Thiazoles as corrosion inhibitors for mild steel in formic and acetic acid solutions

2-(N,N-dimethylamino) benzylidene imino-4-(4-methyl phenyl)-1,3-thiazole (DIMPT), 2-benzylidene imino-4-(4-methyl phenyl)-1,3-thiazole (BIMPT), 2-salicylidene imino-4-(4-methyl phenyl)-1,3-thiazole (SIMPT) and 2-cinnamylidene imino-4-(4-methyl phenyl)-1,3-thiazole (CIMPT) were synthesized in the laboratory and their influence on the inhibition of corrosion of mild steel in 20% formic acid and 20% acetic acid was investigated by weight loss and potentiodynamic polarization techniques. The inhibition efficiency of these compounds was found to vary with their nature and concentration, temperature, immersion time and acid concentration. The values of activation energy and free energy of adsorption of the thiazoles were calculated to investigate the mechanism of corrosion inhibition. The adsorption of all the thiazoles on mild steel surface was found to obey Langmuir adsorption isotherm. The potentiodynamic polarization result revealed that the compounds studied are mixed type inhibitors. Electrochemical impedance spectroscopy was used to investigate the mechanism of corrosion inhibition.