Equilibria and thermodynamic properties of the plutonium-hydrogen system

Equilibrium, kinetic and x ray diffraction data show the existence of two stability regimes in the Pu-H system. A metastable solid solution between CaF/sub 2/-type PuH/sub 1/ /sub 9/ and anti-Fe/sub 3/Al-type PuH/sub 3/ /sub 0/ forms at low temperature and behaves as an ideal solid solution. Equilibrium and calorimetric results show that the enthalpy of formation varies linearly from -38 to -50 kcal/mol between the lower phase boundary and the trihydride. The phase relationships established at high temperature are similar to those of the lanthanide difluoride-lanthanide trifluoride systems. A series of CaF/sub 2/-related phases apparently forms between PuH/sub 1/ /sub 9/ and PuH/sub 2/ /sub 5/; a nonstoichiometric hexagonal (LaF/sub 3/-type) hydride exists in the range PuH/sub 2/ /sub 9/-PuH/sub 3/ /sub 0/. A procedure for preparing pure hexagonal puH/sub 3/ /sub 00/ is described, and the hysteresis behavior of the Pu-H system is discussed