  The separation of isotopes of natural Krypton at the gas-liquid and
liquid-solid phase interfaces was studied under nonequilibrium conditions using
a cryogenic cell and mass spectrometry. Condensate formation during Kr cooling
begins at an equilibrium temperature, which corresponds to the partial pressure
of the dominant isotope 84Kr, and is accompanied by depletion of the gas phase
84Kr with a separation coefficient of ~0.92 due to the excess of the heat of
condensation over the heat of dissolution by 70-100 kJ/mol. The formation of a
solid phase near the freezing point is accompanied by depletion of the gas
phase by heavy isotopes. The separation coefficients 86Kr, 84Kr, 83Kr, 82Kr and
80Kr are about 1.06, 1.11, 0.86, 0.86 and 0.80, respectively, after the
transition of ~30% of the atoms to the solid phase. Pressure-selective
condensation can be used to separate components with close boiling points when
distillation and temperature-selective condensation methods are ineffective,
and freezing out of heavy isotopes can be used to enrich elements with
practically important isotopes.
