Corrosion Inhibition Activity of Isolated Flavonoid from Andrographis echioides leaves

Abstract

Andrographis echioides leaves were used to isolate a flavonoid (medicarpin) that inhibited mild steel corrosion in 1M HCl. Preliminary phytochemical analysis revealed that the A.E leaves were rich in flavonoids. Following a room temperature extraction with methanol, the constituents were fractionated using a Soxhlet apparatus. Chromatographic techniques were used to isolate the constituents from the leaves of Andrographis echioides. Flavonoid compounds were characterized using Spectral studies. Weight loss and corrosion studies were investigated the inhibition activity of an isolated flavonoid (medicarpin). The inhibition efficiency of isolated flavonoid was highest (85.78 percent) at 800 ppm concentration, according to weight loss and electrochemical measurements. The influence of temperature on the corrosion activities of base metal was calculated in the temperature range 293-303K. The inhibitory activity increases with rising inhibitor concentration but decreases with rising temperature. The activation and free energies for the inhibition response sustain the method of physisorption. The adsorption of isolated flavonoid on the base metal is an endothermic process and it follows the Langmuir adsorption isotherm. The potentiostatic study illustrates that isolated flavonoid is a mixed type inhibitor. Surface Morphology examination by SEM and EDAX to reveals the adherence of isolated flavonoid on the mild steel surface.