Effect of HCl Concentration on the Phase and Microstructure of TiO<sub>2</sub> Film Synthesized by Low-Voltage Anodization of Titanium

Abstract

Titanium oxide (Ti-O) films were prepared by low-voltage (i.e., 5-15 V) anodization of titanium plate in different hydrochloric acid (HCl) concentrations. Phase composition and surface microstructure of the anodized sample were investigated through XRD and SEM characterizations. Samples anodized at 15 V and in 0.6, 1.5 and 3.0 M HCl concentrations show higher amount of crystalline TiO2 (i.e., anatase and rutile) phases as compared to other anodizing conditions. The three samples show open pores microstructure on the anodized surface. Samples anodized at lower voltages and in low to medium HCl concentrations also produce loosely bonded amorphous Ti-O granules on top of the crystalline TiO2 phases. After annealing these samples at 400 or 600°C in air, further oxidation occurred on the anodized surface particularly at pores, contribution to slight increase in the crystalline phase. It suspected that the presence of amorphous Ti-O granules on top of crystalline TiO2 phases at initial anodizing stage, hindered movement of OH- and Cl- anions onto the anodized surface, thus inhibited further growth of the crystalline TiO2 phases.