Intermetallic compounds thermodynamic properties

Equilibrium vapor pressures were measured in this study by means of a mass spectrometer/target collection apparatus. Analysis of the temperature dependence of the pressure of each intermetallic yielded heats and entropies of sublimation. Combination of these measured values with corresponding parameters for sublimation of elemental Pu enabled calculation of thermodynamic properties of formation of each condensed phase. Previ ly reported results on the subornation of the PuRu phase and the Pu-Pt and Pu-Ru systems are correlated with current research on the PuOs and Pulr compounds. Thermodynamic properties determined for these Pu-intermetallics are compared to analogous parameters of other actinide compounds in order to establish bonding trends and to test theoretical predictions. 

Plutonium-noble metal compounds have both technological and theoretical importance. Modeling of nuclear fuel interactions with refractory containers and extension of alloy bonding theories to include actinides require accurate thermodynamic properties of these materials. Plutonium was shown to react with noble metals such as platinum, rhodium, iridium, ruthenium, and osmium to form highly stable intermetallics. 

Ellner, M. and Predel, B. (1995) Bond characterization from thermodynamic properties. In Intermetallic Compounds. Principles and Practice, eds. Westbrook, J.H. and Fleischer, R.L. (John Wiley Sons Ltd., Chichester), Vol. 1, p. 91. 

Griessen, R. and Riesterer, T. (1988) Heat of formation models, in Hydrogen in Intermetallic Compounds I Electronic, Thermodynamic and Crystallographic Properties, Preparation, Vol. 63 (ed. L. Schlapbach), Springer Series Topics... 

Most metals of practical importance are actually mixtures of two or more metals. Recall from Section 1.1.3 that these intimate mixtures of metals are called alloys, and when the bond between the metals is partially ionic, they are termed intermetallics. For the purposes of this chapter, and especially this section, we will not need to distinguish between an intermetallic and an alloy, except to note that when a compound is indicated on a phase diagram (e.g., CuAb), it indicates an intermetallic compound. We are concerned only with the thermodynamics that describe the intimate mixing of two species under equilibrium conditions. The factors affecting how two metal atoms mix has already been described in Section 1.1.3. Recall that the solubility of one element in another depends on the relative atomic radii, the electronegativity difference between the two elements, the similarity in crystal structures, and the valencies of the two elements. Thermodynamics does not yet allow us to translate these properties of atoms directly into free energies, but these factors are what contribute to the free energy of... 

Lebedev, V.A., Pyatkov, V.I., Ushenin, S.N., 1983. Thermodynamic properties and phase composition of the alloys of the La-Sb system. In IV All-Union Conference on the Crystal Chemistry of Intermetallic Compounds, Abstracts, Lvov, p. 206. 

Plutonium-noble metal compounds have both technological and theoretical importance. Modeling of nuclear fuel interactions with refractory containers and extension of alloy bonding theories to include actinides require accurate thermodynamic properties of these materials. Plutonium was shown to react with noble metals such as platinum, rhodium, iridium, ruthenium, and osmium to form highly stable intermetallics. Vapor pressures of phases in these systems were measured by the Knudsen effusion technique. Use of mass spectrometer-target collection apparatus to perform thermodynamic studies is discussed. The prominent sublimation reactions for these phases below 2000 K was shown to involve formation of elemental plutonium vapor. Thermodynamic properties determined in this study were correlated with corresponding values obtained from theoretical predictions and from previous measurements on analogous intermetallics. 

In some cases, empirical rules can also relate thermodynamic properties to crystal structures. One of the best-known cases is in the AB5 systems where the equilibrium pressure is linearly correlated to the cell volume. As the cell volume increases, the equilibrium plateau pressure decreases, following a InPn law [64]. However, some exceptions exist to this rule such as in LaPts where electronic effects make the smaller unit cell more stable [65[. Nevertheless, generally, for intermetallic compounds the stability of the hydride increases with the size of the interstices [66]. A limitation of this empirical rule is that comparison between different types of intermetallics is impossible. For example, the stabilities of AB2 alloys cannot be compared with those of AB5 alloys [43]. 

Since the X-ray diffraction studies of Zintl et al. , these members of the family of intermetallic compounds have been of special interest because some of their chemical properties are unusual for intermetallic phases. Many experimental investigations have been reported for binary and ternary B32 type compounds. Besides the crystal structure " , the thermodynamic behavior , electrical conductivity ", magnetic susceptibility , NMR data elastic constants - and optical properties have been studied. Additionally for LiAl electrochemical investigations have been performed in view of the recent interest in fast ionic conductors " . ... 

An account of the gaseous species observed by Knudsen effusion mass spectrometry in the eqilibrium vapor of metals, alloys, oxides, halides, and technical systems is given. The fundamentals and recent developments of this method are briefly reported. Dissociation and atomization enthalpies of selected gaseous species are tabulated. Accounts of the equilibrium studies by Knudsen effusion mass spectrometry in order to obtain thermodynamic properties for condensed phases from gas phase data are additionally given for the aforementioned materials. Table 8 shows as an example the enthalpies and Gibbs energies of formation for different solid intermetallic compounds. A special section (Sect. 

In 1970 van Vucht et al. [41], in the Netherlands, discovered practical hydrides such as LaNis, and in 1974 Reilly and Wiswall, in the United States, discovered Fe-Ti hydrides [42]. In LaNis and other rare earth compounds such as YNis, NdNis and others, the plateau pressures are affected by the A-atom (example La atom) substitution. This led to numerous studies around the world and development of practical hydride work really started. There have been several excellent reviews over the years, among them notably references [2, 26,43-68]. Other notable papers on intermetallics in general, are those of Anderson and Maeland [63], Lou et al. [65, 66, 69], Bowman et al. [70], Cerney et al. [71], Percheron-Guegan and co-workers [29, 72], and Latroche et al. [73]. More recently an internet database has been set by Sandrock and Thomas (lEA/DOE/Sandia National Laboratory) [23], Jai-Young Lee and co-workers [74, 75], Uchida et al. [76], Yvon and Fichner (structural properties) [77], Gupta and Schlapbach (electronic properties) [78], and Flanagan and Oates (thermodynamic properties) [79]. 

The hydrogenation properties of the hydride-forming intermetallic compound was also used as a driving force in alkene, alkane or alcohol dehydrogenation reactions which are thermodynamically unfavorable (Chetina and Lunin 1994). The intermetallic compound can be used both as a catalyst and hydrogen acceptor, but its activity and thermal stability can be enhanced by adding some Rh, Ru or Pt salts at the surface. 

Heat of formation models, in Hydrogen in Intermetallic Compounds I Electronic, Thermodynamic, and Crystallographic Properties, Preparation (ed. 

Griessen R, Riesterer T (1988) Heat of formation models. In Schlapbach L (ed) Hydrogen in intermetallic compounds I electronic, thermodynamic, and crystallographic properties, preparation, vol 63, Series topics in applied physics. Springer, Berlin, pp 219-284... 

The thermodynamic data, Gibbs energies, enthalpies and entropies of formation of intermetallic compounds have been obtained from a literature search. We have also consulted the handbook Selected values of thermodynamic properties of binary alloys by Hultgren et al. (1973a) and a compilation of thermodynamic data on transition metal based alloys done by de Boer et al. in 1988. For the actinide-based alloys a literature search and a critical analysis of the data was done by Rand and Kubaschewski (1963) for uranium compounds, by Rand et al. (1966) for plutonium alloys, by Rand et al. (1975) for thorium alloys, and more recently by Chiotti et al. (1981) for binary actinide alloys. We have included in our review the data obtained from the original publications and also the assessed data of Chiotti et al. (1981) when they were different. 

A semi-empirical model proposed by Miedema, called cellular model [99] of alloy phases, has been proved as an effective mathematical model for the estimation of the thermodynamic properties of metallic systems, including the thermodynamic properties of intermetallic compounds and liquid alloys. According to this model, the difference of electronegativities,, denoting the charge transfer between the atoms of different elements, is the driving force for the formation of intermetallic compounds while another parameter, the difference of parameterof different elements (Table 5.15), is the... 

Although the cellular model proposed by Miedema is rather successful for the semi-quantitative description of the thermodynamic property of intermetallic compounds and liquid alloys. The ignorance of geometrical factor makes this model to be somewhat inaccurate. In some of our work, inclusion of atomic radius ratio can give better results of computation by support vector regression. 

Vassiliev V., Bykov M, Gambino M., Bros J.P. (1993). Thermodynamic properties of the intermetallic compounds MnTe and MnTe2. Z. Metallkunde, Vol. 84, pp. 461-468. 

Some good papers have been published recently. Unfortunately the corresponding experimental data are most often lacking. The point-defect properties calculated from the electronic structure will have to be integrated in a proper thermodynamic theory. Such knowledge will also allow study in important fields that are practically unexplored up to now in intermetallic compounds point defect-impurity interaction, point defect-dislocation interaction, and consequences on the mechanical properties, etc. Considerable work is still required. 

---