DARKEN AND REDLICH-KISTER MODELING OF LIQUID METALLIC PHASES THE PB-SN-BI MIXING ENTHALPY

We use a mathematical model able to fit the full experimental informat ion, but requiring a minimum set of experiments. For ternary solutions , the Darken quadratic formalism is able to accurately fit the experim ental partial excess function in each corner area corresponding to a r elatively high level in one component (x(i) greater than or equal to 0 .33). The Darken formalism requires only 2x2 binary adjustable paramet ers and 1 ternary parameter. In this procedure we need at least 4 bina ry and 1 ternary measurements. Three quadratic representations of the excess function, each one valid in one corner area, cover the whole te rnary system. A single Redlich-Kister polynomial of the fifth degree i s suitable for an accurate representation of the excess function in th e whole diagram and mixes together the three Darken quadratic formalis ms. The method has been tested successfully for the mixing enthalpy of the ternary (Pb, Bi, Sn) liquid phase with an accuracy better than 15 0 J/mol in the whole range of concentration.