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

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.