Self-Healing Coatings for Corrosion Protection of Steel

Abstract

Self-healing coatings belong to a new generation of smart coatings for corrosion control, which have both passive characteristics (from matrix material) and active behavior towards the local environment (through incorporated or surface-mounted compounds acting as inhibitors). The coatings provide a rapid release of a repairing material (e.g., a corrosion inhibitor) after changes in coating integrity by mechanical/chemical damage of the coating or by local pH changes occurring near the metallic surface. Within all classes of materials, the one with the largest self-repair potential belongs to polymers since they display more useful properties than any other material. However, besides these materials, inorganic (including mainly silica, titania, zirconia, etc.), organic, or hybrid layers have been successfully used as matrices for self-repairing coatings. On the other hand, the self-healing agents embedded in the matrices belong to different classes varying from natural compounds (tung oil, spar varnish, camphor, linseed oil, etc.) to synthetic ones (isodecyl diphenyl phosphate, 2-mercaptobenzothiazole, alkyl ammonium salts, etc.). In this context, recent advances in preparation and characterization of different self-healing coatings on steel will be reviewed. The main techniques for obtaining self-healing coatings and the challenges for future research will be also briefly discussed.