The kinetics of H permeation through α-Ti were deduced from mass spectrographic measurements which were performed at 400 to 800C and 0.004 to 2.0torr. The specimens were in the form of hollow cylinders: gaseous H entered the specimen wall at the inside surface and emerged from the specimen at the outside surface. The diffusivity was described by:

D (cm2/s) = 0.0092 exp[-13.98(kcal/mol)/RT]

The surface-dependent nature of H permeation in α-Ti was also established: it was observed that permeation was not proportional to the square root of the input H pressure, that the concentration gradient as calculated from experimental permeation data was lower than it would have been if equilibrium solubility had been established, and that the diffusional frequency factor (as determined under unsteady-state conditions) was lower by a factor of 3 than previous estimates.

D.L.Johnson, H.G.Nelson: Metallurgical Transactions, 1973, 4[2], 569-73