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

P (mol/sPa½m) = 1.4 x 10-7exp[-60.3(kJ/mol)/RT]

while the diffusivity could be described by:

D (m2/s) = 4.0 x 10-8exp[-22.3(kJ/mol)/RT]

The introduction of water vapor into the gas reduced the permeability and the diffusivity. Moreover, the permeability deviated from a square root dependence upon the up-stream pressure. A decrease in the diffusivity was more evident upon decreasing the pressure.

Hydrogen Permeation and Diffusion in Molybdenum. T.Tanabe, Y.Yamanishi, S.Imoto: Journal of Nuclear Materials, 1992, 191-194, 439-43

Figure 13

Activation Energy for H Diffusion

as a Function of the Group Number and Crystal Structure