Surface tension and thermodynamic properties of liquid Ag-Bi solutions
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Surface Tension and Thermodynamic Properties of Liquid Ag-Bi Solutions . W. Ga¸sior, J. Pstrus´, Z. Moser, A. Krzyzak, and K. Fitzner
(Submitted 22 November 2002; in revised form 6 December 2002) With the maximum bubble pressure method, the density and surface tension were measured for five Ag-Bi liquid alloys (XBi = 0.05, 0.15, 0.25, 0.5, and 0.75), as well as for pure silver. The experiments were performed in the temperature range 544-1443 K. Linear dependences of both density and surface tension versus temperature were observed, and therefore the experimental data were described by linear equations. The density dependence on concentration and temperature was derived using the polynomial method. A similar dependence of surface tension on temperature and concentration is presented. Next, the Gibbs energy of formation of solid Bi2O3, as well as activities of Bi in liquid Ag-Bi alloys, were determined by a solidstate electromotive force (emf) technique using the following galvanic cells: Ni, NiO, Pt/O−2/W, AgXBi(1−X), Bi2O3(s). The Gibbs energy of formation of solid Bi2O3 from pure elements was derived: ⌬G0f(␣−Bi2O3) = −598 148 + 309.27T [J ⴢ mol−1] and ⌬G0f(␦−Bi2O3) = −548 009 + 258.94T [J ⴢ mol−1]; the temperature and the heat of the ␣ → ␦ transformation for this solid oxide were calculated as 996 K and 50.14 J · mol−1. Activities of Bi in the liquid alloys were determined in the temperature range from 860-1075 K, for five Ag-Bi alloys (XAg= 0.2, 0.35, 0.5, 0.65, 0.8), and a Redlich-Kister polynomial expansion was used to describe the thermodynamic properties of the liquid phase. Using Thermo-Calc software, the Ag-Bi phase diagram was calculated. Finally, thermodynamic data were used to predict surface tension behavior in the Ag-Bi binary system.
1. Introduction The interrelationship between the shape of a phase diagram and the thermodynamic properties of competitive phases has resulted in a spectacular development of computational techniques that enable binary and multicomponent equilibrium diagrams to be predicted rapidly. The technique needs to combine thermodynamic data obtained from different sources with existing information on phase equilibria. This is sometimes a tedious task, but it finally pays off by producing a critically evaluated phase diagram. Now one is in a position to think about further extension of this approach. In principle, there is no objection to including physical properties (some of them at least) into this scheme, and thereby, achieve a broader correlation between optimized thermodynamic properties, phase equilibria, and physical properties of predicted phases. A mutual interdependence of thermodynamics, structure, and physical properties certainly exists. Not only should the phase diagram be a manifestation of the thermodynamic properties of the system, but the structure and resulting physical properties of predicted phases are obviously correlated, as well. If it were possible to use thermodynamic data to derive physical properties of liquid solutions (or conversely, to derive therm
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