Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-12-29T16:19:40Z No. of bitstreams: 1 AntonioCarlosSilvaDaCosta_TESE.pdf: 7680931 bytes, checksum: 91f08aea889978538206d110a2645e63 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-01-02T16:50:12Z (GMT) No. of bitstreams: 1 AntonioCarlosSilvaDaCosta_TESE.pdf: 7680931 bytes, checksum: 91f08aea889978538206d110a2645e63 (MD5) / Made available in DSpace on 2017-01-02T16:50:12Z (GMT). No. of bitstreams: 1 AntonioCarlosSilvaDaCosta_TESE.pdf: 7680931 bytes, checksum: 91f08aea889978538206d110a2645e63 (MD5) Previous issue date: 2015-02-27 / Ferritas de estrutura espin?lio (MFe2O4; M= metal alcalino terroso ou metal de transi??o) desempenham um papel importante na ci?ncia fundamental e na tecnologia moderna. A ferrita de magn?sio (MgFe2O4) e seus compostos dopados tem recebido especial aten??o devido a sua vasta ?rea de atua??o, que inclui aplica??es em m?dia de alta grava??o, cat?lise heterog?nea, adsor??o, sensores e tecnologias magn?ticas, de um modo geral. Suas propriedades estruturais, el?tricas e magn?ticas dependem da composi??o qu?mica, estrutura, tamanho de part?culas, al?m da substitui??o de c?tions nos s?tios A e/ou B que s?o diretamente influenciados pelo m?todo de s?ntese, as condi??es empregadas no processamento desses materiais (temperatura, taxa de aquecimento e tempo). Neste trabalho, ferritas do tipo Mg1-xBxFe2O4 (B= Ni; Cu; x= 0; 0,25; 0,50; 0,75 e 1) foram preparadas pelo m?todo de combust?o assistido por micro-ondas com a finalidade de avaliar tanto o efeito da substitui??o parcial do magn?sio por n?quel e cobre quanto o tratamento t?rmico sobre as propriedades magn?ticas. Os p?s precursores foram tratados termicamente a 600?C, 800?C e 1000?C/2h e caracterizados por An?lise Termogravim?trica (ATG), Difra??o de Raios X (DRX) em conjunto com o Refinamento pelo m?todo Rietveld, Microscopia eletr?nica de varredura (MEV) e Medidas de histerese magn?ticas realizadas ? temperatura ambiente. De acordo com as curvas termogravim?tricas dos p?s precursores, um comportamento semelhante foi observado para ambos os sistemas de amostras, onde o processo de perda total de massa aconteceu basicamente em duas etapas e na faixa de temperatura entre 30 e 500?C para o sistema Mg1-xNixFe2O4 e entre 30 e 400?C para o sistema Mg1-xCuxFe2O4. Os difratogramas de raios X revelaram a forma??o da fase espin?lio MgFe2O4 (ICSD 76176) de estrutura c?bica, e de fases secund?rias como Fe2O3 (ICSD 88418), NiO (ICSD 9866) e CuO (ICSD 87125) para os sistemas estudados. Em rela??o ?s curvas de histerese, verificou-se uma depend?ncia da magnetiza??o em fun??o do teor de dopante e da temperatura de tratamento t?rmico adotada. / The magnesium ferrite (MgFe2O4) and their doped compounds has received special attention due to its wide area of use, including applications in high recording media, heterogeneous catalysis, adsorption, sensors and magnetic technologies. Its structural, electrical and magnetic properties depend on the chemical composition, structure, particle size, and the replacement of cations in the sites A and/or B, which are directly influenced by the synthesis method, the conditions employed in processing these materials. In this work, ferrites of the type Mg1-xBxFe2O4 (B = Ni, Cu; x = 0, 0.25, 0.50, 0.75 and 1) were prepared by combustion method assisted by microwave in order to evaluate both the effect of partial substitution of Mg2+ for Ni2+ and/or Cu2+ as thermal treatment on the magnetic properties. Precursor powders were treated at the temperatures of 600 ?C, 800 ?C and 1000 ?C with 2h level and characterized by Thermogravimetric Analysis (TGA), X-Ray Diffraction (XRD) and refinement by the Rietveld method, Scanning Electron Microscopy (SEM) and magnetic hysteresis measurements at room temperature. According to the TG curves of the precursor powders, a similar behavior was observed for both systems where the total mass loss process occurred in two stages and in the temperature range between 30 and 500 ?C for Mg1-xNixFe2O4 system (x = 0, 0.25, 0.50 and 0.75) and between 30 and 450 ?C for Mg1-xCuxFe2O4 system (x = 0, 0.25, 0.50 and 0.75). The X-ray diffraction revealed the formation of the spinel phase MgFe2O4 (ICSD 76176) of cubic symmetry, and secondary phases such as ?-Fe2O3 (ICSD 88418), NiO (ICSD 9866) and CuO (ICSD 87125), for the studied systems. Regarding the hysteresis curves, there was a dependence of the magnetization as a function of the dopant content and the heat treatment temperature adopted. For Mg0,25Ni0,75Fe2O4 Mg0,75Cu0,25Fe2O4 and samples treated at 1000 ?C showed the highest saturation magnetization values of 41.9 emu/g and 35.76 emu/g, respectively.

Made available in DSpace on 2014-12-17T15:41:43Z (GMT). No. of bitstreams: 1 JoseEMS.pdf: 2230919 bytes, checksum: f0f4e57c89f3eae4282c6daae0fe0aba (MD5) Previous issue date: 2008-04-18 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / It was synthesized different Ni1-xMgxFe2O4 (0,2 ≤ x ≤ 0,7) compositions by use of citrate precursor method. Initially, the precursory citrates of iron, nickel and magnesium were mixed and homogenized. The stoichiometric compositions were calcined from 350?C to 1200?C at ambient atmosphere or in argon atmosphere. The calcined powders were characterized by XRD, TGA/DTG, FTIR, magnetic measures and reflectivity using the wave guide method. I was observed pure magnetic phase formation between 350?C and 500?C, with formation of ferrite and hematite after 600?C at ambient atmosphere. The calcined powder at argon atmosphere formed pure ferromagnetic phase at 1100?C and 1200?C. The Rietveld analyses calculated the cations level occupation and the crystallite size. The analyses obtained nanometric crystals (11-66 nm), that at 900?C/3h presents micrometric sizes (0,45 - 0,70 Om). The better magnetization results were 54 Am2/Kg for x= 0,2 composition, calcined at 350?C/3h and 30 min, and 55,6 Am2/Kg for x= 0,2 1200?C, calcined in argon. The hysteresis shows characteristics of soft magnetic material. Two magnetization processes were considered, superparamagnetism at low temperature and the magnetic domains formation at high temperatures. The materials presented absorption less or equal the 50 % in ranges specific frequency. As for the 2,0 and 3,0 thickness (in 11,0 - 11,8 GHz), the reflectivity of the x= 0,3, 0,5 and 0,4 compositions, all calcined at 900?C/3h showed agreement with MS and O. Various factors contribute for the final radiation absortion effect, such as, the particle size, the magnetization and the polymer characteristics in the MARE composition. The samples that presented better magnetization does not obtaining high radiation absorption. It is not clear the interrelaction between the magnetization and the radiation absorption in the strip of frequencies studied (8,2 - 12,4 GHz) / Foram sintetizadas diferentes composi??es da ferrita Ni1-xMgxFe2O4 com (0,2 ≤ x ≤ 0,7) pelo uso do m?todo dos citratos precursores. Para se obter a fase estequiom?trica Ni1-xMgxFe2O4, inicialmente foram misturados e homogeneizados os citratos precursores de ferro, n?quel e magn?sio. As composi??es estequiom?tricas foram calcinadas entre as temperaturas de 350?C e 1200?C, em atmosfera ambiente ou de arg?nio. Os p?s calcinados foram caracterizados por DRX, TGA/DTG, FTIR, medidas magn?ticas e refletividade pelo m?todo de guia de ondas. Foi observada a forma??o de fase pura ferrimagn?tica entre 350?C e 500?C, formando ferrita e hematita ap?s 600?C, em atmosfera ambiente. O p? calcinado em atmosfera de arg?nio formou fase ferrimagn?tica pura em 1100?C e 1200?C. A an?lise pelo m?todo de Rietveld calculou o n?vel de ocupa??o dos c?tions e o tamanho de cristalito. A an?lise obteve tamanhos de cristais nanom?tricos, (11 - 66 nm), que a 900?C/3h apresentam tamanhos microm?tricos (0,45 0,70 Om). Os melhores resultados de magnetiza??o foram 54 Am2/Kg para a composi??o x= 0,2, calcinada a 350?C/3h e 30 min, e 55,6 Am2/Kg para x= 0,2 a 1200?C, calcinada em arg?nio. As histereses mostraram um perfil de materiais magn?ticos moles. Dois processos de magnetiza??o foram considerados, o superparamagnetismo a baixa temperatura e a forma??o de dom?nios magn?ticos em altas temperaturas. Os materiais apresentaram absor??o igual ou inferior a 50 % em faixas de freq??ncias espec?ficas. Para as espessuras 3,0 e 2,0 mm (em 11-11,8 GHz), as refletividades das composi??es x= 0,3, x= 0,5 e x= 0,4, todas a 900?C/3h demonstraram concord?ncia com MS e O. V?rios fatores contribuem para o efeito final de absor??o de radia??o, tais como, o tamanho de part?culas, a magnetiza??o, e as caracter?sticas do pol?mero na composi??o do MARE. As amostras que apresentaram maiores magnetiza??es n?o atingiram alta absor??o de radia??o. N?o ficou esclarecido a interrela??o entre a magnetiza??o e a absor??o de radia??o na faixa de freq??ncia estudada (8,2 12,4 GHz)

Made available in DSpace on 2014-12-17T15:42:27Z (GMT). No. of bitstreams: 1 MariaJOSB.pdf: 5434037 bytes, checksum: 1a000204d534c8f41a3acbfce7dfaef5 (MD5) Previous issue date: 2007-09-17 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / It was synthesized MnZn ferrite with general formulae Mn1-xZnxFe2O4 (mol%), 0,3 &#8804; x &#8804; 0,7 by using the citrate precursor method. The precursors decomposition was studied by thermogravimetric analysis (TGA), differential thermogravimetric analysis (DTG), differential thermal analysis (DTA) and Fourier transform infrared (FTIR) of powder calcined at 350?C/3,5h. X-ray diffraction pattern (XRD) of samples was done from 350 to 1200?C/2h using various atmospheres. The power calcined at 350?C/3,5h formed spinel phase. It is necessary atmosphere control to avoid secondary phase such as hematite. From 900 to 1200?C was obtained 90,66 and 100% of MnZn spinel ferrite phase, respectively. Analysis by dispersive energy scanning (EDS) at 350?C shows high Mn and Zn dispersion, indicating that the diffusion process was homogeneous. Semi-quantitative analysis by EDS verified that despite the atmosphere control during calcinations at high temperatures (< 800?C) occurred ZnO evaporation causing stoichiometric deviation. Vibrating sample magnetometer (VSM) measures show soft ferrite material characteristics with Hc from 6,5 x 10-3 to 11,1 x 10-2 T. Saturation magnetization (Ms) and initial permeability (?i) of MnZn spinel phase obtained, respectively, from 14,3 to 83,8 Am2/kg and 14,1 to 62,7 (Am2/kg)T / Foi sintetizada ferrita de MnZn com f?rmula geral Mn1-xZnxFe2O4 (mol%) para 0,3 &#8804; x &#8804; 0,6 com uso do m?todo dos citratos precursores. A decomposi??o dos precursores foi estudada por an?lise termogravim?trica (TGA), termogravim?trica diferencial (DTG), an?lise t?rmica derivada (DTA) e espectroscopia na regi?o do infravermelho (FTIR) dos p?s calcinados em 350?C/3,5h. Foram feitas difra??es de raios X (DRX) entre 350 e 1200?C/2h usando v?rias atmosferas. O p? calcinado a 350?C/3,5h formou fase espin?lio. ? necess?rio o controle da atmosfera para evitar fases secund?rias como a hematita. Em 900 e 1200?C foram obtidos respectivamente, 90,7 e 100% de fase ferrita espin?lio. An?lises por espectroscopia de energia dispersiva (EDS) em 350?C mostrou alta dispers?o de Mn e Zn, indicando que o processo de difus?o foi homog?neo. A an?lise semi-quantitativa por EDS verificou que apesar do controle da atmosfera durante a calcina??o em altas temperaturas (> 800?C), ocorreu vaporiza??o de ZnO causando desvio estequiom?trico. Medidas por magnet?metro de amostra vibrante (MAV) mostraram caracter?sticas de materiais magneticamente macios com Hc de 6,5 x 10-3 at? 11,1 x 10-2 T. A magnetiza??o de satura??o e a permeabilidade inicial da fase espin?lio de MnZn foi obtida entre 14,3 a 83,8 Am2/kg e 14,1 a 62,7 (Am2/kg)T, respectivamente

Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2017-05-15T11:16:01Z No. of bitstreams: 1 2016 - Maria Clara Adum de paiva.pdf: 2279180 bytes, checksum: d1de128b3d5f5984c844a68538cd255e (MD5) / Made available in DSpace on 2017-05-15T11:16:01Z (GMT). No. of bitstreams: 1 2016 - Maria Clara Adum de paiva.pdf: 2279180 bytes, checksum: d1de128b3d5f5984c844a68538cd255e (MD5) Previous issue date: 2016-08-04 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / The demand for electricity production, and the need for thermoelectric use as power generating units, makes it necessary to search for less polluting matrices. In this search the catalytic combustion of methane, both from natural gas and other sources (residue disposal, for example) have shown promising. It is known the use of cobalt oxides is an alternative to the use of catalysts based on noble metals which has shown high performance. In order to potentiate the activity of the cobalt based catalyst, thus reducing both the ignition temperature and the temperature of total burning of methane, this work proposes the production of cobalt-based precursors using different types of layered double hydroxides (LDHs). Cobalt based catalysts partially substituted in layered double hydroxides (LDH Mg, Al and CO32-) were prepared by co-precipitation and impregnation with a nominal content of 9% CoII in LDH, or by impregnating a commercial hydrotalcite (HT). The LDH precursors were characterized by X-ray powder diffraction (XRD) and infrared absorption spectroscopy (FTIR). The XRD patterns indicated a LDH of 3R polytype. XRD showed the presence of Gibbisite in the HT precursor. The infrared spectra of precursor LDHs presented bands related to ?1, ?2 and ?3 vibrations of the carbonate anion, and interlayer water characteristic bands, thus in line with the XRD data. Analysis by XRD of the catalysts after calcination at 800 ?C showed the presence of periclase and spinel phases. Infrared spectra showed bands ascribed to the Mg-O and Co-O stretching in tetrahedral and octahedral sites as well as bands attributed to the Mg-O-Al bond and the cobalt spinel. The catalytic activity of these materials was investigated in the catalytic combustion of methane under kinetic regime, using predetermined reaction conditions to avoid diffusional limitations, resulting in a significant decrease in the combustion temperature, with the higher activity observed for the catalyst prepared by impregnating a commercial HT. Scanning electron microscopy (SEM) and quantitative chemical analysis (EDS) of catalysts with improved performance show both the homogeneous dispersion of the components in the sample surface and the higher aluminum content of the sample supported on HT. / A demanda de produ??o de energia el?trica, e a necessidade do uso de termel?tricas como unidades geradoras de energia, fazem com que seja necess?ria a busca por matrizes menos poluentes. Nessa busca a combust?o catal?tica do metano, tanto proveniente do g?s natural como de outras fontes (res?duo do tratamento de lixo, por exemplo), tem se mostrado promissora. Sabidamente o uso de ?xidos de cobalto ? uma alternativa, que vem mostrando alto desempenho, ao uso de catalisadores a base de metais nobres. Com o intuito de potencializar a atividade do catalisador a base de cobalto, reduzindo assim tanto a temperatura de igni??o quanto a de queima total do metano, esse trabalho prop?e sua produ??o utilizando como precursor diferentes tipos de hidr?xidos duplos lamelares (HDLs). Catalisadores ? base de cobalto parcialmente substitu?dos em hidr?xidos duplos lamelares (HDL de Mg, Al e CO32-) foram preparados por co-precipita??o e impregna??o num teor nominal de 9% de CoII em HDL, ou por impregna??o em hidrotalcita comercial (HT). Os HDLs precursores foram caracterizados por difra??o de raios?X pelo m?todo de p? (DRX) e por espectroscopia de absor??o no infravermelho (FTIR). Os difratogramas indicaram a obten??o de um HDL de politipo 3R. Por meio do DRX foi identificada a presen?a de Gibbisita no suporte de HT. Os espectros de infravermelho dos HDLs precursores presentaram bandas referentes ?s vibra??es ?1, ?2 e ?3 do ?nion carbonato, al?m de bandas caracter?sticas de ?gua interlamelar, estando portanto de acordo com os dados de DRX. A an?lise por difra??o de raios-X dos catalisadores ap?s calcina??o a 800?C mostrou apenas as fases espin?lio e pericl?sio. Os espectros de infravermelho apresentaram bandas atribu?das aos estiramentos Mg?O e Co?O em s?tios tetra?dricos e octa?dricos, assim como bandas caracter?sticas de Mg?O?Al e de Co3O4. A atividade catal?tica desses materiais foi investigada na combust?o catal?tica do metano, em regime cin?tico, empregando-se condi??es reacionais preestabelecidas de forma a evitar limita??es difusionais, obtendo-se uma significativa diminui??o na temperatura de combust?o, sendo que a maior atividade foi observada para o catalisador preparado por impregna??o em HT comercial. Foi realizada microscopia eletr?nica de varredura (MEV) e an?lise qu?mica quantitativa (EDS) para os catalisadores com melhor desempenho, mostrando tanto a dispers?o homog?nea dos componentes na superf?cie das amostras como o maior teor de alum?nio presente na amostra suportada em HT.

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 2014-12-17T14:07:12Z (GMT). No. of bitstreams: 1 RaimisonBA_DISSERT.pdf: 2147079 bytes, checksum: db6881c15458f1e487de74465b7088a0 (MD5) Previous issue date: 2013-07-04 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Magnetic ceramics have been widely investigated, especially with respect to intrinsic and extrinsic characteristics of these materials. Among the magnetic ceramic materials of technological interest, there are the ferrites. On the other hand, the thermal treatment of ceramic materials by microwave energy has offered various advantages such as: optimization of production processes, high heat control, low consumption of time and energy among others. In this work were synthesized powders of Ni-Zn ferrite with compositions Ni1- xZnxFe2O4 (0.25 &#8804; x &#8804; 0.75 mols) by the polymeric precursor route in two heat treatment conditions, conventional oven and microwave energy at 500, 650, 800 and 950?C and its structural, and morphological imaging. The materials were characterized by thermal analysis (TG/ DSC), X-ray diffraction (XRD), absorption spectroscopy in the infrared (FTIR), scanning electron microscopy (SEM), X-ray spectroscopy and energy dispersive (EDS) and vibrating sample magnetometry (VSM). The results of X-ray diffraction confirmed the formation of ferrite with spinel-type cubic structure. The extrinsic characteristics of the powders obtained by microwave calcination and influence significantly the magnetic behavior of ferrites, showing particles ferrimagn?ticas characterized as soft magnetic materials (soft), is of great technological interest. The results obtained led the potential application of microwave energy for calcining powders of Ni-Zn ferrite / Cer?micas magn?ticas t?m sido amplamente investigadas, principalmente com rela??o as caracter?sticas intr?nsecas e extr?nsecas destes materiais. Dentre os materiais cer?micos magn?ticos de interesse tecnol?gico, destacam-se as ferritas. Por outro lado, o tratamento t?rmico de materiais cer?micos por energia de microondas tem oferecido diversas vantagens, tais como: otimiza??o dos processos de obten??o, alto controle de aquecimento, menor consumo de tempo e energia entre outras. Neste trabalho, foram sintetizados p?s de ferritas Ni-Zn com composi??es Ni1-xZnxFe2O4 (0,25 &#8804; x &#8804; 0,75 mols) pela rota dos precursores polim?ricos em duas condi??es de tratamento t?rmico, em forno convencional e por energia de microondas a 500, 650, 800 e 950?C, e sua caracteriza??o estrutural, morfol?gica e magn?tica. Os materiais obtidos foram caracterizados por an?lises t?rmicas (TG/DSC), difra??o de raios x (DRX), espectroscopia de absor??o na regi?o do infravermelho (FTIR), microscopia eletr?nica de varredura (MEV), espectroscopia de raios X por dispers?o de energia (EDS) e magnetometria de amostra vibrante (VSM). Os resultados da difra??o de raios X confirmaram a forma??o da ferrita com estrutura c?bica do tipo espin?lio. As caracter?sticas extr?nsecas dos p?s obtidos e a calcina??o por microondas influenciaram de forma significativa o comportamento magn?tico das ferritas, apresentando part?culas ferrimagn?ticas, caracterizadas como materiais magn?ticos moles (macias), sendo de grande interesse tecnol?gico. Os resultados obtidos induziram o potencial de aplica??o de energia de microondas para a calcina??o de p?s de ferritas Ni-Zn

Made available in DSpace on 2014-12-17T15:41:43Z (GMT). No. of bitstreams: 1 AlyssonEGM.pdf: 4274696 bytes, checksum: 0f940193275b15ce59b4b1f45e3dc11c (MD5) Previous issue date: 2008-09-24 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Were synthesized different ferrites NixZn1-xFe2O4 (0,4 &#8804; x &#8804; 0,6) compositions by using citrate precursor method. Initially, the precursors citrates of iron, nickel and zinc were mixed and homogenized. The stoichiometric compositions were calcined at 350?C without atmosphere control and the calcined powders were pressed in pellets and toroids. The pressed material was sintered from 1100? up to 1200?C in argon atmosphere. The calcined powders were characterized by XRD, TGA/DTG, FTIR, SEM and vibrating sample magnetometer (VSM). All sintered samples were characterized using XRD, SEM, VSM and measurements of magnetic permeability and loss factor were obtained. It was formed pure ferromagnetic phase at all used temperatures. The Rietveld analyses allowed to calculate the cations level occupation and the crystallite size. The analyses obtained nanometric crystals (12-20 nm) to the calcined powder. By SEM, the sintered samples shows grains sizes from 1 to 10 &#956;m. Sintered densities (&#961;) were measured by the Archimedes method and with increasing Zn content, the bulk density decrease. The better magnetization results (105-110 emu/g) were obtained for x=0,6 at all sintering temperatures. The hysteresis shows characteristics of soft magnetic material. Two magnetization processes were considered, superparamagnetism at low temperature and the magnetic domains formation at high temperatures. The sintered toroids presents relative magnetic permeability (&#956;r) from 7 to 32 and loss factor (tan&#948;) of about 1. The frequency response of toroids range from 0,3 kHz to 0,2 GHz. The composition x=0,5 presents both greater &#956;r and tan&#948; values and x=0,6 the most broad range of frequency response. Various microstructural factors show influence on the behavior of &#956;r and tan&#948;, such as: grain size, porosity across grain boundary and inside the grain, grain boundary content and domain walls movement during the process of magnetization at high frequency studies (0,3kKz 0,2 GHz) / Foram sintetizadas diferentes composi??es da ferrita Ni1-xZnxFe2O4 com 0,4 &#8804; x &#8804; 0,6 pelo uso do m?todo dos citratos precursores. Para se obter a fase estequiom?trica do sistema Ni1-xZnxFe2O4 foram misturados e homogeneizados os citratos precursores de ferro, n?quel e zinco. As composi??es estequiom?tricas foram calcinadas em atmosfera ambiente na temperatura de 350?C e depois prensadas em pastilhas e tor?ides. As amostras prensadas foram sinterizadas nas temperaturas de 1100?, 1150? e 1200?C em atmosfera de arg?nio. Os p?s calcinados foram caracterizados por DRX, TGA/DTG, FTIR, MEV e magnetometria de amostra vibrante (MAV) e as amostras sinterizadas por DRX, MEV, MAV, massa espec?fica e medidas de permeabilidade e perdas magn?ticas. Observou-se a forma??o de fase pura ferrimagn?tica em todas as temperaturas aplicadas. A an?lise pelo m?todo de Rietveld calculou o n?vel de ocupa??o dos c?tions e o tamanho de cristalito. Foram obtidos tamanhos de cristais nanom?tricos, de 12 a 20 nm para os p?s calcinados. Por MEV, as amostras sinterizadas apresentam tamanhos de gr?os na faixa de 1 a 10 &#956;m. A massa espec?fica (&#961;) do material sinterizado apresenta uma tend?ncia de diminui??o com a adi??o de Zn. Os melhores resultados de magnetiza??o foram obtidos para x=0,6 nas tr?s temperaturas de sinteriza??o, variando de 105 a 110 emu/g. As histereses mostram um perfil de materiais magn?ticos moles. Dois processos de magnetiza??o foram considerados, o superparamagnetismo a baixa temperatura (350?C) e a forma??o de dom?nios magn?ticos em altas temperaturas. Os materiais sinterizados apresentam permeabilidade (&#956;) de algumas unidades, de 7 a 30, e perdas magn?ticas (tan&#948;) por volta de 1. A resposta em freq??ncia dos n?cleos toroidais est? na faixa de 0,3 kHz a 0,2 GHz. Os maiores valores de &#956; e tan&#948; s?o para x=0,5 e a maior faixa de resposta em freq??ncia ? para x=0,6. V?rios fatores da microestrutura contribuem para o comportamento das grandezas &#956; e tan&#948;, tais como: os tamanhos dos gr?os, porosidade inter e intragranular, quantidade de contornos de gr?os e os aspectos da din?mica das paredes de dom?nios quando excitadas magneticamente sob alta freq??ncia

Made available in DSpace on 2014-12-17T15:42:20Z (GMT). No. of bitstreams: 1 AdilaPGR_DISSERT.pdf: 1981953 bytes, checksum: be68a9256a00a195734cb22cb0bdc5b2 (MD5) Previous issue date: 2014-12-11 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The ferrite composition Ni1 - xCoxFe2O4 (0 &#8804; x &#8804; 0.75) were obtained by the method of microwave assisted synthesis and had their structural and magnetic properties evaluated due to the effect of the substitution of Ni by Co. The compounds were prepared: according to the concept of chemical propellants and heated in the microwave oven with power 7000kw. The synthesized material was characterized by absorption spectroscopy in the infrared (FTIR), Xray diffraction (XRD) using the Rietveld refinement, specific surface area (BET) , scanning electron microscopy (SEM) with aid of energy dispersive analysis (EDS) and magnetic measurements (MAV). The results obtained from these techniques confirmed the feasibility of the method of synthesis employed to obtain the desired spinel structure, the ferrite, nickel ferrite as for nickel doped with cobalt. The results from XRD refinement ally showed the formation of secondary phases concerning stages &#945; - Fe2O3, FeO, (FeCo)O e Ni0. On the other hand, there is an increase in crystallite size with the increase of cobalt in systems, resulting in an increased crystallinity. The results showed that the BET systems showed a reduction in specific surface area with the increase of cobalt and from the SEM, the formation of irregular porous blocks and that the concentration of cobalt decreased the agglomerative state of the system. The magnetic ferrites studied showed different characteristics according to the amount of dopant used, ranging from a very soft magnetic material (easy magnetization and demagnetization ) - for the system without cobalt - a magnetic material with a little stiffer behavior - for systems containing cobalt. The values of the coercive field increased with the increasing growth of cobalt, and the values of saturation magnetization and remanence increased up to x = 0,25 and then reduced. The different magnetic characteristics presented by the systems according to the amount of dopant used, allows the use of these materials as intermediates magnetic / As ferritas de composi??o Ni1&#8722;xCoxFe2O4 (0&#8804;x&#8804;0,75) foram obtidas atrav?s do m?todo de s?ntese assistida por microondas e tiveram suas propriedades estruturais e magn?ticas avaliadas em fun??o do efeito da substitui??o do Ni pelo Co. Os compostos foram preparados de acordo com o conceito da qu?mica dos propelentes e aquecidos em forno micro-ondas com pot?ncia 7000kw. O material sintetizado foi caracterizado por espectroscopia de absor??o na regi?o do infravermelho (FTIR), difra??o de raios X (DRX), com o uso do refinamento pelo m?todo de Rietveld, ?rea superficial espec?fica (BET), microscopia eletr?nica de varredura (MEV) com aux?lio de an?lise por dispers?o de energia (EDS) e medidas magn?ticas (MAV). Os resultados obtidos, a partir destas t?cnicas confirmaram a viabilidade do m?todo de s?ntese empregado para a obten??o da estrutura espin?lio desejada, tanto para a ferrita de n?quel quanto para as ferritas de n?quel dopadas com cobalto. Os resultados do DRX, aliado ao refinamento, mostraram a forma??o de fases secund?rias tais como as fases &#945; - Fe2O3, FeO, (FeCo)O e Ni0. Por outro lado, observou-se um aumento no tamanho do cristalito com o incremento do cobalto nos sistemas, implicando em um aumento da cristalinidade. Os resultados do BET mostraram que os sistemas apresentaram uma redu??o da ?rea superficial espec?fica com o incremento do cobalto e a partir do MEV observou-se a forma??o de blocos porosos irregulares e que o aumento da concentra??o de cobalto dimunuiu o estado de aglomera??o dos sistemas. As ferritas estudadas apresentaram caracter?sticas magn?ticas diferenciadas de acordo com a quantidade do dopante utilizado, variando de um material magn?tico bastante mole (f?cil magnetiza??o e desmagnetiza??o) - para o sistema sem cobalto - a um material magn?tico com comportamento um pouco mais duro - para os sistemas contendo cobalto. Os valores do campo coercitivo aumentaram com o crescente incremento do cobalto, e os valores de magnetiza??o de satura??o e reman?ncia aumentaram at? x=0,25 e depois reduziram. As caracter?sticas magn?ticas diferenciadas apresentadas pelos sistemas, de acordo com a quantidade de dopante utilizado, permite o uso desses materiais como magn?ticos intermedi?rios

Made available in DSpace on 2014-12-17T15:42:21Z (GMT). No. of bitstreams: 1 JoseEMS_TESE.pdf: 5374821 bytes, checksum: 56fe60cd3bbf0a42f7512c62fe5b976e (MD5) Previous issue date: 2013-03-08 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Were synthesized spinel-type ferrites with general formula Ni0,8Mg0.2-xMxFe2O4, where M represents the doping Mn, Co or Mn + Co simultaneously, x ranges for the values 0.02, 0.05 and 0.1. The value of x was divided by 2 in cases where M equals Mn and Co conjugates. We used the citrate precursor method and heat treatment to obtain the phases at 1100?C. The materials were characterized by XRD, TGA/ DTGA, SEM, MAV and reflectivity measurements by the method of waveguide. Powders to 350?C/3.5 h were crystalline and nanosized. According to the results this temperature all powders have a percentage of ferrite phase over 90%. The composition had the addition of Mn and Co simultaneously showed a higher percentage of secondary phase NiO, 5.8%. The TGA/DTGA curves indicate that this sample reached phase (s) crystalline (s) at lowest temperatures. The X-ray diffractograms of the samples calcined at 350?C and 1100?C were treated with the Rietveld refinament technique. The powders calcined at 1100 ?C/3h in air show to be 100% except spinel phase composition with 0.02 doping. The micrographs show clusters of particles with sizes smaller than 1 &#956;m in calcination temperature of 1100?C which agreed with the result of Rietveld refinement. In the compositions doped with Mn were higher values of magnetization (45.90 and 53.20 Am2/kg), which did not cause high microwave absorption. The theoretical calculation of magnetization (MT) was consistent with the results, considering that there was agreement between the increase of magnetization experimental and theoretical. It was observed that there was the interrelation of the final effect of absorption with the thickness of MARE, the composition of ferrimagnetic materials and in particular the specific values of frequency. The analysis shows that the reflectivity increases in the concentration of cobalt increased the frequency range and also for absorption 10.17 GHz and 84%, respectively. The best result of chemical homogeneity and the value of 2.96 x 10-2 tesla coercive field were crucial for high performance ferrite absorber with 0.1 cobalt. The Cobalt has high magnetocrystalline anisotropy, it is associated with an increased coercive field, Hc. Therefore, this property improves the results of reflectivity of spinel ferrites / Foram sintetizadas ferritas do tipo espin?lio com f?rmula geral Ni0,8Mg0,2-xMxFe2O4, onde M representa os dopantes Mn, Co ou Mn + Co simultaneamente, x varia para os valores 0,02; 0,05 e 0,1. O valor de x foi dividido por 2 nos casos em que M equivale a Mn com Co conjugados. Foi utilizado o m?todo dos citratos precursores e tratamento t?rmico na obten??o das fases a 1100?C. Os materiais foram caracterizados por DRX, TGA/DTGA, MEV, MAV e medidas de refletividade pelo m?todo de guia de ondas. Os p?s a 350?C/3,5h foram cristalinos e nanom?tricos. De acordo com os resultados nesta temperatura todos os p?s apresentam um percentual de fase ferrita superior a 90%. A composi??o que teve a adi??o de Mn e Co simultaneamente apresentou maior percentual de fase secund?ria NiO, 5,8%. As curvas TGA/DTGA indicam que essa amostra alcan?ou fase(s) cristalina(s) em temperaturas mais baixas. Os difratogramas de raios X das amostras calcinadas a 350?C e 1100?C foram tratados pela t?cnica de refinamento Rietveld. Os p?s calcinados a 1100?C/3h em atmosfera ambiente mostram ser 100% de fase espin?lio exceto a composi??o com 0,02 de dopantes. As micrografias apresentam aglomerados de part?culas com tamanhos menores que 1 &#956;m na temperatura de calcina??o de 1100?C, o que concordou com o resultado de refinamento Rietveld. Nas composi??es dopadas com Mn ocorreram os maiores valores de magnetiza??o (45,90 e 53,20 Am2/kg), o que n?o acarretou alta absor??o de microondas. O c?lculo te?rico da magnetiza??o (MT) foi coerente com os resultados, considerando-se que houve concord?ncia entre o aumento das magnetiza??es experimental e te?rica. Observa-se que houve interrela??o do efeito final de absor??o com a espessura do MARE, a composi??o do material ferrimagn?tico em particular e os valores espec?ficos de freq??ncia. A an?lise de refletividade indica que o aumento na concentra??o de cobalto aumentou a faixa de freq??ncia e a absor??o para 10,17 GHz e 84%, respectivamente. O resultado indica que a melhor homogeneidade qu?mica e o valor 2,96 x 10-2 tesla de campo coercitivo foram determinantes para o alto desempenho absorvedor da ferrita com 0,1 de cobalto. O Cobalto tem alta anisotropia magnetocristalina, isto est? associado ao aumento do campo coercitivo, Hc. Portanto, essa propriedade melhora os resultados de refletividade das ferritas espin?lio

Made available in DSpace on 2014-12-17T14:06:59Z (GMT). No. of bitstreams: 1 LucianoLMS.pdf: 2498297 bytes, checksum: 4e0c9395aebdb6d0be7a37737a51ca92 (MD5) Previous issue date: 2008-04-29 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Oxide type spinel AB2O4 presents structure adjusted for application in the automobile industry. The spinel of cobalt has many practical applications had its excellent physical and chemical properties such as catalyst in hydrocarbon oxidation reaction. The CeO2 has been used in many of these processes because it assigns to a material with excellent thermal resistance and mechanics, high capacity of oxygen stockage (OSC) among others properties. This work deals with the synthesis, characterization and catalytic application of spinel of cobalt and CeO2 with fluorita structure, obtained for method of Pechini and method of Gel-Combustion. The process of Pechini, the puff was obtained at 300 ?C for 2 h in air. In the process of Gel-Combustion the approximately at 350 ?C material was prepared and burnt for Pyrolysis, both had been calcined at 500 ?C, 700 ?C, 900 ?C and 1050 ?C for 2 h in air. The materials of the calcinations had been characterized by TG/DTA, electronic microscopy of sweepings (MEV), spectroscopy of absorption in the infra-red ray (FTIR) and diffraction of X-rays (DRX). The obtained material reaches the phase oxide at 450 oC for Pechini method and 500 ?C for combustion method. The samples were submitted catalytic reaction of n-hexane on superficies of materials. The reactor function in molar ration of 0, 85 mol.h-1.g-1 and temperature of system was 450 ?C. The sample obtained for Pechini and support in alumine of superficial area of 178,63 m2.g-1 calcined at 700 ?C, give results of catalytic conversions of 39 % and the sample obtained for method of gel-combustion and support in alumina of 150 mesh calcined at 500 ?C result 13 % of conversion. Both method were selective specie C1 / O espin?lio de cobalto tem muitas aplica??es pr?ticas devido as suas excelentes propriedades f?sicas e qu?micas tal como catalisador nas rea??es de oxida??o de hidrocarboneto. O CeO2 tem sido utilizado em muitos processos porque designa um material com excelente resist?ncia t?rmica e mec?nica, alta capacidade de estocagem de oxig?nio (OSC) entre outras propriedades. Este trabalho trata da s?ntese e caracteriza??o e aplica??o catal?tica dos ?xidos de cobalto com estrutura espin?lio e CeO2 com estrutura fluorita, obtidos pelo m?todo de Pechini e pelo m?todo de gel-combust?o. No processo Pechini o puff foi obtido a 300 ?C por 2 h em atmosfera ambiente. No processo de gel-combust?o o material foi preparado e queimado a aproximadamente 350 ?C por igni??o espont?nea e, posteriormente, ambos os p?s foram calcinados a 500 ?C, 700 ?C, 900 ?C e 1050 ?C por 2 h em atmosfera ambiente. Os p?s-resultantes das calcina??es foram caracterizados por TG/DTA, microscopia eletr?nica de varredura (MEV), espectroscopia de absor??o no infravermelho (FTIR) e difra??o de raios X (DRX). O material obtido deve atingir a fase ?xida a 450 ?C, para Pechini e 500 ?C para gel-combust?o. As amostras foram submetidas a rea??es catal?ticas de n-hexano sobre os catalisadores de Ce/Co. O reator operou a uma raz?o F/W fluxo molar de reagente por grama de catalisador de 0,85 mol.h-1.g-1 e temperatura no leito de 450 ?C. Para amostras obtidas por Pechini calcinadas a 700 ?C e suportada em alumina com ?rea superficial de 178,63 m2.g-1 obteve-se 39 % de convers?o catal?tica. Para as amostras obtidas pelo m?todo de gel-combust?o calcinadas a 500 ?C e suportada em alumina da Porogel com 150 mesh obteve cerca de 13 % de convers?o catal?tica. Ambos os m?todos foram seletivos a esp?cie C1.