Phase diagram investigations of K–Sr–U–O system

In continuation of our previous work on phase diagram investigations of alkali metal–alkaline earth metal–uranium oxides, the sub-solidus phase relations in K–Sr–U–O quaternary system were determined at 850 °C in air. A pseudo–ternary phase diagram of UO3–SrO–K2O was drawn using reported ternary compounds in K2O–UO3 and SrO–UO3 systems, a single quaternary compound, K8Sr2U6O24 and various phase mixtures. These compounds and mixtures were synthesized by solid route, by heating K2CO3, SrCO3 and UO3 in different molar proportions at 850 °C. The phase fields of K2O–SrO–UO3 pseudo-ternary phase diagram were established by X-ray powder diffraction analysis. Gibbs energies of formation of binary and ternary uranates were estimated. The Gibbs energies of formations of A8Sr2U6O24 (A = Na/K/Rb/Cs) type compounds for different alkali metals were compared to find a reason for the stability of the compound for sodium, potassium and rubidium and its instability for cesium.