Evaluation of N-containing organic compound as corrosion inhibitor for carbon steel in phosphoric acid

The inhibitor effect of N-1-naphthylethylenediamine dihydrochloride monomethanolate (N-NEDHME) on the corrosion of carbon steel in 2.0 M H3PO4 at 303-328Kwas investigated by weight loss, potentiodynamic polarization and electrochemical impedance. The results show that inhibition efficiency increases with the inhibitor concentration, while decreases with temperature. The value of activation energy (Ea), Arrhenius factor, enthalpy and entropy for N-NEDHME values were discussed. Langmuir isotherm was found to provide an accurate description of the adsorption behaviour of the investigated compound. The thermodynamic parameters (adsorption equilibrium constant (Kads), free energy of adsorption ( DGa°ds ), adsorption heat ( ads DH° ) and adsorption entropy ( ads DS° )) have been calculated and discussed in detail. Polarization curves show that N-NEDHME acts as a mixed-type inhibitor. The experimental data showed a frequency distribution and therefore a modelling element with frequency dispersion behaviour and a constant phase element (CPE) have been used. Quantum chemical calculation was applied to elucidate the adsorption mode of the inhibitor molecule onto steel surface