Smart ZnS@C filler for super-anticorrosive self-healing zinc-rich epoxy coating

The zinc-rich epoxy cathodic protection coating is the most widely used anticorrosion material for marine steel. However, traditional conductive fillers lack the intelligent self-healing effect, which limits the long-term anticorrosion performance. Herein, with uniform carbon-coated ZnS (ZnS@C) nanoballs as the smart active release filler, we propose an anticorrosive and self-healing zinc-rich maleic anhydride epoxy coating. Due to the high pore filling efficiency of the nanoballs, the water vapor transmission rate of the coating with an initial corrosion efficiency of 99.92% and a low-frequency impedance of |Z|_f=10mHz = 3.88 × 10¹⁰ Ω·cm², was reduced by 52%. The carbon-shell of the nanoball increases electron transmission paths in the coating and improves conductivity by nearly two orders of magnitude, which effectively activates more Zn-sites and extends the cathodic protection time. Moreover, once the steel-substrate undergoes regional corrosion, the SO₄²⁻ hydrolyzes from the ZnS-core of the nanoball and reacts with iron ions on the corroded area accurately and intelligently to fill the gap and self-heals into a new dense barrier layer (Fe₂(SO₄)₃, etc.), which significantly improves the shielding protection ability during the long-term usage of the coating. The effective anticorrosion time of the proposed coating could be up to 3,400 h.