Volume 14 Preprint 12


Corrosion Behaviour of Mild Steel in Acid Solutions with S-AITO

V. Chandrasekaran

Keywords: Mild steel, hydrochloric acid, sulphuric acid, Temkin’s adsorption isotherm, potentiostatic polarization, impedance

Abstract:
S-Acetyl Isothiourea Oxalate (S-AITO) was synthesized in the laboratory and this influence on the inhibition of corrosion of mild steel in 1.11 N hydrochloric and 1.12 N sulphuric acids was investigated by weight loss and potentiostatic polarization techniques at 303K, 353K and 403K. These results were confirmed by the impedance technique. The inhibition efficiency increased with increase in concentration of inhibitor and decreased with rise in temperature from 303K to 403K. The maximum inhibition efficiency of S-AITO was found to be 98.42% (0.5% of S-AITO) at 303K in sulphuric acid. The adsorption of this compound on the mild steel surface from the acids has been found to obey Temkin’s adsorption isotherm. The potentiostatic polarization results revealed that S-AITO was a mixed type inhibitor. Some thermodynamic parameters i.e., activation energy (Ea), free energy of adsorption (Gads), enthalpy of adsorption (H) and entropy of adsorption (S) were also calculated from weight loss data.

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1 ISSN 1466-8858 Volume 14, Preprint 12 submitted submitted11 9 April 2011 CORROSION BEHAVIOUR OF MILD SIEEL IN ACID SOLUTIONS WITH S-AITO V. CHANDRASEKARAN* Govt. Arts College, Karur – 639 005, Tamil Nadu, India *E-mail: chandru_v_m@yahoo.co.in Abstract S-Acetyl Isothiourea Oxalate (S-AITO) was synthesized in the laboratory and this influence on the inhibition of corrosion of mild steel in 1.11 N hydrochloric and 1.12 N sulphuric acids was investigated by weight loss and potentiostatic polarization techniques at 303K, 353K and 403K. These results were confirmed by the impedance technique. The inhibition efficiency increased with increase in concentration of inhibitor and decreased with rise in temperature from 303K to 403K. The maximum inhibition efficiency of S-AITO was found to be 98.42% (0.5% of S-AITO) at 303K in sulphuric acid. The adsorption of this compound on the mild steel surface from the acids has been found to obey Temkin’s adsorption isotherm. The potentiostatic polarization results revealed that S-AITO was a mixed type inhibitor. Some thermodynamic parameters i.e., activation energy (Ea), free energy of adsorption (Gads), enthalpy of adsorption (H) and entropy of adsorption (S) were also calculated from weight loss data. Keywords Mild steel, hydrochloric acid, sulphuric acid, Temkin’s adsorption isotherm, potentiostatic polarization, impedance. Introduction Concentrated mineral acids are used extensively in pickling, cleaning, descaling and oil well acidising of metallic materials cause damage of corrosion [1,2]. It has been © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 2 ISSNspeculated 1466-8858 Volume 14, Preprint submitted 11 9 April 2011 that organic inhibitors are more effective12with iron and thatsubmitted polar organic compounds containing sulphur and nitrogen are good corrosion inhibitors for the acidic solutions of metals [3, 4]. Many organic inhibitors with hetero atoms have been studied [5-10]. High electron density of the sulphur and nitrogen atoms in these heteroatoms, help the organic molecules to get chemisorbed onto the metal surface [8]. Due to the aggressiveness of hydrochloric acid and sulphuric acid solutions against structural materials, such as carbon steel, the use of corrosion inhibitors is usually required to minimize the corrosion attack [11-14]. Therefore, in this investigation, the corrosion of mild steel in 1.11N HCl and 1.12N H2SO4 solutions in the absence and presence of S-AITO at 303K to 403K has been studied by weight loss, potentiostatic polarization and impedance techniques. It is aimed at attempting to predict the thermodynamic feasibility in inhibition via, surface coverage of the mild steel by adsorbed S-AITO. The adsorption characteristic of S-AITO was studied in order to across the adsorption isotherm that the experiment data can fit and some thermodynamic parameters of adsorption calculated. Experimental Weight loss measurements Mild steel specimens were cut to the size of 5cm x 1cm from the mild steel sheets having the following percentage composition Fe=99.686, Ni=0.013, Mo = 0.015, Cr = 0.043, S= 0.014, P=0.009, Si-0.007, Mn = 0.196, C=0.017. Weight loss measurements were performed as per ASTM method described previously [15-17]. Weight loss measurements were carried out in 1.11N HCl and 1.12N H2SO4 acids with inhibitor S-Acetyl Isothiourea Oxalate (S-AITO) in the concentration range of 0.1% to 0.5% at 303K to 403K for an immersion period of 2 hours with and without inhibitor. All the solutions were prepared using AR grade chemicals with double distilled water. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 3 ISSN 1466-8858 Inhibitor Volume 14, Preprint submitted submitted 11 9 April was synthesized in the laboratory. The 12 reaction between acetyl chloride and 2011 thiourea gives compound known as S-acetylthiuronium chloride or S-acetyl isothiourea hydrochloride. On mixing a solution of the alkali salt of carboxylic acid (sodium oxalate), the S-acetyl isothiourea oxalate is formed rapidly. Synthesized compound was characterized through the spectral data and the purity was confirmed by thin layer chromatography (TLC). The structure of S-AITO is H2N-C-NH2 + CH3COCl NH2 → [CH3CO- S- C-NH2 ] +Cl– S NH2 2[ CH3CO – S – C – NH2]+Cl – + (COONa)2 → O 2 NH2 CH3 – C – S – C - NH2 2+ (COO) 2− + 2NaCl Potentiostatic polarization /A.C. impedance measurements For potentiostatic measurements, mild steel electrode of 1 cm x 1cm dimensions with stem was cut. The stem and the face of the electrode were marked with araldite, so as to expose an area of 1 cm2. The electrodes are polished using 1/0, 2/0, and 3/0and 4/0 emery papers and degreased with trichloroethylene. Potentiostatic polarization measurements were carried out in three-electrode cell using BAS-100A model instrument. The potential of the test electrode was measured with respect to SCE and platinum was used as auxillary electrode and the experiments were carried out at 302K. The polarization measurements were carried out from a potential range of -200mV to +200mV with respect to open circuit potential, at a scan rate of 1mV/sec. Linear polarization experiments were carried out by applying the potential of ± 20 mV from the corrosion potential and resultant current was measured, then E versus i were made in a linear scale to get linear polarization plots and the slope of the plots © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 4 ISSNhave 1466-8858 the polarization Volume 14, Preprint 12 submitted submitted11 9 April 2011 resistance Rp. In Impedance measurements, Solartron Electrochemical measurement unit (1280B) was used. Impedance measurements were carried out at corrosion potential. The A.C. amplitude of 10mV was applied and the frequency was varied from 10 KHz to 10 MHz. Results and Discussion Weight loss measurements Table I shows the values of inhibition efficiency (IE %), surface coverage () and corrosion rate obtained for different concentrations of inhibitor (S-ATAO) in 1.11N HCl and 1.12N H2SO4 acids for immersion period of 2 hours at 303K to 403K. From the weight loss value, the inhibition efficiency (IE %) and surface coverage were calculated using the following equation [18, 19]. Inhibition efficiency (IE %) Surface Coverage (θ) Wu Wi x100 1 Wu Wu Wi   2 Wu  Where Wu and Wi are the corrosion rates for mild steel in the absence and presence of inhibitor (S-AITO) respectively at the same temperature. It clearly indicates that the addition of inhibitor to the acids (1.11N HCl and 1.12N H2SO4) has reduced the corrosion rate. The inhibition efficiency increased with increase in concentration of inhibitor and decreased with rise in temperature from 303K to 403K. Fig. 1 and 2 show the relation between the inhibition efficiency and temperature for 0.1% to 0.5% of S-AITO in mild steel in 1.11N HCl and 1.12N H2SO4 respectively. The order of the efficiency is decreased with increasing temperature. These results indicate that the process film start to break down with increasing temperature. The values of corrosion rate and inhibition efficiency of the inhibitor were found to depend on the molecular structure of © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 5 ISSNinhibitor. 1466-8858The Volume 14,ofPreprint 12 was 79.21% in 1.11N submitted submitted 11 9 April 2011 maximum inhibition efficiency S-AITO hydrochloric acid and 98.42% in 1.12N sulphuric acid at 0.5% (S-AITO). The maximum inhibition efficiency was obtained in sulphuric acid but not in hydrochloric acid. This is due to that HCl contains chloride ions; generally chloride ions stimulate the corrosion rate. Thermodynamic consideration Table 2 shows the calculated values of activation energy Ea(KJ/mole), free energy of adsorption Gads(KJ/mole), enthalpy of adsorption H (KJ /mole) and entropy of adsorption S (KJ mole-1 K-1) for mild steel corrosion in 1.11 N HCl and 1.12 N H2SO4 with and without inhibitor. Energy of activation (Ea) has been calculated from Arrhenius equation [2022]. log 1 p2 Ea 1  ---------------------3    p1 2.303  R  T1 T2  Where P1 and P2 are the corrosion rate at temperature T1 and T2 respectively. Ea values given in Table 2 shows that the Ea values for the corrosion of mild steel in 1.11N HCl and 1.12N H2SO4 are 39.37 KJ /mole and 20.90 KJ /mole respectively. In acid containing inhibitor, the Ea values are found to be higher than that of the uninhibited system. The higher values of Ea indicate physical adsorption of the inhibitor on metal surface [23]. It is clear that the activation energy increases regularly with increasing the efficiency of the inhibitor. The Free energy of adsorption (Gads) at different temperature was calculated from the following equation [24]. ∆Gads = -RT ln (55.5K) -----------------------4 and K is given by θ K= ----------------------5 C (1- θ) © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 6 ISSN 1466-8858 Where 14, Preprint 12 of inhibitor in mole submitted submitted April  if surface coverage,Volume C is concentration / lit and119K is 2011 equilibrium constant. From Table 2, the negative values of Gads obtained indicate the spontaneous adsorption of the indicator and are usually characteristics of strong interaction with the metal surface. It is found that the Gads are less than (less -ive values) – 40 KJ/ mole indicate that the inhibitor is physically adsorbed on the metal surface [25-26]. The enthalpy of adsorption H and entropy of adsorption S can be calculated form the following equations ∆H = Ea - RT -----------------------------6 ∆G = ∆H - T ∆ S --------------------------7 S can be easily calculated at 303K to 403K for the different concentration of S-AITO. It is also observed that S is increased with increasing the efficiencies of the inhibitor. This is opposite to that we expect, since the adsorption is an exothermic process and is always accompanied by a decrease of entropy. Ateya et al [27] have described this situation as the adsorption of the organic compound, which is accompanied by desorption of water molecules of the surface. Thus while the adsorption process is believed to be exothermic and associated with a decrease in entropy of the solute the opposite is true for the solvent. Therefore, this gain in entropy that accompanied the substitution adsorption process is attributed to the increase in solvent entropy. Adsorption isotherms The electrochemical process on the metal surface is likely to be closely related to the adsorption of inhibitors [28] and the adsorption is known to depend on the chemical structure of the inhibitors [29-30]. The adsorption of the inhibitor molecules from aqueous solution can be regarded as quasisubsitution process [29] between the organic compounds in the aqueous phase, Org (aq) organic aqueous and water molecules at the electrode surface, H2O(S) © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 7 ISSN 1466-8858 Volume 14, Preprint 12 Org (aq) + x H2O(s) = submitted submitted11 9 April 2011 Org(s) + x (H2O)(aq) ------------8 Where x is the size ratio, is the number of water molecules displaced by one molecule of organic inhibitors. Adsorption isotherms are very important determining the mechanism of organo – electro chemical reactions. The most frequently used isotherms are those of Langmuir, Frumkin, Parons, Temkin, Flory – Huggins and Bockris Sinkles [32-35]. All these isotherms are of the general form. f (θ, x) exp (-a θ) = KC------------- 10 Where f (, x) is the configurational factor that depends essentially on the physical model and assumptions underlying the derivation of the isotherm [36]. The mechanism of inhibition of corrosion is generally believed to be due to the formation and maintenance of a protective film on the metal surface. The plot of surface coverage () obtained by weight loss method versus log C (concentration) for different concentrations of the compound show a straight line indicating that the adsorption of the compounds from acids on mild steel surface follow Temkin’s adsorption isotherm. This also pointed to result of their adsorption on the metal surface. Fig 3 and 4 shows the Temkin’s adsorption isotherm for S-AITO. Potentiostatic polarization measurements The polarization behaviour of mild steel functioning as cathode as well as anode in the test solutions is shown in Fig 5 and 6 for 1.11N HCl and 1.12N H2SO4 at 303K for S-AITO. Similar curves were also obtained for 1.11N HCl and 1.12N H2SO4 at 353K and 403K and the electrochemical data obtained from the studies are shown in Table 3. It is evident that S-AITO bring about considerable polarization of the cathode as well as anode. It © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 8 ISSNwas, 1466-8858 therefore, Volume 14, Preprint 12 submitted submitted 11 9 April 2011 inferred that the inhibitive action is of mixed type. The cathodic and anodic Tafel slopes increased with increasing inhibitor concentrations and the increase was predominant in the case of the former indicating that the cathodic inhibition was dominating through the inhibitive active is of mixed nature. The non-constancy of Tafel slopes for different inhibitor concentration reveals that the inhibitor act through their interference in the mechanism of the corrosion processes at the cathode as well as the anode. The corrosion parameters deduced from Tafel polarization such as corrosion current icorr, corrosion potential Ecorr, Tafel constant ba and –bc, inhibition efficiency and Rp are given in Table 3. The icorr values were decrease with the increasing concentration of inhibitor. The inhibition efficiencies were determined from the values of corrosion current and the inhibition efficiency values were found to show same trend, with those obtained from mass loss measurements. Impedance measurements A.C. impedance measurements were carried out at room temperature for corrosion of mild steel in 1.11N HCl and 1.12N H2SO4 after immersion for about 10 minutes. The Nyquist plots for mild steel in uninhibited acid and for the various concentrations of inhibitor are shown in Fig 7 and 8. The impedance parameters and the IE% are given in Table 4. The charge transfer resistance (Rct) value for mild steel in uninhibited HCl and H2SO4 significantly changes after the addition of inhibitor. The Rct values increased with increase in inhibitor concentration. The fact is advocated by the increase in inhibitor efficiency. The semicircular nature of Nyquist plots obtained for all experiments indicates that the corrosion of mild steel is controlled by charge transfer process [37]. The double layer capacitance (Cdl) decreased with increasing inhibitor concentration. The decrease in Cdl values in presence of inhibitor indicates the fact that these additives inhibit corrosion by adsorption on the metal surface [37]. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 9 ISSN 1466-8858 The Volume 14, A.C. Preprint 12 submitted 11 9very April 2011 inhibition efficiency obtained from impedance measurementssubmitted are not in good agreement with these obtained from weight loss studies. Some differences are always noticed when corrosion rates and inhibition efficiencies determined by conventional weight loss method are compared with those obtained from electrochemical techniques. The difference observed can be attributed due to the fact weight loss methods give average corrosion rates where as electrochemical methods give instantaneous corrosion rates [38], weight loss measurements are experiments of long duration which helps in the formulation of inherent and continuous film on the metal surface. This leads to the complete shielding of the metal surface from the corrosive experiments. But electrochemical studies are experiments of short duration and the time will not be enough for the formation of the thick continuous film. This leads to slight difference in the inhibition efficiency [39,40]. Conclusions The conclusions reported in this paper are the following 1. S-AITO acted as efficient corrosion inhibitor in 1.11N HCl and 1.12N H2SO4. 2. The inhibition efficiency increased with increase in concentration of inhibitor (0.1to 0.5%) and decreased with increase in temperature from 303K to 403K. 3. The maximum inhibition efficiency of S-AITO was 79.12% in 1.11N HCl and 98.42% in 1.12N H2SO4 (0.5% of S-AITO). 4. The thermodynamics values obtained from this study Ea, H, and S, indicated that the presence of the inhibitor increase activation energy and the negative values of Gads indicate spontaneous adsorption of the inhibitor on the surface of the mild steel. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 10 ISSN 1466-88585. Volume Preprint 12 submitted submitted11 S-AITO inhibitor corrosion by 14, adsorption mechanism and the adsorption of9 April this 2011 compound from acid solution follows Temkin’s adsorption isotherm at all the concentrations. 6. From the potentiostatic polarization studies, S-AITO acted as mixed type inhibitor. References [1] M.N. Desai and M.B. Desai, Corros. Sci., 24 (1984) 349 [2] D. Sazou, M. Pagitsas and C. Georlies, Electrochim Acta, 38 (1993) 2321 [3] N.Hackerman and R.M. Hard, Corrosion 116 (1961) 166 [4] N. Hackerman, Symp. on Advances in Chelare Chemistry, Brookllyn Polytechnic Institute, 30 (1955) [5] E.E Ebenso, J.J. Ekpe, B.I. Ita, O.E. Offiong and V.J.Ibok, Mater. Chem., Phys., 60 (1999) 79 [6] F.M. Donahue and K.Nobe, J. Electrochem., Soc., 112 (1965) 886 [7] F.M. Donahue and K.Nobe, J. Electrochem. Soc., 114 (1967) 1012 [8] B.I. Ita and O.E. Offiong, Mater.Chem. Phys., 60 (1999) 79 [9] E.E. Ebenso, P.C.Okafor, O.E. Offiong, B.I. Ita, U.J. Ibok and U.J. Ekpe, Bull. Electrochem., 17 (2001) 460 [10] E.E Ebenso, P.C.Okafor, O.E. Offiong, B.I. Ita and U.J. Ekpe, Bull. Electrochem., 17 (2001) 131 [11] R.C.Ayer and N. Hackerman, J.Electrochem, Soc., 111 (1964) 522 [12] G. Schmitt, Inhibition of Acid Media, in Corrosion Inhibitors, W.P. Report (11) 91, Inst. of Material, London (1994) [13] G.Trabanelli, Inhibitors for Chemical Cleaning Treatment in Corrosion Inhibitors, W.P. Report (11) 103, Inst. of Materials, London (1994) [14] G.Trabanelli, F. Zucchi and G. Brunoro, Werkst and Korros., 39 (1988) 589 [15] P. M. Mathar and T. Vasudevanan, Corrosion, 38 (1982) 17 [16] ASTM G 31-72, “Standard Practice for Laboratory Immersion Corrosion Testing of Metals”, West Conshohocken PA: ASTM (1990). [17] M. Ajmal, A.S. Mideen and M.A. Quraishi, Corros. Sci., 36 (1994) 79 [18] I.D. Talati and R. M. Modi, Trans SAEST, 11 (1986) 259 [19] L.A. Al- Shamma, J.M. Saleh and N.A. Hikat, Corros. Sc., 27 (1987) 221 © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 11 ISSN 1466-8858 [20] N. Volume 14, Preprint submitted11 9 April 2011 Subrmanian and K. Ramakrishnaiah, Ind. J. 12 Tech., 8 (1970) 369 submitted [21] E.E. Ebenso, Bull. Electrochem., 19 (2003) 209 [22] P.Okafor, E.E. Ebenso, U.S. Ibok, U.J. Ekpe and M.I. Ikpl, Trans SAEST, 38 (2003) 91 [23] I.N. Putilova, V.P. Batannik and S.S. Balezin, Metallic Corrosion Inhibitors, Pergamon Press, Oxford, (1960) 30-32 [24] M. A. Quraishi and R. Sardar, Bul. Electrochem., 18 (2002) 515 [25] S. Brinic, A. Gurbac, R. Babic and M Metikos-Hukoric, 8th Ear Symo Corrros Inhib, 1 (1995) 1997 [26] G. K. Gomma and M. H. Wahdan, J. Chem. Tech., 2 (1995) 107 [27] B. Ateya, L. Callow and J. Dawson, Br. Corros. J., 15 (1980) 20 [28] N. Hackerman, Corrosion, 18 (1962) 332 t [29] B.G. Atya, B. E. El – Anadouli and F.M. El –Nizamy, Corros. Sci., 24 (1984) 497 [30] X.L. Cheng, H.Y. Ma, S.H.Chen, R. Yu, X. Chen and Z.M.Yao, Corros. Sci, 41 (1999) 321 [31] M. Bouayed, H. Rabaa, A. Srihiri, J.Y. Saillard, A. Ben Bachir and L.A. Beuze, Corros. Sci., 41 (1999) 501 [32] A. N. Frumkin, Z. Phys. Chem., 116 (1985) 484 [33] O. Ikeda, H. Jimbo and H. Maumura, J. Electronal. Chem., 137 (1982) 127 [34] R. Parsons, J. Electronal. Chem., 7 (1964) 136 [35] J. O. M. Bockris and D. A. J. Swinkels, J. Electrochem. Soc., 111 (1964) 736 [36] B. Ateya, B. EI – Anadouli, F. El- Nizamy, Corros. Sci., 24 (1984) 509 [37] M. A. Quraishi, J. Rawad and M. Ajmal, Corrosion, 54 (1998) 996 [38] S. Muralidharan, M. A. Quaraishi, S. V. K. Iyer, Corros. Sci., 37 (1995) 1739 [39] M. A. Quaraishi, M. A.W. Khan, M. Ajmal, S. Muralidharan and S. V. Iyer, J. Appl. Electrochem., 26 (1996) 1253 [40] V. Chandrsekaran, K. Kannan and M. Natesan , International Journal of Pure and Applied Chemistry 1(2006)101. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 12 ISSN 1466-8858 Volume 14, Preprint 12 submitted submitted11 9 April 2011 Table I Calculated values of corrosion rate, inhibition efficiency and surface coverage for S-AITO in 1.11N HCl and1.12 N H2SO4 from weight loss method Temp. 403K Corrosion Surface Rate Coverage () (mmpy) Surface Coverage () Inhibition Efficiency (IE %) Blank 19.838 - - 261.685 - - 0.1% 11.590 0.4157 41.57 35.998 0.86247 86.24 0.2% 9.807 0.5056 50.56 21.064 0.9195 91.95 0.3% 6.129 0.6910 69.10 8.804 0.9663 96.63 0.4% 4.569 0.7696 76.96 6.575 0.9748 97.48 0.5% 4.123 0.7921 79.21 4.123 0.9842 98.42 Blank 780.04 - - 1739.851 - - 0.1% 474.660 0.3914 39.14 965.606 0.4450 44.50 0.2% 418.940 0.4624 46.24 625.236 0.6406 64. 06 0.3% 367.340 0.5290 52.90 535.296 0.6923 69.23 0.4% 269.598 0.6543 65.43 258.676 0.8513 85.13 0.5% 249.871 0.6793 67.93 65.309 0.9624 96.24 Blank 958.807 - - 2050.575 - - 0.1% 624.679 0.3484 34.84 1559.000 0.2396 23.96 0.2% 557.586 0.4184 41.84 1430.800 0.3022 30.22 0.3% 513.006 0.4649 46.49 909.435 0.5564 55.64 0.4% 410.471 0.5718 57.18 819.940 0.6001 60.01 0.5% 377.036 0.6067 60.67 428.638 0.7909 79.09 (%) 353K 1.12N H2SO4 Corrosion Rate (mmpy) S-AITO 303K 1.11N HCl Conc.of Inhibition Efficiency (IE %) © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 13 ISSNTable 1466-8858 II Volume 14, Preprint 12 submitted submitted11 9 April 2011 Calculated values of activation energy Ea (KJ/mole), Free energy of adsorption Gads (KJ / mole), enthalpy of adsorption H (KJ /mole) and entropy of adsorption S (KJ /mole-1 K-1) for mild steel corrosion in 1.11N HCl and 1.12 N H2SO4 with S-AITO. Inhibitor + Acid S –AITO + 1.11N HCl S-AITO + 1.12 N H2SO4 -Gads (KJ / mole) H (KJ/ mole) (KJ/mole-1K-1) 36.44 - Concentration of Inhibitor (%) Ea (KJ /mole) Blank 39.37 0.1% 40.48 15.06 17.24 19.07 37.54 0.1532 0.2% 41.02 14.28 16.06 17.74 38.09 0.1548 0.3% 44.95 15.17 15.66 17.01 42.01 0.1641 0.4% 45.67 15.46 16.34 17.49 42.73 0.1673 0.5% 45.85 15.23 16.02 17.23 42.91 0.1675 Blank 20.90 17.96 - 0.1% 38.26 20.54 17.89 17.30 35.32 0.1526 0.2% 42.83 20.30 18.20 16.04 39.89 0.1643 0.3% 47.09 21.60 17.70 18.25 44.15 0.1794 0.4% 47.15 21.63 19.59 17.88 44.22 0.1862 0.5% 49.00 22.27 23.33 20.23 46.06 0.1874 At At At 303K 353K 403K - - - - - - S © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 14 ISSNTable 1466-8858 III Volume 14, Preprint 12 submitted submitted11 9 April 2011 Potentiostatic polarization parameters for S-AITO in 1.11N HCl and 1.12N H2SO4 Conc. of inhibitor (%) Ecorr Vs SCE (mV) Icorr A/cm2 Tafel slopes (mV / decade) ba IE% LPR Rp (ohm cm2) - bc 302 K 1.11N HCl Blank -510 700 50 150 - 23.26 0.1 S-AITO -549 384 49 147 45.14 41.56 0.2 S-AITO -540 292 49 143 58.28 54.27 0.3 S-AITO -538 205 47 145 70.71 75.18 0.4 S-AITO -534 139 44 140 80.14 105.73 0.5 S-AITO -530 86 43 139 87.71 165.81 Blank -510 700 50 150 - 23.26 0.1 S-AITO -588 273 47 145 61.00 56.46 0.2 S-AITO -570 228 44 143 67.43 64.08 0.3 S-AITO -563 160 40 137 77.14 84.02 0.4 S-AITO -552 88 37 135 87.43 143.29 0.5 S-AITO -540 60 35 130 91.43 199.56 1.12N H2SO4 353 K 1.11N HCl Blank -505 1000 30 175 - 11.20 0.1 S-AITO -530 568 28 170 43.20 18.38 0.2 S-AITO -527 441 28 165 55.90 23.57 0.3 S-AITO -520 380 27 160 62.00 26.40 0.4 S-AITO -518 239 26 157 76.10 40.53 0.5 S-AITO -510 150 23 155 85.00 57.98 Blank -505 1000 30 175 - 11.20 0.1 S-AITO -572 435 30 166 56.50 25.36 0.2 S-AITO -560 359 28 163 64.10 28.90 0.3 S-AITO -553 279 27 160 72.10 35.95 1.12N H2SO4 © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 15 ISSN 1466-8858 0.4 S-AITO -549 Volume 144 2514, Preprint 15812 85.56 0.5 S-AITO -540 125 87.50 72.19 - 7.78 24 155 submitted submitted 65.09 119 April 2011 333 K 1.11N HCl Blank -483 3000 75 190 0.1 S-AITO -520 1823 75 185 39.23 12.71 0.2 S-AITO -512 1403 72 182 53.23 16.63 0.3 S-AITO -507 1214 72 180 59.53 18.39 0.4 S-AITO -502 806 70 174 73.13 26.89 0.5 S-AITO -496 493 68 170 83.57 42.98 Blank -483 3000 75 190 7.78 0.1 S-AITO -540 1365 70 186 54.50 16.18 0.2 S-AITO -543 1149 70 183 61.70 19.13 0.3 S-AITO -530 1029 68 180 65.70 20.83 0.4 S-AITO -523 579 66 174 80.70 35.88 0.5 S-AITO -510 460 65 170 84.67 44.88 1.12N H2SO4 - © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 16 ISSN 1466-8858 Volume 14, Preprint 12 submitted submitted11 9 April 2011 Table IV A.C. impedance parameters for S-AITO in 1.11N HCl and 1.12N H2SO4 Conc. of inhibitor (%) Surface coverage Cdl Rct Inhibition efficiency 2 2 (ohm cm ) (F/cm ) (IE%) (θ) 1.11N HCl Blank 100.12 13.20 - - 0.1 S-AITO 188.97 10.47 47.02 0.4702 0.2 S-AITO 250.62 8.45 60.05 0.6005 0.3 S-AITO 358.87 6.24 72.10 0.7210 0.4 S-AITO 558.57 4.16 82.21 0.8221 0.5 S-AITO 920.42 3.91 89.12 0.8912 Blank 100.12 13.20 - - 0.1 S-AITO 270.92 8.00 63.04 0.6304 0.2 S-AITO 325.62 6.99 69.25 0.6925 0.3 S-AITO 480.12 5.11 79.15 0.7915 0.4 S-AITO 922.14 2.73 89.14 0.8914 0.5 S-AITO 1672.57 1.56 94.01 0.9401 1.12N H2SO4 © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 17 ISSN 1466-885890 Volume 14, Preprint 12 submitted submitted11 9 April 2011 0.10% 80 Inhibition Efficiency (IE %) 0.20% 70 0.30% 0.40% 60 0.50% 50 40 30 20 10 0 0 50 100 150 200 250 300 350 400 450 Temperature in K Fig.1 Relation between the inhibition efficiency and temperature for mild steel corrosion in 1.11N HCl with S-AITO 120 Inhibition Efficiency (IE %) 100 0.10% 80 0.20% 0.30% 0.40% 60 0.50% 40 20 0 0 50 100 150 200 250 300 350 400 450 Temperature in K Fig. 2 Relation between the inhibition efficiency and temperature for mild steel corrosion in 1.12N H2SO4 with S-AITO. © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 18 ISSN 1466-8858 Volume 14, Preprint 12 submitted submitted11 9 April 2011 0.9 Surface coverage (θ) 303 K 353 K 403 K 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 log Concentration (%) Fig. 3 Temkin's adsorption isotherm plot for 1.11N HCl with S-AITO 1.2 303 K 353 K 1 Surface coverage (θ) 403 K 0.8 0.6 0.4 0.2 0 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 log Concentration (%) Fig. 4 Temkin's adsorption isotherm plot for 1.12N H2SO4 © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 19 Volume 14, Preprint 12 10 submitted submitted11 9 April 2011 Current density (mA/cm2 ) ISSN 1466-8858 1 0.5% S-AITO 0.4% S-AITO 0.3% S-AITO 0.1 0.2% S-AITO 0.1% S-AITO Blank 0.01 -1000 -800 -600 -400 -200 0 Potential (mV vs SCE) Fig.5 for 1.11N HCl 2 Current density (mA/cm ) 10 1 0.5% S-AITO 0.4% S-AITO 0.1 0.3%S-AITO 0.2% S-AITO 0.1% S-ATIO Blank 0.01 -800 -700 -600 -500 -400 -300 -200 -100 0 Potential (mV vs SCE) Fig. 5 for 1.12N H2SO4 Figures 5 and 6 Typical potentiostatic curves for mild steel in 1.11N HCl and 1.12N H2SO4 with S-AITO at 303K © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. 20 ISSN 1466-8858 Volume 14, Preprint 12 submitted submitted11 9 April 2011 250 Blank 0.1% S-AITO 0.2% S-AITO Z (Ohm cm2) 200 0.3% S-AITO 0.4% S-AITO 0.5% S-AITO 150 100 50 0 0 200 400 600 800 1000 Z (Ohm cm2) Figure 7 Nyquist plots for mild steel in 1.11N HCl with S-AITO 600 Blank 0.1% S-AITO 500 0.2% S-AITO Z (Ohm cm2) 0.3% S-AITO 0.4% S-AITO 400 0.5% S-AITO 300 200 100 0 0 200 400 600 800 1000 1200 1400 1600 1800 Z (Ohm cm2) Figure 8 Nyquist plots for mild steel in 1.12N H2SO4 with S-AITO © 2011 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work.