Tween-40 as corrosion inhibitor for cold rolled steel in sulphuric acid: Weight loss study, electrochemical characterization, and AFM

The inhibition action of a non-ionic surfactant of tween-40 on the corrosion of cold rolled steel (CRS) in 0.5-7.0 M sulphuric acid (H2SO4) was studied by weight loss and potentiodynamic polarization methods. Atomic force microscope (AFM) provided the surface conditions. The inhibition efficiency increases with the tween-40 concentration, while decreases with the sulphuric acid concentration. The adsorption of inhibitor on the cold rolled steel surface obeys the Langmuir adsorption isotherm equation. Effect of immersion time was studied and discussed. The effect of temperature on the corrosion behavior of cold rolled steel was also studied at four temperatures ranging from 30 to 60 degrees C, the thermodynamic parameters such as adsorption heat, adsorption free energy and adsorption entropy were calculated. A kinetic study of cold rolled steel in uninhibited and inhibited acid was also discussed. The kinetic parameters such as apparent activation energy, pre-exponential factor, rate constant, and reaction constant were calculated for the reactions of corrosion. The inhibition effect is satisfactorily explained by both thermodynamic and kinetic parameters. Polarization curves show that tween-40 is a cathodic-type inhibitor in sulphuric acid. The results obtained from weight loss and potentiodynamic polarization are in good agreement, and the tween-40 inhibition action could also be evidenced by surface AFM images. (c) 2005 Elsevier B.V. All rights reserved.