Дисертації: "Scanning XRF"

1

Miller, Eric J. "High-Resolution Sediment Records of Seismicity and Seasonal Sedimentation from Prince William Sound, Alaska, using XRF Core Scanning." W&M ScholarWorks, 2014. https://scholarworks.wm.edu/etd/1539617947.

Повний текст джерела

Анотація:

The southern coast of Alaska is a climatically sensitive and tectonically active region, however due to its remoteness and harsh climate there are limited long-term historical records of environmental conditions such as storm frequency, river discharge, and earthquakes. In order to determine the potential for Prince William Sound sediments to contain high-resolution paleorecords of these conditions, a suite of 11 gravity cores was collected within the Sound in order to determine the modern day sediment depositional trends and to develop elemental proxies for earthquakes and seasonal sedimentation. 210Pb/137Cs-derived sedimentation rates and grain size trends indicate that there are two distinct sediment sources to the Sound; an allochthonous source of sediment that is advected into the Sound through Hinchinbrook Entrance, and an autochthonous source of sediment from the Columbia Glacier region of the northern Sound. Cyclic variations in grain size were identified in Hinchinbrook Entrance sediments using the XRF Sr/Pb ratio and were interpreted to be the result of seasonal sedimentation; with coarse-grained sediments deposited during the winter when storm-driven wave and currents in the nearshore region are high, and fine-grained sediments deposited during the summer when costal conditions are less energetic and when the discharge and transport of sediments from the Copper River is high. Additionally, light and dark colored laminations in northern Hinchinbrook Entrance sediments were interpreted to be the result of seasonal variations in the supply and preservation of organic matter; with high concentrations of organic matter preserved in the summer when primary production, the flux of terrestrial organic matter from rivers, and costal upwelling of potentially low oxygenated waters is high, and low organic matter concentrations preserved in the winter when primary production and river discharge are low, and when downwelling conditions likely introduce highly oxygenated waters. The use of the XRF Br/Cl ratio as a proxy for marine organic matter suggested that at least a portion of the dark, organic-rich, summer deposits had a marine origin, and may therefore be a potential proxy for seasonal sedimentation under certain conditions. Gravity flow deposits from the northern Sound were identified as having a source from the Columbia Glacier region using the XRF K/Ca ratio. The gravity flows that caused these deposits were identified as being triggered by historically recorded earthquakes, which likely remobilized sediment on the steep slopes of the northern channel and which then flowed downslope to the south. The results of this study indicate that the rapidly accumulating sediments in Hinchinbrook Entrance potentially contain high resolution records of Copper River discharge, storm activity and primary production, whereas sediments in the northern Sound may contain a regional seismic record.

Стилі APA, Harvard, Vancouver, ISO та ін.

2

Dehlinger, Mael. "XAS-XEOL and XRF spectroscopies using near field microscope probes for high-resolution photon collection." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4048/document.

Повний текст джерела

Анотація:

Les microscopes en champ proche permettent d'obtenir la topographie d'un échantillon avec une résolution pouvant atteindre la résolution atomique. Les spectroscopies de rayons-X sont des méthodes de caractérisation qui permettent de déterminer la composition et la structure élémentaire de l'échantillon avec une précision inférieure à l'Ångström. Nous avons choisi de coupler ces deux techniques en collectant localement la luminescence visible issue de l'échantillon par la pointe-sonde d'un microscope à force de cisaillement, constituée d'une fibre optique effilée de faible ouverture. Cette technique a été utilisée pour caractériser des échantillons semiconducteurs micro- et nano-structurés afin d'en obtenir simultanément la topographie et la cartographie de luminescence locale. Afin de pouvoir étendre ce concept à d'autres types de matériaux, la faisabilité de la collecte de la fluorescence X locale a été évaluée avec la microsource. Pour cela la fluorescence X émise par un échantillon a été collectée par un capillaire cylindrique équipant un détecteur EDX. L'influence du diamètre du capillaire sur le niveau de signal a été mesurée. Une simulation numérique a été développée afin d'estimer le niveau de signal obtenu en utilisant un capillaire de 1 µm de diamètre et d'optimiser la géométrie du système. En couplant la microscopie en champ proche et l'analyse XRF, à la lumière de ces résultats, il sera possible d'atteindre 100 nm de résolution latérale en environnement synchrotron et moins de 1 µm à l'aide d'une source de laboratoire. Il serait alors possible de sélectionner un objet particulier sur une surface et d'en faire l'analyse élémentaire
Scanning Probe Microscopes allow to obtain sample topography up to atomic resolution. X-ray spectroscopies allow elemental and structural analysis of a sample with accuracy better than 1 Å. The lateral resolution is limited by the primary beam diameter, currently a few µm². We have chosen to couple this two technics. Local sample visible luminescence is collected through a low aperture sharp optical fibre, probe of a shear force microscope. This technique was used to characterize microstructured semiconducting samples to achieve simultaneously the surface topography and luminescence mapping. The results were obtained using either synchrotron radiation or a laboratory microsource equipped with a polycapillary lens. To extend this concept to a wider variety of materials, local XRF collection by an EDX detector equipped with a cylindrical X-ray capillary was tested. A cobalt sample irradiated with the microsource was used for technique evaluation. The signal magnitude dependence with the capillary diameter was measured. Modelling and numerical calculations were developed to estimate the signal magnitude that could be detected using a 1 µm diameter capillary. The optimal system geometry was determined. Scanning Probe Microscopy combined to XRF analysis could thereby lead to simultaneous acquisition of sample topography and chemical mapping. The expected lateral resolution using synchrotron radiation is 100 nm while sub 1 µm resolution is realistic with a laboratory source. This technique would allow to point a peculiar micro- or nano-object on the surface and to perform its chemical analysis

Стилі APA, Harvard, Vancouver, ISO та ін.

3

Longhini, Elisa <1988&gt. "Scanning macro-XRF: Calculation of Sensitivity and Limits of Detection for common pigments in historical paintings and the investigation of Rembrandt’s ‘Saul and David’." Master's Degree Thesis, Università Ca' Foscari Venezia, 2014. http://hdl.handle.net/10579/4769.

Повний текст джерела

Анотація:

The aim of this research was to study and compare the potential of two mobile scanners MACRO-XRF, through the analysis of multilayered paint samples. Wood and plexiglass mockups were painted with some of the most common oil pigments in art, using a paint film applicator. Only wood samples were analyzed and covered by different thicknesses of lead white, in order to reproduce a real layers sequence frequent in historical painting. The two scanners MA-XRF were: M6 Jetstream, that is the first model of the production run by Bruker; and AXIL scanner, an in-house build scanner of the University of Antwerp. The potential of these two instruments was observed and studied through the change of some fundamental parameters: step size, dwell time and detector geometry. Qualitative considerations were based on elemental maps carried out by Datamuncher package. Furthermore, the best Instrument AXIL scanner set-up was used for quantitative analysis. In order to calculate meaningful data of sensitivity and limit of detection for each marker element, the dwell time was increased up to 2,5 second per pixel. The second part of this study shows a real application of AXIL scanner on Rembrandt’s painting “Saul and David” and the attention was focused on the different use of cobalt in the painting: as a pigment (smalt) or as a drier.

Стилі APA, Harvard, Vancouver, ISO та ін.

4

Cartapanis, Olivier. "Variabilité de la zone de minimum d’oxygène du Pacifique Est équatorial au cours du Quaternaire récent." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4365/document.

Повний текст джерела

Анотація:

Cette thèse a pour objectifs de documenter les variations spatiotemporelles de la zone de minimum d’oxygène (OMZ) du Pacifique Nord-Est, et d’identifier les mécanismes qui ont causé ces variations. L’étude est fondée sur l’analyse géochimique des composants majeurs, mineurs et traces de sédiments prélevés dans le Pacifique Nord-Est, en combinant des mesures par ICP-MS et scanneur XRF. Ces mesures ont permis de distinguer l’effet de la productivité biologique de celui de la ventilation océanique sur l’oxygénation du sédiment. J’ai pu mettre en évidence le rôle prépondérant de la productivité au niveau de la Basse Californie (23°N), qui varie en phase avec les températures en Atlantique Nord durant les 120.000 dernières années. Par ailleurs, la ventilation océanique a probablement joué un rôle important au niveau du golfe de Papagayo (12°N), par l’advection de masses d’eau provenant des hautes latitudes nord et sud. L’intensité de l’OMZ du Pacifique Nord-Est serait donc influencée par des modifications des circulations océaniques et atmosphériques, liées aux climats des hautes latitudes des deux hémisphères
This thesis aims at documenting the spatiotemporal variations of the Oxygen Minimum Zone (OMZ) of the northeastern Pacific, and identifying the mechanisms that caused theses variations. The study is based on the geochemical analyses of major, minor, and trace elements of sediments from the northeastern Pacific, by combining ICP-MS and XRF scans measurements. These measurements allowed distinguishing the effect of biologic productivity and oceanic ventilation on sediment oxygenation. I was able to highlight the predominant impact of the productivity off the Baja California Margin (23°N), which varied in phase with the high northern Atlantic temperature across the past 120,000 years. Moreover, oceanic ventilation did play an important role off the Papagayo Gulf (12°N), because of the advection of water mass coming from the high northern and southern latitudes. OMS intensity in the northeastern Pacific could thus be influenced by changes in the atmospheric and oceanic circulation, in relation to high northern and southern latitudes climates

Стилі APA, Harvard, Vancouver, ISO та ін.

5

Simán, Frans Filip. "Assessment of Machine Learning Applied to X-Ray Fluorescence Core Scan Data from the Zinkgruvan Zn-Pb-Ag Deposit, Bergslagen, Sweden." Thesis, Luleå tekniska universitet, Geovetenskap och miljöteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-82050.

Повний текст джерела

Анотація:

Lithological core logging is a subjective and time consuming endeavour which could possibly be automated, the question is if and to what extent this automation would affect the resulting core logs. This study presents a case from the Zinkgruvan Zn-Pb-Ag mine, Bergslagen, Sweden; in which Classification and Regression Trees and K-means Clustering on the Self Organising Map were applied to X-Ray Flourescence lithogeochemistry data derived from automated core scan technology. These two methods are assessed through comparison to manual core logging. It is found that the X-Ray Fluorescence data are not sufficiently accurate or precise for the purpose of automated full lithological classification since not all elements are successfully quantified. Furthermore, not all lithologies are possible to distinquish with lithogeochemsitry alone furter hindering the success of automated lithological classification. This study concludes that; 1) K-means on the Self Organising Map is the most successful approach, however; this may be influenced by the method of domain validation, 2) the choice of ground truth for learning is important for both supervised learning and the assessment of machine learning accuracy and 3) geology, data resolution and choice of elements are important parameters for machine learning. Both the supervised method of Classification and Regression Trees and the unsupervised method of K-means clustering applied to Self Organising Maps show potential to assist core logging procedures.

Стилі APA, Harvard, Vancouver, ISO та ін.

6

Saffarini, Ghassan. "X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and density study of ternary chalcogenide glasses based on Ge-Se and Ge-S." Thesis, Brunel University, 1991. http://bura.brunel.ac.uk/handle/2438/7396.

Повний текст джерела

Анотація:

Glasses of the systems Ge-Se-X (X = Ga, Sn, Bi, Sb), Ge-S-Y (Y = Ag, Ga, Sn, Bi) and Se-S have been examined using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), density and differential scanning calorimetry (DSC). Two of the compositions, GeSe2 and (GeSe2)92Ga8, have also been examined by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES). The emphasis of the XPS measurements was on the changes in the binding energies with composition of the core peaks of the glasses, and on the plasmon energy losses from the L3M4,5M4,5 Auger lines of Se and Ge. It was found that there were small shifts in the binding energies of the core peaks on substitution but the plasmon energy changed markedly with composition. For the XRD measurements, the focus was on two features : (a) to ensure that the samples prepared were truely amorphous and (b) to confirm the presence of the first sharp diffraction peak (FSDP) on the interference functions. The density measurements showed that the addition of the third element (X or Y) to the binary resulted in an increase in the relative density except for one system, Ge-Se-Sn, which showed the opposite behaviour. The DSC measurements showed that the addition of the third element to the binary resulted in a decrease in the glass transition temperatures. The EXAFS and XANES measurements of GeSe2 and (GeSe2)92Ga8 glasses showed that there was very little change in the local order around the Ge atom in GeSe2 glass with increase in temperature and that the local order around the Ge atom changes on alloying GeSe2 with Ga. Correlations between parameters and measured properties of the ternary alloys have been investigated. It has been found that the parameter , the average coordination number, correlates well with certain structural properties but badly with others. Suggestions are made for an alternative to .

Стилі APA, Harvard, Vancouver, ISO та ін.

7

Motylenko, Mykhaylo. "Beitrag zur Analyse von Disklinationsstrukturen in plastisch verformten Metallen." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2011. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-67416.

Повний текст джерела

Анотація:

Gegenstand der Arbeit ist die Analyse der bei hohen Verformungsgraden in Werkstoffen durch kollektive Bewegung der Versetzungen entstandenen neuen Defektkonfigurationen, die auf der mesoskopischen Skala agieren. Diese so genannte Disklinationen rufen neben starken Gitterdehnungen auch erhebliche lokale Gitterrotationen hervor. Es wurde der Nachweis der Existenz der Disklinationen in plastisch verformten Kristallen geliefert sowie die qualitative und quantitative Analyse der Disklinationskonfigurationen und der Disklinationsstärke durchgeführt. Die Untersuchungen an stark verformten Ein- und Vielkristallen wurden mittels sowohl lokalen Methoden der Transmissions- (TEM, CBED) und Rasterelektronenmikroskopie (REM, EBSD) als auch der integralen Methoden der Röntgenstrukturanalyse (XRD) durchgeführt. Die Ergebnisse haben gezeigt, dass die Entwicklung der Zellblockstruktur mit erheblichem Anstieg der Desorientierungen und Versetzungsdichten in Versetzungswänden verbunden ist und durch die Bildung der Netzwerke von Disklinationen gefördert wird.

Стилі APA, Harvard, Vancouver, ISO та ін.

8

Alajtal, Adel Imhemed. "Raman spectroscopic application for the analysis of organic compounds and minerals of astrobiological significance : the detection and discrimination of organic compounds and mineral analogues in pure and mixed samples of astrobiological significance using raman spectroscopy, XRD and scanning electron microscopy." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/4425.

Повний текст джерела

Анотація:

Raman spectroscopy has been used to characterise both organic and geological samples in order to build a database for the future characterization of biomarker molecules that are of astrobiological relevance. Characteristic geological features and hydrated minerals recently found on the surface of Mars by the NASA planetary rovers Spirit and Opportunity suggest that a possible biosphere could have once existed there. Analytical instrumentation protocols for the unequivocal detection of biomarkers in suitable geological matrices are critical for future unmanned explorations, including the forthcoming ESA ExoMars mission scheduled for 2018. Several geological features found on the surface of Mars by planetary rovers suggest that a possible extinct biosphere could exist based on similar sources of energy as occurred on Earth. For this reason, analytical instrumental protocols for the detection of isolated biomarkers preserved in suitable geological matrices unequivocally and non-destructively have to be evaluated for future unmanned missions. Raman spectroscopy is currently part of the Pasteur instrumentation suite of the ExoMars mission for the remote detection of extant or extinct life signatures in the Martian surface and subsurface. Terrestrial analogues of Martian sites have been identified and the biogeological modifications resulting from extremophilic survival activity have been studied. Here we present the Raman spectral characterization of several examples of organic compounds which have been recorded using 785 nm, 633 nm and 514 nm laser excitation -polycyclic aromatic hydrocarbons (PAHs), organic acids, chlorophyll and carotenoids. Experimental mixtures of ß-carotene in usnic acid, PAHs in usnic acid and PAHs in mineral matrices have also been investigated. Organic compounds and PAHs located under crystalline minerals samples were identified using a 5x objective lens and 785 nm III excitation. The pure compounds and compound mixtures were also analysed using X-ray powder diffraction and scanning electron microscopy (SEM). The results of this study indicate that near infrared laser at 785 nm provided the clearest and the most informative spectra due to the reduction of fluorescence emission. Higher energy lasers operating in the visible region have resulted in the emission of significant background fluorescence. Few samples fluoresce even with the use of 785 nm excitation and FT-Raman spectroscopy remains the instrument of choice for the analysis of these samples.

Стилі APA, Harvard, Vancouver, ISO та ін.

9

Alajtal, Adel I. "Raman spectroscopic application for the analysis of organic compounds and minerals of astrobiological significance. The detection and discrimination of organic compounds and mineral analogues in pure and mixed samples of astrobiological significance using raman spectroscopy, XRD and scanning electron microscopy." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/4425.

Повний текст джерела

Анотація:

Raman spectroscopy has been used to characterise both organic and geological samples in order to build a database for the future characterization of biomarker molecules that are of astrobiological relevance. Characteristic geological features and hydrated minerals recently found on the surface of Mars by the NASA planetary rovers Spirit and Opportunity suggest that a possible biosphere could have once existed there. Analytical instrumentation protocols for the unequivocal detection of biomarkers in suitable geological matrices are critical for future unmanned explorations, including the forthcoming ESA ExoMars mission scheduled for 2018. Several geological features found on the surface of Mars by planetary rovers suggest that a possible extinct biosphere could exist based on similar sources of energy as occurred on Earth. For this reason, analytical instrumental protocols for the detection of isolated biomarkers preserved in suitable geological matrices unequivocally and non-destructively have to be evaluated for future unmanned missions. Raman spectroscopy is currently part of the Pasteur instrumentation suite of the ExoMars mission for the remote detection of extant or extinct life signatures in the Martian surface and subsurface. Terrestrial analogues of Martian sites have been identified and the biogeological modifications resulting from extremophilic survival activity have been studied. Here we present the Raman spectral characterization of several examples of organic compounds which have been recorded using 785 nm, 633 nm and 514 nm laser excitation -polycyclic aromatic hydrocarbons (PAHs), organic acids, chlorophyll and carotenoids. Experimental mixtures of ß-carotene in usnic acid, PAHs in usnic acid and PAHs in mineral matrices have also been investigated. Organic compounds and PAHs located under crystalline minerals samples were identified using a 5x objective lens and 785 nm III excitation. The pure compounds and compound mixtures were also analysed using X-ray powder diffraction and scanning electron microscopy (SEM). The results of this study indicate that near infrared laser at 785 nm provided the clearest and the most informative spectra due to the reduction of fluorescence emission. Higher energy lasers operating in the visible region have resulted in the emission of significant background fluorescence. Few samples fluoresce even with the use of 785 nm excitation and FT-Raman spectroscopy remains the instrument of choice for the analysis of these samples.

Стилі APA, Harvard, Vancouver, ISO та ін.

10

Pappas, Adlreburg Nickolas. "To Make Iron of Iron : A Comprehensive Analytical Study of Spade Shaped Iron Bars." Thesis, Stockholms universitet, Arkeologiska forskningslaboratoriet, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-145694.

Повний текст джерела

Анотація:

This thesis aims to provide adequate analytical information on the spade shaped iron bars of Norrland and central Sweden. While their significance has been thoroughly debated for decades, analytical research on them has been confined to cases of single artefacts or theoretical interpretations of their value, meaning and origin. In this study a comprehensive approach is taken into consideration. Based on X-Ray fluorescence (XRF), scanning electron microscopy (SEM) and metallographical analysis this thesis seeks to facilitate new interpretations on quality, production centres and usage based on analytical results. Aiming to settle some of the long lasting questions regarding the artefacts while producing results which can further the discussion by raising new questions, previously unasked.

Стилі APA, Harvard, Vancouver, ISO та ін.

11

Altun, Naci Emre. "Beneficiation Of Himmetoglu And Beypazari Oil Shales By Flotation And Their Thermal Characterization As An Energy Source." Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12606990/index.pdf.

Повний текст джерела

Анотація:

Processing of Bolu-Himmetoglu (Type I Kerogen) and Ankara-Beypazari (Type II Kerogen) oil shales by flotation techniques were investigated for achieving clean solid fuel substitutes. Materials characterization was done through mineralogical, XRD and FTIR analyses. Flotation responses of the samples were tested with non-ionizing and ionizing collectors of cationic and anionic types. The effects of the collector dosage and pulp pH on cleaning were determined. Other important flotation parameters, conditioning time, flotation time, pulp density, particle size and frother dosage were encountered using a statistical approach, through a full two level factorial experimental design. An advanced flotation procedure, assisted by ultrasonic application, was developed for further improvement in flotation performance. The effects of cleaning on thermal characterstics and combustion kinetics were evaluated with Differential Scanning Calorimetry and ASTM methods while the changes in the emission profiles were assessed using Effluent Gas Analysis. Himmetoglu sample was characterized as a carbonate and organic rich humic oil shale with XRD and FTIR analyses while Beypazari oil shale involved significant carbonate and clay minerals and exhibited a fulvic character with a poor organics content. Reverse flotation with amine acetates provided the most effective means of cleaning with Himmetoglu oil shale. Ash was decreased from 34.76 % to 23.52 % with a combustible recovery of 83.57 % using 800 g/ton Flotigam CA at natural pH and the calorific value increased from 4312 kcal/kg to 5010 kcal/kg. Direct flotation with amines was most effective for Beypazari oil shale cleaning. Using Armoflote 17, ash was reduced from 69.88 % to 53.10 % with 58.64 % combustible recovery using 800 g/ton Armoflote 17 at natural pulp pH and the calorific value of the sample increased from 876 kcal/kg to 2046 kcal/kg. Following optimization, ash of Himmetoglu oil shale decreased to 16.81 % with 84.10 % combustible recovery and calorific value increased to 5564 kcal/kg. For Beypazari oil shale ash decreased to % 48.42 with 59.17 % combustible recovery and the calorific value increased to 2364 kcal/kg. Ultrasonic pre-treatment before flotation further decreased the ash of Himmetoglu sample to 11.82 % with 82.66 % combustible recovery at 15 minutes pre-conditioning time and 50 % power level. For Beypazari oil shale, ash decreased to 34.76 % with 64.78 % combustible recovery after 15 minutes pre-treatment time at 70 % power level. Comparative XRD spectra and SEM analyses revealed that the extent of mineral matter removal relied on the flotation performance. The thermal indicators considerably improved after cleaning and the extent of improvement increased with a decrease in the ash of the concentrates. Kinetic analysis showed the favorable effect of inorganics removal on the effectiveness and easiness of combustion and activation energies decreased after cleaning for both oil shales. The contributions of cleaning on the effectiveness of combustion were also revealed by the increases in the emission rates and total CO2 and CO emission amounts. CO2 emissions due to mineral matter decomposition and harmful SO2 emissions apparently decreased as a consequence of the cleaning of the undesired inorganic contituents and potentially cleaning components. Results of the cleaning and thermal analysis sudies revealed that it was possible to achieve a clean energy source alternative from oil shales through flotation and a significant potential can be anticipated for future use of oil shales as a cost effective and environmental friendly solid fuel substitute in view of Turkey&
#8217
s great oil shale reserves.

Стилі APA, Harvard, Vancouver, ISO та ін.

12

Newton, Thomas Russell. "Investigation of the effect of process parameters on the formation of recast layer in wire-EDM of Inconel 718." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22580.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

13

Burkey, Michael F. "A REVIEW OF IRON SULFIDES AND OXIDES IN COAL MINE WASTE, HUFF RUN WATERSHED, OHIO." Kent State University Honors College / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ksuhonors1525905282950671.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

14

Bahfenne, Silmarilly. "Single crystal Raman spectroscopy of selected arsenite, antimonite and hydroxyantimonate minerals." Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/46234/1/Silmarilly_Bahfenne_Thesis.pdf.

Повний текст джерела

Анотація:

This thesis concentrates on the characterisation of selected arsenite, antimonite, and hydroxyantimonate minerals based on their vibrational spectra. A number of natural arsenite and antimonite minerals were studied by single crystal Raman spectroscopy in order to determine the contribution of bridging and terminal oxygen atoms to the vibrational spectra. A series of natural hydrated antimonate minerals was also compared and contrasted using single crystal Raman spectroscopy to determine the contribution of the isolated antimonate ion. The single crystal data allows each band in the spectrum to be assigned to a symmetry species. The contribution of bridging and terminal oxygen atoms in the case of the arsenite and antimonite minerals was determined by factor group analysis, the results of which are correlated with the observed symmetry species. In certain cases, synthetic analogues of a mineral and/or synthetic compounds isostructural or related to the mineral of interest were also prepared. These synthetic compounds are studied by non-oriented Raman spectroscopy to further aid band assignments of the minerals of interest. Other characterisation techniques include IR spectroscopy, SEM and XRD. From the single crystal data, it was found that good separation between different symmetry species is observed for the minerals studied.

Стилі APA, Harvard, Vancouver, ISO та ін.

15

Sharma, Varun. "Evaluation of novel metalorganic precursors for atomic layer deposition of Nickel-based thin films." Master's thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-166627.

Повний текст джерела

Анотація:

Nickel und Nickel (II) -oxid werden in großem Umfang in fortgeschrittenen elektronischen Geräten verwendet. In der Mikroelektronik-Industrie wird Nickel verwendet werden, um Nickelsilizid bilden. Die Nickelmono Silizid (NiSi) wurde als ausgezeichnetes Material für Source-Drain-Kontaktanwendungen unter 45 nm-CMOS-Technologie entwickelt. Im Vergleich zu anderen Siliziden für die Kontaktanwendungen verwendet wird NiSi wegen seines niedrigen spezifischen Widerstand, niedrigen Kontaktwiderstand, relativ niedrigen Bildungstemperatur und niedrigem Siliziumverbrauchs bevorzugt. Nickel in Nickelbasis-Akkus und ferromagnetischen Direktzugriffsspeicher (RAMs) verwendet. Nickel (II) oxid wird als Transistor-Gate-Oxid und Oxid in resistive RAM genutzt wird. Atomic Layer Deposition (ALD) ist eine spezielle Art der Chemical Vapor Deposition (CVD), das verwendet wird, um sehr glatte sowie homogene Dünnfilme mit hervorragenden Treue auch bei hohen Seitenverhältnissen abzuscheiden. Es basiert auf selbstabschließenden sequentielle Gas-Feststoff-Reaktionen, die eine präzise Steuerung der Filmdicke auf wenige Angström lassen sich auf der Basis. Zur Herstellung der heutigen 3D-elektronische Geräte, sind Technologien wie ALD erforderlich. Trotz der Vielzahl von praktischen Anwendungen von Nickel und Nickel (II) -oxid, sind einige Nickelvorstufen zur thermischen basierend ALD erhältlich. Darüber hinaus haben diese Vorstufen bei schlechten Filmeigenschaften führte und die Prozesseigenschaften wurden ebenfalls begrenzt. Daher in dieser Masterarbeit mussten die Eigenschaften verschiedener neuartiger Nickelvorstufen zu bewerten. Alle neuen Vorstufen heteroleptische (verschiedene Arten von Liganden) und Komplexe wurden vom Hersteller speziell zur thermischen basierend ALD aus reinem Nickel mit H 2 als ein Co-Reaktionsmittel gestaltet. Um die neuartige Vorläufer zu untersuchen, wurde eine neue Methode entwickelt, um kleine Mengen in einer sehr zeitsparend (bis zu 2 g) von Ausgangsstoffen zu testen. Diese Methodologie beinhaltet: TGA / DTA-Kurve analysiert der Vorstufen, thermische Stabilitätstests in dem die Vorläufer (<0,1 g) wurden bei erhöhter Temperatur in einer abgedichteten Umgebung für mehrere Stunden wurde die Abscheidung Experimenten und Film Charakterisierungen erhitzt. Die Abscheidungen wurden mit Hilfe der in situ Quarzmikrowaage überwacht, während die anwendungsbezogenen Filmeigenschaften, wie chemische Zusammensetzung, physikalische Phase, Dicke, Dichte, Härte und Schichtwiderstand wurden mit Hilfe von ex situ Messverfahren untersucht. Vor der Evaluierung neuartiger Nickelvorstufen ein Benchmark ALD-Prozess war vom Referenznickelvorläufer (Ni (AMD)) und Luft als Reaktionspartner entwickelt. Das Hauptziel der Entwicklung und Optimierung von solchen Benchmark-ALD-Prozess war es, Standard-Prozessparameter wie zweite Reaktionspartner Belichtungszeiten, Argonspülung Zeiten, gesamtprozessdruck, beginnend Abscheidungstemperatur und Gasströme zu extrahieren. Diese Standard-Prozessparameter mussten verwendet, um die Prozessentwicklung Aufgabe (das spart Vorläufer Verbrauch) zu verkürzen und die Sublimationstemperatur Optimierung für jede neuartige Vorstufe werden. Die ALD Verhalten wurde in Bezug auf die Wachstumsrate durch Variation des Nickelvorläuferbelichtungszeit, Vorläufer Temperatur und Niederschlagstemperatur überprüft
Nickel and nickel(II) oxide are widely used in advanced electronic devices . In microelectronic industry, nickel is used to form nickel silicide. The nickel mono-silicide (NiSi) has emerged as an excellent material of choice for source-drain contact applications below 45 nm node CMOS technology. As compared to other silicides used for the contact applications, NiSi is preferred because of its low resistivity, low contact resistance, relatively low formation temperature and low silicon consumption. Nickel is used in nickel-based rechargeable batteries and ferromagnetic random access memories (RAMs). Nickel(II) oxide is utilized as transistor gate-oxide and oxide in resistive RAMs. Atomic Layer Deposition (ALD) is a special type of Chemical Vapor Deposition (CVD) technique, that is used to deposit very smooth as well as homogeneous thin films with excellent conformality even at high aspect ratios. It is based on self-terminating sequential gas-solid reactions that allow a precise control of film thickness down to few Angstroms. In order to fabricate todays 3D electronic devices, technologies like ALD are required. In spite of huge number of practical applications of nickel and nickel(II) oxide, a few nickel precursors are available for thermal based ALD. Moreover, these precursors have resulted in poor film qualities and the process properties were also limited. Therefore in this master thesis, the properties of various novel nickel precursors had to be evaluated. All novel precursors are heteroleptic (different types of ligands) complexes and were specially designed by the manufacturer for thermal based ALD of pure nickel with H 2 as a co-reactant. In order to evaluate the novel precursors, a new methodology was designed to test small amounts (down to 2 g) of precursors in a very time efficient way. This methodology includes: TGA/DTA curve analyses of the precursors, thermal stability tests in which the precursors (< 0.1 g) were heated at elevated temperatures in a sealed environment for several hours, deposition experiments, and film characterizations. The depositions were monitored with the help of in situ quartz crystal microbalance, while application related film properties like chemical composition, physical phase, thickness, density, roughness and sheet resistance were investigated with the help of ex situ measurement techniques. Prior to the evaluation of novel nickel precursors, a benchmark ALD process was developed from the reference nickel precursor (Ni(amd)) and air as a co-reactant. The main goal of developing and optimizing such benchmark ALD process was to extract standard process parameters like second-reactant exposure times, Argon purge times, total process pressure, starting deposition temperature and gas flows. These standard process parameters had to be utilized to shorten the process development task (thus saving precursor consumption) and optimize the sublimation temperature for each novel precursor. The ALD behaviour was checked in terms of growth rate by varying the nickel precursor exposure time, precursor temperature and deposition temperature

Стилі APA, Harvard, Vancouver, ISO та ін.

16

Bright, Andrew G. "Mechanistic Insights into the Stabilisation of Biopharmaceuticals using Glycine Derivatives. The Effect of Glycine Derivatives on the Crystallisation, Physical Properties and Behaviour of Commonly used Excipients to Stabilise Antigens, Adjuvants and Proteins in the Solid State." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/15943.

Повний текст джерела

Анотація:

This dissertation has focused on studying the effect of four glycine derivatives on the solid state properties of mannitol, glycine, and sucrose when freeze dried into blended mixtures. The primary goal was to assess their value for use in the stabilisation of vaccines in the solid state, by examining key physical and chemical characteristics, which have been documented to be beneficial to the stabilisation of biopharmaceutical formulations. The novel excipients; dimethyl glycine, and trimethyl glycine, were shown to retard the crystallisation and increase the overall glass transition temperature, of mannitol, when freeze dried as evidenced by DSC and Powder X-ray diffraction. Mannitol’s glass transition temperature increased from 100C to 12.650C and 13.610C when mixed with methyl-glycine and dimethyl glycine respectively. The glycine derivatives did not show the same effect on sucrose which remained amorphous regardless of the concentration of the other excipient. The different behaviour with the sucrose system was thought to be due to relatively high glass transition temperature of sucrose. Conversely glycine remained highly crystalline due it’s relatively low glass transition temperature. The novel excipient formulations were also assessed for their effect on the aggregation of the adjuvant aluminium hydroxide when freeze dried by Dynamic Light Scattering (DLS).The formulations containing the glycine derivatives all caused a decrease in the aggregation size of the adjuvant from ~26 μm, to 185 nm in the presence of methyl glycine. The effects of lysozyme and viral antigen on the adjuvants were also examined showing that the addition of the virus did not affect the size of the aggregates formed, however lysozyme showed significant decreases in the aggregates formed. Examination of the freezing method were also made showing that faster freezing rates produced smaller aggregates of the adjuvant. When investigating the rate at which the excipients lost water during secondary drying there was evidence of the formation of hydrates of glycine, trimethyl glycine, and mannitol has shown that the glycine derivatives have attributes which would be beneficial in stabilising vaccines in the solid state when freeze dried.

Стилі APA, Harvard, Vancouver, ISO та ін.

17

Allain, Vanessa. "Bicouches lipidiques modèles pour l'étude des interactions de substances exogènes avec les membranes biologiques : exemple d'un principe actif squalénisé, le ddC-SQ." Thesis, Paris 11, 2011. http://www.theses.fr/2011PA114843.

Повний текст джерела

Анотація:

Les principes actifs, dans leur chemin vers leur cible thérapeutique, rencontrent une ou plusieurs membranes biologiques (plasmique, intracellulaire). Les interactions entre un principe actif et ces membranes sont importantes : d’une part les propriétés pharmacocinétiques de la molécule active (transport, distribution, accumulation) en dépendent, d’autre part le principe actif peut modifier les propriétés structurales des membranes. L’étude de ces interactions est rendue difficile par la complexité des membranes en termes de composition (lipidique et protéique) et de structure (hétérogénéité de l’organisation). Par conséquent, l’utilisation de systèmes modèles simplifiés est nécessaire. Au cours de ce travail de thèse nous avons cherché à réaliser des bicouches lipidiques modèles dont les caractéristiques se rapprochaient de celles des membranes biologiques en complexifiant progressivement leur composition lipidique. Nous avons ensuite étudié l’interaction d’une molécule anti-VIH squalénisée, le ddC-SQ, avec nos modèles de membrane.Un des rôles essentiels des membranes biologiques étant de séparer deux milieux aqueux de composition ionique différente, nous avons étudié dans un premier temps l’influence de la nature du milieu d’hydratation sur les propriétés thermiques et structurales des bicouches lipidiques. A pH physiologique, nous avons mis en évidence que seuls les ions divalents (à faibles concentrations) induisaient de profondes modifications structurales en provoquant la formation de vésicules unilamellaires dans les systèmes simples. Une seconde partie de nos travaux a consisté à étudier l’interaction d’un antiviral squalénisé, le ddC-squalène (ddC-SQ), avec nos différentes bicouches modèles. Cet analogue nucléosidique a été associé de manière covalente à une chaîne de squalène afin d’améliorer ses propriétés pharmacocinétiques. Cette squalénisation confère à la molécule la capacité de s’auto-assembler en nanoparticules présentant une structure cubique bicontinue. Les résultats obtenus ont révélé que le principe actif squalénisé interagissait fortement avec les membranes à l’inverse de la molécule native. L’organisation structurale des systèmes modèles est profondément modifiée par l’insertion du ddC-SQ, ce qui pourrait influer sur l’activité du composé
Drugs must cross one or more biological membranes (plasma membrane, intracellular membrane) to reach their intracellular target. Interactions between drug and membranes play a significant role in the pharmacokinetic properties of drug such as transport, distribution, accumulation. Moreover, drugs may alter membrane properties. The complexity of the composition (protein and lipid) and the structural properties (heterogeneity) of membranes leads to a difficult investigation of these interactions. Consequently, use of simplified model membranes is needed. In this work, model lipid bilayer systems in which the lipid organization mimics the arrangement of lipids in natural membrane have been developed. In this way, the complexity of lipid composition mixtures has been progressively increased. The primary function of membrane is to physically separate aqueous compartments from their surroundings. The intracellular and extracellular fluids differ in ionic composition. This study firstly consists to estimate the influence of aqueous medium nature on the thermodynamic and structural properties of these model membranes.In physiological conditions (pH 7.4, ionic strength 150 mM), the most significant change was obtained in the presence of divalent ions. Markedly change in lipid organization was observed and the formation of unilamellar vesicles has been evidenced (at low concentrations) in simple model bilayers. Interactions of an antiretroviral nucleoside analogue, the SQddC, with lipid systems constitute the second part of our work. Squalene has been covalently coupled to ddC, in order to improve its therapeutic index. Squalenoylation leads to amphiphilic prodrugs which self-organize as nanoparticles. ddC weakly interacts with lipid membranes while SQddC-SQ can insert into membranes between hydrophobic alkyl chains and induce disruption of lipid organization. Consequently, the efficacy and/or toxicity of this drug could change

Стилі APA, Harvard, Vancouver, ISO та ін.

18

Smith, Thomas. "Studies of p-type semiconductor photoelectrodes for tandem solar cells." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/14522.

Повний текст джерела

Анотація:

Photoelectrodes and photovoltaic devices have been prepared via multiple thin film deposition methods. Aerosol assisted chemical vapour deposition (AACVD), electrodeposition (ED), chemical bath deposition (CBD) and doctor blade technique (DB) have been used to deposit binary and ternary metal oxide films on FTO glass substrates. The prepared thin films were characterised by a combination of SEM (Scanning Electron Microscopy), powder X-ray diffraction, mechanical strength tests and photochemical measurements. Nickel oxide (NiO) thin films prepared by AACVD were determined to have good mechanical strength . with a photocurrent of 7.6 μA cm-2 at 0 V and an onset potential of about 0.10 V. This contrasted with the dark current density of 0.3 μA cm-2 at 0 V. These NiO samples have very high porosity with crystalline columns evidenced by SEM. In comparison with the AACVD methodology, NiO films prepared using a combination of ED and DB show good mechanical strength but a higher photocurrent of 24 μA cm-2 at 0 V and an onset potential of about 0.10 V with a significantly greater dark current density of 7 μA cm-2 at 0 V. The characteristic features shown in the SEM are smaller pores compared to the AACVD method. Copper (II) oxide (CuO) and copper (I) oxide (Cu2O) films were fabricated by AACVD by varying the annealing temperature between 100-325°C in air using a fixed annealing time of 30 min. It was shown by photocurrent density (J-V) measurements that CuO produced at 325 °C was most stable and provided the highest photocurrent of 173 μA cm-2 at 0 V with an onset potential of about 0.23 V. The alignment of zinc oxide (ZnO) nano-rods and nano-tubes fabricated by CBD have been shown to be strongly affected by the seed layer on the FTO substrate. SEM images showed that AACVD provided the best seed layer for aligning the growth of the nano-rods perpendicular to the surface. Nano-rods were successfully altered into nano-tubes using a potassium chloride bath etching method. NiO prepared by both AACVD and the combined ED/DB method were sensitized to absorb more of the solar spectrum using AACVD to deposit CuO over the NiO. A large increase in the photocurrent was observed for the p-type photoelectrode. These p-type photoelectrode showed a photocurrent density of approximately 100 μA cm-2 at 0 V and an onset potential of 0.3 V. This photocathode was then used as a base to produce a solid state p-type solar cell. For the construction of the solid state solar cells several n-type semiconductors were used, these were ZnO, WO3 and BiVO4. WO3 and BiVO4 were successfully produced with BiVO4 proving to be the optimum choice. This cell was then studied more in depth and optimised by controlling the thickness of each layer and annealing temperatures. The best solid state solar cell produced had a Jsc of 0.541 μA cm-2 (541 nA) and a Voc of 0.14 V, TX146 made up of NiO 20 min, CuFe2O4 50 min, CuO 10 min, BiVO4 27 min, using AACVD and then annealed for 30 min at 600°C.

Стилі APA, Harvard, Vancouver, ISO та ін.

19

Gill, Yasir Q. "Preparation and characterization of polyethylene based nanocomposites for potential applications in packaging." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/18052.

Повний текст джерела

Анотація:

The objective of my work was to develop HDPE clay nanocomposites for packaging with superior barrier (gas and water) properties by economical processing technique. This work also represents a comparative study of thermoplastic nanocomposites for packaging based on linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and Nylon12. In this study properties and processing of a series of linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and Nylon 12 nanocomposites based on Na-MMT clay and two different aspect ratio grades of kaolinite clay are discussed.

Стилі APA, Harvard, Vancouver, ISO та ін.

20

Ornek, Cem. "Performance characterisation of duplex stainless steel in nuclear waste storage environment." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/performance-characterisation-of-duplex-stainless-steel-in-nuclear-waste-storage-environment(4db73e9b-c87c-40a6-9778-0b823b1c499f).html.

Повний текст джерела

Анотація:

The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.

Стилі APA, Harvard, Vancouver, ISO та ін.

21

Hales, Matthew Cameron. "Synthesis and characterisation of substituted smithsonite and calcite." Thesis, Queensland University of Technology, 2008. https://eprints.qut.edu.au/16643/1/Matthew_Hales_Thesis.pdf.

Повний текст джерела

Анотація:

Carbonate minerals play a very important role in nature, they represent some of the most diverse and common mineral species on the Planet. They are directly involved in the carbon dioxide (CO2) cycle acting as relatively stable long term chemical storage reservoirs, moderating both global warming trends and oceanaquatic chemistry through carbonate buffering systems. A range of synthetic metal carbonates have been synthesised for analysis under multiple experimental conditions, in order to study the variation in physical and chemical properties such as phase specificity, metal substitution, hydration/hydroxy carbonate formation under varying partial pressures of CO2 and thermal stability. Synthetic samples were characterised by a variety of instrumental analysis techniques in order to investigate chemical purity and phase specificity. Some of the techniques included, vibrational spectroscopy (IR/Raman), thermal analysis (TGA-MS) (thermal Raman), X-Ray diffraction (XRD) and electron microscopy (SEM-EDX). From the instrumental characterisation techniques, it was found that single phase smithsonite, hydrozincite, calcite and nesquehonite could successfully be synthesised under the conditions used. Minor impurities of other minerals and / or phases were found to form under specific chemical or physical conditions such as in the case of hydrozincite / simonkolleite if zinc chloride was used during hydrothermal synthesis.

Стилі APA, Harvard, Vancouver, ISO та ін.

22

Hales, Matthew Cameron. "Synthesis and characterisation of substituted smithsonite and calcite." Queensland University of Technology, 2008. http://eprints.qut.edu.au/16643/.

Повний текст джерела

Анотація:

Carbonate minerals play a very important role in nature, they represent some of the most diverse and common mineral species on the Planet. They are directly involved in the carbon dioxide (CO2) cycle acting as relatively stable long term chemical storage reservoirs, moderating both global warming trends and oceanaquatic chemistry through carbonate buffering systems. A range of synthetic metal carbonates have been synthesised for analysis under multiple experimental conditions, in order to study the variation in physical and chemical properties such as phase specificity, metal substitution, hydration/hydroxy carbonate formation under varying partial pressures of CO2 and thermal stability. Synthetic samples were characterised by a variety of instrumental analysis techniques in order to investigate chemical purity and phase specificity. Some of the techniques included, vibrational spectroscopy (IR/Raman), thermal analysis (TGA-MS) (thermal Raman), X-Ray diffraction (XRD) and electron microscopy (SEM-EDX). From the instrumental characterisation techniques, it was found that single phase smithsonite, hydrozincite, calcite and nesquehonite could successfully be synthesised under the conditions used. Minor impurities of other minerals and / or phases were found to form under specific chemical or physical conditions such as in the case of hydrozincite / simonkolleite if zinc chloride was used during hydrothermal synthesis.

Стилі APA, Harvard, Vancouver, ISO та ін.

23

MAZZINGHI, ANNA. "Sviluppo di strumentazione xrf a scansione per applicazioni ai beni culturali." Doctoral thesis, 2016. http://hdl.handle.net/2158/1044076.

Повний текст джерела

Анотація:

Il progetto di dottorato, svolto presso il laboratorio LABEC dell'Istituto Nazionale di Fisica Nucleare (INFN) di Firenze, si è focalizzato principalmente sullo sviluppo, caratterizzazione e utilizzo di un nuovo spettrometro in Fluorescenza X a scansione per l'analisi composizionale di materiali, che permette di ottenere mappe di distribuzione elementale dell'oggetto di interesse. Grazie alla collaborazione con l'Opificio delle Pietre Dure abbiamo avuto l'opportunità di utilizzare il nostro prototipo per l'analisi di molti dipinti di Grandi Maestri e altri capolavori; nella tesi vengono riportati i risultati più interessanti per mostrare le caratteristiche dello strumento e i principali vantaggi dell'utilizzzo di uno strumento a scansione nel campo dei Beni Culturali- The PhD project, carried out at the LABEC laboratory of the National Institute of Nuclear Physics (INFN) of Florence, was mainly focused in the developing, testing and using of a new X-Ray Fluorescence scanning spectrometer for material composition analysis, which allows acquiring elemental distribution maps of the objects of interest. Thanks to the collaboration with the Opificio delle Pietre Dure, we had the opportunity to use our prototype for the analysis of many paintings by Old Masters and of other artworks; in the thesis the main results are briefly reported in order to show the performance of the instrument and the main advantages of using a scanning device in the Cultural Heritage field.

Стилі APA, Harvard, Vancouver, ISO та ін.

24

Banerjee, Sikhar. "Biogeochemical Evolution of the Western Interior Basin of North America during a Kasimovian Highstand and Regression." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10706.

Повний текст джерела

Анотація:

The purpose of this study is to identify and analyze the geochemical facies of the Hushpuckney Shale using XRF scanning data and the bioturbation indices, which will contribute to a better understanding of the biogeochemical environment prevalent during the deposition of the Hushpuckney Shale. The Hushpuckney Shale Member of the Swope Formation (Kasimovian Stage) preserved in KGS Spencer core 2 - 6, consists of a black shale submember overlain by bioturbated gray shale. Millimeter-scale core description and analysis of XRF scanning data enables identification of geochemical facies within the study core and contributes to understanding the environment of shale deposition. The XRF spectrometer produces X-ray image of the core and abundance values of selected major and trace elements, including iron (Fe), calcium (Ca), sulfur (S), molybdenum (Mo), zinc (Zn), vanadium (V), chromium (Cr), copper (Cu), nickel (Ni), titanium (Ti), zircon (Zr), potassium (K) and phosphorous (P). Canfield and Thamdrup's (2009) classification of geochemical environments is used to recognize oxic/aerobic, manganous-nitrogenous, ferruginous and sulfidic facies within the black shale submember. A modification of Droser and Bottjer's (1986) semi-quantitative field classification of bioturbation is used to identify facies variations within the gray shale submember. Abundance of apatite nodules and lamina in the black shale submember of the study core suggest that black shale sediments accumulated slowly in a sediment-starved basin. A high abundance of sulfide-scavenged elements, including Mo, Zn, V, Ni and Cr, identifies the sulfidic facies in the black shale submember, and indicates deposition in an oxygen-depleted environment with a high concentration of hydrogen sulfide. The overlying ferruginous facies has lower abundances of sulfide-scavenged elements and lacks cryptic Fe-laminations. The uppermost black shale submember facies, the manganous-nitrogenous facies, has cryptic Fe laminations and a relatively high P/Ca ratio. Abundance of cryptic iron laminations and apatite nodules and lamina indicates the syngenetic deposition of iron and phosphate due to Fe-P coupling mechanism. The gray shale submember is burrowed, indicating deposition under oxygenated conditions. Bioturbation indices reveal the variations in the intensity and nature of burrows within the gray shale, which corresponds to the changes in the depositional environment that may be related to the rise and fall of sea-level.

Стилі APA, Harvard, Vancouver, ISO та ін.

25

Falster, Georgina Maja. "Reconstructing Australia’s late Quaternary climate from the geochemistry of lake sediments and snail shells." Thesis, 2019. http://hdl.handle.net/2440/120398.

Повний текст джерела

Анотація:

Australia’s climate is influenced by ocean-atmosphere interactions in the adjacent Indian, Pacific, and Southern oceans, as well as major atmospheric circulation patterns. Australian climates exhibit high inter-annual variability, arising in part from complex interactions between these drivers. Understanding the nature and drivers of Australian climate variability is not only important for land use and management, but also has global relevance, due to Australia’s contribution to the global terrestrial carbon budget. Measurements of Australian temperature and rainfall only extend back to the early 20th century, and hence do not capture the full range of natural climate variability. Proxy-based climate reconstructions are therefore required to understand Australian climate variability on long (centennial to millennial) time scales. The late Quaternary—defined in this thesis as 30 to 10 thousand years before the year 1950 (ka BP)—is a particularly informative interval. It encompasses large changes in global climate dynamics, including both the global Last Glacial Maximum (LGM; 23 to 19 ka BP) and subsequent deglaciation, allowing assessment of the Australian climate response to global change. However, the arid to semi-arid nature of most the continent is not conducive to sedimentary record accumulation, limiting spatial and temporal resolution of existing late Quaternary climate reconstructions. This thesis therefore presents both new late Quaternary palaeoclimate data and new methods for inferring past climate across the Australian continent, through the following research components: 1) A record of late Quaternary moisture balance, inferred from highly resolved x-ray fluorescence and organic carbon isotope measurements of a sedimentary sequence from Lake Surprise in south-eastern Australia (Chapter 3). The regional significance of this record is assessed using a Monte Carlo Empirical Orthogonal Function approach. 2) The high-resolution record is supported by three discrete quantitative temperature estimates, based on the clumped isotope composition (Δ47) of freshwater snail shells from Blanche Cave, also in south-eastern Australia (Chapter 6). Δ47 analysis allows calculation of the growth temperature of carbonate minerals (e.g. snail shells), independent of organism, carbonate phase, or formation water geochemistry. Carbonate Δ47 analysis therefore offers a uniquely direct estimate of past temperatures, that has not previously been applied in Australian palaeoclimate studies. 3) Clumped isotope analysis is highly susceptible to contamination, so this thesis provides a new pretreatment method for obtaining precise and accurate data from carbonates preserved within an organic-rich matrix (Chapter 2). 4) The influence of remote drivers of Australian climate often manifests in distinct spatial patterns of temperature or rainfall. However, the low spatial resolution of existing palaeoclimate records across the continent inhibits detection of spatio-temporal climate trends that would facilitate inference of these drivers. This thesis therefore evaluates the climate proxy potential of land snail shells in Australia, by combining flux balance models with clumped and stable isotope measurements of modern shells collected from a wide spatial and climatic gradient across the continent (Chapters 4 and 5). The palaeoclimate reconstructions provide a coherent record of climate variability prior to and throughout the late Quaternary, and suggest that drivers of south-eastern Australian climate have varied on multi-millennial time scales in response to major shifts in global circulation. Δ47 analysis of freshwater snail shells suggests that between ~41 and 32 ka BP, mean annual air temperatures at Blanche Cave decreased from approximately 12 ± 3.2 °C to 5 ± 4.4 °C i.e. almost ten degrees cooler than modern. These relatively low temperatures preceded a period of regional aridity between 28 and 18.5 ka BP as recorded at Lake Surprise. Together, the data suggest that the south-east Australian climate was probably responding to very different drivers to those that affect the modern climate, possibly dominated by cold Southern Ocean processes. Centennial- to millennial-scale hydroclimate variability was maintained throughout the 28–18.5 ka BP interval. Peak aridity between 21 and 18.5 ka BP probably represents the local expression of the global LGM. A rapid deglacial climate shift occurred between ~18.5 and 16 ka BP, culminating in warmer (15.5 ± 3.6 °C) and wetter conditions probably more like those of the present. The stable isotope geochemistry of modern land snail shells records precipitation amount via two mechanisms: (1) its influence on the δ18O of precipitation (a wet season signal), and (2) its effect on vegetation δ13C (an annual to multi-annual signal). Unlike freshwater snails, land snail Δ47 growth temperatures do not have a straightforward relationship with average air temperatures, but rather are useful for extracting the temperature influence from snail shell δ18O. This is the first study to report δ13C, δ18O, and Δ47 measurements from land snail shells spanning such a large climatic gradient, and also the first to investigate snail isotope-climate relationships across the variable and largely arid Australian environments. The isotope-climate relationships are robust irrespective of species or regional climatology. With land snails widely distributed in Australia, including in arid climates that lack other suitable proxies, these consistent relationships demonstrate that land snail shell isotopes will be a valuable tool for assessing spatio-temporal precipitation variability at a continental scale.
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2019

Стилі APA, Harvard, Vancouver, ISO та ін.

26

Pereira, Paulo Sérgio Marques. "Ligas de Ouro em Pintura: Nova Metodologia de Estudo de Obras de Arte." Master's thesis, 2021. http://hdl.handle.net/10316/98078.

Повний текст джерела

Анотація:

Dissertação de Mestrado em Química Forense apresentada à Faculdade de Ciências e Tecnologia
Nesta dissertação pretendeu-se realizar uma análise comparativa das ligas metálicas presentes em amostra provenientes de Obras de Arte entre o século XIV-XVII.As análises foram efetuadas em amostras provenientes do, Túmulo da Rainha Santa Isabel (TRS), Túmulo da Neta da Rainha Santa Isabel (TNRS), Busto de Santa Clara (BSC), Túmulo de Catarina de Urgel (TCU), Retábulo do Corpo de Deus (RCD), Eira Pedrinha (EP), Retábulo do São Miguel Arcanjo (RASM), Torre da Almedina (TA), Predela da Aparição de Cristo à Virgem (PACV), Lactatio de São Bernardo-Virgem (LSBV), São Gonçalo (SG), Quadros Museu Nacional Machado de Castro, Anunciação(P25), Lamentação de Cristo (P26), Aparição de Cristo à Virgem (P27), Trindade (P90), Capela de Santa Cruz, Capela de São Miguel e Nossa Senhora da Conceição (NSC).As análises efetuadas permitiram obter dados referentes à percentagem dos elementos que compunham as ligas metálicas, mais precisamente da percentagem de ouro (Au), prata (Ag) e cobre (Cu) e para tal recorreu-se a técnicas como a Microscopia Ótica (MO), Espectroscopia de Fluorescência Raio- x de bancada (b-XRF) e SEM-EDS.Após a obtenção dos resultados, estes foram cruzados de forma a tentar obter padrões, que quando comprovados permitiram enquadrar as amostras em estudo numa janela temporal lógica.(TEXTO ADICIONADO APENAS COM O INTUITO DE OBTER OS CARACTERES MÍNIMOS PRA SUBMISSÃO ONLINE, NÃO DEVE SER TIDO EM CONSIDERAÇÃO PARA O RESUMO DA DISSERTAÇÃO. NÃO FOI ADICIONADO TEXTO AO RESUMO DEVIDO A ESTE ENQUADRAR-SE DENTRO DOS LIMITES MÁXIMOS APRESENTADOS EM "https://www.uc.pt/fctuc/dct/estudantes/dissertacoes/normasFormatDissMest" DE 300 PALAVRAS)
In this dissertation, it was intended to carry out a comparative analysis of the metallic alloys present in samples from artworks between the 14th and 17th centuries. The analyzes were carried out on samples from the Tomb of Queen Saint Isabel (TRS), Tomb of Queen Saint Isabel's Granddaughter (TNRS), Bust of Saint Clara (BSC), Tomb of Catarina de Urgel (TCU), Altarpiece of Corpus Christi (RCD), Eira Pedrinha (EP), Archangel Saint Michael Altarpiece (RASM), Almedina Tower (TA), Predela of the Apparition of Christ to the Virgin (PACV), Lactation of Saint Bernardo-Virgem (LSBV), Saint Gonçalo (SG), Art Paintings of the Machado de Castro National Museum, Annunciation (P25), Lamentation of Christ (P26), Apparition of Christ to the Virgin (P27), Trinity (P90), Chapel of Santa Cruz, Chapel of Saint Michael and Nossa Senhora da Conceição (NSC).The analyzes performed allowed us to obtain data regarding the percentage of elements that made up metallic alloys, more precisely the percentage of gold (Au), silver (Ag), and copper (Cu) and for this, techniques such as Optical Microscopy (OM), Benchtop X-Ray Fluorescence Spectroscopy (b-XRF) and SEM-EDS were used.After obtaining the results, these were crossed to try to obtain patterns, which, when proven, allowed us to connect the samples present in this study to an artist and to a logical time window.(TEXTO ADICIONADO APENAS COM O INTUITO DE OBTER OS CARACTERES MÍNIMOS PRA SUBMISSÃO ONLINE, NÃO DEVE SER TIDO EM CONSIDERAÇÃO PARA O RESUMO DA DISSERTAÇÃO. NÃO FOI ADICIONADO TEXTO AO RESUMO DEVIDO A ESTE ENQUADRAR-SE DENTRO DOS LIMITES MÁXIMOS APRESENTADOS EM "https://www.uc.pt/fctuc/dct/estudantes/dissertacoes/normasFormatDissMest" DE 300 PALAVRAS)

Стилі APA, Harvard, Vancouver, ISO та ін.

27

Motylenko, Mykhaylo. "Beitrag zur Analyse von Disklinationsstrukturen in plastisch verformten Metallen." Doctoral thesis, 2009. https://tubaf.qucosa.de/id/qucosa%3A22759.

Повний текст джерела

Анотація:

Gegenstand der Arbeit ist die Analyse der bei hohen Verformungsgraden in Werkstoffen durch kollektive Bewegung der Versetzungen entstandenen neuen Defektkonfigurationen, die auf der mesoskopischen Skala agieren. Diese so genannte Disklinationen rufen neben starken Gitterdehnungen auch erhebliche lokale Gitterrotationen hervor. Es wurde der Nachweis der Existenz der Disklinationen in plastisch verformten Kristallen geliefert sowie die qualitative und quantitative Analyse der Disklinationskonfigurationen und der Disklinationsstärke durchgeführt. Die Untersuchungen an stark verformten Ein- und Vielkristallen wurden mittels sowohl lokalen Methoden der Transmissions- (TEM, CBED) und Rasterelektronenmikroskopie (REM, EBSD) als auch der integralen Methoden der Röntgenstrukturanalyse (XRD) durchgeführt. Die Ergebnisse haben gezeigt, dass die Entwicklung der Zellblockstruktur mit erheblichem Anstieg der Desorientierungen und Versetzungsdichten in Versetzungswänden verbunden ist und durch die Bildung der Netzwerke von Disklinationen gefördert wird.

Стилі APA, Harvard, Vancouver, ISO та ін.

28

Skoczylas, Łukasz. "Polimorfizm wybranych tetrafluoroboranów heksadimetylosulfotlenków metali dwuwartościowych : kobaltu manganu, niklu i cynku." Praca doktorska, 2010. http://ruj.uj.edu.pl/xmlui/handle/item/41690.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

29

Maneshi, Abolfazl. "In-Situ Ethylene Polymerization with Organoclay-Supported Metallocenes for the Preparation of Polyethylene-Clay Nanocomposites." Thesis, 2010. http://hdl.handle.net/10012/5212.

Повний текст джерела

Анотація:

In-situ polymerization is one of the most efficient methods for production of polymer clay nanocomposites. In-situ polymerization of olefins using coordination catalysts is a type of heterogeneous polymerization. In order to achieve acceptable clay nanolayer dispersion in the polyolefin matrix, the clay layer exfoliation and particle break up during the polymerization are essential requirements. A literature review on polyolefin/clay nanocomposite is given in Chapter 2. In Chapter 3, we present a new mathematical model, which is as an extension of the multigrain model (MGM), to describe the intercalative polymerization and expansion of clay interlayer spaces during polymerization using clay-supported metallocenes. The results from the model show that, under the studied conditions, mass transfer is not a strong factor controlling clay exfoliation and particle break up. If the polymerization active sites are supported uniformly on all clay surfaces, effective exfoliation will be achieved after a relative short polymerization time. In practice, obtaining good dispersion of clay nanolayers with uniform properties requires that the active sites be exclusively located on the clay nanolayer surfaces, and not extracted by the solvent to form a homogeneous solution. Factors favouring active site extraction would result in nanocomposites with poor properties. In addition, high polymerization activities, stable polymerization runs, and ease of supporting are other criteria for a successful in-situ polymerization. For this purpose we established a catalyst supporting method by which most of these requirements were met. In this method, the water content on the clay surface, which is considered as poison for the metallocene catalyst, was used to produce MAO upon reaction with trimethylaluminum (TMA). Using this method, polymerization was highly active in absence of MAO cocatalyst, knowing that MAO cocatalyst promotes active site extraction from the clay surface and results in poor powder morphology. Chapter 4 describes the development of this supporting methodology. Chapter 4 also investigates the effect of the organic modification type existing on the clay surface on the success of catalyst supporting and in-situ polymerization. We found that using the proposed supporting procedure, only tertiary ammonium type modification enhanced the in-situ polymerization, whereas the quaternary ammonium worsened the catalyst supporting efficiency and led to catalyst with poor or no polymerization activity. It is suggested that, in addition to enhancing clay surface-organic solvent compatibility (which facilitates catalyst supporting), the tertiary ammonium cation reacts with the in-situ produced MAO and increases the stability of the cocatalyst bonded to the clay surface. The effect of different polymerization conditions on the polymerization behavior and nanocomposite structural properties, such as catalyst loading during supporting, polymerization temperature and triisobutylaluminum (TIBA) concentration, were studied in Chapter 5. It was found that TIBA acts merely as scavenger. High polymerization activities were obtained with low Al/Zr ratios (Al from TIBA) and increased Al concentration decreased the polymerization activity and also the quality of powder morphology. Catalyst loading in the supporting step showed to have an important role in determining the final properties. The clay particles with higher catalyst loading resulted in better exfoliation and powder morphologies The effect of solvent type during catalyst supporting and polymerization was studied in Chapter 6. It was shown that catalyst supporting in n-hexane resulted in polymerizations with higher activities and polymers with higher molecular weight were produced. Polymerization with catalyst supported in hexane showed different ethylene uptake profiles, suggesting different mechanism of exfoliation. It is suggested that using this catalyst, the clay is mostly exfoliated before polymerization started. Similar to the original clay, the catalyst supporting efficiency on the organically modified clay was close to 100 percent. However, comparing the polymerization activities of these catalysts to those that were supported directly in the reactor just before the polymerization (in-reactor, or in-situ, supported catalysts) shows that a considerable fraction of the active sites are deactivated during the prolonged contact between catalyst and clay support surface. In Chapter 5, it was shown that the in-reactor supported catalyst had considerably higher polymerization activities, up to 40 percent of that of the homogeneous catalyst. Nanocomposites made with in-reactor supported catalysts had powder morphology and nanaolayer dispersion comparable to those made with clay-supported catalysts.

Стилі APA, Harvard, Vancouver, ISO та ін.

30

Φούσκας, Αγάπιος. "Μελέτη τροποποιημένων με βόριο καταλυτών Νi/Al2O3 για την αναμόρφωση του μεθανίου με διοξείδιο του άνθρακα". Thesis, 2011. http://hdl.handle.net/10889/4965.

Повний текст джерела

Анотація:

Κατά τις τελευταίες δεκαετίες παρατηρείται συνεχής αύξηση της έντασης του φαινομένου του θερμοκηπίου γεγονός που προκαλεί σημαντικές συνέπειες στο περιβάλλον και στη ζωή μας γενικότερα. Συνεπώς, είναι απαραίτητη η μείωση της ανθρωπογενούς εκπομπής των αερίων που συμβάλλουν στην αύξηση του φαινομένου αυτού. Η εκμετάλλευση και χρήση των δύο πιο σημαντικών θερμοκηπικών αερίων, του μεθανίου και του διοξειδίου του άνθρακα, μπορεί να επιτευχθεί με την αναμόρφωση του CH4 με CO2 ή αλλιώς ξηρή αναμόρφωση του μεθανίου (Dry Reforming of Methane-DRM). Με τη διεργασία DRM τα δύο συγκεκριμένα αέρια μετατρέπονται σε αέριο σύνθεσης (synthesis gas), το οποίο χρησιμοποιείται είτε για τη σύνθεση πληθώρας οργανικών ενώσεων, είτε για την παραγωγή Η2 για ενεργειακούς σκοπούς. Η DRM παρουσιάζει σημαντικά πλεονεκτήματα: δεν απαιτείται η χρήση ύδατος, φθηνό σχετικά κόστος εγκαταστάσεων, χρησιμοποιείται σε χημικά συστήματα μεταφοράς ενέργειας, ενώ και το αέριο σύνθεσης που παράγεται έχει ακόμα κατάλληλη αναλογία για συνθέσεις Fischer–Tropsch. Παρόλα αυτά η DRM δεν έχει εκτεταμένη βιομηχανική εφαρμογή επειδή αντιμετωπίζει ένα σημαντικό μειονέκτημα: ο καταλύτης μετά από κάποιο χρόνο λειτουργίας απενεργοποιείται λόγω του άνθρακα που αποτίθεται πάνω του. Στην παρούσα εργασία μελετήθηκε ο state of the art καταλύτης Ni/Al2O3, τον οποίο τροποποιήσαμε με βόριο σε διάφορους λόγους [Β/(B+Νi)] με κύριο στόχο τη μείωση των ανθρακούχων αποθέσεων. Οι τροποποιημένοι καταλύτες συντέθηκαν με τη μέθοδο του υγρού συνεμποτισμού και χαρακτηρίστηκαν φυσικοχημικά με διάφορες τεχνικές, ώστε να μελετήσουμε την επίδραση του βορίου στην υφή τους (ΒΕΤ, porosimetry, SEM, TEM), στη δομή τους (XRD, UV-Vis DRS) και στην αναγωγιμότητά τους (H2-TPR). Η καταλυτική συμπεριφορά τους για την αντίδραση της ξηρής αναμόρφωσης του μεθανίου αξιολογήθηκε σε αντιδραστήρα σταθερής κλίνης, για 24h, σε συνθήκες: 973Κ, 1 atm, τροφοδοσία 50%CH4-50%CO2. Ο άνθρακας που αποτέθηκε στους χρησιμοποιημένους καταλύτες μετρήθηκε με τη μέθοδο της θερμοπρογραμματισμένης υδρογόνωσης (TPH). Τα ανηγμένα και χρησιμοποιημένα στην DRM καταλυτικά δείγματα μελετήθηκαν επίσης με ηλεκτρονικό μικροσκόπιο σάρωσης (SEM με αναλυτή EDS) και ηλεκτρονικό μικροσκόπιο διαπερατότητας (ΤΕΜ). Βρέθηκε ότι η παρουσία του Β μειώνει σημαντικά την ποσότητα του αποτιθέμενου άνθρακα στους καταλύτες Ni/Al2O3, σε ποσοστό έως και 86%, χωρίς να επηρεάζει ιδιαίτερα τη δραστικότητα και την εκλεκτικότητα των καταλυτών. Σημαντικό ρόλο παίζει το ποσοστό του Β στον καταλύτη, με τον καταλύτη με λόγο Β/(B+Νi) = 0,5 να εμφανίζει τη βέλτιστη συμπεριφορά. Τα αποτελέσματα μας έδειξαν ότι η ιδιαίτερη θετική επίδραση του βορίου οφείλεται κυρίως στο γεγονός ότι ευνοεί τη διασπορά του μεταλλικού νικελίου. Τροποποίηση με βόριο, σε κατάλληλη περιοχή φορτίσεων, του καταλύτη Ni/Al2O3 μεγιστοποιεί το πλήθος των νανοσωματιδίων νικελίου με μέση διάσταση < 6.0 nm, τα οποία, ως γνωστόν, ελαχιστοποιούν την απόθεση άνθρακα.
The intensity of the greenhouse effect is constantly increasing in the last few decades with an adverse effect both on the environment and the humanity. In order to decrease the effect, human-caused emissions should be minimized. The two most important greenhouse gases, methane and carbon dioxide, can be used in the DRM (Dry Reforming of Methane) process. With this process the above mentioned gases are converted to synthesis gas, which is then used for the synthesis of a great number of organic compounds and synthetic fuels (through the Fisher-Tropsch syntheses) or for the production hydrogen to be used as a fuel (energy purposes). The DRM process presents a number of advantages, namely: no water is required, relatively low cost of process plants,it can be used as a Chemical Energy Transfer System and, finally, the produced synthesis gas has adequate CO/H2 ratio for Fisher-Tropsch syntheses. Although DRM is a promising process, its industrial application is hindered by a major drawback: the catalysts are rapidly deactivating due to coking. In the current study, the state of the art catalyst Ni/Al2O3 was studied and modified with boron, using different ratios of Β/(B+Νi). Our primary objective was to reduce coking. The modified catalysts were synthesized by wet co-impregnation and physicochemically characterized in their oxidic, reduced and used forms, using various techniques, in order to investigate the influence of boron on the texture (BET, Porosimetry, SEM, TEM), structure (XRD, UV-Vis DRS) and reducibility (H2-TPR) of the catalysts. The catalytic performance for the DRM process was studied under stable conditions (973Κ, 1 atm and 50%CH4-50%CO2 undiluted feed), for 24h, using a fixed bed reactor. Carbonaceous deposits on the used catalysts were determined by Temperature Programmed Hydrogenation (TPH). Scanning Electron Microscopy (SEM) with EDS analyser and Transmission Electron Microscopy (TEM) were also used in the study of reduced and used catalytic samples. Modifying Ni/Al2O3 catalysts with boron results in a great decrease of the deposited coke (up to 86%), without any significantly influence on the activity and selectivity of the catalysts. A major factor influencing the catalyst is the B loading, with the ratio Β/(B+Νi)=0,5 giving the best results. Boron’s positive effect was mainly attributed to its ability to increase Ni dispersion. Modification of Ni/Al2O3 catalysts, by using the appropriate boron loading, resulted to an increase of the amount of nickel nanoparticles with an average dimension under 6.0 nm, which are known to minimize coke deposition.

Стилі APA, Harvard, Vancouver, ISO та ін.

31

Shahcheraghi, Nikta. "Synthesis of novel plasmonic materials and their optical properties." Thesis, 2016. http://hdl.handle.net/10453/90040.

Повний текст джерела

Анотація:

University of Technology Sydney. Faculty of Science.
The field of ‘plasmonics’ has gained a lot of attention recently. This is because plasmonic phenomena can be used in a wide variety of modern devices, including biosensors, intracellular probes, spectrally-selective coatings, hyperthermal medical treatments, new kinds of photonic devices, nano-optics, scanning microscopy and optical cloaking. One issue with plasmonics, however, is that the metallic materials currently used cause high losses due to conversion of light to heat. The aim of my project was to discover ways to minimize optical losses in materials and nanostructures used for plasmonics. My search for better materials extended over the pure elements, intermetallic alloys and conventional alloys systems. The most promising example from each of these material types was selected for further examination on the basis of their having a low optical loss over some region of the visible spectrum. The representatives were Ag for the pure elements, PtAl₂ for the intermetallic compounds, and α- (Cu,Al) for the metallic alloys. Silver is considered as one of the most desirable materials for plasmonic devices as it has low loss (low ε₂) across the visible spectrum. Unfortunately, silver nanostructures oxidize or corrode in air. My project started with a study of silver nanotriangles which I synthesized using ‘wet chemical’ techniques. The aim of this part of the project was to discover how fast the silver nanoparticles oxidized and whether some means of preventing the oxidation could be found. I used scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and UV-visible spectroscopy to characterize my samples. Unfortunately, while the silver nanotriangles colloids were stable in a sealed bottle for several months, they oxidized within a few days once removed. I did not find a way to prevent this. I did find that silver nanotriangles are able to self-assemble into complex structures that include tip-to-tip or base-to-base, or double- and triple-decker sandwich configurations. The optical properties of these interesting arrangements were explored through computer simulations based on the discrete dipole approximation (DDA). The effect of aspect ratio, gap size and substrate were considered. It has been predicted in the recent literature that the brassy-yellow PtAl₂ intermetallic compound should be capable of exhibiting reasonably strong localized surface plasmon resonances. In this part of my project I investigated ways to fabricate PtAl₂ nanoparticles to test this claim. Ordered arrays of PtAl₂ semi-shells were created using magnetron sputtering by co-depositing Al and P𝑡 onto a template of Synthesis of Novel Plasmonic Materials and Their Optical Properties monodisperse spherical polystyrene particles of 300 nm diameter. Deposition was carried out at an acute angle to the substrate so that the resulting semi-shells could be subsequently separated. I examined the resulting material using X-ray diffraction and scanning electron microscope microscopy and the optical properties were probed by measurement of reflection and transmission spectra. I also performed optical simulations based on the DDA. The results showed that the measured properties were consistent with the occurrence of a localized surface plasmon resonance, which proved that PtAl₂ could be used in plasmonic applications. Finally, I considered the example of a metallic alloy, in this case between Cu and Al. The high electron density of Al (three electrons per atom) was expected to be beneficial because addition of Al to Cu would increase the electron-to-atom ratio of the alloy. This would influence the electronic structure and subsequently the dielectric function and Fermi level. Techniques used included ellipsometry, spectrometry, XRD and SEM. Very good results were obtained for an alloy of Cu with 15 at% Al. I also looked at the effect of crystal structure by comparing γ Cu-Al phase in the metastable and stable states. Samples were deposited at room temperature by magnetron sputtering onto a glass substrate (metastable) then annealed at 500°C for 20 minutes (stable). There was a surprisingly big change in optical properties on going from the metastable to stable states, and a region of very low loss was identified in the spectrum. Overall, the work has proved very successful. While a means to suppress oxidation of Ag was not found, three promising new materials (PtAl₂, Cu-15 at.% Al, and Cu-Al γ-phase) were identified for future plasmonic applications.

Стилі APA, Harvard, Vancouver, ISO та ін.

Дисертації з теми "Scanning XRF"

Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями