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In the present paper the changes in atomic structure and morphology of freestanding amorphous porous anodic alumina (PAA) films under thermal treatment in the range of T = (773-1773) K are summarized. The investigations were carried out by the methods of x-ray study and transmission electron microscopy. It was shown that the transformations under heat treatment up to 973ë are limited by the ordering of aluminium cation sublattice of x-ray amorphous PAA, with no changes in the type of mutual arrangement of Al and O. It was stated that crystallization occurs in the range ô = 973-1113 ë, and by the moment of its completion the phase composition of PAA corresponds to the mixture of γ-Al2O3 and δ-Al2O3. As a result of the annealing up to 1223 ë regular cell structure of PAA still remains. The explanation of the sequence of thermally induced phase transformations of porous alumina was proposed. It was based on the experimentally confirmed principle about different rates of crystallization of pure Al2O3 and the oxide enriched by the electrolyte anions. |