Melting and crystallization of 3He inclusions in two-phase solid 3He-4He mixtures

The peculiar features of the phase diagram for the He-3 - He-4 system make it possible to melt the He-3 inclusions formed during phase separation of the mixture by further cooling and to crystallize them in subsequent heating. The kinetics of these processes is studied On a sample with a molar volume of 20.54 cm(3)/mole (P = 31.7 bar) using pressure measurements. The time dependence of the crystal pressure P(t) is measured on cooling at a rate of similar to 10 mK/h followed by heating. The dependence P(t) has two distinct rises in pressure, the first rise being associated with the phase separation of the mixture and the second one with the melting of the He-3 inclusions formed. It is shown that the melting of the He-3 inclusions is almost complete after the first cooling and the observed pressure jump is in good agreement with the corresponding change in the molar volume. The repeated crystallization of the inclusions is found to give rise to a large pressure gradient near the boundary of the inclusions, suppressing quantum diffusion considerably. This may result in an incomplete crystallization of the inclusions. The experimentally observed difference between the initial and final pressure in the sample corresponds to the fact that approximately 20 % of the He-3 remains in the liquid state.