Acid resistance and failure mechanism of zinc-rich primer/micaceous iron oxide/polyurethane composite coating immersed in 5 wt% sulfuric acid

Abstract

In order to study the reliable resistance to sulfuric acid corrosion of epoxy zinc rich primer/micairon oxide intermediate paint/acrylic polyurethane topcoat composite coatings for power transmission and transformation equipment. In this paper, under the condition of immersion in 5 wt% sulfuric acid, the sulfuric acid resistance behaviour of zinc-rich epoxy/micaceous iron oxide/polyurethane composite coating was evaluated by performing soaking tests for 50 h, 100 h and 150 h, and the failure mechanism of the film was studied. The changes in the surface properties of the coating during sulfuric acid soaking were evaluated by testing the hardness, glossiness and adhesion, and the changes in the capacitance and resistance characteristics of the coating during acid soaking were studied by Electrochemical Impedance Spectroscopy (EIS). The micromorphology and chemical element distribution of the cross-section of the composite coatings were studied by Scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS). The functional group changes were studied by Fourier transform infrared spectroscopy (FT-IR). The results show that the corrosive effect of sulfuric acid solution immersion on acrylic polyurethane is weak, while the hydrolysis of water molecules will lead to aging and failure of acrylic polyurethane. Sulfuric acid leads to the formation of zinc deficient areas in zinc-rich primers, which reduces the cathodic protection effect of zinc-rich primers. The service life of the zinc-rich primer/ Micaceous Iron Oxide/acrylic polyurethane composite coating is less than 150 h.