Comparative Study of Corrosion Inhibition and Adsorption Characteristics of Ethanol Extracts of Andrographis Paniculata (King Bitters) and Vernonia Amygdalina (Bitter Leaf) on Mild Steel on HCL Solutions

The corrosion inhibition performance of ethanol extracts of Andrographis paniculata (king bitters) EEAP and Vernonia amygdalina (bitter leaf ) EEVA on the corrosion of mild steel in 2.0 M HCl solution at the temperature of 30, 40, 50 and 60 °C was investigated using weight loss (gravimetric) and hydrogen evolution (gasometric) techniques respectively. The results indicated that both plant extracts inhibit the corrosion of mild steel in the medium by adsorption. However, EEAP exhibited higher maximum inhibition efficiency (89.7%) than EEVA (76.9%) at 4.0g/L. Generally, inhibition efficiency was found to increase with increase in concentrations of both plant extracts but decrease with increase in temperature. Inhibition mechanisms were deduced from the temperature dependence of the inhibition efficiency as well as from activation parameters that govern the process. Adsorption of both plant extracts on the mild steel coupon was found to obey the Langmuir adsorption isotherm. The phenomenon of physical adsorption is proposed from the obtained thermodynamic parameters.