Thermodynamic properties over (GdAl3+GdAl2) of Gd Al system: A high temperature mass spectrometric study

Abstract Knudsen effusion mass spectrometric studies were conducted on (GdAl 2 +GdAl 3 ) two phase region of Gd Al 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(p Al (g) /Pa) = − (18743 ± 213)/T + (12.61 ± 0.18) (1131–1258 K). Using this relation, the standard enthalpy of reaction GdAl 3 (s) = GdAl 2 (s) + Al(g) and subsequently the standard enthalpy of formation of GdAl 2 (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 GdAl 2 (s) that could be represented as Δ f G T , G d Al 2 ( 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.