Crystallization kinetics particles

Modified amino acids such as N-acyl-dehydroalanine polymers and copolymers with N-vinyl-N-methyl acetamide seem to be particularly effective [396]. The crystallization kinetics in the presence of polyvinylpyrrolidone and tyrosine have been tested by time-resolved experiments [981]. An influence is evident on the particle size distribution of the hydrate [1433]. 

When the crystal purity is plotted against the total crystal mass in the slurry calculated from the mass balances, the purity decrease seems to start at some constant value of the crystal mass as shown in Figure 5. As mentioned earlier in the text, there are possibilities of existence of the D-enantiomer as small particles on the surface of the seed crystals. If we assume that the breeding of the D-enantiomer starts only when that enantiomer has grown to a certain size, the amount of the L-enantiomer crystals must have also increased to a certain value, the latter being proportional to the former. The crystallization kinetics of the both enantiomers are believed to be the same, the relative amounts of crystals of the both enantiomers must therefore be constant before nucleation of the D-enantiomer starts. 

Crystallization kinetics. Figure 5 shows the relation between the dominant particle size Im and the residence time 0 for each run. Im decreases linearly with increase of 0 in log-log plot. The slope of lines decreases with the addition of NaCl. 

In semi-crystalline polymers the interaction of the matrix and the tiller changes both the structure and the crystallinity of the interphase. The changes induced by the interaction in bulk properties are reflected by increased nucleation or by the formation of a transcrystalline layer on the surface of anisotropic particles [48]. The structure of the interphase, however, differs drastically from that of the matrix polymer [49,50]. Because of the preferred adsorption of large molecules, the dimensions of crystalline units can change, and usually decrease. Preferential adsorption of large molecules has also been proved by GPC measurements after separation of adsorbed and non-attached molecules of the matrix [49,50]. Decreased mobility of the chains affects also the kinetics of crystallization. Kinetic hindrance leads to the development of small, imperfect crystallites, forming a crystalline phase of low heat of fusion [51]. 

Now, knowing the strong influence of particles (nuclei-I) on the overall crystallization kinetics, the increase of the crystallization rate with the gel ageing at ambient temperature (6,12,13,44,45) can be explained by the increase in the number of nuclei-I and/or the number of nuclei-II, respectively, during the gel ageing (11,12). 

With the advancement of online measurement techniques such as focused beam reflectance measurement (FBRM) and Fourier transform infrared (FTIR), it is now possible to obtain particle size distribution and solution concentration information rapidly through these in-situ probes. In one experiment, hundreds of data points can be generated. With proper experiment design, the model-based experimental design for crystallization is capable of obtaining high-quality crystallization kinetic data with a small number of experiments. This approach can thus save significant experimental effort and time in the development of crystallization processes. 

In comparison to the original solvent pair of MeOH/IPAC, the compound exhibited significantly different crystallization kinetics in the new DMF/IPAC system. Figure 9-20 shows the microscopic photo of the slurry sample when the antisolvent IP AC was charged to the solvent DMF (normal or forward addition). The particles were much finer in the DMF/IPAC system than those from the original MeOH/IPAC system. Fortuitously, the particle size was similar to that of the milled material and met... 

Because the rate of creation of supersamration in reactive crystallization is dependent on the reaction kinetics, control of particle size can be difficult because slowing down the reaction is often difficult or undesirable. For compounds with fast crystallization kinetics, traditional methods such as reduced concentration and temperamre may help, but the range of improvement may not be significant. 

The crystal growth rates of PVDF, PA-6, and POM amount to at least lOpm/min in the temperature range where their crystallization steps occur (6,52,67). A dispersed particle, therefore, once nucleated, crystallizes promptly and the primary rather than the secondary nucleation is the rate-controlling factor of the crystallization kinetics of the dispersed phase. Thus, the crystallization temperatures as observed in the DSC-cooling run agree roughly with the nucleation temperatures. 

Dirksen JA, Ring TA. Fundamentals of crystallization Kinetic effects on particle size distributions and morphology. Chem Eng Sci 1991 46), 2389-2427. 

Figures 3 and 4 are based on the maintenance of the same crystal shape as the size varies. For small particles, needles or even two-dimensional shapes may predominate, as discussed by Bond (21). More subtle changes may occur, such as the replacement of cubooctahedrons by icosahedrons for crystals of d < 2 nm. For large crystals kinetic effects during the preparation may cause deviations from the expected equilibrium distribution of faces, often assumed to be equal portions of the (111), (100), and...

The multi-component, multiphase nature of polymer blends affects crystallization kinetics, crystalhne morphology and level of crystallinity [Nadkami and Jog, 1991]. In particular, the presence of one polymer may affect the crystallization of the other, the phase boundary enhancing nucleation of crystalhzation. If the two blend components have different crystalhzation temperatures, which is likely, the solid particles of the higher melting component will nucleate crystalhzation of the lower melting component. 

In calcium hydroxide, Na and Ca hardly influence the dominant particle size. Then it is considered that the crystallization kinetics of magnesium hydroxide does not depend on the cation in the crystallizer, but on the properties of each alkali feed as shown in Figure 5. 

Equations E23.2.8 and E23.2.9 can be solved using the appropriate initial and boundary conditions to compute the concentrations of A in the continuous and microphases as functions of time. However, these model equations depend on the average particle diameter, surface area, and volume of the microphase. Because they are constantly changing as more crystals nucleate and grow, complete knowledge of the crystallization kinetics of calcium sulfate is necessary to solve the equations. 

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