Electrochemical studies of the pitting corrosion of tin in citric acid solution containing Cl −

Abstract

The electrochemical behavior of a tin electrode in citric acid solutions of different concentrations was studied by electrochemical techniques. The E/ I curves showed that the anodic behavior of tin exhibits active/passive transition. Passivation is due to the formation of Sn(OH) 4 and/or SnO 2 film on the electrode surface. Addition of NaCl to citric acid solution, enhances the active dissolution of tin and tends to breakdown the passivity at a certain breakdown potential. Cyclic voltammetry and galvanostatic measurements allow the pitting potential ( E pit) and the repassivation potential ( E rp) to be determined. Potentiostatic measurements showed that the overall anodic processes can be described by three stages. The first stage corresponds to the nucleation and growth of a passive oxide layer. The second stages involve pit nucleation and growth and third stage involve repassivation. The impedance spectrum of pure Sn is found to consist of three intersecting capacitive semicircles at the high and medium frequencies with an inductive loop at low frequencies. The capacitive semicircles occurring at the high and medium frequency are due to the dielectric properties of surface oxide film and dissolution of underlying metal, respectively. The inductive loop at low frequencies results from Cl − adsorption at the pitting region. By increasing the potential the pitting corrosion and the fractal dimension of surface due to pitting increase.