A combined redox-competition and negative-feedback SECM study of self-healing anticorrosive coatings

In this paper, the long-term anticorrosive efficiency of a damaged self-healing coating is studied for the first time using scanning electrochemical microscopy (SECM). In the study an epoxy-coating with embedded-capsules containing a silyl-ester is employed. The properties of the silyl-ester as a healing-agent for the protection of AA2024-T3 were evaluated by complementary SECM experiments operating in negative-feedback and redox-competition modes. The experimental approach here presented allowed for monitoring the early-stages of corrosion activity and subsequent healing mechanisms offered by the release of silyl-ester into a relatively large coating defect. This result was observed by detecting the transition of the oxygen reduction response from a redox-competition mode to a negative-feedback behavior. These measurements demonstrated that the silyl-ester is released efficiently after capsules break upon coating damage, covering relatively large areas and gradually healing the damaged-site hindering the corrosion processes and providing an effective protection for at least one month of immersion in chloride solution.

► Encapsulated silyl-ester as healing-agent in organic coatings evaluated by SECM.
► Combined SECM-experiments in redox-competition mode and negative-feedback mode.
► Oxygen transition from active specie involved in corrosion to mediator behaviour.
► Observation of early-stage of corrosion and subsequent healing by released agent.
► Silyl-ester provides effective protection for at least one-month of immersion.