Inhibition of corrosion of an aluminum alloy by Rosemary and Eucalyptus extracted oils in 1M hydrochloric acid medium: Experimental and theoretical study

Abstract

Corrosion is a common phenomenon in metals and alloys. It implies a degradation of material by chemical or electrochemical reactions with the environment. it undergoes a gradual loss of material at the points of contact with the surrounding environment. Among the various types of methods employed, one can use to prevent or retard the corrosion of metals and alloys, one applies a layer of paint, plastic or other protective material on the surface or one covers with a layer zinc. We can also apply an electric current to the surface of the metal to reduce the potential difference between the metal and the environment or even by formulating anti-rust solutions or choosing certain chemicals as anti-corrosion to slow down the corrosion process. The use of inhibitors is one of the best techniques that ensure the protection of metallic materials. This research aims to evaluate the inhibition efficiency of the rosemary (REO) and Eucalyptus Essential Oils (EEO) on aluminum in 1 M hydrochloric acid. The inhibition efficiency of the EOs will be examined using electrochemical methods such as potentiodynamic and potentiostatic polarization, and electrochemical impedance spectroscopy. The results of this research will provide valuable information on the potential use of REO and EEO as eco-friendly corrosion inhibitors for metals in aqueous media. The inhibitory efficiency increases with the concentration of inhibitors and reaches a maximum value of 62% for Eucalyptus and 92% for Rosemary. These results testify to the mixed nature of the two inhibitors Rosemary and Eucalyptus with an anodic predominance. The transient electrochemical method attests to higher charge transfer resistances accompanied by lower and lower double-layer capacitance values when the concentration of rosemary and Eucalyptus increases. These results justify the adsorption of these inhibitors on the metal surface. The results from the three techniques used present a reasonable agreement between them. After testing three adsorption isotherms, it was found that the adsorption mechanism follows the Langmuir isotherm. The calculation of the atomic charges by the DFT/B3LYP method is carried out to assess the protective character of an inhibitor molecule adsorbed namely p-Cymene and Eucalyptol main constituents of the rosemary and eucalyptus essential oil. Monte Carlo Simulations (MC) and Molecular Dynamics (MD) are undertaken at 25°C, to obtain the interaction energy between the two inhibitors and the Al (111) interface.