Influence of Mass and Heat Transfer on Morphologies of Metal Oxide Nanochannel Arrays Prepared by Anodization Method

We discuss the influence of mass and heat transfer on the morphologies of Al, Ti, and Zr nanochannel arrays during anodization process. When these metals are anodized, the nanopores are firstly formed at the metal surface, and the nonuniform distribution of mass transfer in the pores results in the increase of pore depth. The nonuniform temperature distribution and the downward movement of reaction interface lead to the temperature changes and the generation of microcracks inside the pore wall, which results in the conversion of nanopores into nanotubes. The low-valency oxides also make the middle of the pore wall crack easily. The morphologies during metal anodization depend greatly on the temperature at the reaction interface. At low interface temperature, it appears to form the nanopores more easily, and, at high interface temperature, it is more propitious to form the nanotube structure. Many factors including resistivity, thermal conductivity, oxidizing reaction heat, and electric field strength (or current density) affect the reaction interface temperature.