Theoretical and Experimental Studies About the Inhibitive Action of Ruellia tuberosa L on Mild Steel in HCl Medium

Abstract

The inhibiting ability of the leaves of Ruellia tuberosa Linn (RT) extract on the corrosion of mild steel in hydrochloric acid was investigated using mass loss and electrochemical studies. The inhibition efficiency increases with increasing concentration of RT extract and decreases with increasing acid concentration and temperature. The polarization studies reveal that the extract acts as a mixed type inhibitor. Impedance results indicate adsorption of the RT extract on the mild steel surface is through charge transfer reaction. The adsorption of the inhibitor on mild steel surface is exothermic, spontaneous, and is consistent with the mechanism of physical adsorption. In addition, it has been established that the adsorption process obeyed Freundlich isotherm. The adsorption of the chemical constituents of the RT extract on mild steel surface was confirmed by Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The quantum chemical calculations were made to ascertain the possible adsorption sites of the components of the extract on to the metal surface.