Self-healing coatings: An alternative route for anticorrosion protection

Polymer coating systems are classically applied on a metal surface to provide a dense barrier against the corrosive species. Cathodic protection is used for many applications in addition to coatings to protect the metal structures from corrosive attack when the coating is damaged. However, the current demand will increase with the disbonded areas. Moreover, the reactions that take place at the cathode can cause a progressive enlargement of the unbonded area. Self-healing coatings are considered as an alternative route for efficient anticorrosion protection while maintaining a low demand in cathodic protection. Such coatings typically incorporate micro- or nanocapsules that contain film-formers and repair the coating damage when the coating is scratched. Self-healing systems have been developed for metal structures under cathodic protection using specific-film-formers sensitive to the electrical field and pH encountered in the vicinity of a default on a coated structure under cathodic protection. The present paper describes the principle of this novel self-healing concept and discusses the healing efficiency on the basis of laboratory results. Electrochemical impedance spectroscopy was used to evaluate the performance of the barrier efficiency and continuous current demand monitoring assessed the ability of specific-film-formers to provide self-healing and repair defects generated in the coating to the metal.