Formation of ZrO2 with unusual morphology and Zr surface patterning via one-step anodization of zirconium in aqueous electrolyte

A simple one-step anodization of Zr in aqueous electrolyte was employed for the fabrication of nanostructured ZrO₂ with various morphologies as well as for controllable nanostructuring of Zr metal surface. The Zr foils were anodized for various durations (10–30 min) at the constant potential from the range 10–50 V in an electrolyte containing 1 M (NH₄)₂SO₄ and 0.5% wt. NH₄F at room temperature. The morphology of the obtained materials has been verified by SEM and AFM, and correlated in detail with anodizing conditions. Depending on the voltage applied during anodization, both nanotubular and nanoporous zirconia films with a thickness of up to 30 μm were successfully obtained. Moreover, the generation of nanostructured ZrO₂ with unusual morphology consisting of much larger channels/tubes within a “matrix” of narrower species was presented for the first time. Careful adjustment of anodizing conditions allowed for the formation of free-standing and mechanically stable zirconia films without the need for any post-treatment procedures like potential shock or cathodic polarization. Finally, the procedure of Zr anodization was also found to be an effective strategy for the generation of nanosized patterns with precisely defined morphologies on the metal surface.