An investigation was made of the kinetics of H absorption from a 1atm H atmosphere, and into δ-ZrHx specimens, by making accurate measurements of the changes in H pressure as a consequence of H absorption. The absorption kinetics obeyed a parabolic time relationship, and it was calculated that the diffusion behavior, at temperatures of 650 to 800C, could be described by:

D (cm2/s) = 0.25 exp[-17.8(kcal/mol)/RT]

It was suggested that these results indicated the occurrence of an indirect site-exchange mechanism of H atoms between tetrahedral and octahedral interstices. Diffusion below 200C occurred via a direct site-exchange mechanism among tetrahedral interstices, which required a smaller activation energy of approximately 11kcal/mol. The diffusion of H in the hydride was independent of concentration.

P.Paetz, K.Lucke: Zeitschrift für Metallkunde, 1971, 62[9], 657-62

Table 341

Diffusion of Hf in Monocrystals of Nominally Pure α-Zr