Studies on the anodic and cathodic polarization of lead in sodium sulphate solution

Galvanostatic polarization of lead has been studied in 0.1 M Na2SO4 solutions at various current densities. It was found that, at relatively low current densities, the anodic polarization curve does not reach the oxygen evolution potential. This indicates that the anodic dissolution of lead could continue indefinitely at these rates. At high current densities, the anodic polarization curve is characterized by four distinct arrests corresponding to the formation of PbSO4, PbO, PbOn and PbO2, respectively, followed by transformation of PbSO4 to PbO2 on the electrode surface before the evolution of oxygen. The cathodic reduction curve shows three distinct plateaux corresponding to the transformation of PbO2 to PbSO4, PbO2 to PbO and the latter with PbSO4to spongy lead, successively, followed finally by the formation of PbH2. The correlation between the current, i, and the passivation time, t, for lead in 0.1 M Na2SO4 solution was found to follow the relation: log t=A−nlog i, where A and n are constants. The diffusion and migration of the SO42− and Pb2+ ions through the micropores of the anodic film become the controlling step.