The permeability was measured for pressure differentials ranging from 0.0014 to 14000Pa, at between 416 and 1018K. A square-root dependence of the permeability upon the driving pressure was observed at higher pressures. The data could be described by:

P (μmol/m s kPa½) = 7.451 x 100 exp[-63.496(kJ/mol)/RT]

The pressure at which this relationship no longer applied depended upon the H purity.

E.H.Van Deventer, V.A.Maroni: Journal of Nuclear Materials, 1980, 92[1], 103-11