Crystallization germs

Stochastic processes arise more frequently, than perhaps one may think at first sight. We remind the actual movement of a projectile with appropriate dispersion on the target, the formation of crystallization germs, the formation of blisters in... 

Defects, particularly screw dislocations, play an important role in the growth of true crystals [9]. Liquid crystal germs present the defects that were described in detail by Frie-del and Grandjean [21] for smectic A phases. The germs elongate perpendicular to the mean direction of the layers, the surface tension being anisotropic, and the focal domains present in the batonnet are arranged such that the layers lie normal to the isotropic interface. A focal line is often present... 

Keim, m. germ embryo (of crystallization) nucleus, seed sprout, shoot. 

Transfomation from a meta-stable phase, such as supersaturated solution, to a thermodynamically more favorable phase requires first the crystal nucleation of a germ of the new phase. According to the classical nucleation theory, the volume nucleation rate J (cm" sec ), describing the number of nuclei(i.e., a critical germ) formed per volume per time, is given by ... 

We assume, for our analysis on small particles, that the overall crystallization time is limited by the nucleation time for a single germ. 

There is almost no degree of freedom in the choice of the crystallizer type Crystallization in fine chemicals manufacture is usually carried out in jacketed stirred tanks. Coils can also be used to enhance cooling, but crystals are often formed on their surface. This encrustation results in a large increase of the thermal resistance, and, consequently, a decrease of the cooling capability of the tank. Any roughness of inner surfaces of the tank can be a germ for crystals, particularly the cooled surfaces. Therefore, crystallizers are often made with polished cooled surfaces. 

TENGLER, T. and Mersmann, A. Germ. Chem. Eng. 7 (1984) 248-259. Influence of temperature, saturation and flow velocity on crystal growth from solutions. 

Guanidine is a strong base, which is found in a variety of natural products. These products include turnip juice, mushrooms, com germ, rice hulls, mussels, and earthworms from which it can be extracted with alcohol. Guanidine forms deliquescent crystals with a melting point of 50 Celsius. It absorbs carbon dioxide from the air, and is very soluble in water and alcohol. It is manufactured on an industrial scale from sulfur dioxide, carbon dioxide, and ammonia gases. Guanidine is a readily available commercial chemical. 

C.S. Wright. 1992. Crystal structure of a wheat germ agglutinin/ glycophorin-sialoglycopeptide receptor complex Structural basis for cooperative lectin-cell binding J Biol. Chem. 267 14345-14352. (PubMed)... 

These mordant-dyeing properties are found in a much higher degree in the bodies obtained by action of nitrodiazo-compounds on salicylic acid (Germ. Pat. 44170, 16 Nov., 1887). The dyestuff from metanitrodiazobenzene and salicylic acid comes into commerce as Alizarin Yellow G, and produces a fine yellow lake with chromium oxide. The pure dyestuff crystallizes from alcohol in light yellow needles. M.P. about 230°. Its constitution may be expressed by the formula —... 

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