Reference literature melt crystallization

Measurements by DSC at 10 K/min. Line 2 is the melting of the major component of crystal form II. Line 1 refers to the higher melting crystal form I and line 3 to crystal form HI. The dotted line was found on a different set of annealed samples from the literature. 

Table 7-8 gives a brief overview of melt crystallizers with references to further literature. 

A number of systems which in polymer literature are normally referred to as mesophases are obtained under kinetic control. Examples are the smectic phase of isotactic polypropylene [18,19], mesomorphic syndiotac-tic polypropylene [20-22], mesomorphic PET [23,24], and other instances where intermediate degrees of order result after quenching polymers from the melt to temperatures often close to Tg. In these cases disorder is plausibly more static than in bundles close to T0 and these phases usually crystallize upon heating to an appropriate temperature in the stable crystal phases. 

A second rich collection of references on the polymorphic behaviour of organic materials is the compilation by Deffet (1942). This contains information and references to primary sources on 1188 substances that exhibit polymorphism at atmospheric pressure and another 32 that exhibit polymorphic behaviour at elevated pressures. A typical entry contains the number of reported polymorphic forms, their melting points, temperature(s) of transition, crystal system, some physical properties, and literature references, of which there are nearly 1000. Substances are organized by empirical formula with an index organized by compound name (in French). 

TJew references to uranium borates appear in the literature. Larson (12) reported that yellow crystals, whose composition was assumed to be 3UO3 B2O3 (uranyl orthoborate), were obtained among other products from a melt of uranium niobate in boric oxide. Bruhat and Dubois (2) stated that perborate solutions react with uranium oxide to give an anhydrous stable yellow salt of the composition UBO4. No further information has appeared on either of these compounds. 

The behavior of volatile fission products is largely unknown. Brief literature references to iodine and ruthenium are contradictory. It is likely that elemental iodine is the stable species in the melt (16 ), and that some will be volatilized. Possible process modifications to guarantee a unique path for ruthenium have not been considered. The rare gases should escape because of the elevated temperature crystal modification. However, experience with the voloxidation process suggests that this release may not be complete. The behavior of both Kr-85 and tritium must thus be investigated. 

As the temperatures are reduced, solid phases will crystallize from the melt. The Watt and Fereday correlations do not apply to this region. The studies reported here include the temperature region in which crystals can be expected to form. The authors did not find literature references to phase equilibria studies for the Si02"Al203-Ca0-Mg0-Fe0 or SiO2 Al2O3-CaO-MgO systems in the composition region of interest. As a result some speculation on behavior is involved in any extensive interpretation of the data. 

In both, layer and suspension crystallization solid material forms from the melt starting with a nucleus through which a solid/liquid interface is created. As crystallization proceeds the mass of solidified substance steadily increases which causes the interface to move. The impurity components remaining in the melt thereby enrich in front of the solid/liquid interface, forming a concentration boundary layer. The concentration profile in this boundary layer changes as the interface advances which is in literature referred to as moving boundary problem. ... 

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