I have a question about anodic oxidation of Ti metal.
I used Ti metal (3 cm x 3 cm x 1 mm) as an anode and SUS (stainless steel) as a cathode. And electrolyte consists of H2SO4 (0.5 M, final concentration and HF (0.35 - 0.5 %, final concentration). The distance between two electrodes is about 1 cm and volatge is applied for 3.5 h with continuous stirring.
The question is TiO2 nanotubes are usually formed at the interface between Ti and electrolyte NEAR AIR (the boundary). Sometimes, TiO2 nanotubes are formed in the region dipped in the electrolyte.
Why this occurs?