Mean crystallite size

For a fixed filling ratio, the degree of crystallinity and mean crystallite size are somewhat higher in PFCM than in mechanical mixtures of similar composition and similar matrix characteristics [299, 300]. 

A commercial protonic ZSM-5 sample (CBV3020, Zeolyst Int., denoted as HZ5) having a Si/Al bulk ratio of 16.4 (from ICP) and a mean crystallite size of ca. 0.2 J.m (from... 

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). 

Table 9.2.5 Mean Crystallite Size (D) and Mierostrains Coefficient (t ) Inferred from Williamson-Hall Plot for Co,Ni, Powders with Almost the Same Particle Size (dm)...

Table 9.2.6 Mean Crystallite Size ( >) and Microstrains Coefficient (rj) Inferred from Williamson-Hall Plot for Powders in the FeCoNi System...

Results of similar experiments by Gault and his co-workers (93) with a 10-wt % Pt/Al203 catalyst (mean crystallite size 150-200 A) required the assumption that several successive rearrangements took place in the adsorbed phase before desorption. A model was developed in which either a dehydrocy-clization-hydrogenolysis event or a methyl or ethyl shift involving a tertiary atom competed with desorption. By assuming that the isomeric hexanes had the same desorption probability (d) and the different bond-shift processes proceeded with the same chance (r), it was found possible to reproduce the observed initial product distributions with these two independent parameters. In general, values of d 0.5 and t = 0.10-0.20 fitted the results best. As an additional refinement, the ratio of the C2—C3 and C3—C4 bond scission probabilities for methylcyclo-pentane (0) was taken to be 3.3, rather than the statistical value of 2, to improve further the fit. 

Figure 4. Comparison between the mean particle size dg ( ) and the mean crystallite size 3 ( ) of supported PcFe. "Reproduced with permission from Ref. 16. Copyright 1983, Academic Press1".

Typically, core/shell magnetic nanomaterials synthesized according to steps of Subheading 3.1 consist predominantly of a magnetite core with a mean crystallite size of 9-11 nm that can be calculated from the broadening of the X-ray... 

Sample S%et (m g M Total Pore Volume (cm ) Mean Pore Diameters (nm) Mean Crystallite Size s (nm) C/Sn (at%)... 

Among all the precursors studied, precursor 2a appears to be the most useful precursor of nanocrystalline mesoporous Sn02 for application purposes. In comparison with 2d and 2f, compound 2a provides pure cassiterite tin dioxide materials with very low amounts of carbon from calcination at 400 °C, owing to the rather facile elimination of the p-phenylene spacer. After calcination at 400 and 500 °C, the BET surface area (110 and 70 m g ), the mean pore size diameter (5 and 6.5 nm) and the mean crystallite size (4.5 and 7 nm) are close to those reported for tin dioxide materials prepared by the template method after... 

In summary, the nature of the hybrid therefore allows, to some extent, the control of both texture and morphology of the tin dioxide materials obtained after calcination. Nevertheless, treatment at 500 °C leads to similar BET surface area and mean crystallite size, which shows that annealing at very high temperature erases completely the fingerprint of the organic linker. 

X-ray diffraction Mean crystallite size, carbon-carbon pair correlation function... 

Adsorption measurements with different supports or catalysts were carried out by using a mixed solution of cinchonidine and substrate 1 (4 mmol/1 for each) in solvent B. After stirring at 298 K for 1 h, the amount of each compound adsorbed was determined from the decrease in the concentration of the solution, The concentrations were monitored by HPLC. The mean crystallite sizes of Pd in the reduced catalysts were obtained from XRD line broadening. The total surface areas (Sbet) and the areas of Pd metal surface (Spa) were determined using the nitrogen adsorption at 77 K and by the CO chemisorption at 323 K, respectively. 

First, support effects were studied with the catalysts reduced in situ at 298 K in solvent A. As shown in Fig. 1, the ee values for all the catalysts except Pd/C-1 were between 20 and 25% irrespective of the support used for the catalyst preparation, whereas the activity varied significantly, depending on the catalysts. Pd/Ti02-3 was found most active in the catalysts examined. The unexpectedly low activity and selectivity of Pd/C-1 suggest that the Pd particles incorporated in micropores of the support cannot play a role in this reaction both the substrate and the modifier are too bulky to reach the surface of Pd in micropores. The XRD measurements showed that the mean crystallite sizes of Pd were smaller than 3 nm for all the catalysts reduced at 298 K. 

With most catalysts, the heat treatment resulted in much increased selectivities and decreased activities. The increase in the mean crystallite size of Pd was not obvious in XRD measurements except for Pd/Ti02-5, Pd/Ti02-3n, and Pd/Ti02-3i catalysts. Although the degree of Pd dispersion, determined from the CO chemisorption, slightly decreased after the heat treatment of the catalysts as shown in Table 4, it is difficult to explain the effects of the... 

Mean crystallite size of palladium obtained from XRD measurements. 

It is essential for FNiP to be activated in a hydrogen stream to reduce nickel oxide on the surface before modification. Table 2 indicates the effect of the H2-treatment temperature on e.d. ability and on the mean crystallite size of the catalyst [7]. The e.d. ability value and mean crystallite size increased with the elevation of the H2-treatment temperature in the range between 200-300°C. These phenomena would indicate that nickel particles with a larger crystallite size would provide a surface suitable for the TA adsorption of the effective enantio-differentiation. 

H2-treatment temp. / °C e.d. ability / % Mean crystallite size / nm... 

The former indicates the formation of an a-AgCd phase [22] for which a Cd content of 21.8 at.% was estimated, and the latter corresponds to a cubic alloy structure which is richer in Cd [19], Their mean crystallite sizes were 11.4 nm and 18.2 nm, respectively, which is significantly lower than that of Ag particles in Ag/Si02-P (27.6 nm). 

Mean crystallite sizes of the Sn02 particles (D) (Table 2) were calculated using the Scherrer equation. Particles for all three compositions remain small ( 5A) for calcination... 

The basic and most commonly used method for identifying the amorphous structure is X-ray diffraction (XRD). The diffraction patterns consist of broad bands instead of discrete peaks because of the lack of long-range atomic order of the amorphous state. This method is used to follow the changes in the amorphous structure that occur during pretreatment (37, 38), heat treatment (21, 23, 39-44), and reaction (22, 45-49). XRD permits the identification of different intermediate metastable crystalline phases (2,39, 40,50-52). Also, changes in the surface chemical composition induced by catalytic transformation are detected by XRD (46,53,54). Finally, X-ray line broadening is used to determine the mean crystallite size (21, 53). 

Calculation of mean crystallite size, lattice strain and frequency distributions of crystallite sizes from the same XRD line-profiles used for crystallinity determinations. In addition to the application of the Scherrer equation, two single-line methods were used the variance method of Wilson (1963) (Akai and To th 1983 Nieto and Smchez-Navas 1994), and the Voigt method of Langford (1978) in combination with single-line Fourier analysis (Akai et al. 1996, 1997, 2000 Warr 1996 Jiang et al. 1997 Li et al. 

---