Molar Gibbs energy formation of KUO3(s)

The molar Gibbs energy formation of KUO3(s) was determined by measuring the partial pressures of oxygen and potassium over the phase field, KUO3(s) K2U2O7(s) + K2UO4(S) using electromotive force (emf) and Knudsen effusion m ass loss method, respectively. The oxygen potential and the potassium poten tial existing over the phase field and their variation with temperature can be respectively given by: Delta mu(O-2)+/-0.6 (kJ mol(-1)) -499.3 + 0.290 T (K) (941-1150 K) and Delta mu(K) +/- 0.17 kJ mol(-1) = -444.18 + 0.243 T( K) (1265-1328 K). Enthalpy increment measurements on KUO3(s) and K2U2O7(S) were carried out from (369-714 K) to (391-683 K) respectively, using a high temperature Calvet calorimeter. The enthalpy increments, (H-T(0) - H-298.1 5(2)), in kJ mol(-1) for KUO3(s) and K2U2O7(S) can be represented by -39.15 + 0.129T + 0.101 x 10(-4)T(2)(+/-0.7) and -52.99 + 0.1361T + 0.146 x 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 t he threshold oxygen level required for the formation of KUO3. (C) 1999 Else vier Science B.V. All rights reserved.