This thesis is concerned with the preparation of mixed silicon-titanium oxides (Ti02=4.1-21.9wt%) and silicon-zirconium oxides (Zr02=4.1-22.Iwt%) by the sol-gel route. Methods of preparing homogeneous Si02-TiO2 gels and SiO2-Zr02 gels have been explored. In this work bis(acetylacetonato)titanium diisopropoxide or bis(acetylacetonato)zirconium dipropoxide and tetraethyl orthosilicate (TEOS) have been hydrolysed simultaneously in iso-propanol to form homogeneous gels. Using these systems, the effects of the reaction conditions, amount of titania/zirconia present in the gel, drying conditions and thermal treatment of the dry gels on the bulk and structural properties have been investigated by a variety of experimental methods including X-ray diffraction, mid- and near-infrared spectroscopy and gas adsorption techniques. For SiO2-TiO2 powders and monoliths, and SiO2-ZrO3 monoliths, thermal treatment has been found to significantly reduce the surface area (from 750-1.0m2g-1), pore volume (from 0.56-0.001cm3g-1') and relative number of silanol groups on the surface of the sample above 700°C. Average pore diameters remain constant at temperatures below 900°C (ca 54-21Å for monoliths), although the micropore volume does decrease (0.04-0.0cm3g-1) suggesting that smaller pores are destroyed by the heating process. For SiO2-TiO2 powders, the average pore diameter was ca IOÅ larger than for the corresponding monolith suggesting that small pores are destroyed during powdering. At 1100°C, gas adsorption data indicate that the samples are fully densified. This is supported by NIR spectra which detect no silanol groups on the surface of the sample. Structural changes arising from compositional changes and differing thermal treatment regimes have been monitored using mid-infrared spectroscopy and X-ray diffraction. With increasing temperature the silica matrix strengthens and titanium/zirconium are incorporated into the matrix. Monolithic SiO2-TiO2 gels (Ti02=6.34 weight%) remained amorphous at 1100°C, whereas powders began to exhibit diffraction patterns predominantly from anatase at 700°C. Anatase crystallite sizes have been calculated using the Scherrer equation and have been found to be between 16.3 and 5.4nm. Monolithic SiO2-ZrO2 gels containing 4.1 and 4.9 weight% zirconia were found to be amorphous after treatment at 1100°C. Increasing the zirconia content to 6.4 and 22.1 weight% resulted in gels that were amorphous up to 900°C. Further treatment at 1100°C, resulted in tetragonal zirconia and some cristobalite being formed. Crystallite sizes have been calculated as being between 2.7 and 1.6nm for tetragonal zirconia and from 4.1 to 2.8nm for cristobalite. Increasing the levels of titania/zirconia in the sample resulted in higher relative levels of hydrogen-bonded silanol groups. On hydration, the increased levels of titania/zirconia resulted in no observable free silanol groups on the surface suggesting that the surface becomes more hydrophilic as the amount of titania/zirconia present in the sample increases. This suggests that water becomes more tightly bound to Ti-OH /Zr-OH groups on the surface and within the pores, resulting in fewer free silanol type groups. A double alkoxide bis(acetylacetonato)titanium di(triethoxysilane) [Ti(acac)2(OSi(OC2H5)3)2] has also been synthesised and characterised. Mixed Si02-TiO2 gels have also been prepared by the simultaneous hydrolysis of Ti(acac)2(OSi(OC2H5)3)2 and TEOS under acidic conditions in ethanol. The effects of reaction conditions and thermal treatment of the dry gels have been investigated. Increasing the treatment temperature of the samples resulted in the progressive decrease in surface area (533-3.0m2g-1), pore volume (0.18-0.003cm3g-1), micropore volume (0.06-0.00cm3g-1) and relative number of silanol groups on the surface. However, the average pore diameter remained constant at temperatures up to 700°C. Changes in pore volume (0.07-0.005cm3g-1), surface area (300-3.0m2g-1) and average pore diameter (26.9-91.9Å) were largest at 900°C, and the samples were found to be almost completely dense. This was confirmed by the absence of observable silanol groups by NIR spectroscopy. After heating at temperatures up to 900°C, the samples were found to be amorphous by XRD. However increasing the temperature to 1100°C resulted in the formation of some crystalline anatase. The anatase crystal sizes have been calculated as being from 16.3 to 10.8nm in diameter. NIR studies of silica-zirconia and silica-titania gels (prepared by both methods), indicate that decreasing the amount of acid used in the hydrolysis reaction resulted in higher relative levels of hydrogen bonded silanol species. Similarly, decreasing the amount of acid increased the micropore volume and decreased the mesoporosity of the resulting samples. Generally, decreasing the amount of acid used for the hydrolysis for silica-zirconia and silica-titania gels (prepared by both methods), results in a decrease in the overall surface area and pore volume of the resulting material. The resulting isotherms indicate that the samples became less mesoporous as the amount of acid used in the hydrolysis reaction decreased. This was accompanied by an increase in the micropore volume. For SiO2-TiO2 monoliths prepared from a double alkoxide and Si02-ZrO2 monoliths the resulting pore structure is more rigid and composed of smaller pores than that of SiO2-TiO2 powders and monoliths prepared from bis(acetylacetonato)titanium diisopropoxide.

No description available.

Neste trabalho foi desenvolvido um conjunto de ferramentas computacionais, em linguagem de programação Python, para a análise de perfis de difração de raios X, tanto para o estudo quanto para obtenção dos valores microestruturais como tamanhos médios de cristalitos e microdeformações, através de dos métodos de: Scherrer, Single-Line, Williamson-Hall e Warren-Averbach. Para aplicar os métodos de análise de perfis, foram também implementados métodos de remoção da contribuição instrumental pelo método de Stokes e ajuste de funções, remoção de ruídos pelo método de Savitzky-Golay, correção da radiação de fundo pelo método de ajuste linear, correção do fator de Lorentz-Polarização e correção do dubleto Kalfa2 . / In this work, a set of computational tools was developed, in the Python programming language, for the analysis of X-ray diffraction profiles, both for the study and for obtaining the microstructural values, as well as the mean values of crystallites and microdeformations, using Scherrer, Single-Line, Williamson-Hall and Warren-Averbach. To apply the methods of profile analysis, methods were also implemented for the removal of instrumental contributions by the Stokes method and adjustment of functions, removal by the Savitzky-Golay method, correction of the background radiation by the linear adjustment method, correction of the factor of Lorentz-Polarization and correction of dubleto Kalfa2 .

Neste trabalho foi desenvolvido um conjunto de ferramentas computacionais, em linguagem de programação Python, para a análise de perfis de difração de raios X, tanto para o estudo quanto para obtenção dos valores microestruturais como tamanhos médios de cristalitos e microdeformações, através de dos métodos de: Scherrer, Single-Line, Williamson-Hall e Warren-Averbach. Para aplicar os métodos de análise de perfis, foram também implementados métodos de remoção da contribuição instrumental pelo método de Stokes e ajuste de funções, remoção de ruídos pelo método de Savitzky-Golay, correção da radiação de fundo pelo método de ajuste linear, correção do fator de Lorentz-Polarização e correção do dubleto Kalfa2 . / In this work, a set of computational tools was developed, in the Python programming language, for the analysis of X-ray diffraction profiles, both for the study and for obtaining the microstructural values, as well as the mean values of crystallites and microdeformations, using Scherrer, Single-Line, Williamson-Hall and Warren-Averbach. To apply the methods of profile analysis, methods were also implemented for the removal of instrumental contributions by the Stokes method and adjustment of functions, removal by the Savitzky-Golay method, correction of the background radiation by the linear adjustment method, correction of the factor of Lorentz-Polarization and correction of dubleto Kalfa2 .

An improved crystallisation spectrometer has been designed, built and tested. It is to be used by others to gain new knowledge about the solidification of matter by study of the crystallisation of hard sphere colloid samples that are an established model for the behaviour of some aspects of atoms. In this crystallisation spectrometer, expanded and collimated green laser light is Bragg scattered from the colloidal crystals as they form, and the diffracted light is focused by a liquid filled hollow glass hemispherical lens onto low cost CCD array detectors that are rotated about the optical axis to average the intensities around the whole Debye-Scherrer cone of scattered light. The temperature of the sample is controlled to +/-0.1„a, and because of the ability to change the refractive index of the sample particles with temperature, this is utilised to control the amount of scattering from the sample Also, this spectrometer uniquely exploits the refractive index match of the colloidal particles, the solvent, the bath liquid, and the glass used for both the sample bottle and the hollow glass hemisphere. A unique facility has been incorporated to permit tumbling of the sample prior to the measurement commencing to shear-melt any pre-existing crystals. This ensures that the sample is completely fluid and is at the correct temperature at the start of the measurement. The instrument is assembled on an optical table and is computer controlled. Results presented show that this new spectrometer with its use of the whole Debye-Scherrer cone of Bragg scattered light and other enhancements gives insight into the crystallisation process more than one order of magnitude of time earlier than previous light scattering experiments, providing new knowledge about the crystallisation process.

Hochsch. f. Angewandte Wiss., Masterarbeit--St. Gallen, 2007.

Large amounts of money are being applied to the construction of the next generation of spallation sources for neutron scattering. Neutron powder diffraction instruments will be an important element of these facilities and the incorporation of detectors into these instruments with a high neutron capture efficiency is desirable. A new detector design named the Flexible Embedded Fiber Detector (FEFD) has been developed and tested for this thesis. This detector is based on wavelength shifting fibers embedded in a zinc-sulfide lithium-fluoride based scintillator. The virtue of this design is that the detecting surface can be curved around the Debye-Scherrer rings. This virtue is lacking in other detector designs, making them more complex and poorer in performance than our FEFD detectors. Monte Carlo calculations were performed to determine the neutron capture efficiencies of our FEFD detectors, which proved to be much higher than those of the proposed powder diffractometer design for the Spallation Neutron Source and about equal with the efficiency for the ISIS powder diffractometer design. Four FEFD detector prototypes were then fabricated and tested at the Intense Pulsed Neutron Source at Argonne National Laboratory. We find that our measured and calculated relative efficiencies are in good agreement.

Made available in DSpace on 2014-06-12T18:01:50Z (GMT). No. of bitstreams: 2 arquivo2431_1.pdf: 3903715 bytes, checksum: f4ecb374f539aa4e3d0c912da52e2836 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / No presente trabalho foram investigadas propriedades magnéticas dos nanocompósitos ferromagnéticos (Fe1−xCox)y(MnO)1−y, x = 0.4 e 0.6 e y = 0.35, 0.65 e 1, produzidos pela técnica de mecano-síntese. A caracterização estrutural e morfológica das amostras foi feita usando difração de raios x fazendo uso da equação de Scherrer, de gráficos de Williamson-Hall e refinamento Rietveld. Essas análises resultaram em valores de x e y muito próximos dos valores nominais e, dentro da resolução da técnica, não foi detectada a presença de outras fases. As amostras apresentaram valores de tamanho médio dos cristalitos muito próximos (12-14 nm) e valores reduzidos de micro-deformações (1.5% para Fe1−xCox e 0.4% para o MnO). As propriedades magnéticas foram investigadas utilizando várias técnicas de medida (SQUID, magnetometria por extração e magnetometria por amostra vibrante), medidas em um grande intervalo de temperatura T (5-700 K) e em campos magnéticos de até 2 T. A partir dessas medidas foram construídos gráficos de Henkel e curvas de inversão de primeira ordem (FORCs) à temperatura ambiente e em campos de até 1.5 T. Medidas de curvas de histerese foram utilizadas para determinar a dependência da coercividade (HC), da magnetização de saturação (MS) e do campo de exchange-bias (HEB) com T. Procedimentos de medidas de magnetização feitas resfriando a amostra a campo nulo (ZFC) e na presença de campo (FC) foram feitas no intervalo de temperatura 5-300 K para valores pequenos de campo magnético (até 5 mT). Os gráficos de Henkel e FORCs indicaram que na temperatura ambiente as interações magnéticas entre as nanopartículas de Fe1−xCox são predominantemente de origem dipolar e influenciada essencialmente pela quantidade de MnO presente nas amostras. Entretanto, no caso particular da amostra sem MnO, o gráfico de Henkel indicou uma mudança de comportamento acima de 0.25 T passando a interação de dipolar para ser predominantemente de exchange. Acima de 120 K (temperatura de Néel do MnO), as medidas de HC apresentaram um dependência com T do tipo T3/4. Este comportamento é característico de arranjos de partículas tipo Stoner-Wohlfarth orientadas aleatoriamente. Já abaixo de 120 K, HC é fortemente influenciado pela presença de MnO aumentando significativamente com a diminuição da temperatura. Similar crescimento com T foi observado nos valores de HEB o qual é visto apenas em temperaturas abaixo de 120 K. As medidas de MS apresentaram uma dependência tipo Lei de Bloch T3/2 para a amostra sem MnO em todo intervalo de temperatura (5-700 K), enquanto para as demais amostras esse comportamento foi observado para T>120 K. Abaixo dessa temperatura, a adição de MnO produz um aumento em MS. Também foi observado o efeito de exchange-bias para temperaturas inferiores à temperatura de Néel do MnO (120 K), com um significante aumento do campo de exchange-bias com a diminuição da temperatura. Por fim, observamos também um comportamento irreversível nas magnetizações ZFC e FC abaixo de 120 K nas amostras com MnO. Os resultados obtidos abaixo de 120 K foram interpretados como devidos a interações de curto alcance entre as nanopartículas e pela presença de momentos magnéticos não compensados nas interfaces entre partículas

Diploma thesis deals with the methodology of preparation of Alit – the main clinker mineral. The content of this work involves design and optimization of the methodology of preparation of pure Alit polymorphs, analysis of their properties by available analytical methods and evaluation of the change of crystallinity in the process of preparation of these polymorphs by XRD-analysis.

No description available.