Thermodynamic characterization of metal dissolution and adsorption of polyvinyl alcohol-grafted poly(Acrylamide- vinyl sulfonate) on mild steel in hydrochloric acid

Abstract

The corrosion inhibition of mild steel in hydrochloric acid by polyvinyl alcohol-gpoly(acrylamide-vinyl sulfonate) has been studied by weight loss and -electrochemical methods (AC impedance and DC polarisation) techniques in the temperature range of 303 – 343 K. The inhibitor was found to provide an excellent efficiency of more than 90%. Various adsorption isotherms have been employed for fitting the obtained results to confirm the mode of adsorption of the grafted terpolymer on mild steel. Thermodynamic parameters of adsorption such as equilibrium constant, Gibbs free energy, adsorption heat and adsorption entropy were evaluated and discussed. Various parameters that determine the kinetics of mild steel dissolution such as activation energy, enthalpy and entropy were also calculated. Results obtained from various techniques were comparable and suggest that the terpolymer follows chemical adsorption mode for inhibition.