Abstract
Using X-ray photoelectron spectroscopy (ESCA), the surface compositions of the nickel substrates and the cathode films formed in chromic acid solutions were examined as functions of the cathode potential. In the potential range more positive than -0.75Vvs.SCE, where cathodic etching of substrate metal takes place, nickel oxide films formed on the substrate were reduced to metallic nickel and the cathode films consisted of a trivalent chromium compound containing bound water. In the range more negative than -0.75V, the substrate was covered with oxidized nickel and the cathode film was analysed to be a trivalent chromium compound equivalent to CrO(OH)H2O. Further, the hexavalent chromium compound was found on top of the cathode films. At the potential where chromium metal deposits, the oxidized nickel layer was again reduced to metallic nickel. Thus, it is likely that the changes in the surface composition of the nickel substrate play an important role in chromiumdeposition.
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