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Made available in DSpace on 2014-10-09T12:53:12Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:29Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:53:12Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:29Z (GMT). No. of bitstreams: 0 / A borracha de cloropreno é utilizada na confecção de diversos artefatos, como roupas de mergulho e de ginástica, revestimentos de cabos, pneumáticos especiais e na indústria calçadista, entre outros. Apesar de propiciar muitos benefícios, um dos problemas enfrentados atualmente é reaproveitar estes artigos de borracha vulcanizados usados ou com vida útil esgotada, bem como sobras de produção, visando a preservação do meio ambiente. A devulcanização destes produtos pode ser realizada por meio de processos biológicos, químicos e físicos. O objetivo principal deste trabalho foi estudar a reciclagem/reaproveitamento (devulcanização) do cloropreno (DuPont - Neoprene®), pelo processo físico de microondas. Para tanto foi elaborada uma formulação básica com este tipo de borracha, para uso na indústria automobilística. As irradiações das amostras foram feitas em equipamento gerador de microondas desenvolvido no CQMA do IPEN, que opera com freqüência de 2450MHz e potências de 1.000W a 3.000W. As análises das amostras irradiadas com microondas e não irradiadas, foram feitas por meio de ensaios de dureza, densidade, deformação permanente a compressão (DPC), tração, alongamento, cinzas, swelling, teste de envelhecimento e reometria. Os resultados mostraram que a borracha de cloropreno irradiada com microondas apresentou tendência de vulcanizar novamente e poderá substituir algumas partes da borracha virgem em formulações, sem provocar grandes perdas nas propriedades físico-químicas. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Wood drying is essential for preparation of this natural resource for practical applications.Most drying models confirm that the tortuosity of the moisture transport path, associated with high wood density or low moisture permeability, is an important control parameter during the diffusion-controlled drying process. Drying systems, such as kilns, control the external environment in order to manipulate moisture diffusion and transport mechanisms; however they are powerless to manipulate wood density or permeability. Controlled application of microwave energy has been shown to selectively rupture the wood structure creating radial pathways in the wood through which moisture may readily move. New analytical equations that describe simultaneous heat and moisture transport during microwave heating have been derived and validated. These new equations assume that the microwave fields decay exponentially with distance inside the irradiated material and enforce a boundary condition, which allows convective heat transfer at the inter-facial boundary between the moist dielectric material and the air. They demonstrate the importance of applying the theory of simultaneous heat and moisture movement to microwave heating. In this theory a set of synchronised heat and moisture waves propagate through the material with velocities that are vastly different from those predicted by the constant vapour concentration thermal diffusivity of the material. They also correctly predict the “S” shaped temperature versus electric field strength curves discussed by other authors.(For complete abstract open document)

BARROS, Francisco Cláudio de Freitas. Processos oxidativos avançados assistidos por microondas aplicados na remoção de pesticidas em meio aquoso. 2014. 90 f. Tese (Doutorado em química)- Universidade Federal do Ceará, Fortaleza-CE, 2014. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-05-31T19:26:07Z No. of bitstreams: 1 2014_tese_fcfbarros.pdf: 2270924 bytes, checksum: 0233401fd5169501903fef16491b9d07 (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-05-31T23:15:36Z (GMT) No. of bitstreams: 1 2014_tese_fcfbarros.pdf: 2270924 bytes, checksum: 0233401fd5169501903fef16491b9d07 (MD5) / Made available in DSpace on 2016-05-31T23:15:36Z (GMT). No. of bitstreams: 1 2014_tese_fcfbarros.pdf: 2270924 bytes, checksum: 0233401fd5169501903fef16491b9d07 (MD5) Previous issue date: 2014 / The use of pesticides in crop protection has contributed to a massive increase in global food production. However, pesticides have generated a growing concern about your environmental risks. Advanced oxidation processes (AOP) have proved a particularly useful alternative to degrade organic compounds in aqueous medium, converting them into low toxic substances or nontoxic substances. In this work, was evaluated the removal efficiency of the chlorpyrifos pesticide in continuous and batch AOP systems involving microwave radiation, ultraviolet radiation, hydrogen peroxide and titanium dioxide. The MO/UV/H2O2/TiO2 batch system was efficient in the chlorpyrifos removal (100%) using 10% H2O2 solution for most of the microwave power conditions and treatment time. Fractional factorial design was applied to the pesticides treatment in AOP batch system to indicate the optimum values of the parameters: pH, pesticide concentration, oxidizing agent concentration, treatment time, and microwave power. The study of AOP continuous system showed that in 1-hour treatment of 500 mg.L-1 of chlorpyrifos, in alkaline medium, performed a pesticide removal of 87% at 10 ml.min-1 flow rate. Chromatographic analysis of samples treated in AOP continuous system suggests a partial mineralization of the pesticide. / A utilização de pesticidas na proteção de culturas tem contribuído com um aumento maciço na produção mundial de alimentos. Mas apesar de seus efeitos benéficos, os efeitos negativos dos agrotóxicos têm gerado uma crescente preocupação em relação ao risco de contaminação ambiental. Os processos oxidativos avançados (AOP) têm se mostrado uma alternativa particularmente útil para degradar compostos orgânicos em meio aquoso, convertendo-os em substâncias de pouca ou nenhuma toxidade. Ao longo de nosso estudo, foi avaliada a eficiência de remoção do pesticida clorpirifós em sistemas contínuos e descontínuos (batelada) de processos oxidativos avançados envolvendo radiação de microondas, radiação ultravioleta, peróxido de hidrogênio e dióxido de titânio, com resultados promissores. O sistema MO/UV/H2O2/TiO2 de POA descontínuo foi o mais eficiente na remoção de clorpirifós, com 100% de remoção de pesticida em amostras com 10% de H2O2 em quase todas as potências de microondas e tempo de tratamento avaliados. Estudos de planejamento fatorial fracionado aplicado ao tratamento de pesticidas em sistema de POA descontínuo apontaram as condições ótimas de trabalho para os seguintes parâmetros: pH, concentração de pesticida, concentração de agente oxidante, tempo e potência de microondas. O estudo de POA em sistema contínuo mostrou que, ao final de 1 hora, o tratamento de uma amostra de 500 mg.L-1 de clorpirifós em meio alcalino, alcançou uma remoção de 87% do pesticida com velocidade de fluxo de amostra de 10 mL.min-1. Análises cromatográficas das amostras tratadas em POA descontínuo sugerem uma mineralização parcial do pesticida.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / A utilizaÃÃo de pesticidas na proteÃÃo de culturas tem contribuÃdo com um aumento maciÃo na produÃÃo mundial de alimentos. Mas apesar de seus efeitos benÃficos, os efeitos negativos dos agrotÃxicos tÃm gerado uma crescente preocupaÃÃo em relaÃÃo ao risco de contaminaÃÃo ambiental. Os processos oxidativos avanÃados (AOP) tÃm se mostrado uma alternativa particularmente Ãtil para degradar compostos orgÃnicos em meio aquoso, convertendo-os em substÃncias de pouca ou nenhuma toxidade. Ao longo de nosso estudo, foi avaliada a eficiÃncia de remoÃÃo do pesticida clorpirifÃs em sistemas contÃnuos e descontÃnuos (batelada) de processos oxidativos avanÃados envolvendo radiaÃÃo de microondas, radiaÃÃo ultravioleta, perÃxido de hidrogÃnio e diÃxido de titÃnio, com resultados promissores. O sistema MO/UV/H2O2/TiO2 de POA descontÃnuo foi o mais eficiente na remoÃÃo de clorpirifÃs, com 100% de remoÃÃo de pesticida em amostras com 10% de H2O2 em quase todas as potÃncias de microondas e tempo de tratamento avaliados. Estudos de planejamento fatorial fracionado aplicado ao tratamento de pesticidas em sistema de POA descontÃnuo apontaram as condiÃÃes Ãtimas de trabalho para os seguintes parÃmetros: pH, concentraÃÃo de pesticida, concentraÃÃo de agente oxidante, tempo e potÃncia de microondas. O estudo de POA em sistema contÃnuo mostrou que, ao final de 1 hora, o tratamento de uma amostra de 500 mg.L-1 de clorpirifÃs em meio alcalino, alcanÃou uma remoÃÃo de 87% do pesticida com velocidade de fluxo de amostra de 10 mL.min-1. AnÃlises cromatogrÃficas das amostras tratadas em POA descontÃnuo sugerem uma mineralizaÃÃo parcial do pesticida. / The use of pesticides in crop protection has contributed to a massive increase in global food production. However, pesticides have generated a growing concern about your environmental risks. Advanced oxidation processes (AOP) have proved a particularly useful alternative to degrade organic compounds in aqueous medium, converting them into low toxic substances or nontoxic substances. In this work, was evaluated the removal efficiency of the chlorpyrifos pesticide in continuous and batch AOP systems involving microwave radiation, ultraviolet radiation, hydrogen peroxide and titanium dioxide. The MO/UV/H2O2/TiO2 batch system was efficient in the chlorpyrifos removal (100%) using 10% H2O2 solution for most of the microwave power conditions and treatment time. Fractional factorial design was applied to the pesticides treatment in AOP batch system to indicate the optimum values of the parameters: pH, pesticide concentration, oxidizing agent concentration, treatment time, and microwave power. The study of AOP continuous system showed that in 1-hour treatment of 500 mg.L-1 of chlorpyrifos, in alkaline medium, performed a pesticide removal of 87% at 10 ml.min-1 flow rate. Chromatographic analysis of samples treated in AOP continuous system suggests a partial mineralization of the pesticide.

South Africa is the second largest producer of zircon (ZrSiO4) in the world, Australia being the largest. Zircon is notorious for its chemical inertness. Extreme processing conditions such as alkaline fusion (NaOH at 600 °C or Na2CO3 at 1200 °C) are used to extract the zirconium values from the mineral. The purpose of this study was to investigate the use of microwave digestion as an alternative process, and to determine the parameters for this technique for the digestion of zircon with ammonium acid fluoride (AAF) under various conditions. Ammonium acid fluoride is more convenient and safer to use than conventional fluorination methods such as HF and F2. In this study zircon was treated with ammonium acid fluoride (NH4F∙1.5HF) by means of microwave assisted digestion. Reaction times ranged from 10 to 330 minutes at temperatures between 100 °C and 240 °C. Successive microwave digestion steps, interrupted by an aqueous wash procedure, resulted in a >99 % conversion of zircon to the water soluble intermediates (NH4.)3ZrF7 and (NH4)2SiF6. XRD and Raman spectroscopy confirm that zircon was the major phase present in the insoluble fraction of the product after washing. Arrhenius rate laws are derived for both reaction control (progressively shrinking particle) and diffusion control by the product layer. Both models show reasonably good agreement with the experimental data, but diffusion control was accepted as the most probable. The derived diffusion coefficient corresponds to a solid-liquid case. Copyright / Dissertation (MSc)--University of Pretoria, 2013. / Chemical Engineering / unrestricted

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Materials processing using microwave radiation is emerging as a novel and innovative technology that has proven useful in a number of applications. It has various advantages over conventional processing, such as; time and energy saving, very rapid heating rates, considerably reduced processing time and temperature, fine microstructures and improved mechanical properties, better product performance, etc. Microwave irradiation has shown great potential for the processing of different semiconductor materials and inorganic solids for various advanced electronic and optoelectronic devices such as solar cells, batteries, supercapacitors, fuel cells etc. This work intends to investigate the effect of microwave radiation on various semiconductor materials and inorganic solids, in particular the changes in their chemical, physical and photoelectrochemical properties after microwave treatment. Microwaves have been used as an alternative method to conventional thermal annealing for post annealing of widely used semiconductors (TiO2, ZnO nanorods), battery materials (lithium aluminium titanium phosphates), and synthesis of materials (ZnO, Ti0.97Pd0.03O1.97). It is found that, in contrast to conventional thermal annealing, microwave treatment of such materials improves the crystallinity without any structural changes by preserving their nanostructure due to the difference in the heating mechanism (volumetric heating). The results demonstrate that microwave processing is a promising alternative method to the traditional conventional sintering for materials processing for advanced electronic and optoelectronic devices. Also the microwave annealing method offers energy savings of up to ~75%, which would make it highly desirable for industrial scale up.

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