Abstract
The diffusion coefficients at infinite dilution, and the solubility of plutonium and nickel were determined by α. autoradiography. The technique of welded couples was used in conjunction with a polyphase system (Ni saturated with Pu+precipitates of Pu 2Ni 17 attached to pure nickel). The diffusion coefficients were determined from examination of the precipitates existing in contact with the interface after annealing, using Pick's equation for a semi-infinite medium with constant surface concentration. For a sufficiently large proportion of precipitates one can take it that throughout the anneal the interface remains at fixed concentration, which is the solubility limit; this is obtained by extrapolating the concentration/penetration curve. The activation energy, 51 ±5 kcal/mole, is slightly lower than that for the self-diffusion of nickel, 65 ± 5 kcal/mole (the atomic radius of plutonium, 1.69–1.82 Å according to allotropie form, is larger than that of nickel, 1.38 Å). The frequency factor is in the range 0.14–1.14 cm 2/sec. Between 1025° and 1125°C, the solubility of plutonium in nickel is in the range 130–320 × 10 −6 wt %.
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