Green corrosion inhibition potential of Gymnema sylvestre and Sargassum sp. extracts in acidic medium

Abstract

The corrosion inhibition of mild steel (MS) in acidic medium using G. sylvestre and Sargassum sp. leaves extracts were investigated by weight loss measurements, linear sweep voltammetry, and Tafel extrapolation studies. Both the extracts showed considerable corrosion inhibition capacity in acidic medium. The optimum concentrations of G. sylvestre and Sargassum sp. which correspond to the highest inhibition efficiencies were 1200 and 800 ppm respectively. The adsorption data were fitted into Langmuir, Temkin and Freundlich adsorption isotherms and adsorption in the form of physisorption was confirmed by the calculated adsorption Gibbs free energies of about ~ (-20 kJ mol-1) in both cases. Corrosion potential of the steel substrate in 1.0 mol dm-3 HCl is -0.5457 V. In the presence of G. sylvestre (800 ppm) and Sargassum sp. (1200 ppm), the corrosion potential shifted to more negative values of - 0.5492 and - 0.5539 V. Calculated corrosion current densities from Tafel extrapolation studies in A cm-2 are 5.8020×10−5 (HCl), 0.9288×10−5 (G. sylvestre) and 2.0651×10−5 (Sargassum sp.) indicating a mixed type inhibition. The negative shift of corrosion potential in the presence of these inhibitors has been interpreted in terms of their predominant control over the cathodic reaction. According to the outcome of this study, both G. sylvestre and Sargassum sp. extracts can be used as potential green corrosion inhibitors in acidic medium.