Effect of Two-Step Anodization on Structure of TiO2 Nanotube Arrays

A two-step anodic oxidation was used to prepare TiO2 nanotube arrays with controllable structure and reproducibility by the isobarically anodization of pure Ti foil. The morphology and structure of TiO2 nanotube arrays were characterized by high resolution scanning electron microscopy (SEM). Moreover, the formation mechanism of TiO2 nanotube arrays was discussed. While the effects of anodic oxidation voltage and oxidation time on the diameter and length of nanotubes were further studied. The "field-assisted dissolution" model can perfectly explain the four stages of the first oxidation process, combined with the theory of oxygen bubble mould, to produce an electron flow during the growth of the oxide film, and oxygen bubbles hinder the upward growth of the barrier oxide film. The formation of pores resulted by bubbles evolution can be a good explanation of the TiO2 nanotubes which show a large tube containing the structure of small tubes. The results demonstrate that with the increasing of oxidation time and oxidation voltage, the tube diameter, tube length and tube number of large tube have a tendency to increase obviously. The preparation of TiO2 nanotubes by anodic oxidation is simple and easy to operate. It can efficiently and easily prepare TiO2 nanotubes with excellent morphology and broaden its application range.