Electron diffraction pattern, mineral

Combined analyses by XRD and TEM showed that the aurichalcite mineral was sufficiently similar to the synthetic aurichalcite to be used as a model compound, to study the microstructural changes occurring during the catalyst preparation procedures. Calcination of the mineral and synthetic samples led to highly preferred orientations of ZnO. ZnO electron diffraction patterns with [lOlO] and [3031] zone... 

Figure 5a. Mineral aurichalcite calcined at 350°C for 4 hours. Selected area electron diffraction pattern showing ZnO orientations with zone axes of [lOTo] and [3031]. See text for other ZnO orientations. An aurichalcite pattern close to a [101] zone axis is also present.

The best formed plate textures are found in crystals with a layer lattice, and generally in all crystals having the form of thin plates. Diffraction pattern (Fig.7) indicates a texture of this type, and was obtained from crystals in the shape of thin hexagonal plates. The specific role of the oblique-texture type electron diffraction patterns have in the study of clay minerals having layer structures (B.B.Zviagin, 1964, 1967). 

Many compounds, including clay minerals, form needle- or plateshaped crystals. With finely dispersed minerals, the electron diffraction method can give a special kind of diffraction pattern, the texture pattern, which contains a two dimensional distribution of a regularly arranged set of 3D reflections [2], Specimens of fine-grained lamellar or fiber minerals, prepared by sedimentation from suspensions onto supporting surfaces or films, form textures in which the component microcrystals have a preferred orientation. Texture patterns of lamellar crystals tilted with respect to the electron beam are called oblique texture electron diffraction patterns [1]. 

Optical examination of etched polished surfaces or small particles can often identify compounds or different minerals hy shape, color, optical properties, and the response to various etching attempts. A semi-quantitative elemental analysis can he used for elements with atomic number greater than four by SEM equipped with X-ray fluorescence and various electron detectors. The electron probe microanalyzer and Auer microprobe also provide elemental analysis of small areas. The secondary ion mass spectroscope, laser microprobe mass analyzer, and Raman microprobe analyzer can identify elements, compounds, and molecules. Electron diffraction patterns can be obtained with the TEM to determine which crystalline compounds are present. Ferrography is used for the identification of wear particles in lubricating oils. 

Many mineral and synthetic samples examined by Bennett and Gard 17,18) gave typical C-centered orthorhombic diffraction patterns and with few exceptions had streaks in the hOl section, indicating an incomplete c-glide plane. A few crystals gave electron diffraction patterns having diffuse maxima in the hOl streaks, which could be interpreted as representing an I-centered mordenite structure. 

X-ray or electron diffraction analyses are commonly employed to determine mineral species. In the case of biophosphates, these techniques are limited because the material is a complex mixture of organics and inorganics and furthermore the crystallites are small. Thus, resolution of X-ray diffraction pattern of bone and dentin material is rather poor. Electron diffraction pattern is generally better, but there is always the possibility of secondary alteration of the specimen during exposure. Other methods — such as infrared analysis — have their limitations too. In short, there are some analytical problems which may in part account for the conflicting interpretations offered in the literature. 

Several other lines of evidence were cited in support of this hypothesis. The TG curve of C-S-H gel (Fig. 5.3), expressed in terms of H20/Ca ratio, was shown to be intermediate between those of 1.4-nm tobermorite and jennite. The densities and H20/Ca ratios of C-S-H gel are similar to those of 1.4-nm tobermorite, jennite and structurally related minerals of comparable H20/Ca ratios (Table 5.5). The XRD evidence has already been noted of the few selected area electron diffraction patterns that have been obtained from particles of C-S H gel, some were shown to resemble ones of tobermorite minerals, and others that of C-S-H(II). Finally, the occurrence of two types of structure, with differing compositions, could explain the local variability in composition observed in electron optical analyses. 

In an electron microscope, the electron beam is produced by an electron gun, in which the electrons are boiled off a heated filament and then accelerated by a highly stabilized electrical potential difference of some hundreds of kilovolts. An electron beam produced in this way is not coherent, but its degree of coherence can be understood in terms of the concepts of optical coherence theory. Later chapters will show that the nature of electron diffraction patterns from crystals that exhibit long-period superstructures (which are not uncommon in many important rockforming minerals) depends critically on the degree of spatial coherence of the incident electron beam. Therefore, it is important to conclude this chapter with a brief review of the basic ideas of optical coherence. A detailed account of the theory is given by Born and Wolf (1965). 

Figure 26 Electron micrograph of partially mineralized collagen. Magnification is 6 X 10. An electron diffraction pattern is shown in the inset that identifies the mineral as apatite (after Glimcher, 1959 reproduced in...

Other less common elements recorded in these analyses are tin, chromium, and nickel. The tin is found among some of the opaque constituents (minerals) and is thought to be present as the mineral cas-siterite (Sn02), which is reportedly (17) associated with sulfide mineralization. Less is known about the location of the chromium, which may be a minor element in more than one mineral, e.g., pyrite and calcite. Nickel, on the other hand, is associated with sulfur, as can be shown in the X-ray spectra (Figure 10) obtained from a diamond-shaped mineral fragment. The analysis was obtained in the reflection (SEM) mode on the STEM, which excluded the recording of an electron diffraction pattern. The mineral tentatively is identified as millerite, a nickel sulfide (NiS) with no iron and a 1 1 ratio of nickel to sulfur. However, these conclusions must be considered as tentative until positive identification of the nickel sulfide is possible. 

In addition to those minerals associated with the granular constituent, there are numerous submicron-sized minerals that are intimately mixed with other coal macerals. A typical example can be seen in Figure 11, which is a TEM micrograph of vitrinite, where the circular aperture identifies the region from which the electron diffraction pattern, shown in the inset, was obtained. The mineral, which was identified as kaolinite, appears to have been deposited as plates parallel with the coal bedding, based upon an analysis of the diffraction pattern. Also present in these coals is the clay mineral illite, which can be distinguished from kaolinite by both EDX and SAD analyses, lllites contain potassium (K)... 

Although there have been numerous attempts to show the presence of other minerals (brushite, whitlockite and octacalcium phosphate ) as primary constituents of normal bones and teeth, there is no straightforward evidence that such tissues contain any mineral other than dahllite (McConnell, 1973a). This statement applies also to possible precursors within these tissues, and also to a so-called amorphous calcium phosphate, which has been assumed to be present on the basis of spurious, indirect evidence even in the case of nascent dental enamel. An electron diffraction pattern of non-deproteinized bone is shown as Fig. 3.1.12. 

Fig. 20 High magnification of mineralized collagen fibrils. High resolution TEM image of the mineralized coUagen fibril inset is the electron diffraction pattern of the selected area. Reprinted from [232] with permission from Elsevier...

Figure 6c, d, and e. Electron micrographs of mineral aurichalcite calcined at 350°C for 4 hours and reduced in a 2% H2/N2 gas mixture, (c) Selected area diffraction pattern showing a ZnO orientation with a [loTo] zone axis. See text for other ZnO orientations. A Cu pattern with a [211] zone axis and randomly oriented Cu identified by the diffraction rings are shown. 

Minerals are identified by a variety of techniques. Some minerals can be identified on the basis of their elemental compositions, but diffraction or X-ray absorption near-edge structure (XANES) spectroscopy provides more compelling mineral identification. Diffraction patterns, produced either by electron or X-ray beams, provide a direct measurement of the spacing between planes of atoms in the crystal structure. When coupled with element analysis, diffraction provides mineralogical identification. 

Many of the fine minerals shown previously in Figure 7 can be seen to be randomly oriented in fact, some of the platy minerals are found to be perpendicular to the layering. SAD experiments on some of the larger mineral plates typical of those shown in Figure 12 resulted in diffraction patterns of the type shown in the inset. The pattern was indexed as the (hkO) plane of kaolinite, indicating that the electron beam is parallel to the c-axis of the crystal. 

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