Abstract

The influence of Centrosema pubescens leaf extract on electrochemical corrosion behavior of mild steel, exposed to stimulated acidic medium, was investigated. The results of the phytochemical screening revealed the presence of secondary metabolites such as flavonoid, tannins, anthraquinones, terpenoids, alkaloids, phenols and saponnins. The FTIR also revealed aromatics and functional groups such as R-OH, C=O, C-O and C-H which are attributes of good inhibitors. The performance of the extracts was evaluated using gravimetric method of monitoring corrosion rate in different concentrations of 0.1, 0.2, 0.3, 0.4 and 0.5 w/v. Centrosema pubescens gave an inhibition efficiency of 74.91%. This could probably be due to the presence of secondary metabolite and other functional groups revealed by both the phytochemical screening and FTIR spectrum. Thermodynamics data generated suggested co-adsorption through a combination of both physisorption and chemisorption mode of interaction of the inhibitor. The negative free energy indicates that adsorption is spontaneous. The adsorption obeys both Langmuir and Freundlich adsorption isotherms. The degree of linearity is close to unity which indicates strong adsorption of the extracts on the mild steel. Efforts were made to propose a suitable mechanism for the inhibition. The results revealed that Centrosema pubescens could serve as an eco-friendly, alternative to sodium chromate, in the protection of mild steel.