Abstract
2-amino-1, 3, 4-thiadiazoles (AT), 2-amino-5-methyl-1, 3, 4-thiadiazoles (AMT), 2-amino-5-ethyl -1, 3, 4-thiadiazoles (AET) and 2-amino-5-propyl -1, 3, 4-thiadiazoles (APT) were synthesized. FT-IR and NMR studies were done in order to confirm the composition of the synthesized inhibitors. These compounds were evaluated as inhibitors for mild steel in 20% formic acid and 20% acetic acid by weight loss, potentiodynamic polarization and electrochemical impedance techniques. Scanning electron microscopic study (SEM) was also used to investigate the surface morphology of inhibited and uninhibited metal samples. The inhibition efficiency of these compounds was found to vary with the inhibitor concentration, immersion time, temperature and acid concentration. The adsorption of these compounds on the steel surface from both acids were found to obey Langmuir’s adsorption isotherm. These compounds are mixed type inhibitors in both acid solutions. Various thermodynamic parameters (Ea, ΔGads, ΔQ, ΔH, ΔS, t1/2) have also been calculated to investigate the mechanism of corrosion inhibition. Electrochemical impedance study was used to investigate the mechanism of corrosion inhibition.