Synergistic inhibition effect of thioureido imidazoline and cationic surfactants with different alkyl chain lengths on X80 carbon steel in CO2-saturated NaCl solutions

The corrosion inhibition performance of the thioureido imidazoline (TU-IM) corrosion inhibitor, along with three surfactants, was assessed for X80 carbon steels in a CO₂-saturated NaCl solution using weight loss tests, electrochemical and microstructural characterization. Results demonstrate that the corrosion-inhibition efficiency of surfactants improves with increasing alkyl-chain length in the following order: cetyltrimethylammonium bromide (CTAB) > tetradecyltrimethylammonium bromide (TTAB) > dodecyltrimethylammonium bromide (DTAB). A synergistic corrosion inhibition effect between TU-IM and DTAB/TTAB was observed, with the best performance achieved using 10 mg/L TU-IM and 10 mg/L DTAB/TTAB (inhibition efficiency: 97.68 %), which is mainly attributed to the cooperative adsorption of both substances. By contrast, the synergistic inhibition capability of TU-IM with the surfactants decreased as the alkyl-chain length increased, and even an antagonistic effect was noted for the combination of TU-IM + CTAB owing to the competitive adsorption between the surfactant and the corrosion inhibitor.