Electrochemical oxidation of titanium by pulsed discharge in electrolyte

Abstract

We propose a high-voltage (>1000 V) pulsed discharge method of preparation of thin anodic films on valve metals under conditions of extremely high rates of the film growth. The peculiarities of this method have been demonstrated on the anodic oxidation of titanium in sulfuric acid solutions. A light flash at the electrode was generated upon the pulsed anodization of titanium. The emission spectra consist of narrow lines assigned to electronically excited O, H and Ti atoms, indicating that a hot plasma is created at the electrode surface. The current efficiency of TiO 2 anodic film formation exceeds markedly 100% for the pulsed Ti anodization. This non-faradaic yield was associated with the contribution of the plasma-generated high-energy radicals to the oxide growth processes. We applied various techniques to compare the composition, morphology, structure and semiconducting properties of the anodic films prepared by the high-voltage pulsed discharge and the conventional galvanostatic anodization. The anodic TiO 2 films prepared by the high-voltage pulsed discharge have nearly ideal stoichiometric composition and are more amorphous as compared to galvanostatically grown ones. Thin TiO 2 films (50–150 nm) formed in the pulsed regime exhibit significantly higher photocurrent quantum yields at λ < 310 nm and a significantly lower donor concentration.