Influence of Malus domestica and Caesalpinia bonducella Leaf Extracts on the Corrosion Behaviour of Mild Steel in H2SO4 Solution

The electrochemical corrosion behavior of mild steel in 0.5M H2SO4 solution in the presence of apple, Malus domestica (MD); bonduc, Caesalpinia bonducella (CB) leaf extracts were investigated using potentiodynamic polarization curves measurements, electrochemical impedance spectroscopy techniques and Fourier infrared spectroscopy (FTIR) measurements. Polarization curves revealed that both MD and CB leaf extracts act as mixed type inhibitors in sulphuric acid solution. The impedance response consisted of characteristic depressed semicircles clarifying that the corrosion process occurs under charge transfer control. The inhibition efficiency of the leaf extracts increased with increasing the concentration and decreased with temperature. The results showed that CB is more efficient than MD in 0.5M H2SO4 solution. The calculated thermodynamic parameters indicated that the adsorption was a spontaneous, endothermic, and accompanied by a decrease in entropy. The adsorption of MD and CB leaves on steel surface obeys Thermodynamic-Kinetic model, Flory-Huggins model and Temkin model. The thermodynamic parameters indicated that the inhibition of mild steel by MD and CB leaf extracts were by physical adsorption mechanism.