Benzamide, acetamide and acrylamide as Corrosion Inhibitors for Carbon Steel in Hydrochloric Acid Solutions

The corrosion inhibition characteristics of some amide compounds, namely benzamide, acetamide and acrylamide on the carbon steel corrosion in 1 M hydrochloric acid have been investigated at 30oC by weight loss, potentiodynamic polarization, electrochemical frequency modulation (EFM) and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiencies obtained from all methods employed are in good agreement with each other. The obtained results show that benzamide is the best inhibitor with an efficiency of 90.9% at 5 x 10-3 M additive concentration. Generally, the inhibition efficiency increased with increasing the inhibitor concentration. Changes in impedance parameters (charge transfer resistance, Rct, and double-layer capacitance, Cdl) were indicative of adsorption of benzamide on the metal surface, leading to the formation of a protective film. The potentiodynamic polarization measurements indicated that the inhibitors are of mixed type. The adsorption of the inhibitors on the carbon steel surface in the acid solution was found to obey Temkin’s adsorption isotherm. The free energies of adsorption were calculated and discussed. The surface morphology of inhibited carbon steel was analyzed by scanning electron microscope (SEM) and with energy dispersive X-ray spectroscopy (EDX).