ABSTRACT

The corrosion inhibition of zinc in 0.1M H₂SO₄ in the presence of 4-[(4-chlorobenzylidene) amino] benzoic acid (4CBB), 2-[(4-dimethylaminobenzyldene) amino] benzoic acid (2DAB) and 4-[(4-dimethylaminobenzylidene) amino] benzoic acid (4DAB) was studied using gravimetric (weight loss) method at temperatures ranging from 303 K to 343 K. The results showed that inhibition efficiencies of the inhibitors increased as the concentrations increased but decreased with rise in temperature. The efficiencies of 4DAB at the temperatures of study ranged from 38.9% to 36.6% at 5.0g/l concentration. For 4CBB, it ranged from 42.8% to 38.8% at 5.0g/l concentration. The efficiencies of 2DAB were from 38.1% to 35.9%. The efficiencies followed the order: 2DAB˂4DAB˂4CBB. The kinetic data obtained showed that the corrosion process followed first order kinetics. The activation energy, E_a, values obtained for all the inhibited (and uninhibited) solutions were less than 80kJ/mol, indicating that physical adsorption was the predominant mechanism. This was also supported by the fact that free energies of adsorption were less than -40kJ/mol which is required for physisorption. The adsorption data of the inhibitors were fitted to Langmuir, Freundlich and El-Awardy isotherms. Langmuir isotherm gave the best fit to the adsorption data. The calculated free energies of adsorption for 4DAB, 2DAB and 4CBB ranged from -5,122.576J/mol to – 6,390.182J/mol;  -5,185.866J/mol  to -6,690.542J/mol, and, -4,331.062 J/mol to -6,245.603 J/mol; respectively.   The heat of adsorption results, ΔH⁰_ads, showed that the adsorption processes for 4CBB, 2DAB and 4DAB were endothermic.