Volatile corrosion inhibitors (VCIs) compose a class of chemical compounds that have a suitable vapor pressure with which to diffuse throughout an enclosed volume, adsorb onto any exposed metallic surface within the volume, and inhibit corrosion in the adsorbed state. It has been demonstrated previously that the adsorption of volatile corrosion inhibitors (VCIs) depends upon environmental conditions, the variation of which in practical situations may dramatically affect the kinetics of VCI adsorption. Adsorption kinetics influence the overall performance of VCI as they are required to adsorb before corrosion inhibition may occur, although the extent of inhibition cannot necessarily be directly inferred from adsorption monitoring. This study attempts to evaluate VCI performance by utilizing surface enhanced Raman Spectroscopy to monitor the adsorption kinetics of VCI on exposed steel and copper surfaces while simultaneously performing real-time corrosion rate measurements with a multi-electrode array sensor in order to correlate VCI adsorption with corrosion inhibition. The relative efficacies of two VCIs to inhibit corrosion of carbon steel and copper were measured as the time dependent corrosion rate ratio of surfaces with VCI exposure to surfaces without VCI exposure in both humid and ambient environments. The results indicate that corrosion rate increases with initial VCI exposure compared to the same environment without VCI. A reduction in corrosion rate coincident with VCI adsorption was witnessed, but overall VCI containing environments were still found to yield elevated corrosion rates over non-VCI environments. Presumably, a critical concentration of adsorbed VCI is needed before inhibition starts to occur. The duration of this “incubation” period (the time before a critical inhibiting concentration is reached) was found to depend upon the specific VCI, but was on the order of a few days at room temperature. The results may have implications on the proper evaluation of VCI compounds and future development of VCI chemistry.

Subject
Films, Corrosion rate, Trends, Probes, Corrosivity, Adsorption, Volatile corrosion inhibitors, Corrosion attacks, Penetration, Corrosion inhibitors, Environments, Carbon steel, Electrodes
Keywords:
VCI, corrosion sensor, atmospheric corrosion, corrosion inhibition
© 2007 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).
2007
Association for Materials Protection and Performance (AMPP)
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