Analog crystallite

Highly crystalline 0-chitin is obtained from pogonophore tubes and the spines of certain diatoms, and is analogous in both crystallinity and morphology to the cellulose obtained from Valonia cell walls. Intensity data (10) were obtained for 61 observed non-meridional reflections for a specimen of dispersed (sonicated) crystallites of pogonophore tube (Oligobrachia... 

Comparison of the X-ray powder diffraction patterns of AlPOfc-20 and a TMA-sodalite (Figure 8) strongly supports a structural analogy. The rather large line widths in the AlP0 -20 pattern are due to the submicron crystallite size. Both compositions were made with the template, TMA, and both can be indexed in the cubic system. 

According to this concept, the stabilizer function of alumina reduces to paracrystal-line lattice defects an analogous effect is to be expected with Cr203, Sc203, etc. [262], [296]. Another theory is based on the observation that during reduction part of the alumina precipitates with other promoters into the surface of the iron crystallite in a molecularly dispersed distribution [258], [297] or in small islands [254]. This patchy monolayer of alumina acts like a spacer between iron atoms of neighboring crystallites and prevents sintering by means of a skin effect [263]. (See also [101], [110], [253].)... 

Iguchi [266] considered a mechanism in which growing chains are occluded, and thus become non-propagating, by a process kinetically analogous to the interaction of crystallites growing from the polymer melt and following Avrami kinetics. (It was assumed that chemical transfer and termination reactions do not occur.) The polymerization rate is given by the concentrations of monomer and active centres at any time, i.e. Rp = kp [C ], [M],. If the decay of catalytic activity follows the relationship... 

Catalytic reactions can be run over large, massive metal particles as well as the much smaller, dispersed metal crystallites. The massive metal catalysts can be the single crystal catalysts such as those shown in Fig. 3.2 or polycrystalline forms of bulk metal such as wires, foils or ribbons. These latter materials were used somewhat routinely in the early catalytic research efforts that were involved with developing the mechanisms of vapor phase catalytic processes. These materials were considered to be analogs of the supported catalysts in which the effect of the support, if any, was eliminated. 

Figure 28. Top EXAFS analysis strategy used by Frenkel (1999) to determine nanocrystal size in meM particles. The number of observed neighbors is dependent on the crystallite size. The more distant neighbors provide the most sensitive measure of coordination number and thus ciystalhte size. Bottom plot is the analogous function for semiconductor tetrahedrally coordinated stmctures. After Frenkel (1999).

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