Surface Morphology and Phase Transitions of Anodic TiO<sub>2</sub> Films Induced by Hydrothermal Exposure

Abstract

A dense TiO2 film was fabricated on the titanium surface using the anodization technique. Surface morphology and phase structure of anodic TiO2 film were investigated before and after the hydrothermal exposure at 160 °C for 24 h. The hydrothermal solution was 3.5 wt% NaCl solution and the films were either immersed in NaCl solution or exposed to water vapor during the exposure. It was found that the as-prepared anodic TiO2 film consisted primarily of amorphous oxides and exhibited a relatively smooth surface. After the hydrothermal exposure, lots of rod-like crystals were formed on the solution-immersed film, while aggregated fine nanoparticles emerged on the vapor-exposed one. Thin film X-ray diffraction analysis indicated that the hydrothermal exposure transformed amorphous oxides into crystalline anatase. The corrosion behavior investigation showed that the structural transition of anodic TiO2 film during the exposure reduced the corrosion resistance of anodized titanium greatly.