Understanding the anticorrosive protective mechanisms of modified epoxy coatings with improved barrier, active and self-healing functionalities: EIS and spectroscopic techniques

The present investigation adopted long-term in-situ electrochemical and spectroscopic approaches to study the combined active, self-healing and passive protective mechanisms of a new class of innovative anti-corrosive coatings based on epoxy doped with clay nanotubes impregnated with active species for the protection of carbon steel in 3.5% NaCl solution. The suitability of the as-received clay nanotubes to encapsulate the active agents was confirmed by different spectroscopic measurements. Tube end stopper with Ferric ion and polymer encapsulation with chitosan cross-linked with glutaraldehyde were adopted to tunnel the release of the active agents loaded into the nanotubes. The improved passive barrier performances of the various innovative coatings were revealed by the electrochemical impedance spectroscopic, while their active feedback and self-healing abilities were revealed by the optical and spectroscopic techniques. The optical/spectroscopic techniques revealed the degree of pit formation at the steel/coating interface and the iron rust formation around the artificially marked defects, including the ability of the marked defects to self-heal over exposure times. Adhesion and impacts tests were adopted to compare the physical/mechanical properties of the various coatings. The results afforded insights into the effects of exposure time on the protective and failure behaviours of both the reference and modified coatings.