Effectiveness of vinca rosea leaf extract as corrosion inhibitor for mild steel in 1 N HCl medium investigated by adsorption and electrochemical studies

Abstract

The inhibitory effect of ethanol extract of Vinca rosea leaf on mild steel corrosion immersed in 1 N HCl solution was investigated. The kinetic corrosion parameters were determined by weight loss method and electrochemical tests such as potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) for various concentrations of inhibitor ranging from 50–250 ppm. Vinca rosea leaf extract exhibited good inhibition efficiency, IE, 76.36% for 250 ppm. Charge transfer resistance (Rt) measured with EIS increased with increasing concentration of inhibitor showing maximum value of 115.78 Ohm·cm2 for 250 ppm. The shift in corrosion potential (Ecorr) values revealed Vinca rosea leaf extract as a mixed type of inhibitor. Effect of temperature on IE was carried out at 303–333 K. The corrosion rate decreased with increase in inhibitor concentration and increased with the temperature increase. The inhibitive effect was attributed due to the physical adsorption of the extract components on metal surface as approximated by Langmuir adsorption isotherm with of about –17 kJ·mol–1. The 0 ∆Gads preliminary phytochemical screening analysis indicated the presence of alkaloids, phenols, tannins, flavonoids. The various functional groups of the Vinca rosea leaf extract was confirmed by Fourier Transform Infrared (FT-IR) spectroscopic analysis and further confirmed the protective layer formed on the metal surface containing the functional groups. Surface analysis technique, scanning electron microscopy (SEM) and UV-Vis spectroscopic analysis was carried out to know the surface morphology of metal surface with and without inhibitor and the interaction between the inhibitor and metal ion, Fe2+ respectively.