Corrosion inhibition of aluminium in phosphoric acid solution using glutaraldehyde as inhibitor

Abstract

The effect of glutaraldehyde as corrosion inhibitor for aluminum in phosphoric acid solution was studied by using weight loss method and characterized by fourier transform infrared spectroscopic and scanning electron microscopic analysis. The inhibition efficiency increases with increase in inhibitor concentration and decreases with increase in temperature while the corrosion rates increases with rise in temperature and decreases with increase in inhibitor concentration. The value of activation energy (ΔEa) was found to be 32.61 kJ/mol in uninhibited acid solution and increased to 47.33 kJ/mol in the presence of 0.1 M inhibitor concentration. The positive values of the enthalpy of activation (ΔHa) suggest an endothermic nature of the reaction and negative values of activation entropy (ΔSa) shows that the activation complexes in the rate determining step represent an association rather than dissociation. The values of free energies of adsorption were all negative which indicate spontaneity of the process. The phenomenon of physical adsorption is proposed from the values of activation energy and free energy of adsorption. The results also shows that the adsorption of inhibitor molecules on the surface of aluminum is accord with Langmuir adsorption isotherm as to the values of correlation coefficient (R2) obtained were very close to unity. The result of the SEM analysis in the presence of inhibitor shows how the aluminium surface was protected against the aggressive effect of the acid. The new functional group in the FTIR analysis of the corrosion product is an indication of thin layer formation on the aluminium surface.