Electroactive conducting polymers for corrosion control |
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Authors: | Geoffrey M Spinks Anton J Dominis Gordon G Wallace Dennis E Tallman |
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Institution: | Intelligent Polymer Research Institute, University of Wollongong, Northfields Avenue, NSW 2522, Australia, Department of Chemistry, North Dakota State University, Fargo, ND 58105-5516, USA,
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Abstract: | This paper reviews the literature describing the effects of conducting polymer coatings on the corrosion rate of ferrous
alloys (iron, steel and stainless steel). The literature is interpreted in terms of the proposed mechanisms of corrosion protection:
barrier, inhibitor, anodic protection and the mediation of oxygen reduction. The most intriguing aspect of the reported literature
are the studies demonstrating corrosion protection when deliberate defects were introduced into the coating to expose the
bare metal. These studies show that protection afforded by conducting polymer coatings is not due to simple barrier protection
or inhibition alone. Many studies illustrate that the polymer/metal interface is modified to produce passivating oxide layers
and that charge transfer reactions occur between the metal and polymer. These studies support the proposed anodic protection
mechanism, as do the reports of significant ennoblism. On the other hand, there is considerable variation in the reported
shift in corrosion potential and these highlight the influence of substrate preparation, coating composition and mode of application
and the nature of the electrolyte on the corrosion protection provided by the conducting polymer. For example, the evidence
suggests that the emeraldine base form of polyaniline is superior to the emeraldine salt in terms of corrosion protection
for steel. However, the number of direct comparisons is small and the reasons for the differences are not well understood.
Also not well understood are the role of the counterion release and local pH changes on pinhole protection. It is also argued
that the conducting polymer reduces the likelihood of large increases in pH at the polymer/metal interface and so stabilizes
the coating against cathodic disbondment. Further work is clearly needed to increase the protection period by further studies
on the corrosion protection mechanism so that the polymer composition and processing methods may be optimized. |
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