Carbon steel plates were exposed for twelve months to a marine tropical atmosphere The corrosion products formed were analyzed monthly by using scanning electron microscopy (SEM) and infrared spectroscopy (FTIR). This study shows that during the first months of exposure of low relative humidity (mean value 65 %) the corrosion product formed is an amorphous oxyhydroxide At intermediate ages this product transforms into γ-FeOOH (lepidocrocite) and under conditions of higher relative humidity values (about 75 %) at nine to twelve months of exposure the dominant corrosion product is α-FeOOH (goethite). No magnetite (Fe3O4) has been detected at any stage by the techniques we have employed. This could support the statement that the reduction product of oxyhydroxides is rather a ferrous intermediate, which in subsequent stages would be oxidized to unordered Fe(OH)3 and or amorphous FeOOH. The transformation of these latter products into γ and α oxyhydroxides by water loss and crystallization would close the reaction cycle of the natural atmospheric corrosion of steel, where Fe(OH)2 replaces Fe3O4 as the reduced state.

Subject
Scanning electron microscopy, Atmospheric corrosion, Water, Atmosphere, Lepidocrocite, Fourier transform infrared spectrography, Corrosion products, Steel, Rust, Magnetite, Carbon steel, Risk reduction, Oxidation
Keywords:
atmospheric corrosion, tropical marine atmosphere, infrared spectroscopy, scanning electron microscopy, iron oxides, iron hydroxides and oxyhydroxides, oxidation, reduction
© 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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