Gamma-crystalline form

Cocoa butter NF is defined as the fat obtained from the seed of Theobroma Cacao Linne (Family Sterculiaceae) (44). Cocoa butter softens at 30°C and melts at 34°C. It contains four different forms alpha, beta, beta prime, and gamma with melting points of 22°C, 34°C to 35°C, 28°C and 18°C, respectively. The beta form is the most stable and is desired for suppositories. The biggest challenge with the polymorphism of cocoa butter is the impact of the manufacturing process on the characteristics of the suppository itself. When cocoa butter is hastily melted at a temperature greatly exceeding the minimum required temperature and then quickly chilled, the result is metastable crystalline form (a crystals), which may not even... 

PVDF exhibits a complex crystalline polymorphism, which cannot be found in other known synthetic polymers. There are a total of four distinct crystalline forms alpha, beta, gamma, and delta. These are present in different proportions in the material, depending on a variety of factors that affect the development of the crys-... 

PVDF exhibits a complex crystalline polymorphism, which cannot be found in other known synthetic polymers. There are a total of four distinct crystalline forms alpha, beta, gamma, and delta. These are present in different proportions in the material, depending on a variety of factors that affect the development of the crystalline structure, such as pressure, intensity of the electric field, controlled melt crystallization, precipitation from different solvents, or seeding crystallization (e.g., surfactants). The alpha and beta forms are most common in practical situations. Generally, the alpha form is generated in normal melt processing the beta form develops under mechanical deformation of melt-fabricated specimens. The gamma form arises under special circumstances, and the delta form is obtained by distortion of... 

The crystalline form of the gamma isomer, when crystallized from acetone, is rhombohedral crystals, which possess sharp edges, and which belong to the brachypinacoidal class. 

TiClj is a highly colored solid that exists in several crystalline forms, designated as alpha (a), beta (p), gamma (y) and delta (S). The a, y and S forms have layered crystal structures and are violet. The P form has a linear structure and is brown. 

It has recently been shown (6-8) that the anhydrous alumina previously called gamma-alumina may consist of six different crystalline forms. The... 

LijNaBFg doped with Cu and co-doped with P are synthesized by a wet chemical technique and exposed to gamma-rays of Co for their TL properties. The XRD technique shows the crystalline nature of the prepared material. The crystalline form of the materials is characterized by a powder XRD pattern recorded on a Philips P Analytical X Pert Pro diffractometer at room temperature. The XRD pattern of Li2NaBFg is shown in Figure 7.38. This material produced well-defined XRD lines for the powder samples that confirm its crystalline nature. However, for recorded XRD patterns, no matching files are seen in the JCPDS library (limited numbers of files are only available for mixed lithium magnesium borate crystals). The XRD pattern of LijNaBF material did not indicate individual presence of any traces of ammonium fluoride and other likely phases, which is an indirect evidence for the formation of the desired compound. The final product was formed in homogeneous white powder form. 

Heppleston (310, 311) in 1972 reviewed the main theories of the Hbrogenic action of silica likewise classified as (1) solubility, (2) surface, and (3) immunological. The immunological theory is of secondary importance because it does not explain the primary action of silica in stimulating proliferation of connective tissue, llie solubility theory was left by default, but was still inadequate because neither the known surface structures of the different modifications of silica nor their characteristic adsorption of albumin or gamma globulin could be correlated with their relative biological activity. However Stober (312) showed that all crystalline forms except stishovite are relatively active. 

Peppas [24] showed that polycaprolactam (polyamide 6) crystallises in different crystalline forms, which show different characteristic infrared absorbance bands. Based on this he prepared phase diagrams. He evaluated the absorbance coefficients of the bands from the dependence of their intensity on temperature and specific volume of different polyamide 6 samples and described a method for the quantitative determination of the amounts of alpha and gamma modifications and of the amorphous phase. On the basis of these data the densities of the samples were calculated and shown to agree with the values determined experimentally. The specific volume of the amorphous phase was v = 0.917 cm /g, and was independent of any alpha or gamma modifications the samples may have contained. 

However, membranes were not prepared from solution casting due to the crystalline form of the sulfonated polymer. In another report by Fei et al., a hybrid polymer with a polynorbomene backbone and pendent sulfonated cyclic phosphazene side groups was synthesized [93]. Co gamma radiation cross-linking was applied after the polymer film was cast, in order to restrict water swelling. The prepared membranes had relatively low lEC ranging from 0.267 to 0.49 mmol g. It was also found that there... 

Isotactic polypropylene exhibits four crystalline structures alpha, beta, gamma and mesomorphic. Each of these structures forms under specific processing conditions and defines the properties of the polypropylene. In polypropylene containing the alpha, beta, and gamma... 

There are numerous examples of solid state polymerizations. Here we will briefly describe examples based on addition polymers. Generally, the crystalline monomer is irradiated with electrons or some form of high-energy radiation, such as gamma or x-rays. Since many monomers are solids only below room temperature, it is customary to begin irradiation at lower temperatures with the temperature raised only after initial polymerization occurs. (Some reactions are carried to completion at the lower temperature.) After polymerization, the monomer is removed. Table 6.10 contains a list of some of the common monomers that undergo solid-state irradiation polymerization. 

White crystals exists in three crystalline modifications alpha-, beta-, and gamma-Ga203 while the alpha-form is analogous to the corundum form of alumina, the beta-Ga203 is isomorphous with theta-alumina alpha-form converts to beta-modification on calcination at high temperatures (600°C) gamma form is stable at low temperatures density 6.44 g/cm (alpha-Ga203),... 

Silvery-white metal exhibits three crystalline modifications an orthorhombic alpha form, stable at ordinary temperatures and density 20.45 g/cm the alpha-form transforms to a tetragonal beta allotrope of density 19.36 g/cm when heated at 280°C the beta form converts to a body-centered cubic crystaUine gamma modification at 577°C, having a density 18.0 g/cm . 

Trigonal crystalline solid or amorphous powder mineral millerite has a yellow metallic luster color varies from yellow to brownish black density 5.30 to 6.65 g/cm3 exhibits three allotropic modifications (1) the acid-soluble amorphous alpha form obtained from nickel salt solution by precipitation with ammonium sulfide, (2) the alpha form rapidly transforms to a crystalline beta form as a brown colloidal dispersion upon exposure to air, and (3) a rhombo-hedral gamma modification found native as mineral millerite, which also can be prepared artificially under certain conditions. 

Another preparative method in which the rate of precipitation is slow involves slow decomposition of zirconium fluoro complexes [14], These are first prepared by adding an appropriate amount of hydrofluoric acid (HF) to the zirconyl salt and these complexes are decomposed in the presence of phosphoric acid, with a slow stream of nitrogen or water vapor passing through the system. The rate of precipitation of zirconium phosphate is controlled by the rate of removal of HF from the system, and when this is very slow, a highly crystalline a-ZrP is obtained. The gamma form of the metal phosphate differs significantly from the alpha and current discussion will be concerned with the latter phase. 

Similar reaction products are observed with gamma-irradiation in solutionj but in the crystalline solid state, the mechanism appears to be different and no glucose is formed. 

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