The inhibition effect of Mundulea sericea leaf extract (MSLE) on the corrosion of mild steel in 1.0 M HCl and 0.5 M H2SO4 solution was investigated for the first time by mass loss, linear polarization resistance (LPR), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) methods. These studies were carried out at different concentrations, temperatures and durations. The results show that Mundulea sericea is a very potent inhibitor, and is more efficient in 1.0 M HCl than 0.5 M H2SO4. The adsorption of Mundulea sericea on mild steel surfaces in both acid solutions was found to obey the Langmuir and Temkin adsorption isotherms. Polarization curves reveal that Mundulea sericea acts as a mixed-type inhibitor in both acids by simultaneously restraining anodic and cathodic reactions. The electrochemical impedance spectroscopy showed that the charge transfer resistance increases and the double layer capacitance decreases on increasing plant extract concentration. The inhibition efficiency of the extract obtained from impedance and polarization measurements was in good agreement with mass loss measurements. The activation energy as well as other thermodynamic parameters (Ea, ?G, ?H, and ?S) for the present system was calculated. These thermodynamic parameters show strong interaction between inhibitor and mild steel surface. The results obtained show that the extract of Mundulea sericea could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric and sulphuric acid media.

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