Synthesis and characterization of thallium–thorium molybdates and thallium–uranium (IV) molybdates

In quaternary Tl–Th–Mo–O and Tl–U(IV)–Mo–O systems, Tl2Th(MoO4)3, Tl4Th(MoO4)4, Tl2U(MoO4)3 and Tl4U(MoO4)4 were synthesized by reacting Tl2MoO4 with molybdates of thorium and uranium in stoichiometric molar proportions at 773 K. Thallium U(IV) molybdates were prepared in evacuated sealed quartz ampoules. These compounds were characterized by X-ray, thermal and infrared techniques. Powder X-ray diffraction data of all four compounds were indexed on orthorhombic system. When heated in thermoanalyzer in He atmosphere, Tl2U(MoO4)3 and Tl4U(MoO4)4 showed melting at 792 K and 853 K, respectively, whereas heating of both the compounds in air oxidized them to Tl2UO2(MoO4)2. Both Tl2Th(MoO4)3 and Tl4Th(MoO4)4, when heated in air, showed a reversible phase transition followed by melting of the compounds. Isothermal heating of all thallium–thorium and thallium–uranium molybdates at 1573 K led to the formation of ThO2 and U3O8, respectively, as end products.