The absorption of D and H by a spherical specimen with a precisely known radius and density was determined by means of pressure, volume and temperature measurements. The experiments were carried out at temperatures ranging from 298 to 1373K. At temperatures above about 473K, excellent agreement with Fick's second law was found. Deviations from simple diffusion were attributed to the effect of surface conductance. On the basis of known solutions for diffusion in a sphere with surface conductance, the diffusivity (figures 26 and 27) could be described by:

H:     D (m2/s) = 3.512 x 10-7exp[-2759.9/T]

D:     D (m2/s) = 2.219 x 10-7exp[-2538.0/T]

G.L.Powell, J.R.Kirkpatrick: Physical Review B, 1991, 43[9], 6968-76

Figure 26

Diffusivity of D in Pd

Figure 27

Diffusivity of H in Pd