Hydrazide derivatives as corrosion inhibitors for mild steel in 1 M HCl

N-Phenyl oxalic dihydrazide (PODH) and oxalic N-phenylhydrazide N'-phenylthiosemicarbazide (OPHPT), synthesized in our laboratory, were tested as inhibitors for the corrosion of mild steel in molar HCl by electrochemical measurements. Inhibition efficiencies up to 92% for OPHPT and 79% for PODH can be obtained. Polarization curves reveal that PODH and OPHPT act as mixed type inhibitors. Adsorption of these inhibitors on the mild steel surface was found to obey the Langmuir adsorption isotherm. Results show that the rate of corrosion of mild steel increased with increasing temperature over the range 25-55 degrees C both in the presence of inhibitors and in their absence. Activation energies in the presence and absence of PODH and OPHPT were obtained by measuring the temperature dependence of the corrosion current. The reactivity of these compounds was analyzed through theoretical calculations based on density functional theory to explain the different efficiency of these compounds as corrosion inhibitors. (c) 2005 Elsevier B.V All rights reserved.