Formation of self-organized titania nano-tubes by dealloying and anodic oxidation

The dealloying of a titanium aluminum alloy (Ti–8 at. % Al) in 1 M NaOH at a critical potential (Ec) generates an ordered nanoporous structure. The diameter of the pores ranges from 30 to 100 nm with highest population of 60 nm. This is attributed to selective dissolution of Al from the alloy while Ti remains passive. Much less developed nanopores were imaged on alloy surfaces at a potential that is 400 mV less noble than Ec. Subsequent anodization of the nanoporous dealloyed surface in 1 M H3PO4 + 1.0 − 1.5% HF yielded self-organized titania nanotubes of diameters ranging from 40 to 140 nm with highest population of 80 nm. An increase in the potential and time of anodization results in more developed nanotubes. The increase in the diameter scale of the nanostructure upon anodizing is attributed to the effect of fluoride ions and high potential on TiO2. X-ray diffraction and thermogravimetric analyses revealed that the tubes are made of anatase (TiO2).