Influence of Small Amounts of Impurities on Copper Oxidation at 600–1050°C

Abstract

In order to study the influence of small amount of impurities on the copper oxidation kinetics, the oxidation was examined at 600–1050°C in 0.1 MPa oxygen atmosphere using 99.5% (2N) and 99.9999% (6N) pure copper specimens. The influence of impurities has been discussed considering the roles of the nonprotective CuO layer, the impurity layer at the Cu₂O–Cu interface, and the diffusion of copper in the Cu₂O layer. The nonprotective CuO layer for 2N copper can greatly enhance copper oxidation. However, the impurities concentrated at the region near the Cu₂O–Cu interface for 2N copper can slow oxidation. Contrary to the presence of metallic impurities, such as Ni, Sb, and Pb, the nonmetallic elements As and Se dissolved in Cu₂O have a deleterious influence on the outward diffusion of copper. Grain-boundary diffusion in Cu₂O can somewhat contribute to 2N copper oxidation at 850–1050°C, but its effect in enhancing oxidation at 600–800°C is weaker than the effect of the impurity layer at the Cu₂O–Cu interface in impeding oxidation.