High temperature mass spectrometric studies on UGa system: Thermodynamic properties over (U3Ga5Â +Â UGa2) and (UGa2Â +Â UGa3) phase regions

Vaporisation studies over gallium rich biphasic regions (U3Ga5 + UGa2) and (UGa2 + UGa3) in the UGa system were carried out by Knusen effusion mass spectrometry in the temperature ranges of 1208-1366 K and 1133-1338 K, respectively. Ga(g) was the species observed in the mass spectra of the equilibrium vapour over both phase regions. From temperature dependence measurements, pressure-temperature relations were deduced as: log (pGa/Pa) = (−18216 ± 239)/(T/K) + (12.88 ± 0.18) over (U3Ga5 + UGa2) and log (pGa/Pa) = (−16225 ± 124)/(T/K) + (11.78 ± 0.10) over (UGa2 + UGa3). From these data, Gibbs free energy changes for the reactions 3UGa2(s) = U3Ga5(s) + Ga(g) and UGa3(s) = UGa2(s) + Ga(g) were computed and subsequently Gibbs free energies of formation of U3Ga5(s) and UGa3(s) were deduced as ΔfGTo U3Ga5(s) (±5.5) = −352.4 + 0.133 T(K) (kJ mol−1) (1208-1366 K) and ΔfGTo UGa3(s) (±3.8) = −191.9 + 0.082 T(K) (kJ mol−1) (1133-1338 K). The Gibbs free energy of formation of U3Ga5(s) is being reported for the first time.