Photoelectrochemical study of the corrosion product layers on copper in weakly acidic solutions

Abstract

The nature of the surface layers grown on copper electrodes in free corrosion conditions in unbuffered aerated Na 2SO 4 solutions (pH = 3.0–6.0) was investigated by photoelectrochemical methods. The formation of cuprous oxide has been revealed by means of a careful study of the photocurrent spectra obtained in situ. The growth of n-Cu 2O has been observed to occur with or without Cu 2+ ions in solution in a narrow range of pH around five. More acidic solutions seem to favour the formation of p-Cu 2O both in absence as well as in presence of Cu 2+ ions in solution ([Cu 2+] = 0.05 M). The addition of chloride ions in variable amounts ([Cl −] ⩽ 0.1 M) seems to affect mainly the corrosion rate of copper electrodes at low concentrations ([Cl −] ⩽ 10 −2 M). At higher chloride concentrations changes in the semiconducting properties as well as in the nature of the corrosion layers can occur. The presence of complex transients in the photocurrent vs time plots has been related to the presence of chloride ions in solution.