Enthalpy measurements on rare earth hafnates RE2O3·2HfO2 (s) (RE = Sm, Eu, Dy)

Compounds of the general formula RE 2 O 3 ·2HfO 2 with RE = Sm, Eu, Gd, Dy, etc., are considered potential candidate materials for use in the control rods of future nuclear reactors. Sm 2 O 3 ·2HfO 2 , Eu 2 O 3 ·2HfO 2 , and Dy 2 O 3 ·2HfO 2 were prepared by solid-state route and characterized by XRD technique. Enthalpy increment measurements have been carried out on these compounds in the temperature range 730–1679 K by inverse drop method by using a high-temperature differential calorimeter. From the enthalpy values, other thermodynamic functions, namely heat capacity, entropy, and Gibbs energy functions, were computed. The polynomial expressions of enthalpy increments obtained for rare earth hafnate in the temperature range 298–1700 K is given as: H T 0 - H 298 0 / J mol - 1 = 259.890 T + 21.610 × 10 - 3 T 2 + 32.389 × 10 5 T - 1 - 90 , 271 - - Sm 2 O 3 · 2 HfO 2 H T 0 - H 298 0 / J mol - 1 = 261.134 T + 22.273 × 10 - 3 T 2 + 25.988 × 10 5 T - 1 - 88 , 553 - - Eu 2 O 3 · 2 HfO 2 H T 0 - H 298 0 / J mol - 1 = 255.016 T + 18.030 × 10 - 3 T 2 + 29.332 × 10 5 T - 1 - 87 , 474 - - Dy 2 O 3 · 2 HfO 2