Inhibition of the corrosion of mild steel in acidic medium by Vernonia amygdalina : adsorption and thermodynamics study

Abstract

The inhibitive, thermodynamics and adsorptive properties of ethanol extract of vernonia amygdalina for the corrosion of mild steel in 0.4M HNO3 solutions have been investigated using weight loss technique. The extract was found to be a good inhibitor for corrosion of mild steel in HNO3. Inhibition efficiencies obtained ranged from 40.57 to 50.74% and from 38.06 to 49.27% at 303 and 323K respectively. The inhibition efficiency of the extract decreased as temperature and time of immersion increased, but increased with increase in concentration of extract. The inhibition capacity of this extract is attributed to the presence of saponnin, tannin, alkaloid, anthraquinone, flavanoid, cardiac glycosides in the extract. The heat of adsorption obtained ranged from -48.84 to -51.06KJ mol-1 indicating that adsorption of the inhibitor on surface of mild steel was exothermic, spontaneous and follows the mechanism of physical adsorption. Langmuir, Temkin, Frumkin and Flory-Huggins adsorption isotherms were found to conform the adsorption characteristics of the inhibitor.