Orientador: Maria Aparecida Zaghete Bertochi / Banca: Rodrigo Fernando Costa Marques / Banca: Elaine Cristina Paris / O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, POSMAT, tem caráter institucional e integra as atividades de pesquisa em materiais em diversos campi / Resumo: Materiais cerâmicos são utilizados em muitas aplicações, tais como: capacitor de multicamadas, transdutores, sensor piroelétrico, dispositivos elétricos e eletro-ópticos. Nos últimos anos, tem havido uma crescente demanda por materiais de melhor desempenho e funcionalidade. Esta demanda tem acelerado o desenvolvimento de técnicas de síntese para produzir pós com partículas bem definidas em tamanho, forma e cristalinidade. Dentre as técnicas utilizadas até o momento, o método dos precursores poliméricos e o método sol-gel têm sido considerados ideiais para a preparação destes materiais. Porém, apesar dos recentes avanços, muitos aspectos ainda podem ser melhorados para obtenção de titanatos com propriedades físico-químicas otimizadas. Além do método de síntese, as propriedades dos materiais podem ser melhoradas pela inserção de dopantes. Este trabalho visou introduzir Eu3+ e Tb3+ em La0,5Li0,5TiO3 e estudar as propriedades estruturais e ópticas dos pós obtidos pelos métodos Pechini e sol-gel, bem como a aceleração de tais estudos com as propriedades elétricas do material. As caracterizações estruturais revelaram a cristalinidade e a morfologia do titanato de lítio e lantânio nominamente puro e dopado com Eu3+e Tb3+. As caracterizações ópticas e elétricas forneceram informações para melhor entendimento da condutividade desses compostos / Abstract: Ceramic materials have been used in many applications such as multilayer capacitor, transducer, piezoelectric sensor, electrical and electro-optics devices. In recent years there has been a growing demanda for better materials performance and functionality. This demand has accelerated the development of synthesis techiques to produce powders with well-defined particle size, shape and crystalllinity. Among the techniques used so far, the polymeric precursor method and sol-gel method have been considered idel for the preparation of these materials. However, despite recent advances, many aspects can still be improved to obtain titanates with optimized physicochemical properties. The properties of materials can be improved too by insertion of doping. This work aimed to introduce Eu3+ and Tb+3 in La0,5Li0,5TiO3 and to study the structural and optical properties of the obtained powders by Pechini and sol-gel method as well as the correlation of such studies with the electrical properties of the material. The structural characterizations revelated the crystallinity and morphology of lithium lanthanum titanate nominally pure and doped with Eu3+and Tb3+. The optical and electrical characterizations provide information for better understanding of the conductivity of these compounds / Mestre

Made available in DSpace on 2014-06-11T19:30:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-03-05Bitstream added on 2014-06-13T20:00:20Z : No. of bitstreams: 1 fernandes_sl_me_bauru.pdf: 3765170 bytes, checksum: 5b4cc9d35c745ebd586d6828375891fe (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Materiais cerâmicos são utilizados em muitas aplicações, tais como: capacitor de multicamadas, transdutores, sensor piroelétrico, dispositivos elétricos e eletro-ópticos. Nos últimos anos, tem havido uma crescente demanda por materiais de melhor desempenho e funcionalidade. Esta demanda tem acelerado o desenvolvimento de técnicas de síntese para produzir pós com partículas bem definidas em tamanho, forma e cristalinidade. Dentre as técnicas utilizadas até o momento, o método dos precursores poliméricos e o método sol-gel têm sido considerados ideiais para a preparação destes materiais. Porém, apesar dos recentes avanços, muitos aspectos ainda podem ser melhorados para obtenção de titanatos com propriedades físico-químicas otimizadas. Além do método de síntese, as propriedades dos materiais podem ser melhoradas pela inserção de dopantes. Este trabalho visou introduzir Eu3+ e Tb3+ em La0,5Li0,5TiO3 e estudar as propriedades estruturais e ópticas dos pós obtidos pelos métodos Pechini e sol-gel, bem como a aceleração de tais estudos com as propriedades elétricas do material. As caracterizações estruturais revelaram a cristalinidade e a morfologia do titanato de lítio e lantânio nominamente puro e dopado com Eu3+e Tb3+. As caracterizações ópticas e elétricas forneceram informações para melhor entendimento da condutividade desses compostos / Ceramic materials have been used in many applications such as multilayer capacitor, transducer, piezoelectric sensor, electrical and electro-optics devices. In recent years there has been a growing demanda for better materials performance and functionality. This demand has accelerated the development of synthesis techiques to produce powders with well-defined particle size, shape and crystalllinity. Among the techniques used so far, the polymeric precursor method and sol-gel method have been considered idel for the preparation of these materials. However, despite recent advances, many aspects can still be improved to obtain titanates with optimized physicochemical properties. The properties of materials can be improved too by insertion of doping. This work aimed to introduce Eu3+ and Tb+3 in La0,5Li0,5TiO3 and to study the structural and optical properties of the obtained powders by Pechini and sol-gel method as well as the correlation of such studies with the electrical properties of the material. The structural characterizations revelated the crystallinity and morphology of lithium lanthanum titanate nominally pure and doped with Eu3+and Tb3+. The optical and electrical characterizations provide information for better understanding of the conductivity of these compounds

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Os compostos Cs4W11O35 e Rb4W11O35 pertencem à classe dos bronzes hexagonais de valÃncia balanceada com fÃrmula geral ABxW3-xO9 (A = Cs, K, Rb, Cs, Tl; B = Bi, Nb, Ta, Zr, Sc, etc.). Estes materiais dielÃtricos tÃm atraÃdo um grande interesse, uma vez que eles exibem sucessivas transiÃÃes de fase, propriedades ferroelÃtricas e geraÃÃo de segundos harmÃnicos. Embora as estruturas dos cristais Cs4W11O35 e Rb4W11O35 nÃo sejam conhecidas ainda, estudos de difraÃÃo de raios-x mostraram que os hexatungstatos de potÃssio e rubÃdio sÃo isoestruturais e a simetria mais provÃvel à a estrutura ortorrÃmbica, Pbn21, Pbc21, Cmm2. A difraÃÃo de raios-x tambÃm mostrou que os compostos KNbW2O9, RbNbW2O9 e KTaW2O9 sÃo isoestruturais de estrutura ortorrÃmbica, Cmm2 polar sem centro de inversÃo. O objetivo do presente trabalho à investigar as propriedades vibracionais dos compostos Cs4W11O35 e Rb4W11O35 com um foco especial na dependÃncia dos modos vibracionais em baixas temperaturas atravÃs de espectroscopia infravermelha. Apresentamos medidas de infravermelho à temperatura e pressÃo ambiente, de fotoluminescÃncia e cÃlculos clÃssicos de dinÃmica de rede. Relatamos ainda neste trabalho resultados de medidas de espectroscopia Raman a baixas temperaturas no intervalo de 295-38 K e comparamos com medidas de infravermelho no intervalo de 473-73 K. O Cs4W11O35 foi dopado com um pequeno percentual, em torno de 2%, do metal de transiÃÃo Eu3+ com o objetivo de usÃ-lo como Ãon sonda para a realizaÃÃo de medidas de fotoluminescÃncia. Com este procedimento, observamos que o Eu3+, ocupa um sÃtio de baixa simetria. O Rb4W11O35 apresenta duas transiÃÃes de fase a baixas temperaturas, uma em torno de 200 K e outra em torno de 100 K, quando analisado por espectroscopia Raman e infravermelho. O Cs4W11O35 tambÃm apresenta duas transiÃÃes de fase a baixas temperaturas, uma em torno de 165 K e a outra em torno de 110 K, porÃm, tais transiÃÃes sÃo visÃveis somente na espectroscopia Raman; muito provavelmente os modos que sofrem aÃÃo destas transiÃÃes sÃo infravermelho inativos. Pelo fato da estrutura destes materiais ainda nÃo serem totalmente definidas na literatura utilizamos cÃlculos clÃssicos de dinÃmica de rede no K0,26WO3 (KNbW2O9), para analisar o Rb4W11O35 (Cs4W11O35). Uma vez que, tais compostos sÃo hexatungstatos e os mesmos possuem assinatura Raman muito similar, e o fato desses cÃlculos possuÃrem uma boa concordÃncia com os dados experimentais, o entendimento dos principais aspectos das propriedades vibracionais dos hexatungstatos de K0,26WO3 e KNbW2O9, possibilitou uma melhor compreensÃo das modificaÃÃes estruturais observadas por meio das mudanÃas nos espectros Raman e infravermelho dos compostos Rb4W11O35 e Cs4W11O35 durante os experimentos com variaÃÃo de temperatura. Um aspecto importante dos resultados dos cÃlculos vibracionais foi a previsÃo de modos vibracionais tipos tubulares relacionados Ãs cavidades hexagonais dos compostos K0,26WO3 e KNbW2O9. / The Rb4W11O35 and Cs4W11O35 compounds, belongs to the valence balanced hexagonal tungsten materials with ABxW3-xO9 stoichiometry (with A = Cs, K, Rb, Tl, and B = Bi, Nd, Ta, Zr, Sc, etc.) These materials present interesting physical properties like rich sequence of phase transitions (rich polymorphism), ferroelectric properties and second harmonic generation. Despite of the unknown structures, Rb4W11O35 and Cs4W11O35, of that systems (we mean spatial symmetry), X-ray experiments suggest that rubidium and cesium hexatungstates are isostructural with orthorhombic structure belonging possibly to Pbn21, Pbc21 or Cmm2 space group symmetry. In addition, X-ray diffraction showed that the KNbW2O9, RbNbW2O9 KTaW2O9 compounds are isostructural, crystallizing in the polar noncentrosymmetric space group Cmm2. The aim of this study was to investigate the vibrational properties of the compounds Cs4W11O35 and Rb4W11O35 with special focus on the dependence of vibrational modes with low temperature via infrared spectroscopy. We report in this work results light scattering low temperature experiment in the 295-38 K temperature range and comparing the measures in the infrared range 473-73 K. Also present IR spectra and photoluminescence investigation at room temperature and pressure and lattice dynamics phonons calculation in parent structure. The Cs4W11O35 was doped with a small percentage, 2%, Eu3+ transition metal aiming to use it as a probe to perform measurements of photoluminescence ion. With this procedure, we see that Eu3+, occupies a site of low symmetry. The Rb4W11O35 presents phase transitions at low temperatures, around 200 K and the other around 100 K when analyzed by light scattering and IR spectra. The Cs4W11O35 also present two phase transitions at lower temperatures, around 165 K and the other around 110 K, however, such transitions are visible only light scattering, the modes most likely to suffer action of these transitions are inactive IR. Because the structure of these materials are not known in the literature. We have utilized lattice dynamics phonon calculations on network K0,26WO3 (KNbW2O9) to analyze Rb4W11O35 (Cs4W11O35), since such hexatungstatos have very similar Raman signature such calculations have good agreement with experimental data. The objective of this study was to understand the main aspects of the vibrational properties of K0,26WO3 and KNbW2O9. These results allowed us to interpret the transformation mechanisms of the observed temperature induced phase transitions. The lattice dynamics calculations revealed the existence of radial and tangential motions of oxygen atoms belonging to the hexagonal cavities. The tubular like modes command the dynamics of phase transitions in hexagonal tungsten systems.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Neste trabalho utilizou-se reaÃÃes do estado sÃlido com sucesso na produÃÃo de matrizes cerÃmicos compositas a base de Cr0,75Fe1,25O3(CRFO100), Fe0,5Cu0,75Ti0,75O3(FCTO100), Pb(Fe0,5Nb0,5O3) (PFN100) e CaTiO3 (CTO), para o estudo de suas propriedades estruturais e elÃtricas visando o seu possivel uso em circuitaria eletrÃnica, de rÃdio-frequencia e microondas. Os procedimentos envolvidos para obtenÃÃo das amostras seguiram a rota de produÃÃo de cerÃmicas, sendo que numa primeira etapa realizou-se a homogeneizaÃÃo dos pÃs com o objetivo de tornar a reaÃÃo mais eficaz, pois a promoÃÃo do contato por igual dos reagentes facilita a formaÃÃo da substÃncia desejada. ApÃs o procedimento de homogeneizaÃÃo, a obtenÃÃo de cada sÃrie de amostras seguiram suas caracterÃsticas operacionais, como por exemplo: tempo e temperatura de reaÃÃo. As duas primeiras sÃries Cr0,75Fe1,25O3(CRFO100)-- Fe0,5Cu0,75Ti0,75O3 (FCTO100), e Pb(Fe0,5Nb0,5O3) (PFN100)--Cr0,75Fe1,25O3 (CRFO100), foram estudadas por raios-X, MEV, EDSX, espectroscopia MÃssbauer, propriedades elÃtricas em funÃÃo da temperatura, caracterizaÃÃes na faixa de micoondas com a tÃcnica Hakki-Coleman e por Ãltimo a caracterizaÃÃo das amostras como antenas ressoadoras dielÃtricas. A Ãltima sÃrie Cr0,75Fe1,25O3 (CRFO100)-- CaTiO3 (CTO) foi estudada por todas as tÃcnicas mencionadas, com exceÃÃo das tÃcnicas MEV, EDSX, espectroscopia MÃssbauer. Este trabalho tem como objetivo sintetizar, caracterizar novas materiais ceramicos compositos para uso em dispositivos eletrÃnicos, microondas e radio-freqÃÃncia. Foram sintetizadas e caracterizadas amostras com as seguintes estequiometrias: Cr0,75Fe1,25O3 (CRFO100), Fe0,5Cu0,75Ti0,75O3 (FCTO100), Pb(Fe0,5Nb0,5O3) (PFN100) e CaTiO3 (CTO). Mediante a sÃntese das amostras anteriomente relatadas procedeu-se a formaÃÃo dos compÃsitos em diferentes concentraÃÃes e consequente formaÃÃo das sÃries na seguinte ordem: (CRFO)x-(FCTO)100-x, com x= 0, 17, 34, 50, 66, 83 e 100% em massa; (PFN)x -(CRFO)100-x, com x = 0, 10, 50, 90 e 100% em massa e xCRFO- (1- x)CTO com x= 0, 10, 50, 90 e 100% em mol. A identificaÃÃo e o subsequente refinamento dos dados para a primeira sÃrie revelaram uma estrura trigonal para o CRFO100 e uma estutra cÃbica para o FCTO100. no caso da segunda sÃrie o PFN100 apresentou uma estrutura tetragonal e na terceirasÃrie o CTO uma estrutura ortorrÃmbica. Pela espectrosocopia MÃssbauer foram confirmados no caso das duas primeiras sÃries, o estado de oxidaÃÃo do ferro (Fe3+) presente nas amostras analisadas e sua coordenaÃÃo no sÃtio cristalino em funÃÃo da quantidade de ferro presente nos compÃsitos. Com exceÃÃo do PFN100, a morfologia das amostras em geral foi caracterizada pela diversidade de formas e tamanho para todas as amostras das duas primeira sÃries. A anÃlise quÃmica elementar forneceu resultados quantitativos acerca dos elementos presentes nas amostras investigadas. Pelas respostas observadas na faixa de radio-freqÃÃncia, ficou evidenciada uma regiÃo de dispersÃo, caracteristica de processo de polarizaÃÃo dipolar. Experimentos foram realizados com variaÃÃo de temperatura e as propriedades dielÃtricas foram medidas (permissividade e perda dielÃtrica). Foi obtido o TCC (Coeficiente de Temperatura da CapacitÃncia), numa faixa de temperatura de 250C a 1000C, observando que as duas primeiras sÃries apresentaram relaxaÃÃo ativada pela temperatura. Medidas na regiÃo de microondas (300 MHz < f < 30 GHz) foram realizadas, no caso da primeira sÃrie para as amostras CRFO100, CRFO50 e FCTO100. Os resultados apresentados sÃo promissores para aplicaÃÃes como dispositivos em microondas. No caso da segunda sÃrie apenas em duas amostras (CRFO100 e PFN10) foi possÃvel determinar a freqÃÃncia ressonante, permissividade dielÃtrica e a perda dielÃtrica pelo o mÃtodo utilizado neste estudo (mÃtodo Hakki-Coleman), provalvelmente devido a elevada perda dielÃtrica apresentada pelas amostras. Para a terceira sÃrie, em todas as amostras foi possÃvel a localizaÃÃo da frequencia ressonante, permissividade dielÃtrica e a perda dielÃtrica. Para a serie CRFO-CTO foi observada a possibilidade de obtenÃÃo de um composito com TCC=0. Amostras nas tres series estudadas apresentam permissividades dieletricas altas (&#61541;&#61502;10) e algumas com baixas perdas podendo ser usadas na miniaturizaÃÃo em dispositivos de microndas e aplicaÃÃes em telecomunicaÃÃes / In this work the solid state procedure was used, with success, in the production of ceramic matrix composites based in Cr0,75Fe1,25O3(CRFO100), Fe0,5Cu0,75Ti0,75O3 (FCTO100), Pb(Fe0,5Nb0,5O3) (PFN100) e CaTiO3 (CTO), for the study of the structural and electrical properties of these composites for the possible use in electronic, radio-frequency and microwave circuitry. The first two series Cr0,75Fe1,25O3(CRFO100)--Fe0,5Cu0,75Ti0,75O3 (FCTO100), and Pb(Fe0,5Nb0,5O3) (PFN100)--Cr0,75Fe1,25O3 (CRFO100), were studied by the X-ray, MEV, EDSX, MÃssbauer spectroscopy and electrical properties as a function of temperature . The study of the electrical properties at the microwave region was done using the Hakki-Coleman technique and operating the samples as a dielectric resonator antenna. The series Cr0,75Fe1,25O3 (CRFO100)--CaTiO3 (CTO) was studied by all the mentioned techniques, except for the techniques MEV, EDSX and MÃssbauer spectroscopy. This work has the objective to synthesize and to characterize new composite materials for use in electronic, microwave and radio-frequency devices. After the synthesis of the samples the formation of the composites in the following series: (CRFO)x-(FCTO)100-x, with x = 0, 17, 34, 50, 66, 83 and 100% in mass; (PFN)x - (CRFO)100-x, with x = 0, 10, 50, 90 and 100 in mass % and xCRFO - (1-x)CTO with x = 0, 10, 50, 90 and 100 in mol %. The identification and the subsequent refinement of the data for the first series revealed a trigonal structure for the CRFO100 and a cubic structure for the FCTO100. In the case of the second series, the PFN100 present a tetragonal structure and in the third series, the CTO present an ortorhombic structure. The MÃssbauer spectroscopy confirmed in the case of the first two series, the state of oxidation of the iron (Fe3+) and itÂs coordination in all composites. Except for the PFN100, the morphology of the grains in the samples was characterized by the diversity in the form and size for all the samples of the first two series. The elementary chemical analysis supplied quantitative results concerning of the present elements in the investigated samples. It was observed by the RF measurements a dispersion which is characteristic of the process of dipolar polarization. The dielectric properties with temperature was also studied. The TCC (Temperature Coefficient of Capacitance) and activation energy associated to the modulus formalism was obtained in a temperature interval of 25oC to 100oC. Measurements in the microwave region (300 MHz <f <30 GHz) were accomplished in the case of the first series for the samples CRFO100, CRFO50 and FCTO100. For the CRFO-CTO series, a possibility to obtaina composite with TCC=0 was observed. Samples in the tree series are presenting high value of the dielectric permittivity (&#61541;&#61502;10) and low loss, which is necessary to the miniaturization of components to be used in microwave devices, and in telecommunications.

L’identification par radio fréquence (RFID) connectée à des capteurs est une technologie grandissante pour les emballages intelligents. Ces travaux de thèse ont porté sur l’étude des propriétés électriques (impédance et capacité) et diélectriques (permittivité diélectrique et pertes) des protéines notamment le gluten de blé, en fonction des molécules environnementales connues comme des marqueurs de dégradation des denrées alimentaires. Les effets de ces molécules (eau, dioxyde de carbone et éthanol) sur les propriétés électriques et diélectriques du gluten de blé ont été analysés. Dans le but d’effectuer des mesures dans des conditions optimales, plusieurs étapes ont été mises en place:Le développement d’une méthode, permettant une haute exposition du gluten de blé à l’atmosphère environnant, afin d’acquérir des mesures électriques et diélectriques du gluten de blé dans des conditions contrôlées de température, vapeurs et de gaz ;L’analyse des effets des vapeurs et gaz sur les propriétés diélectriques du gluten de blé, ainsi que la détermination de différents paramètres tels que la sensibilité et l’hystérésis, propres aux capteurs ;L’enduction du gluten de blé sur une étiquette RFID, testée en fonction de l’humidité et dans des conditions réelles d’utilisation. Les effets sur la distance de lecture de l’étiquette RFID ont été analysés.Les résultats obtenus sont prometteurs au vu des modifications de la permittivité diélectrique et des pertes, indiquant une modification structurelle de la protéine, qui aurait un impact sur la réponse RFID. La permittivité diélectrique a été augmenté de 5.01±0.06 à 9.22±0.06, de 7.81±0.07 à 12.02±0.03 et de 6.66±0.01 à 11.77±0.01, pour une croissance de 20% à 95% de l’humidité relative, de 0% à 40% de dioxyde de carbone et de 0% à 0.1% d’éthanol respectivement, aboutissant à une sensibilité de 26.70±0.13fF/%RH,31.38±0.06fF/%CO2 et 25.50±0.05pF/%éthanol pour les 3 vapeurs et gaz. Les propriétés diélectriques du gluten et sa sensibilité aux vapeurs et aux gaz offrent de nouvelles perspectives sur la conception de capteurs à bas coûts et écologiques, connectés à des étiquettes RFID passives pour les emballages intelligents et pour le contrôle de la chaîne alimentaire. / Radio frequency identification (RFID) interfaced to sensors is a growing technology for intelligent packaging. The present thesis work is based on the study of the electrical (impedance and capacitance) and dielectric properties (dielectric permittivity and loss) of proteins principally wheat gluten, as a function of environmental molecules known as markers of food degradation. The impacts of those molecules (water, carbon dioxide and ethanol), usually found in food packages, on the electrical and dielectric properties of wheat glutenhave been investigated. In order to perform measurements in the optimum conditions, several steps have been set up:The development of a methodology, allowing a high exposure of wheat gluten to the surrounding atmosphere, offering the possibility to perform electrical measurements and identify dielectric properties of wheat gluten in controlled conditions of vapors and gases ;Analyzing the impact of vapors and gases on the dielectric properties of wheat gluten, and the determination of several parameters such as sensitivity and hysteresis, specific to sensors ;The coating of wheat gluten on a RFID tag, tested as a function relative humidity and in real conditions of use. The subsequent impacts on the reading range of the RFID tag have been analyzed.The results obtained are promising according to modifications of the dielectricpermittivity and loss, indicating a structural modification of the protein, sought to have an impact on the RFID response. The dielectric permittivity was increased from 5.01±0.06 to 9.22±0.06, from 7.81±0.07 to 12.02±0.03 and from 6.66±0.01 to 11.77±0.01, for an increase in relative humidity from 20% to 95%, in carbon dioxide from 0% to 40% and in ethanol from 0% to 0.1%, respectively, resulting in a sensitivity of 26.70±0.13fF/%RH, 31.38±0.06fF/%CO2 and 25.50±0.05pF/%ethanol for the 3 vapors and gases. The dielectric properties of wheat gluten and its sensitivity to vapors and gases offer new insights on theconception of low cost, eco-friendly sensors sought to be interfaced to passive RFID tags for intelligent packaging for food and supply chain monitoring.

No description available.

Yes / Alumina-cubic boron nitride (cBN) composites were prepared using the spark plasma sintering (SPS) technique. Alpha-alumina powders with particle sizes of ∼15 µm and ∼150 nm were used as the matrix while cBN particles with and without nickel coating were used as reinforcement agents. The amount of both coated and uncoated cBN reinforcements for each type of matrix was varied between 10 to 30 wt%. The powder materials were sintered at a temperature of 1400 °C under a constant uniaxial pressure of 50 MPa. We studied the effect of the size of the starting alumina powder particles, as well as the effect of the nickel coating, on the phase transformation from cBN to hBN (hexagonal boron nitride) and on the thermo-mechanical properties of the composites. In contrast to micro-sized alumina, utilization of nano-sized alumina as the starting powder was observed to have played a pivotal role in preventing the cBN-to-hBN transformation. The composites prepared using nano-sized alumina reinforced with nickel-coated 30 wt% cBN showed the highest relative density of 99% along with the highest Vickers hardness (Hv2) value of 29 GPa. Because the compositions made with micro-sized alumina underwent the phase transformation from cBN to hBN, their relative densification as well as hardness values were relatively low (20.9–22.8 GPa). However, the nickel coating on the cBN reinforcement particles hindered the cBN-to-hBN transformation in the micro-sized alumina matrix, resulting in improved hardness values of up to 24.64 GPa.

This project addresses characterization of the material properties of aortic tissue. Understanding of these properties is important for a variety of studies including tissue engineering, effects of aging and diseases, stents engineering, and traumatic aorta rupture. The goal of the presented research was to characterize the stress-strain relationship of aorta in dynamic oscillatory biaxial loading. A setup was developed that supplied pressure loading from the physiological to sub-failure levels (between 7 and 76 kPa) to porcine aorta at frequencies ranging from 0.50Hz to 5.00Hz. Samples tested were constrained at both ends while the deformation and the pressure were recorded. Volumetric strain versus pressure was used to characterize the structural behavior of the material which showed frequency dependency and hysteresis indicating viscoelastic response. An offset method was developed to account for drifting behavior exhibited by some of the samples. The structural behavior of aorta was modeled using a quasi-linear viscoelastic (QLV) creep theory. The QLV model included a logarithmic steady state elastic function v = 0.663 +/- 0.040 + 0.241 +/- 0.011 ln(P) for pressure in kPa, and a Prony series creep function ( J0 = 0.472 +/- 0.021, J2 = 0.109 +/- 0.060, J3 = 0.419 +/- 0.056). Modeling results were then used to determine the relationships between the circumferential and longitudinal stresses and strains of the material. The results exhibited that the stress in the transverse direction was about 1.5 times larger than in the axial direction. However, in the axial direction material was stiffer and the deformation was 30% less. The relaxation function of the material was determined by linearizing the non-linear component of the QLV model and applying to it the linear viscoelastic theory. Furthermore, literature comparison revealed that aorta's creep function, as well as its elastic modulus, is within the range of what has been reported in the literature. In conclusion, an experimental model was developed that can be used to predict the behavior of porcine aorta under physiological and sub-failure conditions at quasi-static and dynamic loading. / Mechanical Engineering

The effects of oxidation by sodium hypochlorite (0, 0.8, 2, and 5%, NaOCl), the presence of endogenous proteins, and amylose content on waxy and common rice flours (WF, CF) and starches (WS, CS) were investigated in terms of in vitro starch digestibility, morphology and surface properties, and thermal and rheological characteristics. The concentration of NaOCl had an effect on all the samples including WF, CF, WS, and CS. The carbonyl and carboxyl group contents increased up to 25 and 10 folds (P < 0.05) of oxidized starches (WS, CS), respectively. Only mild oxidation (P < 0.05) occurred in flours (WF, WS). In addition, endogenous proteins were oxidized according to amino acid analysis and SDS–PAGE results. Glu+Gln, Gly, His, Arg, Tyr, and Lys were more sensitive to NaOCl oxidation. Disulfide bonds, hydrophobic force, and hydrogen bonds were involved in protein polymerization after NaOCl oxidative modification. In granular state, the in vitro starch digestibility of WF, WS, and CS decreased by 5% NaOCl oxidation. After gelatinization, only 2 and 5% oxidized WS had lower digestibility. Scanning electron microscopy and confocal laser scanning microscopy further demonstrated that protein existed on the surface of starch granules and had aggregation by oxidation. X-ray diffraction patterns showed the crystallinity of 5% oxidized flours and starches was reduced compared with all their non-oxidized samples. Thermal and rheological properties were analyzed by differential scanning calorimetry and rheometer, respectively. Starch gelatinization peak temperature of flours (WF, RF) was increased by 3 °C, but starches (WS, CS) had a significantly decrease by 8 °C. Viscoelastic patterns were dramatically changed by oxidation. Oxidized WF and CF had increased in both viscosity and elasticity by oxidation, whereas both WS and CS had significantly lower viscoelasticity after oxidative modification.

Neste trabalho desenvolvemos um potencial empírico para descrever as ligações químicas entre os átomos de silício, nitrogênio e hidrogênio usando a forma funcional de Tersoff. Exploramos as propriedades estruturais do nitreto de silício amorfo (a-SiNx:Hy) via simulação Monte Carlo e comparamos com dados experimentais. A boa descrição do sistema a-SiNx:Hy, para uma faixa de valores da concentração de nitrogênio (0<x<1,5) e da concentração de hidrogênio (0<y<40%) mostra que o modelo é realístico. Dependendo da concentração de nitrogênio, o hidrogênio possui preferência química diferente para ligar-se ao nitrogênio ou ao silício, o que é corroborado por resultados experimentais. Além do que, a incorporação do hidrogênio reduz consideravelmente a concentração de átomos subcoordenados no material. A estrutura eletrônica do amorfo e defeitos pontuais no nitreto de silício cristalino foram estudadas usando cálculos de primeiros princípios resolvendo as equações de Kohn-Sham. Para tal estudo as configurações inicialmente foram criadas via modelo empírico e serviram como entrada para o cálculo ab initio da energia total e das forças. Nossos resultados mostram que o hidrogênio tem um papel importante nas propriedades estruturais e eletrônicas do nitreto de silício amorfo. Em particular, demonstramos que o hidrogênio remove parcialmente níveis do gap de energia devido a saturação de ligações pendentes. / In this work we developed an empirical potential to describe the chemical bond among silicon, nitrogen and hydrogen atoms using the Tersoff functional form. We explored the structural properties of amorphous silicon nitride (a-SiNx:H,) through the Monte Carlo simulations and compared with experimental data. The good description of the a-SiNx:Hy, systems for a wide range of nitrogen contents (0<x<1.5) and hydrogen contents (0<y<40%) show the reliability of this model. Depending on nitrogen content, hydrogen has a different chemical preference to bond to either nitrogen or silicon, which is corroborated by experimental finding. Besides, hydrogen incorporation reduced considerably the concentration of undercoordinated atoms in the material. Electronic structure of amorphous and point defects in crystalline silicon nitride were studied using first-principles calculations solving the Kohn-Sham equations. For such study the configurations were created initially by empirical model as input for the ab initio total energy and forces calculations. Our results show that hydrogen plays an important role in the structural and electronic properties of amorphous silicon nitride. In particularly we demonstrated the role played by hydrogen to remove partially the levels in the energy gap due saturation of the dangling bond.