Theoretical models describing the influence of transport phenomena on the protectiveness of corrosion layers are briefly recalled, together with the impossibility of using the standard electrochemical techniques of imposed polarization, such as the plotting of potential-current density curves, in the case of specimens covered by such layers. This has led to the idea of using "pseudo-polarization" curves, which simply correspond to the trajectory of the free corrosion point in the traditional Tafel representation.

This method suggests that the increase in corrosion rate beneath a layer of undissolved cementite is in fact caused by local acidification of the corrosive medium in the layer, due to exhaustion of the bicarbonate anions which buffer the external medium.

Subject
Cementite, Diffusion layers, Hydrogen concentration, Corrosion rate, Metal surfaces, Diffusion, Slopes, Acidification, Solubility, Acidity, Metals, Surface layers, Deposit corrosion
© 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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