Fabrication and characterization of TiO2–ZrO2–ZrTiO4 nanotubes on TiZr alloy manufactured via anodization

Abstract

Titanium and its alloys are able to grow a stable oxide layer on their surfaces and have been used frequently as substrates for anodization in an electrochemical surface treatment. A nanotubular oxide layer is formed in the presence of fluorine anion (F⁻) via anodization due to the competition between oxide formation and solvatization. In this study, a highly ordered titania–zirconia–zirconium titanate (TiO₂–ZrO₂–ZrTiO₄) nanotubular layer was formed on the surface of Ti50Zr alloy via anodic oxidation in an F⁻ containing electrolyte. The sizes of the nanotubes (i.e., the inner and outer diameters, and wall thicknesses), morphology, crystal structure, hydrophilic properties and components of the TiO₂–ZrO₂–ZrTiO₄ nanotubular layer before and after annealing were examined by scanning electron microscopy (SEM), thin film X-ray diffraction, X-ray photoelectron spectroscopy (XPS) analysis and water contact angle measurements. The results indicated that the inner diameter, outer diameter and wall thickness of the as-formed TiO₂–ZrO₂–ZrTiO₄ nanotubes were distributed in the ranges of 3–120 nm, 12–165 nm and 3–32 nm, respectively, and depended on the F⁻ concentration of the electrolyte and the applied potential during anodization. The number of smaller nanotubes increased with increasing F⁻ concentration and the mean nanotube inner and outer diameters increased with increasing applied potential. The as-formed TiO₂ and ZrTiO₄ nanotubes exhibited an amorphous structure and the as-formed ZrO₂ nanotubes displayed an orthorhombic structure. These phases transformed into anatase TiO₂ and orthorhombic ZrO₂ and ZrTiO₄ after annealing. The hydrophilic properties of the TiO₂–ZrO₂–ZrTiO₄ nanotubular layer were affected by the size distribution of the nanotubes. The surface roughnesses and the nanotubular character transformed the nanotubes to exhibit superhydrophilic properties after annealing. The TiO₂–ZrO₂–ZrTiO₄ nanotubular surface on Ti50Zr alloy exhibited higher surface energy than that of the TiO₂ nanotubular surface on commercially pure (CP) titanium.