The effect of donor density, ND on the critical localized breakdown potential, Eb of the passivity on Ti was investigated in bromide-containing aqueous solutions. Oxide films of approximately fixed thickness were galvanostatically grown on Ti in 0.5M H2SO4 at various current densities. The ND was estimated using Mott–Schottky analysis. The stable localized breakdown induced by bromides manifested itself in potentiodynamic current-potential curves by a sudden current increase at Eb. The passive film on Ti was n-type and oxygen vacancies were considered as majority defects. The Eb tended to decrease as the oxygen vacancy and bromide concentration increased. Additionally, the Eb of anodically grown films was foundto increase with the potential scan rate, inversely of the behaviour observed for the native oxide on Ti, but in concert with corresponding relationships followed by other metals/alloys and predicted by the point defect model. Physico-electrochemical processes leading to growth and breakdown of passivity on Ti could be understood in terms of a point defect model. The higher susceptibility of titanium oxide to local breakdown in presence of bromides than chlorides was interpreted by considering electrochemical reactions occurring at the TiO2|solution interface and their effect on film surface and bulk properties upon increasing the potential during the positive-going potential scan. Finally, was noted that a further understanding of the mechanism of bromide-induced passivity breakdown on Ti might be useful to achieve optimized anodization conditions for ordered oxide nanostructures with desired properties in electrolytes other than fluorides and perhaps at lower anodization potentials.

Understanding the Effect of Bromides on the Stability of Titanium Oxide Films Based on a Point Defect Model. Sazou, D., Saltidou, K., Pagitsas, M.: Electrochimica Acta, 2012, 76, 48–61