Molar Gibbs energy formation of KUO 3(s)

Abstract

The molar Gibbs energy formation of KUO 3(s) was determined by measuring the partial pressures of oxygen and potassium over the phase field, KUO 3(s) + K 2U 2O 7(s) + K 2UO 4(s) using electromotive force (emf) and Knudsen effusion mass loss method, respectively. The oxygen potential and the potassium potential existing over the phase field and their variation with temperature can be respectively given by: Δ μ(O 2) ± 0.6 (kJ mol −1)=−499.3 + 0.290 T (K) (941–1150 K) and Δ μ(K) ± 0.17 kJ mol −1=−444.18 + 0.243 T(K) (1265–1328 K). Enthalpy increment measurements on KUO 3(s) and K 2U 2O 7(s) were carried out from (369–714 K) to (391–683 K) respectively, using a high temperature Calvet calorimeter. The enthalpy increments, ( H 0 T − H 0 298.15), in kJ mol −1 for KUO 3(s) and K 2U 2O 7(s) can be represented by −39.15 + 0.129 T + 0.101 × 10 −4 T 2(±0.7) and −52.99 + 0.1361 T + 0.146 × 10 −3 T 2(±0.7), respectively. From the standard molar Gibbs energy formation data, the equation log C 0=902.6/ T(K) − 2.09 was derived, where C 0 is the threshold oxygen level required for the formation of KUO 3.