Electrochemical and surface investigation of Arctium lappa extract as a sustainable corrosion inhibitor for mild steel in 6.0 M HCl medium

The inhibition effect of Arctium lappa plant extract as an eco-friendly corrosion inhibitor on the mild steel corrosion in 6.0 M hydrochloric acid (HCl) medium has been explored by Tafel polarization measurement, electrochemical impedance spectroscopy (EIS), and optical microscope, atomic force microscopy (AFM) as well as scanning electron microscopy (SEM) observations. Effective groups in the inhibitor composition were identified using the fourier-transform infrared (FT-IR) technique. The ultraviolet-visible (UV–Vis) technique was used to confirm the absorption of inhibitors on the mild steel surface. The durability of the Arctium lappa extract was studied over a period of one month and a half in a strong acidic environment. The efficacy of temperature and associated factors was explored. The EIS results indicated that by increasing the concentration of extract, growths charge transfer resistance (R ct ) and decline the value of double layer capacitance. From the Tafel results obtained from this research, it was determined that the behavior of the extract is of a mixed type of inhibition and efficiency of 98.5 % was attained with the use of 0.005 g L −1 Arctium lappa extract at 298 K. The adsorption mechanism of the used extract on the surface of the metal follows the adsorption isotherm of Langmuir. Optical microscope, SEM and AFM images of mild steel sample (a) freshly polished surface, (b) immersed in corrosive environment, (c) immersed in corrosive environment containing 0.005 g L −1 of Arctium lappa extract. Polarization curves of mild steel in 6 M HCl containing various concentrations of Arctium lappa extract.