Thermochemistry of binary liquid gold alloys: The systems (Au + Cr), (Au + V), (Au + Ti), and (Au + Sc) at 1379 K
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I.
INTRODUCTION
THEpresent communication is part of a systematic thermochemical study of the liquid alloys of transition metals with the noble metals copper, silver, and gold. Initially we studied the solutions of a number of transition metals in liquid copper, with emphasis on the first row transition metals. 1-4 During the past two years these investigations have been extended to the alloys of gold; we have recently reported on the enthalpies of mixing in the liquid alloys of gold with copper and silver, 5 and in the alloys of gold with the late transition metals nickel, cobalt, iron, and manganese. 6 In the present communication we consider the solutions of chromium, vanadium, titanium, and scandium in gold. Hence, we now have enthalpy of mixing information, obtained by the same investigators using the same calorimetric equipment, for the solutions of all the first row transition metals in liquid gold. Our measurements are based on solid-liquid calorimetry carried out at 1379 -+ 2 K. By correcting the observed solid-liquid data for the enthalpies of fusion of the transition metals we also derive approximate information on the liquid-liquid mixing process, i.e., on the mixing of liquid gold with the undercooled, liquid transition metals at 1379 K. The equilibrium phase diagrams of the considered binary systems are shown in Figure 1 (information on (Au + Cr) is from Elliott, 7 on (Au + Ti) from Shunk, 8 and on (Au + V) and (Au + Sc) from Moffattg). Note that (Au + Cr) and (Au + V) both show an extended range of solid solubility of Cr resp. V in Au; for (Au + V) there is a pronounced tendency toward formation of ordered phases at low temperatures. This points toward negative enthalpies of mixing both in the solid and in the liquid state. The (Au + Ti) and (Au + Sc) systems show a number of solid intermetallic phases which give rise to phase diagram maxima. For those binaries we therefore expect large negative mixing enthalpies. Figure 1 also shows that the liquid range of the considered systems at 1379 K is quite restricted, extending from pure gold only to 5 to 10 atomic percent of the second metal. O. J. KLEPPA, Professor of Chemistry and Geophysical Sciences, and LETITIA TOPOR, Senior Research Associate, are with the James Franck Institute, University of Chicago, Chicago, IL 60637. Manuscript submitted June 5, 1984. METALLURGICALTRANSACTIONS A
As far as we know there are no detailed thermodynamic data in the literature for the considered liquid alloys. However, the solid solution of V and Cr in Au at 500 to 800 ~ were studied by the emf method by Eremenko et al. 1o,~1 We shall compare our new enthalpy data for these two liquid systems with corresponding excess Gibbs energies derived from Eremenko's results and phase diagram information. This provides approximate information on the excess entropies of solution of V and Cr dissolved in liquid gold. We shall also compare our experimental enthalpies of solution of the transition metals in liquid gold with predicted values derived from their semi-empirical theory
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