Some Physical and Dielectric Properties of Hydrous Alumina Films

Abstract

Properties of pseudoboehmite films, produced by the reaction of aluminum foil with boiling water, were studied by a variety of techniques. For reaction times of 1–30 min the average film porosity decreased linearly with increasing film weight. The surface area of freshly prepared films was similar to that of alumina gel, but decreased on aging in air. Aging in 1 N   NaNO 3 inhibited the area decrease. The series capacitance decreased on aging in air or nitrate electrolyte. It was determined that with the sample immersed in electrolyte the measured dielectric properties were those of an inner region impermeable to electrolyte. This layer was not the same as a typical barrier oxide. The films exhibited a low frequency dielectric dispersion. From the temperature dependence of the loss maxima the activation energy and relaxation time for the process were found to be 13.4 kcal/mole and 6.2 × 10−15 sec. These are in the range found for other systems containing hydroxyl chains or bound water.