Phase stabilities thermochemical

In Fig. 7.68 the oxidising and sulphiding potentials of four different atmospheric environments, i.e. conventional coal combustion (A), fluidised bed combustion (B), conventional coal gasification (C) and coal gasification using nuclear heat (D), are shown on the thermochemical phase stability... 

A. Fernandez Guillermet, Analysis of thermochemical properties and phase stability in the zirconium-carbon system, Journal of Alloys and Compounds, 217 (1995) 69-89. 

Kau] Kaufman, L., Computer Bases Thermochemical Modeling of Multicomponent Phase Diagrams in Alloys Phase Stability , Stocks, G.M., Gonis, A. (Eds.), Kluwer Acad. Publ., 145-175 (1989) (Calculation, Phase Diagram, Phase Relations, Theory, 43)... 

Takahashi, T. (1979) Comparison between thermochemical and phase stability data for the quartz-coesite-stishovite transformation. Am. Mineral, 64,... 

Gangue minerals and salinity give constraints on the pH range. The thermochemical stability field of adularia, sericite and kaolinite depends on temperature, ionic strength, pH and potassium ion concentration of the aqueous phase. The potassium ion concentration is estimated from the empirical relation of Na+/K+ obtained from analyses of geothermal waters (White, 1965 Ellis, 1969 Fournier and Truesdell, 1973), experimental data on rock-water interactions (e.g., Mottl and Holland, 1978) and assuming that salinity of inclusion fluids is equal to ffZNa+ -h m + in which m is molal concentration. From these data potassium ion concentration was assumed to be 0.1 and 0.2 mol/kg H2O for 200°C and 250°C. 

Holdaway M. J. and Mukhopadhyay B. (1993). A reevaluation of the stability relations of andalusite Thermochemical data and phase diagram for the aluminum silicates. Amer Mineral, 78 298-315. 

Chapter 6 therefore deals in detail with this issue, including the latest attempts to obtain a resolution for a long-standing controversy between the values obtained by thermochemical and first-principle routes for so-called lattice stabilities . This chapter also examines (i) the role of the pressure variable on lattice stability, (ii) the prediction of the values of interaction coefficients for solid phases, (iii) the relative stability of compounds of the same stoichiometry but different crystal structures and (iv) the relative merits of empirical and first-principles routes. 

This ensures that thermochemical (TC) lattice stabilities are firmly anchored to the available experimental evidence. Although the liquid phase might be considered a common denominator, this raises many problems because the structure of liquids is difficult to define it is certainly not as constant as popularly imagined. It is therefore best to anchor the framework for lattice stabilities in the solid state. 

Thermochemical methods generate lattice stabilities based on high-temperature equilibria that yield self-consistent multi-component phase-diagram calculations. However, as they are largely obtained by extrapolation, this means that in some cases they should only be treated as effective lattice stabilities. Particular difficulties may occur in relation to the liquid — glass transition and instances of mechanical instability. 

The active layer must provide the required activity, selectivity and thermochemical stability properties. Different active phases can be adopted depending on the operating constraints and the fuel type. In the following we will mainly focus on CH4 (i.e. the main constituent of natural gas) as the reference fuel for GT applications. In this respect, the combustion catalysts that have been most extensively investigated for configurations based on lean combustion concepts are PdO-based systems and metal-substituted hexaaluminates. 

There is sufficient recent theoretical and experimental evidence to justify serious consideration of H80 as an intermediate in the radiolysis of water. Bernstein (15) has presented thermochemical evidence for the stability of H atom adducts such as HsO and NH4 and estimated (16) the stability of HaO with respect to H20 + H in the gas phase as about 5 kcal./mole. C. E. Melton and P. S. Rudolph of this Laboratory have demonstrated to H. A. Mahlman and the author, by mass spectrometric techniques, the existence of H80, D30, and D2HO in the gas phase. These species were presumably desorbed from the instrument walls. The ratio [H80]/[H20] was 1/200 at a background pressure of 10 8 ton-in an ion source designed to eliminate ion-molecule reactions. 

Modification of porous inorganic materials by carbon makes it possible to obtain porous carboniferous composites with high thermal and chemical stability and strength. To introduce carbon into pores, both gas phase pyrolysis and carbonization through thermochemical solid-phase reactions are employed. The formation of carbon structures depends on carbonization conditions process rate, precursor concentration, presence of catalyst, etc. [1-3]. Phenolic resins, polyimides, carbohydrates, condensed aromatic compounds are most widely used as polymeric and organic precursors[4-6]. 

Halide abstraction reactions are very common and usually fast processes. These reactions have also proved extremely useful for two specific applications in the field of physical organic chemistry. First, for obtaining thermochemical stability data of carboca-tions through the measurement of gas-phase chloride transfer equilibria (equation 1). 

The data given in Tables 2 and 3 are, of course, related to one another through a thermochemical cycle. AHi0n(g) and AHaq differ only by the heats of solvation (hydration in aqueous solution) of the reactants and product, and therefore these heats of solvation must affect the absolute bond energies in the gas phases in such a manner as to cause an inversion in the order of stability in cases of class (b) behaviour (see below). 

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