Micro-Vickers hardness of anodic TiO2 nanotubes in terms of anodizing temperature

초록

Anodic TiO2 nanotubes have been studied for a long time for catalytic applications because of it chemical stability as a host material as well as easy processing technique. However, most academic literatures dealt with its cutting-edge applications but its fundamental mechanical characteristics such as Micro-Vickers hardness were rarely studied. Herein, TiO2 nanotubes with different lengths and walls were prepared by anodization at different temperatures ranging from 0°C to 35°C in ethylene glycol(EG) based electrolyte containing 3 mL deionized water and 0.56g NH4F for different durations. The prepared TiO2 nanotubes were post-treated by annealing at 150 °C for water removal and at 450°C for conversion to anatase phase. Micro-Vickers hardness on different types of TiO2 nanotubes with/without annealing was carefully measured several times at different positions. Average of values was plotted in terms of anodizing variables. We found that conventional TiO2 nanotubes have hardness lower than a Ti foil because of its hollow structures and high porosity. As TiO2 nanotubes were prepared at a low temperature, the hardness increased up to as high as a Ti metal. On the other hands, as anodizing temperature became higher, TiO2 nanotubes grew faster, leading to lower hardness.