A COMPUTER-SIMULATION OF VOLTAMMOGRAMS DESCRIBING THE ACTIVE-PASSIVE TRANSITION OF PB IN SULFURIC-ACID

A computer simulation of active-passive transition voltammograms of Pb in 5M H2SO4 is presented. The model implies alternative pathways lead ing to the formation of inner and outer structurally different PbSO4 l ayers. The inner layer consists of a disordered crystalline conducting phase, which is formed following an instantaneous nucleation and two- dimensional growth mechanism under charge-transfer control. Electrodis solution of Pb proceeds by the diffusion of cations through the inner layer and, when Ph(2+) ion concentration in solution exceeds the criti cal supersaturation concentration, the precipitation of the outer high ly crystalline PbSO4 layer takes place, leading to passivation. Calcul ations are based on previously reported kinetic data. Good agreement w as found between theory and practice.