Thesis (PH. D.)--University of Michigan, 1932. / eContent provider-neutral record in process. Description based on print version record.

The adsorption of two surfactants, n-octadecyltrichlorosilane and perfluorodecyl(ethyl)trichlorosilane, onto silica surfaces, was investigated by Fourier transform infrared attenuated total reflection, (FTIR-ATR), spectroscopy and by atomic force microscopy, (AFM). The rate of formation of the monolayers and the effect of surface coverage on the packing of these long-chain molecules was studied by both methods and the results compared. The silica surface was provided by the native silicon oxide layer on the surface of the silicon ATR prism for FTIR-ATR spectroscopy and by float glass substrates for AFM. Polarized radiation was used in the FTIR-ATR experiments to determine the relative dichroic ratios of cast and self-assembled films on silicon, and these results were compared with a theoretical model. The conclusion was that the cast silane layers were orientationally disordered, whilst the self-assembled layers showed a greater orientational order. In situ FTIR-ATR spectroscopy was employed to study the adsorption of these long-chain silanes at a silica-deuterated toluene interface. The silica surface was provided by the native oxide layer on a silicon ATR prism. The experiment required careful calibration in order to determine the Gibbs surface excess of these silanes on this surface. The Gibbs surface excess was calculated over a variety of silane concentrations, enabling the area occupied by the silane molecules to be calculated. The rates of formation of the monolayers were also determined and compared to the results obtained from the AFM and FTIR-ATR experiments, (not in situ). FTIR-ATR and Raman spectroscopy and microscopy were employed to investigate the interactions in silicon (or quartz)/silane/poly(vinylchloride) laminates. Specifically, (3-aminopropyl)trimethoxysilane and (3-mercaptopropyl)triethoxysilane were the silanes studied. Confocal Raman microscopy was used to discover whether interdiffusion of the silanes into the polymer overlayers had occurred, and also to determine the distribution of the silane molecules over the polymer surface. This was successfully achieved with the laminate containing the mercaptosilane.

The process of making silica aerogels has been studied in detail over the past two decades due to its usage in a wide range of low end applications such as thermal insulators, supercapacitors etc., as well as high end applications like particle physics, space explorations. These applications call for control over the properties of aerogels, such as their transparency, density, porosity, pore size, and integrity. However, despite all the past research, controlling properties of aerogels is still not a fully developed science, a lot more research needs to be done. The literature on silica aerogels does not cover the study of the relation between transparency and cracks in aerogels – which can be a key factor in making aerogels for many applications. Hence, optimization of the transparency and integrity of the aerogels in order to obtain high transparency and low cracks was attempted in this thesis.

No description available.

One of the most significant problems faced in the geothermal power industry is that of scaling due to amorphous silica. The silica can deposit out of super-saturated brine in monomeric form and as colloidal particles. Deposition can occur at problematic rates on pipe surfaces and in the rocks of the re-injection wells. Currently there are a number of methods for controlling deposition but the fundamental mechanisms that govern the transport and attachment of silica are not well understood. Many field experiments on silica scaling have been conducted but, due to differences in brine chemistry and operational conditions, the results are hard to compare. Many laboratory experiments have also been performed but these are difficult to correlate with the field experiments. Previous research has found that hydrodynamics are important for the deposition of colloidal particles and inertial impaction was proposed to be the dominant transport mechanism. These results were analysed and, in contradiction, the dominant transport mechanism of the particles was theoretically expected to be that of diffusion. A series of experiments were planned that could test the effect of hydrodynamics on colloidal silica deposition in cylindrical pipe flow. Three parameters were to be varied in the experiment: particle size (10nm and 100nm), Reynolds number (750 - 23,600) and viscous boundary layer thickness (0.06 - 0.38mm). To perform this experimentation, a Silica Scaling Test Rig was designed, built and commissioned. A method for producing synthetic brine was developed which can provide sols that are stable for at least one month and have a particle size of 10-20nm. Silica deposition has successfully been obtained in three preliminary experiments using the rig. Without the exclusion of air from the rig significant corrosion occurs in the mild steel test piece. Protrusions that were likely to be silica deposits were found to be co-located with the corrosion, suggesting that one process promotes the other. Neither deposition nor corrosion was found on the pipe’s weld seam and heat affected zone. Corrosion was prevented using an oxygen exclusion system and two amorphous silica deposition structures were observed: a flat plate-like structure and a globular structure that consisted of 1-5μm diameter globules that built up on each other. Other field and laboratory experiments have produced globular structures similar to those found in this research. To perform the planned experimentation, future work is required: the silica deposition rate must be increased, colloidal silica sol stability must be improved, and some modifications must be made to the rig.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2009. / Made available in DSpace on 2012-10-24T21:43:06Z (GMT). No. of bitstreams: 1 266490.pdf: 3362494 bytes, checksum: 6f0e40dce0871c4b18b495a44d1a3e28 (MD5) / O presente trabalho tem por objetivo desenvolver uma rota de obtenção de dióxido de silício a partir das cascas de arroz, realizando um pré-tratamento com água régia, solução piranha e pirólise em mufla a 600°C por 4 horas. Com estes procedimentos buscou-se um grau de pureza acima dos 99%, adequado ao uso do material na síntese de uma matriz microporosa que servirá ao desenvolvimento de dispositivos eletrônicos futuramente. Realizou-se, em cada etapa de separação da sílica, análise termogravimétrica, calorimetria diferencial de varredura, espectroscopia de infravermelho com transformada de Fourier, fluorescência e difração de raios X, com o objetivo de conhecer as etapas de separação da matéria orgânica e as mudanças de composição e estrutura ocorridas no pré-tratamento e na pirólise final em mufla. Com o dióxido de silício obtido a partir das cascas de arroz foram sintetizados géis dentro do processo Sol-Gel, com a solubilização alcalina, a precipitação ácida, a moldagem, a gelificação, o crescimento do gel e a secagem para obter o xerogel. Foi verificado que os xerogéis produzidos, ao secarem, apresentaram fraturas causadas por pressões capilares geradas na microporosidade que impossibilitou a preservação do volume inicial, elemento fundamental no projeto de dispositivos eletrônicos. É apresentada uma via para evitar a degradação do volume das amostras, através da secagem supercrítica, utilizando dióxido de carbono na substituição da fase líquida. Isto atenuaria as pressões capilares no ato de remoção dos solventes dispersos, eliminando as correntes de fuga e permitindo a construção dos dispositivos.

Thesis (Ph. D. in Physics)--Vanderbilt University, 2003. / Title from PDF title screen. Includes bibliographical references.

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No description available.

A new hydrophobic hybrid silica film was synthesized by introducing one silicon precursor (as modifiers) into another precursor (network former). Hybrid films have improved properties. Hydrolysis and condensation of dimethyldiethoxysilane (DMDES) (solvent (EtOH) to DMDES molar ratio R = 4, water to DMDES molar ratio r = 4, 0.01 N HCl catalyst) was analyzed using high-resolution liquid 29Si NMR. It was found that after several hours, DMDES hydrolyzed and condensed into linear and cyclic species. Films from triethoxyfluorosilane (TEFS) have been shown to be promising interlayer dielectric materials for future integrated circuit applications due to their low dielectric constant and high mechanical properties (i.e., Young's modulus (E) and hardness (H)). Co-condensing with TEFS, linear structures from DMDES hydrolysis and condensation reactions rendered hybrid films hydrophobic, and cyclic structures induced the formation of pores. Hydrophobicity characterized by contact angle, thermal stability by thermogravimetric analysis (TGA), Fourier transform Infrared spectroscopy (FTIR), contact angle, and dynamic secondary ion mass spectroscopy (DSIMS), dielectric constant determined by impedance measurement, and mechanical properties (E and H) determined by nanoindentation of TEFS and TEFS + DMDES films were compared to study the effect of DMDES on the TEFS structure. Hybrid films were more hydrophobic and thermally stable. DMDES incorporation affected the dielectric constant, but showed little enhancement of mechanical properties.