Thermal analysis was used to study the trapping and transport of H. The dislocations acted as trapping sites for H, and the H trap activation energy at these appeared to be lower than the activation energy for the bulk diffusion of H. It was suggested that both H-trapping at grain boundaries, and short-circuit diffusion through grain boundaries, occurred. The trap binding energy at grain boundaries was estimated to be 20.5kJ/mol. The diffusivity of H could be described by:
D (m2/s) = 7.5 x 10-7 exp[-39.1(kJ/mol)/RT]
S.M.Lee, J.Y.Lee: Metallurgical Transactions A, 1986, 17[2], 181-7
Table 156
Grain Boundary Diffusion of H in Ni
Material | Temperature (K) | D (cm2/s) |
small (25 grains) | 298 | 7.7 x 10-10 |
large (150 grains) | 298 | 4.6 x 10-10 |
98% cold-worked | 298 | 2.2 x 10-10 |
small (25 grains) | 333 | 3.1 x 10-9 |
large (150 grains) | 333 | 1.9 x 10-9 |
98% cold-worked | 333 | 1.1 x 10-9 |
small (25 grains) | 373 | 1.3 x 10-8 |
large (150 grains) | 373 | 1.2 x 10-8 |
98% cold-worked | 373 | 4.6 x 10-9 |