Electrolytic co-deposition of Zn-ZnO and Zn-ZnO-CaCO₃ composite substrates on low-carbon steel

Abstract

Conventionally employed zinc-rich paints and coatings for marine corrosion protection of steel still comprise environmentally unfriendly compounds such as zinc phosphate. This paper is focused on developing eco-friendly zinc ternary composite coatings of Zn-ZnO-CaCO3 utilizing CaCO3 additives derived from tympanotonus fuscatus (periwinkle) shell and calcareous eggshell respectively on low-carbon steel using electrodeposition technique. This is aimed at improving not only the surface corrosion resistance of steel structures in marine environment but also the sustainability of raw materials and minimal environmental pollution. Corrosion studies of uncoated and coated steel samples in simulated marine environment were done using linear polarization technique. Results obtained suggested that CaCO3 (i.e., calcareous eggshell) additive in the composite coating significantly improved the corrosion performance of the substrate. Steel coated with calcareous eggshell additive displayed superior corrosion performance having highest polarization resistance, Rp (156090 Ω), lowest corrosion rate, CR (0.01 mm/year) and highest coating efficiency, Ceff (97%) as against those of uncoated, zinc oxide, and tympanotonus fuscatus shell additives after 30 minutes deposition time. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) results of selected developed coatings indicated presence of a homogeneous surface morphology and a significant amount of calcium in the calcareous eggshell coating.