Exploration of imidazol-4-methylimine thiourea as effective corrosion inhibitor for mild steel in hydrochloric medium: Experimental and theoretical studies

Mild steel is considered to be the most common engineering material and the key problem is its susceptibility to corrosion, a problem that can be effectively addressed by corrosion inhibitors. In this work, thiosemicarbazide chain was innovatively used for modifying the imidazole ring to improve the inhibition effect of imidazole compound and thus a high-effective corrosion inhibitor of imidazol-4-methylimine thiourea (MIT) for mild steel in HCl medium was obtained. The inhibition performance of MIT was evaluated by gravimetric measurements, electrochemical tests, and surface analyses. The results indicated that the optimal concentration of MIT was 200 mg L-1 in 1.0 M HCl solution at 298 K, with an inhibition efficiency of 93.7 %. The adsorption of MIT molecules on mild steel was demonstrated to be an exothermic process according to the Langmuir adsorption isotherm, belonging to a mixed adsorption mechanism of physical and chemical adsorption (& UDelta;G degrees ads = -31.87 kJ mol-1, 298 K), which effectively retards the MS corrosion process by blocking both anodic and cathodic reactions. Furthermore, theoretical calculations based on density functional theory and molecular dynamics simulations indicate that the corrosion inhibition mechanism of MIT molecules is mainly attributed to two effective ways, involving shielding effect of the MIT-adsorption film with multiple anchors and reduction of attacking ions.