High-temperature pH was measured with zirconia membrane electrode with crevice-forming sheath in high purity water. The crevice pH was substantially lower than that of bulk water. Corrosion potential was measured in crevice and on free surface in high-temperature, high-purity water with Type 304 stainless steel (SS), Alloy 600 and their Cr-depleted model alloys. The crevice corrosion potential was 300 to 400 mV lower than that of free surface. The coupling current was observed from free surface cathode to crevice anode. The surface films formed in crevice and on free surface were characterized with Auger electron spectroscopy and laser Ramman spectroscopy. The crevice surface films of Type 304 SS and Alloy 600 were thinner than free surface, but those of Cr-depleted model alloys were thicker than free surface. The most prominent compound was NiFe2O4 in the surface film formed both in crevice and on free surface. The cristallinity and the content of other compounds such as Fe3O4 or NiO were different between crevice and free surface.

Subject
Films, Immersion tests, Water, Metal surfaces, Nickel based alloys, Sodium chloride, Anode surfaces, Acidity, Crevices, Alloys, Electrodes, Corrosion potential, Electrode potential
Keywords:
high-temperature water, crevice corrosion, corrosion potential, pH, surface film
© 1994 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).
1994
Association for Materials Protection and Performance (AMPP)
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