Melting and recrystallization

Melting and recrystallization behavior of virgin PTEE has been studied by dsc (64). A quantitative relationship was found between and the heat of crystallization (A/T) in the molecular weight range of 5.2 x 10 to 4.5 X 1 0, where is heat of crystallization in J/g, which is independent of cooling... 

Whereas certain rocks of igneous origin formed by melting and recrystallization can include minerals enriched in the lanthanides (4), cerium is usually present as a trace element rather than as an essential component. Only a few minerals in which cerium is an essential stmcture-defining component occur in economically significant deposits. Two minerals supply the world s cerium, bastnasite [68909-13-7] LnFCO., and monazite [1306-41 -8] (Ln,Th)PO. ... 

DSC has also been used to evaluate interactions with incorporated drngs. These interactions can be reflected in changes of the melting and recrystallization temperatures or in differences in melting enthalpy [52,68,81]. Direct evidence of the... 

Feenstra et al. (1987a) developed an in-situ "tip DOS flattening" procedure. This procedure uses field emission current to locally heat up the end of the tip, which eventually causes a local melting and recrystallization. Details of this process is as follows ... 

The behavior of wax in these oils can sometimes be influenced by temperature cycling and long-term storage. As the wax melts and recrystallizes through repeated cycles of heating and cooling, the pour point of the oil may be affected. If the pour... 

Current research interest is in the solid phase epitaxial regrowth of amorphous Si using laser processing. RBS has been used to follow the melting and recrystallization of the crystal-amorphous interface (12). This is accomplished by monitoring the backscattered spectrum+with the substrate oriented in a direction that will allow the He to channel along the crystal planes. 

Packaging Materials. As in the case of fibers, thermal analysis can easily distinguish between most polymeric films on the basis of the glass transition and the thermal history dependence of the melt and recrystallization (20, 21). From the analysis of thin films--as, for example, used in plastic bags recovered with drugs—it should be possible to identify by comparison the bag manufacturer and possibly the manufacturing lot. 

Finally, we have attempted to evaluate the possible impact of an intermediate liquid crystalline phase and the possibility of transfer of helical hand information from the melt to the crystal throughout this process. Assuming that the melt is structured, the melt of chiral but racemic polyolefins would be made of stretches of helical stems that are equally partitioned between left- and right-handed helices. Formation of antichiral structures (such as in a iPP) could be interpreted as indicating a possible transfer of information (but the problem of the sequence of helical hands would still remain). This analysis is, however, ruined by the observation that many of these polymers also form chiral structures (frustrated p phase of iPP, Form III of iPBul). For the achiral poly(5-methyl-pentene-l), the chiral, frustrated phase is actually the more stable one, and can be obtained by melting and recrystallization of a less stable antichiral phase. 

The recrystallization procedure yields one of three solid modifications of this compound which have melting points of 65 to 66°, 70 to 71°, and 85 to 86°, respectively. The three forms have identical infrared spectra and the same composition. They differ in their superficial appearance, as may be seen by examination under a microscope. The form which melts at 65 to 66°, when melted and recrystallized by cooling, yields the modification which melts at 70... 

As shown in Fig. 11, the melting peak obtained by DSC is often structured and the clearing transition can be rather broad. The structuring of the melting peak may be an indication of polymorphism in the solid state but more often it is caused by successive meltings and recrystallizations of regions of imperfect crystallinity. The existence of more than one mesophase in the melt has also been observed, and this behavior leads to the presence of two or more liquid crystal transitions in the thermogram... 

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