Equilibrium Relationships in the Uranium-Tungsten-Oxygen System in Oxygen Partial Pressures from 0.01 to 1 atm

Abstract

Equilibrium relationships in the uranium-tungsten-oxygen system have been established as a function of temperature at different oxygen pressures. Isobaric sections in air and oxygen and oxygen partial pressures of 0.01 and 0.07 were constructed, using the thermobalance. Mixtures of U3O8 and WO3 pick up weight in air, forming UWO6, which exists over a wide range of compositions taking both uranium oxides and WO3 in solid solution. The compound WO3 takes a limited amount of uranium oxide in solid solution and U3O8 also dissolves a limited amount of WO3 The miscibility gap between the solid solutions of UWO/sub 6-x/ and U3O/sub 8-y/ on the one hand and the solid solutions of UWO/sub 6-x/ and WO/sub 3-z/ on the other hand decreases by decreasing oxygen partial pressure and/or by increasing temperature. Each group of compatible solutions finally merges into a single phase deficient in oxygen. The two single phases exist over a wide range of compositions and melt over ranges of temperatures depending on the initial composition. Above a critical oxygen partial pressure (between 0.01 and 0.07 atm), solid solutions of UWO/sub 6-x/ and U3O/sub 8-y/, as well as solid solutions of UWO/sub 6-x/ and WO/sub 3-z/, melt partially with isothermal oxygenmore » loss. Increasing the oxygen partial pressure increases the melting temperatures and produces eutectic liquids richer in oxygen.« less