Freestanding ZrO2nanotube membranes made by anodic oxidation and effect of heat treatment on their morphology and crystalline structure

Abstract

An integrated freestanding zirconia (ZrO₂) membrane was fabricated via a two-step electrochemical anodization with a zirconium (Zr) foil, followed by a simple and safe detachment of the formed ZrO₂ membrane. The resulting membrane consists of highly ordered, vertically aligned, and one-side open ZrO₂ nanotube arrays. The effect of heat treatment on the morphology and crystalline structure of the integrated freestanding ZrO₂ membranes was studied using scanning electron microscopy, transmission electron microscopy and X-ray diffraction. These results showed that the nanotubes were stable to annealing at 500 °C and then gradually transformed to wires along their long axis from 600 to 900 °C. The as-prepared samples possessed amorphous structures, while both monoclinic and tetragonal phases were found after annealing at a temperature between 400 °C and 900 °C. The present study not only demonstrates a facile approach to produce high quality ZrO₂ membranes in a simple manner, but also provides valuable insights into the temperature dependent morphology and crystalline transformations in anodic ZrO₂ nanotube arrays.