Ethanol Extract of Vernonia amygdalina Leaf as a Green Corrosion Inhibitor for Carbon Steel in Solution of HCl

Abstract

To investigate the potential of ethanol extract from the bitter leaf as a green corrosion inhibitor for the corrosion of carbon steel, gravimetric, FTIR and scanning electron microscopy analytical techniques were adopted for monitoring the corrosion. Results obtained from gravimetric analysis indicated that the inhibition efficiency of the extract was 98.86, 94.33, 94.81, 95.28 and 96.22 % for 0.1, 0.2, 0.3, 0.4 and 0.5 g/L of the extract. The corrosion and the corrosion inhibition processes were found to follow pseudo-first-order kinetics and at various concentrations, the inhibitor demonstrated the potential to extend the half-life of the metal in the acid solution. The adsorption of the inhibitor suited the Langmuir and Frumkin adsorption models. The inference drawn from the isotherms revealed that there exists an interaction between the inhibitor’s molecules and that the lateral interaction parameter pointed to the attractive behaviour of the inhibitor. The adsorption was spontaneous and agreed with the mechanism of physical adsorption. The scanning electron micrograph of the metal surface after inhibition revealed the formation of a protective layer on the metal surface. Some functional groups that were native to the leaf extract were found to be missing in the FTIR spectrum of corrosion product which suggested that they were used for adsorption while some were shifted, an indication that there was interaction between the adsorbed species.