Crystal, Crystallization

Structure Crystal Crystal Crystal Crystal Amorphous Amorphous Amorphous Amorphous ... 

Contact nucleation is the most common mechanism of secondary nucleation. Crystal-crystal-, crystal-impeller, and crystal-wall collisions are involved. Secondary nuclei arise from microabrasion (crystal surface damage) or ordered cluster removal by fluid shear forces, as noted above. Figure 4-12 shows that for a given substance, impeller speed and material of construction can both play a role. 

Collisional break-up of crystals suspended in stirred vessels may occur as a result of collision between crystal-crystal, crystal-impeller or crystal-vessel, and has been described by many authors e.g. Ottens and de Jong (1973), Kuboi etal. (1984), Mazzarotta (1992). 

Appearance Crystal Colorless crystals Colorless crystals Crystal Crystal... 

Melt Crystallization. Crystallization (qv) from a melt is inherently more attractive than distillation because the heat of fusion is much lower than that of evaporation. It also benefits from lower operating temperature. In addition, organic crystals are virtually insoluble in each other so that a pure product is possible in a one-stage operation. 

Secondary nucleation is crystal formation through a mechanism involving the solute crystals crystals of the solute must be present for secondary nucleation to occur. Thorough reviews have been given (8,9). 

Preferential Removal of Crystals. Crystal size distributions produced ia a perfectiy mixed continuous crystallizer are highly constraiaed the form of the CSD ia such systems is determined entirely by the residence time distribution of a perfectly mixed crystallizer. Greater flexibiUty can be obtained through iatroduction of selective removal devices that alter the residence time distribution of materials flowing from the crystallizer. The... 

Batch Crystallization. Crystal size distributions obtained from batch crystallizers are affected by the mode used to generate supersaturation and the rate at which supersaturation is generated. For example, in a cooling mode there are several avenues that can be followed in reducing the temperature of the batch system, and the same can be said for the generation of supersaturation by evaporation or by addition of a nonsolvent or precipitant. The complexity of a batch operation can be ihustrated by considering the summaries of seeded and unseeded operations shown in Figure 19. 

A suspension of crystals formed from the melt may be contacted by weU-mixed mother Hquor or the crystals may be moved countercurrently to hquor flow ia a vertical or horizontal column. In column crystallizers, crystals are moved ia a specific direction by gravity or rotating blades. The crystals are melted by the addition of heat when they reach a designated end of the crystallizer a portion of the melt is removed as product and the remainder is returned to the system to flow countercurrently to and to wash the product crystals. 

Plastid pigments were received by extraction and crystallization. Crystals of these pigments were dissolved in suitable solvent. 

Fig. 4.6. Cross section of the front end of an SSD (solid-state detector), here Gold contact with a grooved Si(Li) crystal. Crystal and preamplifier are connected with a cooled copper rod and shielded by a case with an end cap and Be window [4.21, 4.29].

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