By analyzing the evaporation kinetics of Al from Nb alloys which contained 0.014 to 0.021at%Al, at 1700 to 2000K, it was deduced that the Al diffusivity was described by:

D (cm2/s) = 4.5 x 102 exp[-102(kcal/g-atom)/RT]

G.I.Nikolaev, N.V.Bodrov: Zhurnal Fizicheskoi Khimii, 1978, 52[6], 1430-3