Comprehensive evaluation of 5-imino-1,2,4-dithiazolidine-3-thione as a corrosion inhibitor for mild steel in hydrochloric acid solution.

The corrosion inhibition performance of 5-imino-1,2,4-dithiazolidine-3-thione (IDTT) on mild steel in 1.0 M HCl solution was comprehensively evaluated using weight loss measurements, electrochemical techniques, adsorption studies, and density functional theory (DFT) calculations. This study uniquely integrates experimental and theoretical approaches to provide a comprehensive understanding of IDTT's adsorption behavior and inhibition mechanism. Weight loss measurements demonstrated a significant reduction in corrosion rate (CR) from 5.74 mg·cm·h⁻ (blank) to 0.31 mg·cm·h at 0.5 mM, achieving a maximum inhibition efficiency (IE%) of 84.3%. Potentiodynamic polarization studies confirmed that IDTT functions as a mixed-type inhibitor, effectively suppressing both anodic and cathodic reactions. The corrosion current density (i) decreased from 9.9 to 2.7 µA·cm at 303 K, while polarization resistance (Rp) increased from 50.3 Ω (blank) to 149.2 Ω at 0.5 mM, indicating enhanced surface protection. Adsorption studies revealed that IDTT follows the Langmuir adsorption isotherm, suggesting monolayer adsorption with an adsorption equilibrium constant (K) of 1.32 × 10 M. The calculated Gibbs free energy of adsorption (ΔG =  -19.83 kJ·mol) indicates that physisorption dominates the adsorption mechanism, ensuring effective surface coverage. DFT calculations provided molecular-level insights into IDTT's inhibition mechanism, revealing a HOMO energy of -8.458 eV and a LUMO energy of 1.2 eV, which confirm strong electronic interactions with the metal surface. Mulliken charge analysis identified sulfur and nitrogen atoms as active adsorption sites, reinforcing IDTT's ability to form a stable protective layer on mild steel. This study demonstrates the novelty of IDTT as a highly efficient corrosion inhibitor, combining experimental validation and computational analysis to establish its adsorption mechanism and surface interactions. The findings highlight IDTT's potential for industrial applications as a sustainable and effective inhibitor for corrosion control in acidic environments.