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The process of Ag2O formation has been investigated in 0.1M, 0.3 M, 1.0Mand 2.0 M NaOH solutions on polycrystalline Ag electrodes by cyclic voltammetry potentiostatic pulse and SEM techniques. The SEM micrographs of the chemically polished Ag surface and the surface after oxide formation revealed considerable roughening of the Ag surface after Ag2O formation and reduction. The roughening was more pronounced at higher NaOH concentrations, indicating that only the first cycle or pulse applied on a freshly polished Ag electrode should be considered in mechanistic studies of Ag2O formation. In the given range of NaOH concentrations, it was shown that the process is not controlled simply by the diffusion of the reacting species.Anucleation phenomenon was clearly detected in all the examined solutions. The SEM micrographs confirm that the two anodic peaks, present on the voltammograms of Ag2O formation correspond to two types of oxide film, i.e., non-homogeneously and homogeneously distributed ones. Potentiostatic formation of the oxide at potentials corresponding to the first and second anodic peak yielded simple cubic Ag2O but of very different grain size.

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We report on the chemical and electrochemical corrosion of Ti, Ti 3 SiC 2 , and Ti 4 AlN 3 in HCl and H 2 SO 4 solutions. The chemical corrosion of Ti 3 SiC 2 under conditions similar to those used industrially for the electrolysis of HCl ͑15% HCl, 65°C͒ is significantly better than that of pure Ti, indicating that it could be a promising substrate for dimensionally stable anodes. The enhanced resistance is attributed to the formation of a thin, passivating SiO 2 -based layer. The same layer protects Ti 3 SiC 2 during its anodic oxidation. After a 4 day period, during which the rate of growth of the SiO 2 -based layer is initially high, but then slows to a steady rate of about 130 m/yr cm 2 is established, which translates to a Ti dissolution rate of ϳ9 ϫ 10 Ϫ4 mol/yr cm 2 . Analysis of Mott-Schottky plots and electrochemical impedance spectra show that the passive films that form onto Ti and Ti 3 SiC 2 in 1 M HCl and 1 M H 2 SO 4 at room temperature are n-type semiconductors dominated by space-charge capacitances. The films forming on Ti 3 SiC 2 have significantly lower space-charge-layer thicknesses and higher donor densities than those that form on Ti. Preliminary results for Ti 4 AlN 3 indicate that the passive film formed is a p-type semiconductor.

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