Made available in DSpace on 2015-03-03T15:43:03Z (GMT). No. of bitstreams: 1 PauloRCS_DISSERT.pdf: 5184228 bytes, checksum: d3e31e6fed97c72238a19b42897cf9b0 (MD5) Previous issue date: 2014-05-27 / Universidade Federal do Rio Grande do Norte / In this work we obtain nickel ferrite by the combustion synthesis method whcih involves synthesising in an oven at temperatures of 750oC, 950oC and 125oC. The precursors oxidizing used were nickel nitrate, ferric as an oxidizing and reducing urea (fuel). After obtaining the mixture, the product was deagglomerated and past through a 270 mesh sieve. To assess the structure, morphology, particle size, magnetic and electrical properties of nanoparticles obtained the samples were sintered and characterized by x-ray distraction (XRD), x-ray fluorescence spectroscopy (FRX); scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), vibrating sample magnetometer (MAV ) and electrical permittivity. The results indicated the majority of phase inverse spinel ferrite and Hematite secondary phase nickel and nickel oxide. Through the intensity of the distraction, the average size of the crystallization peaks were half-height width which was calculated using the Scherrer equation. From observing the peaks of all the reflections, it appears that samples are crystal clear with the formation of nanoparticles. Morphologically, the nanoferritas sintered nickel pellet formation was observed with three systems of particle size below 100mn, which favored the formation of soft pellets. The average size of the grains in their micrometric scale. FRX and EDS showed qualitatively the presence of iron elements nickel and oxygen, where through quantitative data we can observe the presence of the secondary phase. The magnetic properties and the saturation magnetization and the coercive field are in accordance with the nickel, ferrite where the curve of hysteresis has aspects of a soft material. Dielectric constant values are below 10 and low tangent loss / Este trabalho descreve a obten??o de ferrita de n?quel pelo m?todo de s?ntese de combust?o, seguida pela sinteriza??o em forno, ?s temperatura de 750oC, 950oC e 1250oC. Os precursores oxidantes utilizados foram: nitratos de n?quel e ferro III como redutor, foi usada a ur?ia (combust?vel). Depois da obten??o do p?s-misturas, o produto foi desaglomerado e passado em uma peneira de mesch 270. A estrutura, a morfologia, o tamanho das part?culas e as propriedades magn?ticas e el?tricas das nanopart ?culas obtidas das amostras p?s sinterizadas foram caracterizadas por difra??o de raios-X (DRX), espectroscopia de uoresc?ncia de raios-X (FRX), microscopia eletr?nica de varredura (MEV ), espectroscopia de energia dispersiva (EDS), magnet ?metro de amostra vibrante (MAV ) e an?lise el?trica. Os resultados indicaram a fase majorit?ria do espin?lio inverso ferrita de n?quel e a fase secund?ria de hematita e ?xido de n?quel. Atrav?s da intensidade dos picos de difra??o de raios-X e da largura de meia altura no espectro, foi calculado o tamanho m?dio do cristalito pela equa??o Scherrer, observando-se os picos de todas as re ex?es, veri cando a cristalinidade das amostras, e com forma??o de nanopart?culas. Morfologicamente, para as nanoferritas de n?quel sinterizadas, observou-se a forma??o de aglomerados moles nos tr?s sistemas com part?culas de tamanho inferior a 100nm. O tamanho m?dio dos gr?os est? em escala microm?trica. Os espectros de FRX e EDS mostraram qualitativamente a presen?a dos elementos ferro, n?quel e oxig?nio. Atrav?s dos dados quantitativos, pode-se observar a presen?a da fase secund?ria. As propriedades magn?ticas, como a magnetiza??o de satura??o e o campo coercitivo, est?o de acordo com a ferrita de n?quel, em que a curva de histerese tem aspectos de um material mole. Os valores de constante diel?trica est?o abaixo de 10 e baixa tangente de perdas.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-01-04T20:02:52Z No. of bitstreams: 1 AnaPaulaDaSilvaPeres_TESE.pdf: 6039953 bytes, checksum: dab3721993c73bd25b03fa484535a768 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-01-05T20:52:08Z (GMT) No. of bitstreams: 1 AnaPaulaDaSilvaPeres_TESE.pdf: 6039953 bytes, checksum: dab3721993c73bd25b03fa484535a768 (MD5) / Made available in DSpace on 2016-01-05T20:52:08Z (GMT). No. of bitstreams: 1 AnaPaulaDaSilvaPeres_TESE.pdf: 6039953 bytes, checksum: dab3721993c73bd25b03fa484535a768 (MD5) Previous issue date: 2014-09-08 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Nos ?ltimos anos, transportadores s?lidos de oxig?nio adequados t?m sido desenvolvidos para serem utilizados em diferentes processos de Recircula??o Qu?mica. O sucesso desta tecnologia est? diretamente relacionado com a reatividade qu?mica e a capacidade de armazenamento de oxig?nio do transportador. Desta forma, a pesquisa no desenvolvimento de novos materiais que possam ser aplicados ao processo torna-se de fundamental import?ncia. Entre os poss?veis candidatos est?o os transportadores baseados em n?quel e cobre por apresentarem propriedades termodin?micas favor?veis. Neste trabalho, aluminatos do tipo MAl2O4 (M=Mg e Ca) e M0,9B0,1Al2O4 (B=Ni e Cu) usados como suportes, foram sintetizados pela rea??o de combust?o assistida por microondas e calcinados a 900?C/2h. Em seguida, os suportes foram impregnados com 10% (m/m) de n?quel ou cobre e, posteriormente calcinados a 600?C/2h para obten??o dos transportadores s?lidos de oxig?nio, que foram caracterizados por Difra??o de raios X (DRX), Microscopia eletr?nica de varredura (MEV) e Redu??o a temperatura programada (RTP). Rea??es simulando o processo de combust?o por recircula??o qu?mica foram realizados atrav?s de ciclos de redu??o/oxida??o, com o objetivo de avaliar a reatividade dos transportadores. A an?lise de DRX mostrou picos de difra??o de estruturas tipo espin?lio. Nos suportes dopados n?o foram verificadas a presen?a de fases secund?rias, sugerindo que todo o metal foi incorporado ? estrutura do espin?lio. Nos transportadores s?lidos de oxig?nio, as fases NiO e CuO foram observadas ap?s a impregna??o das fases ativas sobre os diferentes suportes. Os resultados das avalia??es dos ciclos qu?micos de redu??o/oxida??o revelaram que os TSO?s impregnados com n?quel em diferentes suportes mostraram-se mais ativos, sendo potenciais candidatos para a aplica??o na tecnologia de Recircula??o Qu?mica. / In recent years, solid carriers suitable oxygen have been developed for use in different chemical processes recirculation. The success of this technology is directly related to the chemical reactivity and the oxygen storage capacity of the carrier. Thus, research into the development of new materials that can be applied to the process becomes extremely important. Possible candidates are the carriers based on nickel and copper for presenting favorable thermodynamic properties. In this work, aluminates type MAl2O4 (M = Mg and Ca) and M0,9B0,1Al2O4 (B = Ni and Cu) that are used as supports were synthesized by combustion reactions assisted by microwave and calcined at 900?C/2h. Then, the carriers were impregnated with 10% (m/m) of nickel or copper, and subsequently calcined at 600?C/2h to obtain the solid oxygen carriers, which were characterized by X-ray diffraction (XRD) Microscopy scanning electron microscopy (SEM) and temperature programmed reduction (TPR). Reactions simulating the combustion process by chemical recirculation were performed by cycles reduction/oxidation, in order to evaluate the reactivity of carriers. XRD analysis revealed diffraction peaks of the spinel type structures. In the doped substrates were verified the presence of secondary phases, suggesting that all the metal was incorporated into the spinel structure. In solid oxygen carriers, the NiO and CuO phases were observed after impregnation of active phases on different media. The results of evaluations of chemical cycles reduction/oxidation revealed that TSO's impregnated with nickel in various media were more active and are potential candidates for use in the chemical recirculation technology

Made available in DSpace on 2014-12-17T14:58:10Z (GMT). No. of bitstreams: 1 MarcioWDM.pdf: 1222615 bytes, checksum: 363df5ee1daf20ddbc955155e60347ed (MD5) Previous issue date: 2006-05-19 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The aluminothermic reduction consists in an exothermic reaction between a metallic oxide and aluminum to produce the metal and the scum. The extracted melted metal of that reaction usually comes mixed with particles of Al2O3 resulting of the reduction, needing of subsequent refine to eliminate the residual impure as well as to eliminate porosities. Seeking to obtain a product in powder form with nanometric size or even submicrometric, the conventional heat source of the reaction aluminothermic , where a resistor is used (ignitor) as ignition source was substituted, for the plasma, that acts more efficient way in each particle of the sample. In that work it was used as metallic oxide the niobium pentoxide (Nb2O5) for the exothermal reaction Nb2O5 + Al. Amounts stoichiometric, substoichiometric and superestoichiometric of aluminum were used. The Nb2O5 powder was mixed with aluminum powder and milled in planetarium of high energy for a period of 6 hours. Those powders were immerged in plasm that acts in a punctual way in each particle, transfering heat, so that the reaction can be initiate and spread integrally for the whole volume of the particle. The mixture of Nb2O5 + Al was characterized through the particle size analysis by laser and X-ray diffraction (DRX) and the obtained product of reaction was characterized using the electronic microscopy of sweeping (MEV) and the formed phases were analyzed by DRX. Niobium powders with inferior sizes to 1 mm were obtained by that method. It is noticed, through the analysis of the obtained results, that is possible to accomplish the aluminothermic reduction process by plasma ignition with final particles with inferior sizes to the original oxide / A redu??o aluminot?rmica consiste na rea??o exot?rmica de um ?xido met?lico com alum?nio para produzir o metal e a esc?ria. O metal fundido extra?do dessa rea??o vem normalmente misturado com part?culas de alumina resultante da redu??o, necessitando de um refino posterior tanto para eliminar as impurezas residuais como tamb?m para eliminar porosidades. Visando obter um produto em forma de p? e com tamanho nanom?trico ou at? mesmo submicrom?trico, foi substitu?da a fonte convencional de calor da rea??o aluminotermica, onde se utiliza um resistor (ignitor) como fonte de igni??o, pelo plasma, que atua de forma mais eficiente em cada part?cula da amostra. Nesse trabalho foi utilizado como ?xido met?lico o pent?xido de ni?bio (Nb2O5) para a rea??o exot?rmica Nb2O5 + Al. Foram utilizadas quantidades estequiom?tricas, subestequiom?tricas e superestequiom?tricas de alum?nio. O p? de Nb2O5 foi misturado com p? de alum?nio e mo?dos em planet?rio de alta energia por um per?odo de 6 horas. Esses p?s foram imersos em plasma que age de forma pontual em cada part?cula, transferindo calor, de modo que a rea??o possa ser iniciada e propagada integralmente para todo o volume da part?cula. A mistura de Nb2O5 + Al foi caracterizada atrav?s da granulometria a laser e difra??o de raios X (DRX) e o produto da rea??o obtido foi caracterizado utilizando a microscopia eletr?nica de varredura (MEV) e as fases formadas foram analisadas por DRX. Nota-se, atrav?s da an?lise dos resultados obtidos, que ? poss?vel realizar o processo de redu??o aluminot?rmica por igni??o a plasma com part?culas finais com tamanhos inferiores ao do ?xido original

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-03-28T19:07:36Z No. of bitstreams: 1 TiagoRobertoDaCosta_TESE.pdf: 4624767 bytes, checksum: b882489e2f56b6e0d740f5f1aaf85b08 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-03-28T23:57:17Z (GMT) No. of bitstreams: 1 TiagoRobertoDaCosta_TESE.pdf: 4624767 bytes, checksum: b882489e2f56b6e0d740f5f1aaf85b08 (MD5) / Made available in DSpace on 2017-03-28T23:57:17Z (GMT). No. of bitstreams: 1 TiagoRobertoDaCosta_TESE.pdf: 4624767 bytes, checksum: b882489e2f56b6e0d740f5f1aaf85b08 (MD5) Previous issue date: 2016-08-05 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / A matriz energ?tica mundial ? basicamente constitu?da a base de combust?veis f?sseis, sendo que diferentes estudos indicam que nas pr?ximas d?cadas n?o haver? mudan?as significativas nesse cen?rio e isso impacta de modo significativo no meio ambiente, pois a queima desses combust?veis para gera??o de energia produz bastante CO2. Sendo o di?xido de carbono o principal g?s de origem antropog?nica, respons?vel pela intensifica??o do efeito estufa. Devido a isso, cientistas e pol?ticos de todo mundo tem sugerido diversas medidas e tecnologias que objetivam a diminui??o das emiss?es de CO2 na atmosfera para as pr?ximas d?cadas. Entre as tecnologias, a Captura e Armazenamento de CO2 (CAC) tem tido um destaque especial nos ?ltimos anos. Estudos realizados pela Ag?ncia Internacional de Energia (International Energy Agency-IEA) quanto o Painel Intergovernamental sobre Mudan?as Clim?ticas (IPCC), sugerindo diversos cen?rios de crescimento econ?micos e de demanda energ?tica, indicam que na maioria dos casos as tecnologias de captura e armazenamento do CO2 contribuem entre 10-55% do esfor?o mundial para reduzir as concentra??es de CO2 na atmosfera at? 2100. Nesse contexto, a combust?o indireta com transportadores s?lidos de oxig?nio (processo Chemical-Looping Combustion-CLC), ? considerada uma das melhores alternativas para reduzir os custos da captura do CO2, principalmente quando comparadas aos processos convencionais, pois n?o necessita da separa??o do CO2 do N2, pois o combust?vel n?o ? misturado diretamente com ar ou oxig?nio. Esta tese de doutorado est? focada no desenvolvimento de cinco transportadores de oxig?nio ? base de mangan?s, os quais foram primeiramente caracterizados com objetivo de determinar quais deles s?o mais promissores para serem avaliados em processos de CLC. As t?cnicas e metodologias de caracteriza??es utilizadas durante a primeira etapa foram: porosimetria por inje??o de merc?rio, resist?ncia ? fratura, difra??o de raios X (DRX), redu??o e oxida??o ? temperatura programada (TPR e TPO), capacidade de transporte de oxig?nio (Roc), composi??o qu?mica, reatividade por termogravimetria e ?ndice de velocidade. Conclu?da essas etapas, verificou-se que os transportadores Mn-ZrMF e Mn-ZrSG apresentaram propriedades apropriadas para serem avaliados em um reator de leito fluidizado descont?nuo, onde os experimentos se assemelham ?s condi??es de CLC. Ao fim dos testes no reator, os transportadores de oxig?nio foram submetidos a algumas t?cnicas de caracteriza??o: DRX, TPR e MEV (Microscopia Eletr?nica de Varredura). O transportador Mn-ZrMF apresentou problemas de aglomera??o durante os testes no reator, sendo considerado inapropriado para prosseguir com os experimentos. Por outro lado, o Mn-ZrSG apresentou elevada reatividade com os combust?veis utilizados (CO > H2 > CH4), n?o sendo verificado o problema da aglomera??o, tendo baixa perda por atrito, com vida m?dia superior a 11.000 horas. Esse material ? bastante promissor para seu uso em CLC de combust?veis s?lidos. / The world?s energy matrix is essentially composed of fossil fuels and different studies show indicate that in the next decades there will be no significant changes in this scenario, which impacts significantly on the environment, since the burning of fossil fuels for power generation gives there main contibution to antropogenic CO2 emissions produces greatest amount of CO2. Carbon dioxide is the main anthropogenic gas responsible for intensifying the greenhouse effect. Because of this, scientists and politicians around the world have suggested a number of strategies and technologies to reduce CO2 emissions to the atmosphere for the next decades. Among these technologies, CO2 capture and storage (CCS) has gained attention in recent years. Studies conducted by the International Energy Agency (IEA) and the Intergovernmental Panel on Climate Change (IPCC) suggest various scenarios of economic growth and energy demand, indicating that in most cases the CO2 capture and storage technologies will contribute between 10-55% of the global effort to reduce CO2 concentrations in the atmosphere by 2100. In this context, the Chemical-Looping Combustion is considered one of the better alternatives to reduce the cost of CO2 capture, especially when compared to conventional capture processes, since it does not require the separation of CO2 from N2, once fuel is not mixed directly with air or oxygen. This doctoral thesis is focused in the development of five manganese-based oxygen carriers, which were first characterized in order to determine which of them are most promising to be evaluated in CLC processes. The techniques and characterization methods used during the first stage were: mercury porosimetry, fracture resistance, X-ray diffraction (XRD), temperature programmed reduction and oxidation (TPR and TPO), oxygen transport capacity (Roc), chemical composition, redox by thermogravimetry and rate index. Completed these steps, it was found that the carriers Mn- ZrMF and ZrSG presented appropriate properties to be evaluated in a discontinuous fluidized bed reactor, where the experiment conditions are subject to the CLC conditions. After the testing reactor, the oxygen carriers were submitted to the following characterization techniques: DRX, TPR and SEM (Scanning Electron Microscopy). Mn-ZrMF carrier presented problems of agglomeration during testing in the reactor, being considered inappropriate for CLC. On the other side, the Mn-ZrSG carrier showed high reactivity with the fuels used (CO> H2> CH4). Due this Mn-ZrSG is appropriate for CO + H2 combustion, but suffer deactivation during CH4 combustion. Do not showed agglomeration problems. The attrition rate was low and the lifetime was than 11.000 hours. Thus this material can be considered suitable to be used in solid fuels CLC.

Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2017-05-30T17:17:07Z No. of bitstreams: 1 2015 - Than?zia Ferraz Santos.pdf: 1742658 bytes, checksum: 07706cbaaa52be04cb7ec04d0d453fa2 (MD5) / Made available in DSpace on 2017-05-30T17:17:07Z (GMT). No. of bitstreams: 1 2015 - Than?zia Ferraz Santos.pdf: 1742658 bytes, checksum: 07706cbaaa52be04cb7ec04d0d453fa2 (MD5) Previous issue date: 2015-08-28 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico - CNPq / In this work, potential energy surfaces for the reactions of hydroxyl radical and 2,5-dimethylfuran were studied using the Density Functional Theory. The stationary points, such as reactants, pre-barrier complex, transition states and products were located at BHandHLYP/aug-cc-pVDZ and M06-2X-cc-pVDZ levels by geometry optimization, followed by the calculations of vibrational frequencies. Single point calculations using CCSD(T) were also explored. Thermodynamics properties of enthalpy, entrophy and Gibbs free energies have been determinated at 298,15 K within the conventional equations of Statistical Thermodynamics. The results suggest different addition mechanisms, since an analysis of the potential energy surface (PES) in BHandHLYP/ aug-cc-pVDZ points to paths going through a pi-type intermediary, while in M06-2X/aug-cc-pVDZ the intermediary would have a sigma-type interaction. About the abstraction reactions, only the PES obtained in M06-2X/aug-cc-pVDZ level points to the formation of a pre-barrier complex. The rate coefficients have been determined on the basis of the Variational Transition State Theory, with the kcvt program. The coefficient obtained at CCSD(T)/aug-cc-pVDZ//BHandHLYP/aug-cc-pVDZ for the mechanism which includes the participation of ?-PC is ???????=48,4?10?11, cm? molec-1 s-1, approximately 4 times higher than the experimental rate coefficient. Deviations of this magnitude are considered satisfactory in theoretical calculation of kinetic parameters. Addition of OH should be the main degradation pathway for furan and its derivatives, during daytime. Moreover, it was possible to clarify the effect of the formation of pre-barrier complexes in the reactions between DMF and OH radicals and propose rate coefficients in the high temperature region, which can be applied in combustion studies / Neste trabalho, as superf?cies de energia potencial para as rea??es do radical hidroxila (OH) com o 2,5-dimetilfurano (DMF) foram estudadas em detalhes, utilizando a Teoria do Funcional de Densidade. Pontos estacion?rios como reagentes, complexos pr?-barreira, estados de transi??o e produtos foram localizados por procedimentos de otimiza??o de geometria, acompanhado do c?lculo das frequ?ncias vibracionais, em n?veis BHandHLYP/aug-cc-pVDZ e M06-2X/aug-cc-pVDZ. C?lculos single point a partir da metodologia coupled-cluster com simples e duplas excita??es com tratamento perturbativo das triplas conectadas, CCSD(T), tamb?m foi explorado. Propriedades termodin?micas de entalpia, entropia e energia livre de Gibbs foram calculadas a 298,15 K atrav?s das equa??es da Termodin?mica Estat?stica. Os resultados sugerem mecanismos de adi??o diferentes, j? que uma an?lise da superf?cie de energia potencial (SEP) em BHandHLYP/aug-cc-pVDZ aponta para caminhos passando por um intermedi?rio do tipo pi, enquanto em M06-2X/aug-cc-pVDZ o intermedi?rio seria do tipo sigma. Na abstra??o, apenas a SEP obtida em M06-2X/aug-cc-pVDZ aponta para a forma??o de um intermedi?rio pr?-barreira. Coeficientes de velocidade foram determinados com base na Teoria do Estado de Transi??o Variacional, com aux?lio do programa kcvt. O coeficiente CCSD(T)/aug-cc-pVDZ//BHandHLYP/aug-cc-pVDZ para o mecanismo que inclui a participa??o do ?-PC ? de ???????=48,4?10?11 cm? molec-1 s-1, superestimado em rela??o ao coeficiente experimental em aproximadamente 4 vezes. Desvios dessa magnitude s?o esperados em c?lculos te?ricos, especialmente quando envolvem mol?culas volumosas. Pode-se constatar que a adi??o de OH deve ser a principal rota de degrada??o para o furano e seus derivados durante o dia. Al?m disso, foi poss?vel esclarecer o efeito da forma??o de intermedi?rios pr?-barreira nas rea??es entre DMF e o radical OH.

Made available in DSpace on 2014-12-17T15:42:14Z (GMT). No. of bitstreams: 1 AndreiaCL_TESE.pdf: 5308625 bytes, checksum: 13df680734f410713c3992d8e7be1c8f (MD5) Previous issue date: 2010-12-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Orthoferrites AFeO3 (A = rare earth) are an important class of perovskite oxides that exhibit weak ferromagnetism. These materials find numerous applications as chemical sensors, cathodes for fuel cells and catalysis, which make them interesting from the standpoint of science and technology. Their structural, electrical and magnetic properties are dependent on many factors such as the preparation method, heat treatment conditions, chemical composition and replacement of cations in sites A and/or B. In this paper, LaFe1-xMnxO3 (0 ≤ x ≤ 1) orthoferrites-type was prepared by Pechini method and Microwave-assisted combustion reaction in order to evaluate the influence of synthesis route on the formation of oxide, as well as the effect of parcial replacement of iron by manganese and heat treatment on the magnetic properties. The precursor powders were calcined at 700?C, 900?C, 1100?C and 1300?C for 4 hours and they were characterized by the techniques: Thermogravimetric analysis (TGA), X ray diffraction (XRD), Refinement by Rietveld method, Scanning electron microscopy (SEM), Reduction temperature programmed (RTP) and Magnetic hysteresis measurements performed at room temperature. According to the XRD patterns, the formation of perovskite phase with orthorhombic structure was observed for the systems where 0 ≤ x ≤ 0.5 and rhombohedral for x = 1. The results also showed a decrease of lattice parameters with the parcial replacement of iron by manganese and consequently a reduction in cell volume. The hysteresis curves exhibited weak ferromagnetism for the systems prepared by both synthesis methods. However, a dependence of magnetization as a function of dopant content was observed for samples produced by Pechini method. As for the systems prepared by combustion reaction, it was found that the secondary phases exert a strong influence on the magnetic behavior / Ortoferritas AFeO3 (A = terra rara) constituem uma importante classe de ?xidos perovskita que exibem ferromagnetismo fraco. Estes materiais encontram in?meras aplica??es como sensores qu?micos, catodos para c?lulas a combust?veis e na ?rea de cat?lise, o que os fazem interessantes do ponto de vista cient?fico e tecnol?gico. Suas propriedades estruturais, el?tricas e magn?ticas s?o dependentes de v?rios fatores tais como: o m?todo de prepara??o, condi??es do tratamento t?rmico, composi??o qu?mica e substitui??o de c?tions nos s?tios A e/ou B. Neste trabalho, ortoferritas do tipo LaFe1-xMnxO3 (0 ≤ x ≤ 1) foram preparadas pelo m?todo Pechini e pela rea??o de combust?o assistida por microondas com a finalidade de avaliar a influ?ncia da rota de s?ntese na forma??o do ?xido, assim como o efeito da substitui??o parcial do ferro por mangan?s e do tratamento t?rmico nas propriedades magn?ticas. Os p?s precursores foram calcinados a 700?C, 900?C, 1100?C e 1300?C por 4 horas e caracterizados atrav?s das t?cnicas: An?lise termogravim?trica (TG), Difra??o de raios X (DRX), Refinamento pelo m?todo de Rietveld, Microscopia eletr?nica de varredura (MEV), Redu??o a temperatura programada (RTP) e Medidas de histerese magn?ticas realizadas ? temperatura ambiente. De acordo com os difratogramas, a forma??o da fase perovskita com estrutura ortorr?mbica foi observada para os sistemas onde 0 ≤ x ≤ 0,5 e, rombo?drica para x = 1. Os resultados tamb?m mostraram uma diminui??o dos par?metros de rede com a substitui??o parcial do ferro por mangan?s e, conseq?entemente uma redu??o do volume da c?lula unit?ria. As curvas de histerese exibiram ferromagnetismo fraco para os sistemas preparados por ambos os m?todos de s?ntese. Entretanto, uma depend?ncia da magnetiza??o em fun??o do teor de dopante foi observada para as amostras produzidas pelo m?todo Pechini. J? para os sistemas preparados por rea??o de combust?o, verificou-se que as fases secund?rias exercem forte influ?ncia no comportamento magn?tico

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 ≤ x ≤ 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 α - 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−xCoxFe2O4 (0≤x≤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 α - 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 2014-12-17T14:06:59Z (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.

Made available in DSpace on 2014-12-17T14:07:02Z (GMT). No. of bitstreams: 1 MichelineRA_DISSERT.pdf: 3734590 bytes, checksum: b9c518dbcf57b2b63cf9d386db2a5df1 (MD5) Previous issue date: 2012-02-07 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Continuous Synthesis by Solution Combustion was employed in this work aiming to obtain tin dioxide nanostructured. Basically, a precursor solution is prepared and then be atomized and sprayed into the flame, where its combustion occurs, leading to the formation of particles. This is a recent technique that shows an enormous potential in oxides deposition, mainly by the low cost of equipment and precursors employed. The tin dioxide (SnO2) nanostructured has been widely used in various applications, especially as gas sensors and varistors. In the case of sensors based on semiconducting ceramics, where surface reactions are responsible for the detection of gases, the importance of surface area and particle size is even greater. The preference for a nanostructured material is based on its significant increase in surface area compared to conventional microcrystalline powders and small particle size, which may benefit certain properties such as high electrical conductivity, high thermal stability, mechanical and chemical. In this work, were employed as precursor solution tin chloride dehydrate diluted in anhydrous ethyl alcohol. Were utilized molar ratio chloride/solvent of 0,75 with the purpose of investigate its influence in the microstructure of produced powder. The solution precursor flux was 3 mL/min. Analysis with X-ray diffraction appointed that a solution precursor with molar ratio chloride/solvent of 0,75 leads to crystalline powder with single phase and all peaks are attributed to phase SnO2. Parameters as distance from the flame with atomizer distance from the capture system with the pilot, molar ratio and solution flux doesn t affect the presence of tin dioxide in the produced powder. In the characterization of the obtained powder techniques were used as thermogravimetric (TGA) and thermodiferential analysis (DTA), particle size by laser diffraction (GDL), crystallographic analysis by X-ray diffraction (XRD), morphology by scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area (BET) and electrical conductivity analysis. The techniques used revealed that the SnO2 exhibits behavior of a semiconductor material, and a potentially promising material for application as varistor and sensor systems for gas / A S?ntese Cont?nua por Combust?o em Solu??o (SCCS) foi empregada na obten??o de p?s de di?xido de estanho nanoestruturados. Basicamente, uma solu??o precursora ? preparada, sendo posteriormente atomizada e aspergida na chama, onde ocorre a combust?o, levando ? forma??o das part?culas. A t?cnica apresenta um grande potencial na produ??o de nanopart?culas, principalmente pelo baixo custo de insumos e equipamentos. O di?xido de estanho (SnO2) nanoestruturado tem sido amplamente utilizado em diversas aplica??es, principalmente como sensores de g?s e varistores. No caso dos sensores ? base de cer?micas semicondutoras, em que as rea??es de superf?cies s?o respons?veis pela detec??o dos gases, a import?ncia da ?rea superficial e do tamanho de part?culas ? ainda maior. A prefer?ncia por um material nanoestruturado deve-se ao fato de que essas entidades apresentam alguns pontos fundamentais tais como, o aumento significativo da ?rea superficial comparados aos p?s microcristalinos convencionais e o reduzido tamanho de part?cula, que pode beneficiar certas propriedades como alta condutividade el?trica, alta estabilidade t?rmica, mec?nica e qu?mica. Neste trabalho, foram empregados como solu??o precursora cloreto de estanho dihidratado dilu?dos em ?lcool et?lico anidro. Foi utilizada a raz?o molar cloreto/solvente de 0,75 no intuito de investigar sua influ?ncia na microestrutura do material obtido. O fluxo da solu??o precursora foi de 3 mL/min. A an?lise por difra??o de raios X da solu??o precursora com raz?o molar cloreto/solvente de 0,75 indicou a obten??o de um p? cristalino e monof?sico e todos os picos s?o atribu?dos a fase SnO2. Par?metros de s?ntese como dist?ncia da chama com o atomizador, dist?ncia do sistema de capta??o com a chama piloto, raz?o molar e fluxo da solu??o precursora n?o afetaram a fase di?xido de estanho no material obtido. Na caracteriza??o do p? obtido, foram utilizadas t?cnicas como an?lises termogravim?tricas (ATG) e termodiferenciais (ATD), granulometria por difra??o de laser (GDL), an?lise cristalogr?fica por difra??o de raios X (DRX), morfologia por microscopia eletr?nica de varredura (MEV), microscopia eletr?nica de transmiss?o (MET), medida de ?rea superficial espec?fica (BET) e ensaio de condutividade el?trica. O conjunto de t?cnicas revelaram que o SnO2 apresenta comportamento de um material semicondutor, sendo um material potencialmente promissor ? aplica??o como varistor e em sistemas de sensores ? gases

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