Corrosion Inhibition Potential of Dithiohydrazodicarbonamide Derivatives for Mild Steel in Acid Media: Synthesis, Experimental, DFT, and Monte Carlo Studies

Abstract

In the present work, new compounds, namely 2-fluoro phenyl-2,5-dithiohydrazodicarbonamide (2FPDC) and 4-fluoro phenyl-2,5-dithiohydrazodicarbonamide (4FPDC), were successfully synthesized and examined as corrosion inhibitors for mild steel in 1 M HCl. The molecular structures were characterized by Fourier transform infrared spectroscopy (FT-IR) and 1H, 13C nuclear magnetic resonance (NMR). A scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), and atomic force microscope (AFM) were conducted to identify the surface morphology of mild steel in the absence and existence of a corrosion inhibitor. Several electrochemical techniques have been conducted to evaluate inhibitor efficiency. The influence of immersion time on the efficiency of inhibitors was also investigated. The electrochemical results showed that both compounds appeared to be mixed type. However, 4FPDC is slightly more efficient than 2FPDC (97.3% compared with 96.5% at 1 × 10−2 M and an immersion time of 5 h). The resistance polarization for inhibitors was found to obey an order of 4FPDC ˃ 2FPDC. The Langmuir isotherm system revealed the best match, and the type of adsorption was physisorption and chemisorption in both compounds. SEM and EDX results have confirmed the presence of particles of inhibitor on the metal surface. A smooth surface was observed in the presence of inhibitors approved by AFM. Quantum chemical results showed that the adsorption of molecules of inhibitor takes place predominantly through protonated structures, and strongly agreed with experimental results. The results reveal that excellent inhibition efficiency was attained even in aggressive conditions, and they can be viewed as novel corrosion inhibitors for mild steel with excellent protection.