Coupons of X60-pipeline steel have been taken directly from electrochemical testing apparatus for characterisation by surface analysis using novel sample transfer methods developed for the analysis of 'wet' samples [1]. In this way the correlation between surface concentration, solution concentration and inhibitor efficiency for a quaternary amine inhibitor has been determined.

The mechanism of surface activity of the quaternary amine inhibitor has been investigated. Firstly, surface analysis data for a liquid film of neat inhibitor has been compared with that for a steel coupon rinsed after exposure to neat inhibitor in a static immersion test. Surface analysis results have then been compared to corrosion rate measurements for a range of increasing inhibitor solution concentrations from 0-100ppm for coupons removed directly from an electrochemical test cell and transferred using a novel cryogenic method for sample transfer. Coupons were exposed to solutions of pre-inhibited, deaerated 3% NaCl solution under 1 bara CO2 at 25°C. Time of flight secondary ion mass spectrometry (ToFSIMS) and X-ray photoelectron spectroscopy (XPS) were the principal surface analysis techniques used.

The results show that the quaternary amine inhibitor achieved efficiencies in excess of 90% at solution concentrations of 40ppm and above. Adsorbed inhibitor was detected both by XPS and ToFSIMS at all concentrations studied. Efficiency and surface coverage of this inhibitor increased directly in proportion to solution concentration. Detailed study of surface analysis results shows that, under these cell conditions, adsorption of quaternary amine proceeds via a simple ionic interaction between the inhibitor and the coupon surface with longer chain amine components preferentially adsorbed.

Subject
Quaternary amines, Steel surfaces, Electrochemical cells, Corrosion rate, Steel coupons, Iron, X-ray spectroscopy, Surface analysis, Chemical inhibition, Nitrogen, Corrosion inhibitors, Carbon, Corrosion coupons
Keywords:
Surface Analysis, Inhibitor, SIMS, ESCA, XPS, Quaternary Amine, adsorption, Linear Polarisation Resistance (LPR)
© 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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