Viability of epoxy-siloxane hybrid coatings for preventing steel corrosion

In this research work, eight coatings consisting of primers, topcoats and combinations of primers/topcoats were evaluated. Salt spray test (SST) and impedance measurements were carried out for evaluating macroscopic failures (blistering, adhesion, etc.) and the electrochemical behaviour of the referred coatings, respectively, which were supported by surface characterization techniques such as scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray mapping (XRM). Coating systems comprising an epoxy-siloxane topcoat have offered a better corrosion protection of the steel substrate than its counterpart with polyurethane topcoat (comparing coating systems with the same primer: 1A and 1B, 2A and 2B). Also, the addition of any of the topcoats has outperformed the properties conferred by the epoxy coating pigmented with zinc phosphate (ZP) and micaceous iron oxide (MIO), which have shown the worst behaviour as a single coat. The single epoxy-siloxane topcoat and the epoxy-polyurethane water-based coating system have also provided excellent protective properties, thus allowing to open up new opportunities to be implemented in real structures.