Thermodynamic properties of dilute solutions of magnesium in zinc
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MOSER
Concentration cells of the type: Mg (s) ] MgC12 in (LiC1-KC1)eut (l) ] Mg-Zn (l) have been employed for a study of the thermodynamic properties of dilute Mg-Zn alloys in the range from 0.01 < XMg < 0.17 and at temperatures below the melting point of Mg, 922 K. The data were discussed in t e r m s of the Krupkowski formulae, Wagner's linear relations of In ~Mg vs XMg and Darken's quadratic formalism.
I N V E S T I G A T I O N S on dilute liquid magnesium-zinc alloys were initiated to show the possibility of application of the Krupkowski activity coefficient formulae x to dilute binary solutions, especially to systems where intermetallic compounds are formed. The results show that the function c0(T), appearing in these formulae, can be determined directly from experimental data for dilute solutions, i.e., from the functional dependence of the limiting activity coefficient of magnesium upon temperature. An asymmetry coefficient m showing in a considerable number of binary systems values 1 _< m _< 2 exceeds 2 in liquid M g - Z n solutions, which further suggest the appearance of intermetallic compounds in the system. The paper also shows that it is possibie to obtain the values of the self-interaction p a r a m e t e r s introduced by Wagner a in his linear equations of the dependence of activity coefficients upon concentration in dilute solutions from the Krupkowski formulae. The Krupkowski formulae represent one possible solution of Gibbs-Duhem equation, and have successfully been applied to binary and multicomponent metal solutions. In the case of the multicomponent systems they were used for interpretation of experimental data in two quaternary systems, namely Zn-Cd-Pb-Sn s and Zn-Cd-Bi-Sn. 4 Krupkowski's formulae, when applied to multicomponent s y s t e m s require only the knowledge of the thermodynamic properties of the respective binary systems. These properties can be evaluated from the partial thermodynamic functions as obtained from emf data of concentration cells or vapor p r e s s u r e measurements. A comparison between Darken's s and Krupkowski's approach has been c a r r i e d out for some liquid t e r n a r y Zn-InzPb solutions, 6 and a good agreement b e tween the molar thermodynamic functions, i.e., the excess free energy and molar enthalpy, was found. A review of the thermodynamic data on the Mg-Zn system can be found in the Supplement to Selected Values of Thermodynamic Properties of Metals and Alloys. 7 Emf methods were used by Chiotti and Stevens, s Eremenko and Tukashenko, 9 and Terpilowski; ~~whereas Kozuka, Moriyama and Kushina n measured the vapor p r e s s u r e of zinc over the liquid Mg-Zn alloys. Chiotti Z. MOSERis Chairman, Department of Theory of Metallurgical Processes, Institute for Metal Research, Polish Academyof Sciences, Krak6w, Poland. This research was done at the Institute of Inorganic Chemistry, The Technical University of Norway, Trondheim, Norway. Manuscript submitted August 8, 1972. METALLURGICALTRANSACTIONS
and Stevens's 8 results are of special interest in the p
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