Representation of thermodynamic properties of ternary systems and its application to the system silver-gold-copper at 13
- PDF / 471,788 Bytes
- 6 Pages / 603.28 x 783.28 pts Page_size
- 45 Downloads / 173 Views
I.
INTRODUCTION
A N A L Y T I C A L equations are required in expressing the thermodynamic properties of ternary systems as a function of composition. The functions are important for precise definition of equilibrium properties and also for subsequent calculation of phase boundaries and surface properties. These functions are particularly useful for systems for which limited experimental data are available in the literature. The purpose of this article is to describe a generalized analytical function and the technique by which the behavior of a ternary system may be evaluated. In the present investigation, the assessment of the thermodynamic data of the Ag-Au-Cu liquid system has been made using the present technique. Although the Ag-Au-Cu system is classified as a weakly interacting one, the present method is made sufficiently generalized so that it may be extended to other systems in order to obtain the necessary Gibbs excess free-energy function. The proposed free-energy excess function in this article consists of 12 binary constants for description of the constituent binaries and three specific ternary constants. The excess free-energy functions of the binary systems are analyzed using a four-constant equation so that the constituent binaries provide 12 such constants in the proposed ternary function. The evaluation of the three specific ternary constants based on the experimental partial excess values of one component of the system is described. An important point is that the binary constants in the ternary function must remain unchanged while assessing the specific ternary constants. This is a primary requirement, as any change of the binary constants in the process of the regressional analysis of the ternary may result in considerable errors in the neighborhood of J.P. HAJRA, Associate Professor, is with the Department of Metallurgy, Indian Institute of Science, Bangalore 560012, India. HONG-KEE LEE, Research Scholar, and MARTIN G. FROHBERG, Professor of Metallurgy, Institute for Metallurgy-General Metallurgy, are with the Technical University Berlin, D-1000 Berlin-15, Federal Republic of Germany. Manuscript submitted April 19, 1991. METALLURGICAL TRANSACTIONS B
the limiting binaries. In an earlier publication on the thermodynamic behavior of the Ag-Au-Cu system by Gallois and Lupis, m it was found that the binary constants pertaining to the Au-Cu system were changed while assessing the ternary constants. The ternary function as formulated by them does not fulfill the limiting Au-Cu binary system. The latter was found to yield excess values which are 3.2 KJ more exothermic than the reported values of Hultgren et al. [21 Our evaluation of the ternary constants is based on the partial experimental excess values of Ag in the system. The latter values in ternary alloys have been measured by Bolsaitis and Skolnick t31 at six different A u / C u ratios using the Knudsen effusion technique in the temperature range of 1330 to 1375 K. An average temperature of 1350 K has been assumed for the present calculation. A
Data Loading...
