The diffusivity of 110Ag in alumina was studied by using radiotracer methods. It was found that the bulk diffusion results (table 5) could be described by the expression:

D (m2/s) = 0.0002 exp[-331(kJ/mol)/RT]

The pipe diffusion results (table 6) could be described by the expression:

D (m4/s) = 4.3 x 10-16 exp[-321(kJ/mol)/RT]

The grain boundary diffusion results could be described by the expression:

D (m3/s) = 9.2 x 10-6 exp[-321(kJ/mol)/RT]

It was suggested that bulk Ag migration occurred via interstitial octahedral sites. The large misfit due to Ag atoms was related to the low activation energy of Ag, as compared with that of the self-interstitial. Much greater diffusion took place along dislocations and grain boundaries. In order to explain the latter data, it was proposed that there existed a mixed diffusion path in which jumps from structurally unoccupied octahedral sites to Al vacancies were very probable. This was combined with an increased vacancy concentration along grain boundaries.

L.Badrour, E.G.Moya, J.Bernardini, F.Moya: Journal of the Physics and Chemistry of Solids, 1989, 50[6], 551-61

Table 5

Bulk Diffusion of Ag in Alumina

Table 6

Pipe Diffusion of Ag in Alumina