Synthesis and Properties of a Rust Conversion Coating Based on Gallic Acid

A weak acid rust converter based on gallic acid was synthesized. On this basis, a new type of rust conversion coating was prepared by combining epoxy resin E-51, butyl glycidyl ether, silane coupling agent (3-aminopropyl triethoxysilane), curing agent T-31 and so on. The corrosion resistance, surface morphology, composition and anti-corrosion mechanism of rust conversion coatings were studied by impact resistance test, adhesion test, electrochemical test, scanning electron microscopy, salt-spray test and X-ray diffraction (XRD). The results show that the rust conversion coating prepared on the surface of rusted 20 steel had a smooth surface, and the contact parts between the coating and the rusted steel were relatively dense, showing strong adhesion. The coating exhibited good corrosion resistance in salt-spray test and electrochemical test. Macromolecular iron compounds were formed by chelating the phenolic hydroxyl in the coating with Fe ion, which inhibited the further expansion of rust. When the rust conversion coating is used, it only needs simple surface floating rust treatment and can be completed by once coating, indicating that it is unnecessary to use traditional “primer + topcoat” complex process.