Submitted by Marcelo Marques da Silva null (marcelomarques657@yahoo.com.br) on 2017-08-31T02:34:55Z No. of bitstreams: 1 Tese_versão_FINAL.pdf: 3504812 bytes, checksum: d5cea839c787579376ad107a79a48213 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-09-01T13:28:41Z (GMT) No. of bitstreams: 1 silva_mm_dr_bauru.pdf: 3504812 bytes, checksum: d5cea839c787579376ad107a79a48213 (MD5) / Made available in DSpace on 2017-09-01T13:28:41Z (GMT). No. of bitstreams: 1 silva_mm_dr_bauru.pdf: 3504812 bytes, checksum: d5cea839c787579376ad107a79a48213 (MD5) Previous issue date: 2017-04-25 / Foi realizado um estudo sobre as propriedades elétricas de filmes finos de óxido de alumínio (Al2O3) obtidos por anodização em solução eletrolítica preparada com ácido tartárico, etileno glicol e água. Filmes de Al2O3 com espessuras entre 20 e 70 nm foram crescidos sobre camadas de alumínio as quais foram depositadas por evaporação em vácuo sobre lâminas de vidro. Utilizou-se o processo de anodização em duas etapas, sendo que na primeira etapa aplica-se uma corrente constante de 0,48 mA/cm2 e monitora a tensão até alcançar o valor final, programado conforme a espessura desejada; e então, na segunda etapa, mantem-se se a tensão final durante 2 minutos, enquanto mede-se a corrente. Os filmes de Al2O3 apresentam constante dielétrica média de aproximadamente sete (ε = 7), tan δ da ordem de 10-3 e resistividade elétrica da ordem de 1013 cm. Estudou-se o efeito do tratamento de superfície pela a deposição de monocamadas dos silanos, octadecil triclorosilano (OTS), hexametildisilazano (HMDS) e do ácido fosfônico (OPA) nas características elétricas. O tratamento com HMDS se mostrou o mais efetivo, diminuindo a corrente de fuga e aumentando campo de ruptura dielétrica. Também foi estudado o efeito do recobrimento, da superfície dos filmes de Al2O3, com filmes dos polímeros isolantes poliestireno (PS), polivinil álcool (PVA), fluoreto de polivinilideno (PVDF) e polimetilmetacrilato (PMMA). A deposição de um filme de PMMA foi a que apresentou os melhores resultados, com redução da corrente de fuga em torno de duas ordens de grandeza em relação aos filmes não tratados. Dispositivos com estrutura metal isolante e semicondutor (MIS) tendo o poli(3-hexyltiofeno) (P3HT) como semicondutor, também foram estudados com a finalidade de avaliar a aplicabilidade do Al2O3 como dielétrico em eletrônica orgânica. Conclui-se que filmes de Al2O3 preparados pela técnica de anodização com tratamento de superfície por deposição de uma monocamada de HMDS ou recoberto com um filme de PMMA é uma boa opção de dielétrico para eletrônica orgânica. / A study about electric properties of aluminum oxide (Al2O3) obtained by anodization of aluminum in a electrolytic solution prepared with tartaric acid, ethylene glycol and water was performed. Thin Al2O3 films from 20 to 70 nm were grown on aluminum layer which were deposited on glass slides by vacuum metallization. It was used the anodization process in two stages, being that in first stage applies a constant current of 0,48 mA/cm2 and monitory the voltage until reach the final value, programmed in according to the desired thickness; and in the second stage, the final voltage is maintained for two minutes, while the current is measured. The Al2O3 films present medium dielectric constant about seven (ε = 7), tan δ in order of 10-3 and resistivity in order of 1013 cm. It was studied the surface treatment effect by monolayers depositions of octadecyl trichlorosilane (OTS), hexamethyldisilazane (HMDS) and phosphonic acid (OPA) on the electrical characteristics. The HMDS treatment proved to be the most effective, reducing the leakage current and increasing the dielectric rupture field. The effect of the addition of polystyrene (PS), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF) and polymethylmethacrylate (PMMA) films on the oxide surface was also studied. The deposition of a PMMA film presented the best results, with reduction of the leakage current around two orders of magnitude in relation to pristine oxide. Devices with metal-insulator-semiconductor (MIS) structure, using the polymeric (3-hexythiophene) (P3HT) as semiconductors, also have been studied in order to evaluate the applicability of Al2O3 films as dielectric in organic electronics. It was concluded that Al2O3 films prepared by anodization, coated with a monolayer of HMDS or a thin PMMA film, are an excellent choice for apply as dielectric in organic electronics.

Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2018-05-24T17:45:39Z No. of bitstreams: 1 texto completo.pdf: 3441417 bytes, checksum: a795290bb5f3cf798dc2cf4939b636d7 (MD5) / Approved for entry into archive by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2018-05-24T17:45:53Z (GMT) No. of bitstreams: 1 texto completo.pdf: 3441417 bytes, checksum: a795290bb5f3cf798dc2cf4939b636d7 (MD5) / Approved for entry into archive by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2018-05-24T17:46:03Z (GMT) No. of bitstreams: 1 texto completo.pdf: 3441417 bytes, checksum: a795290bb5f3cf798dc2cf4939b636d7 (MD5) / Made available in DSpace on 2018-05-24T17:46:13Z (GMT). No. of bitstreams: 1 texto completo.pdf: 3441417 bytes, checksum: a795290bb5f3cf798dc2cf4939b636d7 (MD5) Previous issue date: 2017-02-23 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Na retificação de pequenas séries ou na retificação de geometrias complexas os rebolos de óxido de alumínio (Al2O3) podem ser uma alternativa competitiva em várias aplicações e apresentar um melhor desempenho, quando comparadas aos rebolos superabrasivos, no que tange a qualidade da superfície usinada para grandes taxas de remoção de material. Nesta pesquisa é avaliada a influência de rebolos de Al2O3 com diferentes composições de grãos abrasivos microcristalinos sinterizados e grãos monocristalino eletrofundidos no resultado de retificação do ADI Classe 3. São correlacionadas as variáveis de entrada com as características do processo, como as componentes de forças de retificação, do desgaste radial dos rebolos e o ruído magnético de Barkhausen (RMB), bem como pelo resultado de trabalho, como a rugosidade e a textura das superfícies retificadas. Os resultados mostraram que na retificação com os rebolos com menores porcentagens de grãos microcristalinos sinterizados são gerados as menores rugosidades e menor desgaste radial, e revelaram que para todos os rebolos convencionais ensaiados não se verificam danos de retificação (queima de retificação) com os parâmetros de entrada de processo estabelecidos. Verificou-se uma correlação das amplitudes dos sinais do RMB com os perfis de microdureza geradas pelos diferentes rebolos nas amostras de ADI Classe 3. Os resultados desta pesquisa permitem uma especificação mais adequada de rebolos convencionais para a retificação do ADI, uma vez que há poucas informações sobre a usinabilidade deste material no processo de retificação. / The grinding of low-size inventories or complex geometries with conventional sintered grinding wheels can be a competitive alternative in many applications and has a better performance in compare with superabrasive grinding wheels, regarding the machined surface quality for high material removal rates. In this research is evaluated the Al2O3 grinding wheels influence with different compositions of sintered microcrystalline and monocrystalline electrofused abrasive grains in the ADI Class 3 grinding result. The input variables are correlated with the process characteristics, such as the grinding forces components, the grinding wheels radial wear and the magnetic Barkhausen noise (MBN), as well as the work result, such as the roughness and texture of the ground surfaces. The results showed the grinding wheels with lower sintered abrasive grains percentages generated the lower roughness values and lower radial wear, and revealed that all conventional grinding wheels evaluated caused no thermal damages (grinding burns) with the established input parameters process. It was verified amplitudes MBN correlation with the microhardness profiles generated by different grinding wheels on the ADI samples. The results of this research will contribute to the most appropriate specification of conventional grinding wheels to the ADI grinding, since there is a few information available about the ADI machinability in the grinding process.

Neste trabalho foram preparados e caracterizados catalisadores de platina suportados em g-alumina (g-Al2O3), óxido de zircônio (ZrO2) e em suportes mistos de óxido de zircônio e g-alumina. Os suportes bi-componente contendo (15%) ZrO2/g-Al2O3 foram preparados por dois métodos distintos: no primeiro, utilizou-se uma suspensão ácida de óxido de zircônio comercial e no segundo, óxido de zircônio precipitado a partir do acetato. Os catalisadores foram submetidos a ensaios catalíticos de reforma a vapor de etanol a fim de verificar o efeito do suporte sobre a distribuição dos produtos. As técnicas de caracterização utilizadas foram área superficial específica (B.E.T), redução a temperatura programada (RTP), difração de raios-X (DRX) e espectroscopia de absorção molecular na região UV-VI, que identificou a espécie [PtOxCly]s2-. A conversão do etanol e a distribuição dos produtos variaram para cada suporte testado e para os diferentes tempos de contatos (W/F) utilizados. O catalisador (1%) Pt/g-Al2O3 apresentou a melhor seletividade para a produção de hidrogênio e a menor conversão para o etanol. Os catalisadores que utilizaram o suporte bi-componente (15%) ZrO2/g-Al2O3 e ZrO2 pura apresentaram alta conversão de etanol e baixa seletividade para hidrogênio, além de alta tendência à formação de bio-produtos. / In this work catalysts of platinum supported on g-alumina (g-Al2O3), oxide of zirconium (ZrO2) and mixed oxide of zirconium and g-alumina had been prepared and characterized. The bi-component supports containing ( 15%) ZrO2/g-Al2O3 had been prepared by two different methods : in the first, an acid suspension of comercial oxide of zirconium was used and in the second, oxide of zirconium was precipitated from acetate. The catalysts were tested in ethanol steam reforming reaction to verify the effect of the support on the distribution of the products. For the characterization, the following techniques were used. Superficial specific area (B.E.T,), temperature programmed reduction (TPR.), X-ray powder diffraction (XRD) and spectroscopy of molecular absorption in the UV-vis, for identification of [PtOxCly]s 2- species. The ethanol conversion and product distribution were different for each support tested and for different time of contact (W/F) used. The catalyst (1%) Pt/g-Al2O3 presented the best selectivity for the hydrogen production and the lower conversion for ethanol. The catalysts with bi-component support (15%) ZrO2/ g-Al2O3 and pure ZrO2 presented high ethanol conversion and lower selectivity for hydrogen production with high selectivity and formation of bio-products.

Pesquisas realizadas em todo o mundo exploram a possibilidade de utilizar o hidrogênio como combustível para a geração de energia, já que ele produz a chamada \"energia limpa\". O hidrogênio pode ser obtido a partir das reações de reforma de etanol, fonte renovável, em contraste com o clássico processo de obtenção a partir de derivados de petróleo. Desta forma, há um crescente interesse em pesquisa e desenvolvimento de catalisadores eficientes para gerar hidrogênio. Assim, no presente trabalho foram estudados catalisadores de ródio contendo 0,5; 1 e 3% (m/m) suportados em CeO2, Al2O3 e 20%CeO2- Al2O3 nas reações de reforma a vapor de etanol (RVE) e reforma oxidativa de etanol (ROE) visando a geração de hidrogênio. As amostras foram preparadas pelo método de impregnação úmida e caracterizadas por difração de Raios-X (XRD), área superficial específica - método B.E.T., espectroscopia dispersiva em emissão de Raios-X (EDX), espectroscopia de fotoelétrons excitada por Raios-X (XPS), espectroscopia na região do ultra-violeta e do visível (UV-vis- NIR) e redução à temperatura programada (RTP-H2). Os ensaios catalíticos, realizados entre 400 e 600ºC, mostraram altas conversões de etanol para todos os catalisadores. As maiores produções de H2, a partir das reações de RVE e ROE, foram obtidas à 600ºC com os catalisadores Rh/CeO2 e Rh/20%CeO2-Al2O3. Foi observado que a adição de oxigênio proporcionou um aumento na produção de H2, bem como na razão CO2/CO e nas deposições de carbono. / The researches made in the world explore the possibility in the use of hydrogen like a fuel for energy generation, since it produces the called \"clean energy\". The hydrogen can be obtained through of the ethanol reforming reaction, i.e. renewable source, in contrast with the classical process for obtaining from petroleum derivates. In this way, there is a crescent interest in research and development of efficient catalysts in order to obtain hydrogen. Thus, in this work were studied the rodium catalysts with 0,5; 1 e 3% (w/w) supported on CeO2, Al2O3 e 20%CeO2-Al2O3 for the ethanol steam reforming (ESR) and oxidative reforming (EOR) reactions aiming to the hydrogen generation. The samples were prepared by wet impregnation method and characterized by X-ray diffraction (XRD), specific superficial area - BET method, energy dipersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy (UVvis), and temperature-programmed reduction (TPR-H2). In according to the catalytic tests, performed between 400 and 600ºC, it was obtained higher ethanol conversion values for all catalysts. The highest H2 yield it was obtained at 600ºC, with the Rh/CeO2 e Rh/20%CeO2-Al2O3 catalysts. It was observed that the addition of oxygen caused an increase in H2 production, as well as, in the CO2/CO ratio and in the carbon deposition.

Processing of Bulk Metastable Oxide Ceramics Oxide ceramic materials are extensively used in various modern application domains which require properties such as high temperature stability or creep resistance, wear resistance, chemical stability, useful electronic, optical and magnetic properties. In the diverse arena of materials technology that interlinks processing, structure, properties and performance, the advancement of new processing techniques to develop oxide ceramics facilitates the extension and refinement of their desirable properties and also mitigate their limitation in terms of application. Progress in processing science/technology offers a real impetus to the development of metastable ceramics with novel, non-equilibrium structures that exhibit scientifically interesting properties and have the potential to cater to the requirements of modern application areas. In the absence of the equilibrium state of a material system, metastable states can be formed with amorphous phases, extended solid solutions, metastable crystal structures and nanocrystallinity. Such metastable states can be retained by imposing kinetic constraints, which means that under the conditions of temperature and pressure, atomic mobilities are inadequate for the transformation. Metastable ceramics that are produced using non-equilibrium processing routes, such as rapid solidification, vapour deposition, spray pyrolysis, sol-gel technique etc., have been known to possess potentially useful properties, such as hard and soft magnetic characteristics, semiconductivity, varistor action, optical transmittivity and superconductivity. Apart from possessing attractive properties, a metastable phase may also serve as a precursor to a desired microstructure; for instance, controlled crystallization of an amorphous phase is a possible way enroute to nanocrystalline structure. It was well recognized that the comprehensive study and use of nanostructured and other metastable ceramics requires consolidation of the fine discontinuous forms (powders or flakes) produced from non-equilibrium processing routes, into bulk shapes with greater control on the fine scale of the structure. Such efforts have not been entirely successful. Non-equilibrium processing techniques do not produce the metastable materials in bulk form. Consolidation of metastable ceramics into dense forms needs high temperatures, mechanical activation (in the form of static pressures or shock waves), or a combination of both. Such activation may trigger the transformation of the desired metastable phase into a more stable phase with concurrent grain growth. Conversely, conditions that allow the desired metastable phase to be retained may not be adequate for complete densification. The subject of the present thesis is two-fold: (i) processing of dense amorphous Al2O3-Y2O3 materials through a novel densification route involving hot pressing of amorphous powders, produced by co-precipitation, at low temperatures and moderately high pressures, (ii) detail study of possible deformation mechanisms of the amorphous phase from mechanical testing at elevated temperatures. Unusual deformation behavior of the bulk amorphous material has been related to the densification process. Development of Pressure Consolidation Technique Amorphous powder of composition Al2O3-15 mol% Y2O3 (A15Y) was synthesized by co-precipitating a hydroxide from metal nitrate precursor’s solution by using ammonium hydroxide. Chemical homogeneity was ensured by a molecular level mixing of precursors of aluminium and yttrium at room temperature. The as-precipitated powder undergoes thermal decomposition (pyrolysis) to an amorphous oxide by ~770-800o C. The crystallization temperature was found from thermal analysis to be ~900o C, with γ-Al2O3 as the initial product of crystallization. The true density of the amorphous A15Y phase was measured to be only 2.69 g cm-3 by pycnometry, which is ~2/3 of the assemblage of equilibrium crystalline phases consisted of Al2O3 and YAG. Uniaxial hot pressing was performed with decomposed, classified powders (large agglomerates with sizes more than 10 µm were removed by sedimentation technique) at low temperature of about 630-640o C and moderately high pressure of 710-750 MPa. Pressure was held constant for 30-45 minutes. Cold compaction at pressures of 50-65 MPa for 8-10 minutes was carried out prior to hot pressing to ensure green strength of the compacts. All hot-pressed compacts revealed significant densification (95-96% relative densities) with uniformly distributed fine porosity. X-ray diffraction, electron microscopy analysis, Raman spectroscopy and differential thermal analysis established the amorphous nature of the dense, hot-pressed pellets. The amorphous phase displays an elastic modulus of ~ 50-60 GPa and a hardness of 4-5 GPa, which are considerably lower than those of the crystalline counterpart. Deformation Behavior of Amorphous Al2O3-Y2O3 The experiments described above clearly demonstrated the feasibility of producing bulk metastable ceramics in the Al2O3-Y2O3 system by a novel consolidation (viz., low temperature-high pressure) route of amorphous powders. This section of the thesis concentrates on studying the deformation mechanisms of the amorphous phase, which are found to be characteristic of the temperature domain of the experiment. Uniaxial compression tests at temperatures of 650-850o C with constant engineering strain rates of ~3-4 X 10-4 s-1 were conducted on dense amorphous samples made from the hot-pressed compacts. At a temperature of 850o C, i.e., close to the crystallization temperature, the amorphous phase was characterized by homogeneous deformation with continuous work hardening after yielding, accompanied by an increase in the true density of this glass by 10-12%. X-ray and electron microscopy analysis confirmed that the density increase was not due to the formation of nano-crystals at this high temperature. Raman spectroscopy and differential thermal analysis further corroborates that the glass was amorphous even after deformation. No shear instabilities were formed at the side surfaces due to the deformation. Significantly large compressive longitudinal strains up to about 28% were observed before unloading. Moreover, an interrupted loading-unloading test established that the bulk density increase was monotonic with the existence of multiple amorphous states enroute to a succession of denser structures. A simultaneous increase in both hardness (H) and modulus (E) of the amorphous phase of up to 100% after deformation bolstered this experimental observation of bulk density increment at constant porosity. The above evidence clearly points towards significant structural changes of the amorphous phase during high temperature deformation process and therefore a phenomenon of molecular densification of the amorphous structure through a hierarchy of dense amorphous phases was hypothesized, analogous to density or entropy driven amorphous-to-amorphous phase transitions (polyamorphism). Note that the densification described here does not refer to the conventional removal of porosity in a ceramics. At an intermediate temperature of 725o C, which is significantly (~200o C) below the crystallization temperature, plastic deformation commences at a stress (yield stress) of 700-780 MPa (considerably higher compared to the yield stress at 850o C) and continued to deform plastically with a slowly decreasing flow stress before reaching a plateau. Thus, the glass exhibited flow softening, in contrast to flow hardening observed at 850oC. Plastic deformation of this glass is largely non-viscous through shear instabilities (akin to the low temperature deformation behavior of metallic glass) and resulted in 8% increment in bulk density after deformation. Once again, the amorphous nature of the glass after deformation was confirmed by X-ray and electron microscopy analysis. Therefore, this intermediate temperature domain was characterized by both densification and shear. Deformation at even lower temperature, viz., at the temperature of hot pressing (650o C), was also characterized by elastic-plastic behavior (similar to flow softening described above), with immediate yield drop after yielding and resulted in a fairly large amount of plasticity of about 17% before unloading. The bulk density was found to be increased only by 2%. Another very interesting experimental finding from the present investigation is the time-dependent deformation (viz., creep densification) exhibited by this glass. It was established from the result of longer term creep experiment at 850o C that the glass revealed large uniaxial compression of about 15% with 5.5% densification to a density of 3.02 g cm-3. Strain rate sensitivity of the A15Y glass was revealed by another stress jump test. To summarize, the present thesis elucidates the discovery of a new class of ceramics with unusual physical properties in an amorphous mixture of Al2O3-Y2O3, which is in contrast to the conventional brittle ceramics. This new class of ceramics deforms plastically without any hydrostatic containment, like ductile metal, at temperatures about 1000o C below those at which their crystalline counterpart would deform. The behavior of this amorphous ceramics under stress that leads to unusually large change in shape, density, hardness and modulus with hierarchies of amorphous structures is demonstrated in detail with experimental evidence.

No description available.

No description available.

The master thesis deals mainly with the optimization of machining of ceramic semi-finished products from ZrO2 and Al2O3. The first part with literary research, which describes the steps of the technology of forming ceramic bodies, especially the gelcasting method. The thesis describes possibilities of milling of ceramic materials using CNC technology. The thesis describes the dependence of acquired roughness on bodies and used machining strategies. The best roughness parameters on ZrO2 samples were obtained after they were calcined at 900 ° C, while the lowest roughness was obtained on the samples in the unprotected state for the Al2O3 samples. Samples machined with a spherical milling cutter showed surface roughness Ra = 1 m for ZrO2 and Ra = 1.3 m for Al2O3. It also describes the possibility of machining sharp-edged shapes and fine details where the best results are achieved on ZrO2 samples engraved at 900 and 1100 °C. Tool wear was particularly important when machining samples of Al2O3 ignited at temperatures above 800 °C.

The presented diploma thesis is focused on the preparation and properties of transparent polycrystalline ceramic materials based on Al2O3. Theoretically, the most important technological aspects of the processing of these materials are presented. Detailed attention is given to transparent Al2O3 polycrystalline ceramics doped with rare earth elements. The influence of microstructural parameters on the optical properties (represented by RIT) is investigated on Al2O3 samples doped and codoped with dysprosium, terbium and chromium. A significant effect of the average grain size on the light transmittance of all samples is observed. The highest RIT = 55 % (measured by a laser beam with a wavelength of 632,8 nm) was achieved by an optimized preparation process for a sample doped with 0,05 at. % of dysprosium. For all samples photoluminescent properties are also analysed. The photoluminescent emission spectra correspond to the activation of doping elements. In case of the terbium and chromium codoped samples, the differences in the activation of individual dopants depending on different excitation wavelengths were demonstrated, resulting in different colour emissions for different excitation wavelengths.

The goal of diploma thesis is study of the effect of thermal annealing at different temperatures and different annealing durations on the surface structure of oxide ceramics based on Al2O3 and study of the samples porosity.