Corrosion of Pb–Ca–Sn alloy during potential step cycles

Potential step was applied to Pb–Ca–Sn alloy electrode at various potential and time regimes. No severe corrosion was observed during potential step cycle with cathodic potential under −140 mV or over −40 mV versus Pb/PbSO4 (3.39 M H2SO4), or at constant potential without stepping. On the other hand, the Pb–Ca–Sn alloy was severely corroded during potential step with cathodic potential from −120 mV to −60 mV and with anodic potential of +40 mV or more positive. The corrosion could not be decreased with periodical rest at 0 mV, while it could be decreased with periodical reduction at high polarization of, e.g. −160 mV. It was found out that the severe corrosion occurs when the oxidation of Pb to PbSO4 and partial reduction of passive film of PbSO4 take turns many times.