The Adsorption and Corrosion Inhibition of Some Nonionic Surfactants on Carbon Steel and Brass in Aggressive Media

Abstract

The corrosion inhibition properties of some nonionic surfactants: Triton X100 and Triton A20, for two carbon steels (OL 37 and OLC 45) and brass in 1M H2so4 and 1M HCl was analyzed by weight loss method, potentiostatic and potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and metallurgical microscopy techniques. The addition of the organic inhibitors led in all the cases to inhibition of the corrosion process in acidic solution at different temperatures. Under the critical micelle concentration (CMC), the inhibition of these three surfactants is negligible and at a concentrations higher than the CMC, the inhibiting action of these inhibitors increases rapidly. The inhibition activity analysis of these organic inhibitors was made by assuming that the mechanism of inhibition by organic molecules is chemisorptions and physisorptions. We presume that, these organic compounds inhibit corrosion of carbon steels and brass by a protective mechanism, forming insoluble iron complexes, copper complexes and repairing the porous oxide layers. Polarization curves indicate that they are mixed type of inhibitors. The corrosion parameters obtained from polarization curves and from EIS spectra are in good concordance and point out the inhibitory action of cationic surfactants. The inhibition efficiency was high in all the studied cases. The adsorptions of the organic compounds on the carbon steels surface obeyed Langmuir’s isotherm. The thermodynamic parameters of adsorption enthalpy (ΔH0), adsorption free energy (ΔG0) and adsorption entropy (ΔS0) were calculated. The characterization using Fourier transform infrared spectroscopy (FT-IR) demonstrates the adsorption of organic inhibitors and the formation of corrosion products on the carbon steels and brass surfaces. The inhibition process was attributed to the formation of the adsorbed film on the metal surface and blocking the active sites that protects the metal against corrosive agents. The EIS measurements have confirmed this protection and pointed out the formation of adsorption layers on the electrode surface.