MOLAR GIBBS FREE-ENERGY OF FORMATION OF RB2U4O11(S) BY SOLID OXIDE ELECTROLYTE GALVANIC CELL

The molar Gibbs' free energy of formation of Rb2U4O11 was determined b y measuring the oxygen potentials over the Rb2U4O11 + Rb2U4O12 system using a solid oxide electrolyte galvanic cell with Ni + NiO as referen ce electrode in the temperature range 985-1186 K. It was found by X-ra y diffraction analysis that Rb2U4O11 coexists with Rb2U4O12 up to 1300 K. The molar Gibbs' free energy formation of Rb2U4O11 is calculated f rom the e.m.f. values and can be given by: Delta(f)G(o) (kJ mol(-1)) /-0.65 = -5348.87 + 1.076T (K). The kinetics of oxidation of Rb2U4O11 in air, studied by thermogravimetry indicated that the reaction is pha se boundary controlled with an activation energy of 123.6 kJ mol(-1).