Anodization of Highly Ordered TiO₂ Nanotube Arrays Using Orthogonal Design and Its Wettability

Using orthogonal design of experiments (DOE), the highly ordered TiO₂ nanotube arrays on Ti6Al4V alloy was achieved by anodic oxidation in a standard two-electrode system. According to the L₁₆(4⁵) orthogonal array, sixteen experimental runs were set for anodizing voltage, duration time and H₂O content in the electrolyte with four different levels. Scanning electron microcopy (SEM) images showed the various features of TiO₂ nanotubes anodized at different electrochemical conditions. The long neat nanotube with honeycomb-like structure was also formed in an array. The range analysis and variance analysis of DOE revealed that the voltage was the primary factor to influence the dimension of the anodized TiO₂ nanotubes. The sequence of influential factors was voltage > duration time > H₂O content. The optimal level for the H₂O content and duration time was 4 wt% and 3h, respectively. The surface wettability of Ti6Al4V alloy became hydrophilic and enhanced with the anodizing voltage increasing.