Lavandula Stoechas as a Green Corrosion Inhibitor for Monel 400 in Sulfuric Acid: Electrochemical, Gravimetrical, and AFM Investigations

The inhibiting effect of Lavendula stoechas extract on the corrosion of Monel alloy 400 in 0.5 M sulfuric acid at different temperatures (298–328 K) was evaluated by mass loss measurements and electrochemical techniques, including Electrochemical Impedance Spectroscopy (EIS) and potentiodynamic polarization. The corroded surfaces of metal samples were examined using an atomic force microscope (AFM). Experimental results revealed that the inhibition efficiency increases with increasing inhibitor content and decreases with increasing temperature. The maximum inhibition efficiency was approximately 90.81%, and was reached in the presence of 0.25 g/L inhibitor at 298 K. The inhibitory action of Lavendula extract was realized via the adsorption of phytochemical constituents on the metal surface. The adsorption follows the Langmuir adsorption mechanism. Thermodynamic parameters suggested that the adsorption was spontaneous at different temperatures, supporting a mixed physisorption and chemisorption mechanism. Electrochemical impedance spectroscopy indicated that the inhibitor ameliorates the film formed at the metal/solution interface. Potentiodynamic polarization studies reveal that the inhibitor behaves as a mixed-type inhibitor,  with a predominantly anodic tendency. AFM studies confirmed the adsorption of Lavendula extract on the Monel alloy surface.