Investigation on some Schiff bases as HCl corrosion inhibitors for carbon steel

Potentiodynamic polarisation and ac impedance studies were carried out on the inhibition of carbon steel in 0.1 M hydrochloric acid solution by various Schiff bases containing heteroaromatic substituents. The examined Schiff bases were 2-((1E)-2-aza-2-pyrimidine-2-ylvinyl)thiophene, 2-((1Z)-1-aza-2-(2-pyridyl)vinyl)pyrimidine, 2-((1E)-2-aza-2-(1,3-thiazol-2-yl)vinyl)thiophene, 2-((1Z)-1-aza-2-(2-thienyl)vinyl)benzothiazole. Polarisation curves indicates that studied Schiff bases act essentially as anodic inhibitor. The variation in inhibitive efficiency mainly depends on the type and nature of the substituents present in the inhibitor molecule. Potentiodynamic polarisation and ac impedance measurements carried out at different concentration of studied Schiff bases reveal that these compounds are adsorbed on steel surface and the adsorption obeys Temkin’s adsorption isotherm. From the adsorption isotherms values of equilibrium constant, Kads, values of free energies of adsorption, ΔGads, were calculated. Activation parameters of the corrosion process such as activation energies, Ea, activation enthalpies, ΔH∗, and activation entropies, ΔS∗, were calculated from the obtained corrosion rates at different temperatures.