Standard enthalpies of formation of some 3d, 4d and 5d transition-metal stannides by direct synthesis calorimetry
Introduction
During recent years, we have in this laboratory conducted systematic studies of the thermochemistry of transition-metal alloys with elements of the IIIB and IVB columns in the Periodic Table [1]. These investigations have included work on borides, aluminides, silicides and germanides of transition-metal elements. In the course of these studies, we noted that relatively few alloys of the transition metals with tin had been investigated. The available calorimetric enthalpies of formation for the Fe–Sn, Co–Sn, Ni–Sn systems were measured by Predel and Vogelbein [2], for the Pd–Sn system by Bryant et al. [3], for the Ru–Sn system by Perring et al. [4]and for the Pt–Sn system by Ferro et al. [5]. These results show that the alloys have relatively large negative enthalpies of formation, which indicates that there is a fairly strong bonding between the metals and tin. The V–Sn and Nb–Sn systems are of considerable technological interest because of the superconducting properties of the V3Sn and Nb3Sn compounds 6, 7. The Zr–Sn system is also of special interest because of the technological use of zirconium stannides in pressurized water reactors [8].
Information regarding the phase diagrams of the stannide systems and on the structures of the considered phases is generally available in the literature 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. However, there is no established phase diagram for the Ir–Sn system. Also, the X-ray diffraction patterns of several of the alloys which we studied were not listed in the ASTM powder diffraction file.
The published literature offers some values for the enthalpies of formation of Nb3Sn derived from vapor-pressure measurements [7], and for Pd3Sn from EMF data [3]. For Ru3Sn7 and for PtSn, there are calorimetric values 4, 5. We will compare our results with these data. We will also compare our results with the enthalpy predictions based on the semi-empirical model of Miedema et al. [20].
Finally, we will compare our results with the enthalpies of formation of transition-metal germanides recently studied in this laboratory 21, 22, 23, 24. We will also draw a comparison of the thermochemical behavior of the transition-metal stannides with the behavior of the 3d, 4d and 5d aluminides previously studied by the present authors 25, 26, 27.
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Experimental and materials
The experiments were carried out at 1473±2 K in a single-unit differential microcalorimeter which has been described in an earlier communication from this laboratory [28]. All the experiments were performed under a protective atmosphere of argon gas which was purified by passing it over titanium chips at 1173 K. A BN(boron nitride) crucible was used to contain the samples.
All the materials used were purchased from Johnson Matthey/Aesar, Ward Hill, MA; the purity and particle size of the elements
Results and discussion
The standard enthalpies of formation of the transition-metal stannides determined in this study were obtained from the difference between the results of two sets of measurements. In the first set, the following reaction takes place in the calorimeter:here, m represents the molar ratio Sn/Tr, Tr being the considered transition metal (Ti, V, Zr, Nb, Rh, Ru, Pd, Hf, Ir and Pt) while s denotes solid and l denotes liquid. The reacted pellets were re-used in
Acknowledgements
This investigation has been supported by the Department of Energy under Grant DE-FGO2-88ER4563, and has also benefitted from the MRSEC facilities at the University of Chicago. We are indebted to Dr. Joseph Pluth for his help with generating the X-ray diffraction patterns from the reported unit-cell parameters and the atomic coordinates.
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