Effect of electrolyte composition on TiO2 nanotubular structure formation and its electrochemical evaluation

Nanotubular structures of TiO2 were synthesized on Ti6Al4 V alloy in various electrolytes with and without fluoride ions and were then evaluated by potentiodynamic polarization tests and electrochemical impedance spectroscopy. The resultant surface features were revealed through scanning electron microscopy. It was observed that barrier type oxide film is formed in halide free acidic electrolyte. From potentiodynamic polarization scans it was deduced that high current density in 0.15 M NH4F containing electrolyte corresponded to the formation of TiO2 nanotubes by slow field driven Ti4+ ions diffusion in the electrolyte than field assisted TiO2 growth. Two time constant impedance spectra were simulated to the field assisted charge transfer reactions at high frequency (dissolution of TiO2 by fluoride ions) and at low frequency (adsorption of oxidase ions) regime. X-ray diffraction pattern of as anodized surface revealed oxygen deficient Ti6O phase, which was converted to rutile/anatase phases by heat treatment in air.