Growth and Crystallization of Titanium Oxide Films at Different Anodization Modes

The growth process and crystallizing mechanisms of anodic oxide films on highly pure titanium plates are studied in 0.1 M H2SO4 solution at potentiostatic, potential-sweep and combined anodization modes with the same final voltage of 30 V. The influences of anodization mode on the crystalline behavior, surface morphology, chemical composition and electrochemical properties of titanium anodized films are studied. The results show that the potentiostatically grown film is thicker, rougher and more crystalline than the film formed at potential-sweep and combined modes. The titanium oxide film contains an outer porous layer and an inner barrier layer, and the barrier layer of the slow-grown film is much thicker than that of the fast-grown film. For titanium oxide film formed in the potentiostatic mode, "flower-like" crystalline grains are developed due to very high local current density at the local defect sites of titanium surface. In the case of potential-sweep and combined anodization modes, the crystallization of titanium oxide film is homogeneous, which is mainly caused by the internal compressive stresses.