MOLAR GIBBS ENERGY OF FORMATION OF NAUO3(S)

The sodium pressure over the coexisting phase field, NaUO3 + Na2U2O7 Na2UO4 was measured using Knudsen effusion mass loss (KEML) and Knuds en cell mass spectrometric (KEMS) methods. The sodium pressure over th e coexisting phase field can be represented by: log p(Na)(Pa) +/- 0.04 1 = -22701/T (K) + 17.92 (1117-1193 K). The oxygen potential existing over the above phase field was determined by an oxide electrolyte galv anic cell with air and Ni(s) + NiO(s) as reference systems and can be given by: DELTAmu(O2) (kJ/mol) +/- 0.19 = - 716.9 + 0.335T(K) (968-111 8 K). The molar Gibbs energy of formation of NaUO3 calculated from the oxygen and sodium potentials can be represented by: DELTAG(f)degrees( NaUO3), T(K) +/- 13.4 kJ/mol = -1487.4 + 0.291T(K). The second and thi rd law treatment of the present data yielded the standard enthalpy of formation, (DELTA(f)H(m)degrees, 298.15 K) value of (-1481.4 +/- 13.4) and (-1476.8 +/- 13.4) kJ/mol respectively.