Formation of hexagonally-ordered zircaloy oxide nanostructures with different morphologies using two-step anodization

Highly ordered zircaloy-4 (Zr-4) oxide nanostructures with nanoporous or nanotubular morphologies are prepared using two-step anodization. The first-step anodization in ethylene glycol (EG) electrolyte containing 0.3 wt% ammonium fluoride and 0.2 wt% de-ionized water produced bundled oxide nanotubes on the surface of Zr-4. The as-grown oxide nanotubes obtained by the first-step anodization were detached ultrasonically in ethanol, leaving an ordered concave surface on the Zr-4 substrate. When the Zr-4 substrate with an ordered concave surface was secondly anodized, nanotubes with clear and open top surfaces were fabricated. In addition, the morphologies of the oxide nanostructures could be controlled to have tubular or porous structure only by changing the electrolyte from EG to glycerol in the second anodization.