N-Aminorhodanine as an effective corrosion inhibitor for mild steel in 0.5 M H
2
SO
4
Ali Döner, Gülfeza Kardasß
⇑Çukurova University, Science and Letters Faculty, Chemistry Department, 01330 Adana, Turkey
a r t i c l e
i n f o
Article history: Received 20 May 2011 Accepted 21 August 2011 Available online 27 August 2011 Keywords: A. Mild steel B. EIS B. Polarization C. Acid corrosion
a b s t r a c t
The corrosion inhibition effect of N-aminorhodanine (N-AR) on mild steel (MS) in 0.5 M H2SO4was
stud-ied in both short and long immersion duration using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), chronoamperometry and hydrogen gas evolution. The surface morphology of MS was examined with scanning electron microscopy (SEM) in absence and presence inhibitor. The inhibitor adsorption process on MS surfaces obeys the Langmuir adsorption isotherm. The results show that NAR is a good inhibitor for MS in the acidic medium. The inhi-bition efficiency obtained from potentiodynamic polarization, EIS and LPR up to 98% is determined.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Corrosion of metals and alloys is a fundamental process playing an important role in economies and public safety. Steel has found wide application in a broad spectrum of industries and machinery but it has a tendency for corrosion, which is a fundamental indus-trial concern that has received a considerable amount of attention
[1]. Mild steel is a well-known material used extensively in various
industries. Acid solutions are generally used for the removal of rust and scale in several industrial processes. In this case, sulphuric acid is one of the most widely used agents. Some of the important areas of for its application are industrial acid cleaning, acid pickling, acid
descaling and oil well acidifying[2]. The chemical acid cleaning
causes metal corrosion on the cleaned surfaces even after elimina-tion of the corrosion products. Corrosion inhibitors efficiently reduce the undesirable destructive effect and prevent metal disso-lution. The use of inhibitors for the control of corrosion of metals and alloys, which are in contact with the aggressive environment, is therefore essential. The role of inhibitors added in low concen-trations to corrosive media is to decrease the dissolution of the metal with corrosive medium and is to inhibit the adsorption or
coordination onto the metal surfaces[3–10].
Organic compounds bearing heteroatoms with high electron density such as phosphorous, sulfur, nitrogen, oxygen or those con-taining multiple bonds which are considered as adsorption centers,
are effective as the corrosion inhibitor [11–13]. In general, the
adsorption of an inhibitor on a metal surface depends on the nature and the surface charge of the metal, the adsorption mode, its chem-ical structure and the type of electrolyte solution. The inhibition
efficiency increases in the order of O < N < S < P[14]. Nitrogen and sulphur containing heterocyclic compounds are considered to be effective corrosion inhibitors. Many N-heterocyclic compounds have been used as effective inhibitors for the corrosion of mild steel
in acidic media[15,16]. These compounds can adsorb onto the steel
surface and block active sites, thus decreasing the corrosion rate [17,18].
Rhodanine and its derivatives are heterocyclic compounds with at least four hetereoatoms. They are used in variety of applications ranging from biochemistry to industry and coordination chemistry. The interesting aspect of the chemistry of these compounds is their electron donating power to metal ions, which makes them strong
ligands in coordination compounds[19–22]. These molecules are
considered to be adsorption centers (nitrogen, sulfur and oxygen), and could be used as anti-corrosion agents for protection of metals. Rhodanine and its some derivatives were reported to be good
cor-rosion inhibitors for mild steel[23,24], copper[25,26]and stainless
steel[27]. In present work, the inhibition effect of N-AR on mild
steel corrosion in 0.5 M H2SO4in both short and long immersion
times were studied. The adsorption behavior of N-AR on MS surface is determined. Thermodynamic parameters are also calculated and discussed in detail.
2. Experimental
2.1. Preparation of electrodes
The working electrode was a cylindrical disc cut from a MS specimen with following chemical composition (wt); C (0.17%), Si (0.59%), Mn (1.60%), P (0.04%) and Fe (remainder). The metal disc was coated with polyester except its bottom surface with surface
area of 0.50 cm2. The electrical conductivity was provided by
0010-938X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.corsci.2011.08.032
⇑ Corresponding author. Tel.: +90 322 338 6081; fax: +90 322 338 6070. E-mail address:gulfeza@cu.edu.tr(G. Kardasß).
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Corrosion Science
copper wire. The surface of working electrode was mechanically abraded using different grades of sand papers, which ended with the 1200 grade, prior to use. The disc was cleaned by washing with
bidistilled water, CCl4, bidistilled water, respectively, and finally
dried in the air. For each test, a freshly abraded electrode was used. 2.2. Test solutions
The corrosion tests were performed in 0.5 M H2SO4solution in
absence and presence of various N-AR concentrations, whose
molecular structures are given in Fig. 1. 0.5 M H2SO4 solutions
were prepared with concentrated H2SO4 solution and distilled
water. The concentrations of the inhibitors employed were varied from 10.0 to 0.01 mM. All the test solutions were prepared from analytical grade chemical reagents in distilled water without fur-ther purification. For each experiment, a freshly prepared solution was used. The test solutions were opened to the atmosphere, and the temperature was controlled thermostatically at 298 K. 2.3. Electrochemical measurements
The potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) measurements were carried out using a CHI 604 AC. Electro-chemical Analyzer (Serial No. 64721A) under computer control. A double-wall one-compartment cell with a three-electrode configu-ration was used. The auxiliary electrode was a platinum sheet with
2 cm2surface area. The reference electrode was Ag/AgCl (3 M KCl).
All potential data given in this study were referred to this elec-trode. The working electrode was immersed in test solution for
1 h to establish a steady state open circuit potential (Eocp). After
measuring the Eocp, the electrochemical measurements were
per-formed. The EIS experiments were conducted in the frequency range of 100 kHz to 0.003 Hz at open circuit potential. The ampli-tude was 0.005 V. The polarization curves were obtained in the po-tential ranges from 0.90 V(Ag/AgCl) to 0.00 V(Ag/AgCl) with a scan rate of 0.001 V s1.
In order to investigate the mechanism of inhibition, the EIS experiments were also carried out at different anodic and cathodic overpotentials, which were previously determined from polariza-tion curves. Chronoamperometric measurements were carried out at different anodic (+0.100 V) and cathodic overpotentials (0.100 V) for 3600 s. The LPR measurements were carried out by recording the electrode potential ± 0.010 V around open circuit
po-tential with 0.001 V s1scan rate. The polarization resistance (R
p)
was determined from the slope of the obtained current–potential curves. Calculate the activation energy of the corrosion process, the polarization curves were obtained at various temperatures (25–55 °C) in the absence and the presence of 10.0 mM N-AR. To determine the potential of zero charge of the MS, the impedance of the MS was determined at different potentials in 10.0 mM
N-AR containing 0.5 M H2SO4solutions.
The corrosion behavior of MS in 0.5 M H2SO4solution in the
presence and absence of 10.0 mM N-AR as a function of exposure time was also performed over 120 h. For this purpose, the cathodic and anodic current–potential, EIS, LPR, potential of zero charge
(PZC) and the hydrogen gas evolution (VH2 t) were utilized.
Dur-ing the long-term tests, the workDur-ing electrode was immersed in a
beaker containing 200 mL test solution. After different immersion time, electrochemical measurements were performed under un-stirring conditions. In the hydrogen gas evolution measurements,
a burette filled with 0.5 M H2SO4 solution was placed over the
working electrode. The initial volume of air in the burette was
re-corded and the volume of H2gas evolved from the corrosion
reac-tion was monitored by the volume change in the level of the solution as a function of time at 24 h intervals over 120 h. The long-term tests were carried out at room temperature under un-stirring conditions.
2.4. Scanning electron microscopy studies
The morphology of MS surface after its exposure to 0.5 M H2SO4
solution in the absence and presence of 10.0 mM N-AR for 1 h and 120 h was examined by SEM images. The SEM images were taken using a Carl Zeiss Evo 440 SEM instrument at high vacuum and 10 kV EHT.
3. Results and discussion
3.1. Potentiodynamic polarization measurements
Fig. 2shows the polarization curves recorded on MS in 0.5 M
H2SO4 in the absence and presence of varying concentrations of
N-AR at 25 °C. In the presence of N-AR, the corrosion potential of MS shifted 39–72 mV(Ag/AgCl) anodically compared to the blank. An inhibitor can be classified as cathodic or anodic type if the dis-placement in corrosion potential is more than 85 mV with respect
to corrosion potential of the blank[28]. This indicates that N-AR
acts as a mixed type inhibitor with predominant anodic effective-ness. As it would be expected both anodic and cathodic reactions of MS corrosion in sulphuric acid solution were effectively sup-pressed, and this inhibition effect became more pronounced with increasing N-AR concentration. This result suggests that the addi-tion of the inhibitor reduces the anodic oxidaaddi-tion of MS and also retards the hydrogen reduction reaction. This suppression of the corrosion process can be attributed to the covering of adsorbed
inhibitor molecules on the MS surface[29]. Between corrosion
po-tential and 0.200 V(Ag/AgCl), a good inhibition ability was per-formed which suggests a formation of a protective layer of the adsorbed at the metal surface. At potentials more positive than 0.200 V(Ag/AgCl), which is usually defined as the desorption
potential[30,31]; the inhibition of N-AR on dissolution reaction
re-duces. The observed phenomenon may be the result of a significant dissolution of MS, leading to desorption of inhibitor film from the metal surface. In this case, the desorption rate of the inhibitor is
higher than its adsorption rate[31,32].
Fig. 1. Chemical structure of the N-aminorhodanine (N-AR).
E / V (Ag/AgCl) log I / A cm -2 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 -0.900 -0.800 -0.700 -0.600 -0.500 -0.400 -0.300 -0.200 -0.100 0.000
Fig. 2. Potentiodynamic polarization curves of MS electrode obtained in 0.5 M H2SO4solution (s) and containing 0.1 (+), 0.5 (e), 1.0 (j), 5.0 (D) and 10.0 mM (d) N-AR at 25 °C.
The important corrosion parameters such as corrosion potential (Ecorr) (mV versus Ag/AgAgCl), corrosion current density (icorr),
cor-rosion rate (mm year1) and inhibition efficiency (
g
) values werederived from cathodic current–potential curves are presented in Table 1. The
g
was calculated from polarization measurements according to the relation given below;g
%¼ icorr i 0 corr icorr 100 ð1Þwhere icorrand i0corrare the uninhibited and the inhibited corrosion
current densities, respectively. The corrosion current densities were obtained by the extrapolation of the cathodic current–potential lines to the corresponding corrosion potentials. The corrosion rates were calculated assuming that the whole surface of MS is attacked by corrosion, and no local corrosion is observed.
The analyses of the data in Table 1, revealed that the icorr
decreases considerably with increasing N-AR concentration. In Table 1, icorrvalue decreases from 3.122 to 0.029 mA cm2with
the highest concentration of N-AR (10.0 mM). The obtained
effi-ciencies (
g
) indicate that N-AR acts as an effective inhibitor. Thevalues of
g
increase with the inhibitor concentration reaching itsmaximum value, 99.1% at 10.0 mM. An increase in the inhibitor concentration probably increased the number of inhibitor mole-cules on the surface and thus decreased the corrosion current den-sity. It can be concluded that this inhibitor acts through adsorption on MS surface and formation of a barrier layer on the metal surface. 3.2. Electrochemical impedance spectroscopy (EIS) measurements
Nyquist plots of MS in 0.5 M H2SO4inhibited and uninhibited
solutions containing various concentrations of N-AR are shown in Fig. 3. The Nyquist plot of MS obtained in blank solution was
mag-nified and is added in Fig. 3 as an inset. It is clear that all the
impedance spectra obtained in the absence, and in the presence of inhibitors consist of one depressed capacitive loop. The imped-ance response (diameter of the semicircle) of MS in inhibited
solu-tion has significantly changed after the addisolu-tion of N-AR in the corrosive media, and the impedance of inhibited substrate in-creased with increasing N-AR concentration. As it can be seen from Fig. 3, the Nyquist plots do not yield perfect semicircle as expected from the theory of EIS. The Nyquist plots obtained in the real sys-tem represent a general behavior where the double layer on the interface of metal/solution does not behave as a real capacitor. Electrons and ions control the charge distributions on the metal and the solution side, respectively. As ions are much larger than electrons, the equivalent number of ions on the metal surface occu-pies quite large volume on the solution side of the double layer
[33]. In theFig. 3, the deviation from an ideal semicircle is
gener-ally attributed to the frequency dispersion as well as to the
inho-mogeneities of surface and mass transport resistant[34,35].
The related electrochemical equivalent circuit used to model
the MS/acidic solution interface is shown inFig. 4a, where Rs
rep-resents the uncompensated solution resistance, the Rp, which
cor-responds to the diameter of Nyquist’s plot, includes charge transfer resistance (Rct), diffuse layer resistance (Rd), the accumulated
spe-cies at the metal/solution interface (Ra) and the resistance of
inhib-itor film at the steel surface (Rf) (Rp= Rct+ Rd+ Ra+ Rf)[33,36,37],
and n shows the phase shift which can be explained as the degree
of surface in-homogeneity[38]. The value of n is between 0 and 1
(0 6 n 6 1). This is related to deviation from the ideal capacitive behavior. CPE represents a constant phase element to replace a
double layer capacitance (Cdl) in order to give a more accurate fit
to the experimental results[39]. The impedance parameters
ob-tained by fitting the EIS data to the equivalent circuit are listed inTable 2. In this case, the inhibition efficiency (
g
) can be calcu-lated from the polarization resistance using the following formula;g
%¼ R 0 p Rp R0 p ! 100 ð2Þwhere Rp and R0p are uninhibited and inhibited polarization
resis-tances, respectively.
It is apparent onTable 2that by increasing concentration of the
inhibitor, the CPE values tend to decrease, as the Rp values
in-creased. This decrease in the CPE can be attributed to the decrease in local dielectric constant or an increase in the thickness of the electrical double layer suggesting that the N-AR molecules function
by adsorption at the interface of metal/solution[40,41]. The
thick-ness of the film formed increases with increasing concentrations of the inhibitor, since more N-AR adsorbs on the surface, resulting in lower CPE values. These observations are in a good agreement with previous reports on the inhibition of MS corrosion by sulphuric acid[42,43]. Inhibition efficiencies increase with the concentration
of N-AR, and the maximum,
g
reaches up to 98.8%, which furtherconfirm N-AR exhibits good inhibitive performance for corrosion
of MS in 0.5 M H2SO4. The Rpvalues also calculated from the LPR
technique are given inTable 2with corresponding inhibition
effi-ciencies. LPR method was used for Rp which is confirmed the EIS results. As a result, some of the organic sulfur-containing mole-cules can chemisorb on steel, protect the metal surface and there-fore, inhibit corrosion[44,45]. This is called covered effect. Since in our study, the concentrations of N-AR are high enough, the surface coverage of adsorbed molecules is enhanced and a high surface
coverage is reached[46]. It is known that the surface coverage of
an organic substance on the metal surface depends not only on the structure of the organic substance and the nature of the metal, but also on the experimental conditions such as immersion time
and concentration of molecules[47,48]. The highest surface
cover-age obtains at high enough inhibitor concentration. The surface coverage increases with the increase in inhibitor concentration
[49]. Since more inhibitors molecules are expected to adsorb at
high inhibitor concentrations, the covered effect enhances. This
Table 1
Electrochemical parameters for MS determined from polarization curves at 25 °C. C (mM) Ecorr (mV, Ag/AgCl) icorr (mA cm2) Corrosion rate (mm year1) g% Blank 495 3.122 72.39 – N-AR 0.1 456 0.325 7.54 89.6 0.5 448 0.094 2.18 97.0 1.0 446 0.055 1.28 98.2 5.0 435 0.035 0.81 98.9 10.0 423 0.029 0.67 99.1 0 250 500 750 1000 1250 -1250 -1000 -750 -500 -250 0 Z' / Ω cm2 Z '' / Ω cm 2 0 3 6 9 12 15 -15 -12 -9 -6 -3 0 Z' / Ω cm2 Z'' / Ω cm 2
Fig. 3. Nyquist plots of MS electrode obtained in 0.5 M H2SO4solution (s) (inset) and containing 0.1 (+), 0.5 (e), 1.0 (j), 5.0 (D) and 10.0 mM (d) N-AR (solid lines show fitted results).
results in an increase in Rpand decrease in corrosion rate. On the
other hand, presence of extra –NH2group and N in its molecular
structure, which are considered to be active centers of adsorption. The presence of such groups in molecular structure of inhibitor molecule increases electron density on adsorption centers and leading to an easier electron transfer from the functional group to the metal, producing to greater coordinate bonding and higher
inhibition efficiency[50]. Results obtained from EIS measurements
are in good agreement with that obtained from both potentiody-namic polarization and LPR measurements.
Inhibition effect of N-AR was also studied different immersion times in 0.5 M H2SO4.
The impedance diagrams plotted after different immersion
times are presented inFig. 5for the 10.0 mM (optimum
concentra-tion) N-AR and the blank solution. The insets correspond to differ-ent immersion times of bare MS. The related electrochemical data
are collected inTable 3. As it was seen fromFig. 5, in the
uninhib-ited solution, the Nyquist plots for the MS include only one slightly depressed capacitive semicircle which indicates the corrosion pro-cess in uninhibited solution is mostly controlled by a charge trans-fer process. With an increase in immersion time of MS, polarization
resistance values decreased. Rp values showed a slight decrease
from 12.3Xcm2for unprotected MS to 9.6Xcm2after its 6 h
expo-sure, indicating some corrosion process. After this immersion time
Rpvalues are gradually decreased. The same trend was determined
from the LPR measurements. When MS is dipped in the solution containing N-AR, the immersion time has a significant influence on the size of the impedance spectra and therefore, the corrosion
inhibition efficiency of the inhibitor. It is apparent to Fig. 5, at
the high frequency regions, a weak depressed semicircle and at the low frequency regions, a large depressed semicircle is observed in the Nyquist plots of N-AR. This behavior could be explained that MS surfaces covered with inhibitor molecules, and this layer has the micro pores. The corrosion process could be only occurred the pores. The Rp value corresponding corrosion process is the
sum of the pore resistance (Rpor) and film resistance (Rf). The first
loop was related to the pore resistance (Rpor), and the second one
was attributed to the film resistance (Rf)[36]. The film resistance
has become dominant in the corrosion process as a result of the
formation of the protective N-AR film. The capacitors for the corro-sion process connected each other parallel through the metal and solution side. The total capacitance of the capacitors is equal to the sum of the double-layer capacitance and film capacitance. The corresponding electrical equivalent circuit diagram of different
immersion times for N-AR was given inFig. 4b. The Rpvalue in the
inhibited solution increases up to 24 h, and then tends to decrease, which may be due to the formation of some defects on the film leading to the access of aggressive ions to the metal/inhibitor
inter-face. At the beginning of immersion the initial values of Rp are
around 1058Xcm2gradually increasing during the immersion
un-til 2443Xcm2at 24 h immersion for the inhibited solution (Fig. 5).
After 24 h immersion time, since beginning small amount of the
corrosion process, it may happen to pitting corrosion, the Rpvalues
are slightly decreased.
The values of both polarization resistance and corrosion
inhibi-tion efficiency (
g
) determined from LPR technique as beingassoci-ated over 120 h immersion time is given inTable 3. The
g
valuesobtained from the LPR are comparable and run parallel with those obtained from the EIS.
In order to better understanding the inhibition mechanism of N-AR, EIS experiments were carried out at different anodic and catho-dic overpotentials which were previously determined from the
polarization curves (Fig. 2). The data are presented in Nyquist’s
representation and given inFigs. 6 and 7with the cathodic and
anodic current–potential curves. It can be seen fromFig. 6 that
was observed only one capacitive loop for MS at 0.598 and 0.698 V(Ag/AgCl) (0.100 and 0.200 V(Ag/AgCl) cathodic over-potentials, respectively). It was attributed that at these cathodic
potential regions the reduction of H+ions are completely charge
transfer controlled [36]. Rp values of MS in blank solution at
0.100 and 0.200 V(Ag/AgCl) cathodic overpotentials were
deter-mined 4.3 and 2.8Xcm2, respectively. At same overpotentials,
diameter of the depressed semicircles was increased in the
solu-tion containing 10.0 mM N-AR. Rp values were determined 652
and 78.6Xcm2 for the inhibited solution, respectively. When
N-AR was added in corrosive media, Rp values of at 0.100 and
0.200 V cathodic overpotentials were increased. This phenome-non was explained that, the inhibitor molecules are adsorbed onto
Table 2
Electrochemical parameters for MS electrode corresponding to the EIS and LPR data in 0.5 M H2SO4solution in the absence and presence of various concentrations containing N-AR at 25 °C. C (mM) EIS LPR Rp(O cm2) CPEdl(Y0/106snX1cm2) n g% Rp(O cm2) g% Blank 12.9 497 0.90 – 14.8 – N-AR 0.1 189 343 0.93 93.2 194 92.4 0.5 468 300 0.91 97.2 474 96.9 1.0 791 201 0.92 98.3 878 98.3 5.0 902 168 0.90 98.6 888 98.3 10.0 1058 153 0.89 98.8 1016 98.5 Rs CPE1 RP
(a)
CPE1 RP=R1+R2 CPE2 R1 R2 Rs(b)
Fig. 4. The equivalent circuit model for corrosion process of the MS absence and presence inhibitor (a), after 4 h and longer immersion time presence of inhibitor (b). Rp= Rct+ Rd+ Rafor diagram (a). Rs: uncompensated solution resistance, Rp: polarization resistance, Rct: charge transfer resistance, Rd: diffuse layer resistance, Ra: resistance of accumulated species, R1: film resistance (Rf), R2: pore resistance (Rpor= Rct+ Rd+ Ra), CPE1: film capacitance, CPE2: double layer capacitance.
MS surface and, therefore, impedes by merely blocking the reaction
sites of the MS surface[17,18]. In the anodic regions, the same
trend was observed for MS at 0.398 and 0.298 V(Ag/AgCl)
(0.100 and 0.200 V(Ag/AgCl) anodic overpotentials, respectively)
in 0.5 M H2SO4. Rpvalues of MS in uninhibited solution were
mea-sured as 4.67 and 1.18Xcm2, respectively. However, in inhibited
solution, a different behavior was observed. Nyquist plots of the MS in the 10.0 mM N-AR contains two time constants. At the high frequency region, it was observed one capacitive loop and at the low frequency region, appeared inductive loop. In the literature, inductive loops at low frequencies were commonly related to the
relaxation process[51]. This low-frequency relaxation, due to the
inductive loop, could be attributed to slow reaction, such as the
ad-sorbed reaction intermediates during the metal dissolution [52].
This adsorption behavior is typical for steel in acid solution [53,54]. This low frequency inductive loop may also be attributed to the re-dissolution of the passivated surface at low frequencies
[55]. This inductive loop still appears, even in the presence of the
inhibitor. These findings may indicate that the electrode is still dis-solved by the direct charge-transfer at the inhibitor-adsorbed steel
0 400 800 1200 1600 2000 -2000 -1600 -1200 -800 -400 0 Z' /Ω cm2 Z'' / Ω cm 2
6h
0 3 6 9 12 -14 -11 -8 -5 -2 Z' / Ω cm2 Z' ' / Ω cm 2 0 400 800 1200 1600 2000 -2200 -1800 -1400 -1000 -600 -200 Z' /Ωcm2 Z'' / Ω cm 248h
0 1 2 3 4 5 -5 -4 -3 -2 -1 0 Z'' / Ω cm 2 Z' / Ω cm2 0 250 500 750 1000 1250 1500 1750 -1750 -1500 -1250 -1000 -750 -500 -250 0 Z' /Ωcm2 Z'' / Ω cm 24h
0 3 6 9 12 -14 -11 -8 -5 -2 Z' / Ω cm2 Z' ' / Ω cm 2 0 400 800 1200 1600 2000 2400 2800 -2800 -2400 -2000 -1600 -1200 -800 -400 0 Z' /Ωcm2 Z'' / Ω cm 224h
0 2 4 6 -6 -4 -2 0 Z'' / Ω cm 2 Z' / Ω cm2 0 400 800 1200 1600 2000 -2200 -1800 -1400 -1000 -600 -200 Z' /Ωcm2 Z'' / Ω cm 296h
1 2 3 4 5 -3 -2 -1 0 Z'' / Ω cm 2 Z' / Ω cm2 0 400 800 1200 1600 2000 -2000 -1600 -1200 -800 -400 0 Z' /Ωcm2 Z'' / Ω cm 2120h
1 2 3 4 5 -3 -2 -1 0 Z' / Ω cm2 Z'' / Ω cm 2Fig. 5. Nyquist plots of MS electrodes in 0.5 M H2SO4solution in the absence (inset) and presence of 10.0 mM N-AR after 4 h, 6 h, 24 h, 48 h, 96 h and 120 h exposure time (solid lines show fitted results).
Table 3
Polarization resistance and inhibition efficiencies of MS in 0.5 M H2SO4solution in the absence and presence of 10.0 mM N-AR after different immersion time at 25 °C.
t (h) Blank N-AR EIS LPR EIS LPR Rp(O cm2) Rp(O cm2) Rp(O cm2) g% Rp(O cm2) g% 4 12.3 13.6 1557 99.2 1000 98.6 6 9.6 10.1 1942 99.5 1904 99.5 24 4.4 5.7 2443 99.8 2202 99.7 48 2.6 4.1 2038 99.9 1846 99.8 96 2.6 4.2 2027 99.9 2157 99.8 120 2.7 4.6 1972 99.9 2030 99.8
surface. As it is seen from theFig. 7, the inductive loop at low fre-quencies was also appeared in the presence of the inhibitor. This observation shows that a relaxation of the surface inhibitor film takes place at more positive potentials, which may be the result of significant dissolution of iron leading to desorption of the
inhib-itor from the metal surface[36,42].
3.3. Chronoamperometric measurements
The variation of the hydrogen evolution at the cathodic site and MS dissolution at the anodic site currents as a function of time at 0.100 and +0.100 V overpotentials after 1 h immersion in 0.5 M
H2SO4solutions without and with 10.0 mM N-AR present,
respec-tively are shown inFig. 8. Chronoamperometric curves were given
inFig. 8a for uninhibited and inhibited solutions at 0.100
catho-dic overpotential. It can be seen fromFig. 8a that the highest
cur-rents are recorded for MS in 0.5 M H2SO4in the absence of N-AR. At
this overpotential only it is seen hydrogen evolution. Addition of 10.0 mM N-AR in corrosive media after 1 h immersion of the MS decreased the hydrogen evolution currents. The currents were quite stable over the whole experimental period. Large decreases in the dissolution current must be due to the adsorption of N-AR strongly inhibited and block the corrosion sites on the MS surface.
At the +0.100 V anodic overpotential (Fig. 8b), the highest currents
are observed at the MS. The increase of current with time is indi-cated that the anodic dissolution of MS. In the presence of N-AR (Fig. 8b), the inhibited current values decreased from the first mo-ment of MS immersion. This was attributed to the fact that the N-AR molecules not only block the corrosion sites but also form a protective layer on the MS surface and hence prevent the corrosion
process[17,18,56]. These results agree with the polarization
mea-surements (Fig. 2).
3.4. Hydrogen gas evolution measurements
The accompanied iron dissolution reaction is the cathodic reac-tion to consume the electrons generated in the anodic reacreac-tion as
shown in Eq.(4). In the acidic medium, the Hads, atomic hydrogen
adsorbed on the metal surface reacts by combining with other
ad-sorbed H atoms to form H2gas, which bubbles from the surface.
The corrosion behavior of MS in 0.5 M H2SO4in the absence and
presence of N-AR was, therefore, evaluated by monitoring the vol-ume of hydrogen gas evolved. The relative rapidity and effective-ness of the hydrogen evolution method as well as its suitability for monitoring in situ, any interruption by an inhibitor with regard to gas evolution in metal/corrodent systems have been established in earlier reports[57,58]: Fe ! Feþ2 þ 2e ð3Þ 2Hþ þ 2e! 2H ads! H2 ð4Þ
In order to measure the hydrogen gas evolution in corrosive media, a burette was filled with the test solution and placed over -13.0 -11.0 -9.0 -7.0 -5.0 -3.0 -1.0 -0.810 -0.710 -0.610 -0.510 -0.410 2 3 4 5 6 -1 0 -0.200 V Z'/Ω cm2 Z'/ Ω cm Z'/Ω cm2 Z'/ Ω cm -0.100 V 2 3 4 5 6 7 -2 -1 0 0 25 50 75 -25 0 Z'/Ω cm2 Z'/ Ω cm 2 -0.200 V 0 125 250 375 500 625 -250 -125 0 Z'' Z'/Ω cm2 Z'/ Ω cm 2 -0.100 V E / V (Ag/AgCl) log I / A cm -2 2 2
Fig. 6. Nyquist plots for the MS electrodes at different cathodic over potentials obtained in 0.5 M H2SO4free (s) and containing 10.0 mM N-AR (d) solutions.
-9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 -0.550 -0.450 -0.350 -0.250 -0.150 -0.050 0.050 +0.100 V 1 2 3 4 5 6 -2 -1 0 Z'/Ω cm2 Z'/ Ω cm 2 +0.200 V 2 3 0 Z'/Ω cm2 Z'/ Ω cm 2 +0.100 V 0 5 10152025 -15 -10 -5 0 5 10 Z'/Ω cm2 Z'/ Ω cm 2 +0.200 V 1 2 3 -1 0 Z'/Ω cm2 Z' /Ω c m 2 E / V (Ag/AgCl) log I / A cm -2
Fig. 7. Nyquist plots for the MS electrodes at different anodic over potentials obtained in 0.5 M H2SO4free (s) and containing 10.0 mM N-AR (d) solutions.
- 0.002 0.002 0.006 0.010 0.014 0.018 0 500 1000 1500 2000 2500 3000 3500 4000 Time / s I/Acm -2 Time / s I/Acm -2 -0.002 0.002 0.006 0.010 0.014 0.018 0 500 1000 1500 2000 2500 3000 3500 4000
(a)
(b)
Fig. 8. Chronoamperometric curves for MS at 0.100 (a) and +0.100 V (b) overpotentials in 0.5 M H2SO4solutions: (s) without and (d) with 10.0 mM N-AR.
the working electrode.Fig. 9 shows the variation of volume of hydrogen evolved with time for uninhibited and inhibited
solu-tions at room temperature. It can be seen fromFig. 9, the hydrogen
evolution starts after a certain time from the immersion of the MS in the test solution. It could further be seen that the volume of hydrogen evolved increased with the increase in the time most probably due to the increased surface area of MS as a result of ex-cess dissolution of iron. After addition of N-AR in test solution, hydrogen evolution rate decreases compared to the blank solution.
The volume of H2evolved was found 456 and 1.4 mL cm2in
unin-hibited and inunin-hibited solutions, respectively. The reason of this
de-crease in H2volume in the presence of N-AR, suggesting that N-AR
molecules adsorbed onto the metal surface and blocked the elec-trochemical reaction efficiently by decreasing the available surface area.
3.5. Effect of temperature
To affect the inhibition mechanism of temperature and to calcu-late the activation energies of the corrosion process, polarization measurements were taken at various temperatures in the absence and the presence of N-AR at the optimum concentration (10.0 mM). The anodic and cathodic current–potential curves are
not presented here. The icorrvalue was obtained by extrapolation
of the cathodic Tafel lines of experiments carried out at 25, 35, 45, and 55 °C. The corrosion current density increases with increas-ing temperature both in uninhibited and inhibited solutions. N-AR acts as an efficient inhibitor in the range of temperature studied. As
the temperature increases, Ecorrvalues shift in the positive
direc-tion for the uninhibited soludirec-tion. However, the presence of the
inhibitor molecule Ecorrvalue shifts negative direction. This proves
that the inhibition occurs through the adsorption of the inhibitor on the MS surface.
The activation energy of the corrosion process was calculated
using the Arrhenius equation[59]:
Icorr¼ A expðEa=RTÞ ð5Þ
where icorris corrosion current, Eais the activation energy, R the
universal gas constant and A a constant, T the absolute temperature. Plotting ln icorrversus 1/T, the values of Eacan be calculated from the
slopes of straight lines (Fig. 10).Fig. 10shows the Arrhenius plot for the blank solution and 10.0 mM N-AR, and it is found that almost all the regression coefficients are almost close to 1, which means that
the relationship between lnicorrand 1/T is good. The values of Ea
were found to be 29.54 and 79.22 kJ mol1 for uninhibited and
inhibited solutions, respectively. It was clear that Eaincreased in
the presence of the inhibitor. The higher values of Eaare good
evi-dence for the strong adsorption of N-AR on the MS surface [60,61]. On the other hand, the adsorption phenomenon of an or-ganic molecule is not considered only as a physical or as a chemical
adsorption phenomenon. A wide spectrum of conditions, ranging from the dominance of chemisorption or electrostatic effects arises
from other adsorptions experimental data. The higher Eavalue in
the inhibited solution can be correlated with the increased thick-ness of the double layer, which enhances the activation energy of
the corrosion process[62].
3.6. Adsorption isotherm and thermodynamic consideration
To understand the corrosion inhibition mechanism, the organic compound’s adsorption behavior on the MS surface must be known. For this purpose, adsorption ability of inhibitor molecules must be defined by adsorption isotherms. It is generally assumed that the adsorption isotherm of the inhibitor at the metal/solution interface is the first step in the action mechanism of inhibitors in aggressive acid media. The adsorption process depends on the or-ganic inhibitor molecule’s chemical composition, the temperature and the electrochemical potential at the metal/solution interface.
At the metal/solution interface the solvent H2O molecules could
adsorb. In the presence of the organic inhibitor’s molecules at the metal/solution interface takes place through the replacement of water molecules by organic inhibitor molecules according to
fol-lowing process[63]:
OrgðsolÞþ xH2OðadsÞ! OrgðadsÞþ xH2OðsolÞ ð6Þ
where Org(sol)and Org(ads)are organic molecules in the solution and
adsorbed on the metal surface, respectively. x is the number of water molecules replaced by the organic molecules. For fitting a suitable adsorption isotherm, Langmuir, Temkin, and Freundlich adsorption isotherms are tested. Langmuir adsorption isotherm, which is given by Eq. (7) is found to be more suitable. The straight lines were obtained when Cinh/h were plotted against Cinh(Fig. 12).
Cinh h ¼ 1 Kadsþ Cinh ð7Þ t / h VH2 / mL cm -2 -50 50 150 250 350 450 550 0 24 48 72 96 120 144
Fig. 9. Hydrogen gas volume evolved on MS electrode as a function of exposure time in 0.5 M H2SO4(s) and containing 10.0 mM N-AR (d) solutions.
-5.00 -3.00 -1.00 1.00 3.00 5.00 0.00302 0.00308 0.00314 0.00320 0.00326 0.00332 0.00338 R2= 0.9959 R2= 0.8152 ln i corr (mA cm -2) 1 / T (K-1 )
Fig. 10. The relationship between lnicorrand 1/T for absence (s) and presence (d) 10.0 mM N-AR in 0.5 M H2SO4. 0.00 2.00 4.00 6.00 8.00 10.00 12.00 0.00 2.00 4.00 6.00 8.00 10.00 12.00 R2= 0.9999 Cinh / (mM) Cinh /θ (mM)
Fig. 11. Langmiur adsorption plots of MS in 0.5 M H2SO4 solution containing different concentrations of N-AR at 25 °C.
where Cinhis inhibitor concentration, h is the degree of the coverage
on the metal surface and Kadsis the equilibrium constant for the
adsorption–desorption process.Fig. 11shows the plots of Cinh/h
ver-sus Cinhand the expected linear relationship is obtained, and
corre-lation coefficient is higher than 0.99. The value of Kads was
calculated as 8.72 104M1for N-AR at 25 °C. The high values of
the adsorption equilibrium constants reflect the high adsorption ability of these inhibitors on MS surface.
The adsorption equilibrium constant (Kads) is related to the
standard free energy of adsorption reactionDG0adsby the following
equation:
D
G0ads¼ RT lnð55:5KadsÞ ð8Þwhere R is the universal gas constant and T is the absolute temper-ature. According to Eq.(8),DG0adswas calculated as 38.13 kJ mol1
at 25 °C. The negative values of free energy indicate that adsorption process occurs with the formation of a film adsorbed on the MS sur-face[64]. Generally values ofDG0ads until 20 kJ mol1are
consis-tent with the electrostatic interaction between the charged molecules and the charged metal surface (physical adsorption) [65,66]. Those about 40 kJ mol1or higher involve charge sharing
or a transfer from the inhibitor molecules to the metal surface to
form a coordinate type of bond (chemical adsorption) [67]. This
indicates that the N-AR taken place through electrostatic interaction between the inhibitor molecule and the MS surface. The large
neg-ative value ofDG0
ads reveals that the adsorption is more chemical
than physical adsorption [68,69]. DH0
ads of N-AR on MS surface
was related with the Langmuir adsorption isotherm[27]and was
calculated from following Eq.(9):
h 1 h¼ AC exp
D
H0 RT ! ð9Þwhere T is the temperature, A the independent constant, C the inhibitor concentration, R the universal gas constant,DH0adsthe heat
of adsorption, and h is the surface coverage by the inhibitor
mole-cule. Eq. (9) can be converted to logarithmic scale(10):
ln h 1 h ¼ ln A þ ln C
D
H o ads R : 1 T ð10ÞPlot ln(h/1 h) versus 1/T of 10.0 mM N-AR is not given here (correlation coefficient is 0.821). The slope of the linear parts of
the curve is equal to DH0
ads=R from which the average standard
heat of adsorption DH0
ads was calculated and was equal to
31.31 kJ mol1. The negative value of the standard heat of the
adsorption process indicates that the adsorption process is exo-thermic in nature. This observation further confirms physical
adsorption of the inhibitor on the MS surface in 0.5 M H2SO4
solu-tion. Standard entropy of inhibitor adsorption (DS0ads) can be
calcu-lated using the following equation:
D
G0ads¼D
H 0ads T
D
S0
ads ð11Þ
Value ofDS0adscalculated as 22.88 J mol1K1. This is opposite to
what would be expected, since adsorption is an exothermic process and is always accompanied by a decrease of entropy. The reason could be explained as follows: the adsorption of organic inhibitor molecules from the aqueous solution can be regarded as a quasi-substitution process between the organic compound in the aqueous
phase [Org(sol)] and water molecules at the electrode surface
[H2O(ads)][70]. In this situation, the adsorption of the organic
inhib-itor is accompanied by desorption of water molecules from the sur-face. Thus, while the adsorption process for the inhibitor is believed to be exothermic and associated with a decrease in entropy of the solute, the opposite is true for the solvent. The obtained thermody-namic values are the algebraic sum of the adsorption of organic
molecules and desorption of water molecules[71]. Therefore, the
gain in entropy is attributed to the increase in solvent entropy [71,72]. The positive values ofDS0
adsmean that the adsorption
pro-cess is accompanied by an increase in entropy, which is the driving
force for the adsorption of the inhibitor onto the N-AR surface[70].
3.7. The potential of zero charge (PZC) and inhibition mechanism The present results indicate that N-AR inhibits MS corrosion via physisorption or chemisorption mechanism. The adsorption pro-cess is affected by the chemical structure of the inhibitor, the nat-ure and charge status of the metal surface, the distribution of charge over the whole inhibitor molecule, inhibitor dipole mo-ment, and the adsorption of other ionic species if it is electrostatic
in nature[73]. The surface charge of metal can be defined by the
position of open circuit potential (Eocp) with respect to the PZC,
which plays an important role in the electrostatic adsorption pro-cess. The alternative current (AC) impedance data can be used to determine the PZC value for obtaining more information about
the surface charge of metal[41,74–76]. In order to determine the
PZC, electrochemical impedance spectroscopy study was carried
out with the polarization resistance (Rp) versus potential (E) plots
[41]. The plot of Rpversus applied potential was given inFig. 12.
As it can be seen inFig. 12, the obtained curve seemed parabola,
and the maximum point was shown 0.461 V(Ag/AgCl). This point
can be called the PZC of the MS in 0.5 M H2SO4solution containing
10.0 mM N-AR[77]. The open circuit potential of MS in the same
conditions is 0.421 V(Ag/AgCl), which is more positive than PZC and indicate positively charged MS surface after 1 h of exposure time (Er= Eocp EPZC= 0.040 V(Ag/AgCl), where Eris the Antropov’s
‘‘rational’’). The PCZ results show that the MS suface carries the positive excess charge in presence inhibitor in acid solution.
The reasonable mechanism of NAR inhibition of MS corrosion may be derived based on the adsorption of the inhibitor molecule. N-AR molecules exist as protonated through nitrogen and sulfur atoms in acidic solution in equilibrium with the following equation [78]:
N-AR þ 2Hþ
$ ½N-ARH2þ ð12Þ
The positively charged inhibitor molecule could be adsorbed to MS surface with electrostatic interaction between the negatively
charged SO42and the protonated inhibitor molecules[13,78,79].
Consequently, this is responsible for excess positive charge on the metal surface. On the other hand, N-AR molecules are adsorbed on the MS surface through an unshared pair of electrons present on
S-atoms and N-atoms [17,18]. Therefore, the MS corrosion is
suppressed by the presence of N-AR in 0.5 M H2SO4solution. The
protonated N-AR molecules are also adsorbed onto cathodic sites of MS and reduced the hydrogen evolution. The adsorption of protonated N-AR reduces the rate of the hydrogen evolution. So, the hydrogen gas volume results are supported this observation. 0 300 600 900 1200 1500 -0.550 -0.510 -0.470 -0.430 -0.390 -0.350 EPZC EOCP E / V (Ag/AgCl) Rp / Ω cm 2
Fig. 12. The plots of Rpversus electrode potential for MS containing 10.0 mM N-AR in 0.5 M H2SO4.
3.8. SEM analysis
The SEM images of MS in 0.5 M H2SO4solution in the absence of
the inhibitor after 1 h (a) and 120 h (b) and presence of 10.0 mM N-AR after 1 h (c) and 120 h (d) exposure is given in Fig. 13.
Inspec-tion ofFig. 13a reveals that the MS surfaces after 1 h immersion
in uninhibited 0.5 M H2SO4shows an aggressive attack of the
cor-roding medium on the MS surface. Furthermore, the corrosion products appear uniform, and the surface layer is very rough. After 120 h immersion in uninhibited solution, the MS surface was strongly damaged with the increased number and the depth of
the pits (Fig. 13b). A large number of pits with large size and high
depth distributed over the surface are seen. In contrast, in the
pres-ence of 10.0 mM N-AR after 1 h immersion (Fig. 13c), the specimen
surface was smoother and no pits are observed on the metal sur-face. This is due to the involvement of inhibitor molecules in the interaction with the reaction sites of MS surface, resulting in a de-crease in the contact between iron and the aggressive medium and sequentially exhibited good inhibition effect. After 120 h immer-sion in inhibited solution (Fig. 13d), there is a still protective layer and much less damage on the steel surface. Therefore, it can be concluded that the high inhibition efficiency of N-AR after longer immersion times may be due to the adsorption of inhibitor mole-cules on the active sites of the MS surface which means that, after the longer immersion time, the adsorption is more chemical than physical one.
4. Conclusions
N-aminorhodanine: as a new and effective corrosion inhibitor
on the corrosion of MS in 0.5 M H2SO4solution was studied using
various electrochemical techniques. From the results obtained, the following points can be emphasized;
1. N-AR was an effective inhibitor for corrosion of MS in 0.5 M
H2SO4and the inhibition efficiency increased with increasing
inhibitor concentration.
2. The polarization data indicate suppression of corrosion pro-cesses in the presence of organic compound. This inhibitor behaves as a mixed type inhibitor by inhibiting both anodic metal dissolution and cathodic hydrogen evolution reactions.
3. The adsorption of N-AR on the MS/0.5 M H2SO4interface obeys
the Langmuir adsorption isotherm model. The high value of adsorption equilibrium constant suggested that, N-AR is strongly adsorbed on the MS surface.
4. The increase in activation energy and the free energy of the
adsorption after the addition of N-AR to the 0.5 M H2SO4
solu-tion indicated that the adsorpsolu-tion is more chemical than the physical adsorption.
5. The PZC measurements showed that the MS surface was
posi-tively charged in acidic solution, SO42ions were first adsorbed
on MS surface. Then the positively charged inhibitor molecule adsorbed on to MS surface with electrostatic interaction with
the negatively charged SO42. The electrostatic interaction leads
to more surface coverage and hence greater inhibition.
Acknowledgements
The authors are greatly thankful to Çukurova University Re-search Fund for financial support (Project Number: FEF2009BAP4).
Fig. 13. SEM images of MS samples: after immersion for 1 h (a) and 120 h (b) in 0.5 M H2SO4solution without inhibitor, and after immersion for 1 h (c) and 120 h (d) in 0.5 M H2SO4solution in the presence of 10.0 mM N-AR.
The authors also acknowledge the Genetics and bioengineering Department of Yeditepe University for obtaining the SEM images.
References
[1] F. Bentiss, M. Traisnel, M. Lagrenee, Corros. Sci. 42 (2000) 127–146. [2] M.R. Singh, K. Bhrara, G. Singh, Port. Electrochim. Acta 26 (6) (2008) 479–492. [3] A. Chetouani, K. Medjahed, K.E. Benabadji, B. Hammouti, S. Kertit, A. Mansri,
Prog. Org. Coat. 46 (2003) 312–316.
[4] S.A. Abd El-Maksoud, A.S. Fouda, Mater. Chem. Phys. 93 (2005) 84–90. [5] S.M.A. Hosseini, A. Azimi, Mater. Corros. 59 (2008) 41–45.
[6] H. Kelesß, M. Kelesß, _I. Dehri, O. Serindag˘, Colloids Surf. A Physicochem. Eng. Aspects 320 (2008) 138–145.
[7] S.A. Umoren, Y. Li, F.H. Wang, Corros. Sci. 52 (2010) 1777–1786. [8] K.F. Khaled, Electrochim. Acta 55 (2010) 6523–6532.
[9] R. Alvarez-Bustamante et al., Electrochim. Acta 54 (2009) 5393–5399. [10] B.V. Appa Rao, Md. Yakub Iqbal, B. Sreedhar, Electrochim. Acta 55 (2010) 620–
631.
[11] G. Avcı, Mater. Chem. Phys. 112 (2008) 234–238.
[12] G. Avcı, Colloids Surf. A Physicochem. Eng. Aspects 317 (2008) 730–736. [13] A. Döner, R. Solmaz, M. Özcan, G. Kardasß, Corros. Sci. 53 (2011) 2902–2903. [14] A. Chetouani, B. Hammouti, T. Benhadda, M. Daoudi, Appl. Surf. Sci. 249 (2005)
375–385.
[15] A. Popova, M. Christov, S. Raicheva, E. Sokolova, Corros. Sci. 46 (2004) 1333– 1350.
[16] I.B. Obot, N.O. Obi-Egbedi, S.A. Umoren, Corros. Sci. 51 (2009) 276–282. [17] L. Herrag, B. Hammouti, S. Elkadiri, A. Aouniti, C. Jama, H. Vezin, F. Bentiss,
Corros. Sci. 52 (2010) 3042–3051.
[18] X. Wang, H. Yang, F. Wang, Corros. Sci. 53 (2011) 113–121.
[19] S. Sankarap, F. Apavinasam, M. Pushpanaden, F. Ahmed, Corros. Sci. 32 (1991) 193–203.
[20] S. Jabeena, T.J. Dinesb, R. Withnallc, S.A. Leharnea, B.Z. Chowdhry, Phys. Chem. Chem. Phys. 11 (2009) 7476–7483.
[21] T.M. El-Gogary, A.A. El-Bindary, A.S. Hilali, Spectrochim. Acta Part A 58 (2002) 447–455.
[22] E.S. Raper, Coord. Chem. Rev. 61 (1985) 115–184.
[23] R. Solmaz, G. Kardasß, B. Yazıcı, M. Erbil, Prot. Met. 43 (2007) 476–482. [24] R. Solmaz, M.E. Mert, G. Kardas, B. Yazıcı, M. Erbil, Acta Chim. Sinica 24 (7)
(2008) 1185–1191.
[25] E. Altunbasß, R. Solmaz, G. Kardasß, Mater. Chem. Phys. 121 (2010) 354–358. [26] R. Solmaz, E.A. Sßahin, A. Döner, G. Kardasß, Corros. Sci. 53 (2011) 3231–3240. [27] M. Abdallah, Corros. Sci. 44 (2002) 717–728.
[28] E.S. Ferreira, C. Giancomelli, F.C. Giacomelli, A. Spinelli, Mater. Chem. Phys. 83 (2004) 129–134.
[29] F.M. Mahgoub, B.A. Abdel-Nabey, Y.A. El-Samadisy, Mater. Chem. Phys. 120 (2010) 104–108.
[30] A. Chetouani, A. Aouniti, B. Hammouti, N. Benchat, T. Benhadda, S. Kertit, Corros. Sci. 45 (2003) 1675–1684.
[31] M. El Achouri, S. Kertit, H.M. Gouttaya, B. Nciri, Y. Bensouda, L. Perez, M.R. Infante, K. Elkacemi, Prog. Org. Coat. 43 (2001) 267–273.
[32] B. El Mehdi, B. Mernari, M. Traisnel, F. Bentiss, M. Lagrenee, Mater. Chem. Phys. 77 (2002) 489–496.
[33] M. Özcan, _I. Dehri, M. Erbil, Appl. Surf. Sci. 236 (2004) 155–164. [34] J. Aljourani et al., Corros. Sci. 51 (2009) 1836–1843.
[35] M. Behpour, S.M. Ghoreishi, N. Mohammadi, N. Soltani, M. Salavati-Niasari, Corros. Sci. 52 (2010) 4046–4057.
[36] R. Solmaz, G. Kardasß, M. Çulha, B. Yazıcı, M. Erbil, Electrochim. Acta 53 (2008) 5941–5952.
[37] M. Erbil, Chim. Acta Turc. 1 (1988) 59–70.
[38] M. Özcan, E. Karadag, _I. Dehri, Colloids Surf. A Physicochem. Eng. Aspects 316 (2008) 55–61.
[39] M. Behpour, S.M. Ghoreishi, N. Soltani, M. Salavati-Niasari, Corros. Sci. 51 (2009) 1073–1082.
[40] M.A. Quraishi, J. Rawat, Mater. Chem. Phys. 70 (2001) 95–99.
[41] M. Lagrenee, B. Mernari, B. Bouanis, M. Traisnel, F. Bentiss, Corros. Sci. 44 (2002) 573–588.
[42] R. Solmaz, Corros. Sci. 52 (2010) 3321–3330.
[43] M.A. Amin, K.F. Khaled, Q. Mohsen, H.A. Arida, Corros. Sci. 52 (2010) 1684– 1695.
[44] S.N. Raicheva, B.V. Aleksiev, E.I. Sokolova, Corros. Sci. 34 (1993) 343–350. [45] M.B. Lawson, Corrosion 36 (1980) 493–497.
[46] J. Oudar, Br. Corros. J. 25 (1990) 21–29.
[47] Y. Feng, W.K. Teo, K.S. Siow, Z. Gao, K.L. Tan, A.K. Hsieh, J. Electrochem. Soc. 144 (1997) 55–64.
[48] Z. Quan, X. Wu, S. Chen, S. Zhao, H. Ma, Corrosion 57 (2001) 195. 40–41. [49] S. John, B. Joseph, K.K. Aravindakshan, A. Joseph, Mater. Chem. Phys. 122
(2010) 374–379.
[50] M.A. Hegazy, H.M. Ahmed, A.S. El-Tabei, Corros. Sci. 53 (2011) 671–678. [51] M.A. Amin, S.S. Abd El-Rehim, E.E.F. El-Sherbini, R.S. Bayoumi, Electrochim.
Acta 52 (2007) 3588–3600.
[52] M. Keddam, O.R. Mattos, H. Takenouti, J. Electrochem. Soc. 128 (1981) 257– 266.
[53] I. Epelboin, M. Keddam, J. Electrochem. Soc. 117 (1970) 1052–1056. [54] I. Epelboin, M. Keddam, Electrochim. Acta 17 (1972) 177–186. [55] E.M. Sherif, S.-M. Park, Electrochim. Acta 51 (2006) 1313–1321.
[56] M. El-Sayed Sherif, A. Abdulhakim Almajid, J. Appl. Electrochem. 40 (2010) 1555–1562.
[57] E.E. Ebenso, E.E. Oguzie, Mater. Lett. 59 (2005) 2163–2165. [58] M. Abdallah, Corros. Sci. 46 (2004) 1981–1996.
[59] L. Tang, X. Li, L. Li, Q. Qu, G. Mu, G. Liu, Mater. Chem. Phys. 94 (2005) 353–359. [60] N.A. Negm, M.A.I. Salem, M.F. Zaki, J. Dispersion Sci. Technol. 30 (2009) 1167–
1174.
[61] N.A. Negm, M.F. Zaki, Colloid Surf. A Physicochem. Eng. Aspects 322 (2008) 97– 102.
[62] R. Solmaz, G. Kardasß, B. Yazıcı, M. Erbil, Colloids Surf. A Physicochem. Eng. Aspects 312 (2008) 7–17.
[63] J.O’.M. Bockris, A.K.N. Reddy, Modern Electrochemistry, Vol. 2, Plenum Publishing Corporation, 227 West 17th Street, New York, 1976.
[64] H. Ashassi-Sorkhabi, B. Shaabani, D. Seifzadeh, Appl. Surf. Sci. 239 (2005) 154– 164.
[65] F.M. Donahue, K. Nobe, J. Electrochem. Soc. 112 (1965) 886–891.
[66] E. Kamis, F. Bellucci, R.M. Latanision, E.S.H. El-Ashry, Corrosion 47 (1991) 667– 686.
[67] O.K. Abiola, N.C. Oforka, Mater. Chem. Phys. 83 (2004) 315–322.
[68] A. Yurt, A. Balaban, S. Ustun Kandemir, G. Bereket, B. Erk, Mater. Chem. Phys. 85 (2004) 420–426.
[69] X. Li, S. Deng, H. Fu, T. Li, Electrochim. Acta 54 (2009) 4089–4098. [70] X.H. Li, S.D. Deng, G.N. Mu, H. Fu, Corros. Sci. 50 (2008) 2635–2645. [71] T. Emranuzzaman, S. Kumar, G. Vishwanatham, Udayabhanu, Corros. Eng. Sci.
Technol. 39 (2004) 327–332.
[72] B. Ateya, B. El-Anadauli, F. El-Nizamy, Corros. Sci. 24 (1984) 509–515. [73] H. Ma, S. Chen, B. Yin, S. Zhao, X. Liu, Corros. Sci. 45 (2003) 867–882. [74] M.A. Amin, J. Appl. Electrochem. 36 (2006) 215–226.
[75] A. Lukomska, J. Sobkowski, J. Electroanal. Chem. 567 (2004) 95–102. [76] G. Kardas, R. Solmaz, Corros. Rev. 24 (2006) 151–171.
[77] M. Lebrini, M. Lagrenee, H. Vezin, L. Gengembre, F. Bentiss, Corros. Sci. 47 (2005) 485–505.
[78] N.O. Obi-Egbedi, I.B. Obot, Corros. Sci. 53 (2011) 263–275.
[79] A.Y. Musa, A.A.H. Kadhum, A.B. Mohamad, A.R. Daud, Corros. Sci. 51 (2009) 2393–2399.
