THERMODYNAMIC BEHAVIOR OF COMPLEX-ASSOCIATED TERNARY LIQUID SOLUTIONS- THE PD-PT-GE SYSTEM

This paper deals with the investigation of the chemical order of the P d-Ge, Pt-Ge and Pd-Pt-Ge liquid alloys, the thermodynamic functions of formation of which have been determined previously by calorimetry and Knudsen cell mass spectrometry. The fit between the experimental data and the thermodynamic functions calculated according to the associate d solution models leads to the conclusion that the chemical order in t he Pd-Ge and Pt-Ge binaries corresponds to Pd2Ge and PdGe and to Pt2Ge and PtGe species respectively. The thermodynamic behaviour of the ter nary Pd-Pt-Ge melts, with respect to composition and temperature, has been explained by the competition between Pd and Pt atoms for the form ation of these four types of associates. For application of the model to ternary systems with more than two associates, modification was nee ded, and the so-called ''mixed cluster model'' was proposed according to which the associates with the same stoichiometry are paired and con sidered as mixed clusters.