ANODIC-DISSOLUTION OF LEAD IN PERCHLORIC-ACID SOLUTIONS - THE EFFECT OF SULFURIC-ACID

The anodic dissolution of lead in perchloric acid-sulphuric acid mixtures has been studied using potentiodynamic sweeps and current step measurements. As the surface concentration of lead increases, lead sulphate precipitates at the surface. This solid phase is not in equilibrium with the bulk solution and as a result, chemical dissolution will take place. Thus, for low concentrations of sulphuric acid in perchloric acid, the resulting precipitation is minute and the lead dissolution follows the same mechanism as in pure perchloric acid. However, at higher sulphuric acid concentrations, a complete layer of precipitated lead sulphate can be formed. Under these conditions, the perchlorate ions act as precursors for pitting corrosion. The implication of this on the PbO2 formation is discussed.