Synchrotron XRD

Figure 17.4 A. SEM image of a residual, concentric diatom frustule that has been converted to a predominantly 7 A clay (synchrotron XRD). B). Superimposed EDS image showing density of K, Fe, Si, and Al in a residual frustule (all components present, S subtrated from Fe). Authigenic clays also can occur as cements agglutinating matrix clays. In some cases, the authigenic components are amorphous, 7 A, or 10 A phases (see Michalopoulos and Aller, In Prep., Michalopoulos et al. 2000).

First preliminary variants of DDM were applied in the full-profile X-ray diffraction structure analysis of a series of new silica mesoporous materials and ordered nanopipe mesostructured carbons. DDM allowed stable back-ground-independent full-profile refinement of the structure parameters of these advanced nanomaterials, a result that was unattainable by any other method. To date, DDM has been applied to many various mesoporous and mesostructured substances. The structural parameters of a series of face-centred cubic (Fm3m), body-centred cubic Im3m), and two-dimensional hexagonal (pGmm) mesoporous silicates were determined by DDM from synchrotron XRD. A comprehensive structural analysis of mesoporous silicates SBA-16 (cage-type cubic Irriim), their carbon replicas, and silica/carbon composites was performed by applying DDM. The structure of MCM-48 mesoporous silicate materials was analysed in detail by DDM from different laboratory and synchrotron XRD data. The pore wall thickness of both as-made and... 

Weighted observed (solid), calculated (dashed), and difference (dotted) synchrotron XRD patterns for MCM 48 mesoporous silica (a) and its carbon replica (b) after DDM refinement. 

In the meantime, new characterization tools such as NMR, STEM, EXAFS, FTIR, and synchrotron XRD, etc., have allowed us to peer into the very heart of the zeolite and discern the nature and orientation of the active tetrahedral sites as well as determine the dimensions and connectivity of the zeolite pore systems. 

The advances of our capability in this area were aided by a number of remarkable new developments in analytical instrumentation. These new characterization tools include, among many, NMR, which provides information on the local environment of atoms in the structure (16-17), synchrotron XRD, which provides very high resolution x-ray data from powders (18-19), the application of Rietveld analysis of x-ray or neutron diffraction data to zeolite structure determination (20), and STEM, which provides atomic resolution of the crystal structure and its chemical composition (21), to name just a few. 

Fig. 9.4 a Anion receptors possessing long alkyl chains and b POM images of i Ic, ii 2c, and Hi 3c as mesophases at 170,70, and 196 °C, respectively, upon cooling from Iso. Also shown in bi is the synchrotron XRD pattern of Ic at 120 °C upon coohng from Iso and a proposed Colh model. The XRD by synchrotron irradiation was performed in [42] and the data was basically consistent with the XRD in [35]... 

Fig. 9.5 i POM images and ii synchrotron XRD patterns of (a) lc-Cl -TATA (70 °C for both cases) and (b) 2C C1 -TATA (150 and 101 °C, respectively) upon cooling from Iso along with proposed Colh models based on charge-by-charge and chaige-segiegated assemblies... 

Fig. 9.6 a POM texture and b synchrotron XRD pattern of Ic Cl -TBA at 62 °C upon cooling om Iso and a proposed Coin model based on charge-by-charge assembly... 

Leh] XRD, EPMA synchrotron XRD, mass spectrometry Room temperature / FeS2 + Co... 

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