Thermodynamics of Ca-Ga Alloys

The enthalpies of formation of the intermctallic compounds CaGa4, Ca3Gag, and CaGa2 at 298.15 K, were (Jelermined by high-temperalure liquid gallium solulion calorimetric measurements to be -24.9 ± 4.9 kJ-g at.^-1 , -25.4 ± 2.4 kJ-g at.^-1, and -38.8 ± 4.8 kJ-g at.^-1 , respectively. The enthalpies of formation of CaGa4 at 988 K and that of Ca3Ga8 at 1070 K were determined, using precipitation calorimetry, to be -28.2 ± 1.7 kJ-g at.^-1 and -22.5 ± 1.4 kJ-g at.^-1, respectively. The integral enthalpy of mixing of the (Ca-Ga) liquid alloys (AH(degree)) measured at 1309 K are described by the following Redlich-Kister equation: (AH(omicron)) - Xca. (1 - Xca) f(y)with f(y) = 48.00y^2 - 8.34y -161.16 and y=Xca.-XGa, The partial enthalpy of calcium in gallium at infinite dilution (delta)H(omicron)(ca), deduced from the measured integral enthalpies of mixing at 1309 K, is -104.8 ± 1.7 kJ.g at.^, which is in very good agreement with that derived from the gallium solution calorimetric measurements at 1074 K (-108.2 ± 6.9 kJ-g at. ʹ).