Corrosion inhibition of Q235 and X65 steels in CO2-saturated solution by 2-phenyl imidazoline

This study examined 2-phenyl imidazoline (2-PI) as an eco-friendly corrosion inhibitor for Q235 and X65 steels with various microstructures in CO2-saturated solution. The inhibition performances of the 2-PI inhibitor for both steels were comparatively studied through electrochemical tests, weight-loss method, wire beam electrode (WBE) technique as well as surface analysis. The results demonstrate that the 2-PI compound acts as a mixed-type inhibitor and exhibits effective and durable inhibition performance against general and localized corrosion. The adsorption of 2-PI molecules on steel surfaces is exothermic, spontaneous and follows the Langmuir isotherm model. Furthermore, the steel microstructure strongly influences the adsorption behavior of 2-PI inhibitor, the Q235 steel with a higher pearlite/ferrite ratio promotes the physical adsorption of the protonated 2-PI molecules at lower concentrations, and the X65 steel with a lower pearlite/ferrite ratio enhances the chemical adsorption of the unprotonated 2-PI molecules at higher concentrations. Additionally, the adsorption mechanism was also discussed based on the evaluated thermodynamic data and the results of X-ray photoelectron spectroscopy (XPS) analysis.