Nature of the Corrosion Reaction at the Anodic Oxide Film on Titanium in HCl Solutions

The corrosion of the anodically formed oxide film on titanium has been studied in HCl solutions after the flow of the forming current ceases. Reciprocal capacitance, resistance, and the open circuit electrode potential decrease almost linearly with the square root of the immersion time. Analysis of the kinetic equation governing the corrosion reaction reveals the reactivity of this surface; at the early stage of immersion, dissolution of the oxide dominates the corrosion film thinning/thickening reactions. Regardless of the nature and concentration of the dissolving electrolyte, the results show that the kinetic features encountered during the corrosion process are more or less the same and can be attributed to the inherent properties of the oxide film. The rate of corrosion of this film in HCl solution is slightly lower than that observed in H₂SO₄. This interpretation has been based on the changes in the structural properties of the anodic oxide film across its thickness.