Effect of polarisation mode, time and potential on the properties of the passive layer on lead-tin alloys

Taking into account the dynamic behaviour of the passive layer formed on lead and lead-tin alloys, this work emphasises the effect of the polarisation potential and the polarisation time on the electronic conductivity of the passivation layer. When the lead electrode was polarised in the passivity region (700 mV versus Hg/Hg2SO4 electrode), the polarisation resistance increased but decreased when tin was alloyed. This behaviour is interpreted by the increasing formation of semi-conducting PbO and conducting tin oxide. With a potential incursion in the PbO2 region (1500-2000 mV), semi-conducting lead oxide, PbOx, was formed. The decrease in polarisation resistance is explained by the electronic properties of PbOx which is assumed to be less resistive than PbO, and, subsequently, the increase in polarisation resistance versus time is interpreted by the reduction of PbOx at 700 mV.