Growth dispersion

Use of growth rate diffusivity (Randolph and White, 1977 Tavare and Gar-side, 1982) or size dependent growth (Abegg etal., 1968 Mydlarz and Jones, 1993) have both been proposed as alternative phenomenologieal means to deseribe the effeet of growth dispersion on erystal size distributions the latter being simpler mathematieally than the former, but in all probability both meehanisms ean oeeur. 

An increase in the spread of sizes in a batch crystallization could be due to size dependent growth or also growth dispersion. Whatever the cause, the spreading decreases substantially for the high alcohol content crystallizations. There seems to be no current explanation for this effect. In practical terms, this means that batch growth from alcoholic solutions should give a more uniform product than from aqueous solution. 

A size spread effect was observed. It is comparable with the growth dispersion effects found by Shiau and Berglund (10). The effect decreased with increasing ethanol content. 

Dayton, P. K., Observations of growth, dispersal and population dynamics of some sponges in McMurdo Sound, Antarctica, in Sponge Biology, Levi, C. and Bourny-Esnault, N., Eds., Centre National de la Recherche Scientifique (C. N. R. S.), Paris, 1979, 271. 

Ostwald ripening, growth dispersion, and size-dependent growth... 

It should be emphasized that in a real crystalhzer the assrmrptions of monodisperse seed material and of absence of nucleation and growth dispersion does not apply. The formation of secondary seeds by abrasion can considerably reduce the reqirired batch time in case of a constant supersaturation but impairs the particle size distribution toward smaller sizes. 

Figure 6.4.5. Crystal growth rates in an MSMPR crystallizer, (a) Constant size-independent growth rate, G. (b) Size-dependent growth rates, (c) Intrinsic growth dispersion three crystals i = 1, i = 2 and i = 3 have three fixed growth rates gtj, gr2 and grs, as they grow at different rates, as shown in part(d). (e) Random growth of one crystal with time, (f) Random growth rate of a growing crystal of part (e).

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