Diffraction patterns of amorphous

Figure 5. Examples of diffraction patterns of amorphous polymers (19). Observed x-ray intensity is plotted vertically.

Synthesized copolymers were studied by the X-ray diffraction method. Diffraction patterns of amorphous polymers (Figure 9) show that the interchain distance reaches its maximum (t/i=10.24 A) at short lengths of flexible dimethylsiloxane backbone, n. As the length of dimethylsiloxane backbone increases ( = 21), the interchain distance decreases and for copolymer 5 reaches 7.54 A (Table 6). 

Electron diffraction patterns of amorphous and cryst Sb) 5)C.C.Coffin ... 

Electron diffraction patterns of amorphous and nanocrystallme materials are analyzed to measure the radial distribution fimction (RDF) to provide interatomic distances and their distribution. The principle of RDF analysis using electron diffraction is similar to X ray diffraction with the... 

Figure 2.01 Electron diffraction pattern of amorphous (upper) and crystalline (lower) iron. (After Ichikawa, 1973)...

Figure 7.64 Electron diffraction pattern of amorphous calcium phosphate (ACP) of a plasma-sprayed calcium phosphate coating adjacent to the interface with the Ti6AI4V substrate (Heimann and Wirth, 2006).

It was shown in Section 2.2.3 that the diffraction patterns of amorphous solids are in many respects similar to that of a microcrystalline powder. 

A. Howie, O.L. Krivanek, and M.L. Rudee. Interpretation of electron micrographs and diffraction patterns of amorphous materials. Phil. Mag. 21, 235-255 (1973). 

As the polymerization temperature increases, the diffraction reflections from the crystal phases broaden and blur, and they totally vanish at r > 1000-1100 K. Structures and, respectively, diffraction patterns of amorphous superhard phases of Ceo differ depending on the type of the preceding crystal structures obtained within the given pressure range at a lower temperature. Figure 16.9 presents diffractograms of all three types of amorphous phases. 

The stmcture of activated carbon is best described as a twisted network of defective carbon layer planes, cross-linked by aHphatic bridging groups (6). X-ray diffraction patterns of activated carbon reveal that it is nongraphitic, remaining amorphous because the randomly cross-linked network inhibits reordering of the stmcture even when heated to 3000°C (7). This property of activated carbon contributes to its most unique feature, namely, the highly developed and accessible internal pore stmcture. The surface area, dimensions, and distribution of the pores depend on the precursor and on the conditions of carbonization and activation. Pore sizes are classified (8) by the International Union of Pure and AppHed Chemistry (lUPAC) as micropores (pore width <2 nm), mesopores (pore width 2—50 nm), and macropores (pore width >50 nm) (see Adsorption). 

Fig. 6 displays the X-ray powder diffraction patterns of rhenium oxide. While the as-prepared sample is amorphous to X-ray, the sample soaked in acetone and dried at 100"C clearly exhibits sharp reflections corresponding to Re03. The large difference between the two X-ray patterns suggests that the processing conditions play a key role in the crystallinity and surface characteristics. As shown in the TGA plot of the as-prepared sample (Fig. 7), the weight loss of about 10% below 100 C results from the loss of water. 

It is important to note that this second choice is possible because expression (25) includes the smooth background belonging to the crystalline phases, so it can be separated from the background due to the amorphous phase. A typical example, where the amorphous phase is not available, is the study of crystallization process. In this case, the composition and the diffraction pattern of the amorphous phase can change a lot. 

For the spectra of Ni, peaks corresponding to Ni oxide and Ni metal are observed in the as-prepared sample [28-30]. After the etching with Ar, however, the peak of Ni metal is predominant. This implies that the state of Ni in the Ni-Zn nanoclusters is metallic, although their surface was oxidized under the atmospheric conditions. On the other hand, the identification of Zn state is difficult because the peak positions of Zn and ZnO in ESCA spectra are very close to each other. Furthermore, the B/Ni ratio determined by ESCA was increased with increasing Zn added e.g., Ni B = 73.3 26.7 and 60.6 39.4 for Zn/Ni = 0.0 and 1.0, respectively. Because no crystalline structure was found except for Ti02 from both electron and X-ray diffraction patterns of the respective samples, it can be concluded that formed nanoclusters were amorphous. Ni-Zn nanoclusters would be composed of amorphous intermetallic compounds through the... 

Figure 41.4 shows a typical XRD (X-Ray Diffraction) pattern of TUD-1, along with a TEM image (12). Similar to other mesoporous materials, TUD-1 has a broad peak at low 20. However, it has a broad background peak, commonly called an amorphous halo, and lacks any secondary peaks that are evident for example in the hexagonal MCM-41 and cubic MCM-48 structures. The TEM shows that the pores have no apparent periodicity. In this example the pore diameter is about 5 nm. 

Samples of the poly(dialkylphosphazenes) 1 and 2 displayed X-ray powder diffraction patterns characteristic of crystalline regions in the materials. The peaks in the diffraction pattern of 1 were of lower amplitude and greater angular breadth than those of 2. These data indicate that poly(diethylphosphazene) (2) is highly crystalline while poly(dimethyl-phosphazene) (1) is more amorphous with smaller crystalline zones. This high degree of crystallinity is probably responsible for the insolubility of 2 as noted above. All of the phenyl substituted polymers 3-6 were found to be quite amorphous in the X-ray diffraction studies, a result that is further evidence for an atactic structure of the poly(alkylphenylphosphazenes) 3 and 4 and for a random substitution pattern in the copolymers 5 and 6. 

In the crystalline state of a substance, the molecules are arranged in a defined unit cell that is repeated in a three-dimensional lattice [1], Since the crystal lattice can act as a diffraction grating for X-rays, the X-ray diffraction pattern of a crystal consists of a number of sharp lines or peaks, often with baseline separation. Figure 1 shows the X-ray powder diffraction pattern of the crystalline and amorphous forms of nedocromil sodium trihydrate. 

There is actually no sharp distinction between the crystalline and amorphous states. Each sample of a pharmaceutical solid or other organic material exhibits an X-ray diffraction pattern of a certain sharpness or diffuseness corresponding to a certain mosaic spread, a certain content of crystal defects, and a certain degree of crystallinity. When comparing the X-ray diffuseness or mosaic spread of finely divided (powdered) solids, the particle size should exceed 1 um or should be held constant. The reason is that the X-ray diffuseness increases with decreasing particle size below about 0.1 J,m until the limit of molecular dimension is reached at 1-0.1 nm (10-1 A), when the concept of the crystal with regular repetition of the unit cell ceases to be appropriate. 

In the X-ray powder diffraction patterns of the composites, the disappearance of the broad band centered at 22 °20, typical of amorphous silica, indicates that the zeolitisation of the mineral fraction of the parent composite was complete. In no diffraction pattern any sign of crystallised chitosan could be found. The two methods in which the silica-polymer beads were extracted from the aluminate solution after impregnation (methods A and C) allowed the formation of the expected zeolite X, with traces of gismondine in the case of the method C. The method B, in which excess aluminate solution was present during the hydrothermal treatment, resulted in the formation of zeolite A. 

In the disc method, the powder is compressed by a punch in a die to produce a compacted disc, or tablet. The disc, with one face exposed, is then rotated at a constant speed without wobble in the dissolution medium. For this purpose the disc may be placed in a holder, such as the Wood et al. [Ill] apparatus, or may be left in the die [112]. The dissolution rate, dmldt, is determined as in a batch method, while the wetted surface area is simply the area of the disc exposed to the dissolution medium. The powder x-ray diffraction patterns of the solid after compaction and of the residual solid after dissolution should be compared with that of the original powder to test for possible phase changes during compaction or dissolution. Such phase changes would include polymorphism, solvate formation, or crystallization of an amorphous solid [113],... 

Fig. X-ray diffraction patterns of (A) highly crystalline polymer and (B) amorphous polymer.

In amorphous solids there is a considerable disorder and it is impossible to give a description of their structure comparable to that applicable to crystals. In a crystal indeed the identification of all the atoms in the unit cell, at least in principle, is possible with a precise determination of their coordinates. For a glass, only a statistical description may be obtained to this end different experimental techniques are useful and often complementary to each other. Especially important are the methods based on diffraction experiments only these will be briefly mentioned here. The diffraction pattern of an amorphous alloy does not show sharp diffraction peaks as for crystalline materials but only a few broadened peaks. Much more limited information can thus be extracted and only a statistical description of the structure may be obtained. The so-called radial distribution function is defined as ... 

The transmission electron microscopy (TEM) and correlated electron diffraction patterns of quenched QAB2-4 alloy is shown in Figure 2. When annealed at 773K, by selected-area electron diffraction (SAED) patterns at transmission electron microscopy appears as a bright continuous ring, indicating an amorphous phase. 

The x-ray powder diffraction patterns of bmimCl Crystal (1) and (2) are shown in Fig. 3 [8]. The sharp peaks with distinct patterns indicate that they are different crystals and that neither of them is an amorphous solid. The continuous background notable for Crystal (2) is most likely to arise from the structural disorder existing in the crystal. The x-ray powder diffraction pattern of bmimBr is also shown in Fig. 3 for comparison. The pattern of bmimBr is more close to that of bmimCl Crystal (2) than to Crystal (1). 

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