Crystallites electron micrographs

Figure 5.5. Electron micrographs of different types of diamond film grown on silicon. The white bar shows the scale in micrometres (p.m) (thousandths of a millimetre), (a) The initial stages of diamond growth on a nickel substrate, showing individual diamond crystallites nucleating in scratches and crevices created on the surface by mechanical abrasion, (b) a randomly oriented him,...

Figure 6.8 Scanning electron micrographs of magnesium ammonium phosphate mortar III (Abdelrazig, Sharp El-Jazairi, 1989) (a) after 1 hour, low magnification, (b) after 1 hour, high magnification showing needle-like and cuboid crystallites.

Figure 20 Normalized frequency distributions of crystallite thickness for linear polyethylene fraction, Mn = 76,700, Mw = 80,800 crystallized at 118 °C ( ), electron micrograph histogram ...

X-Ray studies confirm that platinum crystallites exist on carbon supports at least down to a metal content of about 0.03% (2). On the other hand, it has been claimed that nickel crystallites do not exist in nickel/carbon catalysts (50). This requires verification, but it does draw attention to the fact that carbon is not inert toward many metals which can form carbides or intercalation compounds with graphite. In general, it is only with the noble group VIII metals that one can feel reasonably confident that a substantial amount of the metal will be retained on the carbon surface in its elemental form. Judging from Moss s (35) electron micrographs of a reduced 5% platinum charcoal catalyst, the platinum crystallites appear to be at least as finely dispersed on charcoal as on silica or alumina, or possibly more so, but both platinum and palladium (51) supported on carbon appear to be very sensitive to sintering. 

Figure 7 (a, b, d, and e) shows transmission electron micrographs from Pd-Ag films of comparable weight, prepared and annealed at 400°C, and used once to catalyze the oxidation of ethylene at 240°C (40). The structure of this series of alloy films varied consistently with composition. Silver-rich films (e.g., Fig. 7a, 13% Pd) showed extensive coalescence of the crystallites, while at the other end of the composition range (e.g., Fig. 7e,...

Alternatively, it may be possible to demonstrate for the pure metals that the catalytic activity is independent of film weight in a certain weight range. For example, rates of ethylene oxidation were constant over pure palladium films, deposited and annealed at 400°C and weighing between 4 and 40 mg (73). Then, if electron micrographs show that the crystallite size is relatively independent of composition, a satisfactory comparison of catalytic activity can be made at the various alloy compositions. Finally, surface area measurements are less urgently needed when activity varies by orders of magnitude, or where the main interest lies outside the determination of absolute reaction rates. 

Figure 8.2 (a) Electron micrograph of a supported metal catalyst (Rh-Si02) (b) closeup of metal particles ((a) and (b) courtesy of Professor A. Datye) (c) schematic drawing of the atomic structure of a metal crystallite... 

Crystallinity, X-ray, Cu/ZnO/Al O, 31 293 Crystallites, see also Alloy films electron micrographs of, 22 135-138 Crystallography... 

Figure 3J. Transmission electron micrographs of (a) membrane precursor crystallites and (b) a thin, unsupported membrane film.

Figure 3.3.5 shows a high-resolution transmission electron micrograph showing a close-up view of a part of a CdS particle. One may find that the particle consists of randomly oriented crystallites, as is obvious from the clear lattice image of each... 

Transmission electron micrographs (TEM) of submicrometer-size particles show faceted particles, and selected area electron diffraction (SAED) patterns of isolated particles show that they are formed by a small number of crystallites (Fig. 9.2.14a), This result is consistent with the mean size of the crystallites, which can be inferred from the x-ray diffraction lines broadening analysis using a William-son-Hall plot (35) in order to take into account the contribution of microstrains to the line broadening. Over the whole composition range, the mean crystallite size is in the range 40-60 nm for particles with a mean diameter in the range 200-300 nm (Table 9.2.5) (33). 

Mr. McCartney. From a study of electron micrographs, we estimate that a very large proportion of the apparent vitrain band in this meta-anthracite consists of graphite crystallites or platelets. The intensity and sharpness of graphite peaks in diffraction patterns supports this view. 

How can a support effect exist with such poor dispersions of the metallic phase Electron micrographs prove that the distribution of metallic particles is broad and that small crystallites (<10 A) exist which can be located in the zeolitic lattice. Another point is that this effect exists with... 

Transmission electron micrographs and XPS results have been used to show that a catalyst, with a high silica content in the matrix, prevents nickel dispersion (16,18). In fact, in a FCC with a Si-rich (Si/Al = 4.3) surface, XPS data has indicated that calcination and steaming cause nickel (and vanadium) migration to the cracking catalyst surface where nickel sinters. As a result, nickel crystallites 50... 

Figure 4. Transmissions electron micrographs of 2% Ni on catalyst (A) before and (B) after steaming. Steam-aging has little effect on Ni distribution and crystallite size stays unchanged at 50-70. ...

FIGURE 17 Transmission electron micrograph of platinum crystallites on a y-alumina support. The black bar represents 100 A. 

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