Both in-situ ellipsometry and cyclic voltammetry were used to investigate the corrosion behavior of copper electrode in borax solution. Effective-medium model was employed to analyze the optical measurement results. The theoretical results suggested that both the thickness and composition of the oxide film were definite after the electrode processes reached stable states. The divalent oxide CuO was more compact and protective than the monovalent oxide Cu2O. The disproportionation of Cu^+ was probably involved during the reduction process of CuO, which was helpful to improve the anti-corrosive property of the oxide film. It was shown that the reductions of CuO and Cu2O could occur simultaneously under the potential of -0.45V(vs. SCE). The optical results not only were in good agreement with the electrochemical and photoelectrochemical measurements qualitatively, but also could be used to calculate quantitatively the values of the thickness and refractive iodex of the surface film. According to these calculated results and the effective-medium model, the composition of the surface film, which changes with the duration of chemical reactions and provides important evidences for the reaction mechanism studies, could be determined.

Key words: COPPER, CYCLOVOLTAMGRAPH, ELLIPSE POLARIZATION SPECTROMETRY, PASSIVATION, CORROSION, MEDIUM CORROSION TEST, ELECTRODE REACTION