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Synthèse, caractérisations structurale et mécanique de nouveaux matériaux tellurites pour des applications en optique non linéaire / Synthesis, structural and mechanical investigations of new tellurite materials for non-linear optical applicationsGhribi, Nabila 26 January 2015 (has links)
Les matériaux tellurites possèdent des propriétés optiques non linéaires exceptionnelles, avec des valeurs de la susceptibilité optique non linéaire d’ordre trois de l’ordre de 10 à 50 fois supérieures à celle de la silice pure, favorisant alors l’efficacité des effets non linéaires. L’origine de ces propriétés optiques exceptionnelles est associée non seulement à la présence de la paire libre mais aussi à une « délocalisation » électronique très forte le long des ponts Te-O-Te dans des chaînes polymérisées (TeO2)p. Ainsi, nos recherches expérimentales ont porté sur les deux systèmes ternaires suivants : TeO2-TiO2-ZnO (TTZ) et TeO2-GeO2-ZnO (TGZ).Les domaines vitreux ont été délimités, la stabilité thermique augmente en fonction de l’ajout de ZnO, TiO2 et GeO2. L’étude vibrationnelle réalisée par spectroscopie de diffusion Raman et réflectivité spéculaire infrarouge, a mis en évidence une faible dépolymérisation du réseau vitreux par rupture des chaînes formées via des ponts Te-O-Te. Pour les teneurs élevées en ZnO, ce dernier contribue à une compensation de cette rupture par la formation de nouveaux ponts Te-O-Zn et/ou Zn-O-Zn. Une étude complète des propriétés mécaniques a été menée à la fois à température ambiante et en fonction de la température, notamment au passage de la température de transition vitreuse. L’augmentation de la teneur en ZnO dans les verres TTZ et TGZ a augmenté globalement les modules élastiques. Enfin, la diminution de la susceptibilité optique non linéaire du troisième ordre avec l’ajout de ZnO, nous a permis de montrer l’importance de la présence de chaînes composées de ponts Te-O-Te dans la structure du verre à base de dioxyde de tellure. / Tellurite materials possess exceptional nonlinear optical properties, with values of the third-order nonlinear optical susceptibility are 10 to 50 times higher than in pure silica, favoring then the efficiency of the nonlinear effects. The origin of these exceptional optical properties is not only associated with the presence of the electronic lone pair, but also with the very strong electronic "delocalization" along Te-O-Te bridges in polymerized chains (TeO2)p. Our experimental researches concerned the following both ternary glass systems: TeO2-TiO2-ZnO (TTZ) and TeO2-GeO2-ZnO (TGZ).The glass formation domains were determined, the thermal stability increases with the increased amount of ZnO, TiO2 and GeO2. The vibrational study carried out using Raman spectroscopy and specular infrared reflectivity, revealed that the increase of the ZnO amount leads to a slight depolymerization of the glass network by breaking chains formed via Te-O-Te bridges. For higher ZnO contents, the latter contributes to a compensation of this break by the formation of new bridges: Te-O-Zn and/or Zn-O-Zn. Mechanical properties were studied at the same time at room and high temperature, in particular around the glass transition temperature. The increase of the ZnO content in TTZ and TGZ glasses increased globally elastic modulus. Finally, the decrease of the third-order nonlinear optical susceptibility with the increased ZnO concentration emphasizes the role of the presence of chains consisted of Te-O-Te bridges in the structure of the tellurite glass.
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Probing the opto-electronic and mechanical properties of suspended graphene membranes by Raman spectroscopy / Etude de propriétés opto-électroniques et mécaniques de membranes de graphène suspendu par spectroscopie RamanMetten, Dominik 29 January 2016 (has links)
Ce travail présente une étude par diffusion micro-Raman de membranes de graphène suspendu.La spectroscopie Raman est présentée comme un outil rapide et peu invasif pour estimer les contraintes natives dans du graphène suspendu et est utilisée pour en sonder quantitativement la déflexion, induite soit par une différence de pression d’air soit électrostatiquement. Dans des bulles de graphène pressurisées, une analyse minutieuse des intensités et fréquences des principaux modes Raman permet une détermination tout-op que de la topographie de la bulle, du module de Young et des paramètres de Grüneisen du graphène. Une grille électrostatique offre une manière élégante d’introduire à la fois des contraintes et du dopage dans le graphène. Des mesures Raman permettent une détermination précise de la déflection induite par la force électrostatique (jusqu’à l’effondrement irréversible), en très bon accord avec un modèle électromécanique. / This work presents a micro-Raman scattering study of undoped suspended graphene membranes. Raman spectroscopy is introduced as a fast and minimally invasive tool to estimate sample dependent built-in strain in suspended graphene, and is further employed to quantatively probe the membrane deflection, which may be induced either by an air pressure difference or electrostatically. In pressurized graphene blisters, an all-optical determination of the blister topography, the Young’s modulus and the Grüneisen parameters of graphene is achieved by a thorough analysis of the intensity and frequency of the main Raman modes. Electrostatic gating offers an elegant way to simultaneously strain and dope graphene. Raman measurements allow an accurate determination of the electrostatically-induced graphene deflection (up to irreversible collapse), in very good agreement with an electromechanical model.
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Magnetic Nanostructure Application in SERS Detection of Melatonin and Resonance Raman Characterization of Binding of Catechol Moieties with AntibioticSun, Siqi 07 July 2017 (has links)
Raman spectroscopy provides characteristic peaks of the target molecules that can be observed with appropriate laser, spectrometer and detector. These characteristic peaks can reveal ‘fingerprint’ information of a molecule even in a myriad of cases and combinations. It makes Raman spectroscopy a highly sensitive and selective analytical technique. Raman spectroscopy has a variety of chemical, environmental and biological applications. In this dissertation, modified Raman method are applied in life sciences and pharmaceutical studies.
The major challenge against development of Raman spectroscopy is how to improve the intensity of Raman signal. Surface Enhance Raman Scattering (SERS) and resonance Raman(RR) are utilized for conquer this obstacle. In SERS technique, Raman signal is enhanced by introducing metal surface. SERS has a great potential for trace molecular detection since it’s sensitive enough to detect a single molecule. In RR, wavelength is carefully chosen to overlap with (or very near to) an electronic transition of a target molecule. With such overlap, Raman intensity can be increased by factors of 102-106, thus detection limit of target molecule can be significantly decreased. SERS and RR are applied for trace bio-marker detection and bio-system analysis in this study.
In the first chapter, the history, principles and applications of SERS and RR are introduced. Second chapter emphases on instrumental information and experimental methods of the techniques were applied in this study. The third chapter focuses on establishing novel SERS method to detect Alzheimer’s disease related biomarker, melatonin. A novel SERS substrate, Fe3O4/Ag nanostructures is developed, and SERS experimental conditions, such as aggregating agents and pH, are optimized to achieve the most sensitive detection of melatonin. In the fifth chapter, resonance Raman is served as an important analytical tool to identify metal binding and structure-activity relationship of metalloantibiotic, bacitracin. In the last chapter, Raman spectroscopy are applied in material science. Two solar cell materials, regioregular poly(3-hexylthiophene) films and Cu2ZnSnSe4 are characterized by Raman spectroscopy.
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Raman spectroscopy of biological tissue for application in optical diagnosis of malignancyStone, N 25 November 2009 (has links)
The utilisation of near-infraredR aman spectroscopyfo r the discrimination of cancersa nd
pre-cancers from normal tissue in the acro-digestive tract has been evaluated. A
commercially available Raman microspectrometehr as been modified to provide optimum
throughput, sensitivity and fluorescence suppression for epithelial tissue measurements.
Laser excitation at 830nmw as demonstratedto be optimum. High quality (SN ratio 15-20)
NIR-Raman spectrah ave been acquired from oesophageaal nd laryngeal tissues in time
scales under 30 seconds.
Pathological groupings covering the full range of normal and neoplastic tissues in the organs
of interest have been studied. Both fresh (snap frozen) and formalin fixed tissue samples
were investigated,f irstly to indicate whether tissue-typesc an be distinguishedi n vivo and
secondlyt o demonstrateth e use of Raman spectroscopya s a tool for classificationi n the
pathology lab.
Results using multivariate statistical techniques to distinguish between spectra from
specimens exhibiting different tissue pathologies have been extremely promising. Crossvalidation
of the spectral predictive models has shown that three groups of larynx tissue
can be separated with sensitivities and specificities of between 86 and 90% and 87 and
95% respectively. Oesophageal prediction models have demonstrated sensitivities and
specificities of 84 to 97% and 93 to 98% respectively for a three-group consensus model
and 73 to 100% and 92 to 100% for an eight-groupc onsensusm odel.
Epithelial tissues including stomach, tonsil, endometrium, bladder and prostate have been
studiedt o identify further tissuesw hereR amans pectroscopym ay be employedf or detection
of disease.S pectraw ere similar to those obtainedf rom oesophagusa nd larynx, although
sufficiently different for distinct discriminant models to be required. This work has
demonstratedth e genericn atureo f Ramans pectroscopyfo r the detectiona nd classification
of cancersa nd pre-cancerousle sionsi n many tissues.T he evidencep rovided by this study
indicatest hat utilisation of Ramans pectroscopyfo r non-invasived etectiona nd classification
of diseaseis a distinct possibility. Potentiald ifficulties in the transferabilityf rom in vitro to
in vivo have been evaluated and no significant barriers have been observed. However,
further in vivo probe development and optimisation will be required before 'optical biopsy'
with Ramans pectroscopyc anb ecomea reality.
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Étude des propriétés du transport d’eau et Développement d’une nouvelle structure de polymère pour l’optimisation de la gestion de l’eau d’une PEMFC / Study of the water transport properties and Developpement of new polymer stucture for the optimization of water management in a fuel cell PEMFC.Peng, Zhé 27 November 2012 (has links)
Les performances et la durée de vie des piles à combustible à membrane échangeuse de protons (PEMFC) dépendent fortement de la répartition de l'eau dans les assemblages membrane électrodes (AME). Une répartition d'eau homogène et suffisante s'avère indispensable pour obtenir de bonnes performances et une grande durabilité. Fondamentalement, la répartition d'eau dans l'AME, et plus particulièrement dans la membrane, est déterminée par deux mécanismes de transport d'eau : le flux d'électroosmose, induit par les protons véhiculant les molécules d'eau de l'anode vers la cathode, et le flux de diffusion d'eau, de la cathode vers l'anode, résultant du gradient de concentration. Or, ces mécanismes sont pour l'heure encore mal connus malgré les intenses recherches menées sur le sujet. Dans ce contexte, la première partie de cette étude s'appuie sur la détermination et la quantification des mécanismes de transport d'eau dans les différents composants, et notamment dans les membranes, ainsi que sur l'étude de leur couplage. Ces propriétés ont été évaluées en fonction du degré d'hydratation et de la température à l'aide de deux méthodes originales développées dans cette thèse. Afin d'homogénéiser la répartition d'eau, et ainsi d'améliorer les performances des PEMFC, le développement d'une nouvelle structure de membrane à gradient de masse équivalente a fait l'objet de la deuxième partie de l'étude. Cette nouvelle structure membrane a été étudiée par la caractérisation de ses propriétés du transport d'eau, par la détermination de la répartition d'eau ex et in-situ par spectroscopie Raman confocale ainsi que par des tests électrochimiques. Les performances électrochimiques ont été corrélées aux propriétés de transport d'eau, selon l'orientation du gradient de masse équivalente de la membrane par rapport au sens des protons. Nous avons ainsi démontré qu'il est possible de modifier la répartition d'eau et les performances en modifiant le sens de la structure de la membrane par rapport aux réactions électrochimiques. / Water management is a fundamental issue for the improvement of the PEMFC technology. The cell performances and life time depend strongly on the water repartition in the Membrane Electrodes Assembly (MEA). This water repartition within the MEA is mainly governed by two flows across the membrane : electroosmosis, which drags water molecules from the anode to the cathode and often leads to local depletion of water in the membrane at the anode side ; back diffusion (from cathodeto anode) induced by the water concentration gradient generated from the water produced at the cathode side, which allows to hydrate the membrane and the anode. For nowadays, these phenomena are still under debate in spite of numerous researches. In this context, this work is firstly focused on the determination and the quantification of the mechanisms of water transport in different components, particularly in the membranes, as well as their coupling thanks to two original methods developed in this work. In the aim to achieve a more homogeneous water repartition, and consequently to improve the cell performance, a new membrane structure based on an inner gradient of equivalent weight has been fabricated. Its water transport properties, the cell performance, and the ex and in-situ water repartition have been characterised. A consistent relationship between the performance and the membrane water transport properties have been established depending on the direction of the gradient of equivalent weight compared to the protons flow.
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Geothermometry by Raman spectroscopy of dispersed organic matter / Geothermometry by Raman spectroscopy of dispersed organic matterLünsdorf, Nils Keno 30 October 2015 (has links)
Raman-Spektroskopie an kohligem Material (RSCM) ist eine häufig verwendete
Methode, um die maximale Temperatur der Metamorphose oder die thermische Reife
von Kohlen und organikreichen Sedimenten zu bestimmen. Für die Temperaturabschätzung
wurden bereits mehrere Kalibrationskurven ermittelt, jedoch wird die Übertragbarkeit dieser
Kalibrationen auf andere Labore durch methodische Aspekte eingeschränkt und die Vergleichbarkeit
zwischen den Laboren dadurch reduziert. Die subjektive Auswertung von Spektren, das
verwendete Messsystem und die Probenheterogenität bedingen die größte Streuung der Ergebnisswerte
und ein Ansatz, mit dem Ziel die Vergleichbarkeit zu erhöhen, wurde formuliert. Um die
Subjektivität der spektralen Auswertung zu veringern, wurde das ’IFORS’ (Iterative Fitting Of
Raman Spectra) Programm geschrieben, das die automatische, Benutzer-unabhängige Auswertung
von Raman-Spektren ermöglicht. Um die Streuung aufgrund des verwendeten Messsystems
zu reduzieren, wurde ein Referenzprobensatz zusammengestellt, der einen Temperaturbereich
von 160 °C bis 600 °C abdeckt. Während der Probenaufbereitung wurde Resonanz-Raman-
Spektroskopie mit mehreren Anregungswellenlängen an dispersen Vitriniten durchgeführt, die
diagenetische bis epizonale Druck- und Temperaturbedingungen erfahren hatten, um die Gleichwertigkeit
der RSCM-Methode und Vitrinitreflexion zu ermitteln.
Mit Hilfe des IFORS Programms wurde der ’scaled total area’ (STA) Raman Parameter
ermittelt, der das Raman Spektrum von kohligem Material präzise beschreibt. Auf Grundlage
der Resonanz-Raman Daten konnte gezeigt werden, dass die Methodiken der STA-Raman Spektroskopie
und Vitrinitreflexion analog zueinander sind, dass die STA-RSCM Methode gegenüber
der Probenaufbereitung, insbesondere dem Polieren, robust ist, und dass die Resonanz-Raman
Spektren der Vitrinite eine zweistufige molekulare Entwicklung während der Inkohlung und
Graphitisierung aufzeichnen. Während der ersten Stufe, die kurz nach dem Durchschreiten
des Gas-Fensters endet, wachsen vor allem lineare, polyzyklische, aromatische Kohlenwasserstoffe,
während in der anschließenden zweiten Stufe kondensierte Formen von polyzyklischen,
aromatischen Kohlenwasserstoffen wachsen.
Um die Raman Spektren von metamorphem, kohligem Material zu beschreiben, wurde die
STA-RSCM Methodik erweitert und erfolgreich gegen die Temperaturinformation des Referenzprobensatzes
kalibriert, so dass ein neues, überarbeitetes RSCM-Geothermometer vorgestellt
werden konnte, das über einen Temperaturbereich von 160°C bis 600°C zulässig ist. Der Referenzprobensatz
steht öffentlich zur Verfügung und es wird erwartet, dass der Probensatz verbessert
werden kann, wenn er um Proben aus der wissenschaftilchen Gemeinschaft erweitert wird. Wenn
beide Ansätze, die STA-RSCM Methodik und der Referenzprobensatz, miteinander kombiniert
werden, erhöht sich die Vergleichbarkeit zwischen den Laboren und gleichzeitig steht diese
geothermometrische Methode allen Laboren zur Verfügung.
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Deposition and structural properties of silicon carbide thin films for solar cell applications.Khoele, Joshua Relebogile January 2014 (has links)
>Magister Scientiae - MSc / The growth of hydrogenated amorphous silicon carbide (a-SiC:H) thin films deposited by Hot- Wire Chemical Vapour Deposition (HWCVD) for solar cell applications has been studied. The films were characterized for structural properties using Fourier Transform Infrared Spectroscopy FTIR, Elastic Recoil Detection Analysis (ERDA), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Raman Spectroscopy (RS). A low temperature of the substrate heater maintained at 280 °C was used in this thesis due to the demand of low-cost solar cells based on cheap substrate that require deposition at such low temperatures. In this thesis, we showed that the structural properties of a-SiC:H films are dependent on the filament temperature and also on the CH4 gas flow rate. It was shown that in non-stoichiometric a-SiC:H, hydrogen content throughout the deposited films varies with depth. An attempt is done in this study to determine, for the first time the absorption strength of the C-Hn bonds in the 950 -1050 cm-1 band of the FTIR spectrum. Real-time ERDA was used to determine the hydrogen kinetics parameters in a single temperature ramp; a model based on the solution of the diffusion equation is used for this effect.
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The development of analytical methods for PBMR Triso SiC characterizationNgoepe, Noko Nepo 25 August 2010 (has links)
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
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A Raman- and XRD study of the crystal chemistry of cobalt blueMwenesongole, Ellen Musili 29 November 2009 (has links)
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
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Deep subduction of the Seve Nappe Complex in the Scandinavian CaledonidesKlonowska, Iwona January 2017 (has links)
This thesis seeks to improve our understanding of the processes involved in continental collision zones, with a particular focus on subduction-exhumation. The main objective of this work has been to define the tectonometamorphic evolution of the deeply subducted Seve Nappe Complex (SNC) in the Scandinavian Caledonides. I utilize mineralogy, petrology and geochronology to constrain the P-T-t paths of the SNC rocks in Sweden. The research has focused on the high grade rocks of the SNC and resulted in the discovery of metamorphic diamonds within the gneisses in west-central Jämtland and southern Västerbotten. Microdiamonds provided evidence for the ultra-high pressure metamorphism (UHPM) and subduction of continental rocks to mantle depths. The UHPM in these rocks was confirmed by calculations of the P-T conditions. The UHPM is further recorded by eclogites and garnet pyroxenites from northern Jämtland and eclogites from Norrbotten. All these findings provide compelling evidence for regional UHPM of vast parts of the SNC (at least 400 km along the strike of this allochthonous unit). The SNC rocks followed nearly isothermal decompression paths and paragneisses have locally experienced partial melting during exhumation. Formation of the peculiar Ba- and Ti-enriched dark mica in the Tväråklumparna metasediments is related to the latter stage. In-situ monazite dating of the diamond-bearing gneisses from west-central Jämtland supports previous geochronological data inferring that the peak of metamorphism is probably Middle Ordovician and was followed by Early Silurian partial melting. The exact timing of the UHPM here still remains to be resolved. The Lu-Hf garnet and U-Pb zircon dating of eclogite and gneiss from northern Jämtland confirms the Middle Ordovician age of the UHP-HP metamorphism of the SNC rocks. The chemical dating of monazite from the Marsfjället gneiss suggests an earlier UHP history of the Seve rocks in southern Västerbotten as a post-UHP uplift is dated to ca. 470 Ma. Based on the P-T-t data obtained in this thesis, particularly on the evidence for Middle Ordovician UHPM and subsequent Silurian exhumation, a new tectonic model for the Scandinavian Caledonides has been proposed. The outcomes of this thesis therefore improve our understanding of the tectonometamorphic history of the Caledonides.
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