Enhanced anodization growth of self-organized ZrO₂ nanotubes on nanostructured zirconium

To understand the effect of substrate microstructure on formation of ZrO₂ nanotubes, anodic oxidizations of commercially pure zirconium subjected to surface mechanical attrition treatment (SMATed-Zr), SMATed-Zr annealed at 550°C for 10h and unSMATed-Zr in an aqueous solution containing (NH₄)₂SO₄ and NH₄F were investigated. The SMATed-Zr and annealed SMATed-Zr exhibit nanocrystallized surface layers containing high density of grain boundaries compared with unSMATed-Zr. The anodization results show that the formed ZrO₂ nanotube layer on the SMATed-Zr is slightly thicker than that on the annealed SMATed-Zr, but thicker than that on the unSMATed-Zr. It is indicated that nanocrystallized Zr is propitious to the growth of ZrO₂ nanotubes; and grain boundaries, compared with dislocations, play the leading role in accelerating the reaction rate during anodization, in turn enhancing the crystallinity of ZrO₂ nanotubes at top-end.