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Abstract

The inhibition effect of Calotropis gigantea root extract on corrosion of mild steel in hydrochloric acid using weight loss measurement and electrochemical techniques has been reported in this study. The inhibition efficiency of Calotropis gigantea root extract was found to vary with concentration, tempe5rature and immersion time, weight loss method, polarization and Electrochemical Impedance Spectroscopic (EIS) measurement were used to find out corrosion loss and inhibition efficiency. The adsorption study of these compounds of mild steel surface found to obey Temkin’s adsorption isotherm. The value of free energy of adsorption (Gºads), heat of adsorption (Qads), energy of activation (Ea), enthalpy of adsorption (Hºads) and entropy of adsorption (Sºads) were calculated. The potentiodynamic polarization results showed that the compound studied was mixed type inhibitor. The adsorption of Calotropis gigantea root extract obeyed Langmuir adsorption isotherm. Cathodic and anodic polarization curves also show that Calotropis gigantea root extract is a mixed type inhibitor. The calculated thermodynamic parameters indicated that the adsorption was a spontaneous, exothermic process accompanied by an increase in entropy. Present study indicates that Calotropis gigantea root extract is a good inhibitor for the corrosion of mild steel in hydrochloric acid medium.