Eucalyptus leaf extract as a eco-friendly corrosion inhibitor for mild steel in sulfuric and phosphoric acid solutions

Abstract

The adsorption mechanism and inhibitive action of the Eucalyptus plant leaf extract (Eu) on the corrosion of mild steel in 0.5 M H2SO4 and 0.5 M H3PO4 solutions were investigated by potentiodynamic polarization curves measurements and electrochemical impedance spectroscopy technique. Potentiodynamic polarization curves revealed that the Eucalyptus leaf extract acts as a mixed type inhibitor in both acidic solutions. The impedance responses indicated that the corrosion process occurs under activation control. Fourier transform infrared spectroscopy has been used to predict the possible major chemical constituent of the leaf extract. Four adsorption isotherms including Langmuir, kinetic–thermodynamic, Flory–Huggins and Temkin model were used to investigate the mode of inhibition of Eucalyptus leaf extract. The free energy of adsorption showed that the corrosion inhibition takes place by spontaneous physical adsorption of Eucalyptus leaf extract molecules on the mild steel surface. The obtained data indicated that Eucalyptus leaf extract is a more efficient inhibitor of mild steel corrosion in 0.5 M H2SO4 than in 0.5 M H3PO4 solutions. Thermodynamics activation parameters were also calculated and discussed.