In the last years many efforts have been spent to develop colloidal processes that use water instead of organic solvents. The aim of this study was to develop aqueous tape casting systems to produce zirconia tapes. Different types of binder were tested. Rheological properties of the slurries were measured at room temperature. The slurries were cast on a PET carrier with/without a silicone-based coating. Interactions between the slurry and the polymeric substrate were evaluated. It was found that an acrylic binder is more appropriate for colloidal processing. The acrylic-based suspensions showed a pseudoplastic behavior and remained stable after hours. Tapes with thicknesses between 90 and 200 µm were produced. Optimized tapes showed smooth and homogeneous surfaces and adequate plasticity.
Dense electrolytes and flawless laminated YSZ electrolytes can be produce combining aqueous tape casting and constrained calendering. During calendering two or more layers are laminated continuously and the edges (entering and final) are not sealed at the same time avoiding air bubbles to trap between the layers. In this study constrained calendering laminates showed adequate adhesion between layers, and almost 20% thickness reduction after sintering as well as high green and sintered densities.
Aqueous tape casting was used to produce yttria-stabilized zirconia films for electrolyte-supported solid oxide fuel cell (SOFC). Tape casting slurries were prepared varying the binder content between 20 and 25 wt%. A commercial acrylic emulsion served as binder. Rheological measurements of the two slurries were performed. Both slurries showed a shear-thinning behavior. Tapes with 25 wt% binder exhibited adequate flexibility and a smooth and homogeneous surface, free of cracks and other defects. Suitable conditions of lamination were found and a theoretical density of 54% in the laminates was achieved. Laminated tapes showed higher tensile strength compared to single sheets. Tape orientation has a significant influence on the mechanical properties. Tensile strength, elongation to strain, and Young’s modulus measured in samples produced in the direction of casting showed higher property values.
The potential of a natural Mexican zeolite from the northern state of Sonora as microfiltration membranes was evaluated. The zeolite was characterized by x-ray diffraction, scanning electron microscopy (SEM), N2 physisorption and thermal analysis. Clinoptilolite and heulandite were the main components of the zeolite. The crystallinity of this material was confirmed. Two steps made up the manufacturing process of porous membranes: pressing and sintering. It was necessary to use lubricants and agglomerants with different particle size of the zeolite. The best properties of the porous membranes were obtained using zinc stearate (4 wt%) as lubricant, boehmite (15 wt%) as agglomerant and the best particle size ranged from 63 to 300 µm. Moreover it was observed that the zeolite granule distribution improved the press of the materials by approximately 10% in the distribution proposed. The thermal treatment of the porous membranes was carried out at several temperatures (500–1000 °C). The porous membranes obtained were characterized by x-ray diffraction, scanning electron microscopy and N2 physisorption to study the global porosity, phase transformations and pore size distribution. A loss of crystallinity, decreased porosity and a lower specific surface area were found when the sintering temperature was increased. The results of pore distribution suggest that these materials are porous membranes for microfiltration.
Hazardous byproducts emissions such as nitrogen oxides (NOx) and carbon monoxide (CO) might be controlled by the use of radiant porous burners. Those heaters require a solid porous matrix where combustion reaction takes place, reason why the heat transfer is much more efficient. This project was based on a rheology study of an alumina slurry, where parameters like viscosity and tixotropy were the guide to select the appropriate formulation to be used in the fabrication of ceramic foams by the replica method. Low strength samples were produced after the first thermal treatment, explained by the absence of a plasticizer when using PVA as a binder. Incomplete sintered foams were obtained due to an insufficient soak time.
Nos últimos anos as indústrias vêm apresentando um grande interesse em diminuir a poluição gerada por seus processos, procurando alternativas que proporcionem igual ou melhor eficiência nos seus processos. Uma alternativa muito promissora na aplicação de processos que requerem aquecimento por radiação se refere aos queimadores radiantes porosos (SCHEFFLER, COLOMBO, 2004; CATAPAN, 2007). Os queimadores devem ser porosos e constituídos de uma cerâmica que, além de resistir a temperaturas elevadas (>1500°C), deve apresentar alta resistência ao choque térmico. Neste trabalho, foi utilizado o método da réplica para a obtenção de espumas de alumina. Espumas de poliuretano foram impregnadas com suspensões aquosas de 50-70% em massa de sólidos (Al2O3) mais aditivos (ligantes). A viscosidade da suspensão foi avaliada e ajustada a uma impregnação adequada. As espumas impregnadas foram submetidas a um tratamento térmico para degradação do poliuretano a 400°C/1h e, subsequentemente, sinterizadas (entre 1500°C e 1600°C/3h) para densificação das paredes celulares. Permeabilidade e resistência à compressão das espumas foram correlacionadas à microestrutura e à morfologia celular (tamanho e geometria das células). A temperatura de sinterização que apresentou melhores resultados foi 1600°C, promovendo maior densificação e aumento na resistência mecânica.
Rheological behaviour of Al 2 O 3 and CuO suspensions was characterised in order to fabricate Al 2 O 3 /Cu foams as an alternative way to produce foams with better mechanical properties than common Al 2 O 3 foams. Different quantities of raw materials were combined to select the formulations for the ceramic-metal foams. Foams were produced by a double impregnation process, followed by a thermal cycle and a reduction cycle. In this work, materials were characterised trough zeta potential, SEM and optical dilatometry. Foams microstructure and compressive strength were evaluated. Final structures had a compressive resistance of 0.44 ± 0.14 MPa.
RESUMENEn los quemadores radiantes, la fuente de calor requiere un medio poroso en donde se lleva a cabo la reacción de combustión, que hace más eficiente la transferencia de calor. En este trabajo se realizó un estudio de la reología de la suspensión de alúmina fina, cuyos parámetros de viscosidad y tixotropía fueron la base para la selección de la formulación más adecuada para la fabricación de espumas cerá-micas por el método de réplica. Las espumas poliméricas precursoras presentaron mayor porosidad y permeabilidad, en respuesta a la presencia de paredes finas y 99% de celdas abiertas. La mayor resistencia mecánica a la compresión la obtuvo la formulación con mayor carga de sólidos, bajo las mismas condiciones de prueba.Palabras claves: espumas cerámicas, réplica, alúmina, quemadores radiantes ABSTRACTIn radiant porous burners, the heat source requires a solid porous matrix where the combustion reaction takes place, in which the heat transfer is performed more efficiently. This work is based on a study of the alumina suspension rheology, where parameters as viscosity and tixotropy were the guide to select the appropriate formulation for the ceramic foam fabrication by the replica method. The precursor polymeric foams presented higher porosity and permeability, due to their thin walls and 99% open cells. The highest mechanical strength under compression was obtained for the formulation with the highest solid fraction, under the same test conditions.
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