Calculation of physicochemical properties in a ternary system with miscibility gap
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Calculation of Physicochemical Properties in a Ternary System with Miscibility Gap KUO-CHIH CHOU, XIANGMEI ZHONG, and KUANGDI XU For a ternary system with a complete miscible area, one may use geometrical models, such as the Kohler model, Muggianu–Jacob model, Toop model, Hillert model, Lück–Chou model, etc. to calculate thermodynamic properties. However, for the ternary system with a partial miscible area, if that area does not touch the binary edges in a ternary composition triangle, in principle, the geometric model cannot give an accurate estimation for thermodynamic properties due to the absence of accurate binary information at the given temperature. In this article, a special method has been proposed for calculating thermodynamic properties and other physicochemical properties for the partial miscible area in a ternary system if those properties along the miscible boundary are known. Two examples have shown that this method works very well.
I. INTRODUCTION
WITH the development of science and technology, the thermodynamic properties of solution have become more and more important in dealing with the problems related to solutions. It is well known that the geometric model is a powerful tool in estimating thermodynamic properties for a ternary system when the information we have is only limited to binaries and no ternary data are available.[1–15] This method has been widely used to estimate thermodynamic properties for a ternary system as well as to calculate ternary phase diagrams. However, this approach is successful only in the system with a complete miscible area, in other words, the system without any miscibility gap. If the system has a miscibility gap, a large error could be introduced into the calculation, because, in a geometric model, the calculated thermodynamic properties of a ternary system are expressed in a combination of thermodynamic properties of three corresponding binaries with a certain probability weight. For example, the ternary excess Gibbs free energy of mixing, G Em can be expressed as GEm W12 GE12 W23 GE23 W31 GE31
[1]
GEij
where and Wij represent the excess Gibbs free energy of mixing and probability weight of binary system ij at a selected composition point, respectively. According to the different selected binary composition points, the geometric models can be distinguished as the Kohler[5] model, Muggianu–Jacob[6,7] model, Toop[8] model, Hillert[1] model, Lück–Chou[9,10] model, etc.[11–15] For a partial miscible system, the geometric model cannot give accurate thermodynamic properties, since the selected binary composition point sometimes
KUO-CHIH CHOU, Professor and Member of Chinese Academy of Sciences, is with the Department of Physical Chemistry, University of Science and Technology Beijing, Beijing, 100083, People’s Republic of China, and Adjunct Professor, Shanghai University, Shanghai, 200072, People’s Republic of China. Contact e-mail: [email protected] XIANGMEI ZHONG, Postdoctoral Student, is with the Department of Physical C
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