Abstract
Effects of small amounts of copper and oxygen in water on the local cell polarization curve of high purity zinc were studied. Further, the formation of local cells was examined as functions of degree of heterogeneity of the metal surface, and the amounts of dissolved copper and oxygen, especially by observing the microscopic structure of deposited copper. When water is deaerated, corrosion of zinc is controlled by the rate of supply of copper ions which act as oxidizing agent, and copper deposits are observed to occur at the surrounding areas of the surface defects. When not deaerated, the corrosion rate of zinc appears to be determined by the reduction of dissolved oxygen on the copper deposits, and copper deposits directly on the surface defects. This was observed for a copper concentration of 5mg/l. It was found that dissolved oxygen accelerates the corrosion when the copper concentration is below 0.5mg/l but acts to inhibit the corrosion at copper concentrations above 5mg/l.
