Formation, microstructures and crystallization of anodic titanium oxide tubular arrays

Formation of highly ordered TiO2 nanotubular arrays during anodization of titanium can be elucidated by using the equifield strength model and a double-layer structure. The two characteristic microstructural features of anodic titanium oxide (ATO) in comparison with anodic aluminium oxide (AAO), a thin titanium hydroxide layer and an O-ring like surface pattern, were investigated using scanning electron microscopy and high resolution transmission electron microscopy (HRTEM). Field-enhanced dissociation of water is extremely important in the formation of the nanotubes with a double-layer wall and an O-ring-like pattern, and in the determination of porosity. The relations between porosity of the ATO films and the anodization conditions, such as current density and electric field strength, have been established. Crystallization of the anodic TiO2 nanotubular arrays was also achieved and the microstructures were studied by using HRTEM.