THE EFFECT OF SO-4(2) ON THE ELECTROCHEMICAL-BEHAVIOR OF CU IN NEUTRAL MEDIUM

The effect of sulphate ions on the anodic behaviour of copper in neutral aqueous solutions of various Na2SO4 concentrations was studied by cyclic voltammetry and chronocoulometry. The results show that SO42- ions increase film formation on Cu in the passive range but also its anodic dissolution in the transpassive region at potentials as low as 0 V sce. The breakdown of passivity is initiated by nucleation and growth of pits through the passivating film. The cathodic charge due to the reduction of soluble Cu(II) species formed during the transpassive process increases exponentially with holding time in the transpassive region and with SO42- concentration. SO42- ions increase the amount of soluble Cu species. Sweep rate studies indicate that film formation in the presence of SO42- can be reversible or controlled by a chemical step, depending on time scale, pH, and SO42- concentration.