A Mechanism for the Atmospheric Corrosion of Copper Determined by Voltammetry with a Strongly Alkaline Electrolyte

A recently developed voltammetric technique using a strongly alkaline electrolyte ( 6 M KOH + 1 M LiOH ) was successfully applied to clarify a corrosion mechanism of copper under atmospheric conditions. In contrast to conventional potentiometric methods with neutral or weak alkaline electrolytes (e.g., 0.1 M KCl), the developed method could give qualitative and quantitative information about the corrosion products of copper, including oxides (i.e., Cu 2 O and CuO) and hydroxide [ Cu ( OH ) 2 ] . In the presence of water under such atmospheric conditions, Cu ( OH ) 2 was the initial corrosion product formed on a copper surface. However, the surface Cu ( OH ) 2 layer did not grow much but dehydrated to become a layer of CuO. The thus-formed CuO layer grew until it became several molecules thick ( ∼ 2 nm ) . For further progress of corrosion, an inner Cu 2 O layer was generated by the proportionation reaction between the CuO layer and the base metal Cu. The inner Cu 2 O layer grew for the subsequent oxidation until the thickness reached a certain value ( ∼ 35 nm ) . For further oxidation, the top CuO layer grew again preferentially over the inner Cu 2 O layer.