ANODIC-OXIDATION OF TITANIUM IN 1M H2SO4, STUDIED BY RUTHERFORD BACKSCATTERING

At various stages of the anodisation process we follow the growth and composition of anodic films formed galvanostatically on titanium in 1M H2SO4, at ''high'' current density (12 mA cm-2). Rutherford backscattering gives the film thickness and stoichiometry. We find thicknesses in agreement with the literature. Using a new fitting procedure of the RBS spectra allowing to let the film stoichiometry vary continuously from the surface to bulk titanium, we find the oxygen and titanium concentration profiles, of similar shape at different stages of growth, and exhibiting a continuous transition from oxide to metal. Oxygen overstoichiometry is observed in the outer part of the oxide films. The assumption of an hydrogen containing outer layer provides a possible explanation for the excess of oxygen and allows a noticeable improvement of the fitting of RBS spectra. Hydrogen presence is indeed confirmed by ERA measurements. The deep penetration of the oxygen profiles in the bulk points to oxygen dissolution in the metal with a large diffusion coefficient.