Dissolution electrochimique des films anodiques du titane dans l'acide sulfurique

Abstract

Electrochemical dissolution of anodic oxide films on Ti in H 2SO 4 is studied by the use of an optical—electrolytic cell adapted for in situ ellipsometric and electrochemical measurements. Films were grown on electropolished Ti surfaces by anodic oxidation in 0.5 mol dm −3 H 2SO 4 for duration of 30 s, in the potential range from 0 to 100 V. Electrochemical dissolution of these films was performed in the potential range between −0.4 and −0.9 V sce. The potential at which electrochemical dissolution is fastest and homogeneous is determined. In addition it is shown that for potentials more cathodic than −0.8 V, TiH 2 is formed on the electrode surface, if polarization lasts sufficiently long. THe commencement of formation and dissolution of anodic films was monitored by potentiostatic j-E curves and variations of ellipsometric azimuths P and A. by potentiostatic and ellipsometric measurements it was confirmed that complete reduction of anodic films is possible. A possibility is indicated for calculating the refractive index of anodic film during its dissolution by observing the time of successive diminution of film thickness and using the variations of ellipsometric azimuths P and A.