CORROSION INHIBITION OF CARBON STEEL IN HYDROCHLORIC ACID SOLUTION BY SENNA-ITALICA EXTRACT

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1 CORROSION INHIBITION OF CARBON STEEL IN HYDROCHLORIC ACID SOLUTION BY SENNA-ITALICA EXTRACT Ameena Mohsen Al-Bonayan Department of Chemistry, Faculty of Applied Science Girls, Umm Al-Qura University, Makkah Al-Mukarramah, Kingdom of Saudi Arabia, hotmail.com, Tel: ABSTRACT The potential of Senna-Italica extract as a corrosion inhibitor for carbon steel in 1 M HCl was determined using electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and weight loss methods. Surface examination was tested using scanning electron microscope with energy dispersive X-ray spectroscopy (SEM EDX). The adsorption process obeyed Freundlich adsorption isotherm. Maximum inhibition was attained 92.6% at the concentration of 600 ppm for senna-italica extract. Potentiodynamic polarization measurement studies revealed that senna-italica extract behave as a mixed-type inhibitor in 1 M HCl. The inhibition efficiencies of senna-italica extract obtained from the all various measurements were in good agreement. Keywords: Carbon steel, Corrosion inhibition, senna-italica extract, HCl, potentiodynamic polarization, EIS,EFM 1. Introduction Corrosion is a fundamental process playing an important role in economics and safety particularly for metals. The use of inhibitors is one of the most practical methods for protection against corrosion especially in acidic media [1]. Most inhibitors used in industry are organic compounds primarily composed of nitrogen, oxygen and sulphur atoms. Inhibitors containing double or triple bonds play an important role in facilitating the adsorption of these compounds onto metal surfaces [2]. A bond can be formed between the electron pair and/or the π-electron cloud of the donor atoms and the metal surface, thereby reducing corrosive attack in an acidic medium. Many of these compounds are very toxic to humans, have a bad environmental effects and its high-cost [3]. Plant extract is low-cost and environmental safe, so the main advantages of using plant extracts as corrosion inhibitor are economic and safe environment. Up till now, many plant extracts have been used as effective corrosion inhibitors for iron or steel in acidic media, such as: Matricaria recutita [4], Moringa oleifera [5], henna [6], Nypa fruticans Wurmb [7],, olive [8], Phyllanthus amarus [9], Occimum viridis [10], lupine [11], Vernonia amygdalina [12], Hibiscus rosa [13], Strychnos nux-vomica [14], Justicia gendarussa [2], coffee [3], fruit peel [16] and Halfabar [17]. Besides steel, aluminum in acidic [18] and alkaline media [19], zinc in HCl solution [20], and Al 3Mg alloy in neutral NaCl solution [21] were protected against corrosion using some plant extracts. The inhibition performance of plant extract is normally ascribed to the presence of complex organic species, including tannins, alkaloids and nitrogen bases, carbohydrates and proteins as well as hydrolysis products in their composition. These organic compounds usually contain polar functions with nitrogen, sulfur, or oxygen atoms and have triple or conjugated double bonds or aromatic rings in their molecular structures, which are the major adsorption centers. 2. Experimental methods 2.1. Materials and solutions Tests were performed on C-steel specimens of the following composition (weight %):0.200 % C, % Mn, % P, % S, and the remainder Fe. The aggressive solution used was prepared by dilution of analytical reagent grade 37% HCl with bidistilled water. The stock solution (2000 ppm) of senna-italica extract was used to prepare the desired concentrations by dilution with bidistilled water. The concentration range of senna-italica extract used was ppm. 49

2 2.2. Preparation of plant extracts Table (1): Main constituents of senna-italica extracts are shown below: Senna-italica extract (I) (II) 2.3. Weight loss measurements Rectangular specimens of carbon steel with dimensions 2 x 2 x 0.2 cm were abraded with different grades of emery paper, degreased with acetone, rinsed with bidistilled water and dried between filter papers. After weighting accurately, the specimens were immersed in 100 ml of 1 M HCl with and without different concentrations of sennaitalica extract at 30 C. After different immersion periods (each of 30 min till 180 min) the carbon steel samples were taken out, washed with bidistilled water, dried and weighted again. The weight loss values are used to calculate the corrosion rate (CR) in mg cm -2 min -1. The inhibition efficiency (%η) and the degree of surface coverage (θ) were calculated from Eq. (1): %η = θ x 100 = [(R * - R) / R * ] x 100 (1) where R * and R are the corrosion rates of carbon steel in the absence and in the presence of inhibitor, respectively Polarization measurements Electrochemical measurements were performed using a typical three-compartment glass cell consisting of the carbon steel specimen as working electrode (1cm 2 ), saturated calomel electrode (SCE) as a reference electrode, and a platinum foil (1cm 2 ) as a counter electrode. The reference electrode was connected to a Luggin capillary and the tip of the Luggin capillary is made very close to the surface of the working electrode to minimize IR drop. All the measurements were done in solutions open to atmosphere under unstirred conditions. All potential values were reported versus SCE. Prior to each experiment, the electrode was abraded with successive different grades of emery paper, degreased with acetone, also washed with bidistilled water, and finally dried. Tafel polarization curves were obtained by changing the electrode potential automatically from (-0.8 to 1 V vs. SCE) at open circuit potential with a scan rate of 1 mvs -1. The corrosion current is determined by extrapolation of anodic and cathodic Tafel lines (β a and β c) to a point which gives log i corr and the corresponding corrosion potential (E corr) 50

3 for extract free acid and for each concentration of the extract. Then i corr was used for calculation of inhibition efficiency (η %) and surface coverage (θ) as in equation (2): η % = θ x 100 = [1- (i corr(inh) / i corr(free)) ] 100 (2) where i corr(free) and i corr(inh) are the corrosion current densities in the absence and presence of extract, respectively. Impedance measurements were carried out in frequency range from 100 khz to 0.1 Hz with amplitude of 5 mv peak-to-peak using ac signals at open circuit potential. The experimental impedance was analyzed and interpreted based on the equivalent circuit. The main parameters deduced from the analysis of Nyquist diagram are the charge transfer resistance R ct (diameter of high-frequency loop) and the double layer capacity C dl. The inhibition efficiencies and the surface coverage (θ) obtained from the impedance measurements are calculated from equation (3): η % = θ x 100 = [1- (R ct/r ct)] 100 (3) where R o ct and R ct are the charge transfer resistance in the absence and presence of inhibitor, respectively. Electrochemical frequency modulation, EFM, was carried out using two frequencies 2 and 5 Hz. The base frequency was 0.1 Hz, so the waveform repeats after 1 s. The higher frequency must be at least two times the lower one. The higher frequency must also be sufficiently slow that the charging of the double layer does not contribute to the current response. Often, 10 Hz is a reasonable limit. The Intermodulation spectra contain current responses assigned for harmonical and intermodulation current peaks. The large peaks were used to calculate the corrosion current density (i corr), the Tafel slopes (β a and β c) and the causality factors CF-2& CF-3 [22]. The electrode potential was allowed to stabilize 30 min before starting the measurements. All the experiments were conducted at 25 C. All electrochemical measurements were performed using Gamry Instrument (PCI4/750) Potentiostat/Galvanostat/ZRA. This includes a Gamry framework system based on the ESA400. Gamry applications include DC105 software for potentiodynamic polarization, EIS300 software for electrochemical impedance spectroscopy, and EFM140 software for electrochemical frequency modulation measurements via computer for collecting data. Echem Analyst 6.03 software was used for plotting, graphing, and fitting data. To test the reliability and reproducibility of the measurements, duplicate experiments, were performed in each case at the same conditions Surface Examinations The carbon steel surface was prepared by keeping the specimens for 3 days immersion in 1 M HCl in the presence and absence of optimum concentrations of investigated derivatives, after abraded using different emery papers up to 1200 grit size. Then, after this immersion time, the specimens were washed gently with distilled water, carefully dried and mounted into the spectrometer without any further treatment. The corroded carbon steel surfaces were examined using an X-ray diffractometer Philips (pw-1390) with Cu-tube (Cu Ka1, l = A ), a scanning electron microscope (SEM, JOEL, JSM-T20, Japan). 3. RESULTS AND DISCUSSION 3.1. Weight loss measurements Figure (1) shows the weight loss time curves for the corrosion of carbon steel in 1 M HCl in the absence and presence of different concentrations of senna-italica extract. The data of Table (1) show that, the inhibition efficiency increases with increase in inhibitor concentration from ( ) ppm. The maximum inhibition efficiency was achieved at 600 ppm. 51

4 M HCl 100 ppm 200 ppm 300 ppm 400 ppm 500 ppm 600 ppm 2.7 Weight loss, mg cm Time, min Figure (1): Weight loss-time curves for carbon steel dissolution in 1M HCl in the absence and presence of different concentrations of senna-italica extract at 30 C Table (1): Variation of inhibition efficiency (% η) of senna-italica extract with its concentration from weight loss measurements at 120 min immersion in 1M HCl at 30 o C Compound Conc., ppm Corrosion rate, (CR) (mg cm -2 min -1 ) θ % η Blank senna-italica extract

5 3.2. Adsorption isotherms It is generally assumed that the adsorption of the inhibitors on the metal surface is essential step in the inhibition mechanism [23]. To calculate the surface coverage θ it was assumed that the inhibitor efficiency is due mainly to the blocking effect of the adsorbed species and hence η %= 100 x θ [24]. In order to gain insight into the mode of adsorption of the extract on carbon steel surface, the surface coverage values from EFM technique were theoretically fitted into different adsorption isotherms and the values of correlation coefficient (R 2 ) were used to determine the best-fit isotherm. Figure 2 shows the plot Log θ vs. Log C. which is typical of Freundlich adsorption isotherm at 30 C. Perfectly linear plot was obtained with regression constant (R 2 ) exceeding at 30 C Senna-italica extract Log R 2 = Log C, M Figure (2): Curve fitting of corrosion data for carbon steel in 1M HCl in presence of different concentrations of senna-italica extract to the Freundlich isotherm at 30 C The Freundlich isotherm is given by Eq. (4): log θ = log K ads + n log C (4) Where K ads is the adsorption equilibrium constant, n is the interaction parameter and C is the inhibitor concentration is related to the standard free energy of adsorption ΔG ads by Eq. (5): K ads= 1/55.5 exp (-ΔG ads/rt) (5) The value of 55.5 is the concentration of water in solution expressed in mole per liter, R the universal gas constant and T the absolute temperature. The calculated ΔG ads values were also given in Table 2. The negative values of ΔG ads ensure the spontaneity of the adsorption process and the stability of the adsorbed layer on the carbon steel surface [25]. It is well known that values of ΔG ads of the order of -40 kj mol-1 or higher involve charge sharing or transfer from the inhibitor molecules to metal surface to form coordinate type of bond (chemisorption); those of order of -20 kj mol-1 or lower The calculated ΔG ads values (Table 3) were less negative than -20 kjmol-1 indicate, therefore, that the adsorption mechanism of the investigated extract on carbon steel in 1 M HCl solution is typical of physisorption[26, 27]. 53

6 Table (2): Inhibitor equilibrium constant (K ads), free energy of adsorption (ΔG o ads ) number of active sites (1/y) and the interaction parameter (n) for senna-italica additives at 30ºC Inhibitor 1/y Kinetic model K ads, M -1 -ΔG o ads., kj mol -1 n Freundlich model K ads, M -1 - ΔG o ads, kj mol -1 Senna-italica extract Activation Parameters of Corrosion Process To calculate activation thermodynamic parameters of the corrosion reaction such as the apparent energy E a*, the entropy (ΔS * ) and the enthalpy (ΔH * ) of activation, Arrhenius equation and its alternative formulation called transition state equation were used [28]: log k =- E a * /2.303 RT + constant (6) Rate (k) = RT/ Nh exp (ΔS * /R ) exp (-ΔH * /RT ) (7) A plot of logarithm of (Rate) versus 1/T of carbon steel gives straight lines as illustrated in Fig. 3. The slope of these lines is (E a * /2.303R). A plot of logarithm of (Rate/T) versus 1/T of carbon steel gives straight lines as illustrated in Fig. 4. the slope of these lines is (-ΔH * /2.303R) and the intercept of [(log (R/Nh)) + (ΔS * /2.303R)], from which the values of ΔS * and ΔH * were calculated. Table 3 exhibits the values of apparent activation energy E a *, enthalpies H * and entropies S * for carbon steel dissolution in 1M HCl solution. The positive values of the enthalpies (ΔH * ) reflect the endothermic nature of the carbon steel dissolution process in HCl solution. On the other hand, the entropy values (ΔS * ) in the presence and absence of inhibitors are negative. This implied that the activated complex in the rate determining step represents association rather than dissociation step, this reflects the formation of an ordered stable layer of inhibitor on the steel surface [29]. i.e., increasing inhibitor concentration causes an increase in ordering on going from reactants to the activated complex Log k, mg cm -2 min M HCl 100 ppm 200 ppm 300 ppm 400 ppm 500 ppm 600 ppm R 2 =0.998 R 2 =0.998 R 2 =0.997 R 2 =0.998 R 2 =0.999 R 2 =0.999 R 2 = /T, K -1 Figure (3): Arrhenius plots (log k vs 1/T) for C-steel in 1 M HCl in absence and presence of different concentrations of senna-italica extract

7 Log k/t, mg cm -2 min M HCl 100 ppm 200 ppm 300 ppm 400 ppm 500 ppm 600 ppm R 2 =0.998 R 2 =0.998 R 2 =0.997 R 2 =0.998 R 2 =0.999 R 2 =0.999 R 2 = /T, K -1 Figure (4): Transition state plots (log k/t vs 1/T) for C-steel in 1 M HCl in absence and presence of different concentrations of senna-italica extract Table (3): Activation parameters of the dissolution of C-steel in 1 M HCl in the absence and presence of different concentrations of senna-italica extract Inhibitor Free Acid (1 M HCl) senna-italica extracts Conc., ppm Activation parameters * E a * H * - S -1 kj mol -1 kj mol 1 J mol -1 K Potentiodynamic Polarization Measurements Figure 5 illustrates the polarization curves of carbon steel in 1 M HCl solution without and with various concentrations of senna-italica extract at 30 C. The presence of senna-italica extract shifts both anodic and cathodic branches to the lower values of corrosion current densities and thus causes a remarkable decrease in the corrosion rate. The parameters derived from the polarization curves in Figure 5 are given in Table 4. In 1 M HCl solution, the presence of senna-italica extract causes a remarkable decrease in the corrosion rate i.e., shifts both anodic and cathodic curves to lower current densities. In other words, both cathodic and anodic reactions of carbon steel electrode are retarded by senna-italica extract in HCl solution. The Tafel slopes of β a and β c at 25 C do not change 55

8 remarkably upon addition of senna-italica extract, which indicates that the presence of senna-italica extract does not change the mechanism of hydrogen evolution and the metal dissolution process. Generally, an inhibitor can be classified as cathodic or anodic type if the shift of corrosion potential in the presence of the inhibitor is less than 85 mv with respect to that in the absence of the inhibitor [30, 31]. In the presence of senna-italica extract, E corr shifts to less negative but this shift is very small (about mv), which indicates that senna-italica extracts can be arranged as a mixed-type inhibitor, with predominant anodic effectiveness M HCl 100 ppm 200 ppm 300 ppm 400 ppm 500 ppm 600 ppm E, mv vs SCE Log i, ma cm -2 Figure (5): Potentiodynamic polarization curves for the corrosion of carbon steel in 1 M HCl solution without and with various concentrations of senna-italica extracts at 30 C 56

9 Table (4): Effect of concentration of senna-italica extract on the electrochemical parameters calculated using potentiodynamic polarization technique for the corrosion of carbon steel in 1 M HCl at 30 C Concentration, ppm i corr. cm -2 ma -E corr. mv vs SCE β a, mvdec -1 β c, mv dec -1 θ % η 1 M HCl Sennaitalica extract Electrochemical Impedance Spectroscopy (EIS) Measurements Figures 6 shows the Nyquist and Bode diagrams of carbon steel in 1 M HCl solutions containing different concentrations of senna-italica extracts at 30 C. All the impedance spectra exhibit one single depressed semicircle. -20 (a) 1M HCl 100 ppm 200 ppm 300 ppm 400 ppm 500 ppm 600 ppm -15 Z imag, ohm cm Z real,ohm cm -2 57

10 (b) Z / ohm cm Zph, deg f / Hz Figure (6): The Nyquist (a) and Bode (b) plots for corrosion of C-steel in 1M HCl in the absence and presence of different concentrations of senna-italica extract at 30 C R ct Figure (7): Electrical equivalent circuit used to fit the impedance data. The diameter of semicircle increases with the increase of senna-italica extracts concentration. The impedance spectra exhibit one single capacitive loop, which indicates that the corrosion of steel is mainly controlled by a charge transfer process and the presence of senna-italica extract does not change the mechanism of carbon steel dissolution [32]. In addition, these Nyquist diagrams are not perfect semicircles in 1 M HCl that can be attributed to the frequency dispersion effect as a result of the roughness and inhomogeneous of electrode surface [33]. Furthermore, the diameter of the capacitive loop in the presence of inhibitor is larger than that in the absence of inhibitor (blank solution), and increased with the inhibitor concentration. This indicates that the impedance of inhibited substrate increased with the inhibitor concentration. This behavior is usually attributed to the inhomogeneity of the metal surface arising from surface roughness or interfacial phenomena [34], which is typical for solid metal electrodes [35]. Generally, when a non-ideal frequency response is presented, it is commonly accepted to employ the distributed circuit elements in the equivalent circuits. What is most widely used is the constant phase element (CPE), which has a non-integer power dependence on the frequency [36]. Thus, the equivalent circuit depicted in Figure 7 is employed to analyze the impedance spectra, where Rs represents the solution resistance, R ct denotes the chargetransfer resistance, and C dl represents the interfacial capacitance. The values of the interfacial capacitance C dl can be calculated from equation 8: dl 1 2 f max R ct C (8) Where f is the maximum frequency. The values of the parameters such as Rs, R ct, through EIS fitting as well as the derived parameters C dl and η % are listed in Table 6. 58

11 Table (6): Electrochemical kinetic parameters obtained from EIS technique for carbon steel in 1M HCl solutions containing various concentrations of senna-italica extract at 30 C Comp. Conc., ppm R S, Ω cm 2 R ct, Ω cm 2 C dl µfcm 2 x10-4 % η Blank Senna-italica extract Electrochemical Frequency Modulation (EFM) Measurements The EFM is a nondestructive corrosion measurement technique that can directly give values of the corrosion current without prior knowledge of Tafel constants. Like EIS, it is a small ac signal. Intermodulation spectra obtained from EFM measurements of carbon steel in 1 M HCl solution in the absence and presence of 600 ppm of the investigated extract are presented in Figures 8 and 9. Each spectrum is a current response as a function of frequency. The calculated corrosion kinetic parameters at different concentrations of the senna-italica extract in 1 M HCl at 30 C (i corr, β a, β c, CF-2, CF-3 and η %) are given in Table 7. From this Table, the corrosion current densities decrease by increasing the concentration of investigated extract and the inhibition efficiencies increase by increasing investigated extract concentrations. The causality factors in Table 7 are very close to theoretical values which according to EFM theory should guarantee the validity of Tafel slopes and corrosion current densities. Values of causality factors in Table 7 indicate that the measured data are of good quality. The standard values for CF-2 and CF-3 are 2.0 and 3.0, respectively. The deviation of causality factors from their ideal values might due to that the perturbation amplitude was too small or that the resolution of the frequency spectrum is not high enough also another possible explanation that the inhibitor is not performing very well. The results showed good agreement of corrosion kinetic parameters obtained from EFM with the obtained from Tafel extrapolation and EIS methods. 59

12 Figure (8): EFM spectra for C-steel in 1 M HCl (blank) at 30 C Figure (9): EFM spectra for C- steel in 1 M HCl in the presence of 600 ppm from senna-italica extract at 30 C Table (7): Electrochemical kinetic parameters obtained by EFM technique for in 1 M HCl without and with various concentrations of senna-italica extract at 30 o C Comp. Conc., M i corr., µa cm 2 β a, mv dec -1 β c, mv dec -1 CF-2 CF-3 %η Blank Sennaitalica extract

13 3.5. Energy Dispersive X-ray Spectroscopy (EDX) The EDX spectra were used to determine the elements present on the surface of C-steel and after 3 days of exposure to the uninhibited and inhibited 1 M HCl. Figure 10. portrays the EDX analysis of C-steel in 1M HCl only and in the presence of 600 ppm of senna-italica extract. The spectra show additional lines, demonstrating the existence of C (owing to the carbon atoms of pharmaceutical compound). These data show that the carbon and O materials covered the specimen surface. This layer is entirely owing to the inhibitor, because the carbon and O signals are absent on the specimen surface exposed to uninhibited HCl. It is seen that, in addition to Mn, O, C. and Si were present in the spectra. A comparable elemental distribution is shown in Table (8). (a) Figure (10): EDX analysis of C-steel in 1 M HCl solution after immersion for 3 days a) without inhibitor, b) in presence of 600 ppm senna-italica extract. (b) Table (8): Surface composition (weight %) of C-steel alloy after 3h of immersion in HCl without and with the optimum concentrations of the studied inhibitors. (Mass %) Fe Mn C O Si Cl carbon steel alone Blank Senna-italica extract

14 3.6. Scanning Electron Microscopy (SEM) Studies Figure 11 reveals the surface on C-steel alloy after exposure to 1M HCl solution containing 600 ppm of senna-italica extract. It is important to stress out that when the compound is present in the solution, the morphology of C-steel alloy surfaces is quite different from the previous one, and the specimen surfaces were smoother. We noted the formation of a film which is distributed in a random way on the whole surface of the C-steel alloy. This may be interpreted as due to the adsorption of the senna-italica extract compound on the C-steel surface incorporating into the passive film in order to block the active site present on the C-steel surface. Or due to the involvement of inhibitor molecules in the interaction with the reaction sites of C-steel alloy surface, resulting in a decrease in the contact between C-steel and the aggressive medium and sequentially exhibited excellent inhibition effect [37, 38]. (a) (b) Figure (11): SEM images of C-steel in 1 M HCl solution after immersion for 3 days a) without inhibitor, b) in presence of 600 ppm of senna-italica extract Mechanism of Corrosion Inhibition The plant extract of senna-italica extract is composed of numerous naturally occurring organic compounds. Accordingly, the inhibitive action of senna-italica extract could be attributed to the adsorption of its components on the carbon steel surface. The main constituents of senna-italica extract are phytochemical constituents. Most of these phytochemicals are organic compounds that have center for π-electron and presence of hetero atoms such as oxygen; hence, the adsorption of the inhibitor on the surface on carbon steel is enhanced by their presence [39]. Therefore, the inhibition efficiency of methanol extracts of senna-italica is due to the formation of multi-molecular layer of adsorption between iron in the carbon steel and some of these phytochemicals. Results of the present study have shown that senna-italica extract inhibits the acid induced corrosion of carbon steel by virtue of adsorption of its 62

15 components onto the metal surface. The inhibition process is a function of the metal, inhibitor concentration, and temperature as well as inhibitor adsorption abilities, which is so much dependent on the number of adsorption sites. The mode of adsorption (physisorption) observed could be attributed to the fact that senna-italica extract contains many different chemical compounds, which some can be adsorbed physically. This observation may derive the fact that adsorbed organic molecules can influence the behavior of electrochemical reactions involved in corrosion processes in several ways. The action of organic inhibitors depends on the type of interactions between the substance and the metallic surface. The interactions can bring about a change either in electrochemical mechanism or in the surface available for the processes [40]. 4. CONCLUSIONS From the overall experimental results the following conclusions can be deduced: 1. Senna-italica extract is good inhibitor and act as mixed type but mainly act as anodic inhibitors for carbon steel corrosion in 1 M HCl solution. 2. The results obtained from all electrochemical measurements showed that the inhibiting action increases with the inhibitor concentration and decreases with the increasing in temperature. 3. Double layer capacitances decrease with respect to blank solution when the plant extract is added. This fact confirms the adsorption of plant extract molecules on the carbon steel surface. 4. The adsorption of inhibitor on carbon steel surface in HCl solution follows Freundlich isotherm for senna-italica extract. 5. The values of inhibition efficiencies obtained from the different independent quantitative techniques used show the validity of the results. 6. Quantum chemical parameters and molecular dynamics simulation for senna-italica extract were calculated to provide further insight into the mechanism of inhibition of the corrosion process. 5. REFERENCES [1]. G.Trabanelli, Corrosion.,47 (1991) 410. [2]. A.K. Satapathy, G. Gunasekaran, S.C.Sahoo, K.Amit, R.V.Rodrigues, Corros. Sci.,51 (2009)2848. [3]. V.V. Torres, R.S. Amado, C.F. de Sa, T.L. Fernandez, C.A.S. Riehl, A.G. Torres, E. D Elia, Corros. Sci., 53(2011) [4]. D. Gopi, K.M. Govindaraju, L. Kavitha, J.Appl. Electrochem. 40 (2010) [5]. M. Nasibi, D. Zaarei, G. Rashed, E. Ghasemi, Chem. Eng. Comm.200 (2013) 367. [6]. A. Singh, I. Ahamad, D.K. Yadav, V.K. Singh, M.A. Quraishi, Chem. Eng. Comm., 199 (2012) 63. [7]. A. Ostovari, S.M. Hoseinieh, M. Peikari, S.R. Shadizadeh, S.J. Hashemi, Corros. Sci., 51 (2009) [8]. K.O. Orubite, N.C. Oforka, Mater. Lett. 58 (2004) [9]. A.Y. El-Etre, J. Colloid Interface Sci.314 (2007) 578. [10]. P.C. Okafor, M.E. Ikpi, I.E. Uwah, E.E. Ebenso, U. J. Ekpe, S.A. Umoren, Corros. Sci.50 (2008) [11]. E.E. Oguzie, Corros. Sci. 50 (2008) [12]. A.M. Abdel-Gaber, B.A. Abd-El-Nabey, M. Saadawy, Corros. Sci. 51 (2009)1038. [13]. N.O. Eddy, S.A. Odoemelam, A.O. Odiongenyi, Portugaliae Electrochim. Acta. 27 (2009) 33. [14]. K. Anuradha, R. Vimala, B. Narayanasamy, J.A. Selvi, S. Rajendran, Chem. Eng. Comm.,195 (2008)352. [15]. P.B. Raja, M.G. Sethuraman, Pigment & Resin Technology.38 (2009) 33. [16]. J.C. Rocha, JACP. Gomes, E. D Elia, Corros. Sci.52 (2010) [17]. A.M. Abdel-Gaber, B.A. Abd-El-Nabey, I.M. Sidahmed, A.M. El-Zayady, M. Saadawy, Corros. Sci.48 (2006) [18]. A.Y. El-Etre, Corros. Sci.45 (2003) [19]. O.K. Abiola, J.O.E. Otaigbe, O.J. Kio, Corros. Sci.51 (2009) [20]. O.K. Abiola, A.O. James, Corros. Sci. 52 (2010) 661. [21]. J. Halambek, K. Berkovic, J. Vorkapic-Furac, Corros. Sci. 52 (2010) [22]. M. Ebadi, Pharmacodynamic Basis of Herbal Medicine, 2nd ed., CRC Press, New York [23]. R.K. Dinnappa, S.M. Mayanna, J. Appl. Elcreochem.11 (1981) 111. [24]. N. Patel, A. Rawat, S. Jauhari, G. Mehta, European J. Chem.1 (2010)129. [25]. S.A. Umoren, U.F. Ekanem, Chem. Eng. Comm., 197 (2010)1339 [26]. K. Aramaki, N. Hackerman, J. Electrochem. Soc.116 (1969)

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