Calorimetric studies on Rb2U4O11 (s) and Tl2U4O11 (s)

Enthalpy increments of Rb2U4O11 (s) and Tl2U4O11 (s) were determined using a high temperature Calvet microcalorimeter in the temperature range 301–735 K. The enthalpy increment values of Rb2U4O11 (s) and Tl2U4O11 (s) were least square fitted with respect to temperature and are represented by the following polynomial equations H°(T)−H° (298.15 K ) ( J mol −1 )=330.4 T ( K )+7.067×10 −3 T 2 ( K )+6.198×10 5 /T ( K )−106 865 H°(T)−H° (298.15 K ) ( J mol −1 )=368.2 T ( K )+1.244×10 −2 T 2 ( K )+1.375×10 5 /T ( K )−115 489 The heat capacity, Cp,mo(T) is the first differential of Ho(T)−Ho (298.15 K) with respect to temperature. The heat capacity for Rb2U4O11 (s) and Tl2U4O11 (s) can be represented, respectively by C o p (T) ( J mol −1 K −1 )=330.4+14.134×10 −3 T ( K )−6.198×10 5 T −2 ( K ) C o p (T) ( J mol −1 K −1 )=368.2+24.886×10 −3 T ( K )−1.375×10 5 T −2 ( K ) Other thermal properties have been derived from these equations.