Molar Gibbs' free energy of formation of Rb 2U 4O 11(s) by solid oxide electrolyte galvanic cell

Abstract

The molar Gibbs' free energy of formation of Rb 2U 4O 11 was determined by measuring the oxygen potentials over the Rb 2U 4O 11 + Rb 2U 4O 12 system using a solid oxide electrolyte galvanic cell with Ni + NiO as reference electrode in the temperature range 985–1186 K. It was found by X-ray diffraction analysis that Rb 2U 4O 11 coexists with Rb 2U 4O 12 up to 1300 K. The molar Gibbs' free energy formation of Rb 2U 4O 11 is calculated from the e.m.f. values and can be given by: Δ f G° (kJ mol −1) ± 0.65 = −5348.87 + 1.076 T (K). The kinetics of oxidation of Rb 2U 4O 11 in air, studied by thermogravimetry indicated that the reaction is phase boundary controlled with an activation energy of 123.6 kJ mol −1.