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.

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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.

This thesis inquire into experimental decomposition of freon R-22 (CHClF2 - chlorodifluorometan) for different process conditions, by the help of pilot experimental unit in heavy laboratories DEPARTMENT of process and enviromental engineering Brno. This unit can decomposition waste gas, as the case may be combustion gas by the thermic oxidation or catalytic oxidation. Ground was in theoretical research, in which had been executed decomposition of freon R-22 in laboratory. In terms of experimental work were to be execution states for decomposition of freon R-22, next will be decomposition of freon R-22 by catalytic oxidation on catalyst Pt/Al2O3 and consequently this experiment will be analyse. Part of this thesis is exploration of facts basic way to decomposition of freon R-22, accounting of experimental unit and discussion of results.

The work was focused on the preparation of layered ceramic materials and their characterizations. The direct measurment of weight deposite for enhanced description of one component system was studied within this work. The kinetics of electrophoretic deposition obtained from theoretical calculation and from experimental values were confronted. It was prepared a lot of depositions for described kinetic of electrophoretic deposition with applied constant currents. The relative density and porosity were determined on the annealled and sintered bodies. The hardness measurments were performed on sintered bodies and then resulted values were confronted with the used currents. A ceramic composite based on Al2O3 and ZrO2 was prepared by using of precision describtion of electrophoretic deposition kinetic.