Permeation measurements were carried out at 500 to 1100K. The gas contained less than 1ppm of H2O, and the up-stream pressure was between 1Pa and 0.1MPa. It was deduced that the diffusivity could be described by:

D (cm2/s) = 4.0 x 10-4 exp[-5.3(kcal/mol)/RT]

The introduction of water vapor into the gas reduced the diffusivity. A decrease in the diffusivity was more evident upon decreasing the pressure.

T.Tanabe, Y.Yamanishi, S.Imoto: Journal of Nuclear Materials, 1992, 191-194, 439-43