Solid-solution component mechanism

In this case, two components, which are by themselves not photochemically stable, form a durable solid solution. The mechanism for this stabilization is not known. It is, however, certain that these stabilizers, and certain others which were similarly tested, were all amines, which under the influence of light, are subject to loss of a p-electron. If this were the key to such stabilization, a free radical cation (37) would be generated. On the other hand, it has been demonstrated that quinacridonequinone itself initially undergoes rapid photoreduction in conventional binders. Thus, it is extremely likely that the quinacridonequinone (QAQ) molecule abstracts an electron from the binder in its initial process of reduction to generate the intermediate free radical anion 36 (Scheme 18-12). 

The dominant mechanism of purification for column ciystallization of sohd-solution systems is reciystallization. The rate of mass transfer resulting from reciystallization is related to the concentrations of the solid phase and free hquid which are in intimate contac t. A model based on height-of-transfer-unit (HTU) concepts representing the composition profQe in the purification sec tion for the high-melting component of a binaiy solid-solution system has been reported by Powers et al. (in Zief and Wilcox, op. cit., p. 363) for total-reflux operation. Typical data for the purification of a solid-solution system, azobenzene-stilbene, are shown in Fig. 22-10. The column ciystallizer was operated... 

The partial molar entropy of a component may be measured from the temperature dependence of the activity at constant composition the partial molar enthalpy is then determined as a difference between the partial molar Gibbs free energy and the product of temperature and partial molar entropy. As a consequence, entropy and enthalpy data derived from equilibrium measurements generally have much larger errors than do the data for the free energy. Calorimetric techniques should be used whenever possible to measure the enthalpy of solution. Such techniques are relatively easy for liquid metallic solutions, but decidedly difficult for solid solutions. The most accurate data on solid metallic solutions have been obtained by the indirect method of measuring the heats of dissolution of both the alloy and the mechanical mixture of the components into a liquid metal solvent.05... 

Two product barrier layers are formed and the continuation of reaction requires that A is transported across CB and C across AD, assuming that the (usually smaller) cations are the mobile species. The interface reactions involved and the mechanisms of ion migration are similar to those already described for other systems. (It is also possible that solid solutions will be formed.) As Welch [111] has pointed out, reaction between solids, however complex they may be, can (usually) be resolved into a series of interactions between two phases. In complicated processes an increased number of phases, interfaces, and migrant entities must be characterized and this requires an appropriate increase in the number of variables measured, with all the attendant difficulties and limitations. However, the careful selection of components of the reactant mixture (e.g. the use of a common ion) or the imaginative design of reactant disposition can sometimes result in a significant simplification of the problems of interpretation, as is seen in some of the examples cited below. 

For example, a synergistic defoaming occurs when hydrophobic solid particles are used in conjunction with a liquid that is insoluble in the foamy solution [652]. Mechanisms for film rupture by either the solid or the liquid alone have been elucidated, along with explanations for the poor effectiveness, which are observed with many foam systems for these single-component defoamers. 

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. 

Such a proof of the carbon monoxide oxidation was first given by one of us (28). It is very important to remark that the catalysts containing impurities were prepared by firing together in air at 600°C. for 3 hr. a mechanical mixture of the required components in adequate proportions. As pointed out by Fensham (54), this is much too low a temperature to ensure homogeneous solid solutions. Consequently, when a catalyst is described as NiO + 0.1% Li2O, there is no assurance that this nominal composition is realized at all either in the surface layer or in the bulk of the sample. As will be shown, this reservation is quite essential. 

With binary and ternary supercritical mixtures as chromatographic mobile phases, solute retention mechanisms are unclear. Polar modifiers produce a nonlinear relationship between the log of solute partition ratios (k ) and the percentage of modifier in the mobile phase. The only form of liquid chromatography (LC) that produces non-linear retention is liquid-solid adsorption chromatography (LSC) where the retention of solutes follows the adsorption isotherm of the polar modifier (6). Recent measurements confirm that extensive adsorption of both carbon dioxide (7,8) and methanol (8,9) occurs from supercritical methanol/carbon dioxide mixtures. Although extensive adsorption of mobile phase components clearly occurs, a classic adsorption mechanism does not appear to describe chromatographic behavior of polar solutes in packed column SFC. 

Solid solution theory The chemical theories of primary importance to understanding factors controlling carbonate mineral compositions in natural systems are associated with solid solutions. Carbonate minerals of less than pure composition can be viewed as mixtures of component minerals (e.g., SrCC>3 and CaSC>4 in CaCC>3). If the mixtures are of a simple mechanical type then the free energy of formation of the resulting solid will be directly proportional to the composition of the aggregate. Thus, for a two component, a and b, mixture ... 

The various classes of metallic phases that may be encountered in crystalline alloys include substantially pure elements, solid solutions of one element in another and intermetallic compounds. In crystalline form, alloys are subject to the same type of defects as pure metals. Crystalline alloys may consist of a solid solution of one or more elements (solutes) in the major (base) component, or they may contain more than one phase. That is, adjacent grains may have slightly or extremely different compositions and be of identical or disparate crystallographic types. Often, there is one predominant phase, known as the matrix, and other secondary phases, called precipitates. The presence of these kinds of inhomogeneities often results in the alloy having radically different mechanical properties and chemical reactivities from the pure constituent elements. (Noel)5... 

Mechanization and automation are possible in the synthesis of peptides using solid polymeric active esters also. By passing a solution of the amine component in a suitable solvent through a column packed with the solid polymeric activated carboxyl component, mechanization could be effected. The product, the protected peptide, which is in the eluent, is then N-deprotected, and the product in solution is passed... 

A sessile drop experiment can take one of several forms, as shown schematically in Figure 3.7. The classic form shown in Figure 3.7.a calls for a small piece of solid sessile drop material, typically 0.01 ml in volume, to be placed on a substrate and then heated above its melting temperature. The sessile drop can be composed of a pure material or it can be an alloy or a chemical compound. It is not always convenient to prepare alloys or compounds prior to conducting the sessile drop experiment, and a variant of the classic technique, shown in Figure 3.7.b, is to form the alloy or compound in situ from a mechanical mixture of the components, (Mortimer and Nicholas 1973). In some work done in the former Soviet Union, metal alloys were formed in situ by plunging a piece of solid solute into a molten sessile drop of solvent (Naidich and Zhuravlev 1971). 

Deployment of MDPs, which are solid solutions of a transport-active species (typically in the range 30-50 wt %) in an inert host polymer, embodies the concept of full compositional control of mobility (53), Transport molecules are chosen with the aim of rendering accidental contaminants electrically inactive. The concentration of small molecules controls drift mobility. Appropriate choice of a compatible host polymer can then focus on mechanical properties and environmental stability. MDPs are limited by phase separation, crystallization, and leaching by contact with the development system, cleaning solvent, etc. These problems continue to motivate the search for single-component transport polymers. 

Another name for solid hydrogel transformation mechanism is solid-phase mechanism, while solution-mediated transport mechanism is also called liquid-phase mechanism. The main difference in explaining the formation process of zeolites by these two mechanisms lies in whether the liquid component is involved during the crystallization of zeolites. The views of these two mechanisms are opposite to each other and have their own experimental supporting evidence. To date, the liquid-phase mechanism has more experimental support than does the solid-phase mechanism. 

A and, finally, the plane Ass + B is the region of coexistence of both solid phases, i.e. the crystals of the saturated solid solutions of the component in component A and the crystals of the component B. It deals thus again with the mechanical mixture of both the solid phases. 

For the molar Gibbs free energy of the solid solution (G. ) this mixing term is added to the contribution from mechanical mixing of the components to form the solid solution, or... 

Much of the understanding of the solid state mechanism of heterogeneous catalysis stems from fundamental studies of single phase model compounds (1-5). In many cases, the role of a metal component in a catalytic process has been discerned through its incorporation into solid solutions of relatively inert host matrices (O. In the case of the selective oxidation and... 

The two-component crystal may be divided into three categories 1.) mixed crystal (solid solution), 2.) crystalline molecular compounds, 3.) a simple mechanical mixture of component crystals. I propose the term mixed molecular crystal to represent both mixed crystal and crystalline molecular compounds and have used it as such in the title of this chapter. 

When acetylene gas is polymerized in a solid solution of the Shirakawa catalyst and polybutadiene, a heterogenous blend consisting of a amorphous polybutadiene phase and a crystalline polyacetylene phase is formed. (5) The mechanical and electrical properties of this composite are critically dependent on the composition of the blend components and on their relative arrangement. In our initial Blend paper, (5) for example, we showed that the mechanical properties of PA/PB blends are a function of the blend composition, with low polyacetylene compositions ex-... 

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