Growth Process of TiO₂ Nanotubes Based on Electronic Current and Bubble Mold Effect

The formation mechanism of porous anodic oxides remains highly controversial to this day. The traditional “Field-assisted dissolution” theory cannot explain the physical significance of the current-time curve. Based on the theory of electronic current and oxygen bubble mold, this article comparatively studied the anodizing process of Ti under low pressure (10 kPa) and normal pressure (101 kPa). The surface and cross-sectional morphology of TiO₂ nanotubes were characterized by FESEM, and the essential reasons for the differences in the current-time curves under low pressure and normal pressure were analyzed. The results show that low pressure accelerates the release of oxygen bubbles during the Ti anodizing process, resulting in an increase in electronic current. After the acceleration of oxygen evolution, the volume expansion effect of the bubble mold weakens, which leads to a decrease in the inner diameter of TiO₂ nanotubes and a higher pore density.