The inhibition effect of Sulfamethazine (SFMT) on the corrosion of mild steel in 2.0 M phosphoric acid has been investigated by weight loss, polarization potentiodynamic and electrochemical impedance spectroscopy (EIS). SFMT is able to reduce the corrosion of steel effectively in phosphoric acid. Results obtained revealed that these compounds are good mixed-type inhibitors without changing the mechanism of the corrosion process. The effect of temperature on the corrosion behavior of mild steel in phosphoric acid with addition of SFMT was studied in the temperature range 298–328 K. The studied compounds appeared to function through general adsorption following the thermodynamic–kinetic adsorption isotherm. The thermodynamic and activation parameters were determined and discussed. Quantum chemical calculations were applied to theoretically determine the relationship between molecular structure and inhibition efficiency.
