THERMODYNAMIC BEHAVIORS OF Pd-In ALLOYS

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Some thermodynamic parameters of PdIn alloys with 2% to 70% (mole ratio) indium were determined in the temperature range 800 ℃ to 1000 ℃ from e.m.f. measurements on galvanic cells with an oxygenconducting solid electrolyte. Heats of mixing calculated from the activities are in excellent agreement with calorimetric data. The relative partial excess free energy of indium assumes unusually large negative values up to -174 kJ/mol for Pdrich alloys. Two effects were discussed to account for the nonideal properties: the rise of Fermi energy as the valence electrons of indium enter the 4d and 5sp bands of the alloy and the lattice distortion brought about by the different molar volumes of the components; the rise of the Fermi energy, as determined from the activity data, indicates a strict adherence of the alloys to the rigid band model.