Anodic formation of oxide films on titanium surfaces, in various concentrations of aqueous KOH solutions, have been studied using ellipsometry and micro-Raman spectroscopy. By in situ ellipsometric measurements the coefficient of film thickness growth and indexes of refraction of anodic oxide films have been determined. The voltage at which the oxide film breaks down is strongly dependent on the KOH concentration. Further, the solution concentration strongly influences the potential at which the oxide film is transformed from the amorphous state to crystalline form. Using micro-Raman spectroscopy four crystalline forms of titanium oxides, namely, anatase, brookite, corundum, and rutile, have been identified. The crystalline form of the surface oxide is shown to depend on the applied voltage and on the time of anodization. The micro-Raman spectra reveal that brookite and corundum are intermediate forms of the anodic oxide films and the final film formed is primarly composed of an anatase type of TiO2.
Journal of the Electrochemical Society, 2002, pages B491-B498.
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Publisher's link: http://dx.doi.org/10.1149/1.1510134