Tooru Tsuru1 and Shiro Haruyama1
1Department of Metallurgical Engineering, Faculty of Engineering, Tokyo Institute of Technology, Tokyo
Conductance measurements have been carried out of a thin copper film electrode under galvanostatic polarization conditions in a neutral borate buffer solution of pH 8.39, and the conductance- and potential-coulomb diagrams during the formation and reduction of surface oxides have been obtained. Results revealed that the anodic oxide films on Cu were Cu2O, CuO and Cu2O3. The amount of Cu2O formed was almost independent of potential, except for a peak value at -0.1 V. CuO was found to form at potentials more noble than 0.0 V and Cu2O3 more noble than 0.6 V. The thickness of these two oxides increased with increasing potential. The total thickness of the oxide films formed by potentiostatic oxidation for 5 min was 10∼30 Å. In the galvanostatic reduction, the oxides were reduced successively, Cu2O3→CuO → Cu2O → Cu; reactions CuO → Cu2O and Cu2O → Cu were confirmed by resistometry. During an open-circuit decay, Cu2O3 dissolved chemically and CuO was diminished by reaction of Cu+CuO → Cu2O. In galvanostatic oxidation, it was found from resistometry that the anodic formation of Cu2O and CuO occurred similtaniously with a higher ratio of CuO at more anodic potentials.
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