Polycrystalline anodic alumina membranes have been prepared by controlled calcination. Phase transformations, porosity changes and conversion of electrolyte impurities incorporated into the anodic alumina lattice were studied as functions of the calcination temperature (up to 1200 degrees C). A comparative IR investigation of hydroxyl cover of the polycrystalline anodic alumina membranes and pure gamma- and delta-alumina was carried out. Amorphous anodic alumina films calcined at temperatures up to 800 degrees C with a barrier layer in place (thickness of barrier layer ranged from 5 to 90 nm) were prepared and the permeabilities measured, It is hypothesised that the thin layer of relatively pure and dense alumina of the anodic alumina cell prevents migration of ions, water or small molecules through the barrier layer as well as between the adjacent cells.