The use of electrochemical techniques in assessing the porosity of electroless nickel deposits (1-24 μm) on steel substrates from hypophosphite baths is considered. The corrosion rate of the coated samples immersed in 0.125M H2SO4 at 22°C was determined using Tafel extrapolation and was found to decrease with decreasing porosity. Analysis of anodic polarisation curves and current-time data at fixed potentials gave a good indication of the extent of deposit porosity. The use of galvanic coupling experiments between a non-porous coating and test samples of varying deposit thickness was also examined. The shape of the porosity vs. coating thickness curve was similar for all the methods investigated, the porosity decreasing for thicker deposits.

Subject
Iron, Dissolution, Porosity, Pores, Steel, Deposit corrosion, Nickel, Electroless nickel, Galvanic current, Anodic polarization, Electrodes, Corrosion potential, Electrolytes
Keywords:
corrosion resistance, corrosion testing, corrosion potential measurements, electrochemical tests, electroless plating, linear polarisation resistance measurements, nickel coatings on low carbon steel, porosity, Tafel extrapolation
© 1997 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).
1997
Association for Materials Protection and Performance (AMPP)
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