Synsepalum dulcificum Leaves Extract as Green Inhibitor for Mild Steel Corrosion in Hydrochloric Acid

Abstract

Corrosion inhibition efficiency of Synsepalum dulcificum leaves extract for mild steel (mls) in 1.0 M HCl was evaluated by electrochemical and gravimetric methods. The results of the studies showed that S. dulcificum has good inhibitive properties with inhibition efficiency (% I) reaching 94 at 1000 ppm inhibitor concentration. The enthalpy was negative (which indicated the exothermic nature of adsorption of S. Dulcificum) and decreased steadily from -25.28 kJ/mol at 100 ppm to -34.41 kJ/mol at 1000 ppm S. dulcificum concentration. Values of the Gibbs free energy were negative (ΔGads = -13.41 kJ/mol at 303 K and -17.32 kJ/mol at 343 K) suggesting spontaneous adhesion of the S. dulcificum molecules on the surface of mls. The adsorption of S. dulcificum conformed to the Langmuir isotherm model and values of ΔGads also suggested that adsorption of S. dulcificum was physisorptive since values of ΔG ads up to -20 kJ/mol are consistent with physical adsorption. The results of the studies revealed that activation energy increased with increase in S. dulcificum concentration which indicated that the energy required for corrosion of mls increased in the presence of S. dulcificum extract. Potentiodynamic Polarization studies revealed that S. dulcificum functions as mixed type inhibitor since values of corrosion potential (??????????) increased on addition of S. dulcificum with no particular trend. Electrochemical impedance spectroscopy (EIS) analysis revealed that charge transfer resistance (Rct) increased as S. dulcificum concentration increased to reach 1413.3 Ω cm2 at 1000 ppm.