Titanium dissolution and passivation were studied in NaOH aqueous solution using open-circuit potential, potentiodynamic and potentiostatic techniques. Potentiodynamic data showed that the active-passive transition involves active metal dissolution followed by formation of a poorly conducting passive oxide film that passivates the electrode. The critical current density varied with pH as d log jm/dpH = -0.098 in the pH range 11.00-14.00, while the passivation potential is changed according to the following two features: at pH 10.55-13.00, dEm/dpH = -0.06 V; and at pH 13.50-14.00, dEm/dpH = -0.40 V. The apparent activation energy, E*, was calculated from the slope of the Arrhenius plot and was found to be 12.6 kJ mol-1. Current-time transients showed that the growth of titanium oxide passive film is a diffusion-controlled process. XPS measurements indicated that the passive oxide film consists mainly of TiO2 and a mixture of suboxides of Ti2O3 and TiO.
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