CORROSION INHIBITION STUDIES OF COCOA (Theobroma cacao) BEAN SHELL AND KOLA (Kola nitida) TESTA EXTRACTS ON MILD STEEL IN ACID MEDIA

Abstract

The inhibitive effects of ethanolic extracts of cocoa (Theobroma cacao) bean shell and kola (Kola nitida) testa on the corrosion of mild steel in hydrochloric acid solutions were investigated using gravimetric method. Experiments were performed by varying immersion period, concentration of the inhibitors and the temperature of study. The results revealed both samples as potential inhibitors for mild steel corrosion in acid media. Inhibition efficiency increased with increasing concentration of the extracts and temperature. Thermodynamic studies revealed that corrosion inhibition may be due to the spontaneous chemical adsorption of the plant constituents on the surface of mild steel. Adsorption studies revealed that Langmuir adsorption isotherm is the best adsorption model applicable to the adsorption of T. cacao bean shell and K. nitida testa extracts on mild steel. Activation parameters such as activation energies (Ea), activation enthalpy (ΔHo) and activation entropy (ΔSo) were evaluated from the effect of temperature on the corrosion and inhibition process. There was an indication of synergism when potassium halide of different concentrations was introduced with the extract to inhibit corrosion in the acid media. Keywords: corrosion, mild steel, inhibitor, kola nitida, theobroma cacao, inhibition efficiency, Langmuir.