Quantum Chemical Studies, Characterization and Understanding the Inhibition Effect of <i>Pulicaria Jaubertii</i> Oil, Growing in Yemen, as a New Eco-Friendly Inhibitor for C38 Steel Corrosion in 1 M HCl Medium

The inhibitive action of Pulicaria Jaubertii essential oil (PJEO), as green inhibitor, has been investigated on the carbon (C38) steel corrosion in 1 M HCl by using inductively coupled plasmas spectrometry (ICP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and gravimetric measurements. The increasing of oil concentrations increases the carbon steel corrosion resistance (The inhibition efficiency), which rose to 94% in the optimal concentration (2.5 g/l). The specimen surfaces were analysed by using Infra-Red spectroscopy (IR) and scanning electronic microscope (SEM). The obtained results showed the presence of oil molecules adsorbed onto the specimen surface. Langmuir adsorption model was followed by PJ essential oil compounds which adsorbed onto the carbon steel surface to form a protective layer. PJEO was analysed by using gas chromatography coupled with mass spectra before it was used as green inhibitor. Several DFT parameters such as LUMO and HOMO energy, gap energy (ΔE), electronegativity (χ), softness (σ) and global hardness (η) were derived for all major molecules found in PJ oil. The theoretical results showed that there is a good agreement with the experimental data.