Abstract

This work studies the adsorption mechanism of pumpkin pod extract as corrosion inhibitor and its parameters of thermodynamics in carbon dioxide saturated brine environment on carbon steel metal surface. Method of loss in weight was utilized in establishing the rate of oxidation. Appropriate thermodynamics models were deployed to know the Gibbs free change of energy using four adsorption isotherms models. The study on its adsorption mechanism revealed that the experimental data is suitable for the Langmuir, Freundlich, Temkin, and El – Awady but Langmuir isotherm provided the superlative fit. Free energy of Gibb’s adsorption was less than -20KJ/mol maximum limit and negative for Langmuir and Freundlich isotherms except for Temkin whose threshold value is higher than -20KJ/mol, and El – Awady’s isotherm model that gave positive values for the ∆G. The adsorption of pumpkin pod extract on carbon steel in carbon dioxide saturated saline environment is feasible, spontaneous, and occurred by physisorption in accordance with Langmuir isotherm model.

Key words: Gibbs free energy, Corrosion rate, Pumpkin pod, Carbon steel, Corrosion thermodynamics, Adsorption isotherms