Microwave and heat-assisted extracted Melilotus officinalis as a potential eco-friendly corrosion inhibitor for carbon steel in 0.5 M HCl solution

This study investigates, for the first time, the inhibitory capabilities of Melilotus officinalis extract (MOE), extracted via microwave-assisted (MAE) and heat-assisted extraction (HAE), in preventing corrosion of carbon steel (CS) in a 0.5 M HCl solution. Utilized methodologies include conventional weight loss techniques and electrochemical analyses like Tafel polarization and electrochemical impedance spectroscopy (EIS) for measuring MOE's inhibition efficiency (IE) on CS. The adsorption behaviors of MOE on the CS surface were evaluated through different adsorption isotherm models. Additionally, the study assessed the effect of temperature on the extracted MOE's IE% and polarization actions, providing thermodynamic parameters (Ea, ΔS*, and ΔH*) for CS in the acidic solution, both with and without MOE presence. The maximum IE% achieved was 92.3% when the concentration of MOE extracted via the MAE route reached 800 ppm, following a duration of 30 min, as determined by EIS measurements. Finally, surface protection offered by MOE to CS in the acidic solution was verified using scanning electron microscopy (SEM). The results of the study are reviewed and analyzed comprehensively.