Experimental and theoretical assessment of almond gum as an economically and environmentally viable corrosion inhibitor for mild steel in 1 M HCl

Abstract

Almond gum (AG) was studied as an economically and environmentally viable corrosion inhibitor in 1 M HCl on mild steel (MS). Studies such as gravimetric, NMR, FTIR, EIS, PDP, SEM/EDAX, UV–Visible, DFT and Monte Carlo simulation were performed to assess the potency of AG as a green inhibitor. Gravimetric study was done in the temperature range 30°C–60 °C, I.E increased with increasing concentration and temperature giving significant inhibition efficiency (I.E) of 96.37% at 300 ppm at 60 °C.The adsorption of AG on MS followed Langmuir Adsorption Isotherm. Characterization by NMR and FTIR confirmed the structure of AG. UV–Visible study confirmed the existence of complex [Fe+2-AG] on inhibited MS surface. While in 1 M HCl in the presence of AG, MS showed a reduced surface roughness and better surface morphology. Obtained PDP measurements show that AG acts as a mixed type inhibitor but showing predominantly anodic effect while EIS results unveiled the formation of inhibitive layer on the MS surface. I.E calculated from the EIS, PDP showed the same trend as gravimetric. Calculated thermodynamic and activation parameters predicted strong interaction between MS surface and inhibitor. Density functional theory (DFT), condensed Fukui indices (FIs) and Monte Carlo (MC) simulation results further supported the experimental findings.