Anticorrosive Activity of Kigelia pinnata Leaves Extract on Mild Steel in Acidic Media

The corrosion inhibition of mild steel in 1 M H2SO4 and 1 M HCl solution with different concentrations of Kigelia pinnata leaves extract (KPLE) was investigated using mass loss, Tafel polarization, and electrochemical impedance spectroscopy. Inhibition efficiency of KPLE is found to increase with increasing concentration but to decrease with temperature. Polarization measurements reveal that KPLE acts as a mixed type inhibitor in both acids. Impedance curves show that increasing KPLE concentration increases charge transfer resistance and decreases double layer capacitance. The adsorption of KPLE on the mild steel surface obeys the Langmuir adsorption isotherm. The experimental results reveal that KPLE inhibits the corrosion reaction in both acid environments, and inhibition efficiency follows the order H2SO4 > HCl. The kinetic and adsorption parameters for mild steel in acid in the presence and absence of KPLE were evaluated and discussed. The negative value of the standard free energy of adsorption in the presence of inhibitor suggests spontaneous adsorption of inhibitor on the mild steel surface. Protective film formation against corrosion was confirmed by ultraviolet-visible (UV-visible), X-ray diffraction, scanning electron microscopy, and Fourier transform–infrared spectroscopy techniques.