Siga este enlace para ver otros tipos de publicaciones sobre el tema: Silicate glasse.
Tesis sobre el tema "Silicate glasse"
Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros
Consulte los 50 mejores tesis para su investigación sobre el tema "Silicate glasse".
Junto a cada fuente en la lista de referencias hay un botón "Agregar a la bibliografía". Pulsa este botón, y generaremos automáticamente la referencia bibliográfica para la obra elegida en el estilo de cita que necesites: APA, MLA, Harvard, Vancouver, Chicago, etc.
También puede descargar el texto completo de la publicación académica en formato pdf y leer en línea su resumen siempre que esté disponible en los metadatos.
Explore tesis sobre una amplia variedad de disciplinas y organice su bibliografía correctamente.
1
Gaddam, Anuraag. "Structure and crystallization of multicomponent lithium silicate glasses". Doctoral thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/21819.
Texto completoResumen
Doutoramento em Ciência e Engenharia de MateriaisA presente tese tem como objetivo adquirir uma compreensão aprofundada acerca do processo de cristalização de vidros à base de silicato de lítio com a adição de pequenas quantidades de outros componentes. Os principais componentes investigados neste estudo são os óxidos de Mn, Al, B e P. Estudaram-se os efeitos de cada um destes componentes na estrutura do vidro, na separação de fases líquido-líquido, nos processos de nucleação e crescimento de cristais, na microestrutura e no conjunto das fases cristalinas formadas. Os vitro-cerâmicos utilizados neste estudo são produzidos a partir de amostras tridimensionais de vidro fundido e vertido em moldes, ou a partir de pós de frita obtida por arrefecimento dos fundidos em água. A adição de óxidos de Mn aos vidros de silicato de lítio resulta na criação de entidades moleculares individuais de Mn. Por conseguinte, estas entidades moleculares dificultam o todo o processo de cristalização do vidro. Óxidos de Al e B são incorporados na rede de vidro como formadores de rede. Estes componentes, por conseguinte, também diminuem a tendência do vidro para a cristalização. O P2O5 também desempenha um papel de formador de rede do vidro. No entanto, ele aumenta a tendência do vidro para a cristalização. Dá-se uma ênfase especial ao estabelecimento de correlações entre a estrutura do vidro e seu comportamento na cristalização. Estes esforços levaram à introdução de um novo modelo matemático baseado na mecânica estatística para descrever a estrutura de vidro. O modelo foi desenvolvido principalmente para silicatos binários e mais tarde estendido para composições de silicatos multicomponentes.
The present thesis is aimed at gaining an in-depth understanding of the crystallization process in multicomponent lithium silicate based glasses when other components are added in small amounts. The added components investigated in this study are oxides of Mn, Al, B and P. The effects of each of these components on glass structure, liquid-liquid phase separation, crystal nucleation, crystal growth, microstructure and phase assemblage are studied. The glass ceramics used in this study are produced by both bulk glasses obtained by melt quenching as well as by powder methods from glass frits. Oxides of Mn when added to lithium silicate glasses result in creating individual Mn molecular entities. Consequently, these molecular entities hinder the overall crystallization ability of the glass. Oxides of Al and B are incorporated into glass network as network formers. These components consequently decrease the overall crystallization ability of the glass. P2O5 is also incorporated into glass network as network former. However, it increases the overall crystallization ability of the glass. Particular emphasis is given to establishing correlations between glass structure and its corresponding crystallization behaviour. These efforts led to introducing a new mathematical model based on statistical mechanics for describing the glass structure. The model was primarily developed for binary silicates and later on extended to multicomponent silicates.
2
Goel, Ashutosh. "Clinopyroxene based glasses and glass-ceramics for functional applications". Doctoral thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/2323.
Texto completoResumen
Doutoramento em Ciência e Engenharia de MateriaisAs piroxenas são um vasto grupo de silicatos minerais encontrados em muitas rochas ígneas e metamórficas. Na sua forma mais simples, estes silicatos são constituídas por cadeias de SiO3 ligando grupos tetrahédricos de SiO4. A fórmula química geral das piroxenas é M2M1T2O6, onde M2 se refere a catiões geralmente em uma coordenação octaédrica distorcida (Mg2+, Fe2+, Mn2+, Li+, Ca2+, Na+), M1 refere-se a catiões numa coordenação octaédrica regular (Al3+, Fe3+, Ti4+, Cr3+, V3+, Ti3+, Zr4+, Sc3+, Zn2+, Mg2+, Fe2+, Mn2+), e T a catiões em coordenação tetrahédrica (Si4+, Al3+, Fe3+). As piroxenas com estrutura monoclínica são designadas de clinopiroxenes. A estabilidade das clinopyroxenes num espectro de composições químicas amplo, em conjugação com a possibilidade de ajustar as suas propriedades físicas e químicas e a durabilidade química, têm gerado um interesse mundial devido a suas aplicações em ciência e tecnologia de materiais. Este trabalho trata do desenvolvimento de vidros e de vitro-cerâmicos baseadas de clinopiroxenas para aplicações funcionais. O estudo teve objectivos científicos e tecnológicos; nomeadamente, adquirir conhecimentos fundamentais sobre a formação de fases cristalinas e soluções sólidas em determinados sistemas vitro-cerâmicos, e avaliar a viabilidade de aplicação dos novos materiais em diferentes áreas tecnológicas, com especial ênfase sobre a selagem em células de combustível de óxido sólido (SOFC). Com este intuito, prepararam-se vários vidros e materiais vitro-cerâmicos ao longo das juntas Enstatite (MgSiO3) - diopsídio (CaMgSi2O6) e diopsídio (CaMgSi2O6) - Ca - Tschermak (CaAlSi2O6), os quais foram caracterizados através de um vasto leque de técnicas. Todos os vidros foram preparados por fusão-arrefecimento enquanto os vitro-cerâmicos foram obtidos quer por sinterização e cristalização de fritas, quer por nucleação e cristalização de vidros monolíticos. Estudaram-se ainda os efeitos de várias substituições iónicas em composições de diopsídio contendo Al na estrutura, sinterização e no comportamento durante a cristalização de vidros e nas propriedades dos materiais vitro-cerâmicos, com relevância para a sua aplicação como selantes em SOFC. Verificou-se que Foi observado que os vidros/vitro-cerâmicos à base de enstatite não apresentavam as características necessárias para serem usados como materiais selantes em SOFC, enquanto as melhores propriedades apresentadas pelos vitro-cerâmicos à base de diopsídio qualificaram-nos para futuros estudos neste tipo de aplicações. Para além de investigar a adequação dos vitro-cerâmicos à base de clinopyroxene como selantes, esta tese tem também como objetivo estudar a influência dos agentes de nucleação na nucleação em volume dos vitro-cerâmicos resultantes á base de diopsídio, de modo a qualificá-los como potenciais materiais hopedeiros de resíduos nucleares radioactivos.
The pyroxenes are a wide spread group rock-forming silicate minerals found in many igneous and metamorphic rocks. They are silicates that, in their simplest form, contain single SiO3 chains of linked SiO4 tetrahedra. The general chemical formula for pyroxenes is M2M1T2O6, where M2 refers to cations in a generally distorted octahedral coordination (Mg2+, Fe2+, Mn+, Li+, Ca2+, Na+), M1 to cations in a regular octahedral coordination (Al3+, Fe3+, Ti4+, Cr3+, V3+, Ti3+, Zr4+, Sc3+, Zn2+, Mg2+, Fe2+, Mn2+), and T to tetrahedrally coordinated cations (Si4+, Al3+, Fe3+). Monoclinic pyroxenes are called clinopyroxenes. The stability of clinopyroxenes over a broad spectrum of chemical compositions, in conjunction with the possibility of achieving desired physical properties and high chemical durability, has generated a worldwide interest due to their applications in material science and technology. The present work deals with the development of clinopyroxene based glasses and glass-ceramics for functional applications. The objective of the study was dual, both scientific and technological; particularly to gain fundamental knowledge on the formation of crystalline phases and solid solutions in selected glass-ceramic systems, and to evaluate the feasibility for application of new materials in different technological areas with emphasis on sealing in solid oxide fuel cells (SOFC). In this pursuit, various glasses and glass-ceramics along Enstatite (MgSiO3) - Diopside (CaMgSi2O6) and Diopside (CaMgSi2O6) – Ca – Tschermak (CaAlSi2O6) joins have been prepared and characterized by a wide array of characterization techniques. All the glasses were prepared by melt-quenching technique while glass-ceramics were produced either by sintering and crystallization of glass powders or by nucleation and crystallization in monolithic glasses. Furthermore, influence of various ionic substitutions/additions in Alcontaining diopside on the structure, sintering and crystallization behaviour of glasses and properties of resultant glass-ceramics has been investigated, in relevance with final application as sealants in SOFC. It has been observed that enstatite based glasses/glass-ceramics do not exhibit requisite characteristics in order to qualify for the job of sealing in SOFC while the superior properties exhibited by diopside based glass-ceramics qualify them for further experimentation as SOFC sealants. Apart from investigating the suitability of clinopyroxene based glass-ceramics as sealants, this thesis also aims to study the influence of nucleating agents on the volume nucleation in the resultant diopside based glass-ceramics so as to qualify them for further experimentation as hosts for radioactive nuclear wastes.
3
Scannell, Garth. "Understanding the structure and deformation of titanium-containing silicate glasses from their elastic responses to external stimuli". Thesis, Rensselaer Polytechnic Institute, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10158591.
Texto completoResumen
The responses of structure and properties to composition and temperature have been investigated for glasses in TiO2-SiO2 and Na2O-TiO2-SiO2 systems. Additionally, the response of Na2O-TiO2-SiO2 glasses to plastic deformation has been studied. (x)TiO2-(1-x)SiO2 glasses were prepared through the sol-gel process with compositions 0 ≤ x ≤ 10 mol% and compared to commercial glasses prepared through flame hydrolysis deposition with x = 0, 5.4, and 8.3 mol%. (x) Na2O - (y) TiO 2 - (1-x-y) SiO2 glasses were prepared with x = 10, 15, 20, and 25 mol% and y = 4, 7, and 10 mol% through a melt-quench process. Density and index of refraction of glasses was measured through the Archimedes's method and using a prism coupler, respectively. The glass transition temperature of Na2O-TiO2-SiO2 glasses was measured through differential thermal analysis.
The structure and elastic moduli have been studied through Raman spectroscopy and Brillouin light scattering, respectively, at room temperature and in-situ up to 1200 °C for TiO2-SiO2 glasses and up to 800 °C for Na2O-TiO2-SiO2 glasses. Young's modulus was observed to decrease from 72 GPa to 66 GPa with the addition of 8.3 mol% TiO2 in TiO2-SiO2 glasses and to increase from 65 GPa to 73 GPa with the addition of 10 mol% TiO2 in 10 Na2O - (0-10) TiO2-SiO2 glasses. The addition of TiO2 was observed to shift the 460, 490, and 600 cm-1 Raman peaks to lower frequencies in TiO2-SiO2 glasses, suggesting a more open and flexible network, and the 720, 800, and 840 cm -1 Raman peaks to higher frequencies in Na2O-TiO2 -SiO2 glasses, suggesting a lower free volume and stiffer network. The addition of TiO2 has little effect on the temperature response of the elastic moduli in either system, but decreases the thermal expansion and increases the frequency shifts in the 950 and 1100 cm -1 Raman peaks in the TiO2-SiO2 system while the thermal expansion increases with initial additions of TiO2 and then remains constant in the Na2O-TiO2-SiO 2 system.
Changes in structure and property with composition have been discussed, and structural models were proposed. The reduction of thermal expansion and elastic moduli in TiO2-SiO2 glasses occurs through the promotion of cooperative, inter-tetrahedral rotations facilitated by the longer and weaker Ti-O bonds. The increase in elastic moduli in the Na2O-TiO 2-SiO2 glasses occurs through the formation of small clusters with local, relatively high Ti and Na concentrations, promoted by Ti adopting a five-fold coordination in a square-pyramidal geometry. These clusters work to shield the silica network from non-bridging oxygens from the presence of Na while simultaneously increasing the volume bond density of the glass.
For Na2O-TiO2-SiO2 glasses, the response to mechanical damage and plastic deformation has been examined through Vickers indentation experiments at loads from 10 mN to 49 N. Fracture toughness was measured through the single-edge precracked beam method. The permanent deformation volumes around Vickers indents were investigated through atomic force microscopy. Critical loads for crack initiation and cracking patterns were systematically investigated and correlated with the elastic properties of glass. Vickers indents were observed to change from a mixture of radial/median and cone cracks to radial/median and lateral cracks as Poisson's ratio increases. As Poisson's ratio increases hardness decreases from 5.5 GPa to 4.5 GPa, the average radial/median crack length roughly doubles, and fracture toughness remains constant. A minimum in the critical crack initiation load was observed at ν = 0.21–0.22. The volume of glass deformed through shear flow during indentation increases gradually with increasing Poisson's ratio, becomes larger than the densified volume at ν = 0.237. The densified volume increases between ν = 0.18 and ν = 0.21 and decreases rapidly from 16.5 µm3 to 8.7 µm3 at ν = 0.235–0.237. A correlation between the minimum in crack initiation load and the change in deformation mechanisms over the same Poisson’s ratio range was observed.
4
Meng, Ji Xing. "Contribution to the modeling of densification in silicate glasses under very high pressures". Thesis, Rennes 1, 2013. http://www.theses.fr/2013REN1S116/document.
Texto completoResumen
Le comportement à haute pression du verre de silice a été largement étudié dansde différents domaines pour ses propriétés mécanique et physiques, tels que la mécaniquenon-linéaire, laphysiquede haute pression, laphysiquenon-cristallins, laphysique appliquée, lagéophysique, etc. La densification permanente est la propriété la plus fondamentale obtenue à partir de la haute pression. Nous discutons un modèle constitutif décrivant le mécanisme de déformation permanente par la densification sous haute pressionde verre de silice. La loi de comportement proposée dans cette étude considère que la pression est hydrostatique pure. Elle est composée d’une partieélastique et d’autre partie un écoulement décrivant l'évolution des déformations permanentes après l’initiation de ladensification. Dans cette loi, trois critères d’écrouissage sont discutés à l'égard de la dépendance de la densification incrémentale (progressive)aux niveaux de contraintes appliquées. Les mesuresexpérimentales ex-situ et in-situ sont utilisées pour évaluer notre modèle. En misant en œuvre de notre modèle dans Abaqus et SiDoLo(corotational logiciel), l’analyse inverse est utilisée pour déterminer le seuil de la pression de densification, la pression à la saturation et le taux de densification saturée. Les calculs numériques montrent un excellent accord avec les données expérimentales. Il est à noter que notre modèle non seulement réussit à déterminer les propriétés de densification, mais aussi pour prédire les changements de propriétés élastiques, telles que le module de compressibilité, le module de cisaillement, module d’élasticité et le coefficient de Poisson, sous la pression hydrostatique. Dans les perspectives, notre modèle fournit une nouvelle loi pour analyser le comportement à la déformation de silice sous l’état de contraintes complexesHigh-pressure behavior of SiO2 glass has been studied extensively because it has attracted considerable attention in various fields of mechanical and physical sciences, such as non-linear mechanics, high-pressure physics, noncrystalline physics, applied physics, geophysics, etc. Permanent densification is the most fundamental property obtained from very high pressure. We discuss a constitutive model describing the permanent densification induced deformation mechanism of silica. The constitutive law is assumed to be pure hydrostatic pressure, and uses a yield function and a flow rule describing the evolution of permanent strains after initial densification, and three hardening rules discussing the dependence of the incremental densification on the levels of applied stresses. Ex-situ and in-situ experiments are both considered to evaluate our model. Implementing our model to a finite software Abaqus and a corotational framework software SiDoLo, inverse analysis is used to determine the threshold densification pressure, the saturate densification pressure and the saturate value of densification. Numerical results show an excellent agreement to experimental data. It should be noted that our model not only succeeding in determine the densification properties, but also in predicting the changes of elastic properties, such as Bulk modulus, Shear modulus, Young’s modulus and Poisson’s ratio, under hydrostatic pressure. Seen in perspective, our model provides a new rule to analyze the deformation behavior of silica under complex stress states
5
Medina, Francelys A. Lanagan Michael Thomas. "Impedance spectroscopy studies of silica-titania glasses and glass-ceramics". [University Park, Pa.] : Pennsylvania State University, 2009. http://etda.libraries.psu.edu/theses/approved/PSUonlyIndex/ETD-4566/index.html.
Texto completo
6
Barker, Michael Francis. "Crystallization of lithium alumino-silicate glasses and the formation of photomachinable glass ceramics of controlled thermal expansion". Thesis, University of Sheffield, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362506.
Texto completo
7
Damart, Tanguy. "Energy dissipation in oxide glasses". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1189/document.
Texto completoResumen
L'atténuation d'ondes à basse et haute fréquences dans les verres n'est pas encore bien comprise en grande partie car les phénomènes à l'origine de cette dissipation varient grandement en fonction de la fréquence. L’existence de structures complexes et organisation multi échelle dans les verres favorise l'apparition de temps de relaxation allant de la seconde à la femtoseconde et de corrélation prenant place de l’Angström à la centaine de nanomètre. A basse fréquence, une meilleur compréhension de ces phénomènes de dissipation serait bénéfique à de nombreux domaines. Par exemple, les multi-couches recouvrants les miroirs des interféromètres servant à détecter les ondes gravitationnelles sont réalisées à partir de verres d'oxyde (SiO2 et Ta2O5) qui sont une source majeur de dissipation. A haute fréquence, l'étude de la dissipation pose des questions théoriques sur le lien entre asymétrie locale et atténuation acoustique.Durant cette étude, nous avons réalisé une analyse approfondie de l'interaction entre ondes mécaniques et structure des verres en utilisant des techniques de simulations telle que la dynamique moléculaire. En partant de la synthèse de verres de SiO2 et Ta2O5, nous nous sommes appliqués à trouver l'origine structurelle de la dissipation aux différentes échelles de fréquence. A basse fréquence nous avons été capable de catégoriser les déplacements atomiques à l'origine de la dissipation en utilisant la théorie des états à deux niveaux. A haute fréquence, nous avons utilisé une technique de spectroscopie mécanique appuyé par un développement analytique pour montrer l'importance du désordre local dans l’existence de dissipationThe origin of sound attenuation at low and high frequency in glasses stays elusive mainly because of the complex temperature and frequency dependence of the phenomena at its root. Indeed, the presence of complex structures and multi-scale organizations in glasses induce the existence of relaxation time ranging from the second to the femto-second and of spatial correlation ranging from the Angström to a hundred nanometers. At low-frequency, a better understanding of the phenomena at the origin of dissipation would be beneficial to several applications. For example, the multi-layers coating the mirrors of gravitational waves detectors consists of a superposition of two oxide glasses: silicate (SiO2) and tantalum pentoxide (Ta2O5), are an important source of dissipation. At high frequency, the study of dissipation raises theoretical questions about the link between attenuation and dissipation as well as between loclt asymmetry and dissipation. In the present study, we conducted an analysis of the interaction between mechanical waves and the structure of two oxide glasses using simulation techniques such as non-equilibrium molecular dynamics. At high-frequencies, we implemented and used mechanical spectroscopy to measure dissipation numerically and performed in parallel an analytical development based on the projection of the atomic motion on the vibrational eigenmodes. At low-frequencies, we used molecular dynamics to gather sets of thermally activated events that we classed in three categories based on topologically distinct atomic motions and from which we predicted dissipation numerically using a refreshed TLS model
8
SILVA, ANTONIO C. da. "Incorporacao de residuo galvanico em vidro silicato obtido a partir de finos de silica". reponame:Repositório Institucional do IPEN, 2004. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11223.
Texto completoResumen
Made available in DSpace on 2014-10-09T12:49:39Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:00:43Z (GMT). No. of bitstreams: 1 09674.pdf: 5668874 bytes, checksum: 2354e277c07618372ccf5f8088dde3b7 (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
9
Twyman, Helen Louise. "Structural characterisation of silicate and phosphate glasses". Thesis, University of Kent, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534329.
Texto completo
10
Reid, William B. "The electrical characteristics of lithium silicate glasses". Thesis, University of Aberdeen, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328008.
Texto completoResumen
The electrical behaviour of a series of lithium silicate glasses has been characterised by the versatile a.c. impedance technique. The advantage of using a combination of complex plane and spectroscopic plots in the data analysis is shown. The compositional dependence of the conductivities of the phase separated glasses, which exhibit complex two-phase spinodal decomposition or nucleation and growth textures, is related to the volume fraction of the phases present in the conduction pathway and the tortuosity of the effective medium. The compositional dependence of the conductivities of homogeneous lithium silicate glasses is accounted for by postulating a glass structure composed of silicate anion clusters which are surrounded by a lithia-rich phase which constitutes the preferred conduction pathway. Annealing effects are also reported. The effect of surface roughness on the response of the electrode/electrolyte interface, a phenomenon originally reported by de Levie, and contact problems between the metal electrode and the glass electrolyte are discussed. Novel results regarding the effect of gold electrode recrystallisation on the a.c. response of glass electrolytes are reported. The a.c. impedance technique is shown to be a very useful, surface sensitive tool for monitoring interfacial phenomena such as atmospheric corrosion and surface ion-exchange. The technique is also successfully applied to studies of the mechanism of glass-ceramic formation, where the identification of surface crystallisation products and residual glass, by electrical measurement, is possible. Conclusive evidence for the presence of an effective medium conduction mechanism (percolation theory) in the inhomogeneous glass-ceramic, is given. The electrical data are corroborated by electron microscopy, x-ray diffractometry, energy dispersive x-ray analysis and Fourier Transform Infrared Spectroscopy.
11
Tasker, G. William. "X-ray photoelectron spectroscopy of silicate glasses". Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/49574.
Texto completoResumen
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Vita.
Includes bibliographies.
by G. William Tasker.
Ph.D.
12
Bingham, Paul A. "The environment of iron in silicate glasses". Thesis, University of Sheffield, 2001. http://etheses.whiterose.ac.uk/12823/.
Texto completoResumen
Iron species in glass are vital to applications such as solar control, and greater understanding of these species is required. Redox, coordination, distribution and environment of iron in alkali-alkaline earth-silica glasses containing 0-5 molar % Fe203 have been studied using a multi-technique approach. Wet chemical analysis provided values of the Fee+/EFe redox ratio and these are in agreement with those obtained from optical and Mössbauer techniques over a wide range of glass compositions and Fe203 contents. The Fee+/EFe ratio is independent of iron content in the glasses studied, provided that melting conditions allow sufficient equilibration with the furnace atmosphere. As iron content increases, Fe-Fe near-neighbour interactions have an increasing influence on measured properties. Mössbauer parameters indicate a wider range of site occupancies by Fe 2+ and Fe 3+ at low iron contents. Electron spin resonance suggests some clustering of Fe ions even at low iron concentrations. The amount of clustering is proportional to the square of the molar Fe203 content. Increasing alkali / alkaline earth ionic radius ratio promotes clustering at all Fe203 contents. The effects of alkali and alkaline earth ions on the redox, distribution, coordination and environment of Fe ions in these glasses generally fall into two behavioural categories which have been termed "collective" and "selective". Collective behaviour occurs when alkali and alkaline earth ions have similar effects on a property and the overall effect is cumulative. This is characterised by proportionality with theoretical optical basicity of the glass. Many parameters associated with Fe 2+ ions fall into this category. Selective behaviour occurs when alkali and alkaline earth ions have opposing effects on a property, suggesting competition or selectivity between ion types. This is characterised by proportionality with the alkali / alkaline earth ionic radius ratio. The redox ratio and several parameters associated with the clustering, coordination and environment of Fe 3+ ions fall into this category. Glasses containing MgO can exhibit behaviour dissimilar to the other alkaline earth oxides; molar volume, redox, coordination and clustering are affected. These phenomena may be due to some Mg 2+ ions occupying tetrahedral sites.
13
Kanchanarat, Naruporn. "Chain silicate glass ceramics for biomedical applications". Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425562.
Texto completo
14
Uhlmann, Eugenie Victoria. "Glass forming ability, structure and spectroscopic properties of silica-free calcium aluminate based glasses". Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187097.
Texto completoResumen
Calcium aluminate based glasses are interesting because of their unusual optical properties and the fact that they do not contain any traditional glass forming ions. A large focus of the glass literature has been concerned with the study and properties of typical glass forming ions. For this reason, comparatively little is known about the possibility of glass formation and the structure and properties in unusual systems. The present work will describe the limits of glass formation within the calcium aluminate system. The use of non-silicate based stabilizing additives will also be detailed. It has been demonstrated that certain additions to the calcium aluminate system will improve the glass formation tendency without impairing the desired optical properties. The effects of various ions and their impact on the processing and properties of the glasses will be described in the framework of traditional theories of glass formation. Additional optical properties of the calcium aluminate system have also been investigated. Using the Judd-Ofelt model, various spectroscopic properties of calcium aluminate based glasses have been calculated. The stimulated emission cross section, branching ratios, intensity parameters and transition probabilities show interesting variations with compositional manipulations. Attempts to improve the emission cross section will also be described. The structure of calcium aluminate based systems has been studied using NMR and Raman Spectroscopy. The coordination of alumina has been examined with respect to compositional changes. In addition, structural studies have been conducted on calcium aluminate glasses synthesized by the sol-gel method. This method has allowed the formation of higher alumina content glasses. The evolution of structure with heat treatment temperature was followed and a comparison between melt-derived and sol-gel prepared glasses has been made.
15
De, Villiers Daniel Robert. "Non-silicate porous glasses obtained by the leaching of borate-rich glasses". Master's thesis, University of Cape Town, 1985. http://hdl.handle.net/11427/22327.
Texto completoResumen
Bibliography: pages 62-65.Glasses of the composition Na₂O-B₂O₃-X-Y and Na₂O-B₂O₃-Al₂o₃-X-Y were made where X and Y are two of the oxides CeO₂, HfO₂, ThO₂,Y₂O₃,ZrO₂ or Ga₂O₃. The glasses were either quenched or heat treated to promote phase separation and/or crystallization. The materials were subsequently leached in distilled water for periods of up to 96 hours. Leaching resulted in porous glasses or porous crystalline materials. The porous materials had high surface areas and good alkali resistance. A wide variety of compositions of these porous materials had BET surface areas between 100 and 413 m²/g. Selected porous glasses were chemically analysed. The heat resistances of two porous glasses were evaluated by observing the temperatures necessary for densification. Electron micrographs and X-ray diffraction scans were taken where necessary. Part of the glass forming regions for quenched samples of the system Na₂O-B₂O₃-Ga₂O₃-Y₂O₃ having Ga₂O₃ : Y₂O₃ ratios of either 3 : 1 or 3 : 2 were investigated. Part of the glass forming region for quenched samples of the Na₂O-B₂O₃-Y₂O₃ system was also investigated.
16
Clarke, Stuart James. "Neutron diffraction studies of silicate and borate glasses". Thesis, University of Reading, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493994.
Texto completoResumen
Two systems of glasses have been studied: soda-lime-silica and alkali borate glasses. Vitreous boron oxide was included as a standard for comparison with alkali borates. Silica and irradiated vitreous silica were included for low Q diffraction studies as comparison with previous results.
17
Bent, Julian Francis. "An experimental study of some silicate based glasses". Thesis, University of Warwick, 1999. http://wrap.warwick.ac.uk/59603/.
Texto completoResumen
TOF neutron diffraction and multinuclear MAS NMR data are combined to investigate the local structure of three silicate based glass forming systems. The effects of experimental resolution on the structural parameters obtained from neutron diffraction data are considered using simulated correlation functions. The Gaussian fit parameters to a peak in T(r) report a smaller peak width and area than that of the Gaussian broadening. This is due to the contribution of the realspace resolution function. This effect is most dramatic for small values of (u 2) 1/2 and Qmax but is negligible for typical values. The experimental uncertainty in measuring Q is considered for TOF neutron diffraction data. ΔQ is considered constant for data measured at several scattering angles. Some of the scattering intensity is transferred to a tail on the low r side of each peak, the magnitude of which increases with ΔQ. The peak fit parameters (position, width and area) change with increasing ΔQ, both before and after removing the gradient at low r. The Q-space resolution at a fixed scattering angle is considered by broadening i(Q) with a Gaussian of width ΔQ/Q=constant. The peak fit parameters change with increasing ΔQ/Q but not significantly at the resolution quoted for the high angle detectors on LAD. The interpretation of experimental data in terms of glass structure is greatly dependant upon an accurate knowledge of the glass composition. It is considered necessary to determine the concentration of all the cation species by a single or combination of techniques. TOF neutron diffraction and 170 MAS NMR data are reported for several (SnO)x(Si02)1-x glasses and a partially crystallised (SnO)(Si02) sample. 29Si, 119Sn MAS NMR and a powder X-ray diffraction data are also presented for the partially crystallised sample. The tin is present as Sn2+ and is three co-ordinated to oxygen at all compositions. The (SnO)x(Si02)1-x glasses are thought to consist of a network of Sn03/3 and Si04/2 polyhedra. The tin polyhedra may form pairs or chains. The local order in the crystalline phase is thought to be similar to that in the glasses. There are two tin and two silicon sites in the crystal phase of approximate composition (SnO)4(Si02). It has not been possible to refine the crystal structure. 29Si MAS NMR data are presented for (Li20)x(SnO)1-x(Si02), (Na20)x(SnO)1-x (Si02) and (K20)x(SnO)1-x(Si02) glasses and TOP neutron diffraction data for (K20)x(SnO)1-x(Si02). The tin is present as Sn2+ and is three co-ordinated at all compositions. Replacing the tin with modifier oxide reduces the 29Si NMR chemical shift. The modifier cation is thought to depolymerise the tin silicate network, associating with the tin to maintain charge neutrality. 29Si and 31p MAS NMR and TOP neutron diffraction data are presented for (K20- 4Si02)x(P205)1-x, (K20-2Si02)x(P205)1-x and (Si02)x(P205)1-x glasses. Each glass contains SiIV and SiVI species, the potassium tetrasilicate-Pjt), glasses also contain SiV species. The proportion of silicon species changed with thermal history. Each glass is thought to consist of a modified phospho silicate network. The potassium disilicate-Pjo, glasses are thought to consist of a continuous network of Si(OP)3(OSi), Si(OP)4(OSi)2, (p-Q2)- and (P-Q4)+ species. The alkali-free phosphosilicate and potassium tetrasilicate-P2O5, glasses are thought to have similar structures but it is not possible to define the phosphate species. It was not possible to distinguish the different species by neutron diffraction. The phosphosilicate network is thought to be more disordered than modified phosphate and modified silicate networks.
18
Iqbal, Yaseen. "Early stages of crystallisation in lithium silicate glasses". Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245649.
Texto completo
19
West, Michael Stuart. "Radiation-induced luminescence in terbium-doped silicate glasses". W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539623902.
Texto completoResumen
The purpose of this study is to characterize radiation-induced luminescence of terbium-doped silicate glasses. Experiments performed investigated the optical properties, isothermal time-evolution, and temperature dependence of the radiation-induced luminescence of two commercially available terbium-doped glasses. A problem common to this type of glass is the persistent luminescence, or afterglow, that occurs following the end of excitation from an external source of radiation. While the processes that govern characteristic luminescence of rare earth ions, including terbium, are well understood, the processes that give rise to afterglow in doped glasses are not. Identifying the source of long-term luminescence is essential for controlling problems that may arise from practical applications of luminescent glasses.;It was determined that the stimulation of terbium fluorescence is the result of direct excitation from the external radiation source, and indirect excitation from the delayed recombination of charge carriers releasing from traps in the host glass. The range of trap depths is found to be well represented by quasi-continuous distribution functions. The characteristic decay time during the initial response of both glasses studied is approximately 3.5 milliseconds. Decay of the afterglow was observed to persist for several hours, depending on the acquired dose of radiation. Comparison of the response to x-rays and ultraviolet radiation yielded the same results, indicating that the same processes are involved in producing afterglow for both cases. This result suggests a more efficient means of characterizing scintillating glasses by using ultraviolet lasers instead of x-rays.
20
Guan, Qing. "Sodium diffusion in soda-lime-silicate glass around the glass transition temperature /". The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487687115926219.
Texto completo
21
Vickers, Samantha G. "2D PASS-CPMG a new NMR method for quantifying structure in non-crystalline solids /". Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1238098414.
Texto completo
22
Hin, Raveth. "Comportement à l'indentation et à la rayure de verres métalliques et silicatés". Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S141/document.
Texto completoResumen
Le comportement mécanique du verre silico-sodo-calcique soumis à un contact ponctuel peut être amélioré par trempe. Les effets de trempe se manifestent par des gradients de propriétés sur le comportement du verre rendant la modélisation plus complexe. Ce travail a porté sur la modélisation et la simulation des verres non trempés et trempés soumis aux essais de nano-indentation et de nano-rayage. Les outils de simulation par éléments finis ont été développé et validés sur le verre métallique, choisi en raison de son comportement plastique connu. En comparant avec les données expérimentales, nous avons observé que les paramètres du matériau et les conditions expérimentales pouvaient donner la même réponse sur la courbe force-déplacement et l'empreinte. L’identification des propriétés du matériau doit être basée sur des comparaisons avec des simulations considérant la géométrie réelle de l'indenteur, la souplesse de la machine et le tilt de surface de l'échantillon. Les stratégies développées permettent de faire des identifications sur le comportement du verre silico-sodo-calcique. Dans la famille du verre silicaté, le verre silico-sodo-calcique a un comportement plastique semblable au verre de silice qui est affecté non seulement par le mécanisme de cisaillement mais aussi par la densification. Il est essentiel donc d'étudier le comportement densification/cisaillement du verre de silice car il est largement discuté dans la littérature. La comparaison des résultats de simulation par plusieurs modèles avec les courbes force-déplacement et les images d'empreinte a montré que la modélisation de la densification, en prenant en compte l'écrouissage et la modification des modules élastiques, est suffisante pour décrire le comportement des verres silicatés. Enfin, les connaissances sur les simulations des essais à chargement ponctuel et la modélisation du comportement du verre ont guidé une étude sur les effets du gradient de propriétés dans les verres trempées thermiquement et chimiquementThe mechanical behavior of soda-lime-silica glass subjected to contact damage can be improved by tempering. The effects of tempering created tailor properties and the glass behavior more complicated. Therefore, this work studied the modeling and simulation of non-tempered and tempered glasses subjected to the nano-indentation and nano-scratch tests. The finite element simulation tools have been primarily validated and the metallic glass was chosen for the studies because of its known plastic behavior. By comparing with the experimental data, we have observed that the parameters of material model and the experimental conditions could give the same response on load displacement curve and imprint. The evaluation of material properties must be based on the comparisons with fully modeled simulation considering the real geometry of the indenter, the compliance of the instrument and the tilting of the sample surface. The developed strategies allow identification of soda-lime-silica glass behavior. Similar to that of silica glass, the plastic behavior of soda-lime-silica glass is not only affected by the shear mechanism but also the densification. Hence, it is essential to study the shear/densification behavior of silica glass as it is widely discussed in the literature. The comparison of simulation results by several models with the load displacement data and the images of imprint showed that the modeling of densification by taking into account the hardening and the change in elastic moduli is sufficient for describing the behavior of silicate glasses. Finally, the knowledge about the simulation of the contact loading tests and the modeling of glass behavior guided a study on the coupling of tailored properties effects in the thermally and chemically tempered glasses
23
Saravanapavan, Priyadharshini. "Mesoporous calcium silicate gel-glasses : synthesis, structure and bioactivity". Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271675.
Texto completo
24
Tadjiev, Damir R. "Near surface mechanical properties and hydration of silicate glasses". Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527231.
Texto completo
25
Abd, Karim Mohd Mustamam. "A study of tin oxides in silicate based glasses". Thesis, University of Warwick, 1995. http://wrap.warwick.ac.uk/36289/.
Texto completoResumen
The roles of tin in two silicate based glass systems have been investigated by NMR and Môssbauer spectroscopies and by physical property measurements of the glasses. The first glass system investigated was the stannous silicate (binary SnO-Si02) glass. Glasses with SnO contents ranging from 17 to 72 mol.% have been made by melting pelleted powder in an alumina crucible. It was found that alumina crucibles are unsuitable for making glass with <20 mol.% SnO because of attack on the crucible at the high melting temperature (_>_1600°C). Silica crucibles will not withstand such high temperature and tin will attack a platinum crucible. The ability of this system to form glass past the orthosilicate composition has been discussed in terms of the polarizing power of Sn2+ and the structure of SnO. The 119Sn NMR results did not give much structural information due to the high chemical shift anisotropy of Sn 2+ site but they showed that the glass also contains trace amounts of Sn4+species. The 29Si MAS NMR results showed that SnO does not depolymerise the silicate network to the same extent as Na20 or even Pb0. Computer simulations of the 29 Si MAS NMR spectra showed that, for SnO <-30 mol.%, the disposition of Qn species is consistent with the binary model, which means that SnO is acting the role of modifier. For compositions > 30 mol.% SnO, the Qn distribution follows the statistical model and this has been interpreted as SnO now acting as an intermediate. The 119Sn MOssbauer results confirmed this interpretation. The Sn2+ isomer shift decreases with increase of SnO which is indicative of increasing covalent character of the Sn—O bonds while the larger quadrupole splitting suggests distortion of the SnO polyhedral structure in the glass. The relation of the Sn 2+ isomer shift to the quadrupole splitting and the temperature dependence of the isomer shift of Sn2+ indicate the formation of Si—O—Sn linkages at high SnO contents. The decrease of the viscosity of the glass with increasing SnO is small when compared to the decrease of the viscosity in alkali metal and alkaline-earth oxides silicates when the respective modifier oxide is increased in those glasses. The variation of the density, thermal expansion and refractive index with SnO content showed discontinuities in the region of 30-45 mol.% SnO. This has been interpreted as being the point where SnO changes its role from that of modifier to intermediate. The results of differential thermal analysis and devitrification of SnO-Si02 glasses showed that glass with 40 mol.% SnO can be heat treated in the temperature range of 570° to 680 °C to produce metastable SnSiO3 crystals. SnSiO 3 decomposed to SnO + Si02 at temperatures above —700°C and, at temperatures greater than 720°C, oxidation of SnO to Sn02 and Si02(glass) to Si02 (cristobalite) took place. The second glass system is tin-doped float glass. This is glass of the float composition remelted with tin(II) oxalate in silica crucibles under normal atmosphere conditions. In this way it has been demonstrated that we can mimic the tin oxide distribution found within the tin diffusion region in float glass. Synthesis of the glass has shown that both Sn2+ and SO+ can be assimilated simultaneously in the glass but there is a solubility limit for SO+. The 1195n Mbssbauer results showed that Sn2+ and SO+ played different structural roles in the glass. The environment of Sn2+ in glass is similar to that in amorphous SnO while the SO + structure in glass does not change significantly compared to crystalline Sn02. The Debye temperatures and recoil free fractions showed that Sn2+ is less rigidly bound to the network modifier site while SO + is rigidly bound at network former sites in the glass. The different structural roles of 5n 2+ and SO+ in the glass were reflected in the some of the physical properties of the glasses.
26
Kingston, John G. R. "The development and modification of flaws in silicate glasses". Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324542.
Texto completo
27
Williams, Rachel Diana. "The mixed alkali effect in silicate and borate glasses". Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386841.
Texto completo
28
Burgner, Lori Lynn. "Crystallization kinetics of lithium disilicate and sodium silicate glasses". Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/279818.
Texto completoResumen
The formation of metastable crystalline phases in lithium disilicate glass has been a subject of controversy for decades. Here, one aspect of this problem relating to the stability of these non-equilibrium phases when glasses are heated for extended time periods in the nucleation regime is addressed. The results of a systematic experimental investigation on the persistence of metastable phases and the factors that may influence the appearance of such phases, e.g., water content, impurities, glass composition, and glass preparation procedure are presented. Growth rates of lithium disilicate crystals in lithium disilicate glass are measured as a function water concentration in the glass and of temperature in the deeply undercooled regime. The growth rate data obtained in this work are combined with data reported in the literature and used to assess the applicability of standard models of crystal growth for the description of experimental results over a very broad temperature range. The reduced growth rate versus undercooling graph is found to consist of three regimes. For undercoolings less than 140°C, the reduced growth rate curve is suggestive of either 2-D surface nucleation or screw dislocation growth. For undercoolings greater than 400°C, the reduced growth rate plot suggests the operative crystal growth mechanism is 2-D surface nucleation, but detailed calculations cast doubt upon this conclusion. In the intermediate undercooling range, there appears to be some sort of transitional behavior for which none of the standard models appear to be applicable. Further, it is observed that small differences in the viscosity data employed can produce enormous differences in the predicted growth rates at larger undercoolings. Results of the kinetic analyses conducted herein seem to indicate that the nature of the kinetic rate coefficient used in the standard growth models may be incorrect. Nucleation rates of sodium metasilicate crystals in a sodium silicate glass of composition 43Na₂O57SiO₂ (mol%) are investigated using the development technique. The results of this study are compared with the nucleation rate results recently obtained for this composition using a novel DTA method. The two techniques are found to agree within experimental error.
29
Zgambo, Thomas P. (Thomas Patrick). "Calcium Silicates: Glass Content and Hydration Behavior". Thesis, North Texas State University, 1987. https://digital.library.unt.edu/ark:/67531/metadc332357/.
Texto completoResumen
Pure, MgO doped and B2C3 doped monocalcium, dicalcium, and tricalcium silicates were prepared with different glass contents. Characterization of the anhydrous materials was carried out using optical microscopy, infrared absorption spectroscopy, and X-ray powder diffraction. The hydration of these compounds was studied as a function of the glass contents. The hydration studies were conducted at 25°C. Water/solid ratios of 0.5, 1, 10, and 16 were used for the various experiments. The hydration behavior was monitored through calorimetry, conductometry, pH measurements, morphological developments by scanning electron microscopy, phase development by X-ray powder diffraction, and percent combined water by thermogravimetry. A highly sensitive ten cell pseudo-adiabatic microcalorimeter was designed and constructed for early hydration studies. Conductometry was found to be of great utility in monitoring the hydration of monocalcium silicate and the borate doped dicalcium silicates.
30
Escanhoela, Júnior Carlos Augusto [UNESP]. "Condutividade elétrica e polarização térmica de vidros soda-cal-sílica contendo diferentes cátions tetravalentes". Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/91918.
Texto completoResumen
Made available in DSpace on 2014-06-11T19:25:31Z (GMT). No. of bitstreams: 0
Previous issue date: 2011-02-17Bitstream added on 2014-06-13T19:12:21Z : No. of bitstreams: 1
escanhoelajunior_ca_me_rcla.pdf: 2205069 bytes, checksum: 07cd01b4a104f262986c24bd2a7f874b (MD5)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Neste trabalho realizamos a polarização térmica em vidros silicatos com composição (%mol) 22Na2O.8CaO.65SiO2 .5MO2 (M = Si, Ti, Ge, Zr, Sn e Ce). A polarização térmica consiste em aplicar um campo elétrico DC de elevada intensidade (~1 MV/m) em amostras a altas temperaturas. Durante a polarização térmica é gerado um campo elétrico permanente no interior da amostra, na região do anodo, que é responsável por propriedades ópticas nãolineares. Submetemos à polarização térmica amostras dos vidros, com ~1,5 mm de espessura e área de 20 x 20 mm2. Utilizamos eletrodos de Au, com diâmetro de 1 cm. As amostras foram aquecidas no interior de um forno até ~145 oC e aplicamos um campo elétrico de 1 MV/m durante 60 min. Durante a aplicação do campo elétrico, medimos simultaneamente a corrente através do circuito e as temperaturas no forno e na amostra. A corrente elétrica medida no circuito está relacionada com a migração de íons Na+ no interior das amostras do anodo para o catodo. A diminuição da corrente após um determinado tempo de polarização é devido à formação de uma camada com ausência de íons Na+ (camada de depleção) junto ao anodo. Os diferentes cátions tetravalentes, M4+, inseridos no vidro têm funções particulares na estrutura deste e afetam de formas distintas a corrente elétrica. A energia de ativação para a condutividade elétrica em vidros soda-cal-sílica está associada à energia necessária para o íon Na+ transpor a barreira de potencial entre os interstícios adjacentes na rede vítrea. Para determinar a energia de ativação da condutividade elétrica DC, Eσ, destes vidros, submetemos amostras de cada composição a um campo elétrico de 1 MV/m, durante 2 segundos para diferentes temperaturas entre 100 e 220 ºC. Esta energia está relacionada com...
In this work we performed thermal poling in glasses with composition (%mol) 22Na2O.8CaO.65SiO2 .5MO2 (M = Si, Ti, Ge, Zr, Sn and Ce). The thermal poling consist in apply a high intensity DC electric field (~1 MV/m) on samples at high temperatures. During the thermal poling process a permanent electric field is generated in the anode region of the sample, and this field is responsible for nonlinear optical properties of various glasses. We submit to thermal poling samples with ~1.5 mm in thickness and area of 20x20 mm2. We used gold electrodes with a diameter of 1 cm. The samples were heated inside a furnace to ~ 145 oC and an electric field of 1 MV/m was applied for 60 min. During the poling process, we measure simultaneously the current through the circuit and the temperatures in the furnace and of the sample. The electric current of the circuit is related to the migration of sodium ions in the bulk samples from the anode to the cathode. The current decrease with the poling time is due to the formation of a Na+ absent layer (depletion layer) near the anode surface. The different tetravalent cations, M4+, in the glass have different functions in their structures and affect the electrical current in particular manners. The activation energy for electrical conductivity in soda-lime-silica glasses is associated with energy for the Na+ ions to cross the potential barrier, which is submitted to the interstices of the glassy network, and jump into the nearest interstice. The activation energy of DC electrical conductivity, Eσ, of our samples of was determined by applying an electric field of 1 MV/m for 2 seconds, at different temperatures between 100 and 220 ºC. This energy is related to the current, I, through the equation ... The energy calculated is ~0.8 eV. To evaluate the structural and compositional changes of the samples surfaces that were in contact with the ...
31
Gao, Guojun [Verfasser], Doris [Akademischer Betreuer] Ehrt y Lothar [Akademischer Betreuer] Wondraczek. "Tunable photoluminescence from rare earth and transition metal ions activated silicate glasses and glass ceramics / Guojun Gao. Gutachter: Doris Ehrt ; Lothar Wondraczek". Jena : Thüringer Universitäts- und Landesbibliothek Jena, 2014. http://d-nb.info/1048047180/34.
Texto completo
32
Dürig, Tobias [Verfasser] y Vladimir [Akademischer Betreuer] Dyakonov. "Fracture dynamics in silicate glasses / Tobias Dürig. Betreuer: Vladimir Dyakonov". Würzburg : Universitätsbibliothek der Universität Würzburg, 2012. http://d-nb.info/1027669263/34.
Texto completo
33
Yildirim, Erdem Kamil. "O-17 NMR studies of some silicate crystals and glasses". Thesis, University of Warwick, 2000. http://wrap.warwick.ac.uk/49950/.
Texto completoResumen
Crystalline and glassy silicates were investigated by means of 17O NMR. The dependence of the measured efg on the Si-O-Al bond angle was investigated in some crystalline aluminosilicate sodalites and kalsilite. The results show that CQ increases with increasing bond angle while 11 decreases with increasing bond angle and they both follow a similar function to that found for the Si-O-Si bond angle. The cluster calculations also confirm that the dependence of CQ and il on the Si-O-Al bond angle is similar to that of one Si-O-Si linkage. The chemical shift decreases as the bond angle increases. However this dependence does not seem to be monotonic. The structural role of Al in aluminosilicate glasses was studied by means of 17O 3Q MAS NMR in sodium aluminosilicate glasses with Si/Al= 3,1.5,1,0.7.3Q MAS NMR results showed the presence of Si-O-Si species as well as Si-O-Al species in glasses with Si/Al>1. The 3Q MAS NMR spectrum of glass with Si/A1=0.7 displayed the presence of Al-O-Al linkage as well as Si-O-Al. These results showed that as the Si/Al ratio decreases from 3 to 0.7 Si-O-Si linkage is replaced by Al-O-AI linkage as a result of addition of Al into the structure. The structural role of Sn in tin-silicate glasses was also studied mainly by means of 17O MAS NMR. The model developed from the 17O MAS NMR spectra of these glasses showed the possible coexistence of two and three coordinated oxygen atoms in the structure. Therefore some of the Sn has to be in three coordinated to oxygen for charge balancing. The 17O MAS NMR spectra of a partially crystallised sample showed three distinct sites which are assigned as Sn-O-Sn, Si-O-Sn, and Si-O-Si on the basis of their chemical shift. The CQ values obtained from the simulations of these peaks supports this assignment. The 29Si MAS NMR of the same sample showed two crystalline and a glassy peaks which are fitted to two crystalline and two glassy sites. The possible composition of this sample was calculated and found to be SiSn3O10.
34
Rai, Maha. "Molecular dynamics modelling of barium silicate and barium fluorozirconate glasses". Thesis, University of Kent, 2018. https://kar.kent.ac.uk/66702/.
Texto completoResumen
Advancement in science and technology has profoundly depended on new types of glass innovation. The glasses that were studied in this project are binary barium silicate glasses, binary barium fluorozirconate glasses, ZBLAN glasses and 〖Eu〗^(3+) doped ZBLAN glass (the ZBLAN glasses are based on binary barium fluorozirconate glass). The high atomic number of barium in the barium silicate glasses provides high mass and high electron density providing its applications for heat and X-ray shielding. The phenomena such as phase separation in the barium silicate glass will affect its properties of durability and electrical conductivity. On the other hand, ZBLAN glasses have a broad infrared optical transmission window due to the weaker bonding/interaction of F^- ions. Due to the presence of lanthanum in the composition ZBLAN glass can be easily doped with rare-earth ions such as 〖Eu〗^(3+) giving it many optical applications such as optical amplifier and fibre lasers. Hence, it's essential to study the structure of these glasses to understand their properties for applications. This thesis used the classical molecular dynamics modelling technique to study the static atomic structure of glass. Generally, fluoride glasses can be formed by totally replacing oxygen atoms in oxide glasses by fluorine atoms. The oxide silicate glasses are common glasses that follow the Zachriasen rules of glass formation but the fluorozirconate glasses do not and lack fixed structural units. The structure analysis was performed at short-range order (e.g. coordination number, bond length and bond angle), medium-range order (e.g. network connectivity) and long- range order (e.g. phase separation). The related crystals were also simulated in similar conditions to the glasses to compare their atomic structure. Normally at short-range order glass structure is similar to its related crystal but the differences between them starts from the position and number of next nearest neighbours and increases thereafter. Additionally, the new methods such as rotational invariants and grid analysis were used to scrutinise structural units and phase separation respectively. The model of barium silicate glass shows good agreement with experimental diffraction data. The typical bond length and coordination number for Ba were 2.97 Å and approximately 7 respectively. The model did not show any phase separation at low Ba content and hence for further investigation very large models of alkaline earth silicate glasses were studied to see how Ba, Ca and Mg are distributed in the glass. The grid analysis was used to see the distributions which show homogeneity for Ba and Ca and inhomogeneity for Mg cation. The structural units of fluorozirconate glasses were carefully studied as they do not follow the Zachriasen glass model. The coordination number for Zr was mixture of 7 and 8. The rotational invariant analysis shows that the structural units of ZrF_n polyhedra for coordination number 7 and 8 were similar to Augmented Triangular Prism and Biaugmented Triangular Prism respectively. However, rotational invariant values for BaF_n polyhedra tend more towards random. The large complex model of 〖Eu〗^(3+) doped ZBLAN glass was made as it is studied for optical applications. The initial analysis was to observe whether Zr and Ba has similar structural roles as in binary fluorozirconate glass system which they do. Considering the extra elements in ZBLAN glass, Al behaves like a network former and has octahedra structural units whereas La and Na behave like modifiers. In the glass Eu was uniformly distributed with predominantly coordination number of 8 and does not have well defined structural units.
35
Brennand, André Luiz Ribeiro. "Thermal poling of multioxide silicate glasses and ion-exchanged waveguides". Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/15487/.
Texto completoResumen
This Thesis reports a theoretical and experimental study of thermal poling of glasses in which a second order optical nonlinearity is introduced into the glass by applying a potential across the glass at elevated temperature. Thermal poling is the most reported and reproducible procedure for the introduction of the nonlinear susceptibility of 2nd order, c(2), in glasses. The attainment of c(2) of the order of 1pm/V has been reported in a wide range of silica based glasses including glasses suitable for ion exchange, UV-writing and rare earth doping. Effective c(2) of 0.1 pm/V has been demonstrated in poled channel waveguides in silica indicating a poor overlap between c(2) and the waveguide modes. These reported values of c(2) must be increased at least one order of magnitude for glasses and two orders of magnitude for waveguides for practical use. Therefore a good understanding of the poling mechanism which was unclear at the beginning of this work was required for poling optimisation. In this Thesis a poling model based on electrostatics and ion transport theory is developed yielding a method for the evaluation of glasses for poling. A new technique for simultaneous poling and waveguide fabrication by differential ionic drift in glasses that contains more than one mobile ion is demonstrated and poling of K+ ion-exchanged waveguides is achieved. c(2) of the order of 1 pm/V was verified in poled soda lime glass and in found in poled potassium ion-exchanged soda lime glass. A poling time for multioxide glasses some 5 times shorter and minimum temperature 50oC lower than reported in the literature was achieved with constant-current thermal poling in vacuum. A procedure to evaluate the average value, thickness and the location of the c(2) region is established. This study provides an improved understanding of the poling mechanism and may contribute to the achievement of higher c(2) in poled glasses and poled waveguides in glasses.
36
Bowron, Daniel Timothy. "A study of rare earth doped silicate and phosphate glasses". Thesis, University of Kent, 1994. https://kar.kent.ac.uk/38697/.
Texto completoResumen
The complementary techniques of X-ray diffraction and EXAFS have been applied to silicate and phosphate glass systems containing varying quantities of rare earth elements. The silicate systems that have been studied are rare earth doped fibre optic preforms of interest to the optoelectronics and telecommunications industry. Techniques were developed to allow spatially resolved diffraction and EXAFS data to be taken from the small ~1mm diameter core region of the preforms. Absorption maps were made displaying the distribution of the rare earth ions as a function of radial position, and similarly for the germanium codopant incorporated in these systems. The diffraction results show as expected, that silica dominates the structure evident in the preforms whilst EXAFS measurements taken at the germanium K-edge, suggest that this codopant occupies an eightfold coordinated site surrounded by oxygen atoms at 1.7A. The phosphate glasses studied are rare earth metaphosphates of the composition R(PO3)3. X-ray diffraction measurements were taken showing that the network structure of these systems is essentially constructed from PO4 tetrahedra. The EXAFS experiments, performed on a range of glasses over the rare earth LIII edges, show a trend in the first shell distance rare earth-oxygen, consistent with the Lanthanide contraction, the rare earth ions occupy-ing sites with between six and eight-fold coordination of oxygen atoms about the rare earth ions.
37
Newlands, Katrina. "The early stage dissolution characteristics of aluminosilicate glasses". Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=227976.
Texto completoResumen
To reduce CO2 emissions the cement industry has for decades diluted the Portland cement fraction of concrete binders with Supplementary Cementitious Materials (SCM). Defining the reactivity of these aluminosilicate-based materials and their interaction with clinker phases has however challenged the research community and limited their replacement levels. In the present study, to quantify the reactivity of SCMs during early hydration, aluminosilicate glasses with compositions representative of blast furnace slag and fly ash systems were synthesised and exposed to different activator solutions in a continuously stirred closed system reactor for a period up to 3 h. Solution compositions were measured from the very first minutes of dissolution with complementary solid surface analysis. The experimental conditions were designed to avoid precipitation, however an initial Ca maximum in the first 30 min of exposure to the activating solution was a common feature in most dissolution profiles with a subsequent rapid decline, most likely attributable to Ca-reincorporation on the reacting surface. Surface specific analysis confirmed Ca enrichment on the surface and also detected Al enrichment, suggesting the formation of a Ca-modified aluminosilicate phase by a dissolution reprecipitation mechanism on the surface of the glass. Differing chemistries are thought to be responsible for the Ca and Al re-integration on the reacting surface depending on the pH of the solution; near-neutral conditions favour Ca-readsorption and surface condensation reactions, whereas alkaline solutions favour Ca-reintegration via covalently bound phases. The Ca concentration in solution was also observed to control glass alteration. Decreased dissolution rates were in fact observed as Ca concentrations in solution were increased supporting the formation of a C-A-S-H phase on the surface, the formation of which was instead suppressed when a Ca chelating chelating agent (EDTA) was added to the solution resulting in increased glass dissolution. Experiments using in situ AFM and LAOICPOMS are also reported and the significance of the findings to the early hydration reactions of a blended cement system is discussed.
38
LORENZI, ROBERTO. "Silica based functional materials: - Charge transport in nanostructured SnO2: SiO2 thin films. - Second harmonic generation in niobium potassium silicate glasses. - Tapered silica optical microfibres for gas sensors". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2010. http://hdl.handle.net/10281/10933.
Texto completoResumen
"Charge transport in nanostructured
SnO2:SiO2 thin films":
Silica based nanostructured thin films grown on silicon substrates are promising materials for novel light emitter devices. In particular, tin dioxide is a wide band gap n-type semiconductor (Eg=3.6 eV) with an expected band-to-band emission centered in the ultraviolet (344 nm) region of the electromagnetic spectrum. Our group succesfully demonstrated UV emission from such systems, but at the beginning of my work many issues in charge transport processes needed to be explained.
Aim of this project was to clarify electric transport and charge trapping mechanisms. As a result of a materials science approach we can now interpret the experimental data through specific relationships between synthesis conditions, clustering morphology (nanoparticle (NP) size distribution and volumic concetration, interphase substoichiometry, film thickness), and electric response.
The observed phenomena have been analyzed within the percolation theory. Main results concern: electric transport of both holes and electrons is sustained by NP-to-NP hopping events and dielectric enhancement results from oscillating charges (holes) on NPs. "Second Harmonic Generation in potassium niobium silicate glasses": Second harmonic generation (SHG) is a non linear optical process largely employed in current laser technology and photonics. However in almost every application the material employed for these purposes are single crystals. Therefore the possibility to achieve large SHG in amorphous systems may lead to devices with innovative configurations. SHG may occur only if the system is non-centrosymmetric, therefore for glasses it is forbidden due to intrinsic isotropy. The inversion symmetry can be broken up with poling treatments. They consist in applying strong electrostatic field while the sample is stressed by external perturbation (typically heat, electron beam or laser light).
We have explored the effect of thermal poling treatment on potassium niobium silicate glasses on inducing non linear optical properties. The results have revealed a strong SHG associated with structural modifications.
The proposed mechanism involves a rearrangement of niobium oxide groups mediated by non bridging oxygen and potassium ion transport across the glass. These new charge arrangements form a non-centrosymmetric region underneath the anodic contact responsible of the detected SH signal. "Tapered silica optical microfibres for gas sensors": In the last years, tapered silica fibres have attracted much interest in photonic research, because of peculiar properties emerging in waveguides with lateral dimensions of the same order of the guided modes. In particular, in these structures the large evanescent field enables some interesting properties, such as microfluidic sensors and high Q optical resonators (coiling the tapered fibre), non-linear effects and supercontinuum generation. In this project, carried out at the University of Southampton (UK) in the group of Dr. Gilberto Brambilla, we have explored the feasibility of an innovative optical absorption device, based on ring down spectroscopy.
In this case we are interested in a sensor for in-line application: a fluidic channel wrapped with tapered fibre in which the analyte can flow. The large power fraction outside the fibre interacts with the flowing medium and any change in the surrounding optical properties (refractive index or absorption coefficient) leads to a modification of the recorded light intensity propagating in the fibre.
The idea is to exploit ring down time of a silica tapered microcoil resonator as an indicator of the absorption coefficient of a gas (or a liquid) flowing in the channel.
39
Osborne, Zoe Ann. "Nucleation kinetics of phase separation in a sodium silicate glass". Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/284320.
Texto completoResumen
This study was undertaken with the goal of comparing the calculated nucleation rate for phase separation with experimental measurements for a simple glass system. The magnitude and the temperature dependence of the nucleation rate for a sodium silicate glass composition in the binodal regime was calculated. These calculations used a minimum of assumptions in order to determine the limits on certain thermodynamic variables, chiefly surface energy. Many of the values used in these calculations were determined from growth and coarsening measurements made on this system. Nucleation rates, as well as growth and coarsening rates, were then measured in this system for this comparison to theory. It was found that the free energy of mixing models are unable to predict nucleation behavior at temperatures near the immiscibility boundary. In addition, these models predict that the nucleating composition lies outside of the binodal. Although the values measured for the activation energy correspond well to those in the literature, their incorporation into the nucleation expression does not correct for the temperature behavior of the free energy of mixing. It is also unlikely that a temperature dependent surface energy term could account for the poor predictive nature of classical nucleation theory at small undercoolings.
40
Hassani, Hamid. "Structure evolution and mechanical properties of ion-exchanged silicate glass". Doctoral thesis, Università degli studi di Trento, 2019. http://hdl.handle.net/11572/243415.
Texto completoResumen
Soda-lime silicate glass (SLS glass) is one of the most commercialized glasses with a huge extent of applications from homewares and kitchenware appliance to cover for touchscreen gadgets. The latter has gained notable attentions recently since the majority of available touchscreen gadgets have covers from other glass families such as aluminosilicate. Technically, these types of glasses are difficult to produce and very costly, therefore, the prices of articles which are made by these glasses are high. In comparison, soda-lime silicate glass has lower price because of globally growing production and promising future. However, due to the intrinsic weaker mechanical properties, the application of SLS glass as cover of touchscreen gadgets is restricted. Several techniques have been applied to improve the mechanical properties of SLS glass. Among them chemical tempering is one the most promising technique.
Typically, the chemical tempering is done by an ion-exchange process where sodium atoms contained in the glass are substituted by potassium ions diffusing from the molten salt. The effect of variables such as glass composition, molten bath composition, temperature, and time is crucial in the ion-exchange process. Particularly, selecting an unsuitable time and temperature of the process can affect mechanical properties of glass through a stress relaxation phenomenon. Therefore, optimization of the time and temperature can guarantee efficient reinforcement of glass.
In this PhD research, three different temperatures (430°C, 450°C, and 470°C) and five different times (4 h, 8 h, 24 h, 48 h and 168 h) selected for chemical tempering of glass samples in pure molten KNO3 and molten KNO3 systematically poisoned by NaNO3.
The compressive residual stress and case depth were determined by optical methods, the flexural strength was measured by a ring-on-ring test method and the surface chemical composition of the glass was analysed by Energy Dispersion X-ray Spectroscopy (EDXS). The resistivity of treated glass against forming surface cracks was studied by Vickers hardness and scratch test. To study the structural evolution, micro-Raman (μ-Raman) spectroscopy was used.
The results pointed out that below addition of 0.5 wt% NaNO3, the ion-exchange process is always effective. Indeed, compressive residual stress, flexural strength, surface concentration and potassium penetration in Na-containing baths are substantially identical to values recorded on glasses treated in “pure” KNO3. Actually, case depth and interdiffusion coefficient are invariant with respect to the sodium content at least up to 1 wt%. No significative difference between “tin” and “air” side are revealed.
Influence of time of tempering on Na-K exchange process showed that the concentration of K+ on the surface of glass was increased by increasing the duration of of the process. Compressive residual stress, on the other hand, was decreased by time due to the surface structural relaxation. A surface crack tendency under a Vickers indenter and scratch test gave the evident that K/Na ion-exchange process for more than 24 h is responsible for an indent mechanical reinforcement. A structural reorganization of the glass network occurred and a higher number of Q2 and Q3 species were present in the tempered glasses with respect to the pristine one. Such re-polymerization could account for a more plastic behavior under Vickers indentation and scratch test, making the material less susceptible to surface cracking.
The case depth of tempered samples was increased by temperature at the expense of the compressive residual stress due to the stress relaxation. Relative concentration of K+ on the surface, as well, increased by the temperature. The increase in the temperature of ion-exchange process led to increase in the tendency of glass against formation of crack under Vickers indenter and scratch test. The limit of this propensity is tempering at 470 °C for 48 h as the formation of radial cracks and shorter plastic deformation regions under scratch test observed. From structural point of view, Na-K exchange caused reorganization of the glass network which is responsible for a more plastic behavior under Vickers indentation and scratch test.
41
Hassani, Hamid. "Structure evolution and mechanical properties of ion-exchanged silicate glass". Doctoral thesis, Università degli studi di Trento, 2019. http://hdl.handle.net/11572/243415.
Texto completoResumen
Soda-lime silicate glass (SLS glass) is one of the most commercialized glasses with a huge extent of applications from homewares and kitchenware appliance to cover for touchscreen gadgets. The latter has gained notable attentions recently since the majority of available touchscreen gadgets have covers from other glass families such as aluminosilicate. Technically, these types of glasses are difficult to produce and very costly, therefore, the prices of articles which are made by these glasses are high. In comparison, soda-lime silicate glass has lower price because of globally growing production and promising future. However, due to the intrinsic weaker mechanical properties, the application of SLS glass as cover of touchscreen gadgets is restricted. Several techniques have been applied to improve the mechanical properties of SLS glass. Among them chemical tempering is one the most promising technique.
Typically, the chemical tempering is done by an ion-exchange process where sodium atoms contained in the glass are substituted by potassium ions diffusing from the molten salt. The effect of variables such as glass composition, molten bath composition, temperature, and time is crucial in the ion-exchange process. Particularly, selecting an unsuitable time and temperature of the process can affect mechanical properties of glass through a stress relaxation phenomenon. Therefore, optimization of the time and temperature can guarantee efficient reinforcement of glass.
In this PhD research, three different temperatures (430°C, 450°C, and 470°C) and five different times (4 h, 8 h, 24 h, 48 h and 168 h) selected for chemical tempering of glass samples in pure molten KNO3 and molten KNO3 systematically poisoned by NaNO3.
The compressive residual stress and case depth were determined by optical methods, the flexural strength was measured by a ring-on-ring test method and the surface chemical composition of the glass was analysed by Energy Dispersion X-ray Spectroscopy (EDXS). The resistivity of treated glass against forming surface cracks was studied by Vickers hardness and scratch test. To study the structural evolution, micro-Raman (μ-Raman) spectroscopy was used.
The results pointed out that below addition of 0.5 wt% NaNO3, the ion-exchange process is always effective. Indeed, compressive residual stress, flexural strength, surface concentration and potassium penetration in Na-containing baths are substantially identical to values recorded on glasses treated in “pure” KNO3. Actually, case depth and interdiffusion coefficient are invariant with respect to the sodium content at least up to 1 wt%. No significative difference between “tin” and “air” side are revealed.
Influence of time of tempering on Na-K exchange process showed that the concentration of K+ on the surface of glass was increased by increasing the duration of of the process. Compressive residual stress, on the other hand, was decreased by time due to the surface structural relaxation. A surface crack tendency under a Vickers indenter and scratch test gave the evident that K/Na ion-exchange process for more than 24 h is responsible for an indent mechanical reinforcement. A structural reorganization of the glass network occurred and a higher number of Q2 and Q3 species were present in the tempered glasses with respect to the pristine one. Such re-polymerization could account for a more plastic behavior under Vickers indentation and scratch test, making the material less susceptible to surface cracking.
The case depth of tempered samples was increased by temperature at the expense of the compressive residual stress due to the stress relaxation. Relative concentration of K+ on the surface, as well, increased by the temperature. The increase in the temperature of ion-exchange process led to increase in the tendency of glass against formation of crack under Vickers indenter and scratch test. The limit of this propensity is tempering at 470 °C for 48 h as the formation of radial cracks and shorter plastic deformation regions under scratch test observed. From structural point of view, Na-K exchange caused reorganization of the glass network which is responsible for a more plastic behavior under Vickers indentation and scratch test.
42
Student, James John. "Silicate Melt Inclusions in Igneous Petrogenesis". Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/28719.
Texto completoResumen
Silicate melt inclusions are ubiquitous in quartz phenocrysts, yet there are few studies of such inclusions from porphyry copper systems. A melt inclusion forms when magma is trapped in a growing phenocryst. If a phenocryst is able to preserve the original parent magma, then accurate information can be obtained for ancient volcanic systems. In recent igneous systems, melt inclusions are commonly preserved as optically clear homogeneous glass representative of magma stored at depth before eruption. Melt inclusions are difficult to recognize in quartz phenocrysts from porphyry copper system because they are crystalline and hidden by exsolved magmatic volatiles. The inclusions range in size from less than 5 to over 150 μm. In order to evaluate the magmatic contribution to economic mineralization, we conducted three separate studies to determine whether or not crystallized melt inclusions preserve representative samples of magma.
The first study modeled the phase relationships that occur during equilibrium crystallization and melting of haplogranite magma trapped in quartz. Results from the model are similar to observations made during the heating of crystallized melt inclusions from porphyry copper systems. It is necessary to re-melt the crystal and volatile phases before chemical analysis. Micro-explosions caused by heating resulted in the loss of important chemical components. Our second study evaluated several microthermometric heating procedures using synthetic melt inclusions trapped at conditions similar to those inferred for porphyry copper systems. A synthetic hydrous melt was saturated with saline hydrothermal solutions allowing both melt and aqueous fluids to be trapped in quartz. Based on microthermometric measurements from these coeval melt and aqueous fluid inclusions we were able to predict the known trapping temperature and pressure of formation. This technique can be applied to natural samples to constrain trapping pressures and temperatures. It was found that slower heating rates could be used to avoid overheating and that heating under a confining pressure greatly minimizes the decrepitation of inclusions.
The third study examined the copper concentrations in melt inclusions from the Red Mountain, Arizona porphyry copper system. Older andesite magma contains pyroxene with melt inclusions of higher copper concentrations compared to melt inclusions in quartz from quartz latite. The higher water concentrations in crystallized melt inclusions in the quartz, and abundant aqueous fluid inclusions indicates that the exsolution of water from the magma occurred prior to the trapping of melt inclusions in quartz. The lower water concentrations and the absence of aqueous fluid inclusions indicates that the andesite never reached the stage of water exsolution. The results obtained here are consistent with models that suggest that copper is extracted from the melt by saline magmatic fluids, producing a metal-charged hydrothermal solution and leaving behind a metal-depleted melt and serves to identify the potential contribution of melt inclusion studies to constrain the origin of ore metals in porphyry copper deposits.Ph. D.
43
Sonneville, Camille. "Étude des propriétés élastiques des verres d’oxydes sous haute pression : implications structurales". Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10114/document.
Texto completoResumen
Le comportement des verres sous pression, lié à leurs structures topologiques, est un enjeu majeur à la fois fondamental et appliqué. L’anomalie élastique de la silice à 2,5GPa est un phénomène connu et son existence est plus que probable dans le verre de GeO2. Il semblait alors légitime de questionner son existence dans des verres plus répandus de compositions chimiques complexes comme les verres alumino sodo silicatés. L’anomalie élastique a été étudiée in situ par Diffusion Brillouin et Raman pour le verre de GeO2 et trois verres alumino sodo silicaté de compositions chimiques : (Al2O3)X(Na2O)25−X(SiO2)75 où X=0, 6 et 12%. Il a été montré que l’existence de l’anomalie de compressibilité dans le domaine élastique n’était pas réduite qu’à la silice uniquement mais au contraire persistait sur un vaste domaine de compositions chimiques et semblait être liée à la présence d’anneaux à 6 tétraèdres. Au delà de la limite élastique, les modifications structurales à l’origine du phénomène de densification permanente ont été étudiées pour la silice, le verre de GeO2 et six verres d’alumino sodo silicatés (contenant X=0, 2, 6, 9, 12 et 16% d’Al2O3). Tout d’abord nous avons observé par diffusion Brillouin la disparition progressive de l’anomalie élastique de la silice avec la densification. Ce phénomène a été interprété en termes de transformations induites par la pression d’une forme amorphe basse densité (LDA) en une forme amorphe haute densité (HDA) : LDA → HDA. Des études in situ et ex situ par Diffusion Brillouin et Raman, Résonance Magnétique Nucléaire (RMN) et aussi de Spectroscopie d’Absorption des Rayons X proche du seuil (XANES) ont montré que les modifications structurales à l’origine de la densification permanente dépendaient grandement de la composition chimique. En particulier la présence de cation sodique semble favoriser les modifications à courte portée comme la formation d’espèces hautement coordonnées d’aluminium ou encore de silicium ainsi que la dépolymérisation du réseau. Au contraire les verres les plus riches en aluminium semblent montrer une densification plus proche structurellement de celle de la silice pure c’est à dire modifiant principalement l’ordre à moyenne distance avec diminution de l’angle inter-tétraèdre et de la taille des anneauxThe structural study of glasses under pressure is of fundamental interest in Physics, Earth Science and is technologically important for the comprehension of industrial material properties. The elastic anomaly at 2.5GPa in pure silica glass is a well known phenomenon and its existence is more than likely in GeO2 glass. In this work the persistence of the elastic anomaly in more complex and more widely glass compositions as sodium alumino silicate glasses was studied. The elastic anomaly was studied in situ in GeO2 and three sodium alumino silicate glasses by Brillouin and Raman scattering. The studied sodium alumino silicate glasses had the following compositions : (Al2O3)X(Na2O)25−X(SiO2)75 where X=0, 6 et 12% and is the molar percentage of Al2O3. The elastic anomaly was shown to persist in a broad domain of chemical compositions thus its existence is not reduced to pure silica glass. Its existence seems to be linked to the presence of 6 membered rings. Beyond the elastic limit, the structural modifications was studied in pure silica, GeO2 glass and sodium alumino silica glasses (with X=0, 2, 6, 9, 12 et 16% of Al2O3) in order to structurally better understand the densification phenomenon. Firstly the elastic anomaly was studied by Brillouin scattering experiments, was shown to progressively disappear with the densification. This progressive disappearance was interpreted in terms of a progressive structure induced transformation from a Low Density Amorphous form (LDA) into a High Density Amorphous form (HDA) : LDA → HDA. In situ and ex situ studies by Brillouin and Raman scattering, Nuclear Magnetic Resonance (NMR) and X-ray Absorption Near Edge Structure (XANES) showed that the pressure induced structural transformation was highly dependent of the glass chemical composition. For instance the presence of sodium cations promotes short range order modifications, such as formation of highly coordinated species (Al, Si) and network depolymerization. On the other hand, glasses with a high aluminum concentration show a densification process closer to that of pure silica glass, with mainly middle range order structural modifications such as a decrease of the inter-tetrahedral angle or ring size decrease
44
de, Grouchy Charlotte J. L. "Trace element incorporation in silicate melts and glasses at high pressure". Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/22848.
Texto completoResumen
Trace elements are highly fractionated during large-scale melting associated with planetary differentiation events. The resulting partition coefficients are used to constrain a range of geological processes and are known to be influenced by pressure, temperature, and compositional changes in crystalline structures. Although recent studies have shown that melt compositional changes affect the partitioning of trace elements, the degree to which these ratios are influenced by alterations in the melt structure, especially with increasing pressure, is poorly constrained due to the difficulty of collecting structural information on bonding environments in situ. A basic understanding of how these elements are incorporated in silicate melts is critical to interpreting early planetary differentiation and crust forming events. This thesis presents results from both x-ray diffraction and absorption techniques on trace element (Y, Zr, Lu and Nd) incorporation in silicate melt structures. The structure of two rare Earth element doped model end member silicate liquids, a highly polymerised haplogranite (Si- Al-Na-K-O) and a less polymerised anorthite-diopside (Si-Al-Mg-Ca-O), have been studied. The results are the first to identify trace rare Earth element (REE) incorporation in silicate melts at high pressure using x-ray diffraction techniques. The local melt structure around Y and Zr in a highly polymerised haplogranite has been studied using x-ray absorption spectroscopy up to 8GPa and 1650 K. Both elements appear to adopt 8-fold coordination within the melt structure with no variation over the pressure range studied. This was also found for the Lu bonding environment in the same composition where the coordination number of Lu-O was found to be 8, with a bond distance rLu-O = 2:36A in the haplogranite melt. At low pressures, < 5GPa, the bonding environment of Lu-O was found to be dependent on composition with coordination decreasing to CNLu-O = 6 and rLu-O = 2:29A in the anorthite-diopside melt. This compositional variance in coordination number at low pressure is consistent with observations made for Y-O in glasses at ambient conditions and is coincident with a dramatic increase in the partition coefficients previously observed for rare Earth elements (REE) with increasing melt polymerisation. However, an abrupt change in both Lu-O coordination and bond distance is observed at 5GPa in the anorthite-diopside melt, with CNLu-O increasing from 6 to 8-fold and rLu-O from 2.29 to 2.39A. This occurs over a similar pressure range where a reduction in the reported heavy REE partition coefficients is observed. X-ray diffraction experiments up to 60GPa and 2000K have also been performed on the incorporation of the larger light REE, Nd, in basaltic-like melts. The results presented show that incorporation within the anorthite-diopside composition is dependent on the size of the REE. Nd-O initially shows the same 6-fold coordination as Lu-O at ambient conditions, although the change to 8-fold coordination appears to occur at considerably lower pressure between 1-2GPa. Coordination change in both cases can be attributed to collapse of the silicate network and an increase in the average number of available 'crystal like' sites in the liquid, with ionic radius of the REE controlling at which pressure the preference for these sites in the melt occurs. Published mineral-melt partition coefficients for Nd, with major mineral phases such as garnet, show very little variation with pressure, in contrast to Lu. The difference in structural incorporation of Lu and Nd in the melts presented in this thesis could explain this partitioning behaviour. Overall this thesis highlights that important structural changes of the trace element bonding environment in silicate melts occur with both compositional variation and pressure. Melt structural changes with pressure cannot be neglected in predictive models of trace element behaviour, and using a single melt term to normalise the effects of melt on trace element partitioning will not accurately predict partitioning behaviour at depth during magma formation or differentiation.
45
Sujirot, Kuljira. "Silicate glass-ceramics containing fluoride for application in ceramic-matrix-composites". Thesis, Imperial College London, 1995. http://hdl.handle.net/10044/1/7435.
Texto completo
46
Nascimento, Marcio Luis Ferreira. "Condutividade elétrica de vidros de boratos, silicatos e sílico-sulfatos de íons alcalinos". Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-09122001-161054/.
Texto completoResumen
Vidros condutores à base de boratos, silicatos e sílico-sulfatos de íons de metais alcalinos foram preparados a partir da mistura apropriada de pós de óxidos, carbonatos e sulfatos, Eles foram produzidos a partir da fusão e resfriamento rápido em um forno de carbeto de silício de ate 1400ºC. Estes materiais foram analisados pelas técnicas de condutividade em corrente contínua (CC) e por Espectroscopia de Impedância (EI) nas caracterizações elétricas, por Difração de Raios X (DRX) para análise estrutural, Absorção Ótica (AO) par verificar a transmitância e pelas técnicas de Espectroscopia de Emissão de Chama (EEC) e Retroespalhamento de Rutherford (RBS) para identificar as composições. Os difratogramas de Raios X mostraram que se tratam de sólidos amorfos. Os espectros de AO mostraram forte absorção na região do ultravioleta e completa transparência para a luz visível. As técnicas de EEC e RBS indicaram perdas pequenas de óxidos de sódio e lítio porem grandes de sulfatos. Os principais resultados mostraram: a maior condutividade entre os materiais estudados, de 2,3×10-4S/cm para o vidro 53,4Na2O·6,6Na2SO4·40,0SiO2 mol%, caracterizando-o como um condutor iônico rápido (FIC-Fast Ion Conductor); concordância nos valores de condutividade em CC e CA, e uma melhor caracterização das propriedades dielétricas, como capacitância C, freqüência de relaxação f0 e ângulo de descentralização Fi. Alem do comportamento do tipo Arrhenius em todas as amostras foi identificada também uma não-homogeneidade estrutural através de um segundo semicírculo por EI. Por fim, aplicando tensões de até 1kV foram verificados o implante de prata em dois vidros através da técnica de RBS.Conducting glasses based on borates, silicates and silica-sulfates of alkali metals have been prepared from an appropriate mixture of powder of oxides, carbonates and sulfates. They were produced by fusion in a silicon carbide furnace up to 1400ºC and then by fast cooling. These materials have been analyzed with techniques of DC conductivity and Impedance Spectroscopy (IS) for electrical characterizations, by X Ray Diffraction (XRD) for structural analysis, Optical Absorption (OA) to verify the transmittance characteristics and by techniques of Flame Emission Spectroscopy (FES) and Rutherford Backscattering (RBS) to identify their compositions. The X Rays difractrograms have shown that they are amorphous solids. The AO spectra showed strong absorption in UV region and a full transparency for visible light. The FES and RBS techniques indicated little loss of sodium and lithium oxides, however greater loss of sulfates. The main results shown that: among all the samples the largest conductivity, of 2.3×10-4S/cm at 150ºC was found for the glass 53.4Na2O·6.6Na2SO4·40.0SiO2 mol%, characteristic of a FIC (FIC-Fast Ion Conductor) system; also a concordance of DC and AC conductivity values, and a better characterization of dielectrical properties, such as capacitance C, relaxation frequency f0 and depression angle Fi. Besides the Arrhenius in all the samples a structural non-homogeneity was found in a second semicircle by IS. Lastly a successful Ag implant on two glasses was certified by the RBS technique, by application of voltages up to 1kV.
47
Guerra, Christiano Pereira 1966. "Desenvolvimento de sílica vítrea por fusão em chama a partir de lascas de quartzo brasileiro visando aplicações de alta transmitância no médio UV". [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264827.
Texto completoResumen
Orientador: Carlos Kenichi SuzukiTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-23T18:37:21Z (GMT). No. of bitstreams: 1 Guerra_ChristianoPereira_D.pdf: 3352295 bytes, checksum: efe1174275c24c1520729d7316d099fe (MD5) Previous issue date: 2013
Resumo: A sílica vítrea é um material fundamental para a indústria de alta tecnologia devido as suas propriedades únicas. Dentre estas podemos destacar a sua alta pureza aliada ao elevado ponto de fusão e alta transmitância no ultravioleta. É um material muito usado na indústria de semicondutores e em fotônica. Para aplicações na indústria óptica e de lâmpadas especiais, é necessário que a sílica vítrea tenha alta transmitância na região do ultravioleta médio (200 nm - 300 nm) e do visível e contenha um reduzido teor de bolhas. Tarugos de sílica vítrea foram produzidas pelo método de Verneuil a partir da fusão em chama com gás GLP e O2. Foram utilizados pós de quartzo natural brasileiro de diferentes regiões com variados teores de impurezas e pós de quartzo comerciais nacionais e importados. Foi introduzida uma etapa de lixiviação ácida em um dos pós de quartzo comercial brasileiro com o objetivo de diminuir o teor de bolhas na sílica vítrea. As impurezas nos pós de quartzo foram determinadas através da técnica de ICP-MS. A transmitância óptica entre 190-3200 nm foi determinada por espectroscopia óptica. O teor de OH presente nas amostras de sílica foi determinado através da banda de absorção em 2730 nm na região do infravermelho do espectro. O teor de bolhas foi determinado através de microscopia óptica, considerando bolhas maiores que 0,01 mm. Foi avaliada a relação entre a transmitância das amostras de sílica vítrea e os teores de impurezas presentes nos pós de quartzo. Os resultados de transmitância na região do médio UV das amostras de sílica vítrea produzida com pós de quartzo feitos a partir das lascas de quartzo brasileiro foram comparados com a sílica vítrea produzida com pó de quartzo comercial importado. Os teores de bolhas foram avaliados em relação às condições de processo de fusão e temperatura de fusão do tarugo. Os resultados mostram a excelente viabilidade do quartzo brasileiro para a fabricação de sílica vítrea de elevado valor agregado
Abstract: Due to their unique thermal and optical properties, silica glasses are highly demanded for use in the high technology industry. They are widely used in the semiconductor and optics industries. For most of the applications in optical industry it is necessary to present high optical transmittance in the medium ultraviolet region (200 nm - 300 nm) and visible and low content of bubbles. Silica glass rods were produced by the Verneuil method from flame fusion with LPG and O2 gases by using Brazilian natural quartz from various regions of the country and also imported and national commercial quartz powders. An acid leaching procedure in a commercial Brazilian powder quartz was tested with the purpose of reducing the bubbles content in silica glass. The measurements of impurities concentration in the quartz powders were determined by ICP-MS technique. The optical transmittance from 190-3200 nm was determined by optical spectroscopy. The OH content was determined by the absorption band at 2730 nm in the infrared region of the spectrum. The content of bubbles larger than 0.01 mm was determined by optical microscopy. The relationship between the optical transmittance of the silica glass samples and the level of impurities in the quartz powders was evaluated. The results of the average transmittance in the UV region of the silica glass samples produced from Brazilian quartz lascas were correlated with the silica glass produced using imported commercial quartz powders. The concentration of bubbles was evaluated with respect to the process conditions of fusion and ingot melting temperature. The results show an excellent feasibility of application of Brazilian natural quartz to produce high value added silica glass
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
48
Hooper, Paul. "Blast performance of silicone-bonded laminated glass". Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6861.
Texto completoResumen
Blast resistant glazing systems typically use laminated glass to reduce the risk of flying glass debris in an explosion. Laminated glass has a bonded polymer interlayer that retains glass fragments upon fracture. With proper design, the flexibility of the interlayer in laminated glass can offer protection from significantly higher blast loads when compared to an equivalent monolithic pane. This thesis investigates the post-fracture behaviour of laminated glass under blast loading and aims to build the knowledge required to improve design methods for blast resistant glazing. Full-scale open-air blast tests were performed on laminated glass containing a polyvinyl butyral (PVB) interlayer. Test windows ranged in size from 1.5m×1.2m to 3.5m×1.8m and were bonded to robust frames using structural silicone sealant. Blast loads were produced using charge masses of 15 kg to 500 kg (TNT equivalent) and distances of 10m to 30 m. Deflection and shape measurements were obtained using high-speed digital image correlation. Measurements of loading at the joint were also made with strain gauges. The main failure mechanisms observed were the cohesive failure of the bonded silicone joint and tearing of the interlayer. These failure mechanisms were investigated further using a highspeed tensile test machine to reproduce blast loading conditions. Cracked laminated glass samples were loaded in tension at varying rates. Their response was characterised by a rate dependant plateau force which can be used to estimate the maximum load on the glazing joint. Delamination between the PVB and glass was found to play a key role in the laminate response. Thinner PVB and higher strain rates reduced the delamination area, leading to premature tearing of the interlayer. The strength of structural silicone sealant in a blast situation was also investigated. A novel test method was used to determine the bond length required to retain the laminated glass window in a blast event. A nominal strength of not greater than 1.1MPa should be used for design of conventional single-sided silicone joints. A finite element model of the laminated glass response to blast loading was developed using the results of the experimental investigations. The failure predictions of the model were compared against a single-degree-of-freedom (SDOF) model and showed good agreement. Differences in the deflected shape at maximum deflection were seen between the model and those measured in blast testing.
49
Santos, Felipe Antunes. "Vitrocerâmica à base de silicato de lítio para uso como material dentário utilizando casca de arroz como fonte alternativa de silica". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/97/97133/tde-08102013-084019/.
Texto completoResumen
O presente trabalho sugere a substituição da sílica comercial pela sílica obtida da casca de arroz como fonte alternativa para obtenção do dissilicato de lítio, material que pode ser utilizado em aplicações odontológicas. Para esse fim foram desenvolvidos materiais com estequiometria base de 33,33%mol. Li2O e 66,67%mol. SiO2 com e sem adição de óxidos complementares, visando à obtenção de vitrocerâmicas de maior tenacidade, por meio das duas fontes de sílica, comercial e da casca de arroz. Como caracterizações iniciais, foram realizadas difrações de raios X (DRX) para as misturas iniciais das matérias-primas antes e após a fusão para obtenção dos vidros. Para o caso dos materiais sem adição dos óxidos, a caracterização quanto à sua devitrificação, foi realizada por análise térmica diferencial (ATD), utilizando diferentes taxas de aquecimento e granulometrias, para ambas as fontes de sílica. Valores de temperatura de pico de cristalização (Tp), sem adição dos óxidos, ficaram na faixa de 640°C para os materiais de ambas as fontes de sílica. Também por ATD foi analisado o fenômeno de devitrificação dos materiais com adição dos óxidos. Além disso, para observar a existência de fases intermediárias no sistema, foram também realizadas análises por DRX com variação térmica. Para visualizar a alteração microestrutural, de acordo com a variação da temperatura de tratamento térmico (TT), fonte de sílica e influência dos óxidos, foram realizadas caracterizações por microscopia eletrônica de varredura (MEV). O comportamento citotóxico dos materiais frente às colônias celulares foi observado por meio do ensaio de citotoxicidade. As propriedades mecânicas, de acordo com as alterações das variáveis estudadas, foram obtidas por meio de cálculos de dureza e tenacidade à fratura por ensaio Vickers. Foram encontrados valores de tenacidade à fratura de aproximadamente 1,75 MPam1/2 para ambas as fontes de sílica, com adição de óxidos a 660°C (TT). Diante dos resultados obtidos é possível afirmar grande potencialidade na substituição da sílica comercial pela sílica da casca de arroz.This work suggests the replacement of commercial silica by silica obtained from rice husk as alternative source for obtaining lithium disilicate material that can be used in dental application. The lithium disilicate as dental material is a glass-ceramic that has good mechanical properties and chemical stability. For these developments the materials have been obtained using stoichiometry of 33.33%mol. Li2O and 66.67%mol. SiO2, without complementary oxide addition or with, seeking better fracture toughness comportment, to both sources of silica, commercial and from rice husk. As initial characterization X-ray diffraction (XRD) was performed for the mixtures of materials before and after the fusion to obtain the glasses. For materials without oxide addition, the two materials developed were characterized for their devitrification, in other words, the transition from glass to glass-ceramic was observed by differential thermal analysis (DTA), using different heating rates and granulometries. Peak crystallization temperatures (Tp), to both silica sources, heat rate 10°C/min and 1mm of granulometry, was in average values of 640°C. The DTA was used to verify the devitrification in material with oxide addition too. In addition, to observe the possible formation of intermediate phases on stoichiometric system of lithium disilicate, were also carried out high temperature X-ray diffractomery (HTXRD). To view the microstructural changes occurring in the system, according to the variation of heat treatments temperatures (HT), silica source and oxides influence, characterizations were performed by scanning electron microscopy (SEM). The cytotoxic behavior of the materials in cell colonies was observed by the cytotoxicity test. Mechanical properties, Vickers hardness and fracture toughness, were determined by calculus, using Vickers test data. Values of approximately 1.75 MPam½ were obtained for both silica sources with oxide addition to 660°C (HT). Results obtained show great potential in the replacement of commercial silica by rice husk silica.
50
Mekki, Abdelkrim. "X-ray photoelectron spectroscopy and magnetic studies of transition metal silicate glasses". Thesis, University of Warwick, 1997. http://wrap.warwick.ac.uk/51305/.
Texto completoResumen
X-ray photoelectron spectroscopy (XPS) has proved to be a powerful technique in the investigation of the local structure of oxide glasses. In this project, XPS and magnetisation techniques were used to study sodiun silicate glasses doped with various amounts of 3d transition metals. The first glass system had the compositional formula (0.70-x)SiO2-0.30Na2O-xFe2O3 where 0.0 <= x <= 0.20. The quantitative ratio [Fe2]/[FeTotal], for each glass has been determined from the analysis of the Fe 3p spectra. For low Fe2O3 content both iron valencies are present, however, it was found that Fe3+ is the predominant species for high Fe2O3. From the analysis of the O 1s spectra, it was possible to discriminate between bridging and non-bridging oxygen atoms in each glass sample. It was found that the ratio of the non-bridging oxygen content to the total oxygen content increases with increasing iron concentration. It has also been shown that the nonbridging oxygen contribution to the O 1s spectra can be simulated by summing the contributions from SiONa, SiOFe(II) and SiOFe(III) components present in the glass. The second glass system had the compositional form (0.70-x)SiO2-0.30Na2O-xCuO where 0.0 <= x <= 0.20. Evidence of the presence of copper in the Cu+ state for x<=0.15, and both oxidation states, Cu+ and Cu2+, in the glass with x=0.20, was obtained from the "shake up" satellite structure of the Cu 2p core level spectra. A deconvolution procedure was undertaken to determine qualitatively the ratio [Cu2+]/[CuTotal]. The non-bridging oxygen content, obtained from the deconvolution of the O 1s core level spectra, increases with increasing copper oxide content showing that copper acts as a network modifier. The O 1s spectra were modelled in order to separate the contribution from SiOCu and SiONa to the non-bridging oxygen signal. The Na 1s core level spectra seem to be insensitive to change in copper content in the glass, while Si 2p showed some dependence. Magnetization measurements were also performed on the same samples. The M versus H data at different temperatures collapses nicely to a single curve in the M versus H/T representation for all the glass samples investigated, indicating that Cu2+ is behaving paramagnetically in these glasses. The M versus H curves have been fitted with a Brillouin function keeping the number of magnetic ions as the fitting parameter and deducing the number of Cu2+ ions in each glass from the best fit to the experimental data. It was found that the Cu2+ content measured by XPS was much lower that the one found from the magnetic measurements. This might indicate that there is less Cu2+ on the surface than in the bulk of these glass samples. The third glass series investigated has the composition (0.70-x)SiO2-0.30Na2O-xCoO, where 0.0 <= x <= 0.20. The Co 2p spectra showed intense satellite structures about 6 eV above the main photoelectron peaks, and the Co 2p3/2-Co2p1/2 separation was found to be ~ 15.9 eV for all the samples studied. These observations indicate the presence of high-spin Co2+ ions in the glasses. The Co 3p spectra have been fitted with contributions from high-spin Co2+ in both tetrahedral and octahedral coordinations and the ration [Co2+ (oct)]/[Co2+total] increases with CoO content. The O 1s spectra show significant compositionally dependent changes. The concentration ratio of bridging and non-bridging oxygen atoms was determined from these spectra. High-spin Co2+ ions are found to be incorporated in the glass as network modifiers, irrespective of their coordination. The d.c. magnetic susceptibility measurements done on the same samples also suggest that Co2+ ions exist in both tetrahedral and octahedral coordinations. The magnetization versus magnetic field data indicate that the exchange magnetic interaction increases with CoO content in the glass. Thermal expansion coefficient, differential thermal analysis, heat treatment of the parent glass and identification of the crystalline phases present as well as density measurements have been performed on each glass series and these results are discussed in connection with the XPS and magnetic findings.