Effect of Aqueous Extracts of Bitter Leaf Powder on the Corrosion Inhibition of Al-Si Alloy in 0.5 M Caustic Soda Solution

F. A. Ayeni, I. A. Madugu, P. Sukop, A. P. Ihom, O. O. Alabi, R. Okara, M. Abdulwahab

Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Zaria, Nigeria.
National Metallurgical Development Centre, P.M.B. 2116, Jos, Plateau State, Nigeria.

DOI: 10.4236/jmmce.2012.117050                

Abstract

The effect of bitter leaf (Vernonia amygdalina) extract as an inhibitor for aluminium silicon alloy in 0.5 M solution of caustic soda using weight loss method has been investigated. The alloy of composition 9% Si and 91% Al was sand cast at the Foundry Shop of the National Metallurgical Development Centre, Jos, Nigeria. The cast alloy was cut and machined to corrosion coupons and immersed into 0.5 M NaOH solution containing varying inhibitor concentrations (0.1%, 0.2%, 0.3%, 0.5% v/v) within a period of fifteen days. From the result, it was found that the adsorption of Vernonia amygdalina reduced the corrosion rate of this group of alloy in the alkaline medium. The inhibitive action of this plant extract was explained using inhibition efficiency and degree of surface coverage. The most suitable inhibitor concentration was found to be 0.5% with inhibition efficiency of 87%. The mechanism of inhibition is by physical adsorption and the adsorbed molecules of the inhibitor lies on the surface of the alloy blocking the active corrosion sites on the alloy, hence, giving the alloy a higher corrosion resistance in the studied environment.

Keywords

Vernonia amygdalina; Adsorption; Inhibition Efficiency; Surface Coverage

Conflicts of Interest

The authors declare no conflicts of interest.

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