Molecular Dynamic Simulation on the Synergistic Corrosion Inhibition Effect and Mechanism of Quinoline Quaternary Ammonium Salt and L-Methionine

The synergistic effect and synergistic mechanism of quinoline quaternary ammonium salt (QQAS) and L-methionine (L-Met) as Q235 carbon steel corrosion inhibitors in 1.0 M HCl solution were studied by weight-loss and electrochemistry and theoretical methods at 60°C. Both the weight-loss and the electrochemistry experiment results show that there is obvious synergistic effect with a synergistic index of 8.81 between QQAS and L-Met. The results of the electrochemical experiments show that the inhibition efficiency of the mixture corrosion inhibitor reaches 98.46% when the concentration of the mixture inhibitor is 50 mg/L with the molar ratio of QQAS and L-Met of 3 to 1. The quantum chemical parameters calculated at B3LYP/6-311++G** level indicate that QQAS can be preferentially adsorbed for its stronger offer electron ability. The results of molecular dynamics studies show that QQAS is preferentially adsorbed onto the surface of carbon steel forming the framework of the corrosion inhibitor film. And L-Met molecules fills the gap to make the film more condensed. The adsorption energy and the density distribution of the inhibitor and water molecules indicate that the corrosion inhibition performance is the best when the molar ratio of QQAS and L-Met is 3:1. And the synergistic inhibition mechanism is the monolayer adsorption mechanism. These results can provide useful guidance for further study on the synergistic corrosion inhibition effects of QQAS and other compounds.