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

Abstract The ternary cesium molybdates Cs 2 Mo 2 O 7 , Cs 2 Mo 3 O 10 , Cs 2 Mo 5 O 16 and Cs 2 Mo 7 O 22 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 Cs 2 Mo 2 O 7 and Cs 2 Mo 3 O 10 have been measured using solution calorimetry, yielding Δ f H m o (Cs 2 Mo 2 O 7 , cr, 298.15 K) = - (2301.6 ± 4.7) kJ · mol − 1 and Δ f H m o (Cs 2 Mo 3 O 10 , cr, 298.15 K) = -(3075.6 ± 6.5) kJ · mol − 1 , respectively. In addition, the transition temperatures and transition enthalpies of Cs 2 Mo 2 O 7 , Cs 2 Mo 3 O 10 , Cs 2 Mo 5 O 16 and Cs 2 Mo 7 O 22 have been determined using differential scanning calorimetry. Finally, phase diagram equilibria measurements in the Cs 2 MoO 4 -MoO 3 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.