Preparation and characterisation of Tl2Pu(MoO4)3 and Tl4Pu(MoO4)4 in Tl-Pu-Mo-O system by X-ray and thermal methods

The quaternary Tl-Pu-Mo-O system was investigated for the first time and two new quaternary compounds Tl2Pu(MoO4)3 and Tl4Pu(MoO4)4 were synthesized by solid state reactions of Tl2MoO4 with Pu(MoO4)2 in 1:1 and 2:1 molar proportions at 773 K and 823 K, respectively. X-ray powder diffraction data of these compounds were indexed on orthorhombic system. Thermogravimetric (TG) curves of Tl2Pu(MoO4)3 and Tl4Pu(MoO4)4 were recorded in air and no significant weight changes were observed up to 973 K and 1033 K, respectively. Differential thermal analysis (DTA) curves of Tl2Pu(MoO4)3 and Tl4Pu(MoO4)4 showed endothermic peaks due to the melting of the compounds at 838 K and 1013 K, respectively. Non-isothermal kinetics of decomposition of Tl2Pu(MoO4)3 and Tl4Pu(MoO4)4 in air was studied using thermogravimetric technique. Tl2Pu(MoO4)3 and Tl4Pu(MoO4)4 when heated up to 1673 K decomposed to Tl2O and MoO3 in the gaseous form, giving solid PuO2 as an end product. The reactions followed unimolecular nucleation and growth mechanism with activation energies of 106 kJ/mol and 157 kJ/mol, respectively.