SEMI-EXPERIMENTAL MIXING ENTHALPY OF TERNARY LIQUID-PHASES AS A SUPPORT OF PHASE-DIAGRAMS CALCULATION

There exist about 1250 interesting binary systems but more than 22000 ternary ones. For this reason a good experimental investigation of all ternary phase diagrams cannot be expected in the near future. An appr oach to many ternary systems can be achieved by a phase diagram optimi sation, taking into account various experimental incomplete data. In s uch an objective the mixing enthalpy of the ternary liquid phase can b e selected as a general primary thermodynamic information able to scal e the different Gibbs functions of all the phases present in the syste m. In 1991, we have engaged a program to optimise a general procedure with the goal of rapidly obtaining the mixing enthalpy of any ternary metallic liquid phase with the following restrictive conditions: -the use of a limted number of adjustable parameters -rejection of models b ased on the sole knowledge of the three binary border systems -the bas ic experimental method should be the drop calorimetry applied to a lim ited set of experiments, well adapted to the mathematical formalism, - the literature enthalpy data should also be included in this assessmen t Using the proposed method one sole operator is able to establish the complete ternary mixing enthalpy of a ''good'' system in about 4 to 8 weeks depending on the abundance of the literature data. nle mixing e nthalpy of the following systems are presented as an illustration : (A l,Ga,Sn), (Al,Ga,Zn), (In,Pb,Zn), (In,Pb,Sn), (Ln,Sn,Zn), (Pb,Sn,Zn), (Pb,Sb-Sn), (Bi,Pb,Sn).