Transition from nanopores to nanotubes: Self-ordered anodic oxide structures on titanium-aluminides

Self-ordered oxide growth on Al, TiAl, Ti3Al, and Ti in HF containing H2SO4 was investigated. This specific set of intermetallic compounds offers the possibility of a detailed investigation of the influence of the increasing titanium content on key features of anodic oxide nanostructures. A fluoride based electrolyte was successfully applied to create self-ordered nanoporous oxide structures on Al and nanotubular oxide structures on Ti, in order to achieve self-ordered oxide features. A morphological change in the self-organized structures depending on anodization voltage and on alloy composition was observed. The occurrence of these tube separation effects were ascribed to increased stress that occurs within the growing oxides due to increasing volume expansion when altering the composition from Al toward Ti. This separation may be supported by sensitization of the cell boundaries by fluoride species.