THERMODYNAMIC BEHAVIOR OF METALLIC MELTS AT HIGH DILUTION ACCORDING TO THE ASSOCIATED SOLUTION MODEL

The associated solution model developed previously has been applied to binary at high dilution. If A(a)B(b) associates are assumed and the c ontribution of the weak interactions between the species is neglected, it has been pointed out that the value of the partial enthalpy of A i n pure B is close to zero when a not-equal 1 and close to that of the standard enthalpy of formation of the associate when a = 1. The limiti ng partial enthalpies of Pd and Pt in Ge were determined by direct-rea ction calorimetry (the drop method). we found these had values of -108 .9 kJ mol-1 and -108.6 kJ mol-1 respectively at 1272 K. Since these va lues are very close to that of the standard enthalpies of formation of PdGe (-104 kJ mol-1) and PtGe (-106 kJ mol-1) clusters respectively, they confirm the existence of two kinds of associate (Pd2Ge + PdGe and Pt2Ge + PtGe respectively) in the binaries. This conclusion is especi ally useful in the case of the Pd-Ge melts the thermodynamic behaviour of which can be explained in the framework of the model assuming one (Pd2Ge) or two species.