Poly crystalline Solids

Grain boundaries — are the interfaces between crystals or individual grains in poly crystalline solid materials. In a simplest case, the grain boundary separates... 

One way to make the short-lived intermediates amenable to study is to increase their lifetime, usually by irradiation in the solid state and/or at very low temperatures. Then, the intermediates can be detected at the end of the irradiation by ESR or optical absorption spectroscopy. The ESR study of radicals in the solid state is done on single crystals, polycrystalline samples or frozen aqueous solution. In case of polycrystalline samples or frozen aqueous solution the identification of the radicals from the ESR spectra is difficult in many cases and, for better identification, the ESR experiment should be conducted on irradiated single crystals. Later, the method of spin trapping, developed for the liquid phase, was extended to poly crystalline solids, in this technique the polycrystalline solids are y-irradiated and subsequently dissolved in a solution containing the spin trap. 

Surprisingly, many cubic metals behave in a similar fashion, although the effect has been masked by the fact that the mechanical properties are most often measured on poly crystalline solids. For example, the commonplace metallic alloy /3-brass, CuZn, which has the CsCl structure, is noticeably auxetic. A tensile stress applied along the [001] direction... 

In most as-cast poly crystalline solids three distinct zones with different grain structures can be identified (Fig. 6.1), namely ... 

Among the polymers which contain clear crystalline phases are poly(eth-ylene) and PTFE. Their properties, however, are very different from those usually associated with crystalline solids in particular, they tend to exhibit... 

Poly(oxytetramethylene), poly(tetrahydrofuran), may assume the state of a viscous oil, a wax, or a crystalline solid (melting range around 55 °C), depending on the molecular weight. Poly(tetrahydrofuran) telechelics prepared with two OH end groups and in molar masses of 500-4000 g/mol are used widely as soft block in segmented polyurethanes and polyesters (see Sect. 3.4.2.1). 

In a poly crystalline mixture of solid reactants, we might expect the particle size to be of the order of 10 pm even careful and persistent grinding will only reduce the particle size to around 0.1 pm. Diffusion during a ceramic reaction is therefore taking place across anywhere between 100 and 10,000 unit cells. Various ingenious methods, some physical and some chemical, have been pioneered to bring the components of the reaction either into more intimate contact, or into contact at an atomic level, and so reduce this diffusion path in doing so, the reactions can often take place at lower temperatures. 

TEREPHTHALIC ACID. CAS 100-21-01. Cf,H4(COOH)2, formula weight 166.13, crystalline solid sublimes upon heating, sp gr 1.510. The compound is almost insoluble in H2O, only slightly soluble in warm alcohol, and insoluble in ether. Terephtlialic acid (TPA) is a high-tonnage chemical, widely used in the production of synthetic materials, notably polyester fibers (poly-(ethylene terephthalate)). 

Iqbal et al (Ref 56) measured the transmission infrared and laser excited Raman spectra of poly crystalline RDX in the range of 40 to 4000/cm. To aid assignments in the spectral region of 400 to 4000/cm, the spectra of two types of N15-labeled samples and the soln spectra in different solvents were also recorded. From these data it was possible to assign many of the observed bands to intramolecular modes of the RDX molecule. The Raman-active lattice modes also were resolved and found to be comparable to the lattice mode frequencies in solid cyclohexane... 

This salt is a stable, crystalline solid at room temperature. Borane-carbonyl is regenerated by treating the carbonate analog with poly-phosphoric acid 46>. 

The modem method for quantifying the goodness of fit between two adjacent grains in a pure poly crystalline substance (homophase interfaces) or in a multiphase solid (heterophase interfaces) counts the number of lattice points (not... 

The major poly isocyanates used (2) are toluene diisocyanate (TDI) and the less volatile 4,4/-methylene diphenylene diisocyanate (MDI), which, because it is a crystalline solid in the pure form, has to be used in a relatively crude form. The crude polyisocyanate is a mixture of MDI variants that is conveniently a liquid product with a mean functionality greater than 2. The use of a pure, liquid diisocyanate, however, would enable polyurethanes to be formed having relatively enhanced physical properties (2) and would also greatly simplify processing by removing the need to use elevated temperatures, solvents, or isocyanate prepolymers as with MDI. 

Apart fi-om DAB- /en /r-(CN)4, which is a white crystalline solid, all generations are colourless to slightly yellow oils. The amine-terminated dendrimers are transparent, whereas the nitrile-terminated ones are somewhat turbid. The solubility of the dendrimers is determined primarily by the nature of the end group DAR-dendr-(NH2) is soluble in H2O, methanol and toluene, DAB-Jent/r-(CN) in a variety of common organic solvents. The viscosity of the poly(propylene imine) dendrimers is investigated both in THF (intrinsic viscosity. Figure 4) and in the neat form. A maximum in - log[ /] is observed in the plot, which is characteristic for dendrimers [11]. 

Figure 5.35. Adsorbed amount of polylstyrene sulfonate) of three different molar masses as a function of the square root of the NaCl concentration. The adsorbent is crystalline poly-oxymethylene (solid curves) or silica at pH = 2 1 (dashed curve).

Farmer et al. evaluated the conformations and dynamics of poly(di- -hexylsilane). " - " The lowest energy conformer for a polymer containing eight silicon atoms was a helical arrangement with 30° torsional angles in the silane backbone. The authors also monitored different backbone and side chain torsions during dynamics simulations and concluded that the conformation present in the crystalline solid is controlled by intermolecular effects. 

The mono-phenols are liquids or low melting-point crystalline solids, while the poly-phenols are crystalline solids only. The mono-phenols... 

Figure 17. Variations of bulk properties derived from variations of the individual elastic constants of stishovite. (a) Bulk modulus (K) and shear modulus (G). Solid lines are the average of Reuss and Voigt limits the latter are shown as dotted lines (Voigt limit > Reuss limit), (b) Velocities of P (top) and S (lower) waves through a poly crystalline aggregate of stishovite. Circles indicate experimental values obtained by Li et al. (1996) at room pressure and 3GPa. After Carpenter et al. (2000a).

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