Equilibrium Relationships in the Uranium-Manganese-Oxygen System in Air

Equilibrium relationships in the uranium-manganese-oxygen system in air have been investigated as a function of temperature. Various mixtures of U₃O₈ and MnO₂ were heated and from the compositions reached at various temperatures, a ternary isobaric diagram was constructed showing the composition and phase changes occurring in air. Three ternary nonstoichiometric phases were found to exist over wide composition ranges with the nominal compositions MnU₂O₇, MnUO₄, and MnU₂O₆. The MnU₂O₇ dissociated at 1040°C to MnUO₄ and U₃O₈; MnUO₄ was found to be stable only between 930 and 1175°C, while MnU₂O₆ exists above 1130°C.