Polycrystalline samples (with an average grain size of 0.0065mm and little porosity) and monocrystals were sectioned into small parallelopipeds and were exposed to 35S, under a SO2 partial pressure of 0.01atm and an O partial pressure of 0.8 to 1atm. The annealing temperatures ranged from 1173 to 1373K, and the diffusion profiles were determined by sectioning. It was found that the bulk diffusivities (table 72) ranged from 1.07 x 10-13 to 5.0 x 10-13cm2/s, and that the activation energy was 27.6kcal. The grain boundary diffusion coefficients were some 5 orders of magnitude greater than the bulk values (table 73), and the activation energy was about 40kcal. It was concluded that grain boundary diffusion predominated in polycrystalline samples.
M.Benlyamani, F.Ajersch, G.Kennedy: Journal of the Electrochemical Society, 1989, 136[3], 843-6
Table 71
Grain Boundary Diffusion of 18O in Cr2O3
PO2 (Pa) | Temperature (C) | D (cm3/s) |
2.0 x 104 | 1100 | 7.9 x 10-21 |
1.0 x 10-4 | 1100 | 7.0 x 10-21 |
1.6 x 10-1 | 1100 | 2.4 x 10-21 |