Entropy rare earth elements

Table 18.1.3. Crystallographic ionic radii (pm) and hydration entropies (kJ mol 1) of the rare-earth elements in oxidation states +2, +3 and +4...

Table 52 reports the enthalpies and entropies of formation of As-based alloys. With rare-earth elements the enthalpies of formation are known for the 1 1 composition. For the actinides thermodynamic data are known only for the U-As system. The enthalpies of formation of all Ln-As compounds are nearly the same, the enthalpy of formation of U-As being clearly less negative (fig. 135). 

Skochdopole, Griff el, and Spedding 310) have compared measured entropies for the rare earths with theoretically predicted values. Although they do not predict a value for europium, they believe it is somewhat higher than its immediate periodic table neighbors. On this basis, we adopt a value of 17 e. u. for the entropy of europium at 298 K. Spedding and Daane 314) remark that europium is the most volatile of the rare earths. Landolt-Bornstein 208) report available spectroscopic terms from which we have calculated the thermodynamic properties of the ideal monatomic gas. The remaining data listed for this element are estimated and are consistent with the above known facts. These data are intended for use only until measured values become available. 

Schick s work includes the study of borides, carbides, nitrides, and oxides of some elements in Groups IIA, IIIB, IVA, IVB, VB, VIIB, and VIII as well as selected rare earths and actinides. As far as possible, the tables have been made compatible with the JANAF tables. Among the subjects treated are phase diagrams, heat capacities, enthalpies, entropies, enthalpies of phase transformation, formation, and reaction, melting temperatures, triple points, free energies of formation, vapour pressures, compositions of vapour species, ionization and appearance potentials, e.m.f. of cells, and enthalpies of solution and dilution. Volume 1 summarizes the techniques used to analyse data and cites the data analysed, and Volume 2 gives tables of values produced by this study. 

The phase diagrams, the structure of possible intermetallic compounds and the thermodynamic data, enthalpies and entropies of formation or of mixing, of alloys based on rare earths and actinides have been compiled for the purpose of comparing the behavior of rare earths and actinides on alloying. Concerning the rare earths, information has often been obtained for all the elements of the series except of course promethium. Concerning the actinides, the behavior of only three elements of the series, thorium, uranium and plutonium, has been studied because of the lack of data for all the other elements. 

The enthalpies and entropies of formation of intermetallic compounds between transition metals and rare earth or actinide elements are reported in tables 5-15. As can be seen, data are available for late transition metals. For early transition metals some data concerning the U-Zr, U-Nb, U-Mo solid solutions have been found and are reported in table 16. When calorimetric experiments have been performed in the liquid state, the values of the partial or integral enthalpies of mixing are reported in tables 17-20. These data concern only rare-earth-based alloys with Ni, Co, Fe and Mn. 

The enthalpies and entropies of formation of the intermetallic compounds formed between elements of column IVB and rare earths and actinides are reported in tables 41—44. Data concerning liquid alloys, obtained using calorimetric methods, have also been found in the literature, and are reported in tables 45-48. 

The last chapter (134) in this volume is an extensive review by Colinet and Pasturel of the thermodynamic properties of landianide and actinide metallic systems. In addition to compiling useful theiTnodynamic data, such as enthalpies, entropies, and free eneigies of formation and of mixing, the authors have made an extensive comparative analysis of the thermodynamic behavior of the rare earths and actinides when alloyed with metallic elements. They note that when alloyed with non-transition metals, the enthalpies of formation of uranium alloys are less negative than those of the rare earths while those of thorium and plutonium are about the same as the latter. For transition metal alloys the formation enthalpies of thorium and uranium are more negative than diose of the rare earths and plutonium (the latter two are about the same). The anomalous behaviors of cerium, europium and ytterbium in various compounds and alloys are also discussed along with the effect of valence state changes found in uranium and plutonium alloys. 

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