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I.

INTRODUCTION

T H E main trends in thermodynamics of alloys are connected with determining the mutual relations a m o n g thermodynamic properties, physical properties, structure, and the type of phase diagram. Two types of systems are considered, namely, those exhibiting negative and positive deviations from ideal behavior. Most common phase diagrams of systems with negative deviations exhibit the existence of intermetallic or intermediate phases in the solid state. In the liquid state, such systems display the presence of "associates" which influence various properties. The destruction of associates with the increase of temperature lowers their influence, and the system often approaches regular behavior. In the case of positive deviations, binary phase diagrams often display either eutectic or miscibility gaps. Their departure from regularity in the case of limited solubility in the liquid state depends on the undercooling from the critical temperature and of the peculiar properties of one constituent. Bergman and Komarek m analyzed more than 400 binary systems, and in about 300, they found evident departure from regular behavior, often followed by the temperature dependence of integral enthalpy (ACp ~ O) and by the possible change of metallic bonding into ionic or covalent. This can also be combined with the change of partial structure factor, [=,3~Sr introduced to structure analysis by Bhatia and Thomton m and by various attempts to calculate these factors from thermodynamic data to verify the results by direct X-ray diffraction studies, tS] The verification of thermodynamic data is commonly done by phase diagram calculations and by comparison with results from thermal analysis. It is performed in the frame of various intemationaI programs. The main program is directed by ASM INTERNATIONAL in the editing of the Bulletin of Alloys

ZBIGNIEW MOSER, Professor and Department Chairman, WOJCIECH ZAKULSKI, ZDZISEAW PANEK, MARIAN KUCHARSKI, and LESZEK ZABDYR, Research Associates, are with the Institute for Metal Research, Polish Academy of Sciences, 30-059 Krakow, Reymonta 25, Poland. Manuscript submitted December 4, 1989. METALLURGICAL TRANSACTIONS B

Phase Diagrams and subsequent monographs. The CALPHAD Journal and annual CALPHAD meetings should also be mentioned. To make the mentioned correlations between various properties more evident and to prepare thermodynamic data for phase diagrams calculations, accurate data from various techniques and the development o f interpretation methods of experimental results are required. That is why we once again initiated our studies on the Mg-Sn system. The main goal of this paper is to present electromotive force (emf) results for liquid alloys and to use them, after comparison with other data from literature, for joint evaluation to arrive at thermodynamic functions for phase diagram calculations. Also, we intend to check the temperature dependence of the integral enthalpy from calorimetric studies in emf measurements, especially at concentrations close to Mg2Sn. The evalu