Thermodynamics of Ca-Ga alloys

The enthalpies of formation of the intermetallic compounds CaGa4, Ca3Ga8, a nd CaGa2, at 298.15 K, were determined by high-temperature liquid gallium s olution calorimetric measurements to be -24.9 +/- 4.9 kJ.g at.(-1), -25.4 /- 2.4 kJg.at.(-1), and -38.8 +/- 4.8 kJ.g at.(-1), respectively. The entha lpies of formation of CaGa4 at 988 K and that of Ca3Ga8 at 1070 K were dete rmined, using precipitation calorimetry, to be -28.2 +/- 1.7 kJ.g at.(-1) a nd -22.5 +/- 1.4 kJ.g at.(-1), respectively. The integral enthalpy of mixin g of the (Ca-Ga) liquid alloys (Delta H-0) measured at 1309 K are described by the following Redlich-Kister equation: (Delta H-0) = x(Ca) (1 - x(Ca)) f(y) with f(y) = 48.00y(2) - 8.34y - 161.16 and y = x(Ca) - x(Ca) The partial enthalpy of calcium in gallium at infinite dilution (Delta (H) over bar(Ca)(0)), deduced from the measured integral enthalpies of mixing a t 1309 K, is -104.8 +/- 1.7 kJ.g at (-1), which is in very good agreement w ith that derived from the gallium solution calorimetric measurements at 107 4 K (-108.2 +/- 6.9 kJ.g at.(-1)).