Cyclic voltammetric behaviour of copper rich brasses in NaCl solution

Abstract

The electrochemical behaviour of copper rich brasses (containing 13-39%Zn) in aerated NaCl solution (pH = 6·6) was studied by a cyclic voltammetric technique complemented by X-ray diffraction. The behaviour of pure zinc and copper was studied for comparison. For the alloys, in the forward sweep two well defined potential regions can be discerned. In the first or subcritical potential region, preferential dissolution of zinc occurs, and the anodic sweep exhibits two anodic peaks A1 and A2, corresponding to the formation of ZnO and the Zn(II) soluble species respectively. Above the critical potential, the current rises sharply as a result of simultaneous dissolution of copper and zinc. On further increase in anodic potential two additional peaks A3 and A4 appear before the passivation region is reached. Peak A3 is assigned to the formation of CU₂O and CuCl while peak A4 is related to the formation of CuO. It is probable that ZnO is formed within the potential range of these two peaks. X-ray analysis of the passive surface confirms the existence of these compounds. The back sweep shows an activation anodic peak As and three cathodic peaks before attaining the hydrogen evolution potential. The sharpness, heights, and locations of the different peaks depend greatly on the composition of the alloys, the concentration of the electrolyte, and the scan rate.