ENTHALPIES OF FORMATION OF LIQUID AND SOLID (GALLIUM + PALLADIUM) ALLOYS

The enthalpies of formation of liquid (Ga + Pd) alloys were determined by direct reaction calorimetry in the temperature range 1322 < T/K < 1761 and the molar fraction range 0 < x(pd) < 0.87. The enthalpies are very negative with a minimum DELTA(mix)H(m) = -70.4 +/- 3.0 kJ mol-1 at x(Pd) = 0.6, independent of the temperature. Limiting partial molar enthalpies of palladium and gallium were calculated as DELTA-h(m) (Ga liquid in infinity liquid Pd) = -265 +/- 10 kJ mol-1 and DELTA-h(m) (Pd liquid in infinity liquid Ga) = -144 +/- 5 kJ mol-1. The integral molar enthalpy is given by DELTA(mix)H(m) = x(1 - x) (-143.73 - 232.47x + 985.77x2 - 4457.8x3 + 6161.1x4 + 2577.4x5), where x = x(Pd). Moreover, values for the enthalpies of formation and fusion of PdGa, Pd2Ga, and the solid solution (with x(Pd) = 0.8571) have been proposed. These results have been discussed taking into account the equilibrium phase diagram.