The diffusion and trapping of hydrogen in 5N-purity polycrystalline aluminum was investigated using both isothermal and constant heating rate desorption techniques. Constant heating rate desorption was used to elucidate the effects of microstructural trap states upon the apparent diffusivity of hydrogen in aluminum. Isothermal desorption of hydrogen from annealed, uniformly charged, cylindrical specimens was bulk diffusion controlled. The diffusion data exhibited a simple Arrhenius behavior between 30 and 600C and was described, with 95% confidence, by:

D(m2/s) = 1.75 x 10-8exp[-16.2(kJ/mol)/RT]

Constant heating rate desorption spectra revealed three distinct trapping states, with desorption energies of 15.3, 43.5 and 84.8kJ/mol. These trapping states were associated with interstitial lattice sites, dislocations and vacancies, respectively. These trap states helped to explain the large scatter in reported values of the diffusivity of hydrogen in aluminum.

The Diffusion and Trapping of Hydrogen in High Purity Aluminum. G.A.Young, J.R.Scully: Acta Materialia, 1998, 46[18], 6337-49