Joint Effect of Anogessius Leocarpus Gum (AL Gum) Exudate and Halide Ions on the Corrosion of Mild Steel in 0.1 M HCl

In an attempt to improve the corrosion inhibition potential of Anogessius leocarpus gum exudates for mild steel in solutions of HCl, corrosion inhibition efficiencies of the gum, KI, KCl, and KBr were determined experimentally using weight loss and gasometric methods. 0.05 M KI, 0.05 M KBr and 0.05 M KCl were combined with various concentrations of Anogessius leocarpus gum and their combined inhibition efficiencies were used in computing synergistic parameters for the respective combinations. The results obtained indicated that combination of 0.4 and 0.5 g/L of AL gum with 0.05 M solutions of KI and KBr, respectively, enhanced inhibition efficiency of the gum. However, for all concentrations of AL gum, combinations with 0.05 M KCl recorded a remarkable increase in inhibition efficiency, but calculated values of the synergistic parameter indicated that the adsorption of AL gum on mild steel surface is antagonized by the presence of Cl - . Theory of competitive and co-operative adsorption has been used to explain the co-adsorption of the gum and the halides. From calculated values of activation energy (< 80kJ/mol), free energy of adsorption (< -40 kJ/mol) and the variation of inhibition efficiency with temperature, the adsorption characteristics of the gum, halides and that of gum-halide mixtures were found to be consistent with the mechanism of physical adsorption. The adsorption was also found to be endothermic, spontaneous and favored the Langmuir adsorption model.