Crystallinity, crystallization

Crystallinity (crystal defects) Exposure to liquids Drying... 

III.2, III.6, and III.7. Solids tend to be crystalline crystals in equilibrium tend to have plane surfaces and Pc across these is always zero. The vapor pressure of perfect crystals is independent of their dimensions. What is true for vapor pressure, is true for solubility also. 

The removal of side products such as EG, A A, CO2, water and oligomers is controlled by the physics of mass transport in the solid state. This mechanism correlates with particle size, density, crystallinity, crystal structure and perfection, and surface conditions, as well as the desorption of the reaction products from... 

Typical X-ray diffraction patterns of the Fe oxides are shown in Figure 7.16. They provide the three parameters, namely line (angle) position, width and intensity from which the nature of the oxide, its quantity (in a mixture), its unit cell parameters and its crystallinity (crystal size and order) can be deduced. The crystal structure of unknown compounds may also be determined. XRD is still the most reliable way to identify a particular oxide because it is based on the long range order of the atoms, whereas most other methods (e.g. Mossbauer spectroscopy, EXAFS) characterize the atoms and their immediate (short range) environment. 

Crystallinity, crystallization Orientation of the disordered long-chain molecules into repeated patterns. 

Crystallinity. Crystals are an ordered, regular arrangement of units in a repeating, three-dimensional lattice structure. Small molecules, which in the liquid state have three-dimensional mobility, crystallize readily when cooled. It is not so easy for polymers, because a repeating unit cannot move independently of its neighbors in the chain. Nevertheless, some polymers can and do crystallize, though never completely. 

Crystalline, angular displacement causing disorder Crystalline, crystal disordering Crystalline... 

Another thermal separation unit often used for the laboratory scale purification of ionic liquids is recrystallization [125]. It is an attractive option for those ionic liquids that can form solids with a high degree of crystallinity. Crystals of ionic liquids are expected to be pure because each molecule or ion must fit perfectly into the lattice as it leaves the solution. Impurities preferentially remain in solution as they do not fit as well in the lattice. The level of purity of the crystal product finally depends on the extent to which the impurities are incorporated into the lattice or how much solvent is entrapped within the crystal formed. 

Farrow, G. Crystallinity, Crystal Size" and melting point of polypropylene. Polymer 4, 191-197 (1963). 

X-ray diffractometry Identifying polymorphs quantification of degree of crystallinity crystal lattice geometry and solid-state transformations... 

The dissociation properties and the resultant pH values obtained for inorganic ion exchangers are strongly influenced by crystallinities, crystal system, supporting electrolyte, ratio of solution to exchanger, ionic strength and the temperature selected. It is possible, for example, to... 

Heat capacities of polymer are complicated by physical and chemical structural changes, namely by changes in crystallinity, crystal structure, morphology, tacticity, molecular weight and copolymer unit content. Furthermore the picture can be complicated by changes in mechanical, thermal and possibly electrical history of the polymer. 

Defect-free zeolite membranes have so far only been produced for membranes of the MFI (silicalite type) with thicknesses of about 50 im on stainless steel supports and 3-10 pm on alumina and carbon supports. They are produced by in situ methods of zeolite crystals grown directly on the support system. There are some reports of formation of defective membranes with, e.g., zeolite A. Much more research is needed to widen the range of available zeolite membrane types especially small and wide pore systems. The permeance values of the defect-free membranes is lower than that of the amorphous membranes (see Chapter 6) and to improve this the layer thickness must be decreased together with improving the crystal quality (no impurities, no surface layers, high crystallinity, crystal orientation) and microstructure (grain boundary engineering). 

By strictly controlling the conditions of synthesis, modification and pretreatment to obtain catalysts with appropriate crystallinity, crystal size, composition and acidity pattern and so on, we have made a remarkable progress in the improvement of the stability of the catalysts. The duration on stream without MeOH or DME breakthrough extending to 30 hours as shown in Fig.1. 

Contrary to zeolite samples previously known, said of hydrothermal origin, which were characterized by beautiful, very pure, euhedral crystals of centimetre size (Fig. 2a), the new zeolite minerals, occurring in volcaniclastic rocks and said of sedimentary origin, formed usually at lower temperatures and through slower processes. They were crypto-crystalline (crystal size from 0.1 to a few micrometers, usually <10 pm) (Fig. 2b), often co-crystallised with other zeolite species and constantly accompanied by conspicuous quantities of impurities, usually amounting to several tens percent. 

Phenyl hippurate 884 Finely powdered hippuric acid (10 g) is mixed with phenol (7 g), heated on a water-bath, and treated gradually with phosphoryl chloride (6-8 g). The mixture is heated until all is dissolved, then poured into ice-water and neutralized with sodium carbonate solution. The liquid is decanted from the viscous product which is rubbed with water until fully crystalline. Crystallized from ethanol it has m.p. 104°. 

Conversions of a metastable phase into a more stable phase may include the transformation of one polymorphic phase into another, the solvation of an anhydrous phase, the desolvation of a solvate phase, the transformation of an amorphous phase into a crystalline anhydrate or solvate phase, the degradation of a crystalline anhydrate or solvate phase to an amorphous phase, or in the case of digoxin, the conversion of imperfect (less crystalline, more amorphous) crystals with a high density of defects into more perfect (more crystalline) crystals with a lower density of defects. While it is straightforward to determine the equilibrium solubility of a phase that is stable with respect to conversion, the measurement of solubilities of metastable phases that are susceptible to conversion is not a trivial matter. 

Polymer chemists use DSC extensively to study percent crystallinity, crystallization rate, polymerization reaction kinetics, polymer degradation, and the effect of composition on the glass transition temperature, heat capacity determinations, and characterization of polymer blends. Materials scientists, physical chemists, and analytical chemists use DSC to study corrosion, oxidation, reduction, phase changes, catalysts, surface reactions, chemical adsorption and desorption (chemisorption), physical adsorption and desorption (physisorp-tion), fundamental physical properties such as enthalpy, boiling point, and equdibrium vapor pressure. DSC instruments permit the purge gas to be changed automatically, so sample interactions with reactive gas atmospheres can be studied. 

Crystallinity (crystal shape and appearance) Particle size and bnUc density, snrface area... 

Each kind of CNs has a characteristic size, aspect ratio, morphology, crystallinity, crystal structure, and properties. Figure 13.7a shows the microstructure of the T-CNs prepared by acid hydrolyzation. T-CNs have a high-aspect-ratio [20-30 nm wide, 0.5-4 pm in length], are about 100% cellulose, highly crystalline [85-100%] and containing a high fraction of crystal structure [ 90%] [19, 28-30]. After sonicatlon, the T-CNs became much... 

PLA is a crystal clear, transparent material when amorphous that becomes hazier the higher the crystallinity. Crystallized material is opaque. When producing lactide, meso-lactide is formed as a by-product. It is difficult to separate the meso-lactide from the L-lactide in the purification step. When polymerizing L-lactide with small contents of meso-lactide a co-polymer is formed. Increasing meso-lactide leads to decreasing crystallinity. With more than 10-15% meso-lactide the polymer is amorphous. 

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