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ABSTRACT
The inhibitory and adsorptive effects of ethanol extract of Caesapinia bonduc seed coat (EECBSC) on corrosion of mild steel in 1M H2SO4 solution were investigated using gravimetric and electrochemical techniques. Experiments were performed by varying immersion period, concentration of the inhibitor and temperature. The results suggest that EECBSC acts as a good corrosion inhibitor for mild steel in acid medium. Inhibition efficiency increased with increasing concentration of the extract and temperature. Kinetics of the reaction with and without inhibitor follow a first order reaction and the half-lives of the metal increase as the concentration of the extract increases. The adsorption of the inhibitor on the mild steel surface in acid solution was found to obey the Langmuir adsorption isotherm. The activation and thermodynamic parameters of dissolution and adsorption processes were calculated and discussed. The mechanism of inhibition and formation of Fe-inhibitor complex was confirmed by FT-IR spectral analysis. Characterization of EECBSC was carried out using Fourier transform infrared spectroscopy and the results indicate that the inhibition of corrosion of mild steel occurs through adsorption of the inhibitor molecules. The scanning electron microscopy (SEM/EDX) result revealed the formation of a protective layer on the mild steel. Atomic Absorption Spectroscopy (AAS) analysis confirmed that the dissolution of iron (Fe2+) in the uninhibited solution was faster than the inhibited solution. Polarization measurements showed that the EECBSC extract acts as a mixed-type inhibitor.
Keyword: Gravimetric, Electrochemical; corrosion, Inhibition, Caesapinia bonduc; thermodynamics;