Solid solution formation in the U 3O 8 → UO 2 transformation

Abstract

Possibilities were investigated for incorporation of various foreign elements into the crystal lattice of uranium dioxide during its formation in U 3O 8 → UO 2 transformation carried out under the following conditions : Arc-ignition in various gas environments (A, N 2, CO 2, H 2) of U 3O 8-metal oxide mixtures in a graphite electrode, under conditions analogous to those of the spectrochemical analysis of uranium. It has been found that in the rapid and complete U 3O 8→ UO 2 transformation thereby made possible, foreign elements present are incorporated to a limited extent into the lattice of the uranium dioxide formed. For specimens arced in N 2, maximum concentrations retained in solid solutions with UO 2 were: 13 mole % CdO; 4 mole % ZnO; 4 mole % MgO; 7 mole % Bi 2O 3; 1 mole % PbO; 0.1–0.4 mole % CaO, In 2O 3 or NiO; ThO 2 and La 2O 3 were not found to enter UO 2 lattice, but arc-ignition of a U 3O 8-La(NO 3) 3·6H 2O mixture resulted in ready solid solution formation. On the basis of density measurements of solid solutions containing CdO and ZnO respectively, it was concluded that fluorite-type substitutional solid solutions were formed with intact cation lattice, the anion lattice probably remaining intact as well. For specimens arced in H 2, capacity for solid solution formation is reduced. The factors influencing the behaviour of the foreign metal oxides in mixtures with U 3O 8 under investigated conditions are discussed. The possibility of solid solution formation of UO 2 with certain less stable oxides, employing rapid U 3O 8→ UO 2 transformation, is pointed out.