Abstract: The properties of the anodic oxide film formed on Pb and Pb Sn alloy in 4.5 mol/L H₂SO₄ solution at 0.9 V(vs . Hg/Hg₂SO₄) have been investigated by the a.c. technique, open circuit decay curve, and linear sweep voltammetry. It was found that the anodic film grows via a dissolution-precipitation process. The PbO particles in the anodic film may be anodized further by using the interstitial liquid among the PbO particles for ionic transportation. Tin facilitates the process of oxidation of the surface layer of the PbO particles to PbO ^1+x (0<x <1).

Key words: Anodic PbO film, Dissolution-precipitation mechanism, a.c. impedance, Lead-tin alloy