Anodic oxide films on titanium formed in molten salt electrolytes—II. Effect of formation electrolyte on non-stoichiometry of the film

Abstract The effects of formation conditions, especially the electrolyte, on the non-stoichiometry of the anodic oxide films of titanium have been studied. The electrolytes were molten sodium nitrite, molten sodium nitrate and molten mixture of these salts and sodium peroxide, which was used to change the oxide-ion concentration in the melts. Films with the least crystal imperfections are formed in molten sodium nitrite. This result is supported by the build-up curve of formation potential, the photocurrent and the dielectric loss of the film. In other molten salts, impurity concentrations in the films are controlled by oxide-ion concentrations in the melts. At higher temperatures, oxide ion and metal cation are presumed to move easily in the growth of the film and crystallization of the film proceeds rapidly.