It was found that the data for 880 to 1130C could be described by:

D (cm2/s) = 2.4 x 10-7 exp[-38.5(kcal/g-atom)/RT]

H.Lafitau, P.Gendrel, L.Jacque: Comptes Rendus de l’Academie des Sciences – C, 1966, 263, 1033-6