INFLUENCE OF FLUORIDE IONS ON THE PASSIVE DISSOLUTION OF TITANIUM

Steady state, potential step and impedance measurements were used to investigate the influence of fluoride ions on the passive dissolution of Ti in 4.5 M H2SO4 solution. The results indicated that metal dissolution occurs via a surface film, the presence of which was confirmed by a SEM study. Electron diffraction and SIMS measurements have shown this film to be polycrystalline TiO2. A mechanism involving simultaneous formation and dissolution of surface oxide is suggested to explain the results. The ionic current through the film is field-dependent. The dissolution rate of the oxide is determined mainly by the fluoride concentration of the solution. © 1979.