A New Synthesized Corrosion Inhibitor for Mild Steel in 0.5 M H2SO4

The inhibition effect of a new synthesized organic inhibitor , namely 1-(3-Nitrobenzylidene) Thiosemicarbazide (A) on the corrosion of mild steel in 0.5 M sulphuric acid  have been investigated at room temperature using weight loss, electrochemical impedance spectroscopy(EIS) and Tafel polarization  measurements. The inhibition efficiencies obtained from all methods employed are in good agreement with each other. The obtained results show that compound (A) is a very good inhibitor with efficiency of 98% at 100 ppm additive concentration in acid solution. Generally the inhibition efficiency increased with increase of inhibitor concentration. Changes in impedance parameters ( Rct and Cdl ) were indicative of adsorption of compound (A) on the metal surface, leading to the formation of a protective film. Tafel polarization measurements showed that the inhibitor (A) is a mixed type. The adsorption of the inhibitor on the surface of mild steel in 0.5 M sulphuric acid was found to obey Longmuir’s adsorption isotherm. Scanning electron microscopy (SEM) observation, confirmed the existence of an absorbed protective film on the metal surface. The free energy of adsorption process was calculated and discussed.  Key Words: inhibitor, mild steel, AC impedance, corrosion inhibition