The effect of 1-(2-pyridylazo)-2-naphthol on the corrosion of cold rolled steel in acid media - Part 2: Inhibitive action in 0.5 M sulfuric acid

The effects of 1-(2-pyridylazo)-2-naphthol (PAN) and the complex of various concentrations of PAN and 0.1 M NaCl on the corrosion of cold rolled steel in 0.5 M sulfuric acid have been investigated by using weight loss and polarization method. The present study revealed that cold rolled steel in sulfuric acid has been more efficiently inhibited by PAN in the presence of NaCl than single PAN, and inhibition efficiency increases with increasing concentration of PAN in the presence of 0.1 M NaCl. At all experimental temperatures, there is the synergistic effect between PAN and NaCl. The adsorption of single PAN on the cold rolled steel surface in 0.5 M sulfuric acid obeyed the Temkin adsorption isotherm, while the adsorption of the complex of PAN and NaCl accords with the Langmuir adsorption isotherm. Polarization studies show that in 0.5 M sulfric acid single PAN mainly acts as a cathodic inhibitor for steel corrosion, while the complex of PAN and NaCl acts as a mixed type inhibitor for the corrosion of steel. Thermodynamic parameters, such as adsorption heat, adsorption entropy and adsorption free energy are obtained from experimental data of the temperature studies in the inhibition process at four temperatures. The kinetic data, such as apparent activation energy and pre-exponential factor at different concentrations of the inhibitor are calculated, and the effects of the apparent activation energy and pre-exponential factor on the corrosion rate of cold rolled steel are discussed. The inhibition action is satisfactorily explained by using both thermodynamic and kinetic models. The results obtained from weight loss and polarization methods are in good agreement. (c) 2005 Elsevier B.V. All rights reserved.