Knudsen effusion mass spectrometric studies on U-Al system: Thermodynamic properties over (UAl2+UAl3) biphasic region

Knudsen effusion mass spectrometric (KEMS) studies over (UAl2+UAl3) biphasic region in the U-Al system were carried out in the range 1115-1253 K. The vaporisation reaction was found to be incongruent and Al(g) was the neutral species in the vapour in equilibrium with the condensed phase. The temperature dependence of the partial pressure was derived as log(pAl/Pa) = (−18215 ± 157)/T + (12.12 ± 0.13). From the values of the partial pressures, the enthalpy of the reaction UAl3(s) = UAl2(s) + Al(g) at 298.15 K was deduced by applying the second and third law methods. The enthalpy and Gibbs energy of formation of UAl3 were derived from the above data and were found to be ΔfH298.15°  = −112.1 ± 12.8 kJ mol−1 and ΔfGT° (±3.4) = −158.8 + 0.0591 T (kJ mol−1). The vaporisation study on this system had been carried out for the first time.