Ruthenium–ligand complex, an efficient inhibitor of steel corrosion in H3PO4 media

The effect of a ruthenium–ligand complex (RuLC) on the corrosion of steel in 2 M H3PO4 has been investigated at various temperatures using electrochemical techniques (impedance spectroscopy (EIS), polarisation curves) and weight loss measurements. Inhibition efficiency (E%) increases with RuLC concentration to attain 90% at 5 × 10− 4 M. EIS measurements show that the dissolution process of steel occurs under activation control. Polarisation curves indicate that RuLC acts as a cathodic inhibitor. E% values obtained from various methods used are in good agreement. The temperature effect on the corrosion behaviour of steel in 2 M H3PO4 without and with the inhibitor at various concentrations was studied in the temperature range from 298 to 338 K. Thermodynamic parameters such as adsorption heat (ΔHads°), adsorption entropy (ΔSads°) and adsorption free energy (ΔGads°) have been calculated. Kinetic parameters for the corrosion reaction at different concentrations of RuLC were determined. Adsorption of RuLC on the mild steel surface in 2 M H3PO4 follows the Langmuir isotherm model.