Growth rates solution

Alonso C, Salvarezza R C, Vara J M and Arvia A J 1990 The meohanism of silver (I) oxide formation on polyorystalline silver in alkaline solution. Determination of nuoleation and growth rates Electrochim. Acta 35 489-96... 

Over 50 acidic, basic, and neutral aluminum sulfate hydrates have been reported. Only a few of these are well characterized because the exact compositions depend on conditions of precipitation from solution. Variables such as supersaturation, nucleation and crystal growth rates, occlusion, nonequilihrium conditions, and hydrolysis can each play a role ia the final composition. Commercial dry alum is likely not a single crystalline hydrate, but rather it contains significant amounts of amorphous material. 

Fig. 8. Effect of solution velocity on the growth rate of the < 110 > face of MgS04-7H2 0. Concentration of MgSO ...

Effects of Impurities nd Solvent. The presence of impurities usually decreases the growth rates of crystalline materials, and problems associated with the production of crystals smaller than desired are commonly attributed to contamination of feed solutions. Strict protocols should be followed in operating units upstream from a crystallizer to minimize the possibiUty of such occurrences. Equally important is monitoring the composition of recycle streams so as to detect possible accumulation of impurities. Furthermore, crystalliza tion kinetics used in scaleup should be obtained from experiments on solutions as similar as possible to those expected in the full-scale process. 

The effects of a solvent on growth rates have been attributed to two sets of factors (28) one has to do with the effects of solvent on mass transfer of the solute through adjustments in viscosity, density, and diffusivity the second is concerned with the stmcture of the interface between crystal and solvent. The analysis (28) concludes that a solute-solvent system that has a high solubiUty is likely to produce a rough interface and, concomitandy, large crystal growth rates. 

M. Ohara and R. C. Reid, Modeling Cystal Growth Rates from Solution, Prentice-Hall Press, Englewood Cliffs, N.J., 1973. 

Modeling of Chemioal Kinetios and Reaotor Design Evaluate the and the speeifie growth rate X Solution... 

Sinee the kinetie proeesses oeeur eonseeutively, the solution eoneentration adjusts itself so that the rates of the two steps are equal at steady state. In most eases, more than one meehanism influenees a erystal s growth rate. If the different meehanisms take plaee in parallel, then the meehanism resulting in the faster growth eontrols the overall rate. If the proeesses take plaee in series, as in the ease of bulk diffusion followed by surfaee reaetion, then the slower meehanism will eontrol the overall rate. 

Impurities usually eause a reduetion in the growth rates of erystalline materials due to bloeking of kink sites, thereby leading to smaller erystals than required. This is a eommon problem, whieh is often related to eontamination of the feed solution. In some other eases, however, impurities ean enhanee growth rates, thought to be due to a reduetion in interfaeial tension and lienee inerease in surfaee nueleation rates. 

Growth rate fluetuations appear to inerease with an inerease in temperature and supersaturation leading to erystals of the same substanee, in the same solution at identieal supersaturation, exhibiting different growth rates this is thought to be a manifestation of the phenomenon of either size-dependent crystal growth or alternatively, growth rate dispersion. 

Figure 5.7 Effect of solution velocity on crystal growth rates after Miillin and Garside, 1967) number Sh = IcLjD, the partiele Reynolds number...

This equation was then solved numerieally with known values of erystal growth rate (G) and solubility dc jdO) for seeded solutions. It was further assumed that if G f G(L, 6), dc /d6 = eonstant and dAc/d6 = 0 then the simplified equation for ealeulating transient temperature results (Mullin and Nyvlt, 1971)... 

The data plotted in the figure clearly support the predicted positive dependence of crystal size on agitation rate. Precipitation in the crystal film both enhances mass transfer and depletes bulk solute concentration. Thus, in the clear film model plotted by broken lines, bulk crystal sizes are initially slightly smaller than those predicted by the crystal film model but quickly become much larger due to increased yield. Taken together, these data imply that while the initial mean crystal growth rate and mixing rate dependence of size are... 

O Hara, M. and Reid, R.C., 1973. Modelling Crystal Growth Rates from Solution. Englewood Cliffs Prentice-Hall. 

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