ－CＣＨＢ







log119882 = log119860 minus 1198641198862303119877119879

log(119882119879 ) = [log( 119877





Blank

minus13

minus12

minus11

minus10

minus9

minus8

minus7

minus6

ＦＩＡ(W

T)

31 315 32 325 33 335305

103T (＋minus1)

= 1Ｇ－CＣＨＢ

= 5Ｇ－CＣＨＢ






Δ119867lowast119886 = 119864119886 minus 119877119879 (24)




















4 Conclusion





(a) (b)




physisorption[]+

Inh Inh[]+ []+ []+ []+ []+ []+






References




































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






119870ads+ 119899119862inh



119870ads = 11987010158401119910






ln 120579 = ln 120579max minus 1198861205752 (20)


120575 = 119877119879 ln(1 + 1119862inh

) (21)



119864119898 = 1radic2119886 (22)



40 60 80 100 1200 20



ＦＨ



305 310 315 320 325300T (K)

141210

86420

Em

(ＥＧＩＦminus

1)

Em = 025T minus 69267

R2 = 09868

Em = minus00106T2 + 67437T minus 10664

R2 = 09839






minus3

minus25

minus2

minus15

minus1

minus05

0

ＦＩＡ(W

)

31 315 32 325 33 335305

103T (＋minus1)


= 5Ｇ－CＣＨＢ







log119882 = log119860 minus 1198641198862303119877119879

log(119882119879 ) = [log( 119877





Blank

minus13

minus12

minus11

minus10

minus9

minus8

minus7

minus6

ＦＩＡ(W

T)

31 315 32 325 33 335305

103T (＋minus1)

= 1Ｇ－CＣＨＢ

= 5Ｇ－CＣＨＢ






Δ119867lowast119886 = 119864119886 minus 119877119879 (24)




















4 Conclusion





(a) (b)




physisorption[]+

Inh Inh[]+ []+ []+ []+ []+ []+






References




































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




minus3

minus25

minus2

minus15

minus1

minus05

0

ＦＩＡ(W

)

31 315 32 325 33 335305

103T (＋minus1)


= 5Ｇ－CＣＨＢ







log119882 = log119860 minus 1198641198862303119877119879

log(119882119879 ) = [log( 119877





Blank

minus13

minus12

minus11

minus10

minus9

minus8

minus7

minus6

ＦＩＡ(W

T)

31 315 32 325 33 335305

103T (＋minus1)

= 1Ｇ－CＣＨＢ

= 5Ｇ－CＣＨＢ






Δ119867lowast119886 = 119864119886 minus 119877119879 (24)




















4 Conclusion





(a) (b)




physisorption[]+

Inh Inh[]+ []+ []+ []+ []+ []+






References




































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

















4 Conclusion





(a) (b)




physisorption[]+

Inh Inh[]+ []+ []+ []+ []+ []+






References




































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




(a) (b)




physisorption[]+

Inh Inh[]+ []+ []+ []+ []+ []+






References




































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





References




































































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

inhibition of aluminium corrosion in 1.0m hcl by …downloads.hindawi.com/archive/2017/6975248.pdf10...

Documents