Mitigation of erosion and corrosion of steel using nano-composite coating: Polyurethane reinforced with SiO₂-ZnO core-shell nanoparticles

In the present study, we developed a multifunctional surface coating with silica-ZnO (SiO₂-ZnO) core-shell nanoparticles. The idea behind the synthesis of core-shell nanoparticles was to utilize the mechanical strength of silica and the hydrophobicity of ZnO together in a single coating structure. Coating formulations were developed with solvent-based polyurethane binder containing silica-ZnO core-shell nanoparticles at various concentrations (1–4 wt%) on the steel substrate. These nanoparticles were characterized via X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) etc. Further, developed coatings were characterized for their surface wettability through measuring water contact angle. The erosion behaviour of the developed coatings has been analyzed through an air-jet solid particle erosion tester. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization study are used to analyze the corrosion response of the substrate and the coatings. The coatings exhibited lesser Vickers and scratch hardness values then the substrate. The best erosion and corrosion resistant, and nearly superhydrophobic surface was achieved by nanocoating developed with 4 % (wt.) of silica-ZnO core-shell nanoparticles on the substrate material. The erosion performance was significantly improved in this coating as compared to the uncoated substrate (at 30° impact angle, erosion reduction ≈ 98 % and at impact angle 90°, erosion reduction ≈ 96 %). Lowest current density and the highest corrosion potential in polarization tests, and the highest impedance in EIS studies were also observed in the nanocoating developed with 4 % (wt.) SiO₂-ZnO core-shell nanoparticles. Based on the coatings' performance evaluation, they can be used as protective layers for structural marine components.