NEW OBSERVATIONS ON THE ANODIC-OXIDATION OF COPPER IN HOT ACIDIFIED COPPER-SULFATE SOLUTIONS

The anodic oxidation of copper in acidified copper sulfate solution has been investigated by potentiostatic and voltammetric techniques. The morphology and composition of the films were determined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The passive layer is mainly composed of CuSO4. The presence of a Cu2O phase becomes detectable after multiple sweeps and thorough rinsing of the electrode with water at the end of the experiment. The effects of electrolyte composition and temperature on the phenomenon of passivation are also discussed. The initial steps of the copper dissolution were found to obey Tafel kinetics, and the maximum dissolution current, as well as the limiting transpassive current, was controlled by the rate of diffusion of cupric ions. The phenomenon of current oscillations occurs at potentials near the peak current upon scan reversal, suggesting that oscillations only occur with the formation of a sufficiently thick film. Oscillatory behavior disappears when conditions favor salt film stability.