Thermodynamic and Adsorption Influence on the Corrosion Inhibitive Performance of Pawpaw Seed on A36 Mild Steel in 1 M H2SO4 Medium

Abstract

This research work investigated the corrosion inhibitive performance of the nano-sized pawpaw seeds on A36 mild steel in 1 M H2SO4 medium. The metal samples were subjected to corrosive environment (with and without varied concentrations of the inhibitor) using both the weight loss and potentiodynamic polarization tests at different temperatures (278.15–318.15) K for weight loss and (30.15–323.15) K for potentiodynamic polarization study). The equipment used include Thermo scientific ARL OP-TIM’X 166 spectrometer (for metal composition analysis) and Autolab PGSTAT 302 N (for potentiodynamic polarization test). The results obtained showed that the nano-sized pawpaw seed is an effective organic inhibitor with optimum inhibitor concentration of 4 g/cm3 having inhibitor efficiency of 92% from the weight loss test. The inhibition performance of pawpaw seed increased with decrease in temperature for both the gravimetric tests (between 278.15 K and 318.15 K) and potentiodynamic polarization study (between 300.15 K and 323.15 K). The Langmuir adsorption isotherm with correlation coefficient (R2) of 0.99 accurately predicted the adsorption mechanism of the inhibitor on the metal surface. The thermodynamic change in Gibbs free energy (ΔGads) of (-12.9544 to -11.5409) kJ/mol and adsorption equilibrium constant ( Kads) of (1.70–2.99) of the adsorbed inhibitor on metal surface revealed both the spontaneous and physisorption nature of the inhibitor-adsorbed process. Also, the tafel plot showed that the inhibitor acted as a mixed-typed inhibitor.