| The concentrations of oxygen and cation vacancy lattice defects in anodically grown titanium oxide films, and their influence on the film during polarization in halide solutions, has been investigated by different techniques. The overall objectives were to investigate the cation vacancy submergence mechanism of passivity breakdown and the possible existence of cation vacancy condensates at the titanium/titanium oxide film interface.; Voltammograms of titanium oxide films exhibit bifurcated oxidation waves within the passive region. It is shown that the first wave is due to the oxidation of halides, while the second wave is probably caused by halide-induced stoichiometric transformations within the film. The second wave is significantly enhanced when iodide or bromide, especially, are present in solution, but not chloride.; The amount of charge passed through the titanium passive film during oxidation of chloride, bromide, and iodide is related to the Gibbs free energy necessary for halide dehydration, which depends upon the halide radius. This conclusion partially explains the ability of a halide to preferentially initiate passivity breakdown on a certain metal compared to others.; Experimental donor density transients obtained by Mott-Schottky analysis of the titanium oxide films are shown to follow a kinetic model of interaction between halides and oxygen vacancies. Transients in the donor density upon exposure of the film to halides have been attributed to oxygen vacancies and halide-filled oxygen vacancies.; The effect of UV illumination of the passive titanium oxide film was found to increase the oxygen vacancy density. This may be explained by the photo-ionization of neutral oxygen vacancies. The electrons released by this film response contribute to a counter-electric field within the film, which suppresses the applied field.; Finally, the positronic depth-profiling technique of Doppler Broadening Spectroscopy was used to investigate the relative changes in the defect structure of titanium oxide films exposed to acidic bromide solutions for different lengths of time. It was found that an increase in the number of positron annihilation events in the near-surface regions occurs with length of exposure time, which would be in accord with cation vacancies being created at the solution/film interface. |
