Dissertations / Theses on the topic 'Silica'
To see the other types of publications on this topic, follow the link: Silica.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Silica.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Chiaranussati, Preeyanuj. "NMR studies of silicas and platinum/ silica catalysts." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319580.
Full text
2
Lorier, Troy Howard. "The dissolution kinetics of quartz and amorphous silica in natural waters : a baseline for silica reactivity." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/25757.
Full text
3
Spaargaren, Susan Marianne Rosemary. "Radiation effects on silica based waveguides." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267942.
Full text
4
Bashir, Muhammad Ahsan. "Impact of Physical Properties of Silica on the Reaction Kinetics of Silica Supported Metallocenes and Polyethylene Morphology." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1253/document.
Full textAbstract:
Les polyolefins représentent plus de la moitié de la production mondiale de plastiques et 80% de ces polymères sont produits avec des catalyseurs hétérogènes de type Phillips, Ziegler-Natta et métallocènes. En effet, un bon fonctionnement des unités du fait d'un faible encrassement du réacteur ou des autres équipements de l'unité, une activité stable, une bonne morphologie particulaire des polymères et un une densité apparente élevée sont obtenus en utilisant des catalyseurs hétérogènes. D'un autre côté l'hétérogénéisation d'un catalyseur s'accompagne d'une diminution de l'activité et d'un élargissement de la distribution de masses molaires qui est parfois non désiré car cela peut influencer l'aptitude à la transformation et les propriétés mécaniques des polyoléfines. Plusieurs explications ont été avancées dans la littérature afin d'expliquer l'effet de l'immobilisation d'un catalyseur ce qui inclut la résistance diffusionnelle au transport du (des) (co)- monomère(s) vers le site actif et la modification du comportement du catalyseur conduisant à plusieurs espèces actives. Néanmoins l'ensemble de ces explications est en connexion avec les propriétés physiques du support (tailles des particules, surface spécifique, volume poreux, diamètre des pores…) car ce dernier peut en effet impacter la nature des espèces actives ainsi que leur dispersion et la diffusion des monomères. Les catalyseurs métallocène sont considérés comme mono-site et tout changement dans la nature du site actif au cours de son immobilisation et toute résistance au transfert de matière peuvent être détectés par un élargissement de la distribution des masses molaires. Le présent travail a pour objet d'étudier les effets des propriétés physiques des catalyseurs métallocènes supportés sur silice concernant la cinétique de polymérisation et les caractéristiques des polymères produits. Pour cela le traitement thermique de la silice a été fixé à 600°C afin de contrôler son état de surface tandis que la quantité de catalyseur supporté a été gardée autant que possible constante. De plus les protocoles de polymérisation en phases suspension et gaz ont été fixés après avoir évalué différentes conditions de polymérisation et différents composés alkylaluminium. Cette étude systématique a permis d'attribuer les différences observées en termes de cinétique de réaction des catalyseurs métallocènes à la différence des paramètres physiques des silices utilisées comme support et par conséquent à la résistance diffusionnelle au transport du (des) (co)-monomère(s) au(x) site(s) actif(s) durant la polymérisationPolyolefins account for more than half of the world’s plastic production and about 80% of these polyolefins are commercially produced with heterogeneous olefin polymerization catalysts such as Phillips, Ziegler-Natta and metallocenes. Trouble-free plant operation due to low fouling of the reactor or other plant equipment, relatively stable catalytic activity, good polymer morphology and high polymer bulk densities can be achieved by employing heterogeneous olefin polymerization catalysts. On the other hand, heterogenization of the olefin polymerization catalysts lead to drastic reduction in their activities and broadening of the polymer molar mass distribution which is undesirable in some cases because it can influence the processability and mechanical properties of the polyolefin grade. Various explanations have been proposed in the open literature to explain these effects of catalyst immobilization which mainly include existence of diffusion resistance to (co)-monomer(s) transport at the active sites during polymerization and the change of the active site(s) behavior due to immobilization leading to multiple site types on the final supported catalyst. Nevertheless, both of these explanations have a connection with the physical properties (e.g., particle size, surface area, pore volume, pore diameter etc.) of the support because the support can impact the nature of the final active species formed on it, dispersion of the active species throughout the support particles and, last but not the least, the intraparticle diffusion of (co)-monomer(s) during polymerization. Metallocenes are considered as single-site catalysts and any changes in the nature of the active site(s) upon their immobilization on a support or during the course of polymerization due to mass transfer resistance can be detected from the broadening of polyolefin molar mass distribution. Therefore, the present work is an attempt to study the effects of physical properties of silica supported metallocenes on their ethylene polymerization kinetics as well as on the morphology of the produced polyethylene. For this purpose, the surface chemistry of the used commercial silica supports was fixed by dehyroxylating all of them at 600 °C, whereas, the final metal loadings of the supported catalysts were nearly kept constant by preparing them under identical conditions. Furthermore, slurry and gas phase polymerization protocols along with the used aluminum alkyl scavenger (which can also induce chemical effects on the catalytic behavior of supported metallocenes) were also fixed by testing different polymerization protocols and scavengers. Such systematic study has allowed us to attribute the observed differences in the reaction kinetics of the supported metallocenes, explicitly, to the differences in the physical parameters of the silica supports and, consequently, to the existence of diffusion resistance to (co) monomer(s) transport at the active site(s) during the course of polymerization
5
Durham, Simon J. P. "Carbothermal reduction of silica to silicon nitride powder." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74221.
Full textAbstract:
The processing conditions for carbothermal reduction of silica to silicon nitride was found to be sensitive to several key processing parameters: namely the intimacy of mixing of carbon and silica, the temperature, the specific high surface area of carbon, the nitrogen gas purity and the action of the nitrogen gas passing through the reactants.Sol-gel processing was found to provide superior mixing conditions over dry mixing, which allowed for complete conversion to silicon nitride at optimum carbon:silica ratios of 7:1. The ideal reaction temperature was found to be in the range of 1500$ sp circ$C to 1550$ sp circ$C. Suppression of silicon oxynitride and silicon carbide was achieved by ensuring that: (a) the nitrogen gas was gettered of oxygen, and (b) that the gas passed through the reactants. Thermodynamic modelling of the Si-O-N-C system showed that ordinarily the equilibrium conditions for the formation of silicon nitride are very delicate. Slight deviations away from equilibrium leads to the formation of non-equilibrium species such as silicon carbide caused by the build-up of carbon monoxide. Reaction conditions such as allowing nitrogen gas to pass through the reactants beneficially moves the reaction equilibrium well away from the silicon carbide and silicon oxynitride stability regions.
The particle size of silicon nitride produced from carbon and silica precursors was of the order of 2-3 $ mu$m and could only be reduced to sub-micron range by seeding with ultra-fine silicon nitride. It was shown that the mechanism of nucleation and growth of unseeded reactants was first nucleation on the carbon by the reaction between carbon, SiO gas and nitrogen (gas-solid reaction), and then growth of the particles by the gas phase reaction (CO, SiO, N$ sb2$).
6
Pacheco, e. Silva Viviane. "Compositos elastomericos de fibras curtas de silica/silicona." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/250485.
Full textAbstract:
Orientador: Inez Valeria Pagotto YoshidaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
Made available in DSpace on 2018-08-04T13:38:50Z (GMT). No. of bitstreams: 1 PachecoeSilva_Viviane_M.pdf: 4530394 bytes, checksum: 571677ec4e372aa12989ee8eada906a1 (MD5) Previous issue date: 2005
Mestrado
Quimica Inorganica
Mestre em Química
7
Martinez, Nelson Yohan Reidy Richard F. "Wettability of silicon, silicon dioxide, and organosilicate glass." [Denton, Tex.] : University of North Texas, 2009. http://digital.library.unt.edu/ark:/67531/metadc12161.
Full text
8
Savchyn, Oleksandr. "Silicon-sensitized erbium excitation in silicon-rich silica for integrated photonics." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4642.
Full textAbstract:
It is widely accepted that the continued increase of processor performance requires at least partial replacement of electronic interconnects with their photonic counterparts. The implementation of optical interconnects requires the realization of a silicon-based light source, which is challenging task due to the low emission efficiency of silicon. One of the main approaches to address this challenge is the use of doping of silicon based matrices with optical centers, including erbium ions. Erbium ions incorporated in various hosts assume the trivalent state (Er[super]3+) and demonstrate a transition at 1.54 micrometer], coinciding with optical transmission windows in both silicon and silica. Due to the low absorption cross-section and discrete energy levels of the Er[super]3+ ion, indirect excitation is necessary. In late 90s it was demonstrated that the incorporation of excess silicon in erbium-doped silica results in strong erbium sensitization, leading to an increase of the effective absorption cross-section by orders of magnitude. The sensitization was considered to occur via silicon nanocrystals that formed at high annealing temperatures. While a large increase of the absorption cross-section was demonstrated, the incorporation of Si nanocrystals was found to result in a low concentration of excited erbium, as well as silicon related free-carrier absorption. The focus of this dissertation is the investigation of the nature of the sensitization mechanism of erbium in silicon-rich silica. The results presented in the dissertation demonstrate that erbium in silicon-rich silica is predominantly excited by silicon-excess-related luminescence centers, as opposed to the commonly considered silicon nanocrystals. This is a remarkable conclusion that changes the view on the exact origin of erbium sensitization, and that resolves several technical challenges that exist for nanocrystal-based sensitization.; The work shows that in order to sensitize erbium ions in silicon-rich silica there is no need for the presence of silicon nanocrystals, and consequently lower fabrication temperatures can be used. More importantly, the results strongly suggest that higher gain values can be acquired in samples annealed at lower temperature (without silicon nanocrystals) as compared to samples annealed at high temperatures (with silicon nanocrystals). In addition, the maximum gain is predicted to be relatively independent of excitation wavelength, significantly relaxing the requirements on the pump source. Based on the experimental results it is predicted that relatively stable performance of erbium-doped silicon-rich silica is possible up to typical processor operating temperatures of ~ 80 - 90[degrees]C making it a viable material for on-chip devices. The results suggest that low temperature annealed erbium-doped silicon-rich silica is a preferable material for on-chip photonic devices as compared with its high temperature annealed counterpart.; The work shows that the density of indirectly excited erbium ions is significantly larger in samples without silicon nanocrystals (annealed at T[less than]1000[degrees]C) as opposed to samples with silicon nanocrystals (annealed at T[greater than]1000[degrees]C). The density of indirectly excited erbium ions, defining the maximum achievable gain, was demonstrated to be approximately excitation wavelength independent, while the effective erbium absorption cross-section was shown to significantly depend on the excitation wavelength. The excitation mechanism of erbium by luminescence centers was shown to be fast (less than] 30 ns) and capable of erbium sensitization to different energy levels. This multilevel nature of erbium excitation was demonstrated to result in two different mechanisms of the excitation of the first excited state of erbium: fast (less than]30 ns) direct excitation by the luminescence centers, and slow (greater than]2.3 microseconds]) excitation due to the relaxation of erbium ions excited into higher energy levels to the first excited state. Based on photoluminescence studies conducted in the temperature range 15-300K it was shown that the relaxation efficiency of erbium from the second excited state to the first excited state (responsible for the slow excitation mechanism) is temperature independent and approaches unity. The relative stability of the optical properties demonstrated in the temperature range 20-200[degrees]C, implies that relatively stable optical gain can be achieved under realistic on-chip operating conditions. The optimum Si excess concentration corresponding to the highest density of sensitized Er[super]3+ ions is shown to be relatively insensitive to the presence of Si nanocrystals and is ~ 14.5 at.% and ~ 11.5 at.% for samples without and with Si nanocrystals respectively. The presented results and conclusions have significant implications for silicon photonics and the industrial application of Er-doped SiO[sub]2. The work shows that in order to sensitize erbium ions in silicon-rich silica there is no need for the presence of silicon nanocrystals, and consequently lower fabrication temperatures can be used. More importantly, the results strongly suggest that higher gain values can be acquired in samples annealed at lower temperature (without silicon nanocrystals) as compared to samples annealed at high temperatures (with silicon nanocrystals). In addition, the maximum gain is predicted to be relatively independent of excitation wavelength, significantly relaxing the requirements on the pump source. Based on the experimental results it is predicted that relatively stable performance of erbium-doped silicon rich silica is possible up to typical processor operating temperatures of ~ 80 - 90[degrees]C making it a viable material for on-chip devices. The results suggest that low temperature annealed erbium doped silicon-rich silica is a preferable material for on-chip photonic devices as compared with its high temperature annealed counterpart.ID: 029094291; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references.
Ph.D.
Doctorate
Optics and Photonics
9
Ahmad, Nazwin. "Production of high purity silica from Malaysian silica sand." Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427764.
Full text
10
Yoshida, Hisao. "Studies on Photocatalysis by Silica and Silica - Based Materials." Kyoto University, 1998. http://hdl.handle.net/2433/157038.
Full textAbstract:
本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・論文博士
博士(工学)
乙第9830号
論工博第3320号
新制||工||1114(附属図書館)
UT51-98-G429
(主査)教授 吉田 鄕弘, 教授 川﨑 昌博, 教授 横尾 俊信
学位規則第4条第2項該当
11
Wosinski, Lech. "Technology for photonic components in silica/silicon material structure." Doctoral thesis, KTH, Microelectronics and Information Technology, IMIT, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3556.
Full textAbstract:
The main objectives of this thesis were to develop a lowtemperature PECVD process suitable for optoelectronicintegration, and to optimize silica glass composition forUV-induced modifications of a refractive index in PECVDfabricated planar devices. The most important achievement isthe successful development of a low temperature silicadeposition, which for the first time makes it is possible tofabricate good quality low loss integrated components whilekeeping the temperature below 250oC during the entirefabrication process. Two strong absorption peaks thatappear at1.5 mm communication window due to N-H and Si-H bonds have beencompletely eliminated by process optimization. This openspossibilities for monolithic integration with other,temperature sensitive devices, such as semiconductor lasers anddetectors, or polymer-based structures on the common siliconplatform. PECVD technology for low loss amorphous silicon inapplication to SiO2/Si based photonic crystal structures hasbeen also optimized to remove hydrogen incorporated during thedeposition process, responsible for the porosity of thedeposited material and creation of similar to silica absorptionbands.
Change of the refractive index of germanium doped silicaunder UV irradiation is commonly used for fabrication of UVinduced fiber Bragg gratings. Here we describe our achievementsin fabrication of fiber Bragg gratings and their application todistributed sensor systems. Recently we have built up a laserlab for UV treatment in application to planar technology. Wehave demonstrated the high photosensitivity of PECVD depositedGe-doped glasses (not thermally annealed) even without hydrogenloading, leading to a record transmission suppression of 47dBin a Bragg grating photoinduced in a straight buried channelwaveguide. We have also used a UV induced refractive indexchange to introduce other device modifications or functions,such as phase shift, wavelength trimming and control ofpolarization birefringence.The developed low temperature technology and the UVprocessing form a unique technology platform for development ofnovel integrated functional devices for optical communicationsystems.
A substantial part of the thesis has been devoted tostudying different plasma deposition parameters and theirinfluence on the optical characteristics of fabricatedwaveguides to find the processing window giving the besttrade-off between the deposition rate,chamber temperatureduring the process, optical losses and presence of absorptionbands within the interesting wavelength range. The optimalconditions identified in this study are low pressure (300-400mTorr), high dilution of silane in nitrous oxide and high totalflow (2000 sccm), low frequency (380 KHz) RF source and high RFpower levels (800-1000 W).
The thesis provides better understanding of the plasmareactions during the deposition process. RF Power is the keyparameter for increasing the rate of surface processes so as toaccommodate each atomic layer in the lowest energy statepossible. All the process conditions which favor a moreenergetic ion bombardment (i.e. low pressure, low frequency andhigh power) improve the quality of the material, making it moredense and similar to thermal oxide, but after a certain pointthe positive trend with increasing power saturates. As theenergy of the incoming ion increases, a competing effect setsin at the surface: ion induced damage and resputtering.
Finally, the developed technologies were applied for thefabrication of some test and new concept devices for opticalcommunication systems including multimode interference (MMI)-based couplers/splitters, state-of-the-art arrayed waveguidegrating-based multi/ demultiplexers, the first Bragg gratingassisted MMI-based add-drop multiplexer, as well as moreresearch oriented devices such as a Mach-Zehnder switch basedon silica poling and a Photonic Crystal-based coupler.
Keywords:silica-on-silicon technology, PECVD, plasmadeposition, photonic integrated circuits, planar waveguidedevices, UV Bragg gratings, photosensitivity, arrayed waveguidegratings, multimode interference couplers, add-dropmultiplexers.
12
Guesnet, Étienne. "Modélisation du comportement mécanique et thermique des silices nano-architecturées." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI075/document.
Full textAbstract:
Les silices nanostructurées sont des matériaux ultra-poreux (plus de 80% de porosité) utilisés pour la confection de Panneaux Isolants sous Vides (PIV). Elles possèdent des propriétés thermiques exceptionnelles, mais de piètres propriétés mécaniques.L’enjeu de cette thèse est d’étudier ces matériaux aux échelles de la particule (quelques nm), de l’agrégat de particules (quelques dizaines de nm) et de l’agglomérat d’agrégats (quelques centaines de nm), afin de mieux comprendre les comportements mécanique et thermique à l’aide de simulations, et de proposer des pistes pour améliorer le compromis thermique / mécanique. La nature particulaire du matériau et son caractère multi-échelle justifient l’utilisation de méthodes de simulations discrètes (DEM : Discrete Element Method). Un modèle original permettant de générer des agrégats à morphologiecontrôlée (dimension fractale, rayon de giration, porosité) est proposé. Le comportement à la compaction des agrégats est ensuite étudié par simulations DEM. Une approche par cyclage à faible densité a été développée pour obtenir des arrangements initiaux réalistes d’agrégats. La prépondérance des phénomènes adhésifs dans le système rend en effet celui-ci très sensible à l’arrangement initial. La réponse en traction des structures générées par compaction est également évaluée.L’influence de la morphologie des agrégats, de l’adhésion et du frottement ont été étudiées. L’accent est mis sur la comparaison de deux types de silices (pyrogénées et précipitées) présentant des morphologies différentes et pour lesquelles des données expérimentales permettent une confrontation avec les simulations. Les simulations présentées permettent d’apporter des réponses sur l’origine des différences de comportement mécanique observées expérimentalement pour ces deux types de silice.Une modélisation de la conductivité thermique du matériau, avec une focalisation sur la conductivité solide, est également proposéeNanostructured silicas are ultra-porous materials (more than 80 % porosity) used to make Vacuum Insulation Panels (VIP).They have exceptional thermal properties, but poor mechanical properties. The goal of this thesis is to study these materials at the scale of the particle (a few nm), the aggregate of particles (a few tens of nm) and the agglomerate of aggregates (a few hundred nm), in order to better understand mechanical and thermal behaviour using simulations, and to propose ways to improve the thermal / mechanical compromise. The particulate nature of the material and its multi-scale naturejustify the use of Discrete Element Methods (DEM). An original model allowing to generate aggregates with controlledmorphology (fractal dimension, radius of gyration, porosity) is proposed. The compaction behaviour of the aggregates is then studied by DEM. A low-density cycling approach has been developed to obtain realistic initial aggregate arrangements.The preponderance of adhesive phenomena in the system makes it very sensitive to the initial arrangement. The tensile response of structures generated by compaction is also evaluated. The influence of aggregate morphology, adhesion and friction were studied. Emphasis is placed on the comparison of two types of silica (pyrogenic and precipitated) with different morphologies and for which experimental data allow a comparison with simulations. The simulations presented allow us to provide answers on the origin of the differences in mechanical behaviour observed experimentally for these two types of silica.A modeling of the thermal conductivity of the material, with a focus on solid conductivity, is also proposed
13
Yuan, Zheng. "Impact of Colloidal Silica on Silicone Oil-Silica Mixed Antifoams." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1491562587653182.
Full text
14
CALDAROLA, DARIO. "Silica beds and silica monoliths for pollutants removal and HPLC." Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2506223.
Full textAbstract:
This PhD thesis investigates mesostructured porous silica as a system for removal of pollutants and high performance liquid chromatography (HPLC). In these fields typically the materials used consist of a silica substrate modified with a compound, which has a high selectivity towards the analyte of interest. In this thesis two silica modifiers are proposed: cetyltrimetylammonium bromide (CTABr) and glyphosate.
The CTABr was actually the cationic surfactant used as template for the mesostructure, which was not removed from the silica framework as it usually is by calcination. This surfactant was used for the retention of haloacetic acids (HAACs) and nitrate ion. The glyphosate is an aminoacid present in many commercial herbicides and it has a high complexation capability towards metals. It was linked onto the silica surface using an appropriate reagent, the 3-glycidoxypropyltrimethoxysilane. The behavior of HAACs, NO3- and metals has been investigated because they are some of the most dangerous and monitored pollutants in water.
The chosen surface modifiers have been combined with two different systems: silica particles and silica monoliths. The silica particles have been used until the late 1990s for HPLC columns packing, and they are nowadays mainly used as adsorbents of compounds due to their elevated capacity and strong retention capability. The silica monoliths have become the state of the art in HPLC, because of their better mass transfer, higher efficiency and lower analysis time compared to particle packed columns.
Four materials have been prepared combining the two morphologies with each modifier. Physical-chemical characterization has been performed using several techniques (FTIR, N2 isotherms at 77 K, SEM-EDS, XPS and TGA) then the materials capabilities have been investigated in their respective fields of application.
The interesting results obtained with these brand new adsorbents may have a high impact over the fields of waters purification and analysis, which is one of the recent most important topics due to the huge raise of contaminants during the last 150 years.
15
Lebold, Timo. "Mesoporous silica nanostructures." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-118194.
Full text
16
Turquet, François-Xavier. "Insertion of fluorescent manganese compounds - models of catalase - into mesoporous nanoparticles of silica, resol-silica and carbon-silica." Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/666907.
Full textAbstract:
ROS (Reactive Oxygen Species), such as H2O2, HO● and O2-●, are naturally produced by the metabolism of living beings. However, they can appear in large quantities in the case of certain diseases (Alzheimer's, Parkinson's, sclerosis, cancer). Overproduction of ROS leads to higher cell mortality.
Some microorganisms have an Mn-based enzyme capable of catalyzing the disproportionation reaction of H2O2 into O2 and H2O. Several molecules have been synthesized to reproduce this process, however very few of them are active in aqueous environment.
Recently, polynuclear synthetic Mn species have been introduced into mesoporous silica to protect them from the environment. Thus, these complexes of Mn are stable and even see their catalytic activity increase. In order to persevere in this way, this thesis presents new compounds of formula [Mn(bpy)(AntCO2)2]n and [{Mn(bpy)(AntCO2)}2(µ-AntCO2)2(µ-OH2)] for MnII (chain and dinuclear respectively) and [Mn4O2(AntCO2)6(bpy)2(ClO4)2] for MnIII (tetranuclear) based on this concept. These compounds have two types of ligands, 2,2'-bipyridine, commonly found for similar compounds and 9-anthracene carboxylate, a fluorescent ligand added for theragnostic purposes. The resolution of the crystal structure of the MnII dinuclear compound shows a compression along the axis on the direction of the monodentate anthracene carboxylate. Moreover, by hydrolysis the one- dimensional system can be converted to the dinuclear compound.
In the synthesis of the Mn(III) compound some oxidation of the anthracene is observed and two organic compounds are obtained, an anthraquinone and an ester formed by reaction between the quinone and the carboxylate.
The manganese compounds were inserted into silica nanoparticles (NPs), resol (a polyphenol resin)
-silica and carbon-silica hybrids in order to allow their vectorization and to study the compatibility of hybrid NPs with this type of system.
This work explores the magnetic properties of the complexes and the luminescent properties of the coordination compounds and materials.
The Mn(II) compounds show weak antiferromagnetic interaction, and the best way to differentiate these compounds is by EPR spectroscopy: the chain shows a unique band at g~2 while for the dinculear compound the spectrum is more complex, with several features at low fields. Magnetic properties of the Mn(III) compound confirms that it is a tetranuclear with butterfly type geometry with stronger antiferromagnetic interaction between the central ions than between central-terminal ions.
The study of the porosity of the materials and the quantification of the presence of manganese inside the materials shows a good incorporation rate of the compounds. However it seems that the compounds are not present homogenously inside the support and that they are broken into smaller units. This is confirmed with the study of the magnetic properties of the hybrid [Mn]@NPs materials.
In addition, fluoresecence measurement show that both the support and the compounds are luminescent but that both emission are strongly quenched when the compounds are inside the nanoparticles. The study of the optic properties of the materials show that a large amount of the compounds is released when the loaded silica and carbon-silica nanoparticles are redispersed in ethanol. However, resol-silica nanoparticles seem a lot more efficient to retain the complexes inside
and apparently do not need further functionalization to achieve this goal.
Finally, some preliminary test of disproportionation of H2O2 catalyzed by the manganese systems show low to moderate activity of Mn compounds in acetonitrile and paves the way for optimizing hybrid systems in aqueous media.
17
Turquet, François-Xavier. "Insertion of fluorescent manganese compounds – models of catalase – into mesoporous nanoparticles of silica, resol-silica and carbon-silica." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN086.
Full textAbstract:
Les ROS (Reactive Oxygen Species), tels H2O2, HO● et O2-●, sont produites naturellementpar le métabolisme des êtres vivants. Cependant, elles peuvent apparaître en trop grandesquantités dans le cas de certaines maladies (Alzheimer, Parkinson, scléroses, cancers). Lasurproduction de ROS conduit à une mortalité des cellules plus élevée.Certains micro-oragnismes possèdent une enzyme à base de Mn capable de catalyser laréaction de dismutation du H2O2 en O2 et H2O. Plusieurs molécules ont été synthétisées pourreproduire ce procédé, cependant très peu d'entre elle sont actives en environnement aqueux.Récemment, des espèces synthétiques du Mn ont été introduites dans des silicesvoient même leur activité catalytique augmenter. Afin de perséverer dans cette voie, cettethèse présente de nouveaux composés de MnII (dinucléaire et chaîne) et MnIII(tetranucléaire) basés sur ce concept. Ils sont dotés de ligands fluorescents, ajoutés pour desfin théragnostiques. Ces composés ont été insérés dans des nanoparticules (NPs) de silice ethybrides carbone-silice afin, de permettre leur vectorisation et d'étudier la compatibilité desNPs hybrides avec ce type de système.Le travail fourni explore les propriétés magnétiques des complexes, les propriétésluminescentes des composés et matériaux et montre la bonne insertion des composés dans lesNPs hybrides, ne nécessitant pas, contrairement aux NPs de silice pure, de fonctionnalisationsupplémentaire pour la rétention des complexes. Il met aussi en évidence l'activité descomposés du Mn dans l'acétonitrile et ouvre des pistes pour une optimisation des systèmeshybrides en milieu aqueux.Le travail fourni explore les propriétés magnétiques des complexes, les propriétésluminescentes des composés et matériaux et montre la bonne insertion des composés dans lesNPs hybrides, ne nécessitant pas, contrairement aux NPs de silice pure, de fonctionnalisationsupplémentaire pour la rétention des complexes. Il met aussi en évidence l'activité descomposés du Mn dans l'acétonitrile et ouvre des pistes pour une optimisation des systèmeshybrides en milieu aqueuxROS (Reactive Oxygen Species), such as H2O2, HO● and O2-●, are naturally produced by themetabolism of living beings. However, they can appear in large quantities in the case of certaindiseases (Alzheimer's, Parkinson's, sclerosis, cancer). Overproduction of ROS leads to highercell mortality.Some microorganisms have an Mn-based enzyme capable of catalyzing the disproportionationreaction of H2O2 into O2 and H2O. Several molecules have been synthesized to reproduce thisprocess, however very few of them are active in aqueous environment. Recently, synthetic Mn species have been introduced into mesoporous silica to protect themfrom the environment. Thus, these complexes of Mn are stable and even see their catalyticactivity increase. In order to persevere in this way, this thesis presents new compounds ofMnII (dinuclear and chain) and MnIII (tetranuclear) based on this concept. They havefluorescent ligands (9-anthracene carboxylate), added for theragnostic purposes. Thesecompounds were inserted into silica nanoparticles (Nps), resol (a polyphenol resin) -silica andcarbon-silica hybrids in order to allow their vectorization and to study the compatibility ofhybrid NPs with this type of system.This work explores the magnetic properties of the complexes, the luminescent properties of thecompounds and materials and shows the good insertion of the compounds into the hybrid NPs,not requiring, in contrast to pure silica NPs, additional functionalization for the retention of thecomplexes. It also highlights the activity of Mn compounds in acetonitrile and paves the wayfor optimizing hybrid systems in aqueous media
18
ABEL, JOAO L. "Obtencao do carboneto de silicio pela reducao carbotermica da silica." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9443.
Full textAbstract:
Made available in DSpace on 2014-10-09T12:26:50Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:00:49Z (GMT). No. of bitstreams: 0
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
19
Senior, Laura. "Diatom silicon transporters : from protein function to biomimetic silica synthesis." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682342.
Full textAbstract:
Biomineralisation is the synthesis of inorganic materials in biological systems. Many biominerals - such as bone! teeth, and shells - are high-performance composites synthesised with extreme precision under physiological conditions. Understanding biomineralisation is expected to inspire 'green' methods for the manufacture of novel materials. Diatoms are eukaryotic algae that mineralise an external cell wall, or frustule, composed of hydrated silica. Silicification depends upon the uptake of soluble silicon (silicic acid) from the local environment by specific silicic acid transport proteins (SITs). This unusual family of integral membrane proteins are relatively uncharacterised. This project aimed to express and purify 5113 from the diatom Thalassiosira pseudonana (TpSIT3) for further characterisation in vitro, and to explore whether synthetic SIT3 proteoliposomes could be used as a model mineralisation system with potential applications in nanotechnology. TpSIT3 was successfully overexpressed in yeast and purified in the solubilising detergents Fos-choline 12 and octyl glucoside. The purified protein was successfully reconstituted into synthetic liposomes and silicic acid uptake was assessed using two fluorescent assays including a novel method which utilised zinc silicate fluorescence. This method was used to determine that silicic acid transport by TpSIT3 displayed Michaelis-Menten kinetics with a Km of 6.1 ± 2.7 μM, similar to silicic acid uptake studies in diatom cultures. The structure and function of a silicifying cationic peptide were also characterised for the first time. Peptide-mediated silicification only proceeded at ≥2 mM silicic acid when pH was >6.4 and peptide concentration was ≥2.5 mM. These results underpinned efforts to synthesise silica within the int erior lumen of peptide-loaded SIT proteoliposomes. Preliminary electron microscopy and elemental analysis suggested that such an approach was feasible. This thesis thus establishes a series of novel methods that can be used to study silicic acid transport and silica mineralisation in vitro
20
Constable, Andrew N. "Functionalization of Silica Micro-capillaries and Silica Nanoparticles via Polymer Brushes." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1221746490.
Full text
21
Constable, Andrew N. "Functionalization of silica micro-capillaries and silica nanoparticles via polymber brushes." Akron, OH : University of Akron, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1221746490.
Full textAbstract:
Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Science, 2008."December, 2008." Title from electronic dissertation title page (viewed 12/28/2008) Advisor, Roderic P. Quirk; Committee members, Scott Collins, Ali Dhinojwala, Li Jia, Mark D. Soucek; Department Chair, Ali Dhinojwala; Dean of the College, Stephen Z. D. Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
22
Donose, Bogdan Constantin. "Silica-silica nanotribology in electrolyte solutions studied by atomic force microscopy." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/144402.
Full text
23
Boddy, Andrea M. "The effect of product form and silica content of silica fume on its ability to control alkali-silica reaction." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0028/MQ50329.pdf.
Full text
24
Warley, Russell Lee. "Silica-silicone interactions: Non-linear viscoelastic behavior of silica-filled silicone rubber." Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1057089336.
Full text
25
Liu, Yi. "Mesoporous silica/polymer nanocomposites." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31739.
Full textAbstract:
Thesis (Ph.D)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2010.Committee Chair: Jacob. Karl; Committee Member: Griffin. Anselm; Committee Member: Tannenbaum. Rina; Committee Member: Thio. Yonathan S; Committee Member: Yao. Donggang. Part of the SMARTech Electronic Thesis and Dissertation Collection.
26
Gill, Michael. "Polyaniline-silica colloidal nanocomposites." Thesis, University of Sussex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239632.
Full textAbstract:
The work presented in this thesis provides a new route to a colloidal form of polyaniline, which uses colloidal silica as a dispersant. We obtained stable colloidal dispersions of polyaniline-silica composite particles with a 'raspberry' morphology. Compressed pellets of these particles exhibit solid-state conductivities of 1O-!_10-2 S crrr l, which is approximately 1-2 orders of magnitude lower than that of polyaniline bulk powder. This novel colloidal form of polyaniline has significantly improved processability compared to conventionally synthesised polyaniline. The synthesis and chemical characterisations are presented for various polyaniline-silica colloidal nanocomposites. The quantity of polyaniline incorporated into the nanocomposite particles can be controlled by varying the diameter of the silica dispersant, approximately 20% and 60 % polyaniline content being obtained using 120 nm and 10 nm diameter silica respectively. The average particle size ranges of nanocomposites was found to be 150 to 700 nm and 330 to 560 nm, as determined by transmission electron microscopy (TEM) and disc centrifuge photosedimentometry (DCP) respectively. The nanomorphology and surface composition of the polyanilinesilica particles were determined by small angle X-ray scattering (SAXS) and X-ray photoelectron spectroscopy (XPS) respectively. The average inter-particle separation distance of the silica particles within the polyaniline-silica raspberries was determined by SAXS to be 4 nm, a dimension equivalent to molecular polyaniline. The XPS data suggests that the surface of the particles is silica rich, this is consistant with their long term colloidal stability in 1.2 mole dm-3 HCl. The kinetics of polymerisation was studied using 1H NMR spectroscopy to monitor the disappearance of aniline monomer. Polymerisation rates during the synthesis of polyaniline-silica nanocomposites were appreciably faster than the corresponding precipitation polymerisations carried out in the absence of silica dispersants, due primarily to an increase in the second auto-catalytic step of the reaction. Rate constants were determined for both these types of synthesis; the values obtained for the precipitation polymerisations were in reasonably good agreement with literature values.
27
Glaser, K. J. "Computational studies of silica." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1333222/.
Full textAbstract:
There are three areas of research in this thesis. The first is concerned with the silica polymorph, tridymite, with simulations carried out using three computational methods: free energy minimisation, molecular dynamics and Density Functional Theory. A number of tridymite structures with different atomic configurations have been found in nature. The simulations explore various properties of these different forms of tridymite and investigate whether it is possible to distinguish between them using the three computational techniques. It was found that the interatomic potential and simulation technique used, rather than the simulation temperature, were the main factors affecting the resulting structure. There are a number of possible explanations for this result: The techniques may not be sensitive enough to deal with an energy landscape as at as in the case of tridymite. Another reason is that the potentials have been parameterised to distinguish between structures which have reconstructive transitions (where bonds are broken and formed) and may not be able to deal with displacive transitions (where only angles between atoms change) as with tridymite. The final possible explanation is that a number of the known structures may be meta-stable and/or poorly characterised. For the second research area molecular dynamics simulations using a rigid ion two body potential were carried out in order to investigate the properties of silica melts and glasses. A number of different silica crystals were melted to see whether the melts are all similar or whether their properties can be differentiated according to the original crystal structure. At sufficiently high temperatures the starting structure did not affect the properties of the melt. Several properties of silica melts and glasses were investigated: mean square displacement, autocorrelation functions, pair distribution functions, the extent to which silicon and oxygen atoms move together, Arrhenius plots, coordination number, bond lengths and angles. Investigations were also carried out as to whether it is possible to use a shell model to simulate a silica melt. Various properties were calculated and it was found that agreement with experiment was not as accurate as when using the rigid ion model. The third research area is an exploration of the properties of amorphous silica at elevated pressures and a range of temperatures, using molecular dynamics with a rigid ion two body potential. Calculations show that, at low temperatures, the distortion of the tetrahedra is not recovered upon decompression whereas experimental results find complete recovery of the tetrahedra. There is little available experimental data on the behaviour of silica at both high pressures and temperatures. Calculations show that at high temperatures all properties of the initial structure before compression are recovered.
28
Campbell-Rance, Debbie. "Electrodeposited Silica Thin Films." VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/2123.
Full textAbstract:
Sol-gel derived silica thin film synthesis has gained prominence because of the mild processing conditions and widespread understanding of the chemistry of the process. Traditionally, silicate films are prepared by spin- and dip-coating but these materials lack the desired porosity for sensing, separations and catalysis applications. Electrochemical deposition was proposed to improve the porosity of silicate films. The main aims of this work were threefold. First we wanted to elucidate what parameters influenced film formation during electrodeposition. Then we wanted to understand how these parameters affected the morphology of the materials prepared. These films were characterized by profilometry, AFM, and SEM-EDX. Films electrodeposited via cathodic potentials are particle-like, thicker and rougher than spin-coated films. The final goal was to pattern a substrate with silica using photolithography, sol-gel process and electrodeposition. Successful patterning was hindered by the deposition of silica on glass, especially when the gap between ITO bands was smaller than the diffusion layer thickness of the electroactive species.
29
Ness, Sola. "Photosensitivity of planar silica waveguides and bulk silica to 157-nm laser radiation." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0021/MQ45853.pdf.
Full text
30
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.
Full textAbstract:
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
31
Loucaides, Socratis. "Human impact on the silica cycle : reduction of dissolved silica inputs into the ocean as a result of the increasing impervious cover /." Electronic version (PDF), 2003. http://dl.uncw.edu/etd/2003/loucaidess/socratisloucaides.pdf.
Full text
32
Papush, Liana. "Silicon cycling in the Baltic Sea : Trends and budget of dissolved silica." Doctoral thesis, Linköpings universitet, Tema vatten i natur och samhälle, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-70071.
Full textAbstract:
The dissolved silicon (DSi) has a crucial role for growth of a large group of primary producers – diatoms and, hence, impact on functioning of the aquatic food web. This thesis contributes to an increased understanding of the modifications of the DSi cycling in the Baltic Sea. The results provide new information about spatial and temporal changes in DSi concentrations and nutrient ratios for the period 1970-2001 as well as during the 20th century. For the period 1970-2001, the declining DSi trends were found at the majority of monitoring stations all over the Baltic Sea. This decrease is assumed to be mainly due to the ongoing eutrophication. It is supported by the increasing trends of inorganic nitrogen and phosphorus. The trends have implications for the nutrient ratios, DSi:DIN and DSi:DIP, which are important indicators of the state of an ecosystem. The long-term retrospective DSi budget has shown that the DSi concentrations before major hydrological alterations and eutrophication were about twice the present ones. This decrease is related to both eutrophication and anthropogenic perturbations in the catchment. The occurrence of DSi concentrations close to the potentially limiting levels has been also analysed. While DSi concentrations are still high in the northern regions of the Baltic, other areas may be at risk of developing Si limitation if the decrease in DSi concentrations persists. The results depict the Baltic Sea journey from being water body with DSi levels sufficient to support diatom production to one that may experience Si limitation and its adverse ecological consequences.Löst kisel (DSi) har en viktig roll för tillväxten av en stor grupp av primärproducenter – kiselalger, och därmed även påverkar hela den akvatiska näringskedjan. Denna avhandling bidrar till en ökad förståelse av förändringarna i DSi kretsloppet i Östersjön. Resultaten tillhandahåller ny information om rumsliga och tidsmässiga förändringar i DSi koncentrationer såväl för perioden 1970-2001 som för hela 1900-talet. För perioden 1970-2001 återfanns minskade DSi koncentrationer på mätstationer över hela Östersjön. Minskningen antas främst bero på den pågående övergödningen. Detta antagande stöds av stigande halter av oorganiskt kväve och fosfor. Sammantaget har dessa trender en inverkan på ekosystemets tillstånd och näringsämnenas kvoter, DSi: DIN och DSi: DIP. Ur ett längre tidsperspektiv kan man se att innan övergödningen och de stora hydrologiska ombildningar i Östersjöområdet var DSi koncentrationerna ungefär dubbelt så höga som idag. Dagens förekomst av DSi koncentrationer som ligger nära de potentiellt begränsande nivåerna har också analyserats. DSi koncentrationerna är fortfarande höga i norra delar av Östersjön, men är i andra områden i riskzonen för att utveckla Si begränsning om minskningen av DSi koncentrationer fortsätter. Resultaten skildrar Östersjöns resa från att vara ett havsområde med DSi halter som är tillräckliga för att understödja kiselalgernas produktion till ett sådant som kan uppleva Si begränsning och dess negativa ekologiska konsekvenser.
33
Jin, Zhe Electrical Engineering & Telecommuncations UNSW. "Silica-on-silicon lightwave circuits based on multimode interference for optical communications." Awarded by:University of New South Wales. Electrical Engineering and Telecommuncations, 2006. http://handle.unsw.edu.au/1959.4/23993.
Full textAbstract:
The thesis focuses the design and fabrication of silica-on-silicon multimode interference (MMI) devices for optical communications. Firstly, the relationship between different kinds of multimode interference was established for the first time. This gives a clearer understanding of the multimode interference and helps to design better performance optical MMI devices With the consideration of weak lateral light confinement, different kinds of novel approaches to designing high performance MMI devices are developed. The first new approach is for optimization of silica-on-silicon MMI couplers. It is shown that the length of the multimode section can be varied in a well-defined range to find optimal device performance. The range is linked to the propagation constant spacing of fundamental and higher order modes of the multimode waveguide. The second approach is to introduce a new criterion for designing a MMI coupler with central input. According to overlapping interference analysis, one image space should be left for the adjacent output waveguides because of the lateral distribution of alternatively vanishing and non-vanishing images. This consideration is neglected in previous work and is shown to be important for achieving good uniformity MMI power splitters. Thirdly, a new design of silica-on-silicon multimode interference (MMI) device is proposed. Deeply etched air trenches define the boundaries of the multimode section to achieve strong lateral confinement, resulting in lower loss and imbalance. The access waveguides, however, are buried channel and square core, giving low fibre insertion loss and low polarization dependence. The novel design balanced requirement of the strong lateral confinement of the field in the multimode waveguides and the matching between the fiber and the access waveguides. Then a new approach of designing silica-on-silicon optical switches based on cascaded MMI couplers is presented. The approach combines the transfer matrix method, optimisation of the MMI dimensions, and mode propagation analysis (MPA) for calculation of phase shifts. The feasibility of the large port count switches is also discussed. It is shown that the good performance devices can be realized with a large port count of 32. Finally MMI couplers based on silica-on-silicon optical waveguides were fabricated. The Ge-doped silica waveguides were fabricated by HC-PECVD and RIE. Fabrication processes such as thin film deposition and etching are discussed. Good performance devices have been realized.
34
Anderson, Susan Ita. "The effect of silicon, silica and silicates on the osteoblast in vitro." Thesis, University of Nottingham, 2001. http://eprints.nottingham.ac.uk/13541/.
Full textAbstract:
Silica is an essential trace element in human nutrition and dietary deficiency leads to abnormal bone formation in experimental animal studies (Carlisle, 1972, Schwartz 1972). Silica-containing glasses and glass ceramics, within a certain range, are bioactive, forming a strong bond with bone and soft tissue when they are used as bone replacement materials. The aim of this work was to investigate the effect of silica on the osteoblast in vitro with a view to its eventual incorporation into biomaterials to improve bone-bonding properties. Two distinct approaches were used. The first involved the analysis of silica as a nutrient, by supplementing osteoblast growth medium with sodium metasilicate, and evaluating the osteoblast response in terms of cell growth, mineralisation and cytotoxicity. The second approach examined the response of osteoblasts to silica as a biomaterial. A silica gel was used to isolate the effects of silica on the osteoblast in vitro without the effects of the other ions present in bioactive glass. The biocompatibility of patterned silicon wafers was investigated to evaluate the potential use of these materials in the field of biomaterials. Finally, the bioactivity and osteoblast response to a novel silicon/polymer composites as assesseda s a potential biomaterial. The results of nutrition studies showed that in some cases low levels (1-100ppm) of silicate appeared to have a beneficial effect on bone formation in terms of nodule formation and mineralisation. Higher levels of silicate supplementation (>300ppm) caused rapid apoptosis in osteoblasts, fibroblasts and macrophages and affected cell spreading. The biomaterial studies showed that the silica gel surface was bioactive and osteoblasts responded favourably demonstrating enhanced, earlier nodule formation. Bioactive surfaces formed a calcium phosphate (CaPi) layer and released silicic acid when incubated in a simulated body fluid (SBF). Bulk silicon wafers (Si) supported osteoblast growth however, the removal of the oxide layer by wet etching (ESi) imparted bioactive properties to the wafer. Patterned Si/Esi surfaces supported the formation of a CaPi layer over the entire surface and demonstrated osteoblast preferences for bioactive surfaces. The incorporation of silica particles into a bioabsorbable polymer matrix rendered the composite bioactive and supported osteoblast growth. The results of this work demonstrate the importance of silica in bone mineralisation, osteoblast apoptosis and particularly the potential benefits of the use of silica and silicon to improve bone bonding in non-bioactive biomaterials and biosensors.
35
Martinez, Nelson. "Wettability of Silicon, Silicon Dioxide, and Organosilicate Glass." Thesis, University of North Texas, 2009. https://digital.library.unt.edu/ark:/67531/metadc12161/.
Full textAbstract:
Wetting of a substance has been widely investigated since it has many applications to many different fields. Wetting principles can be applied to better select cleans for front end of line (FEOL) and back end of line (BEOL) cleaning processes. These principles can also be used to help determine processes that best repel water from a semiconductor device. It is known that the value of the dielectric constant in an insulator increases when water is absorbed. These contact angle experiments will determine which processes can eliminate water absorption. Wetting is measured by the contact angle between a solid and a liquid. It is known that roughness plays a crucial role on the wetting of a substance. Different surface groups also affect the wetting of a surface. In this work, it was investigated how wetting was affected by different solid surfaces with different chemistries and different roughness. Four different materials were used: silicon; thermally grown silicon dioxide on silicon; chemically vapor deposited (CVD) silicon dioxide on silicon made from tetraethyl orthosilicate (TEOS); and organosilicate glass (OSG) on silicon. The contact angle of each of the samples was measured using a goniometer. The roughness of the samples was measured by atomic force microscopy (AFM). The chemistry of each of the samples were characterized by using X-ray photoelectron spectroscopy (XPS) and grazing angle total attenuated total reflection Fourier transform infrared spectroscopy (FTIR/GATR). Also, the contact angle was measured at the micro scale by using an environmental scanning electron microscope (ESEM).
36
Shehata, Medhat H. "The effects of fly ash and silica fume on alkali-silica reaction in concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58597.pdf.
Full text
37
Tasca, Andrea Luca. "Novel amorphous silica and silica xerogels for the adsorption of organic pollutants from water." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28804.
Full text
38
Moskowitz, Steven. "Atomic force miscroscopy [sic] study of SiO₂/Si(111)--(7x7) grown via atomic oxygen plasma /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/11556.
Full text
39
Chou, Berryinne. "Nano-Scale Modified Inorganic/Organic Hybrid Materials as Proton Conductors." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1144419661.
Full text
40
Watchman, Alan Leslie, and n/a. "Properties and dating of silica skins associated with rock art." University of Canberra. Applied Science, 1996. http://erl.canberra.edu.au./public/adt-AUC20061110.104443.
Full textAbstract:
Hydrated amorphous silicon dioxide (Si02.nH-,O), or opal-A, is deposited naturally
from seepage and runoff water as white or brown rock surface coatings, called 'skins',
that often partly obscure rock paintings and engravings, but occasionally, a thin
translucent silica skin can form a protective film over rock art. White lustrous silica
skins, less than 1 mm thick, occur where seepage water regularly flows from bedding
and joint planes, whereas much thinner brown skins form on the sides of boulders and
cliffs where runoff water periodically flows. To find the degree of silica skin variability
and to determine how climate and rock type affect the properties of silica skins I
collected samples at seven Australian and two Canadian rock painting sites that were
located in temperate, tropical and sub-arctic regions. The skins had developed on
sandstone, quartzite, schist, gneiss and migmatite. I studied the effects of the skins on
rock art stability, documented their compositions, textures and structures to establish
their common properties, and searched for a way to date the silica which would provide
an indication of the minimum age of the underlying art. 1 also made replication
experiments to determine factors that influence the properties of artificial silica skins
and the rates of their precipitation so that I could propose a mechanism for natural silica
skin formation, and ascertain whether an artificial silica skin could act as a protective
rock art conservation measure.
I was able to subdivide the analysed samples into silica skin Types I, II and III on the
basis of their colour (translucent, white or brown), composition (SiO2, Al2O3 and
absorbed water contents) and texture (smooth vitreous or vermiform). I propose that
silica skins initially begin to form on stable rock surfaces by a process involving a
combination of evaporation- and ionic-induced polymerisation of silicic acid in seepage
and runoff water. Condensation reactions, random clustering of small silica spheres
and deposition of the resulting aggregates eventually produce a thin surficial silica film.
Deposition of silica often traps micro-organisms that live in the damp seepage and
runoff water zones, and these fossils in finely laminated skins enable the radiocarbon
dating of silica deposition, and therefore the dating of rock paintings enclosed by silica.
Micro-excavation of silica layers associated with rock art combined with accelerator
mass spectrometry gave preliminary radiocarbon determinations that were either
consistent with, or contradicted, prevailing opinions about the antiquity of the rock art
at selected sites. Experiments using a laser technique for combusting fossilised microorganisms
in finely laminated skins were unable to generate sufficient carbon for
dating. Catalysis of a mixture of equal proportions of methyl-trimethoxy silane and
water produces a translucent stable film that may be suitable as a consolidant, whereas
other artificial silica skins made from silica glass and tetra-ethoxy silane develop microfractures
on drying, and these are unsuitable as rock art consolidants.
41
Basnig, Deomila. "Élaboration de films minces de silice pour des applications en chimie analytique." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0102.
Full textAbstract:
Un film orienté à base de silice mésoporeuse sur une électrode FTO a été préparé par une approche d'auto-assemblage assistée par électrochimie (EASA). Un potentiel de -1,5 V a été appliqué à l'électrode FTO contenant un précurseur de silice préhydrolysée (par exemple, l'orthosilicate de tétraéthyle), en présence d'un modèle (par exemple, le bromure de cétrimonium) et d'un électrolyte. Cette approche permet de générer des nanocanaux de silice alignés verticalement avec des tailles de pores ajustables entre 2 et 3 nm, selon le modèle. Ce travail a montré le comportement voltammétrique et la sélectivité du film de silice mésoporeuse vis-à-vis de divers cations chargés positivement de nature, de taille et de charge différentes. Les résultats ont montré une accumulation et une sélectivité favorisant l'ion le moins chargé positivement : MB⁺ > PQ²⁺ > DQ²⁺ > Ru(bpy)₃²⁺ > Ru(NH₃)₆³⁺. L'augmentation des signaux voltamétriques par rapport à l'électrode FTO nue dépendait fortement du type de sonde. L'accumulation des différentes sondes redox est attribuée à l'orientation verticale du nanocanal qui favorise le transport rapide et la diffusion à la surface de l'électrode. Une caractérisation électrochimique plus poussée a montré une interaction entre le processus contrôlé par la surface et le processus contrôlé par la diffusion, où les espèces adsorbées sont plus importantes dans les milieux dilués. Les résultats ont montré que la modification de la longueur debye et du rayon électrocinétique du nanocanal de silice en raison de la force ionique ou du diamètre du nanocanal affecte également le transport et la détection électrochimique de l'analyte paraquat. Les films de silice mésoporeuse ayant des tailles de pores différentes, préparés en utilisant différents bromure d'alkylammonium comme modèle, donnent des sensibilités différentes, qui pourraient être dues à la différence de charge électrochimique de la surface de la silice, ainsi qu'à la distribution des ions dans le nanocanal. Enfin, une tentative de modification de la surface de la paroi de silice en utilisant de la zircone a également été faite pour étudier le transport des cations, ce qui pourrait ouvrir la voie à une meilleure stabilité du film mésoporeuxOriented mesoporous silica-based film on FTO electrode was prepared via electrochemically-assisted self-assembly approach (EASA). A potential of -1.5V was applied to the FTO electrode containing a prehydrolyzed silica precursor, (e.g. tetraethyl orthosilicate), in the presence of a template (e.g. cetrimonium bromide) and electrolyte. This approach could generate vertically-aligned silica nanochannels with pore sizes adjustable between 2 and 3 nm, depending on the template. This work showed the voltammetric behavior and the selectivity of the mesoporous silica film towards various positively-charged cations of different nature, size, and charge. Results showed an accumulation and selectivity favoring the least positive charged ion: MB⁺ > PQ²⁺ > DQ²⁺ > Ru(bpy)₃²⁺ > Ru(NH₃)₆³⁺. The enhancement of the voltammetric signals relative to the bare FTO electrode was strongly dependent on the probe type. The accumulation of the different redox probe is attributed to the due to the vertical orientation of the nanochannel favoring fast transport and diffusion unto the electrode surface. Further electrochemical characterization showed an interplay of the suface-controlled and diffusion-controlled process, wherein adsorbed species is more prominent in diluted media. Results showed that changing the debye length and electrokinetic radius of the silica nanochannel due to the ionic strength or nanochannel diameter also affects the transport and electrochemical detection of the paraquat analyte. Mesoporous silica films having different pore size, prepared using different alkyl ammonium bromide as template, yield different sensitivities, which could be due to the difference in electrochemical charge of the silica surface, as well as the distribution of ions in the nanochannel. Finally, an attempt to modify the surface of silica wall using zirconia was also made to study the transport of cations, which could pave a way for an improved stability of the mesoporous film
42
McFarlan, Andrew J. "Infrared studies of silica surfaces." Thesis, University of Ottawa (Canada), 1991. http://hdl.handle.net/10393/7852.
Full textAbstract:
The silanol distributions on "as received" aerosil and precipitated silica have been studied (1) by using time-resolved infrared spectroscopy in order to follow a reaction with AlMe$\sb3$, TiCl$\sb4$, or BCl$\sb3$, (2) by spectroscopically comparing the accessibility of probe molecules having different steric dimensions, that react with surface silanols (SiOH) either by chemisorption or H/D exchange, and (3) by gravimetrically measuring surface silanol densities using vacuum microbalance techniques. The results have been used to compare and characterize these non-porous silicas of similar surface area. Initially, H-bonded silanols are relatively more reactive than isolated silanols in the order of reagents, BCl$\sb3$ $>$ TiCl$\sb4$ $>$ AlMe$\sb3$. In the fully hydroxylated "as received" state, the number of silanol groups on either silica which react with various hydrogen sequestering (HS) agents decreases as the size of the agent increases (ZnMe$\sb2$, BCl$\sb3$, TiCl$\sb4$, AlMe$\sb3$ and Me$\sb3$SiNHSiMe$\sb3$ (HMDS) in increasing size). The number of silanols that undergo H/D exchange also decreases as the size of the probe molecule increases (D$\sb2$O, ND$\sb3$, and deuterated methanol, i-propanol and t-butanol). The reaction between HMDS and H-bonded silanols occurs preferentially with the terminal silanols of a chain, and we propose that these silanols occupy sites which are inherently more accessible to this bulky reactant. By following the evolution of the SiOH bands on both silicas in all three spectral regions for 450, 600, and 800$\sp\circ$C activation, we have assigned bands to two types of isolated silanols. The type I silanols are preferentially eliminated between 450 and 800$\sp\circ$C activation and are more abundant on precipitated silica than on aerosil. Type II silanols (isolated single silanols) dominate the surface of highly activated aerosil or precipitated silica. The vibrational spectra are reported for the physically adsorbed complexes, SiOH...X (X = CO, N$\sb2$, and CH$\sb4$) and the nature of their specific interaction with surface SiOH is discussed. Mechanisms are proposed for the room-temperature reaction between SiOH and TMP to produce DMP, and the SiOH catalyzed isomerization of TMP to DMMP. (Abstract shortened by UMI.)
43
Kotrc, Benjamin. "Evolution of Silica Biomineralizing Plankton." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10969.
Full textAbstract:
The post-Paleozoic history of the silica cycle involves just two groups of marine plankton, radiolarians and diatoms. I apply paleobiological methods to better understand the Cenozoic evolution of both groups. The Cenozoic rise in diatom diversity has long been related to a concurrent decline in radiolarian test silicification. I address evolutionary questions on both sides of this coevolutionary coin: Was the taxonomic diversification of diatoms accompanied by morphological diversification? Is our view of morphological diatom diversification affected by sampling biases? What evolutionary mechanisms underlie the macroevolutionary decline in radiolarian silicification? Conventionally, diatom diversification describes a steep, monotonic rise, a view recently questioned due to sampling bias. For a different perspective, I constructed a diatom morphospace based on discrete characters, populated through time using an occurrence-level database. Distances between taxa in morphospace and on a molecular phylogeny are not strongly correlated, suggesting that morphospace was explored early in their evolutionary history, followed by relative stasis. I quantified morphospace occupancy through time using several disparity metrics. Metrics describing average separation of taxa show stasis, while metrics describing occupied volume show an increase with time. Disparity metrics are also subject to sampling biases. Under subsampling, I find that disparity metrics show varied responses: metrics describing separation of taxa into morphospace are unaffected, while those describing occupied volume lose their clear increases. Disparity can have geographic components, analogous to \(\alpha\) and \(\beta\) taxonomic diversity; I find more evidence of stasis in an analysis of \(\bar{\alpha}\) disparity. Overall, these results suggest stasis in Cenozoic diatom disparity. The radiolarian decline in silicification could result from either macroevolutionary processes operating above the species level (punctuated queilibria) or anagenetic changes within lineages. I measured silicification in three phyletic lineages, Stichocorys, Didymocyrtis, and Centrobotrys, from four tropical Pacific DSDP sites. Likelihood-based model fitting finds no strong support for directional evolution, pointing toward selection among species, rather than within species. Each lineage shows a different trajectory, perhaps due to differences in the ecological role played by the test. Because Stichocorys shows close correspondence to the assemblage-level trend, abundance may be an important factor through which within-lineage changes can influence the macroevolutionary pattern.Earth and Planetary Sciences
44
Utting, Katherine Alice. "Silica supported mild base catalysts." Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423602.
Full text
45
Jugdaohsingh, Ravin. "Soluble silica and aluminium bioavailability." Thesis, King's College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312026.
Full text
46
Corradi, Roberto. "Conducting polymer-silica colloidal composites." Thesis, University of Sussex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263866.
Full text
47
Scoble, Josephine Margaret. "Diversity of silica-scaled protists." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:7bc73ed7-418b-49de-963b-81407a7c3a49.
Full textAbstract:
This thesis investigates the diversity of two silica-scaled protist groups, Paraphysomonadida and Thaumatomonadida by light and electron microscopical observations and sequencing (rDNA) on novel clonal cultures. Despite these groups of protist dominating pelagic, littoral as well as inland freshwater and soil habitats, they are taxonomically poorly understood to the extent that any progress in ecological theory is hampered. Now that environmental DNA sequencing is being carried out faster than we can characterise protists from culture it is important that we understand how molecular and physical diversity match up, especially because so many protists are morphospecies. Nearly one hundred isolates were cultured on which both morphological and molecular data was carried out in parallel to reveal around 50 new species of protist from eight different genera: two heterokont genera, Paraphysomonas and Incisomonas n. gen., and six cercozoan genera, Thaumatomonas, Allas, Reckertia, Thaumatospina n. gen., Cowlomonas n. gen., and Scutellomonas n. gen. These data make major contributions to taxonomy and understanding aspects of protist diversity where previously morphological diversity was heavily biased towards over- generalized morphotypes. This thesis quickly showed that gross lumping of morphospecies was true of Paraphysomonas, for which many of the isolates cultured herein might have been regarded as one species (not more than 20). The many cultured isolates exhibited varied cell and scale morphology, and by sequencing (rDNA), it was possible to see the evolution of scale morphology map on to trees. This marriage of molecular and morphological data made it possible to view distinct groups of species that shared scale detail that might have otherwise been overlooked had either method been used alone. This research has shed significant light on how scale morphology can be used as reliable taxonomic marker for protists, the insights of which can be applied to make taxonomic improvements to other silica-scaled protist groups.
48
van, den Heuvel Daniela Brigitte. "Precipitation pathways of amorphous silica." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/13428/.
Full textAbstract:
Amorphous silica is one of the most common phases to precipitate from geothermal fluids. It precipitates by self-assembly of monomeric silica (H4SiO4) via heterogeneous and homogeneous nucleation and subsequent growth of nuclei by addition of dissolved silica. The mechanism and the factors controlling the individual steps of silica precipitation have been studied in numerous laboratory experiments over the last decades and are, despite their complexity, well understood. However, due to the higher complexity of natural geothermal fluids (e.g high fluid flow rates, microbial activity or complex fluid chemistries), these findings cannot be directly applied to the study of silica scaling inside geothermal power plants and silica sinters around hot springs. In the first part of this thesis we present the results from the first ever time-resolved study of silica precipitation inside in-use geothermal pipelines. Silica scales formed primarily via heterogeneous nucleation on steel surfaces, resulting in a silica layer rapidly covering these surfaces. This pathway of silica deposition was controlled by surface roughness, total silica concentration and temperature and allowed the deposition of up to 1 g of silica per day and m2. Homogeneous nucleation also occurred and lead to the formation of silica microspheres which were deposited preferentially into depressions and along edges or were aggregated to fan- and ridge-shaped structures growing towards the flow, depending on the fluid flow regime. While the 3D structures could result in more turbulent flow, decreasing the flow rate, the formation of the silica layer could potentially even be beneficial for the operation of a geothermal power plant as it passivates the surface against corrosion. For the second part of this thesis, we studied the interaction of a silica solution with a protein (=lysozyme), during which hybrid composites were formed. By investigating these final products in detail, we determined that, depending on the timing of the silica-lysozyme interactions (during or after silica polymerisation) and the ratio of silica-to-protein, the resulting composites showed different structures and surface properties. This is of interest for biomineralisation as it elucidates how biomolecules interact with dissolved silica and how microorganisms can control this process.
49
Ertas, Hasan. "Ageing of silica in HPLC." Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/33118.
Full textAbstract:
This study may be divided into two sections which cover different aspects of the reproducibility problems encountered in HPLC. In the first, the study has involved the separation of basic drugs, on different manufacturer's reversed-phase columns in conjunction with an acid buffered acetonitrile/water gradient. The retention reproducibility of each drug was assessed and compared on the basis of the retention index scale of 1-nitroalkanes. The effect of changing gradient run time on the reproducibility of the retention values of the 1-nitroalkanes was demonstrated on reversed-phases of different makers. The optimisation of initial isocratic composition of organic (acetonitrile) was carried out and its effect on the reproducibility of retention of basic drugs was evaluated. The effect of a premixed eluent on the retention reproducibility of selected basic drugs with time intervals between injections was demonstrated. The same method was further extended with or without using helium gas with small flow. The prediction of dwell volume and its effect on retention reproducibility was evaluated. Determination of retention times changes for selected aqueous basic solutes against eluent with different pH values on Capcell ODS column was studied. Applicability of each reversed-phases (Cl8) for the separation of basic analytes was demonstrated. In the second section, a number of different unbonded (bare) silicas were studied in terms of surface analysis using of solid state cross-polarisation (CP) magic angle spinning (MAS) NMR and Fourier Transform (FT) Diffuse Reflectance Infrared Spectra (DRIFT-IR) data. It is believed that silica material used for HPLC separation with eluent undergoes an ageing process with acidic (at pH:2–3) and basic eluents (higher than pH:8). To examine this process more clearly, some basic analytes were selected to evaluate each of the accelerated ageing process followed by showing the final surface properties by the method most commonly used such as solid-state NMR and FT-IR along with BET surface analyser.
50
Ranjan, Rajesh. "Surface Modification of Silica Nanoparticles." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1206558086.
Full text