Chemically bonded phosphate ceramic coatings with self-healing capability for corrosion resistance

Abstract

Chemically bonded phosphate ceramic coatings (FCBPC) modified with organic-inorganic hybrid nano alumina (FAS-Al2O3) were prepared. The effects of FAS-Al2O3 on the morphology, corrosion resistance and self-healing properties of FCBPC are investigated. The results show that FAS-Al2O3 can improve the penetration resistance, bond strength and corrosion resistance of the coating. When the content of FAS-Al2O3 is 1.5 wt%, the impedance value at low frequency (0.01 Hz) of FCBPC3 can reach 1.52 × 106 Ω·cm2. This is mainly attributed to the introduction of organic perfluorinated long chains with low surface energy by fluorinated alkyl silane, which allows nanoparticles to be uniformly dispersed on micron alumina ceramic aggregates to build special micro-nano structures. FAS-Al2O3 can combine with AlPO4 and act as a binder to fill the pores between ceramic aggregates, increasing the cohesion of the coating and the bond strength between the coating and the substrate to the point of blocking or extending the diffusion path of corrosive media inside the coating, which in turn improves the corrosion resistance of coatings. In particular, the coatings exhibit excellent self-healing properties in terms of corrosion resistance after heat treatment. Heat treatment will cause the organic perfluorinated molecules in FAS-Al2O3 to rotate and migrate, and more fluorinated alkyl chains will be exposed, thereby minimizing the surface energy of the coating. In addition, special micro-nano structures are reconfigured due to thermally driven self-migration of organic perfluorinated chains. As a result, the hydrophobicity and impermeability of the coating are restored after heat exposure, reducing the intrusion of corrosive media, and thus the corrosion resistance of the coating has self-healing capability. This work could open up a thought-provoking idea for improving the long-term corrosion protection of phosphate ceramic coatings in high-temperature marine environments.