Corrosion Resistance and Thermal Stability Enhancement of Green Layered Clay/Epoxy Coating

Abstract

A layered clay/epoxy coating was fabricated to investigate the effects of montmorillonite (MMT) and halloysite nanotube (HNT) loading at 0.5, 1.5, and 2.5 parts per hundred resin (phr) on the corrosion resistance and thermal stability of coated mild steel plates. The corrosion study was carried out by Electrochemical Impedance Spectroscopy (EIS) and Tafel polarization. The |Z|0.1Hz value, Rct, and Rp of the layered/clay epoxy coatings containing 1.5 phr of HNT and MMT exhibited the best anticorrosion performance compared to other clay content levels. The |Z|0.1Hz value for the epoxy coating filled with 1.5 phr of MMT (M1.5) is 2.132 × 109 Ω·cm², while it is slightly higher for H1.5 coatings, i.e., 2.629 × 109 Ω·cm². Water absorption trends were consistent with EIS and Tafel polarization studies. The presence of highly compatible nanocontainers clay reduced the total free volume and promoted cross-linking, enhancing anticorrosion performance. Thermal Gravimetry Analysis (TGA) showed that a 1.5 phr loading of MMT in layered/clay epoxy coating demonstrated better thermal stability than a coating embedded with HNT. This improvement can be attributed to the barrier effect of MMT, which retards the diffusion of oxygen molecules into the coating.