Investigations on the self-organized growth of TiO2 nanotube arrays by anodic oxidization

The formation mechanism of a thin film of self organized TiO2 nanotube arrays prepared by anodic oxidization of a pure titanium sheet in electrolyte solutions containing potassium fluoride and sulfate was investigated through near-real time monitoring the anode mass, the current density, and the surface topography during the anodization. Energy dispersive X-ray spectrometry was used to monitor the surface composition change during the anodization. The titanium surface was first electrochemically oxidized to form a layer of dense oxide under which nanotubes were originated. With the protection of the oxide layer, long nanotubes could be formed in electrolyte solutions with relatively high pH. The surface composition analysis indicates that the nanotubes were not totally oxidized to TiO2. However, no other elements but Ti and O were found in the oxide film. This work reveals a way to fabricate long nanotubes with defined sizes.