Photopotential Measurements During Corrosion of Copper in Aqueous Solutions Available to Purchase

Photopotentials of single crystal copper immersed in water and sodium halide solutions have been measured. Experimental results indicated that cuprous oxide formed on copper immersed in water. In sodium halide solutions, cuprous oxide was formed initially, followed by the formation of the cuprous halide film after prolonged immersion. Observed transient and steady-state photopotentials were attributed to the effect of light on barrier junctions at resulting metal-semiconductor film-electrolyte interfaces. According to the Williams model for the photogalvanic or “Becquerel” effects of binary semiconductor-electrolyte systems, the positive valued photopotentials of copper in water, sodium bromide and sodium iodide solutions indicated that the cuprous oxide, cuprous bromide and cuprous iodide films formed on copper in the respective solutions were p-type semiconductors. Negative photopotentials observed for copper in sodium chloride and sodium fluoride solutions suggest that cuprous chloride and cuprous fluoride films were n-type. Magnitude of the photopotentials of copper in all solutions with the exception of sodium chloride was on the order of 1 to 10 mv. Photopotentials of copper in sodium chloride solutions were approximately an order of magnitude larger. Results obtained in this investigation suggest that photoeffects may be an important factor in metallic corrosion.