Thermochemistry of binary alloys of transition metals: The systems Cu-Ce, Me-Pr, and Me-Nd (Me = Cu, Ag, Au)
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I.
INTRODUCTION
DURING recent years, a systematic study of the thermochemistry of binary alloys between transition metals and the noble metals has been pursued in this laboratory. These investigations were initiated by studies of the alloys of Cu with Mn, tl~ with Ti, Zr, and Hf, t2,3~and with Sc, Y, La, Lu, V, and Cr. t4] The emphasis of these studies was placed on the liquid alloys of the two metals. However, in some cases, insight was gained also on the enthalpies of formation of congruent melting compounds in the considered binary systems. Later, these investigations were extended to the alloys of the first-row transition metals with liquid A u . I5'61 These systems were all studied in a high-temperature, Calvet-type microcalorimeter, which is limited to operate at temperatures where fused silica refractories can be used, i . e . , at temperatures below about 1400 K. A few years ago we developed a new high-temperature microcalorimeter which is somewhat similar to the commercial Setaram calorimeter. However, unlike the Setaram unit, which is cycled from day to day between room temperature and high temperature, our new calorimeter is maintained continuously near 1500 K by means of a Pt40Rh resistance heater, tT] Using this new calorimeter, we have extended our studies of noble metal-transition metal systems to the solid and liquid alloys of Ag and Au with Sc, Y, and La, tsl with Ti, Zr, and Hf, tg~ and with V, Nb, and Ta. l~~ Very recently we also used this calorimeter to investigate the solid and liquid alloys of Cu, Ag, and Au with Ce at 1473 K. l~ We found that this calorimeter should be very suitable for further studies of the noble metal-lanthanide metal systems. There is very little reliable information in the published literature on the thermodynamic properties of these alloys, either in the solid or in the liquid state. In fact, for some of these systems, even the phase diagram is missing. On the other hand, where information is available, it is common to find congruent melting intermetallic compounds with the stoichiometries A6Me, K. FITZNER, Associate Professor, is with the Institute for Metals Research, Polish Academy of Sciences, 30-059 Krakow, Poland, O.J. KLEPPA, Emeritus Professor, is with the James Franck Institute, The University of Chicago, Chicago, IL 60637. Manuscript submitted September 23, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
As1Mel4, A2Me, and AMe (A = Cu, Ag, Au; Me = lanthanide metal). In the present work, the standard enthalpies of formation of 14 congruent melting compounds of Cu, Ag, and Au with praseodymium and neodymium have been measured by direct synthesis calorimetry at 1473 --- 2 K; we also carried out measurements on the heats of mixing in the six binary liquid alloy systems at the same temperature. Finally, we have reinvestigated the binary system Cu-Ce. We were concerned about the large scatter of our experimental results for this system reported in our earlier studyt~ll and also with the discrepancy between our results and the measurements of Turchanin et al. l
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