Phase composition determination

K.3.1. High-pressure Methanol Oxidation on Pd(l 11). Figures 53a and b show PM-IRAS surface (p—s) and gas-phase (p + s) spectra acquired during methanol exposure and oxidation at mbar pressures. The gas-phase composition, determined by GC and by PM-IRAS, respectively is shown in Figs 53c and d. After exposure of Pd(l 1 1) to 5 mbar of CH3OH at 300 K, PM-IRAS was used to identify adsorbed CO (vco at approximately 1840 cm , typical of approximately 0.3 ML coverage) as well as formaldehyde (pcHj formaldehyde in two different adsorption geometries... 

CON 00] O CONNOR B., Influence of refinement strategy on Rietveld phase composition determinations , X-ray Anal, vol. 42, p. 204-211,2000. 

Rietveld whole pattern refinement was applied to each pattern to determine the scale factors of all detectable phases. The goodness-of-fit indices for the refinements, (Rwp/Rexp), ranged from 0.02 - 0.03 wliich is adequate for phase composition determination. The weight fraction of phase i at each depth was determined by an external standard ZMV approach ... 

A transmission electron micrograph and a diagrammatic representation of the phase composition (determined by electron dilfraction analysis) of a particle of formed PAM are presented in Fig. 3.26. The electron dilfraction analysis demonstrates the predominance of zones with (3-Pb02 structure in the middle part of the particle. By contrast, the uppermost and bottom parts, which are far more electron-transparent, have an amorphous structure. A PbS04 nucleus is also detected in the bottom part near the amorphous zone. 

Earlier, we had developed the method of phase composition determination for por-Si surface layers by Si L2,3 USXES data by computer fitting of experimental Si L2,3-spectra with the model one [3]. According to the data obtained from USXES... 

The kinetics of the formation of GdSrFe04 has been characterized by the phase composition determined from the X-ray diffraetion data (Figure 14) and by the Fe " fraction in the reaction mixture determined from the Mossbauer data (Figure 15). Both data sets are in a good agreement. 

In the final chapter. Chapter 11, we discuss phase diagrams and thermodynamic modelling, which are becoming increasingly important methods for understanding the phase compositions determined by microstructural analysis. 

In Equation (24), a is the estimated standard deviation for each of the measured variables, i.e. pressure, temperature, and liquid-phase and vapor-phase compositions. The values assigned to a determine the relative weighting between the tieline data and the vapor-liquid equilibrium data this weighting determines how well the ternary system is represented. This weighting depends first, on the estimated accuracy of the ternary data, relative to that of the binary vapor-liquid data and second, on how remote the temperature of the binary data is from that of the ternary data and finally, on how important in a design the liquid-liquid equilibria are relative to the vapor-liquid equilibria. Typical values which we use in data reduction are Op = 1 mm Hg, = 0.05°C, = 0.001, and = 0.003... 

The equilibrium ratios are not fixed in a separation calculation and, even for an isothermal system, they are functions of the phase compositions. Further, the enthalpy balance. Equation (7-3), must be simultaneously satisfied and, unless specified, the flash temperature simultaneously determined. 

THE SUBROUTINE ACCEPTS BOTH A LIQUID FEED OF COMPOSITION XF AT TEMPERATURE TL(K) AND A VAPOR FEED OF COMPOSITION YF AT TVVAPOR FRACTION OF THE FEED BEING VF (MOL BASIS). FDR AN ISOTHERMAL FLASH THE TEMPERATURE T(K) MUST ALSO BE SUPPLIED. THE SUBROUTINE DETERMINES THE V/F RATIO A, THE LIQUID AND VAPOR PHASE COMPOSITIONS X ANO Y, AND FOR AN ADIABATIC FLASHf THE TEMPERATURE T(K). THE EQUILIBRIUM RATIOS K ARE ALSO PROVIDED. IT NORMALLY RETURNS ERF=0 BUT IF COMPONENT COMBINATIONS LACKING DATA ARE INVOLVED IT RETURNS ERF=lf ANO IF NO SOLUTION IS FOUND IT RETURNS ERF -2. FOR FLASH T.LT.TB OR T.GT.TD FLASH RETURNS ERF=3 OR 4 RESPECTIVELY, AND FOR BAD INPUT DATA IT RETURNS ERF=5. 

Liquid phase compositions and phase ratios are calculated by Newton-Raphson iteration for given K values obtained from LILIK. K values are corrected by a linearly accelerated iteration over the phase compositions until a solution is obtained or until it is determined that calculations are too near the plait point for resolution. 

Polymer Composition. The piopeities of foamed plastics aie influenced both by the foam stmctuie and, to a gieatei extent, by the piopeities of the parent polymer. The polymer phase description must include the additives present in that phase as well. The condition or state of the polymer phase (orientation, crystallinity, previous thermal history), as well as its chemical composition, determines the properties of that phase. The polymer state and cell geometry are intimately related because they are determined by common forces exerted during the expansion and stabilization of the foam. 

Since the phase rule treats only the intensive state of a system, it apphes to both closed and open systems. Duhem s theorem, on the other hand, is a nJe relating to closed systems only For any closed system formed initially from given masses of preseribed ehemieal speeies, the equilibrium state is completely determined by any two propeities of the system, provided only that the two propeities are independently variable at the equilibrium state The meaning of eom-pletely determined is that both the intensive and extensive states of the system are fixed not only are T, P, and the phase compositions established, but so also are the masses of the phases. 

In practice, either T or F and either the hquid-phase or vapor-phase composition are specified, thus fixing 1 + (N — 1) = N independent variables. The remaining N variables are then subject to calculation, provided that sufficient information is available to allow determination of all necessary thermodynamic properties. 

The vapor-phase composition is also to be determined, and it, too, is required to initiate calciilations. Assuming both the hquid and vapor phases to be ideal solutions, Eqs. (4-98) and (4-304) combine to give... 

Heat resistance and gas corrosion resistance depends on chemical, phase compositions and stmcture of an alloy. The local corrosion destmction (LCD) of heat resisting alloys (HRS), especially a cast condition, probably, is determined by sweat of alloying elements. 

X-ray Diffraction (XRD) is a powerful technique used to uniquely identify the crystalline phases present in materials and to measure the structural properties (strain state, grain size, epitaxy, phase composition, preferred orientation, and defect structure) of these phases. XRD is also used to determine the thickness of thin films and multilayers, and atomic arrangements in amorphous materials (including polymers) and at inter ces. 

A computer program was compiled to work out the ray-tracing of UV detector of high performance capillary electrophoresis at the investigation of 5 and 6 (98MI59). The capacity factor of 5 at different temperature and at different mobile phase compositions was experimentally determined in bonded-phase chromatography with ion suppression (98MI15). 

The dimensionless K. is regarded as a function of system T and P only and not of phase compositions. It must be exfjerimentally determined. Reference 64 provides charts of R (T,P) for a number of paraffinic hydrocarbons. K. is found to increase with an increase in system T and decrease with an increase in P. Away from the critical point, it is invariably assumed that the K, values of component i are independent of the other components present in the system. In the absence of experimental data, caution must be exercised in the use of K-factor charts for a given application. The term distribution coefficient is also used in the context of a solute (solid or liquid) distributed between two immiscible liquid phases yj and x. are then the equilibrium mole fractions of solute i in each liquid phase. 

The composition dependence of the potential of the Li44Sn phase was determined, as shown in Fig. 9. 

Upon substitution into either one of the equations of stability [Eq. (98) or (99)], we can then determine whether the gas mixture exists in one or two stable phases. If two phases exist at some temperature and pressure, we can calculate the two phase compositions by utilizing the two equilibrium relations... 

The penetration theory has been used to calculate the rate of mass transfer across an interface for conditions where the concentration CAi of solute A in the interfacial layers (y = 0) remained constant throughout the process. When there is no resistance to mass transfer in the other phase, for instance when this consists of pure solute A, there will be no concentration gradient in that phase and the composition at the interface will therefore at all Limes lie the same as the bulk composition. Since the composition of the interfacial layers of the penetration phase is determined by the phase equilibrium relationship, it, too. will remain constant anil the conditions necessary for the penetration theory to apply will hold. If, however, the other phase offers a significant resistance to transfer this condition will not, in general, be fulfilled. 

To differentiate and to be able to determine the differences between the phases that may arise when two compounds are present (or are made to react together), we use what are termed "phase-diagrams" to Illustrate the nature of the interactions between two solid phase compositions. 

Up to this point, we have considered only one solid at a time. However, when two (2) or more solids are present, they can form quite complicated systems which depend upon the nature of each of the solids involved. To differentiate and to be able to determine the differences between the phases that may arise when two compounds are present (or are made to react together), we use what are termed "phase-diagrams to illustrate the nature of the interactions between two solid phase compositions. You will note that some of this material weis presented earlier in Chapter 1. It is presented here again to further emphasize the importance of phase diagrams. 

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