Key Anodization Factors for Determining the Formation of TiO2 Microcones vs Nanotubes

In this study, the key anodization parameters of titanium for the formation of microcones were studied in detail. As the voltage increases, titanium oxides tend to transform from amorphous nanotubes to anatase microcones under certain electrolyte conditions. We found that a very small amount of H2SO4 is essential for the formation ofmicrocones. In addition, if the concentration of HF is too small, a barrier-type oxide is formed. In contrast, the surfaces of the formed nanotubes are quickly dissolved at high concentrations of HF. The formed microcones have an average diameter of 2.58 mu m and a height of 3.88 mu m. The formation mechanism of the TiO2 microcones is related to the changes in the molar volumes of titanium metal and its oxide. From the current-time transients, the current density is considerably higher during the formation of TiO2 microcones compared to the formation of other structures, indicating that a high current leads to extremely high local heating, resulting in the amorphous-to-anatase phase transformation. (C) 2017 The Electrochemical Society.