Water-based rust converter and its polymer composites for surface anticorrosion

A novel water-based rust converter 2-hydroxypropyl 3, 4, 5-trihydroxybenzoate (named as RC-GAE) was prepared by using an esterification reaction between 1, 2-propylene glycol (PG) and gallic acid (GA). The effects of PG and GA mass ratio in the RC-GAEs on the anticorrosion were investigated by the Tafel polarization with the rusty plate samples coated with RC-GAEs in a 3.5 wt% NaCl solution. The rust was converted to a compact black protective rust-conversion film with this rust converter. The metallographic microstructure, morphology, and crystalline phase of the rust-conversion films were conducted systematically by optical microscopy, X-ray diffraction, and scanning electron microscopy with energy-dispersive spectrometry. The corroded plate with uneven and rough brown surface became smoother and darker after treated with converter. X-ray photoelectron spectroscopy indicated that the RC-GAE reacted with Fe²⁺/Fe³⁺ and formed a compact Fe²⁺/Fe³⁺ chelate film that played the role of anticorrosion. Additionally, new water-based anticorrosion coating was prepared by applying a mixture of RC-GAE and other additives to form polymer composites on the rusty steel plates. Both adhesion test and neutral salt spray test indicated that the anticorrosion coating presented a good corrosion resistance and a remarkably strong film adhesion of the new water-based anticorrosion polymer composites coating.