Murraya koenigii as green corrosion inhibitor for mild steel in nitric acid medium

The inhibition behaviour of Murraya koenigii (curry) leaves extract on the corrosion resistance of mild steel (MS) in nitric acid medium has been studied by gravimetric (or weight loss) measurements and scanning electron microscopy. The inhibition efficiency increases with inhibitor concentration and decreases with increase in immersion time period. The temperature effect on the corrosion behaviour of mild steel without and with inhibitor has been studied. Temperature studies reveal that the activation energy increases to 18 kJ/mol with the addition of 500 ppm inhibitor. Mild steel corrosion inhibition efficiency of 62% is obtained with 600 ppm of extract in 0.1N HNO3. The adsorption isotherm studies and the thermodynamic analysis of the results indicate physical adsorption of the inhibitor molecules on the mild steel surface. Scanning electron microscopic studies show the presence of pitting corrosion in uninhibited sample. The energy-dispersive X-ray spectroscopy studies reveal higher carbon content in the inhibited sample which attributs to the presence of adsorbed inhibitor molecules.