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

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 at 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 W03. The miscibility gap between the solid solutions of UWO_6-x and U₃O_8-y on the one hand and the solid solutions of UWO_6-x and WO_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_6-x and U₃O_8-y, as well as solid solutions of UWO_6-x and WO_3-z, melt partially with isothermal oxygen loss. Increasing the oxygen partial pressure increases the melting temperatures and produces eutectic liquids richer in oxygen.