Thermochemistry of binary and
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I.
INTRODUCTION
D U R I N G recent years, a number of binary alloy systems involving the noble metals copper, silver, and gold have been studied calorimetrically in this laboratory. It-9] Most recently, these measurements have been carried out by the direct-synthesis method where the two components are brought to reaction in the hightemperature calorimeter dropped in from room temperature. In the present investigation, such measurements are extended to the binary alloy systems Ce-Cu, Ce-Ag, and Ce-Au and to the ternary liquid systems Cu-Ag-Au and Ce-Ag-Au. As far as we know, there are no thermodynamic data reported in the literature for these ternary alloys. An attempt will be made to analyze the enthalpy data for the considered ternary systems in terms of contributions from the binaries plus ternary interactions. II.
EXPERIMENTAL
A. Materials 1. Copper
Oxygen-free, high-conductivity copper wire of 2-mm diameter and 99.99 pet purity was used to calibrate the calorimeter. The same wire and copper powder, - 1 0 0 mesh, obtained from Johnson Matthey Electronics, Seabrook, NH, (99.9 pct pure) were used for the experiments. 2. Silver
Silver powder, - 100 mesh, of 99.9 pet purity used in this study was from Johnson Matthey Electronics. 3. Gold
Gold powder, spherical, 2 to 5/x, of 99.95 pct purity used in this study was from the Johnson Matthey AESAR Group. We also used some gold wire of 2-mm diameter purchased from Engelhard. K. FITZNER, Associate Professor, is with the Institute of Metals Research, Polish Academy of Sciences, 30-059 Krakow, Poland. O.J. KLEPPA, Emeritus Professor, is with the James Franck Institute, University of Chicago, Chicago, IL 60637. Manuscript submitted August 31, 1992.
METALLURGICAL TRANSACTIONS A
4. Cerium
Cerium ingot of 99.9 pct purity was obtained from Alfa Products. It was filed to produce smooth shavings suitable for the experiments. B. Procedures
The direct synthesis method of reaction calorimetry was used both for the intermetallic phases and for the liquid alloys. The measurements were carried out at 1473 + 2 K in our modified Setaram-type calorimeter. Details of the construction of this unit as well as of the "liner" assembly have been given previously, r~~ In direct synthesis calorimetry, pellets made from pressed metallic powders of the components are prepared at room temperature and then dropped into the high-temperature calorimeter, where they react chemically. The reaction chamber in our calorimeter consists of a thin-walled BN crucible which protects the Pt20Rh liner from the contents of the 15-mm-diameter crucible made from either BeO or BN in which the reaction actually takes place. All experiments were performed in an atmosphere of argon gas purified by passing the gas over titanium chips at about 1173 K. The calibration constant of the calorimeter was determined by dropping weighed pieces (about 0.25 g) of copper wire from room temperature into the calorimeter. For the calibrations, we adopted the enthalpy of copper at 1473 K given by Hultgren et al. ]~lj The cali
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