Sol-gel coatings are commonly used as surface pre-treatments or thin coatings to improve the adhesion and barrier protection offered by the coating system. The reliability of such coatings can be further increased by implementing self-healing concepts ensuring a longer protection of the underlying substrate. Extrinsic self-healing sol-gel coatings, i.e. coatings in which the self-healing capability is achieved by inclusion of nano- and micro-sized particles containing corrosion inhibitors can provide local corrosion protection. Yet cracks in extrinsic self-healing sol-gel coating will not disappear as the matrix is permanently cross-linked and hence immobile. In this work we present a double-layer sol-gel coating capable of mending corrosion protection as well as superficial and interfacial damage by combination of extrinsic and intrinsic healing approaches. In the developed systems, inner layer is a conventional silica-zirconia thin film loaded with both cation- and anion-exchange inhibitors for active corrosion inhibition of the metallic surface. The outer layer is a new family of intrinsic sol-gels coatings based on hybrid epoxy-alkoxysilanes containing dynamic di-sulfide bonds for healing promotion. Upon application of moderate pressures and temperatures, the new systems flow and repair (i.e. close and seal) macroscopic scratches up to an approximate width of 500 μm and restore the barrier properties.
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