THALLIUM URANATES AND OTHER (TL,U,O) COMPOUNDS - A STRUCTURAL AND THERMODYNAMIC STUDY

Tl2U4O11(s) and Tl2U3O9(s) were prepared and characterised in the Tl-U -O ternary system for the first time. Tl2U4O11 was found to be isostru ctural with Rb2U4O11. The partial phase diagram of the Tl-U-O system w as derived from equilibration experiments with several binary and tern ary oxides in the system. The oxygen pressure over the phase fields Tl 2U4O13(s) + Tl2U4O12(s) and Tl2U4O12(s) + Tl2U4O11(s) was determined b y measuring the e.m.f.s in the temperature ranges 805 to 1179 K and 98 4 to 1141 K respectively. The oxygen pressure can be given by InP(O-2) (kPa)+/-0.01 = 31.03-32924/T(K) and InP(O-2)(kPa) +/- 0.01 = 53.23 - 9 3358/T(K) respectively. Using the molar Gibbs free energy of formation of Tl2U4O13(s), the molar Gibbs free energies of formation of Tl2U4O1 2 and Tl2U4O11 were obtained. The kinetics of oxidation of Tl2U4O12 an d Tl2U4O11 in air were also studied using a thermal analyser.