Growth and Features of TiO2 Nanotubes Surfaces on Industrial Titanium by Anodizing in Organic Medium

This work shows the growth of TiO₂ nanotube by anodizing of surfaces metallic titanium and its features as surface. The material used was titanium industrial plates (99 %). The baths were constituted by 98% v/v of ethylene glycol, 2.5 ppm of O₂ (water as a source), 1,700 ppm of F^-, and a pH of 6.6. The concentrations of O₂ were oscillating between 2.3 and 1.9 ppm, and the conductivities in the cell were about 480 μS/cm. The potential was set using a ramp of 6 V/min and a final value of 60 V for 2 h. Along the experiment, constant dripping of water was used.

In a first step, a layer of early oxide was formed. Then, anions migrate through the oxide layer to the Ti/TiO₂ interface and reacted with Ti as shown in reaction (1) and (2). Meantime, the applied electric field ejects Ti⁴⁺ cations from the Ti/TiO₂ interface and made that Ti⁴⁺ move towards the TiO₂/electrolyte interface. The chemical dissolution occurred at the interface of TiO₂/electrolyte, where TiO₂ was dissolved by F⁻ with the help of H⁺ and the field assisted dissolution occurs at the Ti/TiO₂ interface as indicated by reactions (3) and (4) [1].

 

2H2O → O2+ 4e− + 4H+	(1)
Ti + O2→ TiO2	(2)
TiO2+ 6F− + 4H+ → [TiF6]2− + 2H2O	(3)
Ti4+ + 6F−→ [TiF6]2−	(4)

These surfaces showed to be superhydrophilic. Studies about its surface energy, and corrosion resistance were realized, the roughness factor was determined by optical profilometer and cyclic voltammetry. The electroactive surface areas were determined by this technique too.

[1]      T. Xu, J. Lin, J. Chen, and X. Chen, “The effect of pre-pattern on the morphology and growth speed of TiO2 nanotube,” Appl. Surf. Sci., vol. 258, no. 1, pp. 76–80, 2011.