Made available in DSpace on 2014-12-17T14:06:58Z (GMT). No. of bitstreams: 1 WalquiriaJS_DISSERT_PACIAL.pdf: 740304 bytes, checksum: 3d1d601a3873230ed2af2ce67496fdf5 (MD5) Previous issue date: 2011-07-21 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The development and study of detectors sensitive to flammable combustible and toxic gases at low cost is a crucial technology challenge to enable marketable versions to the market in general. Solid state sensors are attractive for commercial purposes by the strength and lifetime, because it isn t consumed in the reaction with the gas. In parallel, the use of synthesis techniques more viable for the applicability on an industrial scale are more attractive to produce commercial products. In this context ceramics with spinel structure were obtained by microwave-assisted combustion for application to flammable fuel gas detectors. Additionally, alternatives organic-reducers were employed to study the influence of those in the synthesis process and the differences in performance and properties of the powders obtained. The organic- reducers were characterized by Thermogravimetry (TG) and Derivative Thermogravimetry (DTG). After synthesis, the samples were heat treated and characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), analysis by specific area by BET Method and Scanning Electron Microscopy (SEM). Quantification of phases and structural parameters were carried through Rietveld method. The methodology was effective to obtain Ni-Mn mixed oxides. The fuels influenced in obtaining spinel phase and morphology of the samples, however samples calcined at 950 ?C there is just the spinel phase in the material regardless of the organic-reducer. Therefore, differences in performance are expected in technological applications when sample equal in phase but with different morphologies are tested / O desenvolvimento e estudo de detectores sens?veis a gases combust?veis inflam?veis e t?xicos de baixo custo ? um desafio tecnol?gico determinante para possibilitar vers?es comercializ?veis ao mercado em geral. Sensores no estado s?lido s?o atrativos para fins comerciais pela robustez e tempo de vida, uma vez que n?o s?o consumidos durante o processo de rea??o com o g?s. Paralelamente, o uso de t?cnicas de s?ntese mais vi?veis pela aplicabilidade em escala industrial s?o mais atrativas para obten??o de produtos comerciais. Dentro desse contexto foram obtidos materiais cer?micos com estrutura espin?lio via combust?o assistida por microondas, visando aplica??o em detectores de gases combust?veis inflam?veis. Adicionalmente foram empregados direcionadores-org?nicos alternativos para estudo da influ?ncia dos mesmos no processo de s?ntese e nas diferen?as nas propriedades e desempenho dos p?s obtidos. Os direcionadores-org?nicos foram caracterizados por Termogravimetria (TG). Ap?s a s?ntese, as amostras foram tratadas termicamente e caracterizadas por Espectroscopia de absor??o na regi?o do infravermelho com Transformada de Fourier (FTIR), Difra??o de Raios X (DRX), Medidas de ?rea espec?fica por BET e Microscopia Eletr?nica de Varredura (MEV). A quantifica??o de fases e a determina??o de par?metros estruturais foram determinados por refinamento atrav?s do M?todo Rietveld. A metodologia empregada foi eficaz para obten??o de ?xidos mistos Ni-Mn. Os combust?veis utilizados influenciaram na obten??o da fase espin?lio e na morfologia das amostras, sendo que as amostras calcinadas a 950?C s?o monof?sicas independentemente do direcionador. Logo, diferen?as de desempenho s?o esperadas em aplica??es tecnol?gicas quando amostras iguais em fase mas com diferentes morfologias s?o testadas

Made available in DSpace on 2014-12-17T14:07:06Z (GMT). No. of bitstreams: 1 RayssaRNMS_DISSERT.pdf: 4171010 bytes, checksum: 0d447597643468751a7d9a8d1824c61d (MD5) Previous issue date: 2012-08-31 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The field of "Materials Chemistry" has been developing in recent years and there has been a great increase of interest in the synthesis and chemical and physical properties of new inorganic solids. New routes of synthesis and synthesis modified has been developed with the aim not only to optimize the processes in laboratory scale, but also on an industrial scale, and make them acceptable by current environmental legislation. The phenomenology of current solid state chemistry properties coupled with the high temperature superconductivity, ferromagnetism, porosity molecular and colors are evidence affected by the synthesis method, which in turn can influence the technological application of these materials. From this understanding, mixed oxides of nickel and zinc nanoparticulate were synthesized by microwave-assisted combustion route using three specific types of organic fuels employing the weight ratios 1:1/2 and 1:1 of cation metallic/fuel, in order to investigate the influence of such proportions to obtain the solids. The new fuels were chosen to replace, for example, urea or glycine that are the fuels most commonly preferred in this kind of synthesis. The powders without heat treatment were studied by Thermogravimetric analysis (TGA), X-Ray Diffraction (XRD) and then calcined at 900?C. After heat treatment, the samples were characterized by analysis of X Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The modified synthesis route porposed was effective for obtaining powders. Both the alternative fuels chosen as the different weight ratios employed, influenced in the morphology and obtaining oxides / O campo da Qu?mica de Materiais vem se desenvolvendo nos ?ltimos anos, tendo havido um grande aumento do interesse na s?ntese e nas propriedades qu?micas e f?sicas de novos s?lidos inorg?nicos. Novas rotas de s?nteses e s?nteses modificadas tem sido desenvolvidas com o intuito n?o apenas de otimizar os processos em escala laboratorial, como tamb?m em escala industrial, al?m de torn?-los aceit?veis pela legisla??o ambiental vigente. A atual fenomelogia da qu?mica do estado s?lido aliada ?s propriedades de supercondutividade ? alta temperatura, ferromagnetismo, porosidade molecular e cores s?o evid?ncias afetadas pelo m?todo de s?ntese, que por sua vez, podem influenciar na aplica??o tecnol?gica desses materiais. Foi a partir desta compreens?o, que ?xidos mistos de n?quel e zinco nanoparticulados foram sintetizados atrav?s da rota combust?o por microondas utilizando tr?s tipos espec?ficos de combust?veis e empregando as raz?es m?ssicas 1:1 e 1:1/2 de c?tions met?licos/combust?vel, com o intuito de averiguar a influ?ncia de tais propor??es na obten??o dos s?lidos. Os novos combust?veis foram escolhidos em substitui??o a ur?ia ou glicina que s?o mais comumente preferidos nesse tipo de s?ntese. Os p?s sem tratamento t?rmico foram estudados atrav?s da An?lise Termogravim?trica (ATG) e da Difra??o de Raios-X (DRX), sendo, em seguida, submetidos ao tratamento t?rmico ? 900?C. Ap?s as calcina??es, foram caracterizados atrav?s das an?lises Difra??o de raiosx (DRX) e Microscopia Eletr?nica de Varredura (MEV). A rota de s?ntese modificada foi eficaz para obten??o dos p?s. Tanto os combust?veis alternativos escolhidos quanto as diferentes raz?es m?ssicas empregadas, influenciaram na morfologia e na obten??o dos ?xidos