Thermodynamics and adsorption study of the corrosion inhibition of mild steel by Euphorbia heterophylla L. extract in 1.5 ​M HCl

Abstract

This work investigates the thermodynamics parameters and adsorption mechanism of Euphorbia heterophylla L. extract as a corrosion inhibitor for mild steel in 1.5 ​M HCl. The gravimetric method was used to determine the inhibition efficiency and corrosion rate. Relevant thermodynamic equations were employed to determine the activation energy, enthalpy change and entropy change. The adsorption isotherms were used to evaluate the Gibbs free energy change. Observation from the results of the study showed that the activation energy of an inhibited process was higher when compared with the uninhibited process. Also, the enthalpy change was positive and less than 100 ​KJ/mol threshold. The adsorption study showed that the data fit into the Langmuir, Flory-Huggins, El-Awary’s and Temkin isotherms but Flory-Hugins gave the best fit. The Gibb’s free energy change of adsorption was negative and less than the −20 ​KJ/mol threshold. As concluded from the results, the adsorption of Euphorbia heterophylla L. on mild steel in 1.5 ​M HCl medium is feasible, spontaneous and it occurred by physical adsorption according to Flory-Hugins isotherm model.