Solid phase composition, activity

The composition and reactivity of the liquid phase (known as the soil solution) is defined by the quality of the incoming water and affected by fluxes of matter and energy originating from the vicinity of the solid phase, microbiological activity, and the gas phase. To understand the properties of the subsurface hquid phase, it is first necessary to consider the structure of the water molecule. 

Activity Coefficients and Predictions of Solid Phase Composition... 

In the specific case of a "strictly congruent" dissolution process occurring in an aqueous phase with a [B+]/[C+] activity ratio equal to the B+/C+ ratio in the solid, primary-saturation can be approximately found by drawing a straight vertical line on the Lippmann diagram from the solid-phase composition to the solutus (see figure 1). For an exact calculation, the following relations may be used to determine the primary saturation state ... 

Menon and Landau" point out a number of complications associated with modeling alloy deposition. First, the values for the kinetics parameters of the alloy species are likely to be different from those measured for the pure components. Furthermore, these parameters may vary with the composition of the alloy. Determination of such parameters can be done experimentally from measured alloy composition in well-controlled deposition experiments. A second issue has to do with the difficulty in determining the activities of the alloy components in the solid phase. The activity, which affects the electrode kinetics equation (82), is unity for single-component deposition however, in multicomponent alloy deposition it varies with the nature of the deposited alloy." ... 

Various pc electrode models have been tested.827 Using the independent diffuse layer electrode model74,262 the value of E n = -0.88 V (SCE) can be simulated for Cd + Pb alloys with 63% Pb if bulk and surface compositions coincide. However, large deviations of calculated and experimental C,E curves are observed at a 0. Better correspondence between experimental and calculated C,E curves was obtained with the common diffuse-layer electrode model,262 if the Pb percentage in the solid phase is taken as 20%. However, the calculated C, at a Ois noticeably lower than the experimental one. It has been concluded that Pb is the surface-active component in Cd + Pb alloys, but there are noticeable deviations from electrical double-layer models for composite electrodes.827... 

Hence the value of p in Eq. (3.10) coincides with that in Eq (3.6). For singlecomponent liquid and solid phases of constant composition, the activity is also always taken to be unity. 

When the standard states for the solid and liquid species correspond to the pure species at 1 atm pressure or at a low equilibrium vapor pressure of the condensed phase, the activities of the pure species at equilibrium are taken as unity at all moderate pressures. Consequently, the gas phase composition at equilibrium will not be... 

US patent 6,723,728, Polymorphic and other crystalline forms cis-FTC [106], The present invention relates to polymorphic and other crystalline forms of (—)-and ( )-cA-(4-amino-5-fluoro-l-(2-(hydroxymethyl)-l,3-oxathiolan-5-yl)-2(lH)-pyrimidinone, or FTC) [106]. Solid phases of (—)-cz>FTC that were designated as amorphous (—)-FTC, and Forms II and III were found to be distinguishable from Form I by X-ray powder diffraction, thermal analysis properties, and their methods of manufacture. A hydrated crystalline form of ( )-cA-FTC and a dehydrated form of the hydrate, were also disclosed, and can similarly be distinguished from other forms of FTC by X-ray powder diffraction, thermal properties, and their methods of manufacture. These FTC forms can be used in the manufacture of other forms of FTC, or as active ingredients in pharmaceutical compositions. Particularly preferred uses of these forms are in the treatment of HIV or hepatitis B. 

The difference between the upper and the lower curves for phase composition and texture, at equal water activity, is the result of the solid gain after osmotic treatment. The higher the solid uptake, the higher the difference in texture. Compared to simple air dehydration, the combination of osmotic dehydration and air dehydration can produce a softer product at low water activity, which is more pleasant to eat by hand, or to incorporate into pastry, ice cream, cheese, yogurt (Giangiacomo et al., 1994), and so on. 

In principle, Gibbs free energies of transfer for trihalides can be obtained from solubilities in water and in nonaqueous or mixed aqueous solutions. However, there are two major obstacles here. The first is the prevalence of hydrates and solvates. This may complicate the calculation of AGtr(LnX3) values, for application of the standard formula connecting AGt, with solubilities requires that the composition of the solid phase be the same in equilibrium with the two solvent media in question. The other major hurdle is that solubilities of the trichlorides, tribromides, and triiodides in water are so high that knowledge of activity coefficients, which indeed are known to be far from unity 4b), is essential (201). These can, indeed, be measured, but such measurements require much time, care, and patience. 

Consider a nonporous catalyst having an active component of a complex (unknown) composition, deposited over a known support (known parameters the true density of a support and its partial mass, ms). We have no information on the type of active component, only its partial mass, mc= 1 —ms. Also known is the density of solid phase of a catalyst as a whole. Allocate the partitions for this PS, and determine (a) a partial volume of the active component (b) the hue density of the active component. 

Once the composition of the aqueous solution phase has been determined, the activity of an electrolyte having the same chemical formula as the assumed precipitate can be calculated (11,12). This calculation may utilize either mean ionic activity coefficients and total concentrations of the ions in the electrolyte, or single-ion activity coefficients and free-species concentrations of the ions in the electrolyte (11). If the latter approach is used, the computed electrolyte activity is termed an ion-activity product (12). Regardless of which approach is adopted, the calculated electrolyte activity is compared to the solubility product constant of the assumed precipitate as a test for the existence of the solid phase. If the calculated ion-activity product is smaller than the candidate solubility product constant, the corresponding solid phase is concluded not to have formed in the time period of the solubility measurements. Ihis judgment must be tempered, of course, in light of the precision with which both electrolyte activities and solubility product constants can be determined (12). 

This permits provisional calculation of the compositional dependence of the equilibrium constant and determination of provisional values of the solid phase activity coefficients (discussed below). The equilibrium constant and activity coefficients are termed provisional because it is not possible to determine if stoichiometric saturation has been established without independent knowledge of the compositional dependence of the equilibrium constant, such as would be provided from independent thermodynamic measurements. Using the provisional activity coefficient data we may compare the observed solid solution-aqueous solution compositions with those calculated at equilibrium. Agreement between the calculated and observed values confirms, within the experimental data uncertainties, the establishment of equilibrium. The true solid solution thermodynamic properties are then defined to be equal to the provisional values. 

By examining the compositional dependence of the equilibrium constant, the provisional thermodynamic properties of the solid solutions can be determined. Activity coefficients for solid phase components may be derived from an application of the Gibbs-Duhem equation to the measured compositional dependence of the equilibrium constant in binary solid solutions (10). 

Therefore, passivation of the positive electrode by poorly conducting PbS04 can be reduced [348]. The porosity is important because it enables the expansion during the solid phase volume increase, which accompanies the transformation of Pb02 to PbS04. In the most popular construction, the electrode paste material (mixture of metallic lead with lead oxides) is held in a framework composed of lead alloys with additions of tin, antimony, selenium, and calcium [348]. Antimony improves the mechanical stability however, it increases the resistance and facilitates the selfdischarge of the battery. Better results are obtained for low antimony content and/or for lead-calcium alloys [203]. Methods of positive electrodes improvement, from the point of view of lead oxide technology have been discussed [350]. Influence of different factors on life cycle, nature, and composition of the positive active mass has been studied by Pavlov with coworkers [200, 351, 352]. 

The concentrations in the solid phases, Cj and c, are determined by the solnbilities and diffusivities of hydrogen in A and B, and so they are not eqnal. The thermodynamic activity of hydrogen has a single valne at the interface, however. (Refer to Section 3.0.1 for a description of thermodynamic activity.) Hence, the treatment of diffusion flux in a composite wall is simplified by considering activity gradients rather than concentration gradients. If the dissolution of hydrogen gas in the solid follows the reaction... 

Propene to acrolein. Hildenbrand and Lintz87,88 have used solid electrolyte potentiometry to study the effect of the phase composition of a copper oxide catalyst on the selectivity and yield of acrolein during the partial oxidation of propene in the temperature range of 420-510°C. Potentiometric techniques were used to determine the catalyst oxygen activity, and hence the stable copper phase, under working conditions. Hildenbrand and Lintz used kinetic measurements to confirm that the thermodynamically stable phase had been formed (it is known that propene is totally oxidised over CuO but partially oxidised over ). 

So far we have derived an expression for the free energy of the solid phase under consideration after Libowitz, and discussed the composition or temperature dependence of the activity derived from this expression of free energy. Let us now consider non-stoichiometry from another point of view. 

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