Postsealing changes in porous aluminum oxide films obtained in sulfuric acid solutions

The behavior of sealed and unsealed porous aluminum oxide films during aging and autosealing-aging in various media is studied. The quality of the anodic layers and the degree of sealing and aging are assessed. The results of electrochemical impedance spectroscopy are compared with those provided by standard quality control tests, scanning and transmission electron microscopies, gas adsorption porosimetry, and microhardness tests involving specimens sealed to a different extent. These techniques provide complementary information on the different stages of the sealing and autosealing processes (viz, pore plugging; pore wall dissolution; precipitation, crystallization, and agglomeration of hydrated alumina; formation of the intermediate layer), and on the aging stage and its duration. (C) 2000 The Electrochemical Society. S0013-4651(99)05-048-X. All rights reserved.