Crystallization during

Dissolve 12 g. of aniline hydrochloride and 6 g. of urea in 50 ml. of warm water, and then filter the solution through a fluted filter to remove any suspended impurities which may have been introduced with the aniline hydrochloride. Transfer the clear filtrate to a 200 ml. conical flask, fit the latter with a reflux water-condenser, and boil the solution gently over a gauze for about hours. Crystals of diphenylurea usually start to separate after about 30-40 minutes boiling. Occasionally however, the solution becomes supersaturated with the diphenylurea and therefore remains clear in this case, if the solution is vigorously shaken after about 40 minutes heating, a sudden separation of the crystalline diphenyl compound will usually occur. The further deposition of the crystals during the re-... 

A typical heat treatment cycle, as illustrated in Figure 1, comprises both nucleation and crystallization temperature holds, but some glass-ceramics are designed to nucleate and/or crystallize during the ramp itself, eliminating the need for multiple holds. 

Crystallization. Raw natural mbber may freeze or crystallize during transit or prolonged storage, particularly at subzero temperatures. The mbber then becomes hard, inelastic, and usually much paler in color. This phenomenon is reversible and must be differentiated from storage hardening. The rate of crystallization is temperature-dependent and is most rapid at —26° C. Once at this temperature, natural mbber attains its maximum crystallinity within hours, and this maximum is no more than 30% of the total mbber. 

The use of a wide-bore condenser and a simple receiver, without a stopcock, is preferable. Usually the product does not solidify at once, but occasionally it crystallizes during distillation. The use of a fraction cutter is not necessary or advisable. 

The sebacil may tend to crystallize during filtration if the reaction mixture is too cool,... 

A solution of 10.0 g. (0.25 mole) of sodium hydroxide in 250 ml. of water is prepared in a 1-1. round-bottomed flask equipped with a reflux condenser and a mechanical stirrer. Twenty-five grams (0.065 mole) of N,N-dimethylaminomethylferrocene methiodide is added to the solution. The resulting suspension is heated to reflux temperature with stirring. At this point the solid is in solution. Within 5 minutes oil starts to separate from the solution and trimethylamine starts to come off. At the end of 3.5 hours, at which time the evolution of the amine has virtually ceased, the reaction mixture is allowed to cool to room temperature. The oil generally crystallizes during the cooling. The mixture is stirred with 150 ml. of ether until the oil or solid is all dissolved in the ether. The ether layer is separated in a separatory funnel and the aqueous layer is extracted with two additional 150-ml. portions of ether. The combined ether extracts are washed once with water and dried over sodium sulfate. 

Hydroxycortisone BMD) (48) A solution of 4 g of 17a,20 20,21-bis-methylenedioxypregn-4-ene-3,l 1-dione (cortisone BMD) (46) dissolved in 300 ml of t-butanol and 5 ml of water is treated with 34 ml of 35 % hydrogen peroxide and 0.45 g of osmium tetroxide predissolved in 36 ml of /-butanol. The resulting mixture is allowed to stand at room temperature for 2 days. Diol (47) which crystallizes during the reaction is collected by filtration and washed with /-butanol and water. The filtrate is diluted with ethyl acetate and washed sequentially with aqueous sodium chloride, aqueous 10% sodium bisulfite, aqueous 10% sodium bicarbonate and finally with water to neutrality. The solvent is evaporated and a second crop of the diol (47) is collected, providing a total of about 3.8 g. 

N. Miyazaki, S. Okuyama. Development of finite element computer program for dislocation density analysis of bulk semiconductor single crystals during Czochralski growth. J Cryst Growth 183 S, 1998. 

In a 250-ml. round-bottomed flask equipped with a gas-inlet tube and reflux condenser 20 g. (0.094 mole) of N.N -diphenyl-ethylenediamine (1,2-dianilinoethane) (Note 1) and 100 ml. of purified triethyl orthoformate (Note 2) are heated by an oil bath under nitrogen (Note 3) for 5 hours. The oil bath is maintained between 190° and 200°, and water is allowed to stand in the condenser. The water in the condenser begins to boil slowly, and the alcohol which is produced is allowed to escape (Note 4). The reaction product which crystallizes during the reaction is filtered after cooling and washed with ether. There is obtained 19-20 g. (91 95%) of product, m.p. 285° (dec.) (Note 5). 

Figure 52.7. Difference spectra of the Nafion-Ti02 film coated on the ATR crystal during UV illuntination for (a) 2 1 and (b) 1 1 Nafion Ti02 weight ratio films.

Many polymers solidify into a semi-crystalline morphology. Their crystallization process, driven by thermodynamic forces, is hindered due to entanglements of the macromolecules, and the crystallization kinetics is restricted by the polymer s molecular diffusion. Therefore, crystalline lamellae and amorphous regions coexist in semi-crystalline polymers. The formation of crystals during the crystallization process results in a decrease of molecular mobility, since the crystalline regions act as crosslinks which connect the molecules into a sample spanning network. 

Although 550 suffices to dissolve the w-nitroacetophenone it is desirable to bring the alcoholic solution to a boil to avoid crystallization during filtration. 

To prevent the formation of wine crystals during the bottling process, winemakers use a method known as cold stabilization. By lowering the temperature of the wine to 19-23°F for several days or weeks, the solubility of tartrate crystals is lowered, forcing the crystals to sediment. The resulting wine is then filtered off the tartrate deposit. The temperature dependence of the solubility of potassium bitartrate is readily apparent in the following comparison while 162 ml of water at room temperature dissolves 1 g of the salt, only 16 ml of water at 100°C are needed to solubilize the same amount of saltJ l Recent developments employ a technique known as electrodialysis to remove tartrate, bitartrate, and potassium ions from newly fermented wine at the winery before potassium bitartrate crystals form. 

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