Thermodynamic properties over two phase region of Gd–Al system: Knudsen effusion mass spectrometric study

Abstract

Vaporisation behaviour of <GdAl2(cr)+GdAl(cr)> two phase region of Gd-Al system was investigated by employing Knudsen Effusion Mass Spectrometry (KEMS) in the temperature range 1158–1323 K. Al(g) was the neutral species observed in the equilibrium vapour and partial pressure-Temperature (p-T) relation over this two phase region was deduced as log (pAl/Pa) = (−20282 ± 260)/T + (13.06 ± 0.21). The standard enthalpy change, at 298.15 K, of the reaction (GdAl2(cr) = GdAl(cr) + Al(g)) was evaluated by second law method. ΔfHm,GdAlcr,298.15Ko was deduced to be − 83.8 ± 11.8 kJ mol−1. The expression for standard molar Gibbs energy of formation of GdAl(s) derived is given as, ΔfGm,GdAlcr,To = (−101.7 ± 6.6) + (0.00667 ± 0.00560)T kJ mol−1. These data are being reported for the first time.