L-Citrulline: An active corrosion inhibitor component of watermelon rind extract for mild steel in HCl medium

The contribution of l-citrulline (CTL) to the corrosion inhibition effect of aqueous rind extract (RE) from watermelon for mild steel in HCl solution was investigated using electrochemical (electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP)) and weight loss techniques at 25 °C and 60 °C. Results obtained show that both CTL and RE inhibited acid-induced corrosion of mild steel. Inhibition efficiency increased with increase in concentration reaching the maximum value of 46.30% and 90.20% respectively at the highest concentration (1000 ppm) studied from weight loss measurements. Inhibition efficiency was also observed to decrease with increase in solution temperature. l-citrulline was found to be responsible for about 51.33% to the overall inhibition efficiency of RE. Polarization studies indicate that both l-citrulline and RE function as mixed-type corrosion inhibitors. The corrosion inhibition effect of l-citrulline and RE is assumed to occur by physisorption of l-citrulline and components of RE on the mild steel surface which can be approximated by Temkin adsorption isotherm model.