New insights into the Cs-Mo-O system: Experimental studies of the Cs₂MoO₄-MoO₃ pseudo-binary system

The ternary cesium molybdates Cs₂Mo₂O₇, Cs₂Mo₃O₁₀, Cs₂Mo₅O₁₆ and Cs₂Mo₇O₂₂ have been synthesized in this work using a solid state route and their structures have been characterized using X-ray diffraction. The enthalpies of formation of Cs₂Mo₂O₇ and Cs₂Mo₃O₁₀ have been measured using solution calorimetry, yielding Δ_fH_m^o(Cs₂Mo₂O₇, cr, 298.15 K) = −(2301.6 ± 4.7) kJ · mol⁻¹ and Δ_fH_m^o(Cs₂Mo₃O₁₀, cr, 298.15 K) = −(3075.6 ± 6.5) kJ · mol⁻¹, respectively. In addition, the transition temperatures and transition enthalpies of Cs₂Mo₂O₇, Cs₂Mo₃O₁₀, Cs₂Mo₅O₁₆ and Cs₂Mo₇O₂₂ have been determined using differential scanning calorimetry. Finally, phase diagram equilibria measurements in the Cs₂MoO₄-MoO₃ pseudo-binary section have been performed, that have yielded generally slightly lower transition temperatures than reported in previous studies. Those data can serve as valuable input for thermodynamic modelling purposes of the fission products chemistry in Light Water Reactors and next generation Sodium-cooled Fast Reactors and Lead-cooled Fast Reactors.