Inhibition effect of two organic compounds pyridine-pyrazole type in acidic corrosion of steel

The inhibition of the corrosion of steel in 1 M HCl by two pyridine-pyrazole type organic compounds N-containing: (5-methyl-1-pyridin-2-yl-1H-pyrazol-3-yl)methanol (PI) and ethyl 5-methyl-1-pyridin-2-yl-1H-pyrazol-3-carboxylate (P2) has been studied at 308 K by weight loss, electrochemical polarisation, polarisation resistance and electrochemical impedance spectroscopy (EIS) measurements. The inhibition efficiencies obtained from cathodic Tafel plots gravimetric and EIS methods were in good agreement. The results obtained reveal that these compounds are efficient inhibitors. The inhibition efficiency increases with the increase of inhibitor concentration and reached 94 % for PI at 10(-3) M. Potentiodynamic polarisation studies clearly reveal that the presence of inhibitors P1 and P2 does not change the mechanism of hydrogen evolution and that they act essentially as cathodic inhibitors. The temperature effect on the corrosion behaviour of steel in I M HCl without and with the inhibitors at 10(-3) M was studied in the temperature range from 308 to 353 K. The inhibitors were adsorbed on the steel surface according to the Frumkin adsorption isotherm model. From the adsorption isotherm some thermodynamic data for the adsorption process (f, K and Delta G degrees(ads)) are calculated and discussed. EIS measurements show that the increase of the transfer resistance with the inhibitor concentration. (c) 2005 Elsevier B.V. All rights reserved.