Inorganic–organic sol gel hybrid coatings for corrosion protection of metals

Inorganic–organic hybrid coatings by sol–gel process are very suitable for fighting corrosion. Inorganic sols in hybrid coatings not only increase adhesion by forming chemical bonds between metals and hybrid coatings, but also improve comprehensive performances of polymer in the coatings. Different organic polymers or organic functionalities are introduced into gel network to achieve tailored properties, such as hydrophobic properties, increasing cross-linking density, etc. As for corrosion protection of metals organic components of hybrid coatings are selected to repel water and form dense thick films and reduce coating porosity. The factors, such as the ratio of inorganic and organic components, cure temperature, pigments in hybrid coatings, need to be optimized for attaining hybrid films with the maximum corrosion resistance. Electro-deposition technique offers relatively thick homogeneous defect-free hybrid coatings in comparison to dip or spin coating techniques. Green cerium ions and non-ionizable organic inhibitors are more developed in hybrid coatings nowadays than other corrosion inhibitors. Long-term corrosion resistance techniques of inhibitors are discussed. The inhibitors entrapped in the nanocontainers are doped in hybrid films to prolong release of the inhibitors to damaged zones, which is discussed in detail. Among all the nanocontainers of corrosion inhibitors the prospective techniques which show superior corrosion protection are cyclodextrin/organic inhibitor inclusion complexes and layer by layer assembly of organic corrosion inhibitors in nanocontainers. Super-hydrophobic property of hybrid coatings derives from low surface tension and surface roughness of hybrid coatings, which endues the films with excellent corrosion protection for metals, but the durable property of super-hydrophobic coatings needs to be improved for industrial application. An ideal multiple model of hybrid coatings for superior anti-corrosion of metals proposed is a combination of super-hydrophobic hybrid coatings and underlying hybrid coatings doped with sustained release of corrosion inhibitors on metal substrates.