In situ synthesis of zirconia nanotube crystallines by direct anodization

Zirconia nanotube crystallines were obtained using a direct anodization method in 1 M (NH4)2SO4 electrolyte containing 0.5 wt.% NH4F at different applied voltages (10–50 V). The microstructure and crystal structure of zirconia nanotubes were characterized by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Under optimum conditions zirconia nanotubes with a diameter of up to 40 nm and a length of up to 12 μm were prepared. The as-prepared nanotubes are of orthorhombic phase when the voltage applied is less than or equal to 30 V. Some crystallines of monoclinic phase emerge when increase the voltage to 50 V.