The present study reports on the in situ oxidation of copper to Cu2O and subsequent reduction to metallic copper in an environmental scanning electron microscope. The oxidation was carried out at approximately 125 μm oxygen pressure while the reduction was done at the same pressure using H2 gas. The first visible signs of oxidation occurred in about 2 min: submicron size nuclei of Cu2O formed randomly on the metal surface. No preferred nucleation along grain boundaries could be observed. The surface was completely covered with Cu2O in about 30 min of oxidation time, the final average grain size of Cu2O being approximately 3 μm. The reduction kinetics of Cu2O were slower than the oxidation kinetics, the first visible copper nuclei appearing only after about 6 min of reduction. A reduction mechanism is suggested where the diffusion of copper vacancies from the copper particle-Cu2O interface to the Cu2O-H2 interface limits the overall kinetics. Based on this assumption, a copper supersaturation corresponding to a copper activity of 1.0005 in Cu2O has been calculated.
All Science Journal Classification (ASJC) codes
- Inorganic Chemistry
- Metals and Alloys
- Materials Chemistry