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No / A macrocycle, 6, has been synthesized in high yield from 2,5-di(pyrazol-1-yl)hydroquinone and 1,1`-fc[B(Me)NMe2]2 {fc = Fe(C5H4)2}. The molecule incorporates two redox-active 1,1`-ferrocenylene units in its backbone and contains four chiral boron centers, each of them possessing the same configuration. It is demonstrated that crystal structures of organometallics of moderate complexity can be solved from high-resolution X-ray powder diffraction patterns, once the connectivity between the functional groups is known.

Texture, i.e. preferred orientation, can cause large systematic errors in quantitative analysis of crystalline materials using x-ray powder diffraction (XRPD) data. Various mathematical forms have been proposed for the application of preferred orientation corrections. The most promising of these appears to be the single-parameter March (1932) model proposed by Dollase (1986).Li and O'Connor (1989) applied the March model to determine the level of preferred orientation in various gibbsites using two procedures. The first involved the Rietveld (1969) least squares pattern-fitting method. Each pattern was Rietveld-analysed in two ways, initially assuming random orientation of the crystallites and subsequently with the March model. The second procedure for preferred orientation analysis, described here as the line ratio method, determines preferred orientation factors according to the intensity ratios of carefully selected line pairs.In the thesis the procedures proposed by Li and O'Connor for texture analysis have been evaluated with XRPD data sets for molybdite, calcite and kaolinite. The results indicate that while the March formula improves agreement between the' calculated and measured patterns in Rietveld analysis, other forms of systematic error in the intensity data appear to limit the effectiveness of the March formula in general. It has been found also that the line ratio method improves agreement between the data sets, but less effectively than the Rietveld method. It is proposed that extinction is likely to be the most influential source of systematic error competing with texture.

The majority of the metallic elements adopt simple, high-symmetry structures at ambient pressure. These consist of a highly-ordered arrangement of atoms, which can be described by a crystal lattice that is periodic in three dimensions. It may be expected that close-packed structures, such as face-centred cubic (fcc) and hexagonal close-packed (hcp), would be favoured at high pressures due to the increase in density. However, many of these elements transform to lowsymmetry, complex structures on compression. In particular, a number have been observed to adopt incommensurately-modulated structures at high pressure. In these structures, atoms are displaced from their average positions by a modulation wave, the wavelength of which is an irrational multiple of the lattice periodicity. Diamond-anvil cells (DACs) can be used to compress materials to over a million times atmospheric pressure. In these devices, a small sample is compressed between the tips of two diamond anvils. The atomic arrangement of materials at extreme pressures can then be probed using the intense x-ray beams provided by synchrotron sources. In this work, the high-pressure crystal structures of the lanthanide elements europium (Eu) and samarium (Sm) have been investigated using angle-dispersive x-ray powder dffraction techniques. The high-pressure structural behaviour of Eu has been found to be remarkably different from that of the other lanthanide elements. Two new high-pressure phases of Eu are reported, both of which have an incommensurately-modulated crystal structure.

In this work, the crystallographic structure and its changes under thermal treatment of different systems consisting of metal oxide nanoparticles is studied. The principal method used throughout the thesis is x-ray powder diffraction enriched with grazing incidence small angle x-ray scattering when the nanoparticles form an ordered structure or with x-ray absorption spectroscopy when additional information on local crystallographic structure is required. For all the systems the preparation conditions were optimized according to the crystallographic data for further applications.

This experimental work aims to characterize the SiC layer of various Tri-Structural Isotropic (TRISO) coated fuel particles. In the first part of the work, Raman spectroscopy is used to qualitatively characterize the SiC TRISO layer and to identify the presence of silicon from peak positions. Free silicon poses a significant threat to the integrity of the SiC layer because it melts at 1414oC, significantly lower than the maximum operating temperature of 1550oC. Crystalline silicon is characterized with qualitative Raman spectroscopy by a 520 cm-1 peak. Silicon is found to be preferentially concentrated along the SiC layer close to the inner pyrolytic carbon (IPyC) layer. Samples that were only mounted and polished are compared with those that have in addition also been etched. Disordering of the crystals and peak splitting necessitated the use of peak de-convolution. The 3C, 6H and 15R polytypes of SiC were identified. The second part of the Raman spectroscopy work involves the development of calibration curves using peak areas from known binary mixtures (5%, 25%, 50% and 75% Si) to quantify the amount of silicon found relative to SiC. Initially the SiC polytypes used in these mixtures are 3C, 4H and 6H. Reasonably good logarithmic calibration fits were obtained with R2 values of 0.996, 0.966 and 0.988 respectively. However some error accompanied the calibration values and an average of ten analyses yielded a more reliable average. The calibration curve results made it possible to estimate the silicon content throughout the SiC layer for each sample, when combining the results of the qualitative and quantitative Raman spectroscopic study. Samples PO6 and PO8 revealed high peaks of crystalline silicon. When peak areas were quantified and related to the 3C calibration curve, as much as 60% silicon was calculated for both samples. Etching was found to slightly lower the silicon to SiC ratio. The calibration accuracy for the binary mixtures was checked by plotting calculated values against weighed-off values, yielding 3C, 4H and 6H straight-line fits with R2 values of 0.983, 0.941 and 0.981 respectively. These binary mixtures were analyzed with the SEM, which revealed variable particle size and segregation of silicon and SiC. Quantitative Raman spectroscopy is however known to be affected by a significant number of variables that are difficult to control. Attempts were made to decrease the scatter of the results from the calibration curve to yield more precise results. Two pure samples of silicon and SiC were studied separately, in attempts to better understand particle size and distortion effects. Distortion was found to have a greater impact on the scatter of peak area values than particle size. The scatter associated with pure sample peak areas casts doubt on the accuracy of the binary calibration curves. Rietveld analysis using X-ray powder diffraction is used to further support the Raman spectroscopy work by qualitatively and quantitatively characterizing the phases involved in each TRISO particle, to a greater degree of accuracy than the Raman spectroscopy. Refinement components include 2H graphite, quartz, SiC (3C, 6H, 8H and 15R), silicon and tetragonal ZrO2. Oxidized samples were compared with unoxidized samples. The outer pyrolytic carbon (OPyC) layer was oxidized (to improve the accuracy of quantitative measurements). Graphite percentages dominated the refinements with values ranging from 57% to 90% for unoxidized samples and 28% to 83% for oxidized samples. The 3C SiC polytype is the most abundant polytype and constitutes 78% to 83% of the SiC (unoxidized samples) and 82% to 90% (oxidized samples). Trace percentages of silicon were detected for PO6 (0.4%), PO8 (0.6%) and PO10 (0.1%) Quantitative XRD results are known to be accurate to around 1% at the 3ó level. Calibration curves were also subsequently constructed from the same samples as those used for quantitative Raman spectroscopy by comparing the weighed-off values to the measured ones. The 3C, 4H and 6H R2-fits are 0.991, 0.978 and 0.984 respectively. All the milled samples contained significant α-Fe which contaminated the samples from the grinding process. After dissolving the α-Fe in HCl a sample was tested to check the effect of the α-Fe specifically on microabsorption. Microabsorption was found to be an insignificant effect. The second part of the XRD work focused on the high-temperature stability of SiC up to 1400oC. Al2O3 was used as the standard and the instrument was calibrated using its two independent lattice parameter values along the a-axis and c-axis to make temperature corrections. Temperature corrected curves (of SiC and graphite) were constructed, which superimposed the theoretical Al2O3 curve along the a-axis and c-axis. The linear thermal expansion coefficients of SiC and graphite could then be determined from corrected lattice parameter values. The thermal expansion coefficients of G102 SiC had similar values to the literature values up to 800oC. Thereafter the experimental values had significantly higher thermal expansivity when compared to literature values. PO4 and PO9 thermal expansion coefficient values were higher below 500oC, but much closer as temperatures approached 1400oC. There was little correlation between G102, PO4 and PO9 graphite c-axis thermal expansion coefficient curves and literature values. The third section of the work involves the characterization of the SiC layers of three of the samples by transmission electron microscopy using their selected area electron diffraction patterns. This facilitates the unequivocal characterization of the SiC polytypes. The 3C and 6H polytypes were identified. There is substantial disorder in the crystals. Planar defects of differing periodicity are seen along the [111] direction of the 3C polytype. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted

The aim of this research project was to synthesise both the normal and inverse cobalt aluminate spinels by various methods and characterise them mainly by Raman spectroscopy with the support of X-ray powder diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), energy disperse spectroscopy (EDS), and scanning electron microscopy (SEM). Four different synthesis methods (glycine-gel, citrate-gel, polyol and solid-state) were used to synthesise the cobalt aluminate powders with the general formula CoIICoIIIxAl2-xO4 (where x = 0-2). The gel or powder precursors were annealed at various temperatures ranging from 350ºC - 1000ºC. The properties of the intermediate and final products, influenced by the synthesis method, processing temperature, processing time and particle size, were compared. Raman spectra and XRD patterns indicating the presence of both normal and inverse cobalt aluminate spinel were observed. The inverse spinel was identified both as a transitional phase as well as a final phase, depending on the synthesis method and annealing temperature used. The various synthesis methods were also used to gain further insight into the crystal chemistry of cobalt aluminate. The solid-state method is the more traditional synthesis method. Solution techniques (glycine-gel, citrate-gel and polyol) were used in an attempt to synthesise blue cobalt aluminate at relatively low temperatures and processing times in order to obtain homogeneous, nanosized crystals with broad applicability. The polyol method was found to be most favourable for the synthesis of blue cobalt aluminate with regard to processing temperature and processing time. The various characterisation methods used, show that the intensity of the colour of the powders produced are strongly related to the degree of material crystallinity as well as Al/Co ratio. Inverse (Co2AlO4) and Co3O4 spinels are formed at lower temperatures or when the Co/Al ratio is greater than 0.5. The normal spinel (CoAl2O4) is produced at higher temperatures or when the Co/Al ratio is 0.5. The XRD patterns of CoAl2O4, Co2AlO4 and Co3O4, are very similar because they share the same spinel cubic structure (space group Fd3m) differing only slightly in the lattice size. It has been demonstrated that Raman and XRD can be used to distinguish between inverse and normal spinels while FT-IR and EDS are useful for assessing the purity of the powders produced. As predicted by group theory, five Raman and four IR active vibrations were evident in the results. / Dissertation (MSc)--University of Pretoria, 2009. / Chemistry / unrestricted

No / Bulk crystallisation of protein therapeutic molecules towards their controlled drug delivery is of interest to the biopharmaceutical industry. The complexity of biotherapeutic molecules is likely to lead to complex material properties of crystals in the solid state and to complex transitions. This complexity is explored using batch crystallised lysozyme as a model. The effects of drying and milling on the solid-state transformations of lysozyme crystals were monitored using differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), FT-Raman, and enzymatic assay. XRPD was used to characterise crystallinity and these data supported those of crystalline lysozyme which gave a distinctive DSC thermogram. The apparent denaturation temperature (Tm) of the amorphous lysozyme was ∼201 °C, while the Tm of the crystalline form was ∼187 °C. Raman spectra supported a more α-helix rich structure of crystalline lysozyme. This structure is consistent with reduced cooperative unit sizes compared to the amorphous lysozyme and is consistent with a reduction in the Tm of the crystalline form. Evidence was obtained that milling also induced denaturation in the solid-state, with the denatured lysozyme showing no thermal transition. The denaturation of the crystalline lysozyme occurred mainly through its amorphous form. Interestingly, the mechanical denaturation of lysozyme did not affect its biological activity on dissolution. Lysozyme crystals on drying did not become amorphous, while milling-time played a crucial role in the crystalline-amorphous-denatured transformations of lysozyme crystals. DSC is shown to be a key tool to monitor quantitatively these transformations.

<p> The addition compounds of selenium tetrafluoride with sulfur trioxide, boron trifluoride, and arsenic, antimony, bismuth, vanadium, niobium and tantalum pentafluorides have been prepared. These compounds have been studied in the solid state using X-ray powder diffraction, and infra-red and Raman spectroscopy; in the molten state using Raman spectroscopy, nuclear magnetic resonance spectroscopy, and conductimetric and viscosity measurements; and in solution using Raman spectroscopy, cryoscopy, conductivity and nuclear magnetic resonance spectroscopy.</p> <p> The compound SeF4SO3 has a fluorosulfate-bridged polymeric structure. The remaining compounds have fluorine-bridged structures, this interaction being the strongest in SeF4BF3 and SeF4VF5 and decreasing in the order SeF4NbF5 SeF4TaF5 SeF4AsF5 SeF4SbF5 SeF4BiF5.</p> <p> The characteristics of the SeF3+ group are discussed. The properties of fluorine bridging and various methods of detecting such interactions are also considered.</p> / Thesis / Doctor of Philosophy (PhD)

In this diploma thesis there was studied a composition of a solid fraction of the atmospheric aerosol of the daily measurements from Pilsen by X-ray powder diffraction by the method of the parallel beam. The phase analysis was accomplished by comparing of the diffraction dates with a database of compounds usually occurring in the solid fraction of the atmospheric aerosol in this area. This database was created from works published earlier. In these samples there were also identified asbestos fibers of actinolite by the scanning electron microscope with EDS module. In this thesis there was also described a transport of several anthropogenic compounds of the atmospheric aerosol in dependence on a meteorological situation. Powered by TCPDF (www.tcpdf.org)