It was recalled that the kinetics of Ag penetration into monocrystalline and polycrystalline samples were strongly affected by the presence of linear defects at below 1200C. It was observed that the bulk diffusion coefficients obtained for polycrystalline samples (table 2) were in fairly good agreement with those calculated using the relationship for monocrystalline samples. The results were little influenced by the difference in purity of the 2 types of sample. This was attributed to the size of the Ag+ ion, which was much greater than that of the Al3+ ion. The results, taken together, could be interpreted as representing an interstitial-type mechanism in which Ag diffused via unoccupied octahedral sites. Thus, the activation energy of 331kJ/mol corresponded to the migration energy of Ag atoms displaced from one octahedral site to a neighboring one.

A.Badrour, E.G.Moya, J.Bernardini, F.Moya: Scripta Metallurgica, 1986, 20[9], 1217-22

Table 2

Bulk Diffusion of Ag in Al2O3