Boswellia serrata gum as highly efficient and sustainable corrosion inhibitor for low carbon steel in 1 M HCl solution: Experimental and DFT studies

Boswellia serrata gum (BSG) was studied as a new sustainable corrosion inhibitor for the protection of low carbon steel (LCS) in 1 M HCI solution employing standard experimental techniques. FT-IR was accomplished to characterize the inhibitor and to assess the functional groups which caused its adsorption on the surface of LCS. Compared to other studied plant exudates BSG acted as a more efficient inhibitor at relatively lower concentration thus qualifying it as cost-effective and more practical acid inhibitor. The corrosion mitigating efficacy are both temperature and concentration dependent. The inhibition efficiency decreased with temperature but progressively increased with increase in BSG concentration; the maximum efficiency of 91.9% is observed at 30 degrees C at BSG concentration of 500 ppm. As evidenced by PDP measurements BSG acted as mixed type inhibitor with dominant anodic effect. The existence of protective layer, attributed to the adsorbed constituent polysaccharides, at the LCS surface was revealed by EIS measurements. The adsorption of the studied inhibitor on LCS surface obeyed Langmuir adsorption isotherm. Gravimetric data supported well the electrochemical results and further established that inhibition efficacy of BSG remains appreciably high during long exposure to the studied medium revealing its extra stability in HCI solution. SEM/EDX/AFM results substantiated the inhibitive effect of adsorbed BSG constituents on the LCS surface. Spectroscopic studies like UV-visible and FT-IR indicated the existence of [inhibitor-Fe2+] in inhibited acid solution. Mechanism of inhibition was also researched by computing relevant activation and thermodynamic parameters and experimental results are corroborated by computed quantum chemical parameters. (C) 2018 Elsevier B.V. All rights reserved.