At temperatures above 425°C the kinetics of oxidation of high purity aluminum is a complex phenomenon. Duplex films are formed consisting of both amorphous and crystalline γ-Al2O3. Although several explanations have been advanced to account for the complex oxidation mechanism(1-6) only the work of Beck et. al(4) accounts for the total oxidation process in any detail. These workers showed that the oxidation behavior of high purity aluminum was due to two mutually independent processes which occur simultaneously. The first of these is the formation of a layer of amorphous γ-Al2O3 with poorly developed long range order. The second process is the nucleation and growth of crystals of γ-Al2O3 at the amorphous oxide-metal interface. The success of Beck et. al(4) lies in the fact that they were able to separate the kinetics of formation of the amorphous oxide from the overall film growth by determining local amorphous film thicknesses between crystals of γ-Al2O3 by means of electron opacity measurements. In this way, they were able to show that the amorphous oxide formed according to a simple parabolic rate law likely by the egress of aluminum ions and electrons to the amorphous oxide-gas interface and their reaction there with oxygen to form amorphous γ-Al2O3. The rate of formation of the amorphous oxide was shown to be completely independent of the presence of the underlying crystals of γ-Al2O3.

Subject
Ions, Oxide formation, Aluminum, Oxide films, Metal oxides, Purity, Constants, Film formation, Crystal growth, Aluminum alloys, Cations, Alloys, Oxidation
© 1979 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1979
Association for Materials Protection and Performance (AMPP)
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