Passivation of titanium in molybdate-containing sulphuric acid solution

The effect of molybdate ions on the passivation reaction of commercial pure (CP) Ti in sulphuric acid solution was studied by conducting an immersion test, measuring dc polarization curves and electrochemical impedance spectroscopy (EIS). It is found that the addition of molybdate in boiling sulphuric acid with concentrations higher than 10 −3 M could greatly reduce the corrosion rate to a negligible value. dc Polarization curves showed that the passivation behaviour was strongly affected by the solution temperature as well as the concentration of molybdate ion present in the sulphuric acid. The passive film resistance ( R pf) determined by EIS was found to increase with the externally applied anodic potential and/or with the molybdate ion concentration. The increase of R pf is mainly attributed to the thickening process of oxide film at more noble potentials.