Abstract:
The corrosion inhibition potential of Dioclea reflexa and Crescentia cujete on mild steel in 2 M HCl was assessed by Weight loss method, Potentiodynamic Polarization Measurement , Atomic Absorption Spectroscopy (AAS), Fourier Transform Infrared (FT-IR) Spectroscopy and Scanning Electron Microscopy (SEM) with Electron Dispersive Spectroscopy (EDS) analysis. Preliminary investigation of the phytochemical constituents revealed that tanins, glycocides, terpenoids and phenol are present in Dioclea reflexa extract while saponins, tanins, alkaloid, glycosides, terpenoids, steroids and phenol are present in Crescentia cujete extract. The inhibition efficiency increased with increasing concentration of the inhibitor in acidic medium. The result of weight loss studies correlated well with those of polarization study and it revealed that both extracts act as mixed type inhibitors. From the result of weight loss studies at various temperatures, the mode of adsorption is confirmed to be chemisorption due to increase in the inhibition efficiency and activation energy with rise in the temperature. The positive values of enthalpy (ΔHo) observed in the absence and presence of the extracts revealed the endothermic nature of the mild steel dissolution process. The adsorption of the extracts on the metal surface was found to be in conformity with Langmuir Adsorption Isotherm, Temkin Adsorption Isotherm and Freundlich Adsorption Isotherm, but was best fitted into Langmuir Adsorption Isotherm which implies a monolayer adsorption. Kinetics of the reaction followed a first order reaction and the calculated half-lives increased with increase in extracts concentration. Atomic Absorption Spectroscopic analysis confirmed that the dissolution of iron (Fe2+) in the uninhibited solution was faster than the inhibited solution. Fourier Transform Infrared (FT-IR) spectroscopy and Scanning Electron Microscopy (SEM) with Electron Dispersive Spectroscopy (EDS) studies confirmed that corrosion inhibition of mild steel occurs through adsorption of the inhibition molecules.
