Synergistic effect between two quaternary ammonium salts and thiourea as corrosion inhibitors for X70 steels in CO2 saturated 3.5% NaCl solution

Pyridine and quinoline quaternary ammonium salts (1-CPN and 1-CQN) were synthesized. The synergistic effects with different molar ratios of TU were investigated using weight loss, electrochemical measurements, surface characterization and theoretical calculations. The results showed that 1-CPN and 1-CQN had significant synergistic corrosion inhibition effects when combined with TU. The best synergistic effect occurred at 1-CPN/1-CQN: TU = 3:1, which had been proved by weight loss, electrochemical measurements and theoretical calculations. The mixture of 1-CPN/1-CQN with TU produced a denser adsorption film on the X70 steels surface, effectively inhibiting the corrosion process. Additionally, an intermolecular synergistic mechanism was proposed.