Analytical & Bioanalytical Electrochemistry

Transcription

1 Anal. Bioanal. Electrochem., Vol. 1, No. 4, 2009, Analytical & Bioanalytical Electrochemistry 2009 by CEE Full Paper Use of Electrochemical Impedance Spectroscopy to Study the Corrosion of Tin in Citrate Solution Es hagh D. Zobayri, 1 Ahmad Rouhollahi, 1, * Mojtaba Hadi, 1 Habibollah Khajesharifi 2 1 Department of Chemistry, Faculty of Sciences, K.N. Toosi University of Technology, Tehran, Iran 2 Department of Chemistry, Faculty of Sciences, Yasouj University, Yasooj, Iran * Corresponding Author; Tel.: ; Fax: s: rouhollahi@kntu.ac.ir Received: 23 November 2009 / Accepted: 27 December 2009 / Published online: 30 December 2009 Abstract- The corrosion and passivation of tin anode in citrate (0.01 to 1.0 M) solution was investigated using steady state polarization, impedance spectroscopy and cyclic voltammetric techniques. Before permanent passive region, two anodic peaks were observed in the anodic polarization curve, corresponding to the consecutive electroformation of Sn(II) and Sn(IV) species. The corrosion current was calculated by the Tafel extrapolation procedure at different concentrations of citrate ion and different ph values. Also, the corrosion resistance at the corrosion potential was calculated from the Nyquist diagram of different concentration of citrate ion. It was found the latter gives more precise results. Keywords- Tin electrode, Corrosion, Passivity, Impedance spectroscopy

2 Anal. Bioanal. Electrochem., Vol. 1, No. 4, 2009, INTRODUCTION The most widely use of tin is its coating of steel in canning industry and subsequently, the corrosion behavior and passivation of tin in organic acids has attracted the attention of many workers [1-19]. Also, the effects of some inorganic anions on the corrosion of tin in inorganic solution have been investigated [11-13, 20-21]. In most case the anodic sweep of tin anode in these solutions exhibit active/passive regions. In the active region, tin dissolves as Sn(II) ions, which are then oxidized to Sn(IV). Passivation results from film formation on the surface by solution-precipitation mechanism. According to these studies, the corrosion behavior and the passivation of tin anode strongly depend on the experimental conditions [22-24]. The present work was devoted to study the corrosion rate and anodic behavior of tin in citrate ion solution using impedance spectroscopy and potentiodynamic techniques. The influence of the concentration of citrate and ph was investigated as well. 2. EXPERIMENTAL A rod of tin (99.99%) was used as a working electrode, which was axially embedded in epoxy resin to offer an active flat disc surface with an apparent exposed surface area of 0.07 cm 2. The electrodes were polished with 0.05 µm α-alumina powder on a polishing cloth to achieve a mirror surface and then rinsed with doubly distilled water and soaked for 15 min prior to each experiment. A graphite rod was used as a counter electrode. The potentials were measured against an Ag/AgCl (3 M KCl) reference electrode. The potentiodynamic measurements were made by using a potentiostat (Autolab, model PGSTAT 30) controlled by GPES software. The electrochemical impedance measurements were obtained by using the same apparatus and were controlled by FRA software. The frequency range was scanned from 10 5 to 10-3 Hz. Apparatus of ph meter (Metrohm, model E-516) was used to measure the ph values. All experiments were carried out at room temperature. All solutions prepared from analytical grade chemicals and doubly distilled water. For each experiment, freshly prepared solutions and a freshly polished electrode were employed. 3. RESULTS AND DISCUSSION Fig. 1 shows the cyclic voltammogram of tin electrode in 0.5 M citrate ion solution. The voltammogram was started at -1.3 and reversed at 0.4 V (vs. Ag/AgCl) at the scan rate of 20 mv s -1. In the positive sweep, the cathodic current corresponding to hydrogen evolution reaction decreases continually to zero at the zero current potential at ca. -1 V (vs. Ag/AgCl). The anodic region on the positive going sweep shows a transition from active to passive state. In the active region, a well-defined peak at -3 mv (vs. Ag/AgCl) is observed because of the formation of Sn(II) species that are oxidized to Sn(IV) [6,8,9]. A slump in the current of this

3 Anal. Bioanal. Electrochem., Vol. 1, No. 4, 2009, peak occurs due to the passivation. The passive region starts from ca. 0.1 V (vs. Ag/AgCl) with a very low and constant current density, which extends up to 0.4 V (vs. Ag/AgCl) without any sign for oxygen evolution. The passivity is attributed to the hydrolysis of Sn (IV) and its subsequent dehydration [9,22-25]. Sn (OH) 4 is highly insoluble, precipitates of which give rise to a passivation film. The generated hydroxides can be converted to the corresponding oxides by aging processes. Therefore, passivation is due to the formation of Sn(OH) 4 and/or SnO 2 film which entirely blocks the active sites on the surface of tin in the passive region potentials [22-24]. In the cathodic direction, the reverse scan exhibits a small cathodic peak at -0.6 V (vs. Ag/AgCl), which may be related to the reduction of the passive oxide film [22]. The anodic charge of the anodic scan is much higher than that of the cathodic scan. It shows the reduction of the oxide film is incomplete and a thin layer of the oxide film remains on the surface [23]. Fig. 1. Cyclic voltammogram of tin in 0.5 M citrate ion solution at the scan rate of 20 mv s The effect of ph on the dissolution of tin in citrate solution The passivation of tin can occur in the solution with different ph values except phs lower than about 1 and higher than about 12. At phs lower than 1 the anodic processes could be described by the following (corresponding to purbaix diagrams [26-27]): Sn Sn e - Sn 2+ Sn e - and at the phs higher than 12: Sn + 3H 2 O Sn(OH) H + + 2e - Sn(OH) 3 - SnO H + + 2e - The tafel plots of tin electrode in 0.5 M citrate ion solution in different phs with the scan rate of 2 mv s -1 are shown in Fig. 2(A). It is observed that an increase in ph decreases the

4 Anal. Bioanal. Electrochem., Vol. 1, No. 4, 2009, corrosion potential of tin. The plot of the corrosion current versus the ph values is shown in Fig. 2(B), which displays the corrosion current is increasing in ph of 4 and the H + ions have an acceleration effect on the corrosion of tin in citrate solution. Fig. 2. (A) Tafel plots of tin in 0.5 M citrate ion solution at the scan rate of 2 mv s -1 and the ph values of a) 1.9, b) 3, c) 4.5, d) 6, e) 8, and f) (B) Relation between I corr versus ph in 0.5 M citrate ion solution 3.2. The effect of citrate concentration on the dissolution of tin The effects of citrate concentration on the corrosion current of tin anode were evaluated by the impedance spectroscopy technique. The experiments were conducted at 25 C. Fig. 3(A) shows the Nyquist diagram of tin electrode in 0.5 M citrate ion solution. The Nyquist diagram is recorded at the corrosion potential and represents a slight semicircle at high frequencies followed by a linear behavior at the lower one, which was simulated by FRA

5 Anal. Bioanal. Electrochem., Vol. 1, No. 4, 2009, software with suggested equivalent circuit R 1 (C 1 [R 2 W 1 ])) [28] shown in Fig. 3(B). The high frequency semicircles are attributed to the combination of double layer capacitance (C 1 ) and corrosion resistance (R 2 ). The linear behavior at low frequencies with a Warburg impedance (n = 0.5) is ascribed to the mass transport of the aggressive citrate ion in the oxide layer. The inverse of the corrosion resistance (1/R 2 ) versus the concentration of citrate ion is shown in Fig. 3(C). It is observed that an increase in citrate concentration increases the corrosion intensity of tin probably because of the adsorption of citrate on the surface of tin and the formation of soluble complex species [22]. Fig. 3. (A) Nyquist diagram of tin in 0.5 M citrate ion solution. (B) Equivalent circuit compatible with the Nyquist diagram. (C) 1/R 2 versus citrate concentration The effects of citrate concentration on the dissolution of tin were also researched using steady state polarization and tafel analysis. The tafel plots of tin electrode were recorded in different concentration of citrate ion with the scan rate of 2 mv s -1. The corrosion current of tin electrode versus logarithm of citrate ion concentration is shown in Fig. 4. It is observed that an increase in citrate concentration increases the corrosion current of tin electrode. Therefore, by this method, it is possible to evaluate the anodic corrosion of tin. By comparing

6 Anal. Bioanal. Electrochem., Vol. 1, No. 4, 2009, Fig. 3(C) (R 2 = 0.997) with Fig. 4 (R 2 = 0.851) it can be inferred the impedance spectroscopy technique has more precise result than that of the steady state polarization technique. Fig. 4. Relation between I corr versus logarithm of citrate concentration (mol/l) 4. CONCLUSION Impedance spectroscopy and cyclic voltammetric techniques were used to study the corrosion and passivation of tin in citrate solution. It was observed that the corrosion potential of tin increases with the increase of H + ion concentration but the tafel analysis showed that this has an acceleration effect on the corrosion of tin. Also, by the impedance spectroscopy and steady state polarization techniques, it was observed that the corrosion of tin increase with the increase of the citrate concentration. REFERENCES [1] J. C. Sherlock, and S. C. Britton, Br. Corros. J. 8 (1973) 210. [2] H. Leidheiser Jr., A. F. Rauch, E. M. Ibrahim, and R. D. Granata, J. Electrochem. Soc. 103 (1982) [3] B. F. Giannetti, P. T. Sumodjo, and T. Rabockai, J. Appl. Electrochem. 20 (1990) 672. [4] V. K. Gouda, E. N. Rizkalla, S. Abd El Wahab, and E. M. Ibrahim, Corros. Sci. 21 (1981) 1. [5] M. S. Morad, and A. A. Hermas, J. Chem. Technol. Biotechnol. 76 (2001) 401. [6] B. F. Giannetti, P. T. Sumodjo, T. Rabockai, M. Souza, and J. Barboza, Electrochim. Acta 37 (1992) 143. [7] A. El Sayed, F. H. Assaf, and S. S. Abd El Rehim, J. Ind. Chem. 19 (1991) 207. [8] F. H. Assaf, A. El Sayed, and S. S. Abd El Rehim, Bull. Electrochem. 7 (1991) 405.

7 Anal. Bioanal. Electrochem., Vol. 1, No. 4, 2009, [9] M. Seruga, and M. Metikos-Hukovic, J. Electroanal. Chem. 334 (1992) 223. [10] M. Seruga, M. Metikos-Hukovic, T. Valla, M. Milun, H. Hoffschultz, and K. Wandelt, J. Electroanal. Chem. 407 (1996) 83. [11] B. N. Stirrup, and N. A. Hampson, J. Electroanal. Chem. 73 (1976) 189. [12] T. Laitinen, K. Salmi, G. Sundholm, P. Viniikka, and A. Yli-Pentii, Electrochim. Acta 37 (1992) [13] Y. M. Chen, T. J. O Keefe, and W. J. James, Thin Solid Films 129 (1985) 205. [14] I. A. Ammar, S. Darwish, M. W. Khalil, and S. Eltaher, Mat. Chem. Phys. 21 (1989) 1. [15] C. M. V. B. Almeida, B. F. Giannetti, and T. Rabóczkay, J. Appl. Electrochem. 29 (1999) 123. [16] C. M. V. B. Almeida, B. F. Giannetti, and T. Rabockai, J. Electroanal. Chem. 422 (1997) 185. [17] S. Kapusta, and N. Hackerman, Electrochim. Acta 25 (1980) 625. [18] S. S. Abd El Rehim, F. Taha, M. B. Saleh, and S. A. Mohamed, Corros. Sci. 33 (1992) [19] M. Drogowska, L. Brossard, and H. Menard, J. Appl. Electrochem. 19 (1989) 231. [20] A. A. Al Suhybani, Br. Corros. J. 24 (1989) 204. [21] H. Mansour, J. Electrochem, Soc. India 33 (1984) 33. [22] S. S. Abdel Rehima, S. M. Sayyah, and M. M. El Deeb, Corrosion Science 46 (2004) [23] S. S. Abdel Rehim, S. M. Sayyah, M. M. El Deeb, Mater. Chem. Phys. 80 (2003) 696. [24] A. E. Smith, Analyst 98 (1973) 209. [25] M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solution, Pergamon, London, [26] F. Seby, M. Potin-Gautier, E. Giffaut., and O. F. X. Donard, Geochim. Cosmochim. Acta 65 (2001) [27] S. A. M. Refaey, and S. S. Abd El Rehim, Electrochim. Acta 42 (1997) 667. [28] F. Rouell, and F. T-Chemla, J. Solid State Electrochem. 7 (2003) 171. Copyright 2009 by CEE (Center of Excellence in Electrochemistry) ANALYTICAL & BIOANALYTICAL ELECTROCHEMISTRY ( Reproduction is permitted for noncommercial purposes.