Corrosion Inhibition, Adsorption and Thermodynamic Properties of Poly (Sodium 4-Styrenesulfonate) on Carbon Steel in Phosphoric Acid Medium

The use of polymers as corrosion inhibitors has attracted much attention due to their low prices, inherent stability, availability and cost-effectiveness. The corrosion inhibiting effect of poly(sodium-4-styrenesulfonate) on carbon steel in phosphoric acid solution has been investigated using weight loss and scanning electron microscopy techniques (SEM) and theoretical calculations based on density functional theory (DFT). In the presence of 1.0x10(-3) mol/L of inhibitor, a maximum inhibition effect of 98.06 % was observed. The influence of the concentration of the inhibitor, the temperature of the solution and the immersion time on the corrosion of carbon steel was investigated. Activation parameters such as activation energy (E-act), activation enthalpy (Delta H-act), activation entropy (Delta S-act), heat of adsorption (Q(ads)) and adsorption free energy (Delta G(ads)) were evaluated based on the effect of temperature on the corrosion and inhibition processes. It was found that the adsorption behaviour of poly(sodium-4-styrenesulfonate) (PSS) follows the Langmuir isotherm and the free energy change values indicate mixed chemical and physical adsorption on the carbon steel surface. The results obtained with the different methods agree well.