Effects of dissolved oxygen concentration on corrosion rates of SUS304 in high temperature pure water were examined at temperatures between 200 and 320 C by using impedance analysis techniques. A significant reduction of the corrosion rate above 260 °C and independency of the corrosion rate on dissolved oxygen concentrations at 320 °C were observed as unique phenomena. To understand these, the structures of oxide films were examined by scanning electron microscopy, secondary ion mass spectroscopy, and electrical capacity measurements. The oxide films could be divided into outer and inner layers. The outer layer was characterized by the decrease of Cr content towards the surface of the oxide films. The inner layer was a residual oxide layer in which no decrease of Cr content occurred.

The inner oxide film layer was insulated and effectively suppressed corrosion above 260 °C. At 320 °C, thickness of the inner oxide film layer became independent of dissolved oxygen concentration and showed a good correspondence with the corrosion rate behavior. It was supposed that the cracked layer, formed by breakdown, became thicker, balancing the growth of the inner oxide film at 320°C.

Subject
Scanning electron microscopy, Steel structures, Water, Corrosion rate, Oxide formation, Oxide layers, Oxide films, Constants, Oxide surfaces, Surface layers, Dissolved oxygen, Electrodes, High temperature
© 1986 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).
1986
Association for Materials Protection and Performance (AMPP)
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