Abstract
The present study examines the influence of surface pretreatment on the evolution of nanotubular (T) and nanoporous (P) oxide film morphologies on titanium foil anodized potentiostatically, at 20 V, in fluoride-containing 1 M H(3)PO(4) electrolyte. The foil was used in the untreated, mechanically/chembreically polished or preanodized conditions. The preanodization resulted in fluoride-free barrier films. Mainly T regions were produced on polished foil during subsequent anodizing in fluoride-containing 1 M H(3)PO(4) electrolyte. In contrast, the P regions dominated on polished foil preanodized to 20 V. Both P and T regions resulted with rolled foil preanodized to 20 V or polished foil preanodized to 10 V. Raman spectroscopy disclosed anatase and rutile at P regions, whereas T regions are mainly amorphous. The P film thickened at a constant rate of 6x10(-2) nm s(-1), while the T film reached a limiting thickness of similar to 700 nm due to the relatively high solubility of the amorphous oxide. The presence of P film resulted in increased currents during anodizing. Furthermore, the results suggest that the formation of T film depends upon the access of F(-) ions to the titanium/film interface, resulting in the stabilization of a mainly amorphous film structure.