Synergistic Effect of Leaf Extracts of Cordia sebestena L. and Iodide Ions on the Corrosion Inhibition of Mild Steel in Sulphuric Acid

The inhibitive action of leaf extracts of Cordia sebestena on corrosion of mild steel in 0.5 M H2SO4 solution was studied by weight loss measurement at 303-333K. Results indicate that leaf extracts of Cordia sebestena is a good inhibitor for mild steel corrosion in 0.5 M H2SO4. The inhibition efficiency was found to increase with increase in extracts concentration. A maximum inhibition efficiency of 95.79% was obtained for 50% v/v at 303K, which increased to 99.09% in the presence of 5mM KI. Temperature studies revealed a decrease in inhibition efficiency with increase in temperature, which suggests physical adsorption mechanism. The adsorption characteristics of leaf extracts of Cordia sebestena on mild steel surface obeys Langmuir isotherm. Both kinetic parameters and thermodynamics of adsorption (enthalpy of adsorption, entropy of adsorption and Gibbs free energy) were calculated and discussed. The values of synergism parameter were greater than unity, which suggests synergistic effect between the leaf extracts and KI.