Standard enthalpies of formation for some samarium alloys, Sm + Me (Me = Ni, Rh, Pd, Pt), determined by high-temperature
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I.
INTRODUCTION
THE thermodynamic properties of the binary alloys formed between early transition metals and late transition metals are of significant interest both in industry and in theoretical studies of the solid state. Since the early 1980s, systematic studies of the thermochemistry of such alloys have been a long-term project of this laboratory. The early work included a pioneering investigation of the thermochemistry of liquid alloys of copper with titanium at 1372 K;[1] a study of the thermochemistry of the binary alloys formed between copper, an element from Group IB, and all the elements from Group IV in the periodic table;[2] a study of the binary alloys formed between lanthanum, an element from Group III, and nickel, an element from Group VIII;[3] and a study of the binary alloys formed between Sc, Y, La, and Lu, all elements from Group III, and copper.[4] These early studies included heat of mixing measurements on liquid alloys, solution calorimetry in liquid copper at 1373 K, as well as direct synthesis calorimetry of relatively lowmelting intermetallic compounds. However, when these studies were extended to alloys formed between elements from Group IV and from Group VIII, it was inferred that the direct synthesis method might not work at 1373 K because these alloys have much higher melting points than the alloys studied previously. In 1984, a new calorimetric method, which is now called ‘‘solute-solvent drop calorimetry,’’ was developed in this laboratory by Topor and Kleppa in their study of the thermochemistry of LaB6.[5] This compound has a melting point of about 2973 K and is an important electron emitter. The new method was used from 1986 to 1988 to determine the standard enthalpies of formation of 18 equiatomic alloys of the Group IV elements Ti, Zr, and Hf with a number of elements from Group VIII. A review of these studies was given by Topor and Kleppa in 1989.[6] QITI GUO, Research Scientist, and OLE J. KLEPPA, Professor Emeritus, are with The James Franck Institute, The University of Chicago, Chicago, IL 60637. Manuscript submitted December 9, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
When work on these equiatomic alloys was initiated, the enthalpies of formation of some of the same compounds had recently been determined by direct synthesis calorimetry at somewhat higher temperatures by Gachon et al.[7] A comparison of the solute-solvent drop data with the corresponding data of Gachon et al. indicated that in most cases the agreement was good to excellent. This encouraged us to adopt the less cumbersome and less time-consuming direct synthesis approach when our investigations were extended to the intermetallic compounds formed between transition metals from Group III and Group VIII. Consequently, Selhaoui and Kleppa in 1993 reported new standard enthalpy of formation data for alloys of Sc 1 Me,[8] Y 1 Me,[9] La 1 Me,[10] Ce 1 Me, and Lu 1 Me.[11] In recent years, the present authors have reported new standard enthalpy of formation values for alloys of Pr 1 Me,[12] Nd 1 Me,[13] Gd
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