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

The behavior of sealed and unsealed porous aluminum oxide films during agin g and autosealing-aging in various media is studied. The quality of the ano dic 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 microsc opies, gas adsorption porosimetry, and microhardness tests involving specim ens sealed to a different extent. These techniques provide complementary in formation 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 So ciety. S0013-4651(99)05-048-X. All rights reserved.