New epoxy resin as a high-performance corrosion inhibitor for steel: experimental and theoretical investigations

Abstract

In this study, a novel epoxy resin, triglycidyl-dibenzylidene-thiosemicarbazide (TGDBTSC), was firstly synthesized and evaluated as an efficient defensive agent for mild steel in 1 M HCl. Electrochemical studied demonstrated excellent protection performance, with efficiencies reaching 93.2% at a concentration of 10⁻³ M. The corrosion current density exhibited a substantial decline, from 983 to 66 µA cm⁻², as measured by Potentiodynamic Polarization (PDP), while the charge transfer resistance underwent an increase from 34.7 to 312.8 Ω cm², as measured by Electrochemical Impedance Spectroscopy (EIS). Thermodynamic studies revealed an activation energy of 40.57 kJ·mol⁻¹ and an enthalpy of activation of 37.97 kJ·mol⁻¹, indicating an endothermic adsorption process. At approximately 328 K, the inhibition efficiency remained high (86.5%), thereby confirming the thermal stability of TGDBTSC. Surface analysis revealed a smooth and compact surface morphology of protected steel, accompanied by inhibitor adsorption. Density Functional Theory (DFT) calculations revealed a smaller energy gap (ΔE_gap = 2.965 eV) and higher electron-donating ability (ΔN = 0.450) for the protonated form of TGDBTSC. Monte Carlo (MC) and molecular dynamics (MD) simulations further corroborated the strong adsorption affinity, with adsorption energies of − 180.65 kcal/mol and radial distribution function (RDF) peaks between 1.5 and 3.0 Å, indicative of chemisorption. These findings confirm the potential of TGDBTSC as a highly effective, durable, and thermally stable inhibitor for acid-treated steel corrosion.