Crystal seeds mean diameter

A comparative study [10] is made for crystal-growth kinetics of Na2HP04 in SCISR and a fluidized bed crystallizer (FBC). The details of the latter cem be found in [11]. Experiments are carried out at rigorously controlled super-saturations without nucleation. The overall growth rate coefficient, K, are determined from the measured values for the initial mean diameter, t/po, masses of seed crystals before and after growth. The results show that the values for K measured in ISC are systematically greater than those in FBC by 15 to 20%, as can be seen in Table 2. On the other hand, the values for the overall active energy measured in ISC and FBC are essentially the same. 

A similar table summarizing the experimental data measured in the FBC. with the same mean diameters of crystal seeds, r/ l0, and under the same operating temperatures, T, was also obtained but it is not given here. 

The mean observed active energies obtained by regression of the experimental data for various crystal seeds with different mean diameters and in different crystallizers are listed in Table 12.4, where, similarly, the subscripts IS and FB denote the parameters in the impinging stream crystallizer and the fluidized bed crystallizer, respectively. ... 

To produce crystals with a mean diameter X and a narrow particle size distribution, control of the seed number is necessary. A crystal size density distribution, i. e., a balance for the number of crystals in each size... 

Figure 10.3 shows crystals obtained with different amounts of seeds (micronized substance with a mean diameter of around 3 pm). The grid lines have a distance of 100 pm. It should be noted that in this case the crystal size obtained with spontaneous nudeation is larger than that obtained with seeding. 

In comparison to other conventionally produced semicrystalline thermoplastics, PHB and the HB-HV copolymers have remarkably low nucleation densities in the absence of self-seeding or deliberately introduced nucleants (Table 5.6). This low nucleation density, which in practice means that it is possible to grow spherulites several millimetres in diameter on crystallization from the melt, is attributed to the purity of the fermentation-produced polymer, and in particular to the absence of inorganic catalysts residues. This absence of heterogeneous nucleation has led to a great deal of academic interest in the PHBV range of polymers as systems for the study of homogeneous nucleation kinetics, but the poor nucleation of the pure polymer is also of commercial... 

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