Inhibition Reaction Behaviour of Combined Grapefruit and Lemongrass Plant Distillates on Plain Carbon Steel Degradation

Abstract

Applications of harmless fluid derivative for the sustenance of carbon steel in corrosive environments are more appropriate for environmental sustainability and safety of personnel. Admixture of grapefruit and lemongrass distillates was assessed for their protective performance on plain carbon steel within 0.5 M of H2SO4 and HCl solution through weight loss analysis and optical macroscopy studies. Results shows the plant extracts effectively stifled corrosion in both acids with inhibition value range (lowest to highest) of 98.65%-99.5% in H2SO4 solution and 96.31%- 98.39% in HCl. PCS in H2SO4 and HCl electrolyte at 0% extract concentrate were 5.330 mm/y and 2.701 mm/y. Inclusion of the distillate to the electrolyte significantly reduced the corrosion rates in both acids to midpoint values of 0.0448 mm/y and 0.072 mm/y at 240 h of test. The oil extract strongly adsorbed unto the steel surface by means of chemisorption with midpoint Gibbs free energy value above -44 Kjmol-1 signifying strong covalent bonding. The extract adsorption aligned with Langmuir and Frumkin adsorption isotherms with interaction coefficient above 0.9. Optical images of steel surface without inhibitor showed a severely corroded morphology and significant reduction in thickness. The protected steel substantially differs the earlier observation due to the presence of the oil extract which passivated the steel exterior.