The anodic behaviour of tin in alkaline solutions—II. 0·1 M sodium carbonate and 0·005 M potassium chromate solutions

Abstract

Tin anodically polarized in 0·1 M sodium carbonate solution shows similarity to polarization in 0·1 M sodium borate only at the higher current densities, e.g. 56 μA/cm 2. This is due to the high solubility of tin oxides in deaerated sodium carbonate. At low current densities passivation does not take place. In contrast, passivation in 0·005 M potassium chromate solution occurs at a very low current density, 2·8 μA/cm 2. Stannous oxide is oxidized to stannic oxide above a potential of +0·2 V relative to Ag/AgCl. In the case of the chromate solution, however, the oxide-film thickness increases even after the oxygen-evolution potential is reached, which does not occur in carbonate or borate solution.