Highly efficient Ligularia fischeri green extract for the protection against corrosion of mild steel in acidic medium: Electrochemical and spectroscopic investigations

A methanol extract of Ligularia fischeri was studied for its inhibitive effect on the corrosion of mild steel in a 1 M hydrochloric acid medium, using the metrics of weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The corrosion rate of mild steel and Ligularia fischeri's inhibition efficiencies were calculated. The inhibition efficiency [eta (%)] was observed to increase with increasing concentrations of Ligularia fischeri. A maximum inhibition efficiency of 92% was achieved using 500 ppm of the inhibitor. The weight loss experiments were performed at different temperatures to understand the thermodynamic mechanism of inhibition. A mixed inhibition mechanism was proposed for the effects of Ligularia fischeri extract, as revealed by the potentiodynamic polarization technique. A solution analysis by atomic absorption spectroscopy (AAS) for mild steel showed decreased dissolution of iron in the presence of Ligularia fischeri. The adsorption mechanism and surface morphology of the mild steel, both with and without the inhibitor, were studied using UV-visible, Fourier transform infrared (FT-IR), Raman, wide-angle X-ray diffraction (WAXD), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDS), and atomic force microscopy (AFM). (C) 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.