Recycled eggshell waste in zinc-rich epoxy coating for corrosion protection of mild steel in a controlled elevated temperature saline environment

Abstract

Eggshell wastes have attracted interest in the fabrication of anticorrosion coatings due to chemical compositions (high calcite content) and widespread availability. This study presents the use of chemically and thermally treated eggshell nanoparticles as fillers in a zinc-rich epoxy matrix in corrosion protection of mild steel in sodium chloride solution at an elevated temperature. Three samples of zinc-rich coatings containing “as ball-milled” eggshell, chemically and thermally treated eggshell nanoparticles were fabricated to form zinc-rich eggshell nanoparticles epoxy (ZENE) coatings. The structural characterizations indicated that chemical and thermal treatment removed the protein materials from eggshell nanoparticles, leading to a 10-fold increase in electrical conductivities and prolonged the cathodic sacrificial behaviour of the ZENE coatings throughout the immersion period. The electrochemical impedance study of these coatings after immersion in an elevated-temperature corrosive environment showed that chemically-treated eggshells in comparison with thermally-treated ones could effectively remove protein materials from the eggshell nanoparticles. These nanoparticles as fillers in the zinc-epoxy matrix significantly enhanced the anticorrosion performance by improving the cathodic as well as barrier protection properties of the coating. A proposed corrosion protection mechanism of the ZENE coatings in 3.5 wt% NaCl solution revealed that the improved electrical conductivity of the treated eggshell nanoparticles enhanced the galvanic contact at the interstitial spaces between the zinc particles while prolonging the zinc cathodic sacrificial behaviour. Thus, this study demonstrated the sustainable use of eggshell wastes in enhancing the anticorrosion properties of zinc-rich epoxy coatings.