Crystallization during processing

Examples of an initially metastable phase that relaxes to a more stable phase are to be found in solutions, in suspensions, and in some solid dosage forms [31]. In solutions, the metastable form will have a higher solubility than its more stable form (and a higher free energy), so a solution of the less stable form may be supersaturated with respect to the more stable form, which then crystallizes during processing. The stable form can be a solvate or an anhydrous form. Cortisone acetate suspensions represent a well-known example where a transition to a... 

Mackert Jr JR, Russell CM. Leucite crystallization during processing of a heat-pressed dental ceramic. International Journal of Prosthodontic 1996 9(3) 261-265. 

A partially crystalline polymer that is not fully crystallized during processing will shrink when heated to a certain temperature. When the chain mobility is increased enough for the chain to begin to form into crystallites, the polymer will shrink, since the crystallites occupy less volume than the amorphous regions. This behavior can be seen if one heats a nonoriented PET or nylon film. Most often it is associated with nonpackaging applications like the shrinkage of polyester fabrics when washed in water that is too hot. 

In the presence of excess fatty acid, different soap crystalline phase compounds can form, commonly referred to as acid—soaps. Acid—soap crystals are composed of stoichiometric amounts of soap and fatty acid and associate in similar bilayer stmctures as pure soap crystals. There are a number of different documented acid—soap crystals. The existence of crystals of the composition 2 acid—1 soap, 1 acid—1 soap, and 1 acid—2 soap has been reported (13). The presence of the acid—soaps can also have a dramatic impact on the physical and performance properties of the finished soap. The presence of acid—soaps increases the plasticity of the soap during processing and decreases product firmness, potentially to the point of stickiness during processing. Furthermore, the presence of the acid—soap changes the character of the lather, decreasing the bubble size and subsequently increasing lather stabiUty and... 

An example of an analysis done on polysilicon and single-crystal Czochralski silicon (CZ) is shown in Table 1. As can be seen, polysilicon, which was used to grow the crystal, is dirtier than the CZ silicon. This is expected, since segregation coefficients limit the incorporation of each element into the crystal boule during the crystal growth process. All values shown in the table are from bulk analysis. Table 2 shows NAA data obtained in an experiment where surface analysis was accom-... 

Jones, A.G., Hostomsky, J. and Waclii, S., 1996. Modelling and analysis of particle formation during agglomerative crystal precipitation processes. Chemical Engineering Communications, 146, 105-130. 

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