Crystallization from supersaturated solutions

Crystallization from supersaturated solutions can occur by two processes, formation of new crystals or nucleation and growth on existing crystals. The internal surfaces of the scrubber can provide nucleation sites, thus resulting in scale formation. For many crystal systems, growth will occur without nucleation if suflBcient seed crystals are provided. Work by other investigators (3) has shown that supersaturated calcium sulfate solutions can be effectively desupersaturated by circulation of 1-5% gypsum seed crystals. 

PRIMARY NUCLEATION. In scientific usage, nucleation refers to the birth of very small bodies of a new phase within a supersaturated homogenous existing phase. Basically, the phenomenon of nucleation is the same for crystallization from solution, crystallization from a melt, condensation of fog drops in a supercooled vapor, and generation of bubbles in a superheated liquid. In all instances, nucleation is a consequence of rapid local fluctuations on a molecular scale in a homogenous phase that is in a state of metastable equilibrium. The basic phenomenon is called homogeneous nucleation, which is further restricted to the formation of new particles within a phase iminfluenced in any way by solids of... 

Table 1 lists theoretically possible polymorphs of chiral drugs and practical examples [13,21,28 35]. The most common are polymorphic enantiomers, polymorphic racemic compounds, and the existence of both a racemic conglomerate and a racemic compound of a chiral drug. Polymorphs may be discovered by crystallization from supersaturated solutions in various solvents, by solvent-mediated polymorphic transformation, by crystallization of amorphous solids under different conditions. 

Polyethylene is recognized as a semicrystalline polymer, where the prefix semi indicates that the material is not perfectly crystaUine (such as low molar mass compounds, e.g. dimethoxy biphenyl, which forms amazing crystals from supersaturated solutions) but rather is a nanophase-separated material that consists... 

All three types may be present in heat exchangers. Any object such as loose scale or other deposits resting on a metal surface can give rise to a concentration cell and hence to crevice corrosion, which is reported to be the most potentially damaging type of corrosion in a water cooling system. Corrosion products can nucleate crystallization from supersaturated solutions or subcooled melts, anchor... 

Bassam Z. Shakhashiri, "Crystallization from Supersaturated Solutions of Sodium Acetate," Chemical Demonstrations A Handbook for Teachers of Chemistry, Vol. 1 (The University of Wisconsin Press, Madison, 1983) pp. 27-30. 

The majority of the enantiomer separation methods based on crystallization involves solvent or solvent mixtures. Crystallizations from supersaturated solutions can be used both at the sepraration of enantiomeric mixtures, and at the separation of diastereoisomeiic mixtures. 

Lactose monohydrate By crystallization from supersaturated lactose solutions Binder, Diluent... 

Several applications of the SAMs have been demonstrated rather convincingly, e.g., as surface modifiers in corrosion protection or to manipulate the electron transfer rates from proteins to electrode surfaces [5], as alignment layers for liquid-crystalline samples [6], or for the induction of the nucleation and growth of inorganic crystals from supersaturated salt solutions [7],... 

S) Resolution by inoculated crystallization. Optically selective crystallization from supersaturated solution of a racemate after inoculation with unsym-metrical crystalline nuclei. 

Ammonium tetraborate tetrahydrate is prepared by crystallization from an aqueous solution of boric acid and ammonia having a B202 (NH4)20 ratio of 1.8 2.1. Ammonium pentaborate is similarly produced from an aqueous solution of boric acid and ammonia having a B202 (NH4)20 ratio of 5. Supersaturated solutions are easily formed and the rate of crystallization is proportional to the extent of supersaturation (130). A process for the production... 

Larson, M.A. and Klekar, S. A., 1973. In-situ measurement of supersaturation in crystallization from solution. Presented at American Institute of Chemical Engineers 66th Annual Meeting, Philadelphia, November. 

Sodium carboxymethyl chitin and phosphoryl chitin had most evident influences on the crystallization of calcium phosphate from supersaturated solutions. They potently inhibited the growth of hydroxyapatite and retarded the rate of spontaneous calcium phosphate precipitation. These chitin derivatives were incorporated into the precipitate and influenced both the phase and morphology of the calcium phosphate formed (flaky precipitate resembling octacalcium phosphate instead of spherical clusters in the absence of polysaccharide) [175]. 

A carboxylate derivative of a fully aromatic, water-soluble, hyperbranched polyphenylene is considered as a unimolecular micelle due to its ability to complex and solubilize non-polar guest molecules [23]. The carboxylic acid derivative of hyperbranched polyphenylene polymer (HBP) (My,=5750-7077, Mn=3810-3910) consists of 40-60 phenyl units that branch outward from a central point forming a roughly spherical molecule with carboxylates on the outer surface. The free acid form of HBP was suspended in distilled water and dissolved by adding a minimum quantity of NaOH. The solution was adjusted to pH 6.2 with aqueous HCl. Calcium carbonate crystals were growth from supersaturated calcium hydrogencarbonate solution at room temperature. HBP gave... 

Thus, we see that the digestive ripening process leads to highly monodispersed nanoparticles that can come together to form ordered superstructures similar to atoms or molecules that form crystals from a supersaturated solution. Then if the superstructure formation can indeed be related to atomic/molecular crystallization, it should also be possible to make these supercrystals more soluble in the solvent with a change of temperature. Indeed, the optical spectra of the three colloids prepared by the different thiols discussed above exhibit only the gold plasmon band at 80 °C suggesting the solubilization of these superlattices at the elevated temperatures [49]. 

EXAMPLE 16.1. A solution at 0°C contains 119g of sodium acetate per lOOg of water. If more sodium acetate is added, it does not dissolve, and no sodium acetate crystallizes from solution either. Describe the following solutions as saturated, unsaturated, or supersaturated. (a) lOOg sodium acetate in lOOg water at 0°C. (b) 150g sodium acetate in lOOg water at 0°C. (c) 11.9g sodium acetate in lO.Og water at 0°C. 

It is clear that low concentration, high temperature and long reaction time resulted in large particles. The formation of LDHs occurs by precipitation from supersaturated metal solution upon adjusting the pH. The crystal growth of the precipitation... 

Remove the hot saturated sugar solution carefully from the heat source and allow it to cool slowly. A supersaturated solution should result. A smooth container is critical so that the sugar doesn t start to crystallize before you re ready. 

The extraction apparatus is used chiefly for dissolving out sparingly soluble constituents from mixtures, and for isolating natural products from (dry) vegetable or animal material. Occasionally it is very useful for recrystallising sparingly soluble substances from the extraction thimble by means of an appropriate solvent (especially ether). As a rule, crystals of the dissolved material separate already from the solution in the flask during the process of extraction. This solution soon becomes supersaturated even while hot. 

In the present work, a constant composition method has been used to investigate the growth of HAP from solutions of low supersaturation and in the presence of different background electrolytes. The influence of magnesium and strontium ions both on the rate of crystallization and upon the electrokinetic properties of the crystallite surfaces has also been investigated. 

Crystallization Crystallization is used to separate the API from its solvent and impurities, or to separate racemic mixtures in solution. Crystallization occurs from a supersaturated solution. Important conditions are the temperature, concentration, stirring rate, and heating and cooling rate. Seeding with the desired API can assist in providing nucleation sites for the preferential crystallization of the API. 

For a solution supersaturated with solute, crystallization cannot take place in the absence of a higher-order process known as nucleation. In one sense, nucleation refers to any process affording a route for a substance from one physical phase to another, usually in the direction... 

The kinetic behaviour of fructose crystallization from aqueous ethanolIc solutions, typical in composition to those operated on an industrial scale, is strongly dependent on supersaturation, solvent composition and temperature. Provided the supersaturation is kept below 35 C of subcooling, nucleation does not occur. 

This observation is in accordance with the phenomena of the crystallization in the resolution operation mentioned above in the following points. There are no clear, definite critical supersaturations above which nucleation of D-threonine occurs. Ohtsuki (2), however, reported supersolubility curve for this system, who gave the value of the supersaturation width At=7 C at 50 C. Their definition of the metastablllty was that no nucleation of the enantiomer other than seeded one was observed for two hours of resolution experiments. According to this definition, the supersolubility can be determined to lie somewhere between At=8 and 5 C from the present experimental data, this being in agreement with his result. If the crystallization proceeds further, however, D-threonine crystals may start to crystallize from the solution even if the initial supersaturation is 5 C. In this sense it is no longer the metastablllty limit. 

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