The corrosion inhibition efficiency of Sulfapyridine(SFP) for carbon steel in 2.0 M H3PO4 has been studied using weight loss, polarization, electrochemical and impedance spectroscopy techniques. The results show that SFP is a good inhibitor in 2.0 M H3PO4. Effects of temperature and acid concentration on inhibitive performance were investigated. Polarization curves reveal that SFP acts as a mixed-type inhibitor. The electrochemical impedance spectroscopy showed that the charge transfer resistance increases and the double layer capacitance decreases on increasing Sulfapyridine concentration. Activation energy of corrosion and other thermodynamic parameters such as standard free energy, standard enthalpy, and standard entropy of the adsorption process revealed better and well-ordered physical adsorption mechanism in the presence of Sulfapyridine. Adsorption isotherms in absence or presence of SFP as inhibitor appropriately fit the Langmuir isotherm. Theoretical investigations have established that the interaction of SFP with the metal steel surface is mainly through the Nitrogen, oxygen atoms, sulphonyl group and the p system of the aromatic ring.
