Anodic titania nanotubes grown on titanium tubular electrodes.

In the past decade, research into growth and application of anodic titania nanotubes has been focused on planar titanium electrodes. Although patterned, curved, or cylindrical substrates were also employed in a number of applications, the study of nanotubes grown on a titanium tubular electrode is rather inadequate, despite their expected uses in thermal fluids. In this study, growth of titania nanotubes on tubular electrodes was investigated. It was found that nanotubes are formed at both outer and inner surfaces of the electrode. The nanotube length (or growth rate in the first 30 min) at the outer surface decreases gradually from the side facing the cathode to that at the other side, while the length at the inner surface smears out this trend. This is due to the effect of the electric field emanating from the potential drop in the organic electrolyte. The variation of nanotube diameter just echoes such a tendency of potential drop. The influence of electrode orientation during anodization on the resulting features of nanotubes was also examined and discussed. The nanotube geometry is thus tailorable for particular applications.