Anodic Oxide Film Formation on Tin

Thin anodic oxide films have been grown on tin by the galvanostatic technique in buffer solutions (pH 4.20 to 12.06) up to 2 to 2.8 V_SCE. The similarity observed between the anodic-charging curves on tin and those on valve metals indicates that an amorphous barrier oxide is first formed on tin, and his oxide undergoes mechanical failures that cause O₂ evolution as the thickness increases. The behavior of tin during anodic oxidation resembles in many respects the kinetics of anodization of valve metals. This conclusion has been deduced from the linearity between the logarithm of current density (CD) and (1) the logarithm of the oxide formation rate, (2) the reciprocal capacity, and (3) the potential. Ionic transport under high electric fields according to the Verwey model is responsible for oxide growth on tin. While the efficiency for oxide formation is high for solutions of pH = 10 and below, it decreases appreciably at pH = 12 because of the increase of oxide dissolution.