Nanoscale Investigation of Anodization Process of Titanium

Titanium dioxide is one of the most versatile materials with applications ranging from biomedical and solar cells to photo catalysts. The main method to fabricate titanium dioxide is anodization. Numerous research works have been performed to determine the appropriate processing parameters for anodization such as electrolyte concentrations, voltage, anodization time, and so forth. During this research, a lab-on chip electrochemical setup was used to study the anodization process of the titanium in real time. The anodization process can be divided into three stages based on the current-time transient in aqueous electrolytes. In Stage I, oxide barrier layer forms and the electrical current decreases quickly. In stage II, electrical current subsequently rises and porous layer forms. In stage III, current becomes stable and the nanoscale TiO₂ forms. For the anodization using fluoride containing electrolytes, the stage I and stage II can be finished in 20 minutes. Using the in situ setup, the current-time characteristics and the real time morphology evolution of the anode can be observed. The results provide fundamental insights of the mechanisms related to the nanoscale TiO₂ formation and structure evolution in real time. The morphology of the nanotubes changes with different concentrations of fluoride ions and different amount of waters (0.1-5 wt%) in the electrolyte. The nanotubes change from smooth to ribbed when the water concentration is above a critical threshold. In this research, by applying different amount of water and concentration of fluoride ions, the effect of fluoride ion concentration and water on the morphology of nanotubes can be investigated.