Corrosion Inhibitive Effect and Adsorption Behaviour of Hibiscus Sabdariffa Extract on Mild Steel in Acidic Media

The inhibiting action of the calyx extract of Hibiscus sabdariffa on mild steel corrosion in 2 M HCl and 1 M H 2SO 4 solutions was assessed using a gasometric technique. The results demonstrate that Hibiscus sabdariffa extract suppressed the corrosion reaction in both acid media and inhibition efficiency increased with extract concentration with slightly higher values obtained in 1 M H 2SO 4. Synergistic effects increased the efficiency of the extract in the presence of halide additives. Adsorption characteristics of the extract were approximated by the Langmuir isotherm. The inhibition mechanisms, estimated from the temperature dependence of inhibition efficiency as well from kinetic and activation parameters show that the extract functioned via mixed- inhibition mechanism. It is suggested that molecular as well as protonated organic species in the extract contribute to the observed inhibiting action.