Synergistic influence of iodide ions on the inhibition of corrosion of mild steel in sulphuric acid by n-hexyl amine

The synergistic influence caused by iodide ions on the inhibition of corrosion of mild steel in 0.5M H2SO4 in the presence of n-hexyl amine (nHA) has been studied using potentiodynamic polarization, linear polarization and a.c. impedance technique. n-HA accelerates the corrosion of mild steel at lower concentrations but inhibits the corrosion at higher concentrations. The addition of iodide ions enhances the inhibition efficiency to a considerable extent. The adsorption of this compound is found to obey Temkin's adsorption isotherm. The increase in surface coverage in the presence of iodide ions indicates that iodide ions enhance the adsorption of n-HA on the metal surface. Defines and evaluates synergism parameter (S-l). Values of the parameter which are more than unity indicate the fact that the enhanced inhibition efficiency in the presence of iodide ions is only due to synergism and there is a definite contribution from the inhibitor molecule. n-HA is then adsorbed by coulombic interaction on the metal surface, where iodide ions are already adsorbed and thus reduces the corrosion rate.