First principles study on formation mechanism of anodization process of titanium

Anodized TiO2 nanotube array (TNA) is a promising material which has attracted wide attentions but its presumed growth mechanism remains enigmatic yet. In this research, Density Functional Theory (DFT) was applied to determine the growth mechanism of TNA on the surface of titanium foil. The firstprinciples within the generalized gradient approximation (GGA) and Perdew-Burke-Emzerhof (PBE) exchange-correlation function based on the density functional theory was employed to calculate anodization process on anatase TiO2 (001) surface. Calculation results indicated that the chain reaction model for multimolecular HF destructive adsorption on surface of TiO2 layer was the key step of anodization to form the initial defects. The HF molecule inclined to adsorb on the defective site owing to the low adsorption energy, resulting in the successive corrosion to deepen the defect and finally to form the nanotube. Complex ion [TiF6]2– can be formed in electrolyte by interaction with 5c-Ti and F- in this corrosion process. This theoretically calculation confirms the growth mechanism hypothesis of TNA.