Síntese, processamento coloidal e sinterização de compósitos nanoestruturados do sistema LZS (Li2O-ZrO2-SiO2)+Al2O3

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2016.Compósitos do sistema LZS+Al2O3 foram obtidos por meio de duas rotas de processamento. Na Rota A, o sistema LZS (19,58Li2O.11,10ZrO2. 69,32SiO2) foi obtido a partir da fusão das matérias-primas (carbonato de lítio, quartzo e silicato de zircônio). As fritas obtidas foram moídas e misturadas com nanopartículas de Al2O3 (13 nm; 1-5 %). Na Rota B, os sistemas LZS e LZS+Al2O3 foram obtidos por meio do processamento coloidal de óxidos nanoestruturados de precursores (SiO2, ZrO2, Al2O3 e um precursor de lítio obtido da reação de Li2CO3 e ácido acético). As suspensões obtidas foram congeladas em nitrogênio líquido e liofilizadas. As nanoestruturas obtidas apresentaram ~25 nm de diâmetro. Os pós resultantes das duas rotas foram conformados por prensagem uniaxial e colagem de fitas. Posteriormente foram sinterizados e suas propriedades foram avaliadas. A incorporação de nanopartículas de Al2O3 em matriz LZS reduziu significativamente o coeficiente de expansão térmica (CET). Os compósitos obtidos por meio da Rota A sinterizados a 900 ºC obtiveram densidades relativas de 92 a 98%, apresentaram silicato de zircônio e espodumênio-ß como principais fases cristalinas, dureza entre 4,6 e 6 GPa, módulo de elasticidade entre 78 e 111 GPa. Por outro lado, os compósitos nanoestruturados, produzidos pela Rota B apresentaram as fases cristalinas Li2ZrSi6O15, dissilicato de lítio, e silicato de zircônio. A baixa sinterabilidade dos compósitos, demonstrou a necessidade do uso de técnicas não convencionais de sinterização, como o Spark Plasma Sintering (SPS). Os curtos tempos de processo de SPS (1 min), não permitem que a zircônia reaja para formar silicato de zircônio, já que a evolução das fases depende da reação da alumina para formar outras fases cristalinas. O CET obtido pelos compósitos sinterizados por SPS não resultou tão baixo quanto aos sinterizados de forma convencional, no entanto, tiveram as maiores densidades e melhores propriedades mecânicas, ou seja, dureza entre 5 e 9 GPa e módulo de elasticidade entre 78 e 105 GPa. Após processamento coloidal dos pós obtidos pelas duas rotas de processamento, foram produzidas fitas flexíveis, homogêneas, livre de trincas e de fácil descolagem do substrato. Arquiteturas complexas foram obtidas, como laminados 4 camadas com concentrações graduais de nanopartículas de Al2O3, o vitrocerâmico LZS foi laminado em bicamadas com o aço inoxidável AISI 316L e o compósito nanoestruturado 5AnB com wafer de silício e foram obtidas bicamadas livres de trincas e delaminações.Abstract : LZS/Al2O3 composites were obtained by two processing routes. In Route A, the LZS system (19.58Li2O·11.10ZrO2·69.32SiO2) was obtained by melt of raw materials (lithium carbonate, quartz and zirconium silicate). The frits were milled and mixed with Al2O3 nanoparticles (13 nm; 1-5vol.%). In Route B, the LZS and LZS + Al2O3 systems were obtained by colloidal processing of the oxide precursors nanoparticle (SiO2, ZrO2, Al2O3, and a lithium precursor obtained by reaction of Li2CO3 and acetic acid). The suspensions were frozen in liquid nitrogen and lyophilized. The nanostructure obtained showed ~ 25 nm in diameter. The resulting powders of the two routes were conformed by uniaxial pressing and tape casting. Subsequently, they were sintered and their properties were evaluated. The Al2O3 addition resulted in reduced the coefficient of thermal expansion (CTE). The composites obtained through Route A sintered at 900 ºC obtained relative densities of 92 to 98%, presented zirconium silicate and ß-spodumene as the main crystalline phases, hardness between 4.6 and 6 GPa, modulus of elasticity between 78 and 111 GPa. On the other hand, the nanostructured composites produced by Route B presented the crystalline phases Li2ZrSi6O15, lithium disilicate, and zirconium silicate. The low sinterability of the composites demonstrated the need for the use of non conventional sintering techniques, such as Spark Plasma Sintering (SPS). The short SPS process times (1 min) do not allow the zirconia to react to form zirconium silicate, since the evolution of the phases depends on the reaction of the alumina to form other crystalline phases. The CTE obtained by the composites sintered by SPS was not as low as conventional sintered, however, they had the highest densities and better mechanical properties, that is, hardness between 5 and 9 GPa and modulus of elasticity between 78 and 105 GPa. After colloidal processing of the powders obtained by the two processing routes, flexible, homogeneous strips were produced, free of cracks and easy take-off of the substrate. Complex architectures were obtained as 4 layer laminates with graded concentrations of Al2O3 nanoparticles, the LZS glass ceramic was laminated in bilayers with AISI 316L stainless steel and 5AnB nanostructured composite with silicon wafer and freezings were obtained from cracks and delaminations

Síntese e caracterização de compósitos de vitrocerâmica do sistema LZS/A12O3-a para aplicações na tecnologia LTCC

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2013Neste trabalho, misturas de precursor vitrocerâmico particulado (matriz vitrocerâmica) de composição 9,56Li2O.22,36.ZrO2.68,08SiO2 (5 µm) e partículas (350 nm) de Al2O3- , (1-40 vol.%) foram preparadas e processadas com o propósito de estudar a influência da alumina sobre as propriedades térmicas e elétricas dos compósitos (LZS/Al2O3- ) obtidos para aplicações na tecnologia LTCC. Os compósitos obtidos, sinterizados entre 800 e 950ºC por 30 a 120 min, com densidades relativas entre 85 e 93%, apresentaram silicato de zircônio e espodumênio-? como principais fases cristalinas. A resistência à flexão máxima (290 MPa) foi alcançada para compósitos com 1% Al2O3- . Para compósitos contendo entre 1 e 10% Al2O3- , sinterizados a 900ºC/30 min, as condutividades elétrica e térmica e o coeficiente de expansão térmica linear, variaram entre 3,35 e 1,21 x 10-10 S/cm, 4,65 e 2,98 W/mK, 9,54 e 3,36 x 10-6 °C-1, respectivamente. 2013-12-06T00:25:49

Conversão de CO2 em nanotubos de carbono utilizando eletrólitos de Li2CO3 e CaCO3 fundidos

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Influence of CVD parameters on Co- TiO2/CNT properties : a route to enhance energy harvesting from sunlight

Carbon nanotubes (CNTs) have been employed to enhance the photoactivity of titanium dioxide (TiO2). In this work, CNTs were deposited by chemical vapor deposition (CVD) onto the surface of anodized Co-TiO2 nanotubes. The influence of CVD parameters (time and temperature) on the Co-TiO2/CNT structure and properties was investigated. We studied three synthesis times (10, 20, and 30 min) and two synthesis temperatures (700 and 800°C). The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray diffraction (XRD). The photocurrent performance of the electrodes was determined by linear voltammetry. The results showed the successful formation of Co-TiO2/CNT hybrid structures. The shortest synthesis time produced higher quality CNTs. The samples synthesized at 700 and 800°C for 10 min exhibited a current density of 1.13 mA.cm−2 and 7.84 mA.cm−2, respectively, which is 9 and 65 times greater than the Co-TiO2 sample. The synergistic effect of the CNT deposition and the crystalline phase composition significantly improved the photoresponse of TiO2. The proper choice of synthesis parameters allowed the control of the sample structure, leading to the production of electrodes with better light-harvesting performance

Eggshells as agro‐industrial waste substitute for CaCO3 in glass foams: A study on obtaining lower thermal conductivity

In this work, discarded glass bottles (GB) and eggshells (ES) were used to produce foam glass designed for thermal insulation. The literature on the thermal conductivity of foam glasses produced with eggshells is sparse. This material was used as pore‐forming agent at 3% and 5% weight fractions to obtain a foam glass with low thermal conductivity. Homogenized powders were uniaxially pressed, and the compacts were fired at three temperatures (800, 850, and 900°C). Raw materials were characterized by chemical analysis and particle size distribution. The foam glasses were characterized by their porosity, phases, compressive strength, and thermal conductivity. The best insulating properties were obtained for the composition containing 5 wt% ES fired at 800°C. This sample displayed a porosity of 91.4% while its thermal conductivity was of 0.037 W/m.K, with a compressive strength of 1.12 ± 0.38 MPa. Crystalline phases were observed in samples fired at 850 and 900°C as a result of the devitrification process. The final properties of the materials are comparable to those of commercial foam glasses obtained from non‐renewable, more expensive raw materials, a great indicator that the studied compositions could be used as an environmentally friendly substitute

Enhancement of magnetic and dielectric properties of KNbO3–CoFe2O4 multiferroic composites via thermal treatment

In this work, multiferroic composites were produced from CoFe2O4 and KNbO3 mixtures via control of the heat treatment temperature. For this, CoFe2O4 nanoparticles were produced by sol-gel method, while KNbO3 was synthesized by microwave-assisted hydrothermal synthesis. The powders were homogenized and subjected to heat treatment at 300, 400 and 500 ◦C for 5 h. The structural, electrical and magnetic properties were characterized. The results of X-ray diffraction indicated that there was no formation of secondary phases with heat treatment. Raman vibrational modes confirmed the presence of KNbO3 and CoFe2O4 in the prepared composites. SEM analysis showed that the composite microstructure consists of smaller ferrite particles arranged on the surface of largest cubic KNbO3 particles. The improvement of coercivity (HC = 382.1Oe) and dielectric constant (ε’~7860) was observed for the composite thermally treated at 300 ◦C. The obtained results show the potential application of KN:CFO composites for multifunctional devices

Evaluation of the influence of glycerol in ceramic matrix

O presente trabalho avalia os efeitos da adição de glicerol sobre a porosidade e resistência mecânica de um material cerâmico. As amostras foram compactadas por prensagem uniaxial e submetidas a temperaturas de queima de 950 °C e 1100 °C, com taxa de aquecimento de 7 °C min-1 . Foram realizados ensaios físicos e mecânicos para analisar porosidade aparente, absorção de água, retração linear e resistência mecânica a flexão. Os resultados mostram que a adição de 10% de glicerol à argila melhora principalmente suas propriedades mecânicas, podendo ser um aditivo promissor para gerar materiais cerâmicos estruturais com microestrutura mais resistente.The present work evaluates the effects of the glycerol addition on the porosity and mechanical resistance of a ceramic material. Samples were compacted by uniaxial pressing and were submitted to different sintering temperatures, 950 °C and 1100° C, with a heating rate of 7 °C min-1 . Physical and mechanical analysis were performed to evaluate porosity, water absorption and linear retraction. The results show that the addition of 10% of glycerol into the clay mainly improves its mechanical properties, being able to be a promising additive to generate structural materials with more resistant microstructure

Evaluation of the addition of soda-lime glass and yerba mate wastes in ceramic matrix

O presente trabalho avaliou os efeitos da adição de resíduos de vidro sodo-cálcico e de erva-mate sobre a absorção de água, porosidade e resistência mecânica de um material cerâmico. Os pós homogeneizados foram compactados por prensagem uniaxial e submetidos a queima de 900 e 1100 °C a 2 °C.min-1. Os resultados mostraram que a adição de vidro e erva-mate à argila produziu materiais cerâmicos com retração linear entre 0,3 e 6%, absorção de água entre 5,3 e 34%, porosidade aparente de até 41% e resistência mecânica entre 0,5 e 20 MPa. Os materiais queimados a 1100 °C foram os que obtiveram as melhores combinações de propriedades, podendo ser aplicados na produção de blocos, telhas ou revestimento cerâmico de acordo com as necessidades específicas da aplicação.The present work evaluated the effects of the addition of soda-lime glass and yerba mate wastes on the water absorption, porosity and mechanical resistance of a ceramic material. The homogenized powders were compacted by uniaxial pressing and subjected to firing at 900 and 1100 °C at 2 °C.min-1. The results showed that the addition of sodalime glass and yerba mate to the clay produced ceramic materials with linear shrinkage between 0.3 and 6%, water absorption between 5.3 and 34%, apparent porosity of up to 41% and mechanical strength between 0.5 and 20 MPa. The materials fired at 1100 °C resulted in the best combinations of properties and can be applied in the production of blocks, roof tiles or ceramic tiles according to the specific needs of the application

Porous ceramic supported TiO2 nanoparticles : enhanced photocatalytic activity for Rhodamine B degradation

Photocatalytic processes are an efficient and important technique to mineralize organic contaminants in aqueous effluents. However, it is paramount that there is a way to recover the catalyst after degradation. Based on this problem, this research seeks to evaluate the photocatalytic properties of TiO2 under porous ceramics support for the degradation of Rhodamine B (RhB). TiO2 was synthesized by sol-gel, dried at 100 ◦C and calcined at 400 ◦C. The morphological, optical and structural proprieties of the particles were characterized. The XRD patterns of samples calcined at 400 ◦C showed only the anatase phase, confirmed by Raman. Not heat-treated xerogel was amorphous. The agglomerates are composed of fine particles, in the nanometric scale of 15nm. The bandgap of the powder is 3.21 eV, and the surface area is 60.1m2 g−1. To evaluate its photocatalytic activity, the anatase TiO2 was supported in a porous ceramic substrate by a dip-coating process. The heterogeneous photocatalysis showed excellent results, with the degradation of up to 83% of RhB. It was possible obtained with successful an efficient technique for the treatment of wastewater with Anatase nanoparticles supported in the ceramic support obtained from of reuse of the residues.Los procesos fotocatalíticos son técnicas eficientes para la mineralización de contaminantes orgánicos en efluentes acuosos. Sin embargo, es fundamental que haya una forma de recuperar el catalizador después de la degradación. En base a este problema, esta investigación busca evaluar las propiedades fotocatalíticas del dióxido de titanio (TiO2) bajo el soporte de cerámica porosa para la degradación de la rodamina B (RhB). El TiO2 se sintetizó mediante sol-gel, se secó a 100 ◦C y se calcinó a 400 ◦C. Se caracterizaron las propiedades morfológicas, ópticas y estructurales de las partículas. Los patrones DRX de las muestras calcinadas a 400 ◦C mostraron solo la fase anatasa, confirmada por Raman. El xerogel no tratado térmicamente era amorfo. Los aglomerados están compuestos de partículas finas, en la escala de 15nm. El intervalo de banda es de 3,21 eV, y el área de superficie es de 60,1m2.g−1. Para evaluar la actividad fotocatalítica, se recubrió un sustrato cerámico poroso mediante el proceso de recubrimiento por inmersión. La fotocatálisis heterogénea mostró excelentes resultados, con la degradación de hasta el 83% de la RhB. Fue posible obtener con éxito una técnica eficiente para el tratamiento de aguas residuales con nanopartículas de anatasa soportadas en el soporte cerámico obtenido de la reutilización de los residuos