Thermodynamic properties of ternary liquid Cu-Mg-Ni alloys
- PDF / 814,361 Bytes
- 10 Pages / 603.28 x 783.28 pts Page_size
- 55 Downloads / 197 Views
I.
INTRODUCTION
THE general features of the phase relationships in the ternary Cu-Mg-Ni system were described in the compilation by Chang et al. m However, a number of details such as the mutual solid solubility of the corresponding binary intermetallic compounds and their homogeneity ranges in the ternary field are not well established, and several contradicting reports can be found in the literature. E2-51 The liquidus surface in Reference 1 is based mainly on the results of thermal analyses by Mikheeva and Babayan t61 who employed corundum crucibles both for the preparation o f the alloys and for the measurements themselves. Due to the chemical reaction of magnesium with A1203 at elevated temperatures, systematic errors are likely to be expected in their data. While the thermodynamic properties of the limiting binary systems are well documented in the literature, tT-l~ thermodynamic information on the ternary system is limited to the calorimetric data by Predel and Ruge tl~j for solid alloys in the pseudobinary section Cu2Mg-MgNi2. Thus, it was the objective of the present investigation to determine magnesium vapor pressures over ternary Cu-Mg-Ni alloys using a well-established isopiestic method 112Jand to derive the corresponding partial thermodynamic properties of magnesium. Integral Gibbs energies of mixing for liquid alloys could be computed by a Gibbs-Duhem integration. It was also hoped to obtain additional information on some of the phase boundaries in the ternary system from the thermodynamic measurements. The ultimate goal would be to provide a set of thermodynamic (and phase diagram) data which could be used for an optimization of the ternary Cu-Mg-Ni system. II.
EXPERIMENTAL PROCEDURE
The general principles of the isopiestic equilibration technique and its application to the measurement of magnesium vapor pressures have been described in earlier T. GNANASEKARAN, formerly Research Assistant with the Institut fiir Anorganische Chemie, Universit~it Wien, is Scientific Officer, Materials Chemistry Division, Chemical Group, IGCAR, Kalpakkam, Tamilnadu 603 102, India. HERBERT IPSER, Assistant Professor, is with the lnstitut ftir Anorganische Cbemie, Universit/it Wien, Wahringerstr. 42, A-1090 Wien, Austria. Manuscript submitted May 3, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS B
publications, t12,13A41 Copper-nickel master alloys with atomic ratios of 2.0, 1.0, and 0.5 were prepared, and they were equilibrated with the vapor from a magnesium reservoir as discussed in the next section. A. Master Alloys Starting materials for the binary master alloys were nickel foil (0.5 mm, 99.997 pct metallic purity from Johnson & Matthey, Chemicals Ltd., London, UK) and copper wire (1-mm diameter, 99.999 pct metallic purity from Alfa Products, FRG). Appropriate amounts of the elements were weighed into a boron nitride crucible which was placed into an outer silica container and sealed under vacuum. The alloys were melted inductively and quenched to room temperature. The resulting ingots were first annealed in a v
Data Loading...
