Synergistic Inhibition Effect of 9-(4-Chlorophenyl)-1,2,3,4-tetrahydroacridines and Tween-80 for Mild Steel Corrosion in Acid Medium

The synergistic inhibition effect of Tween-80 and 1,2,3,4-tetrahydroacridines, including 9-(4-chlorophenyl)-2-methyl-1,2,3,4-tetrahydroacridine (CMT) and ethyl 9-(4-chlorophenyl)-1,2,3,4-tetrahydroacridine-2-carboxylate (ECT), on mild steel corrosion in 1 M HCl was investigated by using weight loss tests, electrochemical techniques, and surface morphology (SEM/SECM). The results indicated that the mixtures of CMT/ECT and Tween-80 strongly inhibit the corrosion of mild steel compared to individual inhibitors, and the adsorption mode belongs to the Langmuir isothermal type. Electrochemical measurements showed that the mixtures were mixed-type inhibitors, and a double-layer structure film with the inner layer of Tween-80 and the outer layer of CMT/ECT was formed on the steel surface. That the calculated synergistic parameter value was larger than unity illustrates that the enhancement of inhibition in the presence of Tween-80 is only due to synergistic action. Surface analysis techniques (SEM/SECM) verified that CMT and ECT were absorbed on the steel surface along with Tween-80 in the presence of mixtures, effectively controlling the metal corrosion.