Condensed equilibria in the uranium(III)-uranium(IV) fluoride system

Abstract

The phase diagram of the condensed system UF 3-UF 4 was established experimentally. The system is characterized by the occurrence of a single eutectic invariant point, at 32 mole% UF 3, m.p. 865°C; by the absence of intermediate compounds; and by the behavior of UF 3 acting as crystalline solvent for U 4+. Solid state equilibria were found to differ substantially from those reported previously by British and Russian workers. Uranium(IV) was found to undergo substitutional solid solution in UF 3, reaching a maximum solubility at the solidus at UF 3-UF 4 (67-33 mole%). As was to be expected analogous solution behavior with UF 4 acting as a solute for U 3+, does not occur.