EFFECT OF HALIDE IONS ADDITIVES ON THE CORROSION INHIBITION OF ALUMINUM IN HCl BY POLYACRYLAMIDE

The influence of bromide and iodide ions on the inhibitive effect of polyacrylamide (PA) on aluminum corrosion in HCl solution was studied using weight loss, hydrogen evolution, and thermometric techniques at 30 and 60 degrees C. The results show that the halide additives synergistically increased the inhibition efficiency of polyacrylamide. The increase in inhibition efficiency (%I) was found to be more pronounced in I- than Br- ions. The observed difference in behavior of both halide additives could be linked to the differences in their atomic radii as well as electronegativity. The values of synergism parameter (S-1) obtained for the halides are greater than unity, suggesting that the improved inhibition efficiency of polyacrylamide caused by the addition of the halide ions is due to synergistic effect. Corrosion inhibition could be attributed to adsorption of inhibitor molecules on the Al surface via physical mechanism. The adsorption process followed the kinetic-thermodynamic model of El-Awady adsorption isotherm. These results were further corroborated by kinetic and thermodynamic parameters for corrosion and adsorption processes evaluated from experimental data.