Measurements were carried out at temperatures ranging from -78 to 204C by directly determining T diffusion gradients. The 6Li(n,a)3H reaction was used to inject T into the specimens and to produce initial T concentrations of 0.0065 to 0.013ppm[wt]. Two diffusion components were identified in the concentration profiles: one was a surface trapping region which was approximately 5µ thick, and the other was a normal diffusion profile that was characteristic of bulk diffusion. Measurements of T surface release confirmed the existence of a surface trapping layer. The bulk diffusion component was consistent with classical diffusion theory and was described by:

D (cm2/s) = 0.00021 exp[-8.50(kcal)/RT]

The surface trapping was attributed to oxide films which formed on the alloy at room temperature. The apparent diffusion coefficients for the surface region were consistent with:

D (cm2/s) = 4.0 x 10-14 exp[-7.20(kcal)/RT]

at 25 to 411C.

J.H.Austin, T.S.Elleman, K.Verghese: Journal of Nuclear Materials, 1974, 51[3], 321-9