Evaluation of corrosion performance of a self-healing epoxy-based coating containing linseed oil-filled microcapsules via electrochemical impedance spectroscopy

Linseed oil filled urea-formaldehyde microcapsules with various sizes were prepared via in-situ polymerization. To understand the healing performance of linseed oil as a healing agent and the progression of corrosion processes beneath the healed area, long term corrosion performance of scratched epoxy-based coating samples containing microcapsules was evaluated using Electrochemical Impedance Spectroscopy (EIS) as well as salt spray testing over a period of 6-days. EIS results were fitted to various equivalent circuit models and a modified model for the justification of the observed corrosion behavior was proposed. It was found that the addition of microcapsules enhances the corrosion resistance of the scratched samples, the extent of which depends on the microcapsule size and loading. At a given loading, corrosion resistance increased with increasing microcapsule size, however, the effect of microcapsule size was more significant than that of loading. Moreover, with increased exposure time to the salt solution, the corrosion behavior of scratched coated samples shifted from uniform corrosion to crevice corrosion. EIS results showed that although linseed-oil can significantly improve the corrosion performance of the damaged coating in short term however it rapidly decreases with time and hence this should be taken into account in designing of microcapsule's core composition. (C) 2017 Elsevier B.V. All rights reserved.