Kinetic–Thermodynamic Properties of a Polyacrylamide on Corrosion Inhibition for C-Steel in 1.0 M HCl Medium: Part 2

Abstract

In this second part, the adsorption and thermodynamics properties of a polyacrylamide PA on corrosion inhibition of in 1.0 M HCl solution were analyzed by means of potentiodynamic polarization and electrochemical impedance spectroscopy techniques. Besides, the effects of temperature as well as the immersion time, on the inhibition efficiency, at 3 × 10−6 mol L−1 of PA, were also investigated. The adsorption data were modeled using six linearized forms of adsorption isotherms corresponding to Langmuir, Flory–Huggins, Temkin, Frumkin, Freundlich as well as the kinetic–thermodynamic model of El-Awady. The Langmuir model was first ruled out notwithstanding the highest value of linear regression coefficient and a slope close to unity. Secondly, it was found, according to both El-Awady and Flory–Huggins models, that exactly three molecules of water were replaced by one PA molecule. Thirdly, it was shown the presence of repulsive lateral interactions in the adsorbed inhibitory layer confirmed by the negative sign of the interaction parameters of Temkin and Frumkin isotherms. The effect of immersion period revealed significant improvement of the charge transfer resistance and accordingly the inhibiting efficiency which reach circa 96% after 6 h. The confrontation of thermodynamic (Kads, ΔrGads°) along with the kinetic parameters (A, Ea) showed that the adsorption of PA molecules onto C-steel surface involved both chemical and physical adsorption but predominantly chemisorption.