In der vorliegenden Arbeit wurden Röntgentechniken benutzt um die Struktur von dünnen (etwa 40 nm) CrSi2-Schichten, die unter UHV-Bedingungen mittels reaktive Koabscheidung und template-Verfahren auf Si(001) hergestellt wurden, zu charakterisieren. Die Ergebnisse wurden mit TEM-, SEM- und RBS-Untersuchungen korreliert und ergänzt. Die XRD-Analysen zeigen, dass die beiden Abscheideverfahren immer zur Bildung der CrSi2-Phase führen, wobei die Kristallite mit einer bevorzugten Orientierungsbeziehung CrSi2(001)[100] || Si(001)[110] wachsen. Im ersten Teil der Arbeit wurde die Cr-Si-Koabscheidung benutzt um die Prozessparameter zu bestimmen, die zum Wachstum epitaktischer Schichten führen können. Die Strukturuntersuchungen zeigen, dass nur bei einer Substrattemperatur von 700°C nahezu geschlossene Schichten mit Kristalliten, welche lateral eine Größe bis zu 300 nm haben und neben der bevorzugten noch andere Orientierungen zum Substrat aufweisen, entstehen. Als zweite Herstellungsmethode wurde das template-Verfahren verwendet, wo die Cr-Si-Koabscheidung auf ein vorher in-situ präpariertes ultradünnes CrSi2-template erfolgt. Die Morphologie und die Stärke der bevorzugten Orientierung der CrSi2-Schichten sind stark von der template-Dicke abhängig. Die Abscheidung auf CrSi2-templates, welche aus einer Cr-Schicht mit nominaler Dicker von 0,35 nm bis 0,52 nm entstehen, führt zum Wachstum weitgehend geschlossener, homogener und epitaktischer CrSi2-Schichten. Ein Modell, das den Einfluss der template-Dicke auf die Qualität der CrSi2-Schichten erklären kann, wird vorgeschlagen.

An increasing number of fields would benefit from a single analytical probe that can characterise bulk objects that vary in morphology and/or material composition. These fields include security screening, medicine and material science. In this study the X-ray region is shown to be an effective probe for the characterisation of materials. The most prominent analytical techniques that utilise X-radiation are reviewed. The study then focuses on methods of amalgamating the three dimensional power of kinetic depth X-ray (KDFX) imaging with the materials discrimination of angular dispersive X-ray diffraction (ADXRD), thus providing KDEX with a much needed material specific counterpart. A knowledge of the sample position is essential for the correct interpretation of diffraction signatures. Two different sensor geometries (i.e. circumferential and linear) that are able to collect end interpret multiple unknown material diffraction patterns and attribute them to their respective loci within an inspection volume are investigated. The circumferential and linear detector geometries are hypothesised, simulated and then tested in an experimental setting with the later demonstrating a greater ability at discerning between mixed diffraction patterns produced by differing materials. Factors known to confound the linear diffraction method such as sample thickness and radiation energy have been explored and quantified with a possible means of mitigation being identified (i.e. via increasing the sample to detector distance). A series of diffraction patterns (following the linear diffraction appoach) were obtained from a single phantom object that was simultaneously interrogated via KDEX imaging. Areas containing diffraction signatures matched from a threat library have been highlighted in the KDEX imagery via colour encoding and match index is inferred by intensity. This union is the first example of its kind and is called diffraction enhanced KDEX imagery. Finally an additional source of information obtained from object disparity is explored as an alternative means of calculating sample loci. This offers a greater level of integration between these two complimentary techniques as object disparity could be used to reinforce the results produced by the linear diffraction geometry.

The jarosite group of minerals is part of the alunite supergroup, which consists of more than 40 different mineral species that have the general formula AB3(TO4)2(OH, H2O)6. There is extensive solid-solution in the A, B and T sites within the alunite supergroup. Jarosite group minerals are common in acid mine waste and there is evidence of jarosite existing on Mars. Members of the jarosite - natrojarosite – hydronium jarosite (K,Na, H3O)Fe3(SO4)2(OH)6 solid-solution series were synthesized and investigated by Rietveld analysis of X-ray powder diffraction data. The synthesized samples have full iron occupancy, where in many previous studies there was significant vacancies in the B site. Well-defined trends can be seen in the unit cell parameters, bond lengths A – O and Fe - O across the solid-solution series in the synthetic samples. Based on unit cell parameters many natural samples appear to have full iron occupancy and correlate well with the synthetic samples from this study. In addition, the infrared spectra of the samples were analyzed. The atomic structure of ammoniojarosite, (NH4)Fe3(SO4)2(OH)6, has been solved using single-crystal X-ray diffraction to wR 3.64% and R 1.4%. The atomic coordinates of the hydrogen atoms of the NH4 group have been located and it was found that the ammonium group has two different orientations with equal probability. Samples in the ammoniojarosite – hydronium jarosite solid-solution series were synthesized and analyzed using powder X-ray diffraction and Rietveld refinement. It was found that an incomplete solid-solution series exists between jarosite and plumbojarosite, Pb[Fe3(SO4)2(OH)6]2, based on experimental and mineralogical data. At the studied synthesis conditions, lead solubility in jarosite is extremely limited with occupancy of 2% in the potassium site. Increased Pb in the iv starting solution resulted in no increased substitution of Pb into jarosite, but an increased substitution of H3O+. The stable isotope (H) geochemistry of hydronium jarosite, (H3O,K)Fe3(SO4)2(O,OH)6, and the effect that the presence of hydronium in the crystal structure has on exchange rates of stable isotope values of jarosite with hydronium substitution has been investigated in this study. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2008-05-07 18:21:45.136

This thesis will introduce the study of methane as a mineral. Along with ammonia and water, methane is one of the main planetary-forming materials in the outer solar system. The topic of `new mineralogy of the outer solar system' is outlined and introduced, and previous studies in the area are discussed. This review identities a lack of highpressure structural knowledge on methane when compared to ammonia and water. The significance of this knowledge for the study of the planets Neptune and Uranus is discussed. The crystal structures of methane above 5.2 GPa were, prior to this thesis, unknown. To tackle this long-standing problem an integrated approach of high-pressure diffraction techniques had to be used. The dominance of hydrogen within the structures of methane necessitated the use of neutron diffraction. The difficulties and limitations of highpressure neutron powder diffraction are presented. It will be shown that the complexity of the subsequent structures required the use of single-crystal x-ray diffraction. Using a combination of x-ray and neutron diffraction the structures of methane phase A (5.2 - 10 GPa) and B (10 - 25 GPa) were solved. The structure of phase A, was shown to conform to an indexing from literature [Nakahata 99] of a rhombohedral unit cell with α ≈ 89.3° and a ≈ 8.6 Å. Powder data were insufficient to determine atomic positions for this phase, and a single-crystal xray diffraction study was undertaken. The process of growing samples for this study is described as well as data collection. As a result of these studies the carbon atoms were located within methane phase A, and the density of the structure confined. The heavy atom structure, of phase A, was refined against neutron powder diffraction data, enabling positions of hydrogen atoms to be found. Preliminary powder diffraction studies of methane phase B found that the structure did not conform to the unit cell described within the literature. The phase was instead assigned to a cubic unit cell with a ≈ 11.73 Å. Similarly to the studies of phase A, a single-crystal x-ray diffraction study was undertaken. This was complicated by the presence of a contaminant within the sample area. This contaminant was shown to have no effect on the structural results. From a single-crystal study the heavy atom structure of phase B was found. The thesis charts the attempt, but ultimate failure, to obtain neutron powder diffraction on this phase. Comparisons of phase B with the higher pressure phase HP (25 GPa +) led to the conclusion that there would still be some disorder within the hydrogen atoms of phase B. Other studies have been carried out on the methane phase diagram. A Raman spectroscopy study, in the literature, on the low-temperature and high-pressure region of the phase diagrams (20 K up to 30 GPa) had suggested the existence of 3 additional phases of methane. A low-temperature, high-pressure neutron diffraction experiment was undertaken to try and characterise these phases. It was found that the phase A structure persisted under all conditions (to 20 K and 5 GPa) throwing the original results into question. During the growth of single-crystals for the above studies on phase A and B, a high-temperature solid-solid phase transition was observed. This transition line was mapped out and the phase resulting from it characterised with high-temperature single-crystal x-ray diffraction.

A family of oxygen-deficient perovskite phases with compositions, Ca₂Mn_2-xNb_xO_γ has been synthesised and characterised using X-ray Powder Diffraction and Thermogravimetry. Property characterisation has included the study of electrical properties by Impedance Spectroscopy and the investigation of magnetic properties for one composition, x = 1.0. Some compositions were tested for possible application as electrode materials in gas sensors. The Ca₂Mn_2-xNb_xO_γ system 0 ≤ x ≤ 1.2, with variable oxygen content, γ, can accommodate up to 20% vacancies at oxygen sites and Mn occurs in valence states ranging from +2 to +4. Depending on the B-cation ratio and oxygen content, two solid solution form: an extensive GdFeO₃-type solid solution over the entire range of cation content, 0 ≤ x ≤ 1.2, with zero or small oxygen deficiencies and a closely-related, grossly oxygen-deficient solid solution over the range 0.3 ≤ x ≤ 0.8 with a simple cubic perovskite structure. Unit cell volume and orthorhombic GdFeO₃-type distortion vary greatly with Mn valency, oxygen content and B-cation content. The orthorhombic GdFeO₃-type structure of composition x = 1.0 was refined by the Rietveld method. Mn and Nb are disordered over the B-sites. Jahn-Teller activity of Mn³⁺ does not result in cooperative distortions of (Mn,Nb)O₆ octahedra, but it was observed to effect the oxygen stoichiometry. The Nb-rich composition, x = 1.0, can accommodate large amounts of Ca-vacancies (up to 10%). Electrical conductivity varies greatly with the composition. Results suggest that t_2g electrons are responsible for a variation of conductivity and activation energy rather than e_g electrons. Conductivities are believed to depend mainly on the degree of π-orbital overlap between Mn and oxygen and hence, on interatomic distances. At low temperatures, the material exhibits spin glass-like behaviour.

No description available.

There are many causes of structural failure. One of the most important factors leading to material failure is residual stress. This stress represents effects left in structures after processing or removal of external loads including changes in shape and crystallite size. In aggregate, residual stress changes the mechanical behaviour of materials. Various measurement techniques encompassing destructive, semi destructive, and non-destructive testing can be used to measure residual stresses. Thin plates are common in engineering applications. This thesis analyzes residual stresses on circular AISI 1020 steel alloy plates after removal of external loads using two-dimensional X-ray diffraction. Two identical thin circular plates are used in this experiment; one of which is statically loaded. The other plate is used as a control specimen. Residual stresses in the plates are measured using two-dimensional X-ray diffraction and the measurements are compared to those obtained using finite element analysis. It was found that experimentally measured residual stress occurred due to manufacture processing. Also, modules A and B showed the external effect of applying not enough to reach the plastic region to deform specimen 2 and obtain residual stress results distribution.

Στην παρούσα μεταπτυχιακή εργασία πραγματοποιήθηκε μελέτη του πολυμορφισμού της ινσουλίνης μέσω της κρυσταλλογραφίας ακτίνων-Χ. Για το σκοπό αυτό πραγματοποιήθηκαν πολυάριθμα πειράματα κρυστάλλωσης της ινσουλίνης υπό διαφορετικές συνθήκες (pH, οργανικοί προσδέτες). Οι κρύσταλλοι που προέκυψαν χρησιμοποιήθηκαν σε πειράματα περίθλασης ακτίνων-Χ τα οποία πραγματοποιήθηκαν στο Ευρωπαϊκό σύγχροτρον, ESRF, της Γαλλίας και στο Ελβετικό σύγχροτρον, SLS. Η τεχνική που ακολουθήθηκε για τα πειράματα περίθλασης ήταν αυτή του powder diffraction, η οποία τα τελευταία χρόνια έχει αναδειχθεί σε ένα σημαντικό εργαλείο χαρακτηρισμού των πρωτεϊνικών πολυκρυσταλλικών ιζημάτων. Από τη μελέτη αυτή, προέκυψαν διάφορα πολύμορφα της ινσουλίνης που χαρακτηρίζονται από διαφορετικές συμμετρίες, ενώ πραγματοποιήθηκε ο προσδιορισμός κάθε κρυσταλλικής φάσης στο επίπεδο της μοναδιαίας κυψελίδας. Ενδιαφέρον αποτελεί ο εντοπισμός δύο νέων κρυσταλλικών φάσεων της ινσουλίνης, μονοκλινούς συμμετρίας, οι οποίες ενδέχεται να είναι υψηλής φαρμακευτικής σημασίας. / In this thesis the polymorphism of insulin via X-ray powder crystallography has been carried out. For this purpose numerous experiments of insulin crystallization have been performed under different conditions (pH, organic ligands). The resulting crystals were employed in X-ray diffraction experiments, which took place at the European synchrotron, ESRF, in France and at the Swiss synchrotron, SLS. The technique employed for the X- Ray diffraction experiments, was the powder diffraction method, which has been proven to be an important tool for the determination of polycrystalline protein precipitants during the last decade. From this study, a number of insulin polymorphs were identified in different crystal systems and furthermore, each crystalline phase was determined at the level of unit cell symmetry and dimensions. An interesting point occurs from the characterization of two novel insulin phases, belonging to monoclinic symmetry, which are potentially associated with high pharmaceutical importance.

Coal is a combustible sedimentary rock composed of a complex heterogeneous mixture of mostly organic constituents and minor inorganic phases. Coal is a vital energy resource providing more than half of the electric power generated in the United States. However, coal combustion is responsible for a significant portion of anthropogenic release of different toxic elements including sulfur into the environment. Therefore, deciphering the residence of the different fractions of sulfur in coal is essential. In this study, eight different sulfur fractions from Pennsylvanian-age coal samples collected from the Murphysboro, Mount Rorah, Springfield (No. 5), and Herrin (No. 6) coal seams from the Illinois Basin were separated using a wet sequential chemical extraction procedure in order to evaluate the coal quality and to test the efficiency of this technique. The average weight percent of sulfur in each seam was 1.98%, 2.1%, 2.26%, and 2.4%, respectively, showing that the coal samples were of medium-sulfur-type. Among the eight different sulfur fractions extracted, kerogen sulfur was found to be the most abundant, followed by sulfate sulfur, fulvic acid sulfur, pyritic sulfur, and elemental sulfur. However, XRD and coal petrography revealed the significant amounts of pyrite still present in the coal sample even after pyritic sulfur extraction, indicating that the finely disseminated pyrite in the coal was not completely removed during the sequential extraction. The sulfur isotopic study showed the average δ34S values of pyritic sulfur and sulfate sulfur in the Murphysboro coals as 7.82 / and 2.44 / and that of Mount Rorah coals were 10.68 / and 7.87 /, respectively. The heavier δ34S values of pyritic sulfur compared to the sulfate sulfur can be explained by a bacterial sulfate reduction (BSR) model in a closed system where most of the sulfate reservoir was consumed at the top of the seam. Similarly, the average δ34S values of elemental sulfur for the same coals (8.05 / and 14.54 /, respectively) were also heavier than the sulfate sulfur which suggests the pyrite oxidation followed by disproportionation of intermediate sulfur species. The δ34S values of handpicked pyrite samples and the mercury concentration for the Herrin (No.6) and Springfield (No. 5) coals indicated at least two stages of hydrothermal inputs into these coal seams. SEM/EDS and petrographic microscopy of the Illinois coal samples revealed the presence of different syngenetic and epigenetic sulfur-containing minerals such as framboidal pyrite, euhedral pyrite, galena, anhydrite, anglesite, and also non-sulfur containing minerals such as calcite and clay. Based on these results, it can be said that sulfur in Illinois coals is present in different phases extractable by wet sequential chemical extraction however; care should be taken during each individual extraction step to obtain better results.

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