Equisetum hyemale: a new candidate for green corrosion inhibitor family

Abstract

Plant extracts are a possible better alternative source of eco-friendly corrosion inhibitors for metallic materials. Herein, methanol extract of Equisetum hyemale (EHE) has been studied as an eco-friendly inhibitor for the corrosion protection of mild steel (MS) in 1.0 M H2SO4. The corrosion inhibition effects of Equisetum hyemale were evaluated by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and surface analyses. The weight loss results divulged a decrease in corrosion inhibition efficiency (IE) with temperature. Moreover, IE increased until six hours of immersion, then decreased afterward. Similarly, EIS studies showed an increase in charge transfer resistance together with a decrease in double-layer capacitance. The current density decreased with an increment of the inhibitor concentration without affecting the reaction mechanism. Surface characterization indicated the surface coverage of the MS by the phytochemicals present in the EHE. Thermodynamic parameters such as free energy, enthalpy, entropy of adsorption, and activation energy calculations supported a mixed type of adsorption involving both physical and chemical interactions. The molecular adsorption of the phytochemicals showed a spontaneous and consistent behavior with the Langmuir adsorption isotherm model.