An investigation was made of the absorption of H, from a 1atm H atmosphere and into ultra-high purity specimens with various grain sizes, by using hardness measurements to determine the H diffusion profiles. Diffusion data (table 92) were deduced from the results. The values, for temperatures ranging from 200 to 700C, could be described by:

D (cm2/s) = 1.85 x 10-2 exp[-10.1(kcal/mol)/RT]

Grain size variations from 0.13 to 0.43mm no observable effect upon the diffusion data.

T.O.Ogurtani: Metallurgical Transactions, 1971, 2[11], 3035-8

Table 92

Diffusivity of H into Polycrystallinea Nb

a: grain-size = 0.26mm