The synergistic effect of polyacrylamide and iodide ions on the corrosion inhibition of mild steel in H2SO4

The corrosion inhibition of mild steel in 1 M H2SO4 using polyacrylamide (PA) in the presence of iodide ions was studied at 30–60 °C using weight loss and hydrogen evolution methods. Results obtained showed that inhibition efficiency increased with increase in concentration of PA and decreased with increase in temperature. The inhibition efficiency of PA synergistically increased on addition of KI. The adsorption of PA alone and in combination with iodide ions on the metal surface is found to obey Freundlich, Temkin and Flory–Huggins adsorption isotherms at all temperatures studied. Phenomenon of physical adsorption is proposed from the values of Ea and ΔGads° obtained. Synergism parameter evaluated is found to be greater than unity for all concentrations of PA indicating that the enhanced inhibition efficiency of PA caused by addition of iodide ion is only due to synergism. Adsorption of PA and (PA + KI) on to mild steel surface is spontaneous.