Formation Mechanism of Self-Organized TiO2 Nanotube Arrays

This paper investigates the formation mechanism of TiO2 nanotubes on pure Ti foil. Oxygen formed on the anode controls the final dimension of the TiO2 nanotubes. The length of the TiO2 nanotubes is as long as 15 mu m obtained in the electrolyte containing ethylene glycol and water (98:2 v/v) + 0.3 wt% NH4F for 24 hours. Bent anode was employed to show that there is no nanotube formed on the bent part. Different anodization times were used to examine the influence of fluorine ions. We also used different types of Ti foils, processed under cold rolled condition, and hot-rolled followed by annealing to evaluate the effect of pre-processing condition on the oxygen formation at their surfaces. Electrochemically and chemically treated Ti foils with exposed grain boundaries were used to reveal the growth of nanotubes on the Ti grains. Finally, a dissolution model was used to calculate the dissolved mass of TiO2.