Differential reflectometry of corrosion products of copper

The new technique of differential reflectometry was applied to study some fundamental corrosion processes for copper. Free corrosion in air for one day yielded differential reflectograms characteristic of mixed oxides of Cu₂O and CuO. With increasing time of exposure to air, the reflectograms evolved into typical CuO patterns. Similarly, free corrosion of copper in distilled water yielded mixed oxides of Cu₂O and CuO. Holding copper potentiostatically near the boundary between these two corrosion products as shown on the Pourbaix diagram always yielded at first a mixed oxide which turned into the stable species after several days of polarization. It was further found that copper held potentiostatically first in the CuO region and then in the Cu₂O region of the Pourbaix diagram does not lose the characteristic patterns of CuO. This suggests that the sudden shift in potential induces growth of Cu₂O under the existing CuO layer without dissolving the CuO.