Effect of iodide ions on the synergistic inhibition of the corrosion of manganese-14 steel in acidic media

We investigate the synergistic effect of iodide ions on the corrosion inhib ition of manganese-14 steel in 0.5 M H2SO4 in the presence of cyclohexylami ne using potentiodynamic polarization and linear polarization techniques. I n 0.5 M H2SO4, the corrosion rates of the steel decrease when amine the con centration decreases, while the inhibition efficiencies increase. The addit ion of iodide ions enhances the inhibition efficiency considerably. The pre sence of iodide ions increases the degree of surface coverage, while at low concentrations cyclohexylamine forms an insoluble complex by undergoing ad sorption. The synergism parameters (S-theta) calculated from surface covera ge in the case of cyclohexylamine are found to be larger than unity. In add ition, the adsorption of this amine on manganese-14 steel is found to follo w a Langmuir isotherm. Thus inhibition occurs by adsorption. (C) 2000 Elsev ier Science B.V. All rights reserved.