Evaluation of Brachystegia Eurycoma Leaves Extract as a Source of Green Inhibitor for Mild Steel in Acid Solution

Abstract

The aim of this work is to investigate the corrosion inhibition of B. eurycoma leaves extract as a natural inhibitor for mild steel corrosion in 1 M H2SO4 solution. The corrosion inhibition activity was analyzed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The surface roughness and its properties through Scan electron microscopy (SEM). The obtained result from EIS divulge that the gradual increase in the B. eurycoma l eaves extract inhibitor concentration and time of immersion leads to progressive increase in inhibition efficiency. At the end of 8 hrs immersion time and inhibitor concentration of 1000mg/l the highest inhibition efficiency of (80%) and surface coverage of 70% were achieved. The potentiodynamic polarization results indicated that addition of B. eurycoma leaves extract hindered the reaction rates of anodic and cathodic reactions and performed as mix type inhibitor. The result also revealed that in the presence of B. eurycoma leaves extract the value of corrosion density of mild steel reduced considerably from 265.2µA/cm2 for sample without inhibitor to 67.8µA/cm2 for sample in 1000mg/l of the inhibitor. Again, it was observed that in the presence B. eurycoma leaves extract the mechanism of hydrogen (effervescence) evolution was unique whereas the anodic dissolution of iron mechanism experienced the impact of the inhibitor. SEM inspection revealed that the mild steel surface showed smoother and lower damage in the presence of inhibitor. Obvious correlations were found between corrosion inhibition efficiency and some quantum chemical parameters such as energy of highest occupied molecular orbital (EHOMO), energy of lowest unoccupied molecular orbital (ELUMO), energy gap (EL–H) and electronic density etc. The obtained results were further elucidated with frontier molecular orbital theory.