Thermodynamic data solids, 550 consistency

Figure 4.11 Phase diagram of the hypothetical binary system A-B consisting of regular solid and liquid solutions. 2 4 = 20 kJ mol-1 and Qso = 15 kJ mol-1. Thermodynamic data for components A and B as in Figure 4.10.

All but one of the reactions in Figure 4 lead to the formation of the soluble TiO + ion this seems consistent with the observed changes in the visible absorption spectrum of the solid electrode. It may also be that other titanium species are formed in solution, such as peroxytitanium complexes like H Ti05 We have no direct evidence as to the identity of the solution species at this time, and have limited the candidate corrosion reactions shown in Figure 4 to those for which thermodynamic data are readily available. Nonetheless, the fact that titanium is observed in the electrolyte only upon extensive photocorrosion (and then in smaller amounts than strontium) suggests that the initial photocorrosion process involves the loss of strontium from the SrTi03, with the formation of Sr(0Ac)2 or SrSO. ... 

The infrared spectrum29 indicates the solid to be typically ionic. It decomposes rapidly above 573 K,30 consistent with the thermodynamic data. The reported melting point is uncertain. The transition is given in Table 5.14, and thermodynamic data in Tables 5.15 to 5.17. Decomposition is reported to be reversible and to yield no intermediates 31... 

Figure 2 Condensation of major rock-forming phases from a gas of solar composition (Anders and Grevesse, 1989) at a total pressure of 10 atm. This calculation was done with the best currently available internally consistent thermodynamic data for solid and gaseous phases and includes nonideal solid solution models for melilite, Ca-rich pyroxene, feldspar, and metal. This calculation is the same as the one shown in Yoneda and Grossman (1995, table 1...

None of the thermodynamic databases accompanying the modeling codes are comprehensive compilations of all the aqueous and mineral species we may encounter. Neither has it been ensured that the thermodynamic data are internally consistent. Code developers and releasing agencies make no statement about what are the best thermodynamic properties of a solid or aqueous species or about the internal consistency of the data they assume this to be the responsibility of the modeler. 

Chemical modeling results for aqueous systems is dependent on the primary thermodynamic and kinetic data needed to perform the calculations. For aqueous equilibrium computations, a large number of thermodynamic properties of solute-solute, solute-gas and solute-solid reactions are available for application to natural waters and other aqueous systems. Unfortunately, an internally consistent thermodynamic data base that is accurate for all modeling objectives, has not been achieved. Nor is it likely to be achieved in the near future. The best that can be hoped for is a tolerable level of inconsistency, with continuing progress toward the utopian goal through national and international consensus. 

IX.1.3.3.6 The consistency of the thermodynamic data for hydrated solid thorinm snlphates... 

Aqueous Solvation.—A review, covering the 1968—1972 publications, deals with physical properties, thermodynamics, and structures of non-aqueous and aqueous-non-aqueous solutions of electrolytes, and complete hydration limits. Thermodynamic aspects of ionic hydration also reviewed include the thermodynamic theory of solvation the molecular interpretation of ionic hydration hydration of gaseous ions (AG s, H s, and AA s) thermodynamic properties of ions at infinite dilution in water, solvent isotope effect in hydration reference solvents and ionic hydration and excess properties. A third review on the hydration of ions emphasizes the structure of water in the gaseous, liquid, and solid states the size of ions and the hydration numbers of ions and the structure of the hydrated shell from measurements of mobility, compressibility, activity, and from n.m.r. spectra. Pure water and aqueous LiCl at concentrations up to saturation have been examined by neutron and X-ray diffraction. For the neutron studies LiCl and D2O are employed. The data are consistent with a simple model involving only... 

The bubble point tests conducted in methanol/water mixtures were worked up to show properties of the three-phase interfaces along the complex contact line in SS304 LAD screens. In particular, the variation with F2 of the solid/vapor interfacial tension /sv differed from that of the solid/liquid interface j/sl- The data are consistent with the Langmuir isotherm description of the thermodynamics of adsorption. The result of the analysis is that the co-areas Amin are 0.32 nm /molecule for the SS304— vapor interface and 1.77 nm /molecule for the SS304—solution interface. This implies that that methanol molecules form a dense, liquid-like monolayer at the interface of SS304 with the vapor phase, while the methanol molecules are very dilute in the interface between SS304 and the solution of methanol/water. 

This solid solution still makes up the bulk of the solid particles after equilibration in an aqueous solution (59), since solid state diffusion is negligible at room temperature in these apatites (60), which have a melting point around 1500°C. These considerations and controversial results justify a thermodynamic analysis of the solubility data obtained by Moreno et al (58 ). We shall consider below whether the data of Moreno et al (58) is consistent with the required thermodynamic relationships for 1) an ideal solid solution, 2) a regular solid solution, 3) a subregular solid solution and 4) a mixed regular, subregular model for solid solutions. 

The basic question is how to perform extrapolations so as to obtain a consistent set of values, taking into account various complications such as the potential presence of mechanical instability. Additional complications arise for elements which have a magnetic component in their Gibbs energy, as this gives rise to a markedly non-linear contribution with temperature. This chapter will concern itself with various aspects of these problems and also how to estimate the thermodynamic properties of metastable solid solutions and compound phases, where similar problems arise when it is impossible to obtain data by experimental methods. 

The case of binary solid-liquid equilibrium permits one to focus on liquid-phase nonidealities because the activity coefficient of solid component ij, Yjj, equals unity. Aselage et al. (148) investigated the liquid-solution behavior in the well-characterized Ga-Sb and In-Sb systems. The availability of a thermodynamically consistent data base (measurements of liquidus, component activity, and enthalpy of mixing) provided the opportunity to examine a variety of solution models. Little difference was found among seven models in their ability to fit the combined data base, although asymmetric models are expected to perform better in some systems. 

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