Photo-Electrochemical Investigation of Anodic Oxide Films on cast Ti-Mo Alloys. I. Anodic behaviour and effect of Alloy Composition

The anodic behaviour of cast Ti–Mo alloys, having different Mo contents (6–20 wt.%), was investigatedin acidic and neutral aerated aqueous solutions. All sample showed a valve-metal behaviour, owing toformation and thickening of barrier-type anodic oxides displaying interference colours. Growth kineticsof passive films is influenced by both anodizing electrolyte and composition of the starting alloy. Thislast parameter was found to change also the solid-state properties of the films, explored by photoelectrochemicaland impedance spectroscopy experiments. Thicker films (Uf = 8 V/MSE) grown on alloys richer inMo showed more resistive character and a photocurrent sign inversion under negative bias, that revealedan insulating character, whereas corresponding films grown on alloys with lower Mo content, as well asthinner films, behaved as n-type semiconductors. Results are discussed in terms of formation of a mixedTi–Mo oxide phase.