The synergistic inhibition effect between imidazoline-based dissymmetric bis-quaternary ammonium salts and thiourea on Q235 steel in CO₂ corrosion process

The inhibition effect of imidazoline-based dissymmetric bis-quaternary ammonium salt (DBA) and Thiourea (TU) on Q235 steel in CO₂-saturated simulated oilfield-produced water was studied by means of the weight-loss method, polarization and electrochemical impedance spectroscopy (EIS). The polarization measurements reveal that the compound inhibitors are anodic-type inhibitors that mainly inhibit the anodic process. EIS results show that the changes in the impedance parameters are due to the formation of a protective layer on the Q235 steel surface by the adsorption of inhibitor molecules. The results of energy dispersive X-ray spectroscopy and scanning electron microscopy confirm the existence of the protective layer. The results also show that adsorption model obeys to the Flory-Huggins adsorption isotherm. The synergism parameter suggests that the synergistic effect is obvious at concentrations of 100 and 200 mg L^-1, and there is a cooperative mechanism between the DBA and TU.