Copper Corrosion II. Kinetic Studies

Experimental methods are described for studying rates of formation of solu-ble and insoluble corrosion products of copper exposed to water containing dis-solved 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 o 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 r metallic phase is replaced uring kinetic measurements demonstrate hat a cu-prous oxide film on copper may have ither 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 dis-solution and film growth are kinetically l inked processes. P re l iminary work (Part I; preceding paper) indi-cated the need for concurrent measurements of rates of format ion of soluble and insoluble corrosion prod-ucts in the Cu, H20, O~, CO2 system. The technique developed for this purpose was designed to break a wide area of new ground, rather than to obtain pre-cise kinetic data