Fabrication and high-temperature structural characterization study of porous anodic alumina membranes

Porous anodic alumina (PAA) membranes with highly ordered array of nanopores were prepared by two-step anodization process. Studies on structural and thermal properties and the thermal stability of the prepared PAA membranes were carried out. Investigation using scanning electron microscopy, atomic force microscopy, X-ray diffraction, thermal analysis and infrared spectroscopy was performed on the prepared PAA membranes at room temperature and in the temperature range 600-1,400 degrees C. The as-prepared PAA membranes revealed the amorphous nature. Polycrystalline PAA membranes were obtained by annealing carried out at different temperatures. Annealing study confirmed that the heat treatment transformed the amorphous PAA membranes to their crystalline phases, namely, gamma-alumina at about 870 degrees C and then to alpha-alumina around 1,250 degrees C.