Diffusional control in the intergranular corrosion of some hcp metals in iodine alcoholic solutions

Abstract

Some hexagonal closed-packed metals (titanium, zirconium and one of its alloys, Zircaloy-4) were found to undergo intergranular attack in solutions of iodine in different alcohols at room temperature. It was determined that the rate-controlling step of the intergranular corrosion was the diffusion of iodine-alcoholic complexes to the front of the attack. The diffusion coefficients of the different iodine–alcohol complexes in the respective solutions of iodine in alcohol were measured. These measurements agree with the calculated values of the diffusion coefficients obtained by means of the Einstein–Stokes equation where molecular modelling was used to estimate the size of the species involved. In addition, the value obtained in iodine–methanol solution is in agreement with that found in literature measured by means of a rotating disk electrode.