Vigna unguiculata Coat Extract as Green Corrosion Inhibitor for Steel Pipeline in HCl

The inhibitive performance of aqueous Vigna unguiculata coat extract on the corrosion of pipeline steel in 0.5 M HCl solution was studied by electrochemical, Gravimetric and UV-Visible spectroscopy techniques at varying temperatures. The extract was characterized using Gas Chromatography-Mass Spectrometer, GC-MS analysis. The results revealed that increase in concentration of extract yielded an increased inhibition efficiency up to 86.7% at 303 K; but showed a reversed trend at elevated temperature. The potentiodynamic polarization data indicate that aqueous Vigna unguiculata is a mixed type inhibitor of steel pipeline corrosion in acidic environment, while the electrochemical impedance spectroscopy result showed the extract's activity was on the solution-metal interface. Also, adsorption of aqueous Vigna unguiculata coat molecules on steel pipeline followed Temkin isotherm. The GC-MS results showed presence of heavy hetro-molecules. While, the adsorption of extract film deposited on the steel surface was characterized using FT-IR. The thermodynamic data strongly suggests that the mode of adsorption involved both physisorption and chemisorption.