Thermodynamic properties over (GdAl3+GdAl2) of GdAl system: AÂ high temperature mass spectrometric study

Knudsen effusion mass spectrometric studies were conducted on (GdAl2+GdAl3) two phase region of GdAl system over the range of temperature 1131-1258 K. Al(g) was found to be the neutral species observed over the equilibrium vapour. The partial pressure of Al (g) measured as a function of temperature over this two phase region yielded the pressure - temperature (p-T) relation: log(pAl (g)/Pa) = − (18743 ± 213)/T + (12.61 ± 0.18) (1131-1258 K). Using this relation, the standard enthalpy of reaction GdAl3(s) = GdAl2(s) + Al(g) and subsequently the standard enthalpy of formation of GdAl2(s) were derived to be 354.6 ± 17.1 and −148.7 ± 17.1 (kJ mol−1), respectively. Also an analytical expression for the Gibbs free energy of formation of GdAl2(s) that could be represented as ΔfGT,GdAl2(s)° = − (179.2 ± 4.4) + (0.0470 ± 0.0039) T (kJ mol−1) (1131-1258 K) was deduced. The vaporisation studies are being reported for the first time.