Stigmasterol extracted from Ficus hispida leaves as a green inhibitor for the mild steel corrosion in 1 M HCl solution

The anticorrosive potential of Ficus hispida leaf extract (FHLE) as a corrosion inhibitor in 1 M HCl was investigated using weight loss measurement as well as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Stigmasterol as the major constituent of F. hispida was confirmed by Gas Chromatography-Mass Spectrometry (GC-MS). Inhibition efficiency of 90% was achieved with 250 ppm of FHLE at 308 K. Temperature studies revealed an increase in inhibition efficiency with decrease in temperature and activation energies increased in the presence of the extract. Cathodic and anodic polarization curves revealed that FHLE acts as mixed type inhibitor, but cathodic effect was more pronounced. Impedance diagrams showed that increasing FHLE concentration, increased charge transfer resistance and decreased double layer capacitance. The adsorption of FHLE on mild steel surface obeyed Langmuir adsorption isotherm. The morphology of the surface was examined by scanning electron microscopy (SEM) and the surface composition was evaluated using energy-dispersive X-ray (EDX) spectroscopy to verify the presence of inhibitor on the mild steel surface. The adsorbed film on the mild steel surface containing the FHLE inhibitor was also characterized by diffuse reflectance Fourier transform infrared spectroscopy (DRFT-IR) and X-ray diffraction (XRD) studies. (C) 2015 The Authors. Published by Elsevier B.V. on behalf of King Saud University.