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Estudo da viabiliza??o do uso da mistura h?brida ferrocarbonila / ferrita de NI0,5Zn0,5Fe2o4 como material absorvedor de radia??o eletromagn?ticaRodrigues, Manuella Karla da Cruz 31 August 2010 (has links)
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Previous issue date: 2010-08-31 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Were synthesized ferrites of NiZn on systems Ni0,5Zn0,5Fe2O4, the
precursors citrate method. The decomposition of the precursors was studied by
thermogravimetric analysis and spectroscopy in the infrared region, the
temperature of 350?C/3h. The evolution of the phases formed after calcinations
at 350?C/3h, 600, 1000 and 1100?C/2h was accompanied by X-ray diffraction
using the Rietveld refinement method for better identification os structures
formed. Was observed for samples calcined at different temperatures increased
crystallinity with increasing calcination temperature, being observed for the
samples calcined at 900 and 1100 ? C/2h was the precipitation of a secondary
phase, the phase hematite. The ferrocarbonila of industrial origin was analyzed
by X-ray diffraction and Rietveld for the identification of its structure. The
carbonyl iron was added NiZn ferrite calcined at 350?C/3h, 600, 900, 1000 and
1100?C/2h to the formation of hybrid mixtures. They were then analyzed by Xray
diffraction and Rietveld. The NiZn ferrite and ferrocarbonila as well as the
hybrid mixtures were subjected to analysis of scanning electron microscopy,
magnetic measurements and reflectivity. The magnetic measurements indicated
that the ferrite, the ferrocarbonila, as well as hybrid mixtures showed
characteristics of soft magnetic material. The addition of ferrocarbonila in all
compositions showed an increase in the results of magnetic measurements and
reflectivity. Best result was observed in the increase of the magnetization for the
hybrid mixture of Ferrocarbonila / ferrite of NiZn calcined at 600?C/2h. The
mixture Ferrocarbonila / ferrite calcined 1000?C/2h presented better absorption
of electromagnetic radiation in the microwave / Foram sintetizadas ferritas de NiZn no sistema Ni0,5Zn0,5Fe2O4, pelo
m?todo dos citratos precursores. A decomposi??o dos precursores foi estudada
por an?lise termogravim?trica e espectroscopia na regi?o do infravermelho na
temperatura de 350?C/3h. A evolu??o das fases formadas ap?s calcina??es a
350?C/3h, 600, 1000 e 1100?C/2h foi acompanhada por difra??o de raios X
utilizando o refinamento de Rietveld para melhor identifica??o das estruturas
formadas. Foi observado para as amostras calcinadas em diferentes
temperaturas o aumento da cristalinidade com o aumento da temperatura de
calcina??o, sendo verificado que para as amostras calcinadas a 900 e
1100?C/2h ocorreu a precipita??o de uma fase secund?ria, a fase hematita. A
ferrocarbonila de proced?ncia industrial foi analisada por Difra??o de raios X e
por Rietveld para a identifica??o de sua estrutura. A ferrocarbonila foi
adicionada ? ferrita de NiZn calcinada a 350?C/3h, 600, 1000 e 1100?C/2h para
a forma??o das misturas h?bridas. Em seguida foram analisadas por difra??o
de raios X e por Rietveld. A ferrita de NiZn, a ferrocarbonila, assim como as
misturas h?bridas foram submetidas ? an?lises de Microscopia Eletr?nica de
Varredura, medidas magn?ticas e refletividade. As medidas magn?ticas
indicaram que a ferrita, a ferrocarbonila, como tamb?m as misturas h?bridas
apresentaram caracter?sticas de material magn?tico macios. A adi??o de
ferrocarbonila em todas as composi??es indicou um aumento nos resultados de
medidas magn?ticas e de refletividade. Foi verificado melhor resultado no
aumento da magnetiza??o para a mistura h?brida de Ferrocarbonila/ferrita de
NiZn calcinada 600?C/2h. A mistura Ferrocarbonila/ferrita calcinada 1000?C/2h
apresentou melhor resultado absor??o da radia??o eletromagn?tica na faixa de
microondas em rela??o ?s outras misturas
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Estudo das caracter?sticas magn?ticas e absorvedoras das ferritas de nizn, niznmn, mnzn, nimg, nicuzn e nicuznmg obtidas via m?todo do citrato precursorPessoa, R?gia Chacon 22 December 2009 (has links)
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Previous issue date: 2009-12-22 / Universidade Estadual de Roraima / Were synthesized systems Ni0,5Zn0,5Fe2O4, i0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 and Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, the precursors citrate method. The decomposition of the precursors was studied by thermogravimetric analysis and spectroscopy in the infrared region, the temperature of 350?C/3h. The evolution of the phases formed after calcinations at 350, 500, 900 and 1100?C/3h was accompanied by X-ray diffraction using the Rietveld refinement to better identify the structures formed. The
materials were also analyzed by scanning electron microscopy, magnetic measurements and analysis of the reflectivity of the material. The samples calcined at different temperatures showed an increase of crystallinity with increasing calcination temperature, verifying that for some compositions at temperatures above 500?C precipitates of second phase such as hematite and CuO. The compositions of manganese present in the structure diffusion processes slower due to the ionic
radius of manganese is greater than for other ions substitutes, a fact that delays the stabilization of spinel structure and promotes the precipitation of second phase. The compositions presented with copper precipitation CuO phase at a temperature of 900 and 1100?C/3h This occurs according to the literature because the concentration of copper in the structure is greater than 0.25 mol%. The magnetic measurements revealed features of a soft ferrimagnetic material, resulting in better magnetic properties for the NiZn ferrite and NiCuZnMg at high temperatures. The reflectivity measurements showed greater absorption of electromagnetic radiation in the microwave band for the samples calcined at 1100?C/3h, which has higher crystallite size and consequently the formation of multi-domain, increasing the magnetization of the material. The results of absorption agreed with the magnetic measurements,
indicating among the ferrites studied, those of NiZn and NiCuZnMg as better absorbing the incident radiation. / Foram sintetizados os sistemas Ni0,5Zn0,5Fe2O4, Ni0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 e Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, pelo m?todo dos citratos precursores. A decomposi??o dos precursores foi estudada por an?lise termogravim?trica e espectroscopia na regi?o do infravermelho, na temperatura de 350?C/3h. A evolu??o das fases formadas ap?s as calcina??es a
350, 500, 900 e 1100?C/3h foi acompanhada por difra??o de raios X utilizando o refinamento de Rietveld, para melhor identifica??o das estruturas formadas. Os materiais foram tamb?m analisados por microscopia eletr?nica de varredura,
medidas magn?ticas e an?lise da refletividade do material. As amostras calcinadas em diferentes temperaturas indicaram um aumento da cristalinidade com o aumento da temperatura de calcina??o, verificando-se que, para algumas composi??es, em
temperaturas acima de 500?C ocorre a precipita??o de segunda fase, como hematita e CuO. As composi??es com mangan?s na estrutura apresentaram processos de difus?o mais lentos devido ao raio i?nico do mangan?s ser maior em rela??o aos outros ?ons substituintes, fato que retarda a estabiliza??o da estrutura espin?lio e favorece a precipita??o de segunda fase. As composi??es com cobre apresentaram precipita??o da fase CuO na temperatura de 900 e 1100?C/3h, fato que ocorre segundo a literatura porque a concentra??o de cobre na estrutura ? maior que 0,25 mol%. As medidas magn?ticas revelaram racter?sticas de um material ferrimagn?tico macio, obtendo-se melhores ar?metros magn?ticos para as ferritas de NiZn e NiCuZnMg em altas temperaturas. As medidas de refletividade mostraram
maior absor??o da radia??o eletromagn?tica na faixa de microondas para as amostras calcinadas a 1100?C/3h, que tem maior tamanho do cristalito e em conseq??ncia forma??o de multidom?nios, aumentando a magnetiza??o do material.
Os resultados de absor??o concordaram com as medidas magn?ticas, indicando dentre as ferritas estudadas, as de NiZn e NiCuZnMg como melhores absorvedoras da radia??o incidente.
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A Novel Chip Resistor Spacecloth For Radar Absorbing MaterialsSudhendra, Chandrika 09 1900 (has links)
Spacecloth design and development is vital and crucial in Radar Absorbing Materials (RAM) for achieving Low Observability in an Aircraft or an Unmanned Air Vehicle(UAV). The RAM design translates into the spacecloth design. The spacecloths form the constituent layers in a broadband Jaumann absorber in which case they have to be designed for various values of surface resistivity. The design specifications of spacecloth(s) in RAMS is well understood and documented in literature. But the design of spacecloth hitherto, has been the domain of materials' scientists wherein the specified properties of the spacecloth are achieved by an iterative, trial and error process, by mixing various constituents in different proportions to get the design specified surface resistivity in the final end-product. In an effort to bridge this gap, a novel spacecloth for RAM applications is proposed in the thesis. It is proposed that a repetitive geometrical grid network of chip resistors simulates spacecloth. The sheet resistivity of the spacecloth is derived by analyzing various geometries like square, rectangle, triangle and hexagonal grids. The transmission and reflection loss for the chip resistor spacecloth is derived. The design of chip resistor spacecloths for operation at S and C bands is given followed by experimental verification using waveguide simulator experiments. Numerical study of multilayer RAM has been carried out with exponential taper variation of surface resistivities for constituent spacecloth layers and design curves are given for multilayer RAM both for normal and oblique incidence for TE and TM polarizations.
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