Abstract:
The inhibitive action of Caesalpinia bonduc and Mucuna flagellipes leaves extracts on mild steel corrosion in H2SO4 solution was studied using gravimetric method and electrochemical polarization technique. The results indicate that the extracts functioned as good inhibitor in acidic environment. Corrosion rates decreased with increase in extracts concentration but the inhibition efficiency increased with extracts concentration. Temperature studies revealed an increase in the inhibition efficiency with rise in temperature and activation energies decreased in the presence of the extracts, suggesting a chemical adsorption process. The positive values for enthalpy (ΔHo) both in the absence and presence of the extracts suggest the endothermic nature of the mild steel dissolution process. The negative values of Gibbs free energy for both extracts indicate the spontaneity and feasibility of the reaction. Caesalpinia bonduc and Mucuna flagellipes leaves extracts was found to conform to the Freundlich adsorption isotherm, Langmuir adsorption isotherm and Temkin adsorption isotherm but were best fitted into the Langmuir adsorption isotherm. Kinetics of the reaction in the presence of both extracts revealed that it follows a first order reaction and calculated half-lives increase as the concentration of the extracts increases. Atomic absorption spectroscopic analysis confirmed that the dissolution of Fe in the un-inhibited solution was faster than the inhibited solution. Fourier transform infrared (FT-IR) spectroscopy and Scanning electron microscopy (SEM) studies confirm that the inhibition of corrosion of mild steel occurs through adsorption of the inhibition molecules. The polarization studies showed that Caesalpinia bonduc and Mucuna flagellipes leaves extracts acts as mixed- type inhibitor. Preliminary investigation of the phytochemical constituents revealed that the extracts contains tannins, saponins, terpenoids, flavonoids, and alkanoids.
