Platelet crystals

In summary, large (>lpm) single crystal platelets of aurichalcite produced highly dispersed Cu and ZnO particles with dimensions on the order of 5 nm, as a result of standard catalyst preparation procedures used in the treatment of the precipitate precursors. The overall platelet dimensions were maintained throughout the preparation treatments, but the platelets became porous and polycrystalline to accommodate the changing chemical structure and density of the Cu and Zn components. The morphology of ZnO and Cu in the reduced catalysts appear to be completely determined by the crystallography of aurichalcite. 

Figure 6 a. Structure of topping powder in the dry state with close-packed globular fat particles (f) (diameter less than 0.5 ftra). b. Crystallization and transformation of the globular structure of fat particles into thin layers of crystal platelets (c). Reprinted from reference 21, courtesy of Verlag Th. Mann. 

The flocculated fat globules of whipped cream contain fewer contact points, and the foam is therefore not as stiff as in toppings in which the aggregated crystal platelets have a large surface area, many contact points and thus increased stiffness. This means that an acceptable topping foam may be formed at a much lower fat content than is the case with liquid whipping creams. 

Most of the R2Ni2Pb plumbides have been grown in the form of single crystal platelets either via a lead flux or by special annealing procedures (Chinchure et al., 2003). The surfaces of such crystals show terrace-like structures. The single crystals then allow direction dependent magnetic measurements. 

Photochemical Diodes. A CdS single crystal platelet used in conjunction with Pt to drive the HER from sulfide solutions. 489... 

A recent study of the mechanism of Ziegler-Natta catal rets has been published by Rodriguez and coworkers 120). These authors showed by dectron microscopy that active sites are found mainly at growth spirals, on lateral surfaces, and on surface defects of the hexagonal a-TiClg crystal platelets. The active site has been proposed to be linked to a surface titanium atom with two chlorine vacancies of the otherwise octahedrally coordinated titanium. In a schematic two dimensional representation the proposed mechanism for propylene polymerization is as follows 120) ... 

One aspect of the processing of clay-rich batches for quality products is so-called draining or maturing storage in damp atmospheres for several weeks or months (in China some of the clay for porcelain manufacture has been drained for several hundred years ) During storage, water probably seeps between the crystal platelets of the clay minerals with the aid of bacteria and a homogeneously moistened paste with improved plasticity is formed. 

Huang and Gallagher [87] carried out a comprehensive study, using TG and DSC, of the influence of / (HjO) on the kinetics of dehydration of samples of powder, pressed pellets and single crystals (platelets and cubic). The rate of dehydration of pellets lay between those of crystals (slow) and powders (fast). The apparent activation energies varied with a, fi om 220 kJ mol for powder at low ar, to 61 kJ mol for pellets at high a. Because the rate is influenced by self-generated water, the results for crystals are the most reproducible. 

There are also substances which sublime at higher temperatures and which can be collected at not-too-low temperatures (e.g. at room temperature) as large, very thin, free-standing crystal platelets of high quality. Among these are for example anthracene and pentacene. More about this subject will follow in Sect. 3.3, on crystal growth. 

Fig. 4.9 X-ray topography to allow the visualisation of dislocations here, defects in a benzile crystal which was grown from solution. In the centre, one can recognise the loop of a platinum wire which suspended the seed crystal platelet in the solution. Many linear dislocations start at inclusions in the surface of...

Fig. 10.8 The temperature dependence of the resistance of -(ET)2l3 at standard pressure. Above crystal platelets. Below crystal needles. The resistance R relative to its value at 300 K is plotted. After [M1], Fig. 5.36. 

The phenomenon of electroluminescence in organic soUds has been known since the 1960 s at that time. Pope et al. [1] and Helfrich and Schneider [2] discovered and investigated the electroluminescence of anthracene crystals between two electrodes, an anode and a cathode. The thickness of the highly-purified anthracene crystal platelets was large in these first experiments 10-20 /wm or 1-5 mm. The two electrodes on the surfaces of the crystal platelets were silver paste or liquid, highly concentrated solutions of NaCl. The necessary external voltages varied between 50 and 2000 V. Later, Williams and Schadt [3] were the first to construct a display , likewise from anthracene crystals, but with solid, laterally-structured electrodes, and they encapsulated it to prevent its degradation in the air. 

Fig. 4.32. Magnetic domains in a YIG single-crystal platelet, observed by the Faraday effect (a) zero field (b) field normal to the platelet plane H 40 A/m).

The jxSR study by Grosse et al. (1999) used mosaics of oriented single-crystal platelets. LaS, the lower concentration limit (x = 0), is diamagnetic. The ZF spectra are static Gaussian Kubo-Toyabe patterns originating from the nuclear moments on La. Full decoupling needs only LF=10G. Between 300 K and 4K only a minute change in static width is seen, which can be accounted for by thermal contraction. These data show that effects of muon diffusion are not discemable. US, the upper concentration limit (x = 1) is a FM (7c = 177 K and fiu = 1.7 Ub). The reduction in moment was... 

Peterson, J. M. (1966) Thermal initiation of screw dislocations in pol5mer crystal platelets, J. Appl. Phys., 37, 4047 050. 

We used diacetylene single crystal platelets, approx. 20 pm to 200 pm thick and some mm in area, cleaved from a parent TS6 crystal parallel to the (100) surface. 

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