The Effectiveness of Vernonia amygdalina and Allium cepa Extract Mixture as Corrosion Inhibitor on Mild Steel in Hydrochloric Acid Solution

A combination of bitter leaf (Vernonia amygdalina) and white onion (Allium cepa) extract is more effective together as an inhibitor on mild steel in hydrochloric acid solution than if they were used separately. In this study, series of weight loss experiments were carried out. Hydrochloric acid and varying concentrations of inhibitors were tested with mild steel coupons. The experimental set-up was left to stand for four (4) days with 24 hours periodic washing, drying and weighing of the metal plates. Increase in the concentration of the leaves extract reduces the rate of corrosion of the mild steel in the corrosion medium. Analyses of the experimental results were done using a quadratic model to determine the optimum inhibition efficiency as well the corresponding concentration and time; a surface plot was used to illustrate these optimum conditions. The surface plot of the mixture of Allium cepa and Vernonia amygdalina extract shows that maximum inhibition efficiency can be achieved at 94.94% after 20.4hrs and 49.5ml concentration which is higher than the maximum inhibition efficiency of Allium cepa (93.4%) and Vernonia amygdalina (88.52%) extract used individually.