Corrosion inhibition behaviour on carbon steel in well-water by Ethanolic extract of Portulaca quadrifida (Chicken weed) leaves

Objectives: To evaluate the corrosion inhibition of an ethanolic extract of Portulaca quadrifida (PQ) leaves on the carbon steel surface in well-water by using a weight-loss study with various immersion periods, temperatures, and pH. The kinetic and thermodynamic parameters are calculated for various temperatures. Methods: The protective film has been analyzed by using SEM, EDX and AFM studies. The inhibition action of PQ extract was analyzed by potentiodynamic polarization study, the electrochemical impedance studies are used to the analysis the protective layer formed on the carbon steel surface. Findings: The maximum inhibition efficiency is found to be 92% for 500ppm of PQ and 30ppm of Zn2+ ions at 303K. The synergistic effect exists between ethanolic extract of Portulaca quadrifida leaves and Zn2+ ions by synergistic parameters. The ethanolic extract of PQ leaves acts as a mixed-type inhibitor. The activation energy (Ea) values indicate that the adsorption of PQ leaves extract on the carbon steel surface. The enthalpy of adsorption (ΔH) values suggests that the reaction is endothermic. The free energy of adsorption (ΔGads) values is negative and less than the -20KJmol-1. The negative values of ΔSads are confirmed to form an ordered stable layer of the inhibitor molecule on the carbon steel surface as well as a stable equilibrium between the adsorption and desorption processes. The adsorption isotherm is best fitted with the Langmuir model. Novelty: The ΔGads values indicate that the adsorption of inhibitor on the carbon steel surface belongs to the physisorption as well as the adsorption layer has an electrostatic character. The adsorption process of the inhibitor is spontaneous. The thermodynamic parameters give a strong interaction between the inhibitor molecules and carbon steel surface. Four adsorption isotherms including Langmuir, El-Awady, Flory-Huggins, and Temkin models, investigate the mode of inhibition of PQ leaves extract.