Corrosion Inhibition of Mild Steel in Sulphuric Acid Environment Using Millet Starch and Potassium Iodide

Millet starch (MS) was extracted from millet grains and modified using a physical method (pre-gelatinization). The corrosion inhibition effectiveness of millet starch on mild steel corrosion in 0.5 M H2SO4 solution was investigated using weight loss measurement, potentiodynamic polarization and chemical quantum methods. The results obtained show that pure millet starch and its combination with potassium iodide effectively reduced the corrosion of mild steel in 0.5 M H2SO4 solution with an inhibition efficiency of 87.14% and 94.03% respectively.The increase in inhibition on addition of potassium iodide showed synergistic effect. In addition, millet starch was found to function essentially as a mixed-type inhibitor by adsorption on the mild steel surface according to the polarization curves. The mode of inhibition adsorption was best modeled using Langmuir adsorption isotherm. The calculated values of ∆Gads, Ea and ∆Hads suggested physisorption mechanism. Theoretical quantum chemical calculations were performed to confirm the ability of starch to adsorb onto mild steel surface.