Phase study in SrO–UO3–MoO3 system

Abstract The sub-solidus phase relations in SrO–UO3–MoO3 system were determined at 1023 K in air. Various compounds in SrO–UO3, UO3–MoO3, SrO–MoO3 and Sr–Mo–U–O systems were synthesized by solid state method, reacting SrCO3(s), UO3(s) and MoO3(s) in desired molar proportions at 1023 K. A pseudo-ternary phase diagram of SrO–UO3–MoO3 system was drawn on the basis of phase mixtures obtained in the present work. A single quaternary compound, SrUMo4O16(s) was identified. The compound melts at 1043 K and decomposes above 1173 K to give SrMoO4(s) and U3O8(s). SrUMo4O16 showed positive thermal expansion under vacuum from ambient to 873 K with an average volume expansion coefficient αv = 9.73 × 10−6 K−1. The molar heat capacity of SrUMo4O16(s) was measured using differential scanning calorimeter. Using the thermodynamic data, oxygen, MoO3 and strontium potential diagrams of SrO–UO3–MoO3 system have been computed at 1023 K.