Sustainable corrosion inhibition of EH40 steel in seawater using carboxymethyl chitosan/L-lysine composite

The corrosion inhibition of marine engineering steels in oceanic environments remains a critical challenge for various industrial applications. In this study, a non-toxic and environmentally benign composite corrosion inhibitor was developed by blending carboxymethyl chitosan (CMCS) and L-lysine (Lys). Weight loss measurements, electrochemical tests and surface characterization were performed at room temperature (25 ± 2℃) to systematically evaluate and study the inhibitory effects and mechanism of the composite inhibitor on EH40 steel corrosion in seawater under varying concentration ratios (CMCS:Lys) and immersion durations (2 h and 3, 7, 14 days). And simulate the corrosion inhibitor molecules and surface adsorption behavior through DFT and MD calculations to support the experimental content. The results demonstrated that the composite inhibitor effectively suppressed the seawater-induced corrosion of EH40 steel. The optimal corrosion inhibition performance was achieved at a CMCS:Lys concentration ratio of 3:2, where the protective film on the steel surface exhibited the maximum stability and compactness. Also, the corrosion inhibition rate and absolute synergistic parameters of the corrosion inhibitor increase with the increase of immersion time. Surface analysis was conducted in combination with theoretical calculations to reveal that CMCS and Lys molecules possess multiple active adsorption sites, enabling their adsorption onto the EH40 steel surface via N and O heteroatoms. This adsorption mechanism facilitated the formation of a stable passivation layer, thereby leading to the exceptional inhibitory effect on corrosion.