Corrosion Inhibition Of Michelia Alba Leaves Extract For Steel Materials

Steel materials are used widely in many industries such as reaction vessels, pipesboiler and so on. Pickling is an important part of industrial production. Frequentlyincurs corrosion problems when it contacts with acid during acid pickling and cleaningprocesses. Thus, Corrosion has been a serious problem. The use of inhibitors is one ofthe most practical methods for protection against corrosion in acidic media.In this paper, the acid pickling inhibitor was extracted from Michelia alba leaves.The inhibition effect of the Michelia alba leaves extract on the corrosion of steelmaterials has been studied by free corrosion potential-time curves and Tafelpolarization curves. By Fourier transform infrared spectroscopy (FTIR), the effectivecorrosion inhibition composition of Michelia alba leaves extract was preliminarilyinvestigated. The surface morphologies of the steel materials samples in hydrochloricacid solution without and with inhabitior has been characterized by Scanning ElectronMicroscope(SEM). The relationship between corrosion inhibitior efficiency ofmolecules was studied using quantum chemistry calculation. The results show that:The Michelia alba leaves extractive exhibits a very good permance as a mixedinhibitor for steel materials corrosion in hydrochloric acid. The inhibition efficiencyincreased with increasing the extract concentration to exceed80%at0.422g/L.Inhibition efficiency increases with temperature. The adsorption of the extractcomponents on the steel materials surface belonged to the physical adsorption, whichfollowed Langmuir adsorption isotherm. The calculated adsorption thermodynamicparameters indicated that the adsorption was a spontaneous, endothermic processaccompanied by an increase in entropy for steel materials. The adsorption did modifythe apparent activation energy of the corrosion process of steel materials.The Michelia alba leaves extract contains oxygen and nitrogen atoms in functionalgroups (–COOH, O–H, C=O, N–H, C–N, C–O), epoxy group and aromatic ring, whichmeets the general structural consideration of the corrosion inhibitors. The presence of auniform and dense adsorptive film over the steel materials surface, which efficientlyinhibits the corrosion of steel materials.According to literatures and Fourier transform infrared spectroscopy， we preliminary inferred that the Michelia alba leaves extract contains four main activeingredients: ascorbic acid (AA), octadecanoic acid(OA), p-hydroxybenzoic acid (p-HA) and liriodendrin. The highest occupied molecular orbital for scorbic acid (AA) islocated on the lactone nucleus while the molecular orbital of octadecanoic acid (OA)mainly concentrated on the heteroatoms O; The lowest unoccupied molecular orbitaland highest occupied molecular orbital of planar molecular p-hydroxybenzoic acid(p-HA) and liriodendrin were both delocalized with the benzene ring and heteroatom,benzene ring plane and heteroatom were both the electrophilic and cleophilic reactionadsorption. Liriodendron has the greater highest occupied molecular orbital energy andelectron capability of LUMO, minimum gap. Moreover, Liriodendron has the highestvalue of dipole moments, polarizabilities and molar volume. So, the corrosion inhibitionof the liriodendrin is the best of all for steel materials.