Initiation of crystallization

The screw clamp may be adjusted so that there will be a spattering on the upper, cool part of the flask, while the pressure is still maintained below 30 mm. Under these conditions, the initiation of crystallization is speeded. 

Fig. 12 Normalized invariant /orient of DPLS intensity for PET as a function of annealing time at 80 °C [11]. The invariant giving orientation fluctuations is normalized to that for a sufficiently annealed sample which was taken to be unity. Arrow indicates the initiation of crystallization...

Initiation of crystallization, either spontaneously or by seeding with a small quantity of lactose crystals. 

A key to the development of osteoblasts appears to be an osteoblast-specific transcription factor OS/2 or Cbfal.693-695 Mutations in human Cbfal are linked to a series of skeletal defects.696 A unique change accompanying conversion of a precursor cell into an osteoblast is the formation of a 49-residue y-carboxyglutamate (Gla)-containing protein called osteocalcin.697 (See also Box 15-F). It is the most abundant noncollagenous protein of bone. Its three Gla residues doubtless help to bind calcium ions and osteocalcin may be an initiator of crystallization. Osteocalcin has also been found in fish scales.698 Also present in bone is a 74-residue matrix Gla protein which has 5 Gla residues.699... 

The initiation of crystallization indicates the optimum reaction temperature for the catalyzed cyanosilylation of p-benzo-quinone. The use of higher temperatures results in excessive darkening of the product and a decrease in yield. 

Crystallization from an overall viewpoint represents transfer of a material from solution (or even a gas) to a solid phase by cooling, evaporation, or a combination of both. But there is more to it. Of considerable importance are economics, crystal size distribution, purity, and the shape of the crystals. Impurities or mother solution are carried along only in the surface or occlusions in the crystals. The partical size distribution depends on the distribution of seed crystals, which are injected into the crystallizer prior to initiation of crystallization (batch) or continuously from recycled undersized particles, the mixing in the system, the crystal growth rate, and the degree of supersaturation of the mother liquor. As in shown in the figures, both batch and continuous crystallization are used in industry. 

In production, the API solution is usually clear-filtered prior to the initiation of crystallization in order to remove any solid dust particles or abraded particles from seals, and so forth, which might otherwise contaminate the API. 

In most cases, workers who calculate apatite saturation temperatures fail to make these corrections (in part due to their difficulty) although in some systems the corrections are small (for example, volcanic systems with low degrees of crystallization), however, they may be significant for mafic systems where initiation of crystallization of apatite occurs significantly below the liquidus. For the calculations that follow, either the AST can be used, or calculations can be performed using model temperatures (e.g., see... 

Fig. 6-1. The influence of the saturation ratio = (Ca JfCOa J/Kso.cacoj) on the initiation of crystal formation for CaCOa-...

Nncleation depends on the total surface area of the crystals. If the total crystal surface area is relatively small in relation to the degree of supersaturation, nuclei, i.e., small crystals, will be formed after the initiation of crystallization. However, if the crystal surface area is sufficiently large, the level of snpersaturation will be reduced through the growth of existing crystals. 

Legend has it that an organic chemist resisted an invitation to leave a weU-worn laboratory for new quarters because he suspected that the older laboratory (in which many crystallizations had been carried out) harbored seed crystals for a large variety of substances the chemist needed. Carried by dust from the earlier work, these traces of material presumably aided the successful initiation of crystallization of reluctant materials. Further support for this legend comes from the often quoted (but never substantiated) belief that after a material was first crystallized in a particular laboratory, subsequent crystallizations of the material, regardless of its purity or origin, were always easier. 

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