Fluoride compounds thermodynamic data

Thermodynamic data show that the stabilities of the caesium chloride-metal chloride complexes are greater than the conesponding sodium and potassium compounds, and tire fluorides form complexes more readily tlrair the chlorides, in the solid state. It would seem that tire stabilities of these compounds would transfer into tire liquid state. In fact, it has been possible to account for the heats of formation of molten salt mixtures by the assumption that molten complex salts contain complex as well as simple anions, so tlrat tire heat of formation of the liquid mixtures is tire mole fraction weighted product of the pure components and the complex. For example, in the CsCl-ZrCU system the heat of formation is given on each side of tire complex compound composition, the mole fraction of the compound... 

The (C4F,) compound is thermally less stable than carbon fluorides with a higher F C ratio. Decomposition starts at > 100°C thermodynamic data on (C4pj) are given in ref. 7. 

AH of reaction (17) is an estimate since PuCl4(s) has not been synthesized AfH° [PuCl4(s)] = — 964 kJ is an estimate (Fuger et al. 1983). The dramatic difference in these enthalpies [Pu(IV) is more stable than Pu(III) in this complex chloride by -95-( —4) = - 91 kJ or almost 1.0 V, in comparison with the binary chloride] shows how acid-base effects influence oxidation-reduction properties. As noted above, there are few known lanthanide (IV) complex halides and no thermodynamic data on even these few halides, so no quantitative comparison can be made. Nevertheless it does show how complexation effects by basic complexants make high f-element oxidation states attainable. Perhaps the most dramatic evidence of the enhancement of high oxidation state by a basic fluoride is the existence of the Nd(IV) and Dy (IV) compounds such as Cs2(Cs, Rb, K) (Nd, Dy)Cl2 these AjRF, double fluorides are the only known Nd (IV) and Dy(IV) compounds. 

Three binary fluorides of xenon are known XeF2, XeF4, and XeFe. XeFg is not known see Fluorides Solid-state Chemistry). The fluorides are readily prepared from the elements and are thermodynamically stable. Full characterization data is available for these compounds, including gas-phase Xe and F NMR data. The commercial availability of Xep2 has greatly increased the study and use of this reagent. ... 

Thus we are fully justified in observing that spontaneous interaction between nickel and tantalum containing chloride, chloride-fluoride, and fluoride melts results in the predominant formation of NisTa intermetallic compound on the surface of the nickel samples. This corresponds with the published thermodynamics and kinetics data for the nickel-tantalum system. 

McCarthy et al., 1996 Melville et al., 2000 Robbins and Barrow, 1974 Rubinoff et al., 2003 Sauer et al., 1996 Schall et al., 1983, 1987 Shenyavskaya et al., 1965, 1968 Simard and James, 1992 Uttam and Joshi, 1995 Uttam et al., 1997 Verges et al., 1999 Xin and Klynning, 1994), molecular constants for most fluorides RF and some chlorides RCl have been determined only for the ground electronic state. These data are sufficient for reasonably estimating molecular constants for unknovm compounds in this state. Thus, the possibility appears to use the rigid rotator-harmonic oscillator model in calculations of the thermodynamic functions for the entire series of RF and RCl molecules. 

The highlight of the chapter is the presentation in an analytical form of the temperature dependences of the reduced Gibbs free energy for 105 individual compounds, supplemented by the listing of their formation enthalpy under standard conditions AfH°(0), as well as of the atomization enthalpies AatH°(0) for the gaseous compoimds and the sublimation enthalpies AsubW°(0) for solid-state samples. These extensive data represent complete and consistent sets and may therefore be incorporated into relevant databases or individual programs for routine calculations of the thermodynamic parameters for equilibria involving the participation of rare-earth fluorides or chlorides. 

In ternary compounds of the type (A,B)X, the point defect concentrations and hence the deviation from stoichiometry depend on the concentrations of the two cations. Since in general the equilibrium constants of the different point defect equilibria in ternary compounds are composition dependent, their thermodynamic treatment is mote difficult, and usually much more experimental data are required than in the case of the binary compounds. The complexity of the ternary compounds is the reason why point defect chemistry has been worked out more or less quantitatively only for some oxide and fluoride systems, using the concepts of Kroger and Vink, Kroger, Schmalzried and Wagner, and Schmalzried. ... 

Extensive studies have been performed for the determination of the vapor pressures and the vaporization thermodynamics of rare-earth fluorides. The majority of the data are based on mass spectrometric work and originate from the laboratories of Suvorov, Margrave and Searcy. Table 1 summarizes the reported vapor pressures and thermodynamic functions of sublimation, vaporization and (in two cases) dimerization of rare-earth fluorides. The data are not in full agreement in those cases that the same compound has been studied by different research groups. The reader should also refer to the articles of Myers and Graves (1977a,b) for selected third-law values for the enthalpy of sublimation, A//5298-... 

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