Copper Corrosion: II . Kinetic Studies

Abstract

Experimental methods are described for studying rates of formation of soluble and insoluble corrosion products of copper exposed to water containing dissolved oxygen and carbon dioxide. Coulometric reduction indicates that the films formed on copper under these conditions are predominantly of cuprous oxide. Generation of cupric bicarbonate in solution and film growth are constant in rate over long periods, and both are kinetically of first order with respect to dissolved oxygen. Dependence of these rates on the concentration of dissolved carbon dioxide follows no obvious kinetic law, but is such as to suggest that the initial pH of solution is a major factor. Experiments in which either solution or metallic phase is replaced during kinetic measurements demonstrate that a cuprous oxide film on copper may have either an activating or a passivating effect, depending on its mode of generation. The evidence indicates the existence of an electrochemical mechanism for general corrosion of copper by which dissolution and film growth are kinetically linked processes.