Adsorption and Thermodynamic Studies of Carica Papaya Leaves Extract (Yellow) as Corrosion Inhibitor for Mild Steel in Acidic Medium

Abstract

The inhibitive effects of plant leaf, Carica papaya leaves extract (yellow), CPLE (yellow) was studied on mild steel in 1.0 M HCl solution at 30oC using the gravimetric, electrochemical methods and Fourier transform infrared spectroscopy, FT-IR technique. The analysis of spectra obtained from FT-IR revealed that some functional groups present in the original spectrum were missing in the spectra of the corrosion products, an indication of interaction between the mild steel and inhibitor. The corrosion rate decreases noticeably with increase in inhibitor concentrations, that is, the inhibition efficiency (% IE) increases with increase in the inhibitor concentration. The progressive increase of the extract shows greater reduction of corrosion rate, given maximum inhibitive efficiency of 94.68% at 0.5g L-1 at 30oC. The Tafel and potentiodynamic polarization studies revealed that the CPLE (yellow) functioned as mixed-type inhibitor. The adsorption mechanism of the extract on the mild steel surface was found to obey El-Awady isotherm model. The thermodynamic evaluation deduced proposed a physisorption with the mild steel surface and spontaneous adsorption of CPLE (yellow). FT-IR was used to confirm the formation of a protective layer on the mild steel surface.