Electrochemical, surface, and theoretical studies on amine-based organic compounds as efficient corrosion inhibitors for mild steel in 1 M HCl

The present article examines the inhibitory efficiency of two synthesized amine-based organic molecules, namely 11-(2-chlorophenyl)-3,3-dimethyl-2,3,4,5,10,11-hexahydro-1H-dibenzo[be][1,4]diazepin-1-one (CDHD) and 3,3-dimethyl-11-phenyl-2,3,4,5,10,11-hexahydro-1H-dibenzo[be][1,4]diazepin-1-one (DPHD), in reducing the corrosion of mild steel in a 1 M hydrochloric acid solution. These inhibitors were synthesized and characterized by NMR spectroscopy, and their corrosion inhibition performance was evaluated using gravimetric and electrochemical techniques, including open circuit potential (OCP), Tafel polarization, and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization curves showed that the tested compounds act as mixed-type inhibitors. EIS analyses indicated that the charge transfer resistance increased from 22.7 Ω.cm² to 397.8 Ω.cm² and 606.2 Ω·cm² at a concentration of 10⁻³ M of CDHD and DPHD, respectively. Additionally, it was found that the adsorption of both compounds on the mild steel surface follows the Langmuir adsorption isotherm equation. These compounds also retained their inhibition efficiency at high temperatures. Surface morphology and elemental composition analyses of steel samples, performed using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), confirmed the formation of a barrier layer covering the mild steel surface. Furthermore, quantum chemical calculations using density functional theory (DFT) provided insights into the reactivity and adsorption characteristics of the inhibitors, validated by molecular dynamic simulations. The study highlights the high efficiency of both inhibitors, with inhibition efficiencies reaching 95.9 % for DPHD at a concentration of 10⁻³ M, emphasizing their potential as environmentally friendly corrosion inhibitors for industrial applications.