Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 4(1), 41-49, January (2014) Res. J. Chem. Sci. International Science Congress Association 41 Synergistic effect of Thiomalic acid and Zinc ions in Corrosion control of Carbon Steel in Aqueous Solution Prabakaran M. Ramesh S. *, and Periasamy V. Department of Chemistry, The Gandhigram Rural Institute, Deemed University, Gandhigram-624302, Dindigul, Tamil Nadu, INDIAAvailable online at: www.isca.in, www.isca.me Received 12th December 2013, revised 2nd January 2014, accepted 16th January 2014Abstract The synergistic effect has been studied in the presence of a dicarboxylic acid inhibitor with or without bivalent cation like zinc ions. A protective film has been formed on the carbon steel surface in aqueous solution using a synergistic combination of an environmentally friendly dicarboxylic acid (thiomailc acid) and zinc ions. The corrosion inhibition effect of thiomalic acid with zinc ions on carbon steel has been carried out by gravimetric studies and electrochemical techniques. Potentiodynamic polarization studies reveal that the inhibitor system is of a mixed type. Impedance studies point out that a protective film is formed on the carbon steel surface in the presence of the inhibitor formulation. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to investigate the nature of protective film formed on the carbon steel surface and for explaining the mechanistic aspects of the inhibition process. Keywords: Corrosion, synergistic effect, carbon steel, protective film, FTIR, SEM. Introduction Because of its good mechanical properties, availability and relatively reasonable cost carbon steel is the most worldwide used material for industrial and domestic applications. Several techniques have been applied in order to reduce the corrosion of metals. The use of inhibitors was one of the most practical and efficient methods for protection against corrosion. Corrosion inhibitors are substances added in very small concentrations that they effectively reduce the corrosion rate. Generally, organic compounds having heteroatom O, N, P and S are found to have basicity and electron density, thus assist in corrosion inhibition. Compounds with functional groups containing hetero-atoms which can donate a lone pair of electrons are found to be useful as corrosion inhibitors for metals4,5. These compounds are still continuously investigated as inhibitors for corrosion of metals in industry. The selection criteria for various inhibitors include low concentration, more adherance to environmental regulations, environmental friendliness and cost effectiveness. Carboxylic and dicarboxylic acids and salts thereof are very widely used as corrosion inhibiting agents and has been the subject of various workers6-8. An inexpensive way to protect the metals from corrosion is by using carboxylic acids. Carboxylic acid derivatives alone or both with other additives can effectively inhibit the corrosion of metals. One of the most important effects in inhibition process that serves as the basis for most of the modern corrosion inhibiting formulations is synergism. Synergistic effect existing among dicarboxylic acids and Zn2+on the inhibition of corrosion of metals has been studied by various workers10,11. An organic compound namely dicarboxylic acid was investigated as a corrosion inhibitor for carbon steel in this study.The inhibitive properties and synergistic effect with an organic compound viz., Thiomalic acid (TMA) and Zn2+ ions in controlling the corrosion of carbon steel was studied in aqueous solution using gravimetric method and electrochemical methods viz., potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) were used to analyze the protective film formed on the carbon steel surface and a suitable mechanism of corrosion inhibition is proposed. An aqueous solution of 60 ppm chloride has been chosen as control because of the water used in cooling water systems is generally either demineralized water or unpolluted surface water. Material and Methods Preparation of specimens: The specimens of carbon steel 0.02-0.03 % S, 0.03-0.08 % P, 0.4-0.5 % Mn, 0.1-0.2 % C and the rest iron of dimensions 3.5 cm x 1.5 cm x 0.2 cm, were polished with 1/0, 2/0, 3/0, 4/0, 5/0, and 6/0 emery polishing papers respectively. They were degreased with acetone, dried and used for gravimetric studies, FTIR and SEM. The dimensions of the specimens used for electrochemical studies were 1.0 cm x 1.0 cm x 0.2 cm. Gravimetric measurements: The polished carbon steel specimens in triplicate were weighed and immersed, in 100 ml test solution (control solution) and solutions containing various concentrations of TMA in the absence and presence of Zn2+ions, for a period of seven days. Then after washing and drying the carbon steel specimens were reweighed. The weights of the carbon steel specimens before and after immersion were determined using Mettler Balance AE 240 model. Corrosion Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(1), 41-49, January (2014) Res. J. Chem. Sci. International Science Congress Association 42 rates (CR) of carbon steel in the absence and presence of TMA and Zn2+ ions are expressed in mdd. The CR was calculated according to the following equation CR(mdd) = W/St (1) Where W (mg) is the weight loss, S (cm) is the surface area and t (days) is the immersion period. Inhibition efficiencies (IE) were calculated by using the equation 100(%)IECRCRCR where CR and CR are the corrosion rate in the absence and presence of inhibitor respectively. Electrochemical studies: Electrochemical measurements were carried out in a conventional three-electrode cell consisting of carbon steel working electrode (WE), a platinum counter electrode (CE) and a saturated calomel electrode (SCE) as reference electrode, using CH electrochemical workstation (Model No: CHI 760D, manufactured by CH Instruments, Austin, USA) at 30ºC. Before starting the experiments, the working electrodes were immersed in the test solution for 30 min before starting the experiment until a steady state potential reached. EIS measurements were carried out with a frequency range of 100 KHz to 0.1 Hz with AC amplitude of 5 mV at OCP. The impedance data were analyzed using EC-Lab software. From the Nyquist plots, the charge transfer resistance (Rct), constant phase element (CPE) and constant exponent (n) were obtained. The inhibition efficiencies (IE) were calculated using the formula 100(%)IE ictctct where Rct and R’ct are the charge transfer resistance values in the presence and absence of the inhibitor. The potentiodynamic polarization curves were recorded from cathodic to anodic (OCP ± 200 mV) potential with a scan rate of 1 mV/s. From the Tafel polarization curves, the corrosion current density values (Icorr) and corrosion potential (Ecorr) were obtained. The inhibition efficiencies (IE) were calculated from corr values using the equation, 100(%)IE corrcorrcorr where Icorr and I’corr are the corrosion current densities in case of uninhibited and inhibited solutions, respectively. Surface examination studies: The carbon steel specimens were immersed in various test solutions for a period of 7 days. Then, they were taken out and dried. The protective film formed on the carbon steel surface was characterized by FTIR and SEM. FTIR spectroscopy: FTIR spectra were taken out with a resolution of 4 cm-1 over the range of 4000-400 cm-1 wave number using a JASCO 460 PLUS Spectrophotometer. The spectra of pure TMA and the surface film formed on the carbon steel surface were done using KBr pellet method. Scanning electron microscopy: SEM has been used to investigate the surface morphology. The surface features of carbon steel were examined after exposure to solution after 7 days with and without inhibitor. The SEM images of the surfaces of the carbon steel specimens were obtained using VEGA3 model. Results and Discussion Gravimetric method: The corrosion rate of carbon steel in control solution in the absence and presence of the inhibitor formulations containing various amounts of TMA and Zn2+ ions are given in table-1. Figure-1 shows the variation of inhibition efficiency with concentration of TMA. The CR of carbon steel in control solution was accelerated in the presence of TMA alone. Zinc ions are found to be corrosive. However, a combination of TMA and Zn2+ ions exhibited a higher corrosion inhibition capacity. Even at low concentrations of Zn2+ ions such as 10, 20 and 50 ppm in combination with TMA at 250 ppm, an inhibition efficiency of 94% was observed. Interestingly, the combination containing Zn2+ ions at 50 ppm and TMA at a low level such as 150 ppm gave an inhibition efficiency of 92%. But, with increasing concentration of Zn2+ions from 50 ppm to 75 ppm, keeping TMA constant at 150 ppm, the maximum inhibition efficiency was obtained. The optimum concentration of each components is essential to protecting the carbon steel by forming an insoluble film. All these observations indicate that 150 ppm of TMA is necessary and also adequate to form a protective fim on the carbon steel surface. The decrease in inhibition efficiency at higher concentrations of TMA can be interpreted in terms of the formation of a soluble complex between Fe2+ and TMA. The formulation of 150 ppm TMA and 75 ppm Zn2+ ions afforded 97% corrosion inhibition efficiency. This is indicative of the strong synergistic effect of TMA and Zn2+ ions combination. A thin multicolored film was observed on the surface of the inhibited carbon steel after 7 days of immersion during the gravimetric method. Effect of pH: The inhibitor system containing TMA (150 ppm) and Zn2+ (75 ppm) was selected for further studies at the pH range of 3-11 because of its good inhibiton efficiency. The effect of pH on the corrosion inhibition efficiency of 150 ppm TMA and 75 ppm Zn2+ ions is shown in figure-2. It is evident from the results that the corrosion inhibition efficiency of the inhibitor system decreases on increasing pH range from 7-11 and decreasing pH from 5-3. The synergistic inhibitor formulation is effective in the pH range 5-7 only. (2) (3) (4) Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(1), 41-49, January (2014) Res. J. Chem. Sci. International Science Congress Association 43 Table-1 Values of inhibition efficiencies (%) obtained from TMA-Zn2+ system by gravimetric studies TMA (ppm) Zn 2+ (ppm) 10 20 50 75 100 125 150 CR IE CR IE CR IE CR IE CR IE CR IE CR IE 10 25 50 75 100 150 200 250 8.84 8.68 8.53 8.25 7.95 7.81 6.79 8.66 34 35 36 38 40 41 49 35 7.81 6.89 4.99 3.09 1.86 1.44 1.64 1.33 41 48 62 77 86 89 88 90 8.10 6.91 4.70 2.06 1.24 1.03 0.83 0.82 39 48 65 85 91 92 94 94 8.42 6.27 2.91 1.55 0.52 0.41 0.41 0.52 37 53 78 88 96 97 97 96 6.84 5.03 3.13 1.13 0.41 0.41 0.31 0.41 49 62 76 91 97 97 98 97 9.18 6.89 4.99 2.47 1.55 1.03 0.71 0.51 31 48 62 81 88 92 95 96 9.26 5.24 3.55 1.54 1.24 0.82 0.72 0.72 30 61 73 88 91 94 95 95 Figure-1 Variation of Inhibition efficiency with concentration of TMA Figure-2 Effect of pH 0501001502002502030405060708090100 I.E (%)Concentration of TMA (ppm) 10 ppm Zn2+ 20 ppm Zn2+ 50 ppm Zn2+ 75 ppm Zn2+ 100 ppm Zn2+ 125 ppm Zn2+ 150 ppm Zn2+ 234567891011122030405060708090100 Inhibition efficiency (%)pH Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(1), 41-49, January (2014) Res. J. Chem. Sci. International Science Congress Association 44 EIS measurements: EIS is one of the simple and reliable techniques for corrosion measurements. EIS techniques can provide valuable kinetic parameters for electron transfer reactions at the iron/electrolyte interface12. The corrosion inhibition of carbon steel in control solution with and without inhibitor was also investigated by EIS measurements. The charge transfer resistance (Rct), constant phase element (CPE) and constant exponent (n) obtained from the Nyquist plots and the calculated inhibition efficiency values (IE) are shown in table-2. Figure-3 shows the impedance behaviour of carbon steel corrosion in the form of Nyquist plots. From Nyquist plots in figure-3, it is found that the obtained Nyquist plots are not perfect semicircles due to frequency dispersion and this behaviour can be attributed to roughness and in-homogeneities of the electrode surface13,14. When there is non-ideal frequency response, it is common practice to use distributed circuit elements in an equivalent circuit. The most widely employed is the constant phase element (CPE). In general, a CPE is used in a model in place of a capacitor to compensate for inhomogeneity in the system. Therefore, a constant phase element (CPE) is used instead of a capacitive element to get a more accurate fit of experimental data sets using generally more complicated equivalent circuits15. The impendence of CPE is defined as CPE (6) is the modulus, j is the imaginary root; is the angular frequency and n is the surface irregularity16. Depending on the value of exponent n, ZCPE represents a resistance with R= Y-1; for n= -1, an inductance with C=Y17. The value range of a real electrode of n is often between 0 and 1. The smaller the value of n, the rougher the electrode surface and the more serious the corrosion of the electrode18. The electrical equivalent circuit model shown in figure-4 was used to analyze the obtained impedance data. The model consists of the solution resistance (R), the charge-transfer resistance of the interfacial corrosion reaction (Rct) and the constant phase angle element (CPE). Excellent fit with this model was obtained with our experimental data. Such an equivalent circuit was also discussed by several researchers19,20 who obtained similar depressed semicircles with single time constant. In the present study, the Rct of the surface film formed in the presence of the synergistic combination containing TMA (150 ppm) and Zn2+ ions (75 ppm) has an Rct value of 12854 , which is higher than the values of the surface films obtained in the presence of the individual constitutents, i.e., 1248 for 150 ppm TMA and 790 for 75 ppm Zn2+ ions. A larger value of ct implies the high inhibition efficiency. The corrosion inhibition efficiency of the synergistic combination obtained from impedance studies is 93%, which is in agreement with the efficiency obtained from the gravimetric studies. The CPE value of the metal/solution interface was 582 µFcm-2 in the absence of the inhibitor. A decrease in the CPE value (198 µFcm-2) of the metal/solution interface is obtained in the persence of the inhibitor. The high CPE value is due to a large increase in the surface area caused by the presence of corrosion products on the carbon steel surface. Thus for the inhibitor solution a decrease in the CPE value can be explained by a decrease in the quantity of the corrosion products due to increase in the inhibition effect. They also concluded that the protective film consists of carboxylate-metal complexes. This is in concerdance with the synergistic inhibition offered by the combination. Potentiodynamic polarization studies: The Potentiodynamic polarization curves of carbon steel immersed in aqueous solution in the absence and presence of various inhibitor formulations are given in figure-5. The Tafel parameters, i.e., corrosion potential (Ecorr), corrosion current density (Icorr), anodic Tafel slope (), cathodic Tafel slope () and the inhibition efficiencies (IE) are obtained from polarization studies are shown in table-3. An examination of the Tafel slopes revealed that addition of Zn2+ ions (75 ppm) alone to the control solution shifted the carhodic Tafel slopes (39 mV/decade) to a larger extent than it did the anodic Tafel solpe (30 mV/decade). Addition of 150 ppm TMA alone to the control solution shifted predominantly the anodic Tafel slpoe (13 mV/decade) in comparison to the cathodic Tafel slpoe (9 mV/decade). The synergistic combination of 150 ppm TMA and 75 ppm Zn2+ ions also shifted the carhodic Tafel slopes (78 mV/decade) to a much greater extent when compared to the shifting of the anodic Tafel solpe (68 mV/decade). The corrosion potential (Ecorr) is shifted to -556.42 mV/SCE and its corrosion current density (Icorr) is also reduced when compared to the control. The Icorr is significantly decreased from 22.68 µA/cm to 1.41 µA/cm, corresponding to an inhibition efficiency of 94%. Thus, the synergistic mixture of 150 ppm TMA and 75 ppm Zn2+ is proved to be an effective corrosion inhibitor for carbon steel. These results indicate that the binary inhibitor formulation retards both the anodic dissolution of carbon steel and oxygen reduction at cathodic sites in the corrosion inhibition process. It can be inferred from the above results the inhibitor combination of TMA and Zn2+ ions acts as a mixed inhibitor. Similar carboxylate-based formulations were reported to be mixed inhibitors10. FTIR Studies: The FT-IR spectrum of pure TMA is shown in figure-6a. The C=O stretching frequency of carboxyl group appears at 1700.91 cm-1. The C-S stretching vibration has been assigned to the region 700-600 cm-l (14). The peak that appeared at 611.32 cm-1 is assigned to the C-S group and the other peak at 2564.86 cm-1 is assigned to the S–H group. The FTIR spectrum of the protective film formed on the carbon steel surface after immersion in control solution containing of TMA (150 ppm) and Zn2+ (75 ppm) is shown in figure-6b. The C=O stretching frequency has shifted from 1700.91 cm-1 to 1569.77 cm-1. This indicates that the TMA has coordinated with Fe2+ on the metal surface through oxygen atom of C=O group resulting in the formation of Fe2+-TMA complex. The peak at 1392.35 cm-1 indicates the presence of Zn(OH)on the carbon steel Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(1), 41-49, January (2014) Res. J. Chem. Sci. International Science Congress Association 45 surface film21. The broad band of the OH stretching and bending modes of water or hydroxides within the protective film appeared at 3180.04 cm-1. There are many weak bands in the region between 1,200 and 400 cm-1. The peak at 464.75 cm-1implies the presence of ferric and ferrous oxide and hydroxide in the protective film22. The FTIR spectra suggests that the protective film may consist of [Fe2+/Zn2+–TMA], Zn(OH)2 and small amounts of oxides and hydroxides of iron. Table-2 Corrosion parameters obtained from potentiodynamic polarization studies for carbon steel immersed in the absence and in the presence of inhibitor Inhibitior system Tafel parameters TMA (ppm) Zn 2+ (ppm) corr(mV/SCE) corr (µA/cm (mV/decade) (mV/decade) IEP (%) - - -487.62 22.68 209 212 - 150 - -477.23 17.30 196 203 24 - 75 -581.29 43.70 239 251 - 150 75 -556.42 1.41 277 290 94 Table-3 Corrosion parameters of carbon steel immersed in the presence and absence of inhibitor obtained by A.C. impedance spectra Inhibitor system ct CPE (µF/cm n IE (%) TMA (ppm) Zn 2+ (ppm) 0 0 958 582 0.78 - 0 75 790 682 0.84 - 150 0 1248 370 0.92 23 150 75 12854 198 0.96 93 Figure-3 AC impedance spectra of carbon steel immersed in various test solutions Re(Z)/Ohm10,0005,000 -Im(Z)/Ohm7,5007,0006,5006,0005,5005,0004,5004,0003,5003,0002,5002,0001,5001,000500 Control solution 150 ppm TML 75 ppm Zinc 150 ppm TML + 75 ppm Zinc Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(1), 41-49, January (2014) Res. J. Chem. Sci. International Science Congress Association 46 Figure-4 Equivalent electrical circuit fitted by the Nyquist plotsFigure-5 Tafel plots of carbon steel immersed in various test solutionsFigure-6 FTIR Spectra for (a) pure TMA (b) Surface film - Ewe/V0.70.60.50.40.3 log (|I/mA|)-1-1.5-2-2.5-3-3.5-4-4.5 Control solution 150 ppm TML 75 ppm Zinc 150 ppm TML + 75 ppm Zinc Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(1), 41-49, January (2014) Res. J. Chem. Sci. International Science Congress Association 47 Scanning electron microscopy: SEM analysis was carried out for characterizing the inhibitive film formed on the carbon steel surface. Figure-7(a, b) presents the micrograph obtained for the carbon steel sample after exposure to the corrosive environment, and figure-7(c, d) reveals the surface on the carbon steel after exposure to the control solution containing the inhibitor, 150 ppm TMA, 75 ppm and Zn2+ ions. It can be seen from figure-7(a, b) that in the absence of any inhibitor there is dendrite type of growth of porous and non-protective oxides and hydroxides of iron. Figure-7(c, d) shows SEM photograph of the surface film formed over the carbon steel surface, which suppresses the rate of corrosion23. The absence of any dendritic type of growth of iron oxides is clear. This is essentially because of the protective nature of the surface film and formation of insoluble complex on the carbon steel surface24. So, SEM analysis shows the protective nature of the surface film25. Figure-7 SEM images of (a) and (b) carbon steel immersed in control solution, (c) and (d) carbon steel immersed in TMA-Zn2+ ions c b a Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(1), 41-49, January (2014) Res. J. Chem. Sci. International Science Congress Association 48 Mechanism of protection: In order to explain all the experimental results, the following mechanism of corrosion inhibition can be proposed: When carbon steel is immersed in neutral aqueous environment the anodic reaction is 2e Fe Fe (7) Fe2+ further undergoes oxidation in the presence of oxygen available in the aqueous solution e FeeFe¾® (8) and the cathodic reaction is: 4OH4e2H (9) When the environment containing control solution (60 ppm Clions)/150 ppm TMA/75 ppm Zn2+ was prepared, a [Zn2+-TMA] complex was formed in the solution. Besides this complex, there is presence of free TMA and Zn2+ ions. When the metal was immersed in this environment, the [Zn2+TMA] complex diffused from the bulk of the solution onto the surface of the metal and further complexes with Fe2+/Fe3+ ions available due to initial corrosion. Free TMA molecule diffuse from bulk of the solution to the metal surface and form [Fe2+/Fe3+-TMA] complexes. These complexes fill the pores of the film formed on the surface and make it protective. Free Zn2+ ions diffuse from the bulk of the solution to the metal surface and form Zn(OH) at the local cathodic sites. Thus, the corrosion is controlled by the protective film consisting of Zn(OH) and metal-inhibitor complex, viz., [Fe2+/Fe3+-TMA]. Formation of Zn(OH) controls the cathodic reaction and formation of (metal-inhibitor) complexes controls the anodic reaction. Hence, the inhibition is under mixed control. Similar reports of complex formation have been observed in the literature11,23,24,26. Conclusion The present work shows an excellent inhibitive effect among TMA and Zn2+ in corrosion protection of carbon steel. The inhibitor system 150 ppm TMA and 75 ppm Zn2+ is effective and has 97% inhibition efficiency. The inhibitor system is effective in the pH range 5 to 7. The inhibitor formulation acts as a mixed inhibitor. EIS study reveal that the presence of a protective film on the carbon steel surface. FTIR spectral data appear to show that the protective film may consists of [Fe3+/Fe2+/Zn2+-TMA] complex, Zn(OH), hydroxides and oxides of iron. The protective film formation is also confirmed by SEM study. This inhibitor formulation consisting of TMA and Zn2+ can be used as a potential inhibitor to prevent the corrosion of carbon steel in aqueous solution. Acknowledgement M. Prabakaran is grateful to the UGC for the fellowship under Research Fellowship in Sciences for Meritorious Students. Authors thank the Co-ordinator, UGC-SAP, Gandhigram Rural Institute for his help and also thank the authorities of Gandhigram Rural Institute for the encouragement. References 1.Kumar S., Sharma D., Yadav P. and Yadav M., Experimental and quantum chemical studies on corrosion inhibition effect of synthesized organic compounds on N80 steel in hydrochloric acid, Ind. Eng. Chem. Res., 52 (39), 14019–14029 (2013)2.Gerengi H., Anticorrosive Properties of Date Palm (Phoenix dactylifera L.) Fruit Juice on 7075 Type Aluminum Alloy in 3.5% NaCl Solution, Ind. Eng. Chem. Res., 51, 12835 12843 (2012)3.Quraishi M.A., Ansari F.A. and Jamal D., Thiourea derivatives as corrosion inhibitors for mild steel in formic acid, Mater. Chem. Phys., 77 (3), 687-690 (2002)4.Deng S. Li X. and Fu H., Two pyrazine derivatives as inhibitors of the cold rolled steel corrosion in hydrochloric acid solution, Corros. Sci.,53, 822-828 (2011)5.Labriti B. Dkhireche N. Touir R. Ebn Touhami M. Sfaira M. El Hallaoui A., Hammouti B. and Alami A., Arab. J. Sci. Eng.,37, 1293-1303 (2012)6.Yoo S.H. Kim Y.W. Chung K. Kim N.K. and Kim J. S., Corrosion inhibition properties of triazine derivatives containing carboxylic acid and amine groups in 1.0 M HCl solution, Ind. Eng. Chem. Res., 52 (32), 10880–10889 (2013)7.Ghareba S. and Omanovic S., 12-Aminododecanoic acid as a corrosion inhibitor for carbon steel, Electrochim. Acta.,56, 3890–3898 (2011)8.Rammelt U. Koehler S. and Reinhard G., Electrochemical characterisation of the ability of dicarboxylic acid salts to the corrosion inhibition of mild steel in aqueous solutions, Corros. Sci., 53, 3515-3520 (2011)9.Demadis K.D., Mantzaridis C. and Lykoudis P., Effects of structural differences on metallic corrosion inhibition by metal-polyphosphonate thin film. Ind. Eng. Chem. Res., 45, 7795-7800 (2006)10.Florence G.R.H. Antony A.N. Sahayaraj J.W. Amalraj A.J. and Rajendran S., Corrosion inhibition of carbon steel by adipic acid-Zn2+ system, Ind. J. Chem. Technol., 12, 472-476 (2005) Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(1), 41-49, January (2014) Res. J. Chem. Sci. International Science Congress Association 49 11.Manivannan M. and Rajendran S., Corrosion Inhibition of Carbon steel by Succinic acid –Zn2+ system, Res. J. Chem. Sci., 1(8), 42-48 (2011)12.Sayed El. and Sherit M., Effects of 5-(3-aminophenyl)-tetrazole on the inhibition of unalloyed iron corrosion in aerated 3.5% sodium chloride solutions as a corrosion inhibitor, Mater. Chem. Phys., 129, 961-967 (2011) 13.Juttner K., Electrochemical impedance spectroscopy (EIS) of corrosion processes on inhomogeneous surfaces, Elecrochim. Acta.,35, 1501-1508 (1990) 14.Benali O. Benmehdi H. Hasnaoui O., Selles C. and Salghi R., Green corrosion inhibitor: inhibitive action of tannin extract of Chamaerops humilis plant for the corrosion of mild steel in 0.5 M HSO, J. Mater. Environ. Sci., 4 (1), 127-138 (2013)15.Macdonald J.R. and Johnson W.B., Impedance Spectroscopy, John Wiley and Sons, New York, (1987)16.Li G.Y. Ma H.Y., Jiao Y.L. and Chen S.H., An impedance investigation of corrosion protection of copper by self-assembled monolayers of alkanethiols in aqueous solution, J. Serb. Chem Soc., 69, 791-805 (2004) 17.Macdonald J.R., Impedance spectroscopy and its use in analyzing the steady-state AC response of solid and liquid electrolytes, J. Electroanal. Chem., 223, 25-50 (1987)18.Khaled K.F. and Hackerman N., Ortho-substituted anilines to inhibit copper corrosion in aerated 0.5 M hydrochloric acid, Electrochim. Acta., 49, 485-495 (2004) 19.Alagta A. Felhosi I. Telegdi J. Bertoti I. and Kalman E., Effect of metal ions on corrosion inhibition of pimeloyl-1,5-di-hydroxamic acid for steel in neutral solution, Corros. Sci., 49, 2754-2766 (2007) 20.Ebenso E.E. Kabanda M.M. Murulana L.C. Singh A.K. and Shukla S.K., Electrochemical and quantum chemical investigation of some azine and thiazine dyes as potential corrosion inhibitors for mild steel in hydrochloric acid solution, Ind. Eng. Chem. Res., 51, 12940–12958 (2012)21.Sekine I. and Hirakawa Y., Effect of 1-Hydroxyethylidene-1, 1-Diphosphonic Acid on the Corrosion of SS 41 Steel in 0.3% Sodium Chloride Solution, Corrosion., 42, 272-277 (1986) 22.Nakayama N., Inhibitory effects of nitrilotris (methylenephosphonic acid) on cathodic reactions of steels in saturated Ca(OH) solutions, Corros. Sci., 42, 1897-1920 (2000)23.Prabakaran M., Venkatesh M., Ramesh S. and Periasamy V., Corrosion inhibition behavior of propyl phosphonic acid–Zn2+ system for carbon steel in aqueous solution, Appl. Surf. Sci., 276, 592-603 (2013)24.Brightson Arul Jacob Y. Sayee Kannan R. and Jeyasundari J., Synergistic effect of triisopropanolamine in aqueous solution by sodium St–Zn2+ System, Res. J. Chem. Sci., 3(4), 54-58 (2013)25.Sachin H.P., Praveen B.M. and Abd Hamid S.B., Corrosion inhibition of zinc by a new inhibitor in hydrochloric acid medium, Res. J. Chem. Sci., 3(11), 82-89 (2013)26.Mary Anbarasi C. and Rajendran S., Surface protection of carbon steel by butanesulphonic acid–zinc ion system, Res. J. Chem. Sci., 2(12), 21-26 (2012)