Inhibitive action of bipyrazolic type organic compounds towards corrosion of pure iron in acidic media

Inhibitory effect of some new synthesized bipyrazole compounds, namely, N,N-bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-N-(4-methylphenyl)amine (P1) and methyl-1-[((methylphenyl){[3-(methoxycarbonyl)-5-methyl-1H-pyrazol-1-yl]methyl} amino)methyl]-5-methyl-1H-pyrazole-3-carboxylate (P2) on corrosion of pure iron in 1 M HCl solution has been studied using chemical technique as weight loss and electrochemical techniques as potentiodynamic polarization, linear polarization and impedance. The inhibition efficiencies obtained from gravimetric, cathodic Tafel plots, linear polarization resistance and EIS methods are in good agreement. The results obtained reveal that these compounds are efficient inhibitors. The inhibition efficiency increases with the increase of inhibitor concentration to reach 93% for P1 at 2.5 × 10 -4 M. Potentiodynamic polarisation studies clearly reveal that P1 and P2 act as mixed-type inhibitors without change of the mechanism of hydrogen evolution. The temperature effect on the corrosion behaviour of iron in 1 M HCl without and with the inhibitors at 2.5 × 10 -4 M has been studied in the temperature range from 298 to 353 K. EIS measurements show that the increase of the transfer resistance with the inhibitor concentration. The inhibitors are adsorbed on the iron surface according to the Langmuir adsorption isotherm model. From the adsorption isotherm some thermodynamic data for the adsorption process (K and ΔGads°) are calculated and discussed. © 2004 Elsevier B.V. All rights reserved.