Crystalline supports diffraction

There are no known examples of supported clusters dispersed in crystallo-graphically equivalent positions on a crystalline support. Thus, no structures have been determined by X-ray diffraction crystallography, and the best available methods for structure determination are various spectroscopies (with interpretations based on comparisons with spectra of known compoimds) and microscopy. The more nearly uniform the clusters and their bonding to a support, the more nearly definitive are the spectroscopic methods however, the uniformities of these samples are not easy to assess, and the best microscopic methods are limited by the smallness of the clusters and their tendency to be affected by the electron beam in a transmission electron microscope furthermore, most supported metal clusters are highly reactive and... 

Diffraction from Crystalline Supports. Although diffraction conveniently boosts particle contrast in ratio images,... 

Because x-rays are particularly penetrating, they are very usefiil in probing solids, but are not as well suited for the analysis of surfaces. X-ray diffraction (XRD) methods are nevertheless used routinely in the characterization of powders and of supported catalysts to extract infomration about the degree of crystallinity and the nature and crystallographic phases of oxides, nitrides and carbides [, ]. Particle size and dispersion data are often acquired with XRD as well. 

Electron microscopy and X-ray diffraction experiments conducted on resilin-containing insect cuticle provided further support for resilin existing in the rubbery state as a crosslinked random network of protein chains. No fine structure was revealed by the electron microscopy experiments and zero crystallinity could be detected from the X-ray diffraction experiments. Furthermore, the diffraction... 

Some other situation is realized in a case of TEG-tin CMs. Electron microscopy studies of the obtained TEG-Sn powders revealed the uniform coverage of TEG surface by tin particles. Tin particles are of spherical shape and their sizes are about 40-80 nm, i.e. somewhat higher than in a case of silicon particles. Low scatter of particle sizes is observed as in a case of TEG-silicon system. However, as it is clearly seen from the data of the X-ray structure analysis (Figure 4) tin particles deposited on the surface of graphite support are in crystalline state. The distinct and narrow tin reflections at the X-ray diffraction pattern evidence this fact. 

The crystallinity of zeolites was determined by X-ray powder diffraction with a Broker D8 Advance X-ray powder diffractometer. Diffractograms of both zeolites exhibited good crystallinity and characteristic diffraction lines with no additional crystalline phases. This was further supported by SEM images. 

The assumption of membrane softness is supported by a theoretical argument of Nelson et al., who showed that a flexible membrane cannot have crystalline order in thermal equilibrium at nonzero temperature, because thermal fluctuations induce dislocations, which destroy this order on long length scales.188 189 The assumption is also supported by two types of experimental evidence for diacetylenic lipid tubules. First, Treanor and Pace found a distinct fluid character in NMR and electron spin resonance experiments on lipid tubules.190 Second, Brandow et al. found that tubule membranes can flow to seal up cuts from an atomic force microscope tip, suggesting that the membrane has no shear modulus on experimental time scales.191 However, conflicting evidence comes from X-ray and electron diffraction experiments on diacetylenic lipid tubules. These experiments found sharp diffraction peaks, which indicate crystalline order in tubule membranes, at least over the length scales probed by the diffraction techniques.123,192 193... 

The same type of ring-closure reaction that leads to the [3,2- ]-fused 50 can also result, in principle, in formation of a [3,4- ]-fused ring system (see Sections 11.16.5.2 and 11.16.7). This case has been found when an amino group was present in the triazole ring, and formation of 51 has been supported by X-ray diffraction. The crystalline structure... 

The total surface areas determined by the N2 BET method for the calcined, supported catalysts are listed in Table II. The X-ray diffraction (XRD) results showed diffraction peaks from a cubic lattice with a unit cell distance of 6.1 A were present on all of the calcined catalysts. Both C03O4 and C0AI2O4 have structures consistent with that lattice spacing, making assignment of the type of crystalline cobalt species present on the alumina supports difficult. 

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are the techniques most widely used for the characterization of crystallinity and polymorphism of solid lipid particles. Although DSC is usually more sensitive in detecting crystalline material, XRD is much more reliable in determining the type of polymorph present in the dispersions because it provides structural data. In contrast, DSC can detect the type of polymorph only indirectly via the transition temperatures and enthalpies. Because these parameters may be different from those observed in the bulk material, particularly for small colloidal particles [1,62], assigmnent of polymorphic forms in DSC curves should be supported by x-ray data. 

Reliable assessment of the arrangement and crystallinity of AA monolayers supported by a Pb2+ subphase is equally elusive. Our data is best accommodated in terms of an AA Pb2+ = 3 4 ratio (Fig. 115). Grazing incidence X-ray diffraction measurements of lead arachidate monolayers demonstrated the existence of long-range ordering (250 A) of Pb2+ [109]. 

When poly (vinyl chloride) contains 5 to 10% of various plasticizers, a small increase in modulus and tensile strength occurs (J, 4). According to Horsley (4). this is due to an increase in the degree of order and crystallinity of the system, and the theory is supported by x-ray diffraction patterns. According to Ghersa (J), a contributing factor is the steric hindrance of plasticizer molecules which, attached with polar groups to poly (vinyl chloride) chains, could act as cross links. 

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