Exploring Rosemary Essential Oil as an Eco-Friendly Corrosion Inhibitor for low-alloy Steel in 1 M H2SO4: Electrochemical Studies, Weight Loss, and Computational insights

This work explores the potential of rosemary essential oil (REO) as an environmentally friendly corrosion inhibitor for low-alloy steel in 1 M H ₂ SO ₄ . The chemical composition of the oil, dominated by eucalyptol and α-pinene, was first established by GC-FID analysis. The inhibitory performance of REO was evaluated using gravimetric measurements, potentiodynamic polarization, electrochemical impedance spectroscopy, and temperature-dependent tests. These experiments consistently showed that REO reduces the corrosion rate by forming a protective layer on the steel surface, with optimal performance observed at 1.5 g/L. The decrease in corrosion current density, the widening of the Nyquist loops, and the reduction in double layer capacitance confirm the progressive coverage of the surface achieved by the active constituents of the oil. Thermodynamic and kinetic parameters further indicate that the inhibitor increases the energy barrier of the corrosion reaction and maintains good stability at high temperatures. Adsorption studies have revealed that REO constituents follow a Langmuir adsorption model and exhibit spontaneous adsorption due to a strong affinity with the metal surface. Additional DFT calculations, molecular electrostatic potential (MEP) analyses, and Monte Carlo simulations highlight the predominant role of oxygenated monoterpenes, particularly eucalyptol, isoborneol, and terpineols in stabilizing the organic film through electron-donating interactions.