The temperature dependence of the bulk diffusivity of 182Ta in W single crystals was investigated, at 2020 to 2900K, by using the radiometric diffusion-zone sectioning method and materials of at least 4N-purity. It was found that the data:

D (cm2/s) = 6.2 x 100 exp[-143.7(kcal/mol)/RT]

could be explained in terms of the Lazarus-LeClaire vacancy model. The activation energy for Ta diffusion was generally less than that for self-diffusion. It was suggested that little or no positive excess charge was present on Ta in W.

N.K.Arkhipova, S.M.Klotsman, I.P.Polikarpova, G.N.Tatarinova, A.N.Timofeev, L.M.Veretennikov: Physical Review B, 1984, 30[4], 1788-96

The best linear fits to the solute diffusion data ([5] to [25]) yield:

H (sd): Ln[Do] = 1.49E – 21 (R2 = 0.87); W(sd): Ln[Do] = 0.33E – 16.1 (R2 = 0.63)