Texture, diffraction

One of the shortcomings of oblique-texture diffraction pattern is the formation of the dead zone around the texture axis and, thus, the absence of reflections located outside the interference field of the pattern. To reduce of dead zone, one has to obtain diffraction patterns as to maximum possible tilt angles of the texture axis to the beam (60-80°). 

The position of any reflection with given Miller indices hkl can be calculated once all unit cell parameters have been determined. This allows starting the last but very important procedure in the analysis of a texture diffraction pattern - estimating the integrated intensities of the diffraction... 

Figure 5 Textured diffraction pattern from a meteoritic chon-drule collected using short wavelength synchrotron radiation (A = 0.5 A) and a CCD area detector. The image displays sharp diffraction spots from olivine and pyroxene single crystals, and powder diffraction rings from the polycrystaUine matrix of the chondrule.

X-ray diffraction consists of the measurement of the coherent scattering of x-rays (phenomenon 4 above). X-ray diffraction is used to determine the identity of crystalline phases in a multiphase powder sample and the atomic and molecular stmctures of single crystals. It can also be used to determine stmctural details of polymers, fibers, thin films, and amorphous soflds and to study stress, texture, and particle size. 

Other excellent methods of phase identification include TEM and electron diffraction. These may be more useful for low-Z materials, ultrathin films, and for characterizing small areas, including individual grains. For multiphase films with incomplete texture, these methods and XRD are complementary, since in commonly used geometries, they probe atomic planes perpendicular and parallel to the thin film surface, respectively. 

Grain size in textured films. For films having a preferred growth direction—e.g., (111)—LEED can be used to determine the preferred direction and the grain size parallel to the surfrce. The preferred direction is obtained from the symmetry of the diffraction patterns, while the grain size is obtained from the shape in angle of diffracted beams. 

Metallurgists originally, and now materials scientists (as well as solid-state chemists) have used erystallographic methods, certainly, for the determination of the structures of intermetallic compounds, but also for such subsidiary parepistemes as the study of the orientation relationships involved in phase transformations, and the study of preferred orientations, alias texture (statistically preferential alignment of the crystal axes of the individual grains in a polycrystalline assembly) however, those who pursue such concerns are not members of the aristocracy The study of texture both by X-ray diffraction and by computer simulation has become a huge sub-subsidiary field, very recently marked by the publication of a major book (Kocks el al. 1998). 

The phase behavior of polybibenzoates has been investigated mainly by DSC, variable-temperature x-ray diffraction, and optical microscopy. However, only the first two techniques are useful in the case of polymers with the high-molecular weights required for materials with good mechanical properties and, in such cases, revealing textures are not usually observed by optical microscopy. 

A univocal confirmation of the development of crystalline aggregation in the fiber is the occurrence of layer reflexes Oil, HI, ill, and 101 on the textural x-ray diffraction pattern. The details of organization of the space lattice are defined by the parameters of the unit cell and the number of polymers felling into one cell. The data, established by different authors, are presented in Table 2. Daubenny and Bunn s [8] pioneer findings are considered the most probable for space lattices occurring in PET fibers. 

The parallelization of crystallites, occurring as a result of fiber drawing, which consists in assuming by crystallite axes-positions more or less mutually parallel, leads to the development of texture within the fiber. In the case of PET fibers, this is a specific texture, different from that of other kinds of chemical fibers. It is called axial-tilted texture. The occurrence of such a texture is proved by the displacement of x-ray reflexes of paratropic lattice planes in relation to the equator of the texture dif-fractogram and by the deviation from the rectilinear arrangement of oblique diffraction planes. With the preservation of the principle of rotational symmetry, the inclination of all the crystallites axes in relation to the fiber axis is a characteristic of such a type of texture. The angle formed by the axes of particular crystallites (the translation direction of space lattice [c]) and the... 

Figure 9-7. Elastic electron-diffraction pattern of a highly textured hcxaphenyl film. The Miller indices arc assigned using the intcrplauar spacings calculated in Kef. 11371. Inset Intensity of the f020) peak as a function of the angle between momentum transfer and the Teflon rubbing direction (see text) - taken from Ref. 138. ...

Thermotropic liquid-crystalline properties of different metal alkanesulfonates are studied by microscopy and X-ray diffraction [59]. Sodium soaps show smectic polymorphism of smectic A and smectic B phases. Ammonium soaps only show smectic A phases but polymorphism in the crystalline state. Calcium soaps show columnar mesophases. In Figs. 32 and 33 some textures and x-ray diffraction patterns are depicted. 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

Since the to angle tracks the 29 value, we need specify only 2 9, tp and x in order to correctly label the intensities read by the detector. In orientation texture studies the diffracted intensity is mapped as a function of a and x for a fixed 29. This provides (under appropriate assumptions) a measure of the probability... 

Structural and textural characterisation of pure SBA-15 and hybrid GFP/SBA-15 Pure SBA-15 and GFP/SBA-15 hybrid were characterised by X-ray powder diffraction, HRTEM and volumetric analysis. Calcined SBA-15 (Fig. 1, curve A) show the typical XRD pattern of an ordered hexagonal network of mesopores with (10), (11) and (20) reflections. The presence of well resolved (11) and (20) peaks indicate that the calcined material used for the preparation of the hybrid materials have a long-range order. The hexagonal XRD pattern was still clearly observed in the hybrid material (GFP/SBA-15), as all the three main reflections were found (Fig. 1, curve B), indicating that the sonication and the GFP physical adsorption does not affect the framework integrity of the material. 

The chemical compositions of the samples were obtained by ICP in a Varian 715-ES ICP-Optical Emission Spectrometer. Powder X-ray diffraction was performed in a Philips X pert diffractometer using monochromatized CuKa. The crystallinity of the zeolites was obtained from the intensity of the most intense reflection at 23° 20 considering the parent HZ5 sample as 100% crystalline. Textural properties were obtained by nitrogen physisorption at -196°C in a Micromeritics ASAP 2000 equipment. Surface areas were calculated by the B.E.T. approach and the micropore volumes were derived from the corresponding /-plots. Prior to the adsorption measurements the samples were degassed at 400°C and vacuum overnight. 

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