X-ray diffraction lines

In this chapter shock modification of powders (their specific area, x-ray diffraction lines, and point defects) measurements via analytical electron microscopy, magnetization and Mossbauer spectroscopy shock activation of catalysis, solution, solid-state chemical reactions, sintering, and structural transformations enhanced solid-state reactivity. 

Table 7.2. Shock-modified powders X-ray diffraction line broadening.

Fig. 7.2. X -ray diffraction line broadening studies in inorganic powders by Morosin and co-workers show evidence for large plastic deformation with residual strain characteristic of cold-worked metals [86M02].

Fig. 7.3. Crystallite size determined from x-ray diffraction line broadening studies show substantial shock-induced reductions. The chemical reactivity of such powders would be expected to be greatly enhanced [86M02].

Most surface area measurements are based on the interpretation of the low temperature equilibrium adsorption of nitrogen or of krypton on the solid using the BET theory [33,269,276—278]. There is an extensive literature devoted to area determinations from gas adsorption data. Estimates of surfaces may also be obtained from electron micrographs, X-ray diffraction line broadening [279] and changes in the catalytic activity of the solid phase [ 280]. 

The X-ray diffraction lines corresponding to Mg(OH)2 were distinctive. The basal line (001) was very broad, the prism line (110) was very sharp and the other lines hkl) were intermediate in breadth. This was interpreted as implying that Mg(OH)a crystallites adopt an exaggerated sheet-like morphology in this system (Urwongse Sorrell, 1980b). The (001) line... 

The strongest x-ray diffraction line is then the (00 n+1) line, with corresponding reticular distance d oon+i) of ... 

Coherency strains, resulting in the broadening of the x-ray diffraction lines (more pronounced for the [100] and [110] than for the [111] orientation). 

The TiO, though of proper stoichiometry, lacks full cubic symmetry as seen by splitting of the X-ray diffraction lines. The lattice parameter given in Table II is an average value. 

This material may be removed by reheating the sample to 850°, followed by the same annealing procedure outlined above. The X-ray diffraction pattern for 2H(a)-TaS2 may be used for identification. The following d values have been obtained for major low angle X-ray diffraction lines (and intensities) 6.05 (1) 3.025 (0.06) 2.8709 (0.32) 2.7933 (0.07) 2.3937 (0.80) and 2.3389 (0.04) A. Note that it is difficult to obtain the ideal intensities because of preferred orientation of the crystallites. This material is a superconducting metal with Te = 0.8 0.05°K.2... 

The pyridine intercalate is blue-black. Examination of the individual platelets under a microscope reveals a characteristic exfoliated appearance. Hexagonal symmetry is retained with a = 3.325 A and c/2 = 12.03 A. Comparison with the slab thickness for the parent 2H(a)-TaS2 shows a c-axis expansion, 8, of 5.99 A. The following d values have been obtained for low-angle X-ray diffraction lines 12.03, 6.015,4.010,3.008, 2.880, and 2.859 A. 2TaS2 C5HsN is also super conducting with a transition temperature of 3.5 0.3°K2,3... 

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). 

WIDE-ANGLE X-RAY DIFFRACTION LINE-BROADENING FOR CRYSTALLITE SIZE AND STRAIN... 

Phosphorescence. Phosphorescence of Fe3+-doped Gels. In H20. In all systems studied the phosphorescence of the initial Fe3+-doped gel showed a wreak emission at 690 nm with a shoulder at ca. 720 nm. Emission and excitation spectra were similar to those shown in Figure 1. The phosphorescence comes from the Ai - 47 transition while the various other transitions in the Fe3+ ion in tetrahedral coordination are apparent in the excitation spectrum (8, 10). Throughout the induction period emission intensity increased only slightly, the peak at 690 nm increasing somewhat more than the shoulder at 720 nm. After induction the signal rose rapidly until a constant intensity was attained. The rapid increase in intensity of the phosphorescence signal after induction ended paralleled the intensity increase of the x-ray diffraction lines. 

Scherrer equation is typically within 10% of that observed directly by TEM (Table 27.1), indicating that lattice disorder in the LP particles does not significantly broaden the X-ray diffraction lines. 

A series of other condis crystals are the larger cyclo-alkanes, analyzed by Gross-mann 171). Figure 23 illustrates the transition behavior of cyclotetracosane and cyclo-hexanonacontane. The melting transition of cyclotetracosane has only about 1/4 the heat of transition at the disordering to the condis phase. The condis phase has a much higher symmetry and fewer X-ray diffraction lines. Infrared and Raman spectroscopy indicate that practically no additional conformational isomers are introduced on... 

Improved catalytic performance, selectivity and resistance to fusion, over bismuth molybdate catalysts was reported by McClellan (90) for catalysts obtained by chemically combining bismuth, molybdenum, phosphorus, and silica. After calcination at 450°C, the bismuth phosphomolybdate-on-silica catalyst showed an X-ray pattern of mainly crystalline Bi2(Mo04)3 which subsequently was converted to a new, substantially amorphous, phase after calcination at 800°C. Substantially morphous meant that the X-ray diffraction lines were broad diffuse bands of low intensity. The pattern of lines for this novel phase indicated a scheelite structure. A special interaction of silica with bismuth molybdate was also suggested by Callahan et al. (91). 

Figure 8. A comparison of X-ray diffraction lines for AuSn particles upon heating to 275 °C and 450°C. (a) as received, 18 nm average crystallite size (b) 275°C, 25 nm (c) 450°C, 36 nm (according to Scherrer Treatment of crystallite sizes).

The Ru02 particles can not be reduced at room temperature, but reduce readily at 773 K. The ruthenium particles produced after this reduction procedure are estimated to be 16 nm in diameter from x-ray diffraction line width analysis. The reduction results in further loss of crystallinity, reflected by a drop in surface area and microporosity (Table 2). In addition, the position of the asymmetric T-O stretching vibration is at 1071 cm" 1, indicating a very silicon-rich material. 

The first structure determination of a compound of berkelium, the dioxide, was carried out in 1962 (5). Four X-ray diffraction lines were obtained from 4 ng of BkC>2 and indexed on the basis of a face-centered cubic structure with a0 = 0.533 0.001 nm. 

In order to study the growth of particles with temperature, anatase powder (preheated to 150°C) was heated for a period of 3 h at 400, 600, 800 and 1000°C. Marked increase in particle size was noticed in the 600-1000°C region, as indicated by the photo-micrographs. The specific surface area (B.E.T.) of anatase heated at 400°C was 55 m2/g and decreased markedly for samples heated to higher temperatures. The crystallite size normal to the (101) and (110) reflecting planes of anatase and rutile samples was calculated by measuring the X-ray diffraction line-widths of the samples heated at 200, 400, 600, 800 and 1000°C for 3 h. The Scherrer equation corrected for instrumental line-broadening by Warren s equation was employed for the calculation.16 The line-width of the sample heated at 1000°C was taken as the reference. The crystallite size increases rapidly after 600°C (fig. lb). The transformation of pure anatase also starts only above 600°C. 

Fig. 7. The average particle sizes of copper ( ), its CuO precursor (O), and zinc oxide (A) determined from X-ray diffraction line broadening (41). [Reprinted with permission from J. Phys. Chem. 83, 3118 (1979). Copyright (1979) American Chemical Society.]...

Many polymeric solids consist largely of folded chain lamellae and that the breadth of X-ray diffraction lines is caused by the crystallite size distribution and by the disorder within the lamella. 

Figure 1. Comparison of measured structure factors of x-ray diffraction lines with those calculated on basis of octahedral and tetrahedral...

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