Effect of Processing Temperature on the Morphology and Crystal Structure of Anodic TiO2 Nanotubes

In the present work, we have investigated the influence of temperature on the morphology of anodically produced self-organized titanium oxide nanotubes (TiNTs). TiNTs are synthesized by two-step anodization in ethylene glycol-based electrolytes containing ammonium fluoride and deionized water. Experiments are performed at constant anodization voltage of 50 V for 2 h. An investigation by the SEM images reveals that if the temperature is kept constant during the anodizing experiment, variation in the average tube diameter is significantly reduced. Degree of pore arrangement, pore size and oxide thickness increased with the increase in temperature as observed at a range of electrolyte temperatures fixed between 5°C and 40°C. However, if the temperature is not controlled during the anodization experiment, then due to the exothermic nature of the reactions to the formation of TiNTs, the temperature of the electrolyte continues to increase. This variation in electrolyte bath temperature introduces strong variations in tube diameter (10–160 nm) along the length of the tubes. Current profiles, recorded during the anodization experiments, predict the effect of constant and varying experimental temperatures as well. In both cases, XRD results show the complete anatase crystal structure of nanotubes upon annealing at 450°C. The present work highlights the importance of fixed processing temperature during the anodization experiments in order to develop an ordered array of nanotubes with a uniform tube diameter.