Methanolic and Aqueous Extracts of Corn Silk as Corrosion Inhibitor for Mild Steel in Hydrochloric Acid at Different Temperatures

This research work presents a study on the methanolic and aqueous extracts of corn silk for their corrosion inhibitive effect on mild steel in 0.5M HCl media at 303K, 313K and 323K using the weight loss method. Various concentrations of Corn Silk Methanolic Extract (CSME) and Corn Silk Aqueous Extract (CSAE) (0.1w/v, 0.2w/v, 0.3w/v, 0.4w/v and 0.5w/v) were prepared from the shadow-dried corn silk. Inhibition efficiency of 95.07%, 90.91%, 83.40%; and 79.43%, 72.55%, 66.30% was obtained respectively for CSME and CSAE at 303K, 313K and 323K for the highest concentration of extracts (0.5w/v). The Inhibition efficiency increased with increase in concentration of the extracts and decreased as temperature increased. The results obtained from both extracts were compared and it showed that the methanolic extract was a better inhibitor than the aqueous extract. From this present work, both extracts was shown to be most effective at 303K than at 313K and 323K. It was observed that both extracts inhibited the corrosion of mild steel in acidic media through physical adsorption by forming a barrier on the surface of the metal. Data obtained obeyed Langmuir adsorption isotherm. The Kinetic study of the process proposed a first order reaction type. The usefulness of a waste material as corrosion inhibitor is once more reported.

Keywords
inhibition efficiency; corn silk; methanolic extract; first order; adsorption isotherm.