Equilibrium and Thermodynamic Characteristics of the Corrosion Inhibition of Mild Steel Using Sweet Prayer Leaf Extract in Alkaline Medium

The usage of synthetic-based inhibitors for protection of metals against corrosion is always accompanied by environmental and economic challenges, including a threat to human health. Therefore, the corrosion inhibition efficiency of sweet prayer (Thaumatococcus danielli) leaf extract on mild steel in alkaline medium (NaOH) was investigated. The effects of temperature and concentration of the inhibitor on corrosion inhibitive potential of the leaf extract were evaluated. The equilibrium data were subjected to isotherm analysis (Langmuir, Freundlich and Temkin models). Langmuir model was the best model that provided information on the adsorption of the corrosion systems. The values of Langmuir equilibrium constant (KL) increased from 0.1581 g/L to 0.6523 g/L as the temperature increased from 298 K to 333 K. The findings revealed that sweet prayer leaf extract at different concentrations had inhibitive effects of mild steel on alkaline medium. The values of activation energy of the inhibited corrosion systems were greater than that of obtained for uninhibited system. Thermodynamic study revealed a feasible and spontaneous adsorption of sweet prayer leaf extract on mild steel. The trends of inhibition efficiencies and the results obtained from the thermodynamic parameters suggested a physical adsorption mechanism. The study proved that the sweet prayer leaf extract could serve as a low-cost corrosion inhibitor of mild steel in alkaline medium.