A POTENTIOSTATIC STUDY OF THE OXIDATION O F PBSO4 INTO PBO2 AT 3 ELECTRODE MATERIALS - PB AND PB-SB, PB-CA ALLOYS

The different processes occuring during the oxidation of lead sulfate into lead dioxide in sulfuric acid solutions have been determined, inc luding the initial nucleation process, the period of crystal growth, a nd the final phase of overlapping of the crystallization sites. This s tudy was performed using the potential step technique under potentiost atic conditions. Three different electrode material compositions were investigated in order to compare their efficiencies as positive plates employed in lead acid batteries. These electrodes were : pure lead, a ntimony-lead alloy and calcium-lead alloy. The transient responses, we re analysed following the classical theory of electrocrystallization. For the three types of electrode materials, it was concluded that the initial step was a three-dimensional and instantaneous nucleation of P bO2 inside the layer of PbSO4 followed by an hemispherical diffusion c ontrolled growth of the crystallites through the overall thickness of the PbSO4 layer.