Electrochemical behavior of tin anode in ascorbic acid solutions

Abstract

The anodic behavior of tin in ascorbic acid (AA) solutions was investigated using cyclic and/or linear sweep voltammetry and chronopotentiometry method and complemented by XRD and SEM examination. The results showed that the cyclic voltammetric curves in 0.5 M ascorbic acid at 18 ± 0.5 °C involves active/passive transition followed by pitting corrosion. In the active region, Sn dissolves as Sn2+ and Sn4+ and dissolution process is under diffusion control. Passivation is due to deposition of Sn(OH)4 and/or SnO2 on the electrode surface. Pitting corrosion is attributed to local dissolution of the passive film by the adsorbed AA molecules and initiating of pitting attack at a pitting potential Eb. Increasing the acid concentration and temperature enhances the anodic dissolution and shifts Eb to more active direction. Addition of Cl−, Br− and I− in AA enhances both the anodic dissolution and pitting corrosion of Sn. The extent of enhancements depends upon the type and concentration of halide added. The chronopotentiometry curves at constant current densities revealed that increasing the imposed current density decreases the time needed to passivation tp. Addition of low concentrations of Cl−(<5 × 10−5 M) in 0.5 M AA induces pitting corrosion while higher concentrations of Cl− prevent the passivation and the electrode remains in its active state.