Composition of crystals

Table I lists the results of spectroscopic studies of iV,iV-dimethylaniline in zeolite samples 1, 2, 3, and 4. The spectral data show that the correlation of the number of different types of sites depends on the temperature of preliminary thermal activation, and the amount of different types of sites depends on the composition of crystals for various samples of zeolites treated at one temperature. Among the zeolites studied, sample 3 differs from samples 1,2, and 4 by its activity in the dark. The crystal compositions show that this sample has the highest degree of exchange of Na+ for NH4+.

Given Equation (16) we derived, by nonlinear least-squares fitting, values of r from a total of 82 experiments in which three or more clinopyroxene-liquid REE partition coefficients were measured and in which the compositions of crystal and liquid phases were well constrained. Adopted radii values for individual REE were those of Shannon (1976) for 3+ ions in VIII coordination. Resulting values of range from 0.979 A to 1.055 A. We performed stepwise linear regression of the derived values of r against all major compositional parameters, pressure and temperature. The result was that the only important parameters appeared to be the octahedral (Ml) A1 content and the calcium content of the M2-site. Fitting Tq to these parameters yields an equation which reproduces the 82 points with a standard deviation of 0.009 A (i.e., less than the difference in ionic radius between adjacent REE) ... 

In some zeolite crystallization in heterogenous aluminosilicate systems, temperature is mainly a kinetic factor whereas the nature and composition of crystals are determined by concentrations and correlations of components. Studies of their chemical structure and the peculiarities of crystallization kinetics show that a solubility equilibrium exists between the solid and liquid phases of gels. Gel crystallization on heating is preceded by increased component concentrations in the liquid phase, which determines the composition of the zeolite crystals formed. Decreases in liquid component concentrations are compensated by dissolution of the solid phase of gels. This explains the linear rate of crystal growth during the first part of the crystallization process. Crystal size distribution for zeolite A and the linear rate of crystal growth indicate the autocatalysis of zeolite crystallization. 

As follows from our published data (37, 39) and the data of Table I on the crystallization of any zeolite in the heterogenous aluminosilicate systems, the nature and composition of crystals are determined directly by the composition of the liquid phase. Concentrations and correlations of components in the liquid phases of the heterogenous aluminosilicate mixtures needed for the beginning of crystallization can be reached by dissolving the solid phase. The rate of dissolution increases with increasing temperature and alkali concentration, reducing the induction period (16,20). 

As the nuclei and crystals grow at the expense of components of the liquid phase of gels, the composition of crystals should depend on that of the liquid phase. This is confirmed by the data given in Table VI. 

To understand how temperature influences the composition of crystals that form, it is useful to examine typical solubility-temperature diagrams for substances exhibiting monotropic and enantiotropic behavior [15], In Fig. la, Form II, having the lower solubility, is more stable than Form I. These two noninterchangeable polymorphs are monotropic over the entire temperature range shown. For indomethacin, such a relationship exists between Forms I and II, and between Forms II and III. 

Experiments were done, using a batch crystallizer apparatus as shown in Fig.l, varying the Mg/P molar ratio from 1-4. The experimental conditions are shown in Table 2. During the process of batch crystallization, the mixed suspension was sampled at the determined crystallization time. The samples were filtered through 0.45 fjL m membrane filter, and the concentrations in the filtrate were measured. Also sampled crystals were obtained when the concentration was observed to be constant, to be observed by SEM and be analyzed by the Xray diffractometer. The composition of crystals was analyzed after dissolution by a pH 2 HCl solution. 

Compositions derived from tensimetric experiment ( 0.004) Compositions of powdered samples from the chemical method ( 0.08) Compositions of crystals from the chemical method ( 0.01)... 

Degree of Precipitation and Composition of Crystals of PEO/PS Block Copolymers B and E Obtained in Ethylbenzene (EB) and Amyl Acetate (AA) at Different... 

Thus, in a quantitative manner, the dimensions and composition of crystals of block polymers can be related to the composition of the parent block copolymer and to the thermodynamic goodness of the solvent used as crystallization medium. 

This expression is known as the logarithmic distribution law (Doener-Hoskins rule). Chemical compositions of crystal and aqueous solution vary depending on k. 

We have thus demonstrated that (1) anionic surfactants can control the composition of crystallizing calcium oxalates (Fig. 8), whereas (2) both anionic and cationic surfactants inhibit the solution-mediated phase transformation of COD into the thermodynamically stable COM (Fig. 9). Both results can be readily explained if one considers the respective adsorption isotherms and adsorption densities of surfactants at COM and COD crystal/solution interfaces (see Fig. 10 and Table 2) [68,69]. 

During the dehydration of a salt hydrate both the structure and the composition of the initial crystal change to produce the new crystalline phase and water vapor. The processes are therefore more complex than the transformation at constant composition of crystals such as tin ( ), sulfur ( ), and silver nitrate ( ). 

The expression (14.16) establishes the interrelationships between crystallization rate, feeding rate and composition, growing crystal diameter and composition. Appropriately, all of those values acquire the status of controlling parameters and they can be used to control the composition of crystals grown. 

The base and impurity compositions of crystals are influenced by the crystal growth kinetics. Growth by sublimation is performed at rather low temperatures, below 0.7 T. In addition, the normal growth rates are considerably higher than those of self-diffusion of the components, i.e., of silicon and carbon, in the lattice. It follows that SiC crystal growth takes place in the... 

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