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

This research work investigated the corrosion inhibitive performance of the nano-sized pawpaw seeds on A36 mild steel in 1 M H 2 SO 4 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/cm 3 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 ( R 2 ) of 0.99 accurately predicted the adsorption mechanism of the inhibitor on the metal surface. The thermodynamic change in Gibbs free energy (ΔG ads ) of (-12.9544 to -11.5409) kJ/mol and adsorption equilibrium constant (K ads ) 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.