Inhibition of mild steel corrosion in HCl using aqueous and alcoholic extracts of Crotalaria Pallida – A combination of experimental, simulation and theoretical studies

Abstract

The viability of using the leaves of Crotalaria Pallida, a well-known medicinal plant, as an efficient corrosion inhibitor for mild steel in HCl media has been studied and the results are summarized in this paper. Methods including weight loss monitoring, electrochemical impedance analysis, polarisation techniques, have been used and the mechanism of action was further investigated using Biovia material studio software. The theoretical background of the inhibitor and the probable methods of interaction were carried out using Gaussian 09 packages. Ethanol extract are rich in fatty acids which are absent in the water extracts; makes them more anticorrosive. The presence of fatty acids was confirmed using spectral analysis. Linolenic acid, oleic acid, and linoleic acids are the major fatty acids in the alcohol extract. The 4 (V/V %) alcohol extract has 95% efficiency while the same volume percentage of water extract has only 87% efficiency. The efficiency decreases with an increase in acid concentration and temperature, suggesting the physisorption of plant constituents on the metal surface. The AFM and XPS results support the protection of mild steel by the adsorption of constituent phytochemicals in the leaves extract. Adsorption of these phytochemicals follows Langmuir unimolecular model. The polarisation technique confirms the mixed type behaviour of the active species of the extract. Inhibition efficiency is more for linoleic acid than the others which are confirmed by both DFT and material studio calculations.