Natural Elettaria cardamomum Essential Oil as a Sustainable and a Green Corrosion Inhibitor for Mild Steel in 1.0 M HCl Solution: Electrochemical and Computational Methods

Elettaria cardamomum essential oil (EO) was verified as a safe and green corrosion inhibitor against the corrosion of mild steel in 1.0 M HCl solution through electrochemical (Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) measurements), and computational studies. The studied EO inhibits corrosion of mild steel in 1.0 M HCl, and their corrosion inhibition efficiencies increase with increase in concentration. Elettaria cardamomum achieved a significant inhibition efficiency of 88% for a concentration of 2 g/L of inhibitor concentration. PDP findings show that the examined EO behaved as a cathodic-type inhibitor. EIS data revealed the adsorptive nature of the EO molecules on the steel surface. SEM/EDS analysis shows the adsorption of the EO molecules on the surface of mild steel to form a protective film that blocked steel surface from the acid attack. The DFT results proved that 1,8-cineole and α-terpinylacetate have a high electron-accepting capacity and interact actively with the iron surface, which may be responsible for the inhibition ability of the studied EO.