Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 3(4), 54-58, April (2013) Res. J. Chem. Sci. International Science Congress Association 54 Synergistic Effect of Triisopropanolamine in Aqueous Solution by Sodium St–Zn2+ SystemBrightson Arul Jacob Y.1,*, Sayee Kannan R. and Jeyasundari J.1 Department of Chemistry, NMSSVN College, Madurai-625019, Tamilnadu, INDIA Department of Chemistry, Thiagarajar College, Madurai-625009, Tamilnadu, INDIAAvailable online at: www.isca.in Received 27th February 2013, revised 8th March 2013, accepted 8th April 2013Abstract The aim of this present work is to study the corrosion behavior of mild steel in aqueous solution containing 60ppm Cl in the presence of TIPA (Triisopropanolamine)-Zn2+-ST (Sodium Tungstate). Weight loss study has been employed to evaluate the inhibition efficiency of this system. It was found that the inhibition efficiency of TIPA-Zn2+ was improved from 63% to 97% by the addition of 150 ppm of ST. The corrosion rate was calculated in the presence and absence of inhibitor. The protective film consists of Fe2+-Wo2-, Fe2+ - TIPA complex on anodic site and Zn (OH) complex at cathodic site. A mechanism for the inhibition of corrosion is proposed based on the above results. TIPA and Sodium tungstate (NaWO) as a corrosion inhibitors of mild steel in aqueous solution containing 60 ppm Cl was investigated by potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The surface of the specimen has been examined using, scanning electron microscope Keywords: Mild steel, corrosion inhibition, impedance spectra, scanning electron microscope. Introduction The principles and practice of corrosion inhibition in recent years have begun taking into account health and safety considerations. The use of hazardous chemicals has been restricted with no contact with the environment. Hence, there is a search for non-toxic, eco-friendly corrosion inhibitors. Several inhibitors have been used for cooling water systems. When studying inhibiting phenomena, the investigators have discovered that some oxyanions can be used as corrosion inhibitors because, through their functional groups, they form complexes with metal ions and on the metal surfaces. These complexes occupy a large surface area, thereby blanketing the surface and protecting the metals from corrosive agents present in the solution. The inhibitor protection with inorganic compounds in neutral media is most often based on the principle of formation of passive films of oxide or salt types. These films decrease the rate of transfer of oxygen to the metal surface. The good chemical stability and solubility in water make possible their use in oil production, in the formulation of detergents, and in the inhibition of corrosion and scale formation. Amines that are reported as good organic inhibitor for aqueous acid solution have been used as inhibitor in this chemical. Oxyanions, such as tungstate5,6, molybdate7,8, and chromates have been used as corrosion inhibitors. Tungstate is more effective than molybdate in terms of its inhibition efficiency. Both tungstate and molybdate passivate iron only in the presence of air. The protective action of MoO2- and WO2- in distilled water and in the presence of corrosive ions is approximately identical. MoO2- was found to be more effective. Tungstate proved to be an effective corrosion inhibitor for Al9-11 and with zinc12 in neutral, acidic, and basic solutions. Protection of corrosion of carbon steel by inhibitors in chloride containing solutions has been reported13. Tungstate and Molybdate were found to be effective inhibitors for cold rolling steel in hydrochloric acid solution14. In spite of the advantage of combining zinc salts with certain inhibitors, they have been found to adversely affect the water released during the cooling process. Therefore, the permissible limit of zinc in water/wastewater has been restricted to a maximum value of 2 mg/l15. Molecular structure of sodium tungstate is shown in scheme 1. Scheme-1 Sodium tungstate The present study evaluates the synergistic effect of TIPA-Zn2+ system estimates the influence of ST on the IE of TIPA-Zn2+system studies mechanistic aspects of corrosion inhibition by electro chemical studies. Material and Methods Preparation of the specimen: In our experiments, mild steel samples having composition of C, 0.1 %; Mn, 0.4%; P, 0.06; S, 0.026 were used. For weight loss experiments, coupons were cut Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(4), 54-58, April (2013) Res. J. Chem. Sci. International Science Congress Association 55 in the form 1.0cm x 4.0cm x 0.2cm. The surface of the specimen was polished using successive grades of emery paper, from 1/0 to 4/0, washed with soap solution and then by running tap water followed by double distilled water, finally degreased with acetone, dried in air and kept in a desiccator. Later, the samples were weighed and immersed in 300 mL of test solution in a glass beaker for a fixed interval of time. The samples were kept in the beaker in such a way that both the surfaces were in contact with the solution. Weight loss method: Mild steel specimens were immersed in aqueous solution containing 60 ppm Cl- and concentrations of the inhibitor (TIPA, ST) in the absence and presence of Zn2+. The weights of the specimens before and after immersion were determined using a Digital Balance (Model A x 62 SHIMADZU). The corrosion products were cleaned with Clark’s Solution.The corrosion IE was been calculated using the equation. IE = 100[1- W2 ] % Where, W is the weight loss value in the absence of inhibitor and W is the weight loss value in the presence of the inhibitor. Electrochemical Tests: Electrochemical tests to investigate the effect of TIPA in aqueous solution by ST–Zn2+ system on the corrosion behavior of mild steel electrochemical tests of potentiodynamic polarization measurements were carried out. The tests were carried out in aqueous solution containing 60 ppm Cl at room temperature. Potentiodynamic polarization Study: The potentiodynamic polarization measurements were conducted on EG and G potentiostat/galvanostat Model 263A. The experiments were carried out using a corrosion cell, with Ag/AgCl electrodes (saturated KCl) as reference and Pt as counter electrode. The potentiodynamic polarization measurements were carried out using a scan rate of 0.166mV commencing at a potential above 250mV more active than stable open circuit potential. However, before starting the scanning at each concentration, the specimen was stabilized for about 30mts for attaining a steady state which was shown by a stable potential. The real part (Z’) and imaginary part (Z”) of the cell impedance were measured in Ohms for frequencies. The R (charge transfer resistance) and Cdl (double layer capacitance) values were calculated. Cdl values were calculated using the following relationship. SEM Analysis: SEM provides a pictorial representation in the surface to understand the nature of the surface film in the absence and presence of inhibitors and extent of corrosion of carbon steel. The surface morphology of the samples after performing the weight loss experiments was observed carefully and analyzed by a JEOL JSM-840A scanning electron microscope at an operating voltage of 10 kV. Results and Discussion Weight- loss study: Corrosion inhibition of the binary inhibitor system TIPA- Zn2+- ST is shown in table 1 to 3. TIPA alone has some inhibition efficiency of 46%. 100ppm of TIPA and 50 ppm of Zn2+ shows 63% inhibition efficiency. After the addition of sodium tungstate (150 ppm) the inhibition efficiency increases from 63% to 97%. Interestingly, addition of 150 ppm of ST to this binary inhibitors system increases the IE from 63% to 77%. The improvement in the protection efficiency is attributed to a synergistic effect with results from the combination of the binary inhibitors. As a result of this complex formation, the inhibitor molecules are readily transported from the bulk to the metal surface. Table- 1 Corrosion rates of (CR mdd) mild steel immersed in an aqueous solution containing 60 ppm of Cl and the inhibition efficiencies obtained by weight loss methodCl - ppmTIPA ppm IE % CR mdd 60 50 28 8.12 60 100 47 13.34 60 150 31 8.99 60 200 31 8.99 60 250 25 7.25 Table-2 Corrosion rates (CR mdd) mild steel immersed in an aqueous solution containing 60 ppm Cl and the inhibition efficiencies (IE%) obtained by weight loss method Cl - ppmTIPA ppm Zn 2+ ppm IE % CR mdd 60 0 0 - 29 60 0 50 23 6.67 60 50 50 18 5.04 60 100 5 63 18.13 60 150 50 38 10.8 60 200 50 34 10 60 250 50 18 5.22 Table-3 Corrosion rates (CR mdd) mild steel immersed in an aqueous solution containing 60 ppm Cl and the inhibition efficiencies obtained by weight loss methodCl - ppm TIPA ppm Zn 2+ ppm ST ppm IE % CR mdd 60 100 50 50 90.62 2.72 60 100 50 100 87.5 3.63 60 100 50 150 96.87 0.91 60 100 50 200 93.75 1.81 60 100 50 250 81.25 5.45 12C R f = p t dl max Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(4), 54-58, April (2013) Res. J. Chem. Sci. International Science Congress Association 56 Potentio dynamic Polarization study: The Polarization curves of carbon steel immersed in an aqueous solution containing 60 ppm Cl- are shown in figure-1. Figure-1 Polarization curves of mild steel immersed in various test solutions a) 60 ppm Cl (Blank) b) TIPA (100 ppm) + Zn2+(50 ppm)+ ST (150 ppm) The corrosion parameters namely, corrosion potential (Ecorr) anodic tafel slope (b), cathodic tafel slope (b) linear. Polarization resistance (LPR) and corrosion current (Icorr) are give in table 3. When carbon steel is immersed in 60 ppm Clthe corrosion potential is -583 mv Vs SCE. When the addition of inhibitions 100 ppm of TIPA, 50 ppm of Zn2+ and 250 ppm of ST, the corrosion potential in -336 mV Vs SCE. The LPR increases from 1.693 x 10 to 7.8 x 10 ohm cm and corrosion current decreases from 1.873 x 10-6 A/cm to 4.47 x 10-7 A/cm. These observations indicate that when carbon steel surface is protective film formed on the metal surface. The corrosion current for the formulation of TIPA-Zn2+-ST has decreased to 8.90x10-10 A/cm. AC impedance spectroscopy: The AC impedance spectra of mild steel immersed in aqueous solutions containing 60 ppm Cl in the absence and presence of inhibitors are shown in figure 2 (Nyquist plots) and figure 3 (Bode plots). The AC impedance parameters, namely charge transfer resistance (R) and double layer capacitance Cdl and log Z/ohm are calculated. The impedance values derived from Bode plots are also given in table 5. It is observed that when carbon steel immersed in aqueous solution containing 60 ppm Cl the R value is 1834 ohm cm. The Cdl value is 5.07 x 10-7 F/cm. The impedance value (log Z/ohm) is 3.411. When inhibitors (100 ppm TIPA + 50 ppm Zn2+ + 150 ppm ST) added the R values increases from 1834 to 2556 ohm cm. The Cdl value decreases from 5.07 x 10-7to 8.90 x 10-10 F/cm. The impedance value increases from 3.4110 to 3.4820. These observations suggest that a protective film formed on the metal surface16-18. Figure-2 AC impedance spectra of mild steel immersed in various test solutions (Nyquist Plot) a) 60 ppm Cl (Blank) b) TIPA (100 ppm) + Zn2+ (50 ppm) + ST (150 ppm) Figure-3 AC impedance spectra of mild steel immersed in various test solutions (Bode Plot) a) 60 ppm Cl(Blank) Table-4 Corrosion parameters of mild steel immersed in an aqueous solution containing 60 ppm of Cl obtained from potentiodynamic polarization study System Ecorr mV Vs SCE mV/decade mV/decade LPR ohm cmI Corr A/cm Aqueous solution containing 60 ppm Cl - -583 170 127 1.693 x 10 4 1.873 x 10 - 6 Aqueous solution containing 60 ppm Cl - +TIPA (100 ppm) + Zn2+ (50 ppm) + ST (150 ppm) -336 290 112 7.80 x 10 4.47 x 10-7 Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(4), 54-58, April (2013) Res. J. Chem. Sci. International Science Congress Association 57 Table-5 Corrosion parameters of mild steel immersed in aqueous solution containing 60 ppm Cl obtained by AC impedance spectra System R cmdl F/cmImpedance [log(Z/ohm)] Aqueous solution containing 60 ppm Cl - 1834 5.07×10 - 7 3.4110 Aqueous solution containing 60 ppm Cl - +TIPA (100 ppm) + Zn 2+ (50 ppm) + ST (150 ppm) 2556 8.90× 10-10 3.4820 Figure-4 AC impedance spectra of carbon steel immersed in various test solutions (Bode Plot) a) 60 ppm Cl + TIPA (100 ppm) + Zn2+ (50 ppm) + ST (150 ppm) Figure-5.1 SEM micrographs of a) Mild steel (Control); Magnification-X 500 b) Mild Steel (Control); Magnification-X 1000SEM analysis of metal surface: The SEM images of different magnification (X500, X1000) of mild steel specimen immersed in aqueous solution contain 60 ppm of Cl for 1 day in the absence and presence of inhibitor system are shown in figure 5.1(a,b) respectively. The SEM micrographs of mild steel surface was immersed in an aqueous solution containing 60 ppm Cl. Figure 5.2(c,d) shown the roughness of the metal surface. figure 5.2(e,f) indicates that in the presence of 100 ppm TIPA + 50 ppm Zn2+ + 150 ppm ST in an aqueous solution containing 60 ppm Cl- , the surface coverage increased with in turn results in the formation of insoluble complex on the surface of the metal. In the presence of TIPA, Zn2+ and ST system, the surface is covered by a thin layer of inhibitor which effectively control the dissolution of mild steel19-22. Figure-5.2 SEM micrographs of a) 60 ppm Cl Magnification-X 500 b) 60 ppm Cl Magnification-X 1000, c) 60 ppm Cl + TIPA (100 ppm) + Zn2+ (50 ppm) + ST (150 ppm) Magnification –X500, d) 60 ppm Cl + TIPA (100 ppm) + Zn2+ (50 ppm) + ST (150 ppm) Magnification –X1000 Conclusion The results of the weight loss study shows that the formulation consisting of 100 ppm TIPA, 50 ppm of Zn2+ and 150 ppm ST has 96.87% IE i. A synergistic effect exists between Zn2+ and TIPA and ST system. ii. Ac impedance spectra reveal that the protective film formed on the metal surface. iii. When the solution containing 60 ppm of Cl, 50 ppm of Zn2+ and 100 ppm of TIPA and 150 ppm of ST, there is a formulation of Zn2+TIPA complex and Zn2+ -ST complex in solution. iv. When mild steel is immersed in this solution, the Zn2+-TIPA, Zn2+-ST complex diffuses from the bulk of the solution towards metal surface. v. On the metal surface Zn2+-TIPA-ST complex is converted in to Fe2+-TIPA, Fe2+-ST complex on the anodic sites. Zn2+ is released. vi. Zn2+-TIPA, Zn2+-ST+Fe2+ Fe2+-ST, Fe2+TIPA+Zn2+, vii. The released Zn2+ combines with OH to form Zn (OH) on the cathodic sites. viii. Zn2+ + 2OH Zn(OH). Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 3(4), 54-58, April (2013) Res. J. Chem. Sci. 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