Ennobled open-circuit potential (Ecorr) for stainless steel exposed to fresh river water is investigated using microelectrodes to measure dissolved oxygen, hydrogen peroxide, and local Ecorr within the biofilm. Results indicate the biofilm is uniformly aerobic and does not contain elevated levels of cathodic depolarizers. Development of ennobled potential is observed to correlate with Ecorr near beginning of exposure and occurs on surfaces exhibiting as little as 20% biofilm coverage. Galvanostatic measurements of coupon capacitance reveal a strong correlation between capacitance and Ecorr as the latter increases during microbial colonization. Cathodic reduction measurements indicate that an increase in surface Fe2O3 content occurs for stainless steel samples that develop ennobled potential. Results suggest an ennoblement mechanism involving modifications of the metal-oxide surface. A new interpretation of cathodic polarization behavior for ennobled stainless steel is given based on proposed changes in cathodic reaction rates that occur on the microbially modified oxide surface during polarization.

Subject
Steel surfaces, Water, Steel coupons, Rivers, Biofilms, Capacitance, Ennoblement, Electric potential, Oxygen, Corrosion coupons, Stainless steel, Risk reduction, Corrosion potential
Keywords:
stainless steel, biofilm, ennoblement, oxygen, hydrogen peroxide, open-circuit potential, passive film, microelectrode, cathodic depolarizer, capacitance
© 1995 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).
1995
Association for Materials Protection and Performance (AMPP)
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