Phasengleichgewichte in den systemen scandiumoxidoxide der actiniden (Th-Am)

Abstract

In the systems scandium oxide-actinide oxide (Th-Am) there exists, in the region of the individual components between 1100–1550 °C, only one fluorite phase (Me, Sc) O 2± x ; intermediate, ordered phases were not observed. The relatively small solubility of ScO 1.5 is significantly larger in the hypostoichiometric and hyperstoichiometric dioxides than in the stoichiometric compound, and it increases with increasing temperature and a decreasing difference in ionic radii ¦ r 4+ Me − r 3+ Sc ¦. The maximum average valence of uranium and neptunium in the oxidised fluorite phases (U, Sc) O 2+ x and (Np, Sc) O 2+ x is smaller than in the analogous systems with lanthanide oxides. The solubility of ScO 1.5 in the actinide oxides MeO 2+ x between 1100 °C and 1550 °C is given as are the phase diagrams of the systems UO 2-UO 3-ScO 1.5 and NpO-NpO 2.1-ScO 1.5 at 1250 °C.