A microstructural investigation of low-temperature crystalline alumina films grown on aluminum

Crystalline aluminum hydrous oxide [γ-AlO(OH)] thin films were prepared by hydration of a high cubicity tunnel-etched aluminum foil in deionized water at 95 and 55 °C for different lengths of time. The films obtained were examined by field emission-scanning electron microscopy, X-ray diffraction and grazing angle-Fourier transform infrared spectroscopy. Hydration at 95 °C (from 15 s hydration time up to 3 h) showed the presence of only one crystalline phase with crystallite sizes ∼6 nm, identified as pseudo-boehmite. A second phase, bayerite, was found to be growing from the pseudo-boshmite film at much longer hydration times. However, a shorter induction time (below 3 h) for bayerite growth was observed during hydration process at 55 °C.