New bipyrazolic derivatives as corrosion inhibitors of steel in 1Â M HCl

The inhibition of corrosion of steel in molar hydrochloric acid solution by two bipyrazolic compounds is studied by weight loss and electrochemical polarisation measurements. The two methods give consistent results. The polarisation curves indicate that the bipyrazolic compounds act as mixed-type inhibitors. These compounds are efficient inhibitors. The inhibition efficiency increases with the increase of inhibitor concentration to reach 96 and 92% at 5 × 10−4 M for Bipyr 1 and Bipyr 2, respectively. The temperature effect on the corrosion behaviour of steel in 1 M HCl with and without the bipyrazolic compounds at 5 × 10−4 M is studied in the temperature range from 308 to 353 K. The adsorption of inhibitors on the steel surface is found to obey the Frumkin adsorption isotherm model. From the adsorption isotherm, some thermodynamic data for the adsorption process (f, K and ΔGads∘) are calculated and discussed.