ELECTROCHEMICAL-BEHAVIOR OF TIN IN BICARBONATE SOLUTION AT PH8

The anodic oxidation of tin in 0.1 to 1 m bicarbonate solutions at pH 8 has been studied. The process may be divided into three potential regions: (1) a short active dissolution (Tafel) region; (ii) a dissolution-precipitation region; and (iii) a large region of electrode passivity. The rate-determining step of the reaction in the active-dissolution region is attributed to the diffusion of an ionic species into the solution, the diffusing species being generated at the metal surface. In the region of the first oxidation peak, the reaction rate is controlled by diffusion of CO3(2-) species in solution. When the potential becomes more positive than -0.1V(sce), a highly passivating (most likely SnO2) film is formed on the electrode surface.