Crystal parameters

Physical Properties of PBT. Unlike PET, the polymer PBT exists in two polymorphs called the a- and p-forms, which have distinctly different crystal stmctures. The two forms are interconvertible under mechanical stress (158,159). Both crystal forms are triclinic and the crystal parameters are shown in Table 7. 

Other crystallization parameters have been determined for some of the polymers. The dependence of the melting temperature on the crystallization temperature for the orthorhombic form of POX (T = 323K) and both monoclinic (T = 348K) and orthorhombic (T = 329K) modifications of PDMOX has been determined (284). The enthalpy of fusion, Aff, for the same polymers has been determined by the polymer diluent method and by calorimetry at different levels of crystallinity (284). for POX was found to be 150.9 J/g (36.1 cal/g) for the dimethyl derivative, it ranged from 85.6 to 107.0 J/g (20.5—25.6 cal/g). Numerous crystal stmcture studies have been made (285—292). Isothermal crystallization rates of POX from the melt have been determined from 19 to —50 C (293,294). Similar studies have been made for PDMOX from 22 to 44°C (295,296). 

Table 1 Hsts the properties of several semiconductors relevant to device design and epitaxy. The properties are appropriate to the 2incblende crystal stmcture in those cases where hexagonal polytypes exist, ie, ZnS and ZnSe. This first group of crystal parameters appHes to the growth of epitaxial heterostmctures the cubic lattice constant, a the elastic constants, congment sublimation temperature, T. Eor growth of defect-free...

The nonnuclear chemistry of Fr reduces to studies of coprecipitation in which Fr shows the behavior of the heavier alkali metal. Coprecipitation is followed by ion exchange to concentrate Fr Physical (mp, density, crystal parameters) and chemical (thermodynamics, solvation entropies) properties are theoretically derived or extrapolated from the trends exhibited by the other alkali metals. 

The question arises about the crystal parameters which could be relevant for the clathrate properties and may reflect the observed inclusion selectivites. 

Fig. 5.6 (A) TEM micrograph of alginate-Ni50Co5o nanocomposites (B) correlation between alginate-NiCo solid solution composition and face-centered cubic crystal parameters. (Adapted from [50]).

Poly(butyleneterephthalate) (PBT), 20 31. See also PBT entries Poly(l,4-butyleneterephthalate) (PBT) chemical properties of, 20 65 crystal parameters for, 20 64t economic aspects of, 20 67-68 flame retardant, 20 64-65 mechanical properties of, 20 65-66 physical properties of, 20 64-65 principal world manufacturers of, 20 67t uses for, 20 63-64 Poly(butyl methacrylate)-5/oc -... 

G. Eulitz [13] studied the correlation between chemical constitution and tinctorial strength directly on dissolved pigment samples. He was able to exclude physical crystal parameters, such as particle size distribution and degree of dispersion, by achieving molecular dispersion. His analysis demonstrated the following ... 

Table 20. Crystal parameters and bond distances in lanthanide dipicolinates 204—206)...

The crystallization process can be illustrated by a phase diagram that shows which state (liquid, crystalline, or amorphous solid [precipitate]) is stable under a variety of crystallization parameters. It provides a means of quantifying the influence of the parameters such as the concentrations of protein, precipitant(s), additive(s), pH, and temperature on the production of crystals. Hence phase diagrams form the basis for the design of crystal growth conditions (McPherson, 1999 Ducruix and Giege, 1992 Ducruix and Giege, 1999 Chayen et ah, 1996 and references therein). 

A very common occurrence in crystallization is the formation of clusters of non-diffracting crystals or crystalline precipitate that can not be improved by merely fine tuning the crystallization parameters. In such cases a working phase diagram can be constructed based on the conditions that give the low... 

While the surface of clean metal films appears to be homogeneous with regard to heat of adsorption and surface coverage (the latter within the limits of size of different crystallographic sites), the rate of hydrogenation of ethylene is markedly dependent on the crystal parameter. 

Fig. 10. Catalytic activity as a function of crystal parameter (Beeck).

Sorption capacity is one of the major properties used for industrial applications of zeolites. H. Lee reviews the aspects of zeolites used as adsorbents. The other papers in the section deal with the theory of sorption and diffusion in porous systems, the variation of sorption behavior upon modification, and the variation of crystal parameters upon adsorption. NMR and ESR studies of sorption complexes are reported. H. Resing reviews the mobility of adsorbed species in zeolites studied by NMR. 

This paper reports in detail our investigation on the factors influencing the formation of MCM-41 in fluoride medium, and the optimization of crystallization parameters of MCM-41. Since it is found in this study that siliceous MCM-41 structure could form in different media like [F] or [Cl] medium, the so-called salt effects were always present in both cases due to the presence of large amount of salts (such as NaBr, NaCl and NaF). However, this study shows that only siliceous MCM-41 synthesized in fluoride medium has higher hydrothermal stability during heating in boiling water. 

Considering these problems, we tested a computer extrapolation (6) for sucrose, shown in the conformation maps in Figure 4. Four sets of crystal parameters were used, those from the structure of sucrose (S) (45) and those from the sucrose component of raffinose pentahydrate... 

Fedders and Muller (213) have derived an estimate of the solid-inter-action parameter from another point of view, which ascribes the mixing enthalpy to bond distortions associated with the alloy formation and relates these distortions to the macroscopic elastic properties of the crystal. They concluded that the results based on elastic-crystal parameters yield a similar form for the thermodynamic properties as those estimated by DLP model based on optical-crystal parameters. 

Variation of heats of adsor-ption on different major crystal faces of copper. The effect of the crystal face of the adsorbent on physical adsorption has been treated theoretically by Barrer (153) for covalent surfaces and by Orr (151) and by Lenel (154) for dielectric surfaces. The vertical interactions between a nonpolar molecule and a polycrystalline metal surface have been independently treated by Lennard-Jones (155), by Bardeen (156), and by Margenau and Pollard (157). Considering the theoretical limitations involved in the last treatment, the observed agreement between the values calculated theoretically and the experimental values is acceptable. At present no explicit theoretical treatment of the physical adsorption of a nonpolar gas molecule on a single crystal metal surface in terms of the crystal parameter and geometry of the latter is available. 

Table IT. Unit cell formula and crystal parameters of the eiliceoua HFI-type zeolitea (as synthesized and ( > calcined)...

---