Insight into the Anti-Corrosion Mechanism of Halogen Anions in Bisimidazoline Derivatives as Corrosion Inhibitor for Q235 Steel in 1.0 mol/L HCl

Quaternary ammonium salts have high corrosion inhibition performance, but anions have a significant impact on their corrosion inhibition performance. Based on this, the effects of I⁻ and Br⁻ on the corrosion inhibition performance in bisimidazole were investigated carefully. In this work, two imidazoline derivatives (MZB and MZI) were synthesized and their structures were verified by infrared spectrum (IR) and nuclear magnetic resonance (NMR). The corrosion inhibition performance and mechanism were evaluated comprehensively through weight loss, electrochemical experiments and theoretical calculations. The weight loss experiment showed that the corrosion inhibition rates of MZB and MZI at the concentration of 2.0 mmol/L were 94.52% and 95.52%, respectively, and followed the Langmuir isotherm adsorption. The open circuit potential and potentiodynamic polarization curve (Tafel) demonstrated that MZB and MZI were cathodic corrosion inhibitors, electrochemical impedance spectroscopy studies have shown that with the concentration of MZB and MZI increased, their corrosion inhibition ability improved gradually, at the concentration of 2.0 mmol/L, their corrosion rates were 96.82% and 97.57%, and the addition of corrosion inhibitors mainly increased the film resistance (R_f) and charge transfer resistance (R_ct) within the corrosion inhibition system, thereby improving their corrosion inhibition efficiency. XPS, EDS and IR further confirmed that MZB and MZI can adsorb on the surface of Q235 to form a stable protective film. Density functional theory and molecular dynamics simulation further confirm this theory from the molecular level.