The diffusivity of H in grain-refined material was measured by using a vacuum hot-extraction method. Four samples, with various grain sizes, were prepared by melting, adding Ti and B, casting, re-melting and solidifying unidirectionally. The grain-refined samples contained small particles within the matrix. The H diffusivity obeyed Arrhenius-type behavior at 573 to 873K. The results for air-melted Al-0.05wt%Ti samples could be described by:

D(cm2/s) = 2.04 x 100 exp[-15.6(kcal/mol)/RT]

and the results for Al-0.05wt%Ti samples which had been cast under flowing N could be described by:

D(cm2/s) = 2.22 x 10-2 exp[-8.9(kcal/mol)/RT]

The equivalent relationships for Al-0.1wt%Ti samples could be described by:

D(cm2/s) = 9.10 x 101 exp[-22.7(kcal/mol)/RT]

and

D(cm2/s) = 1.39 x 100 exp[-15.9(kcal/mol)/RT]

respectively. The diffusivity was not affected by the small particles in the matrix, and depended only upon the grain size. A so-called grain-boundary cross effect, which referred to fast diffusion along grain boundaries and suppressed diffusion due to H trapping at nodes or grain boundary junctions, was confirmed. A linear relationship was found between the logarithm of the pre-exponential factor and the activation energy.

M.Ichimura, Y.Sasajima: Materials Transactions, 1993, 34[5], 404-9

The best linear fits to the solute diffusion data ([562] to [565], [567] to [570], [573] to [577], [581] to [585], [592] to [599], [608] to [611], [623] to [626]) yield:

Au: Ln[Do] = 0.67E – 20.7 (R2 = 0.999); Co: Ln[Do] = 0.43E – 12 (R2 = 0.69);

Cu: Ln[Do] = 0.69E – 22.7 (R2 = 0.99); Fe: Ln[Do] = 0.56E – 20.5 (R2 = 0.996);

H: Ln[Do] = 0.63E – 9.45 (R2 = 0.96); Mn: Ln[Do] = 0.52E – 21.4 (R2 = 0.993);

Zn: Ln[Do] = 0.77E – 24 (R2 = 0.99)