Experimental and Theoretical Elucidation on the Inhibitive Performance of Landophia heudelotii Gum Extract on Acid Corrosion of Cold-Rolled Steel

Abstract—Investigation of inhibitive performance of Landophia heudelotii gum (LG) extract on acid corrosion of cold-rolled steel was conducted using gravimetric, electrochemical impedance spectroscopy (EIS), quantum chemical computation and molecular dynamics simulation techniques. Resultantly, LG extract significantly inhibited the corrosive action of the acid solutions (0.5 M H₂SO₄ and 0.5 M HCl solutions), and the effect was remarkable at elevated temperature of 40°C where the LG extract displayed highest inhibition efficiency (IE %) of 87.8 at 2.5 g/L and 81.6 at 2.0 g/L concentration in 0.5 M H₂SO₄ and 0.5 M HCl solutions, respectively. Adsorption and thermodynamic considerations suggest that the inhibiting molecules (quercetin, epicatechin, naringerin and kaempferol) were physically adsorbed on the metal surface. EIS results revealed that the charge transfer resistance (R_ct) values were higher in 0.5 M H₂SO₄ solution than in 0.5 M HCl solution. Quantum chemical computation showed that epicatechin inhibiting molecule possessed the highest tendency to donate and accept electrons from the metal surface. Interestingly, epicatechin was confirmed to exhibit highest adsorption energy via molecular dynamic simulation.