[Article] www.whxb.pku.edu.cn

物理化学学报(Wuli Huaxue Xuebao)Acta Phys. -Chim. Sin. 2013, 29 (10), 2221-2231October

Received: May 22, 2013; Revised: July 25, 2013; Published on Web: July 30, 2013.∗Corresponding author. Email: xianghong-li@163.com; Tel: +86-871-63863377.The project was supported by the National Natural Science Foundation of China (51361027).国家自然科学基金(51361027)资助项目

© Editorial office of Acta Physico-Chimica Sinica

doi: 10.3866/PKU.WHXB201307301

嘧啶衍生物对钢在盐酸溶液中的缓蚀作用

李向红 1,2,* 谢小光 1

(1云南大学化学科学与工程学院,昆明 650091; 2西南林业大学理学院,昆明 650224)

摘要: 采用失重法、动电位极化曲线、电化学阻抗谱(EIS)、量子化学计算研究了两种嘧啶衍生物(2-羟基嘧啶(HP)和2-巯基嘧啶(MP))在1.0−5.0 mol∙L−1 HCl溶液中对冷轧钢(CRS)的缓蚀作用.结果表明: HP和MP在1.0 mol∙L−1 HCl溶液中对冷轧钢具有良好的缓蚀作用,且在钢表面的吸附符合Langmuir吸附等温式.缓蚀率随缓蚀剂浓度的增加而增大,但随盐酸浓度的增加而减小.求出了相应的吸附热力学参数(吸附平衡常数(K),吸附自由能(ΔG0))和腐蚀动力学参数(表观活化能(Ea)、指前因子(A)、腐蚀速率常数(k)、动力学常数(B)),并根据这些参数讨论了缓蚀作用机理.动电位极化曲线表明, MP和HP均为混合抑制型缓蚀剂; EIS谱呈单一容抗弧,电荷转移电阻随缓蚀剂浓度的增加而增大.两种嘧啶化合物的缓蚀率排序为MP>HP.量子化学计算结果表明,MP比HP更具吸附活性,缓蚀性能的理论计算和实验结果相一致.

关键词: 缓蚀剂; 2-羟基嘧啶; 2-巯基嘧啶; 钢; 盐酸; 吸附; 量子化学计算中图分类号: O646

Inhibition Effect of Pyrimidine Derivatives on the Corrosion ofSteel in Hydrochloric Acid Solution

LI Xiang-Hong1,2,* XIE Xiao-Guang1

(1School of Chemical Science and Technology, Yunnan University, Kunming 650091, P. R. China;2Faculty of Science, Southwest Forestry University, Kunming 650224, P. R. China)

Abstract: The inhibition effect of two pyrimidine derivatives, 2- hydroxypyrimidine (HP) and 2-mercaptopyrimidine (MP), on the corrosion of cold rolled steel (CRS) in 1.0−5.0 mol∙L−1 HCl is investigatedby mass loss, potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), andquantum chemical calculations. The results show that HP and MP are both good inhibitors of corrosion ofCRS in 1.0 mol∙L−1 HCl solution. The adsorption of these inhibitors onto the CRS surface obeys the Langmuiradsorption isotherm. Inhibition efficiency increases with inhibitor concentration, and decreases withhydrochloric acid concentration. The thermodynamic parameters of adsorption (adsorption equilibriumconstant (K) and adsorption free energy (ΔG0)) and kinetic parameters of corrosion (apparent activationenergy (Ea), pre-exponential factor (A), corrosion rate constant (k), and kinetic reaction constant (B)) arealso calculated. Based on these parameters, the mechanism of inhibition is discussed. Potentiodynamicpolarization curves show that HP and MP act as mixed-type inhibitors. EIS exhibit one capacitive loop, andthe charge transfer resistance increases with inhibitor concentration. The results of quantum chemicalcalculations indicate that MP exhibits higher adsorptive ability than HP, which is in good agreement with theexperimental data.

Key Words: Corrosion inhibitor; 2-Hydroxypyrimidine; 2-Mercaptopyrimidine; Steel;Hydrochloric acid; Adsorption; Quantum chemical calculation

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1 IntroductionN-heterocyclic compounds are considered to be the most ef-

fective corrosion inhibitors for metals in acid media.1 They ex-hibit inhibition by adsorption on the metal surface, and the ad-sorption takes place through nitrogen, oxygen, and sulfur at-oms, as well as those with triple or conjugated double bonds oraromatic rings in their molecular structures. A stronger coordi-nation bond formed between inhibitor and metal is always re-lated to good inhibitive performance; as consequence, inhibi-tion efficiency should increase in the order: O<N<S<P.2 If asubstitution polar group (―NH2, ―OH, ―SH, etc.) is addedto the N-heterocyclic ring, the electron density of N-heterocy-clic ring is increased, and subsequently, it facilitates the adsorp-tion ability.3

As an important kind of N-heterocyclic compound, pyrimi-dine derivatives whose molecules possess the pyrimidine ringwith two N heteroatoms could also be deemed as good poten-tial inhibitors. 2- Mercaptopyrimidine (MP) was reported as agood corrosion inhibitor for non-ferrous metals in acid media,such as zinc in HCl solution,4 aluminium in HCl solution,5 cop-per in H2SO4 solution.6 Besides non-ferrous metals, the inhibi-tion effects of pyrimidine derivatives on the steel corrosion inacid media were studied. In 1993, Zucchi et al.7 investigatedthe corrosion inhibition of steel in H2SO4 solution by some py-rimidine derivatives. In 2001, Wang8 reported the corrosion in-hibition by MP for steel in H3PO4 solution, and the maximuminhibition efficiency (η) in 3.0 mol∙L−1 H3PO4 solution is 98%at 10.0 mmol∙L− 1. According to our recent work,9 2-aminopy-rimidne (AP) also acts as a good corrosion inhibitor on the cor-rosion of steel in 1.0 mol∙L−1 HCl solution, and the η is 92.4%at 20 °C when the concentration of AP is 10.0 mmol∙L−1. How-ever, another pyrimidine derivative of uracil (Ur) exhibits poorinhibitive ability for steel in H3PO4

10 and H2SO411 solutions.

Through these studies, the efficiency of pyrimidine compoundmainly depends on the substitution group in the pyrimidinering. Accordingly, there is a great need to obtain the correlationbetween the molecular structure and inhibitive performance.

Quantum chemical calculation has been proven to be a veryuseful method in corrosion inhibitor studies.12 − 14 Using quan-tum chemical calculation, the theoretical parameters of inhibi-tor molecule can be obtained, and then, theoretically speaking,the inhibitive mechanism can be directly accounted for thechemical reactivity of the compound under study. It is foundthat the inhibition activity of a given inhibitor is directly corre-lated with the theoretical parameters including the highest oc-cupied molecular orbital energy (EHOMO), the lowest unoccupiedmolecular orbital (ELUMO), dipole moment (μ), atomic charge,and Fukui inces.15 However, many quantum parameters aboutorganic inhibitors are calculated in gas phase. In fact, acid in-hibitors are used in acidic water solutions, and they could beprotonated. Thus, in the field of theoretical calculation of acidinhibitors, the solvent effect and the protonated inhibitor mole-cules should be taken into account.

In this paper, the inhibition effect of two pyrimidine deriva-tives of 2-hydroxypyrimidine (HP) and MP on the corrosion ofcold rolled steel (CRS) in 1.0 mol∙L−1 HCl solution is studiedusing weight loss, potentiodynamic polarization curves, andelectrochemical impedance spectroscopy (EIS) methods. Theadsorption isotherm of inhibitor on steel surface and the stan-dard adsorption free energy (ΔG0) are obtained. Quantumchemical calculation of density functional theory (DFT) includ-ing the solvent effect is applied to elucidate the relationship be-tween the inhibitor molecular structure and inhibition efficien-cy. The difference in inhibition performance between neutralinhibitor molecule and protonated inhibitor molecule is furtherinvestigated. It is expected to get general information on the ad-sorption and inhibition effect of pyrimidine derivatives on steelin HCl solution.

2 Experimental2.1 Materials and inhibitors

Weight loss and electrochemical tests were performed oncold rolled steel with the following composition: 0.05% C,0.02% Si, 0.28% Mn, 0.023% P, 0.019% S, and the remainderFe. Two pyrimidine derivatives of 2- hydroxypyrimidine (HP,C4H4N2O) and 2- mercaptopyrimidine (MP, C4H4N2S) were ob-tained from Shanghai Chemical Reagent Company of China.Fig.1 shows the molecular structures of HP and MP, and theyare of good solubility in water. The aggressive solution of 1.0mol∙L − 1 HCl solution was prepared by dilution of AR grade37% HCl with distilled water. The concentration range of inhib-itor is 1.0−10.0 mmol∙L−1.2.2 Weight loss measurements

The CRS rectangular coupons of 2.5 cm×2.0 cm×0.04 cmwere abraded by a series of emery paper (grade 320-500-800)and then washed with distilled water, degreased with acetone,and finally dried at room temperature. After weighing usingdigital balance with sensitivity of ±0.1 mg, the specimens wereimmersed in glass beakers containing 250 mL 1.0 mol∙L−1 HClsolution without and with different concentrations of inhibitorusing glass hooks and rods. The temperature was controlled at(25.0±0.1) °C using a water thermostat bath. All the aggressiveacid solutions were open to air without bubbling. After immer-sion for 6 h, the specimens were taken out, washed with bristlebrush under running water to remove the corrosion product,dried with a hot air stream, and re-weighed accurately. In orderto get good reproducibility, experiments were carried out in

Fig.1 Chemical molecular structures of twopyrimidine derivatives

(a) 2-hydroxypyrimidine (HP); (b) 2-mercaptopyrimidine (MP)

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LI Xiang-Hong et al.: Inhibition Effect of Pyrimidine Derivatives on the Corrosion of Steel in Hydrochloric AcidNo.10

triplicate. The average mass loss of three parallel CRS sheetswas obtained, and then the inhibition efficiency (ηw) was calcu-lated.1

2.3 Electrochemical measurementsElectrochemical experiments were carried out in the conven-

tional three-electrode system with a platinum counter electrode(CE) and a saturated calomel electrode (SCE) coupled to a fineLuggin capillary as the reference electrode. In order to mini-mize Ohmic contribution, the Luggin capillary was placedclose to the working electrode (WE) which was in the form ofa square CRS embedded in polyvinyl chloride (PVC) holder us-ing epoxy resin so that the flat surface was the only surface inthe electrode. The working surface area was 1.0 cm×1.0 cm,and prepared as described above (Section 2.2). The electrodewas immersed in test solution at open circuit potential (OCP)for 2 h to be sufficient to attain a stable state before measure-ment. All electrochemical measurements were carried out at25 °C using PARSTAT 2273 advanced electrochemical system(Princeton Applied Research).

The potential of potentiodynamic polarization curves was in-creased at 0.5 mV∙s−1 and started from a potential of −250 mVto +250 mV (versus OCP). Inhibition efficiency (ηp) was calcu-lated through the corrosion current density (icorr) values.1 Elec-trochemical impedance spectroscopy (EIS) was carried out atOCP over a frequency range of 10 mHz−100 kHz using a 10mV root mean square (RMS) voltage excitation. The numberof points per decade is 30. Inhibition efficiency (ηR) was esti-mated using the charge transfer resistance (Rt) values.1

2.4 Quantum chemical calculationsQuantum chemical calculations were performed with DMol3

numerical based DFT in Materials Studio 4.1 software fromAccelrys Inc.16 Geometrical optimizations and frequency calcu-lations were carried out with the generalized gradient approxi-mation (GGA) functional of Becke exchange plus Lee-Yang-Parr correlation (BLYP)17 in conjunction with double numericalplus d-functions (DND) basis set.18 Fine convergence criteriaand global orbital cutoffs were employed on basis set defini-tions. Considering the solvent effects, all the geometries werere-optimized at the BLYP/DND level by using COSMO (con-ductor- like screening model)19 and defining water as the sol-vent. Through the frequency analysis, it is found that all opti-mized species have no imaginary frequencies.

3 Results and discussion3.1 Effect of pyrimidine derivatives on inhibition

efficiencyFig.2 shows the relationship between inhibition efficiency

(ηw) values obtained from weight loss method and the concen-trations of HP and MP in 1.0 mol∙L − 1 HCl solution at 25 °C.Apparently, ηw increases with the increase of the inhibitor con-centration. This behavior is due to the fact that the adsorptioncoverage of inhibitor on steel surface increases with the inhibi-tor concentration. For both pyrimidine compounds, when the

concentration reaches about 5.0 mmol∙L − 1, ηw reaches certainvalue and changes slightly with a further increase in the inhibi-tor concentration. At 10.0 mmol∙L−1, the maximum ηw is 87.2%for HP and 95.4% for MP, which indicates that two studied py-rimidine compounds act as good corrosion inhibitors for CRSin 1.0 mol∙L− 1 HCl solution. Inhibition efficiency follows theorder of MP>HP. It is evident that the difference in inhibitionefficiency of HP and MP was related to the presence of ―OHand―SH on the pyrimidine ring.3.2 Adsorption isotherm and adsorption free energy

(ΔG0)Fundamental information on the adsorption of inhibitor on

metal surface can be obtained by the adsorption isotherm.Several isotherms such as Frumkin, Langmuir, Temkin,Freundlich, Bockris-Swinkels, and Flory-Huggins isothermsare employed to fit the experimental data. It is found that theadsorption of the studied inhibitors on steel surface obeysLangmuir adsorption isotherm equation:11

cθ = 1

K + c (1)

where c is the concentration of inhibitor, K the adsorption equi-librium constant, and θ is the surface coverage and calculatedby the ration ηw.

The straight lines of c/θ against c for two inhibitors areshown in Fig.3, and the corresponding linear regression param-eters are listed in Table 1. Both straight lines have very goodlinear fit with the linear regression coefficients (r) up to 0.99and the slopes also very close to 1.0, which suggests that theadsorption of the pyrimidine inhibitors on steel surface obeysLangmuir adsorption isotherm. Also, the adsorptive equilibri-um constant (K) follows the order: MP>HP.

Generally, large value of K means the more stability of ad-sorptive inhibitor on metal surface, and then the better inhibi-tion performance of a given inhibitor. This is in good agree-ment with the values of ηw obtained from Fig.2.

The adsorption equilibrium constant K is related to the stan-dard adsorption free energy ΔG0 according to the followingequation:20

K = 155.5exp

-ΔG0

RT (2)

Fig.2 Relationship between inhibition efficiency (ηw) andconcentration of inhibitor (c) in 1.0 mol∙L−1 HCl solution at 25 °C

weight loss method, immersion time: 6 h

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where R is the gas constant (8.314 J∙K−1∙mol−1), T is the abso-lute temperature (K), and the value 55.5 is the concentration ofwater in solution in mol∙L − 1.20 The ΔG0 values are calculatedand also given in Table 1. Generally, values of ΔG0 up to −20 kJ∙mol−1 are consistent with the electrostatic interaction betweenthe charged molecules and the charged metal (physisorption)while those more negative than −40 kJ∙mol − 1 involve sharingor transfer of electrons from the inhibitor molecules to the met-al surface to form a co-ordinate type of bond (chemisorption).21

In the present study, the value of ΔG0 is found to be within therange from −40 to −20 kJ∙mol−1; probably means that the ad-sorption of each pyrimidine inhibitor on steel surface containsboth physical adsorption and chemical adsorption. It may be as-sumed that adsorption occurs firstly through the physical forc-es, and then the removal of water molecules from the surface isaccompanied by chemical interaction between the metal sur-face and inhibitor.22

3.3 Effect of temperatureTemperature is an important kinetic factor that influences

the corrosion rate of metal and modifies the adsorption of in-hibitor on electrode surface. In order to study the effect of tem-perature on the corrosion inhibition, experiments were conduct-ed at 25 to 50 °C at an interval of 5 °C. Effect of temperatureon inhibition efficiency (ηw) of 10.0 mmol ∙ L − 1 inhibitor isshown in Fig.4. Clearly, inhibition efficiency of either HP orMP fluctuates slightly with the experimental temperature. At50 °C, ηw is 83.2% for HP and 95.3% for MP, which reflectsthat the adsorption film of pyrimidine inhibitor is more stableeven at higher temperature.

According to Arrhenius equation, the natural logarithm ofthe corrosion rate (lnv) is a linear function with 1/T:11

ln v = -Ea

RT + ln A (3)

where Ea and A represent apparent activation energy and pre-exponential factor, respectively. The corrosion rate (v) was cal-culated from the following equation:

v = WSt (4)

where W is the average mass loss of three parallel CRS sheets(g), S is the total area of one CRS specimen (m2), and t is theimmersion time.

The linear regressions between ln v and 1/T were calculated,and the parameters are given in Table 2. Fig.5 shows the Arrhe-nius straight lines of lnv vs 1/T for the blank and different in-hibitors. All the linear regression coefficients (r) are very closeto 1, which indicates that the corrosion of steel functioningwith temperature follows Arrhenius equation.

Kinetic parameter of apparent activation energy (Ea) is im-portant to study the inhibitive mechanism. Compared with un-inhibited solution, the increase of Ea in inhibited solution maybe interpreted as the physical adsorption.22 In visa, a drop in Ea

Inhibitor

−

HP

MP

r

0.9972

0.9971

0.9811

Ea/(kJ∙mol−1)

60.4

70.8

64.1

A/(g∙m−2∙h−1)

2.84×1011

2.23×1012

6.18×1010

Table 2 Parameters of the straight lines of lnv−1/T in1.0 mol∙L−1 HCl solution

Table 1 Parameters of the straight lines of c/θ−c and adsorptionfree energy (ΔG0) in 1.0 mol∙L−1 HCl solution at 25 °C

Inhibitor

HP

MP

r

0.9999

0.9997

Slope

1.04

0.97

K/(L∙mol−1)

9.19×102

1.22×103

ΔG0/(kJ∙mol−1)

−26.9

−27.6

weight loss method, immersion time: 6 h; r: linear correlation coefficient

Fig.3 Langmuir isotherm adsorption modes of HP and MPon the CRS surface in 1.0 mol∙L−1 HCl solution at 25 °C

from weight loss measurement

Fig.4 Relationship between inhibition efficiency (ηw) andtemperature in 1.0 mol∙L−1 HCl solution

weight loss method, immersion time: 6 h

Fig.5 Arrhenius plots related to the corrosion rate of CRS forvarious inhibitors in 1.0 mol∙L−1 HCl solution

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with respect to the uninhibited solution probably indicates che-misorption.23 However, the criteria of Ea can not be taken as de-cisive due to competitive adsorption with water whose removalfrom the surface requires also some activation energy.24 Accord-ing to Solmaz et al.,25 the adsorption phenomenon of an organ-ic molecule is not considered as a mere physical or mere chem-ical adsorption phenomenon. In addition, Moretti et al.26 pro-posed that the adsorption criteria of chemisorption or physi-sorption could be decided by other adsorption parameters. Ac-cording to the adsorption parameter of ΔG0 mentioned above inSection 3.2, the adsorption of oxime inhibitor would involveboth physical and chemical processes. Thus, in the presentstudy, the value of Ea in the presence of each inhibitor is higherthan that in the uninhibited HCl solution, which does not neces-sarily mean that the adsorption of inhibitor is mere the physicaladsorption.27 In a word, both physical adsorption and chemicaladsorption would be considered simultaneously for the adsorp-tion of either HP or MP.

According to Eq.(3), it can be seen that the lower A and thehigher Ea lead to the lower corrosion rate (v) and exhibit inhibi-tion performance. After adding HP to the acid media, the valueof A is higher than that in uninhibited solution. Accordingly,the decrease in corrosion rate after adding inhibitor to acid me-dia is mostly caused by the increase of Ea. On the other hand,in the presence of MP, the decrease in corrosion rate is mostlycaused by the combination of the increase of Ea and the in-crease of A. In a word, the effect of A on the corrosion rateneeded to be considered, especially for MP inhibitor.3.4 Effect of immersion time

The immersion time is another important parameter in as-sessing the stability of inhibitive behavior, so it is necessary toevaluate the inhibition efficiency for a long immersion time. Inthe present study, effect of immersion time (1−156 h) on corro-sion inhibition of 10.0 mmol∙L−1 HP and 10.0 mmol∙L−1 MP in1.0 mol ∙ L − 1 HCl solution at 25 °C was investigated usingweight loss method. Dependence inhibition efficiency (ηw) onthe immersion time (t) is shown in Fig.6. For both HP and MP,inhibition efficiency is higher than 60% when the immersiontime is only 1 h, which indicates that the adsorption rate of py-rimidine inhibitor adsorbing on the steel surface is relativelyhigh. Also, the changed rule of ηw for two inhibitors is similar.ηw firstly increases with immersion time from 1 to 6 h, andthen fluctuates slightly (<4% ) with prolonging time to 156 h.The reasons could be attributed to the adsorptive film of inhibi-tor that rests upon the immersion time. The adsorptive filmreaches more compact and uniform along with prolonging im-mersion time (1− 6 h), and then the adsorptive film becomesthe relative saturated state within 6−156 h.3.5 Effect of acid concentration

In order to study the effect of acid concentration on the cor-rosion of steel in the presence of 10.0 mmol∙L−1 inhibitor, de-pendence of inhibition efficiency (ηw) on the concentration ofHCl solution (1.0−5.0 mol∙L−1) at 25 °C is shown in Fig.7 (im-

mersion time is 6 h). For either HP or MP inhibitor, ηw decreas-es almost linearly with the HCl concentration. In 5.0 mol∙L − 1

HCl solution, ηw values are reduced to 55.6% and 60.4% forHP and MP, respectively. At same acid concentration solution,inhibition performance still follows the order: MP>HP.

It is found that the corrosion rate (v) against the molar con-centration of acid (C) obeys the kinetic expression reported byMathur and Vasudevan:29

lnv=lnk+BC (5)where k is the rate constant, and B is the reaction constant. Thestraight lines of lnv versus C are shown in Fig.8, and the corre-sponding kinetic parameters are listed in Table 3.

The rate constant of k means the corrosion ability of acid formetal.29 Inspection of Table 3 reveals that in the presence of py-rimidine derivatives, there is a drop of k to more extent, whichindicates that the steel corrosion is retarded by the inhibitors ofHP and MP. Furthermore, the value of k for MP is lower thanthat for HP, which confirms that the inhibition performance ofMP is more superior to that of HP. According to Eq.(5), B isthe slope of the line lnv−C, thus B reflects the changed extentof v with the acid concentration.29 It is observed that the valueof B in the presence of inhibitor is larger than that of blankHCl solution, which suggests that the changed extent of corro-sion rate with acid concentration in inhibited acid is larger than

Fig.6 Relationship between inhibition efficiency (ηw) andimmersion time (t) in 1.0 mol∙L−1 HCl solution at 25 °C

weight loss method

Fig.7 Relationship between inhibition efficiency (ηw) andacid concentration (C) at 25 °C

weight loss method, immersion time: 6 h

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Acta Phys. -Chim. Sin. 2013 Vol.29

that in uninhibited acid. In addition, the value of B for MP ishigher than that for HP, which indicates that the changed de-gree of corrosion rate with acid concentration for MP is greaterthan that for HP.3.6 Potentiodynamic polarization curves

Potentiodynamic polarization curves of CRS in 1.0 mol∙L−1

HCl solution in the presence of different concentrations of HPand MP at 25 °C are shown in Fig.9. Obviously, the presenceof each pyrimidine compound causes a remarkable decrease inthe corrosion rate, i.e., shifts both anodic and cathodic curvesto lower current densities. In other words, both cathodic and an-odic reactions of CRS electrode are drastically inhibited, whichindicates that the pyrimidine compounds act as mixed-type in-hibitors.

The potentiodynamic polarization parameters including cor-rosion current densities (icorr), corrosion potential (Ecorr), cathod-ic Tafel slope (bc), anodic Tafel slope (ba), and inhibition effi-ciency (ηp) are listed in Table 4. It can be seen from Table 4that icorr decreases sharply with the increase of the concentra-tion of each pyrimidine inhibitor. In the presence of the inhibi-tor concentration of 10.0 mmol∙L−1, the corrosion current den-sity decreases from 319.4 μA∙cm−2 to 31.6 and 11.5 μA∙cm− 2

in the case of HP and MP, respectively. Correspondingly, ηp in-creases with the inhibitor concentration, due to the increase inthe blocked fraction of the electrode surface by adsorption. At10.0 mmol ∙L − 1 inhibitor concentration, inhibition efficiency(ηp) reaches up to a maximum of 90.1% for HP and 96.4% forMP, which again confirms that both pyrimidine derivatives aregood inhibitors for steel in 1.0 mol∙L−1 HCl solution, and ηp fol-lows the order: MP>HP. Compared with the corrosion potential(Ecorr) in 1.0 mol∙L−1 HCl solution without inhibitor, Ecorr in thepresence of HP or MP does not change, which indicates that allstudied pyrimidine derivatives act as mixed-type inhibitors.30

Furthermore, in the presence of each inhibitor, the slightchange of Tafel slopes of bc and ba indicates that the mecha-nism of steel does not change. According to Cao,30 the inhibi-tion is caused by geometric blocking effect. Namely, the inhibi-tion effect comes from the reduction of the reaction area on thesurface of the corroding metal.3.7 Electrochemical impedance spectroscopy (EIS)

Fig.10 represents the Nyquist diagrams for CRS in 1.0 mol∙L − 1 HCl solution in the presence of HP and MP at 25 °C. Ascan be seen from the figures, all the impedance spectra exhibitone single capacitive loop, which indicates that the corrosionof steel is mainly controlled by the charge transfer process, andusually related to the charge transfer of the corrosion process

Inhibitor

−

HP

MP

c(mmol∙L−1)

0.0

1.0

5.0

10.0

1.0

5.0

10.0

Ecorr

mV (vs SCE)

−440

−435

−444

−426

−431

−434

−432

icorr

(μA∙cm−2)

319.4

144.0

53.6

31.6

116.9

26.9

11.5

−bc

(mV∙dec−1)

101

118

119

126

105

111

113

ba

(mV∙dec−1)

51

61

60

61

57

55

58

ηp

%

−

54.9

83.2

90.1

63.4

91.6

96.4

Fig.8 Straight lines of lnv versus C at 25 °Cimmersion time: 6 h

Fig.9 Potentiodynamic polarization curves for CRS in1.0 mol∙L−1 HCl solution without and with different

concentrations of inhibitors at 25 °CImmersion time is 2 h. (A) HP; (B) MP

Table 4 Potentiodynamic polarization parameters for thecorrosion of CRS in 1.0 mol∙L−1 HCl solution containing

different concentrations of HP and MP at 25 °C

immersion time: 2 h

Inhibitor

−

HP

MP

r

0.9974

0.9945

0.9944

k/(g∙m−2∙h−1)

4.59

0.46

0.15

B/(g∙m−2∙h−1∙L∙mol−1)

0.39

0.73

0.91

Table 3 Parameters of the linear regression between lnv and Cfor the corrosion of steel in HCl solution

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and double layer behavior.31 In addition, the shape is main-tained throughout all tested inhibitor concentrations comparedwith that of blank solution, indicating that there is almost nochange in the corrosion mechanism which occurs due to the in-hibitor addition.32

The diameter of the capacitive loop in the presence of inhibi-tor is larger than that in the absence of inhibitor (blank solu-tion) and increases with the inhibitor concentration. This sug-gests that the impedance of inhibited substrate increases withthe inhibitor concentration. Further inspection of Fig.10 re-veals that there is a little difference between HP and MP at lowinhibitor concentration (1.0 mmol∙L−1), while there is large dif-ference at high inhibitor concentration (10.0 mmol∙L− 1). Suchbehavior may be considered the suggestion that physisorptionat lower concentration and chemisorption at higher concentra-tion for a given inhibitor.

Noticeably, these capacitive loops are not perfect semicir-cles that can be attributed to the frequency dispersion effect asa result of the roughness and inhomogeneousness of the elec-trode surface.33 Accordingly, the EIS data are simulated by theequivalent circuit shown in Fig.10B. Rs and Rt are the solutionresistance and charge transfer resistance, respectively. CPE isconstant phase element to replace a double layer capacitance(Cdl) for more accurate fit. The solid lines in Fig.10 correspondto the fitted plots for EIS experiment data using this electric cir-cuit, which indicates that the experimental data can be fitted us-ing this equivalent circuit.

The CPE is composed of a component Qdl and a coefficient awhich quantifies different physical phenomena like surface in-homogeneousness resulting from surface roughness, inhibitoradsorption, porous layer formation, etc. The double layer ca-pacitance (Cdl) can be simulated via CPE, and calculated fromthe following equation:34

Cdl=Qdl×(2πfmax)a−1 (6)where fmax represents the frequency at which the imaginary val-ue reaches a maximum on the Nyquist plot. The electrochemi-cal parameters of Rs, Rt, CPE, a, Cdl, and ηR are listed in Table5. The chi-squared (χ2) is used to evaluate the precision of thefitted data.35 Table 5 shows that χ2 value is low, which confirmsthat the fitted data and the experimental data are in good agree-ment. It is observed that Rs is very small, which confirms thatthe IR drop could be neglect. Rt value increases prominentlywhile Cdl reduces with the concentration of inhibitor. A largecharge transfer resistance is associated with a slower corrodingsystem. At any given inhibitor concentration, Rt(HP) <Rt(MP),which confirms that MP shows better inhibitive performancebetween two pyrimidine compounds. According to Cao,30 the sin-gle capacitive loop again indicates that the adsorption mode ofeach pyrimidine inhibitor is geometric blocking effect.Through the light of the tendency to form a stronger coordina-tion bond, S atom shows more stable coordination ability thanO atom, which results in that it could be more easily for MP tochemisorb on steel than HP.

The decrease in Cdl in comparing with that in blank solution

Fig.10 Nyquist plots of the corrosion of CRS in 1.0 mol∙L−1 HCl solution without and with different concentrations of inhibitors at 25 °CImmersion time is 2 h. The points represent experimental data and continuous line in figure corresponds to the EIS diagram fitted using the

equivalent electric circuit. (A) HP; (B) MP

Table 5 EIS parameters for the corrosion of CRS in 1.0 mol∙L−1 HCl solution containing HP or MP at 25 °CInhibitor

−

HP

MP

c/(mmol∙L−1)

0.0

1.0

5.0

10.0

1.0

5.0

10.0

Rt/(Ω∙cm2)

0.77

0.84

1.08

0.72

0.67

0.86

0.71

Rt/(Ω∙cm2)

30.4

67.0

206.6

273.3

75.0

278.9

448.7

CPE/(μΩ−1∙sa∙cm−2)

413.4

245.0

170.5

148.5

214.9

124.6

94.2

a

0.924

0.917

0.923

0.847

0.908

0.922

0.892

Cdl/(μF∙cm−2)

368

187

95

71

174

68

47

102χ2

1.11

1.36

1.28

2.30

1.22

1.17

1.55

ηR/%

−

54.6

85.3

88.9

59.5

89.1

93.2

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Acta Phys. -Chim. Sin. 2013 Vol.29

(without inhibitor), which can result from a decrease in localdielectric constant and/or an increase in the thickness of theelectrical double layer, suggests that the inhibitor moleculesfunction by adsorption at the metal/solution interface.36 ηR in-creases with the concentration of inhibitor, and follows the or-der: ηR(MP) >ηR(HP). The ηR values at 10.0 mmol ∙ L − 1 are88.9% and 93.2% for HP and MP, respectively. These resultsagain confirm that all pyrimidine derivatives exhibit good in-hibitive performance for CRS in HCl solution.

Inhibition efficiencies obtained from weight loss (ηw), poten-tiodynamic polarization curves (ηp), and EIS (ηR) are in goodreasonably agreement.3.8 Quantum chemical calculations

In order to investigate the adsorption mode through light onthe pyrimidine molecular structure, quantum chemical calcula-tions were carried out. It is well known that the N-heterocycliccompound could be protonated in the acid solution. Accordingto some quantum chemical studies about protonated N-hetero-cyclic inhibitor in HCl solution,37 the proton affinity is clearlyfavored toward the hetero N atom of N-heterocyclic ring.Fig.11 shows the optimized molecular structures of two neutraland their protonated pyrimidine derivatives. Through quantumchemical calculations, the protonated affiliation energy (PA)values of HP and MP are 1088.8 and 1091.5 kJ∙mol−1, respec-tively. This result indicates that two studied pyrimidine deriva-tives are easily protonated. From Fig.11, the pyrimidine ringand substitution group (―OH, ―SH) are in one plane. It iswell known that inhibitor can form coordination bonds be-tween the unshared electron pair of O, N, or S atom and the un-occupied d orbit of Fe. The larger negative charge of the atom,the better is the action as an electronic donor. Mulliken chargesof the atoms are listed in Table 6. By careful examination of

the values of Mulliken charges, the larger negative atoms arefound in N1, N3, O7, and S7, which are active adsorptive cen-ters that could donate the lone electron pairs to the unfilled or-bits of Fe. When pyrimidine compounds are protonated, theMulliken charge of N5 becomes more negative than N3, whilethe Mulliken charge of O7 or S7 increases. This result impliesthat if the inhibitor is protonated, N5 exhibits more active thanN3, while the adsorptive ability of O7 or S7 would decrease.

Fukui function is necessary in understanding the local siteselectivity. The Fukui function ( f (r)) is defined as:38

f (r) =

∂ρ(r)∂N

V (r)(7)

The nucleophic attack Fukui function ( f (r)+) and electophilicattack Fukui function ( f (r)-) can be calculated as:39

f (r)+ = qi(N + 1)- qi(N) (8)f (r)- = qi(N)- qi(N - 1) (9)

where qi(N+1), qi(N), qi(N−1) are charge values of atom i forcation, neutral, and anion, respectively. The values of f (r)+

and f (r)- are also listed in Table 6. Generally, high values off (r)+ and f (r)- mean the high capacity of the atom to gainand lost electron, respectively. For the nucleophic attack, themost reactive site is C2 and C6 for all neutral and protonatedmolecules, which can accept electrons from metal surface toform back-donating bond. The difference of f (r)+ index of re-activity between HP, and MP is small. But when compoundsare protonated, f (r)+ values follow the order of p-HP>HP; p-MP>MP. This result implies that the nucleophic attack activityof protonated molecule decreases. On the other hand, the val-ues of f (r)- indicate that it will happen on the N3 for HP, O7for p-HP and S7 for MP and p-MP, which can denote electronsto metal surface to form coordinate bond. The atom of S7 has

Atom

C1

C2

N3

C4

N5

C6

O7

S7

Mulliken charge

HP

−0.208

−0.013

−0.381

0.556

−0.396

−0.014

−0.606

−

MP

−0.222

−0.040

−0.344

0.356

−0.342

−0.039

−

−0.347

p-HP

−0.173

0.026

−0.318

0.690

−0.452

0.077

−0.543

−

p-MP

−0.196

−0.004

−0.290

0.479

−0.411

0.057

−

−0.196

f (r)+

HP

0.023

0.174

0.128

0.057

0.123

0.174

0.041

−

MP

0.018

0.176

0.120

0.026

0.116

0.175

−

0.103

p-HP

0.028

0.188

0.102

0.069

0.077

0.179

0.055

−

p-MP

0.024

0.186

0.081

0.041

0.079

0.162

−

0.137

f (r)-HP

0.053

0.065

0.203

0.114

0.183

0.062

0.041

−

MP

0.085

0.036

0.067

0.020

0.065

0.036

−

0.476

p-HP

0.141

0.062

0.106

0.077

0.051

0.105

0.165

−

p-MP

0.082

0.035

0.073

0.027

0.038

0.051

−

0.459

Table 6 Quantum chemical parameters of Mulliken charge, f (r)+ and f (r)- for neutral and protonated pyrimidine molecules

Fig.11 Optimized molecular structures of the neutral and protonated pyrimidine derivatives

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LI Xiang-Hong et al.: Inhibition Effect of Pyrimidine Derivatives on the Corrosion of Steel in Hydrochloric AcidNo.10

the largest f (r)- value among N3, O7, and S7 atoms, whichindicates that the adsorptive ability of S atom is higher than Natom. Accordingly, the better inhibition efficiency of MP is re-lated to the higher adsorptive ability of S atom of―SH.

The dipole moment (μ) is widely used to represent the polari-ty of the molecule, and related to the inhibitive ability. Thelarge value of dipole moment probably increases the inhibitoradsorption through electronic force.40 In Table 7, the μ of HP islarger than that of MP. On the contrary, the inhibition efficien-cy follows the order: MP>HP. These results indicate that thebetter inhibitive performance of MP might not be arisen formintermolecular electrostatic force. Table 7 shows that the pro-tonated molecules of p-HP and p-MP have larger dipole mo-ment values than corresponding neutral molecules of HP andMP. Thus, p-HP and p-MP could be easily adsorbed via physi-cal adsorption compared with HP and MP. It is well known thatthe charge of the metal surface can be determined from the val-ue of Ecorr−Eq=0 (Ecorr: corrosion potential, Eq=0: zero charge poten-tial).41 The Eq=0 of iron is −530 mV (vs SCE) in HCl solution,42

and the value of Ecorr obtained in 1.0 mol∙L−1 HCl solution is− 440 mV (vs SCE). Thus, the steel surface charges positivecharge in HCl solution because of Ecorr−Eq=0>0. Since the acidanion of Cl − could be specifically adsorbed, it creates excessnegatives charge towards the solution and favors more adsorp-tion of the cations, p-HP or p-MP may adsorb on the negativelycharged metal surface. In other words, there may be a syner-gism between anion (Cl−) and protonated inhibitor.

Besides the above mentioned quantum chemical parameters,the global reactivity of a molecule depends on molecular distri-butions. HOMO is often associated with the capacity of a mole-cule to donate electrons, whereas LUMO represents the abilityof the molecule to accept electrons. The electric/orbital densitydistributions of HOMO and LUMO for the studied inhibitors(neutral and protonated molecules) are shown in Fig.12, respec-tively. It is found that that the electron density of the frontierorbital is well proportioned. For four molecules, the electrondensities of both HOMO and LUMO are localized principallyon the pyrimidine ring, which indicates that the pyrimidinering could be both the acceptor of the electron and the donor ofthe electron. That is, there is electron transferring in the interac-tion between the pyrimidine ring and metal surface. The ad-sorption of inhibitor on steel may be in a manner in which theplane of the pyrimidine ring is parallel to the metal surface. Itshould be noted that HOMO density is absent on O7 atom forHP, whereas present on S7 for MP. The result indicates that the

substituted S7 atom on pyrimidine ring of MP is an additionaladsorption centre in comparison with the substituted O7 atomof HP. Accordingly, the efficiency of MP is higher than that ofHP. The LUMO density is absent on either O7 of HP or S7 ofMP; however, LUMO density is located on either O7 of p-HPor S7 of p-MP. Thus, it is reasonable to deduce that the proton-ated molecule exhibits better adsorptive ability than neutralmolecule.

The values of energy of the highest occupied molecular or-bital (EHOMO), energy of the lowest unoccupied molecular orbit-al (ELUMO), and the separation energy (ELUMO−EHOMO, ΔE) are alsopresented in Table 7. High value of EHOMO indicates a tendencyof the molecule to donate electrons to act with acceptor mole-cules with low-energy, empty molecular orbital.3 Similarly, theELUMO represents the ability of the molecule to accept electrons,and the lower value of ELUMO suggests the molecule acceptselectrons more probable.3 From Table 7, EHOMO obeys the order:MP>HP, while ELUMO obeys the order: MP<HP. When com-pound is protonated, the order is still same. Obviously, the twosequences are in completely accordance with the order of inhi-bition efficiency. This may explain that the better inhibition ef-ficiency of MP molecule than HP is due to both lower ELUMO

and higher EHOMO. Both EHOMO and ELUMO values of protonatedmolecules decrease compared with those of neutral molecules,

Fig.12 Frontier molecule orbital density distributionsof pyrimidine compounds(left) HOMO; (right) LUMO

Table 7 Quantum chemical parameters of μ, EHOMO, ELUMO, ΔE,and ΔN for neutral and protonated pyrimidine molecules

Molecule

HP

MP

p-HP

p-MP

1030μ/(C∙m)

3.8495

3.5148

5.9086

4.7736

EHOMO/eV

−6.215

−5.943

−4.613

−6.097

ELUMO/eV

−2.241

−2.334

−3.624

−3.691

ΔE/eV

3.974

3.609

3.989

3.216

ΔN

0.698

0.793

0.346

0.529

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Acta Phys. -Chim. Sin. 2013 Vol.29

Therefore, it could be deduced that the protonated moleculestrengthens accepting electrons from metal surface while weak-ens donating electrons to Fe atom.

The separation energy (energy gap) ΔE (ELUMO−EHOMO) is animportant parameter as a function of reactivity of the inhibitormolecule towards the adsorption on metallic surface. As ΔE de-creases, the reactivity of the molecule increases in visa, whichfacilitates adsorption and enhances the efficiency of inhibitor.3

Inspection of the data in Table 7 shows that the ΔE value fol-lows the order of MP<HP and p-MP<p-HP, which confirmsthat MP (or p-MP) facilitates its adsorption on the metal sur-face so that it has higher inhibition efficiency. Furthermore, ΔEvalue of protonated molecule is lower than neutral molecule,which again confirms that the protonated molecule exhibits bet-ter inhibitive performance than neutral molecule.

The energies of HOMO and LUMO of the inhibitor mole-cule are related to the ionization potential (I ) and the electronaffinity (Y), respectively, by the following relations: 45

I=−EHOMO (10)Y=−ELUMO (11)Then absolute electronegativity (β) and global hardness (γ)

of the inhibitor molecule are approximated as follows:44

β= I + Y2 (12)

γ= I -Y2 (13)

The fraction of electrons transferred from the inhibitor tometallic surface (ΔN) is calculated depending on the quantumchemical method:45

ΔN = βFe - βinh

2(γFe + γ inh)(14)

For Fe, the theoretical values of βFe and γFe are 7 and 0 eV, re-spectively.46 The values of ΔN are also listed in Table 7. Ac-cording to some studies,46 values of ΔN exhibit inhibitive per-formance resulted from electrons donations. If ΔN<3.6, the in-hibition efficiency increases with the increase in electron-dona-tion ability to the metal surface.47 It can be seen from Table 7that ΔN follows the order of MP>HP and p-MP>p-HP, which isin good agreement with the order of inhibition efficiency ofthese inhibitors. When the compounds are protonated, ΔN fol-lows the order of p-HP>HP and p-MP<MP, which again impliesthat the ability of donating electrons decreases for protonatedmolecule.

4 Conclusions(1) Two pyrimidine derivatives of HP and MP act as good in-

hibitors for the corrosion of CRS in 1.0 mol∙L−1 HCl solution.Inhibition efficiency (ηw) increases with the inhibitor concentra-tion, and the maximum ηw is 83.6% for HP and 95.4% for MPat 10.0 mmol∙L−1. Inhibition efficiency follows the order: MP>HP.

(2) The adsorption of either MP or HP obeys Langmuir ad-sorption isotherm. The parameter of adsorption free energy(ΔG0) indicates that the adsorption involves both physical ad-

sorption and chemical adsorption.(3) Both HP and MP are arranged as mixed- type inhibitors

in 1.0 mol∙L−1 HCl solution. EIS spectra exhibit one capacitiveloop, and the presence of each inhibitor enhances Rt while re-duces Cdl.

(4) The large protonated affiliation energy (PA) values con-firm that two studied pyrimidine derivatives are easily protonat-ed. The chemical molecules of HP, MP, p-HP, and p-MP are inone plane. The larger negative Mulliken charges are found inN1, N3, O7, and S7, which are adsorptive centers. The nu-cleophic attack active atoms are C2 and C6 atoms. The electro-philic attack active atoms are N3 for HP, O7 for p-HP, S7 forMP and p-MP.

(5) The electron densities of both HOMO and LUMO are lo-calized principally on the pyrimidine ring. The pyrimidine ringcould be both the acceptor of the electron and the donor of theelectron. The better inhibition efficiency of MP than HP couldbe explained with the quantum parameters of ELUMO, EHOMO, ΔE,and ΔN.

(6) The protonated molecules of p- HP and p- MP could beeasily adsorbed via physical adsorption; there may be a syner-gism between anion (Cl −) and protonated inhibitor. Comparingwith neutral molecule, the protonated molecule exhibits betterinhibitive performance. The protonated molecule strengthensaccepting electrons while weakens donating electrons.

References(1) Li, X. H.; Deng, S. D.; Fu, H. Acta Phys. -Chim. Sin. 2011, 27,

2841. [李向红,邓书端,付 惠.物理化学学报, 2011, 27,

2841.] doi: 10.3866/PKU.WHXB20112841

(2) Bentiss, F.; Traisnel, M.; Gengembre, L.; Lagrenée, M. Appl.Surf. Sci. 1999, 152, 237. doi: 10.1016/S0169-4332(99)00322-0

(3) Yan, Y.; Li, W. H.; Cai, L. K.; Hou, B. R. Electrochim. Acta

2008, 53, 5953. doi: 10.1016/j.electacta.2008.03.065

(4) Wang, L. J. Yunnan Univ. 2001, 23, 203. [王 林.云南大学学

报, 2001, 23, 203.]

(5) Monticell, C.; Brunoro, G.; Frignani, A. J. Electrochem. Soc.

1992, 139, 706.

(6) Lin, Z. H.; Wang, F. C.; Tian, Z. Q. Acta Phys. -Chim. Sin. 1992,8, 87. [林仲华,王逢春,田中群.物理化学学报, 1992, 8, 87.]

doi: 10.3866/PKU.WHXB19920116

(7) Zucchi, F.; Trabanelli, G.; Brunoro, G. Mater. Corros. 1993, 44,

264.

(8) Wang, L. Corrosion Sci. 2001, 41, 1637.

(9) Li, X. H.; Deng, S. D.; Fu, H. Chin. J. Appl. Chem. 2012, 29,

209. [李向红,邓书端,付 惠.应用化学, 2012, 29, 209.]

(10) Makhlouf, M. T.; El-Shahawy, A. S.; El-Shatory, S. A. Mater.

Chem. Phys. 1996, 43, 153. doi: 10.1016/0254-0584(95)01611-

W

(11) Li, X. H.; Deng, S. D.; Fu, H. Corrosion Sci. 2009, 51, 1344.

doi: 10.1016/j.corsci.2009.03.023

(12) Kokalj, A.; Peljhan, S.; Finšgar, M.; Milošev, I. J. Am. Chem.

2230

LI Xiang-Hong et al.: Inhibition Effect of Pyrimidine Derivatives on the Corrosion of Steel in Hydrochloric AcidNo.10

Soc. 2010, 132, 16657. doi: 10.1021/ja107704y

(13) Feng, L. J.; Yang, H. Y.; Wang, F. H. Electrochim. Acta 2011,

58, 427. doi: 10.1016/j.electacta.2011.09.063

(14) El Adnani, Z.; Mcharfi, M.; Sfaira, M.; Benzakour, M.;

Benjelloun, A. T.; Ebn Touhami, M. Corrosion Sci. 2013, 68,

223. doi: 10.1016/j.corsci.2012.11.020

(15) Zhang, J.; Zhao, W. M.; Guo, W. Y.; Wang, Y.; Li, Z. P. Acta

Phys. -Chim. Sin. 2008, 24, 1239. [张 军,赵卫民,郭文跃,

王 勇,李中谱.物理化学学报, 2008, 24, 1239.] doi: 10.3866/

PKU.WHXB20080720

(16) Materials Studio 4.1; Accelrys Inc.: San Diego, CA, 2006.

(17) Becke, A. D. J. Chem. Phys. 1988, 88, 2547. doi: 10.1063/

1.454033

(18) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. doi:

10.1103/PhysRevB.37.785

(19) Klamt, A.; Schüürmann, G. J. Chem. Soc. Perkin. Trans. 1993,

2, 799.

(20) Cano, E.; Polo, J. L.; Iglesia, A. L.; Bastidas, J. M. Adsorption

2004, 10, 219. doi: 10.1023/B:ADSO.0000046358.35572.4c

(21) Zhang, F.; Tang, Y. M.; Cao, Z. Y.; Jing, W. H.; Wu, Z. L.; Chen,

Y. Z. Corrosion Sci. 2012, 61, 1. doi: 10.1016/j.corsci.

2012.03.045

(22) Behpour, M.; Ghoreishi, S. M.; Soltani, N.; Salavati-Niasari, M.

Corrosion Sci. 2009, 51, 1073. doi: 10.1016/j.corsci.2009.02.011

(23) Bentiss, F.; Lebrini, M.; Lagrenée, M. Corrosion Sci. 2005, 47,

2915. doi: 10.1016/j.corsci.2005.05.034

(24) Vračar, L. M.; Dražć, D. M. Corrosion Sci. 2002, 44, 1669. doi:

10.1016/S0010-938X(01)00166-4

(25) Solmaz, R.; Kardas, G.; Yazici, B.; Erbil, M. Colloids Surf. A

2008, 312, 7. doi: 10.1016/j.colsurfa.2007.06.035

(26) Moretti, G.; Guidi, F.; Grion, G. Corrosion Sci. 2004, 46, 387.

doi: 10.1016/S0010-938X(03)00150-1

(27) Li, X. H.; Deng, S. D.; Mu, G. N.; Fu, H.; Yang, F. Z. CorrosionSci. 2008, 50, 420. doi: 10.1016/j.corsci.2007.08.014

(28) Granese, S. L.; Rosales, B. M.; Oviede, C.; Zerbino, J. O.

Corrosion Sci. 1992, 33, 1439. doi: 10.1016/0010-938X(92)

90182-3

(29) Mathur, P. B.; Vasudevan, T. Corrosion 1982, 38, 171. doi:

10.5006/1.3579270

(30) Cao, C. Corrosion Sci. 1996, 38, 2073. doi: 10.1016/S0010-

938X(96)00034-0

(31) Behpour, M.; Ghoreishi, S. M.; Mohammadi, N.; Soltani, N.;

Salavati-Niasari, M. Corrosion Sci. 2010, 52, 4046. doi:

10.1016/j.corsci.2010.08.020

(32) Labjar, N.; Lebrini, M.; Bentiss, F.; Chihib, N. E.; El Hajjaji, S.;

Jama, C. Mater. Chem. Phys. 2010, 119, 330. doi: 10.1016/j.

matchemphys.2009.09.006

(33) Lebrini, M.; Lagrenée, M.; Vezin, H.; Traisnel, M.; Bentiss, F.

Corrosion Sci. 2007, 49, 2254. doi: 10.1016/j.corsci.2006.10.029

(34) Priya, A. R. S.; Muralidharam, V. S.; Subramania, A. Corrosion

2008, 64, 541. doi: 10.5006/1.3278490

(35) Osório, W. R.; Moutinho, D. J.; Peixoto, L. C.; Ferreira, I. L.;

Garcia, A. Electrochim. Acta 2011, 56, 8412. doi: 10.1016/j.

electacta.2011.07.028

(36) Lagrenée, M.; Mernari, B.; Bouanis, M.; Traisnel, M.; Bentiss,

F. Corrosion Sci. 2002, 44, 573. doi: 10.1016/S0010-938X(01)

00075-0

(37) Li, D. Z.; Zhang, S. G.; Bian, H.; Zhang, L. C. Comput. Appl.

Chem. 2009, 26, 324. [李大枝,张士国,卞 贺,张立超.计算

机与应用化学, 2009, 26, 324. ]

(38) Parr, R. G.; Yang, W. J. Am. Chem. Soc. 1984, 106, 4049. doi:

10.1021/ja00326a036

(39) Gómez, B.; Likhanova, N. V.; Aguilar, M. A. D.; Olivares, O.;

Hallen, J. M.; Martínez-Magadán, J. M. J. Phys. Chem. A 2005,

109, 8950. doi: 10.1021/jp052188k

(40) Lashkari, M.; Arshadi, M. R. Chem. Phys. 2004, 299, 131. doi:

10.1016/j.chemphys.2003.12.019

(41) Schweinsberg, D. P.; Ashworth, V. Corrosion Sci. 1988, 28, 539.

doi: 10.1016/0010-938X(88)90022-4

(42) Banerjee, G.; Malhotra, S. N. Corrosion 1992, 48, 10. doi:

10.5006/1.3315912

(43) Feng, Y.; Chen, S.; Zhang, H.; Li, P.; Wu, L.; Guo, W. Appl.

Surf. Sci. 2006, 253, 2812. doi: 10.1016/j.apsusc.2006.05.061

(44) Ju, H.; Kai, Z. P.; Li, Y. Corrosion Sci. 2008, 50, 865. doi:

10.1016/j.corsci.2007.10.009

(45) Lukovits, I.; Kálmán, E.; Zucchi, F. Corrosion 2001, 57, 3. doi:

10.5006/1.3290328

(46) Sastri, V. S.; Perumareddi, J. R. Corrosion 1997, 53, 617. doi:

10.5006/1.3290294

(47) Awad, M. K.; Mustafa, M. R.; Elnga, M. M. A. J. Mol.

Struct. -Theochem 2010, 959, 66. doi: 10.1016/j.theochem.

2010.08.008

2231