Estudo da síntese e sinterização de pós compósitos do sistema Ta-Cu

Ta-Cu bulk composites combine high mechanical resistance of the Ta with high electrical and thermal conductivity of the Cu. These are important characteristics to electrical contacts, microwave absorber and heat skinks. However, the low wettability of Ta under Cu liquid and insolubility mutual these elements come hard sintering this composite. High-energy milling (HEM) produces composite powders with high homogeneity and refines the grain size. This work focus to study Ta-20wt%Cu composite powders prepared by mechanical mixture and HEM with two different conditions of milling in a planetary ball mill and then their sintering using hydrogen plasma furnace and a resistive vacuum furnace. After milling, the powders were pressed in a steel dye at a pressure of 200 MPa. The cylindrical samples pressed were sintered by resistive vacuum furnace at 10-4torr with a sintering temperature at 1100ºC / 60 minutes and with heat rate at 10ºC/min and were sintered by plasma furnace with sintering temperatures at 550, 660 and 800ºC without isotherm under hydrogen atmosphere with heat rate at 80ºC/min. The characterizations of the powders produced were analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and laser granulometry. After the sintering the samples were analyzed by SEM, XRD and density and mass loss tests. The results had shown that to high intense milling condition produced composite particles with shorter milling time and amorphization of both phases after 50 hours of milling. The composite particles can produce denser structure than mixed powders, if heated above the Cu melting point. After the Cu to arrive in the melting point, liquid copper leaves the composite particles and fills the pores

Compendio de telecomunicaciones 3. Conceptos básicos de ingeniería de Radiopropagación

Este libro, desarrolla de manera directa y sencilla el fenómeno de la propagación de las señales electromagnéticas en las bandas de frecuencia de microondas. Aborda la teoría y criterios técnicos y prácticos concernientes al diseño de los radioenlaces puntos a punto (P-P), tanto análogos como digitales. Se incluyen anexos técnicos donde los estudiantes dispondrán de información especializada generada por los fabricantes internacionales de sistemas de Radio y Mux, así como los accesorios de protección y estructuras metálicos propias de estos sistemas (torres para antenas, sistemas de tierra, pararrayos, luces de obstrucción, etc.). Se confía que este libro sea de gran utilidad en la formación de los estudiantes de esta ingeniería.

Síntesis y caracterización de materiales nanoestructurados con potencial aplicación como un sensor de glucosa

El presente proyecto se llevó a cabo con el fin de contribuir al desarrollo de nuevos materiales para ser implementados en dispositivos para el sensado de glucosa no ezimaticos, en este trabajo se realizaron diversos estudios sobre desarrollo de nanofibras de carbón decoradas con nanoestructuras de ZnO y CuO, en el que según reportes realizados por diversos investigadores tanto el ZnO como el CuO han presentado excelentes resultados para ser implementados en sensores de glucosa no enzimáticos gracias a las propiedades físicas y químicas que estos presentan, además que las nanofibras presentan alta porosidad, buena conducción y pueden funcionalizarse fácilmente por lo que es ampliamente utilizada como sustrato para depósito de nanoestructuras de semiconductores. Las nanofibras de carbón fueron obtenidas mediante la técnica de electrohilado utilizando como materia prima poliacrilonitrilo y posteriormente fueron sometidas a una calcinación en una atmosfera inerte. Las nanofibras de carbón fueron pre-tratadas para el depósito y crecimiento de las nanoestructuras de ZnO y CuO en donde se utilizó síntesis por hidrotermal para crecimiento de los semiconductores. La caracterización morfológica y estructural se lleco a cabo por Microscopia Electrónica de Barrido (SEM), Microcopia Electrónica de Transmisión (TEM), la composición química y cristalográfica de los materiales se determinó por medios de Espectroscopia de Infrarrojo de Transformada de Furier (FTIR), Espectroscopia de Energía Dispersiva de rayos X (EDXS), Difracción de Rayos X (DRX), así mismo se llevó a cabo el Análisis Térmico Diferencial y Análisis Térmico Gravimétrico simultáneamente, finalmente los materiales fueron caracterizados electroquímicamente por Voltamperometría Cíclica (CV) para conocer si este material podría tener potencial aplicación en sensores de glucosa no enzimático. Contribuciones y Conclusiones: Se establecieron las óptimas condiciones para obtención de las NFCs utilizando PAN como precursor mediante la técnica de electrohilado, además se consiguió determinar las condiciones para una carbonización controlada en una atmosfera de airenitrógeno. Así mismo se determinaron las condiciones óptimas para la producción de nanoestructuras de ZnO/CuO mediante el sembrado y crecimiento de nanopartículas sobre las NFCs. La diversidad en la morfología y la cantidad de material en la superficie de las nanofibras son de gran importancia en la eficiencia del material ya que ésta se ve perjudicada cuando se tiene pobres cantidades depositadas. Por otro lado, el ZnO no presenta sensibilidad por sí sólo, ante la presencia de la glucosa, del mismo modo el CuO presentó la misma incapacidad de detección. El uso de CuO como catalizador en el ZnO ha demostrado que el electrodo modificado de NFCs/ZnO-CuO presenta propiedades para oxidar la glucosa, en comparación a los de NFCs/ZnO y NFCs/CuO los cueles no presentaron ninguna actividad de oxidación para esta. Lo que permitió tener una idea que al depositar estos dos materiales depositados en el mismo sustrato, la eficiencia de éstos incrementa, lo cual podría contribuir a investigaciones futuras para estos materiales.

Geologia, petrologia, geocronologia e mineralizações sulfetadas do complexo ézio, província mineral de carajás, Brasil

Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, Pós-Graduação em Geologia, 2015.

Síntesis de nanopartículas derivadas de biopolímeros extraídos de biomasa por métodos térmicos

La celulosa como un biopolímero sustentable y renovable, ha sido ampliamente estudiada para la generación de materiales que cuenten con características físicas y químicas versátiles. Los procesos para la extracción de celulosa se han modificado para lograr la conformación de celulosa nano y microfibrilada estos procesos son estudiados para conseguir mayores rendimientos y operaciones sustentables. En el presente proyecto para la formación de nanopartículas de celulosa se utiliza un proceso de irradiación de microondas, partiendo de una extracción primaria de la celulosa de dos residuos agroindustriales y un residuo de la industria del papel, mediante un pre-tratamiento posteriormente aplicar el proceso de hidrólisis asistida por microondas para la producción de las nanopartículas.

Síntese e caracterização de nanocompósitos de carbon-dot e lantanídeos

Dissertação (mestrado)—Universidade de Brasília, Instituto de Química, 2015.

Síntesis de BaBiO₃ y Sr₂Bi₂O₅ para su evaluación en procesos fotoinducidos en la degradación de rodamina b y conversión del agua.

Propósito y Método del estudio: En este trabajo se estudió la influencia del método de síntesis en las propiedades fisicoquímicas, fotocatalíticas y fotoelectroquímicas del BaBiO3 y el Sr2Bi2O5. En primera instancia, se realizó la síntesis de los materiales por la técnica de estado sólido (pos-tratamiento con molienda mecánica) e hidrotermal. Para la síntesis en hidrotermal se exploraron 3 diferentes temperaturas: 130, 150, 170 °C. Los materiales obtenidos fueron caracterizados mediante Difracción de Rayos-X (DRX), Espectroscopía de Reflectancia Difusa (ERD), Microscopía Electrónica de Barrido (MEB) y Fisisorción de Nitrógeno. Posteriormente se realizó la evaluación de las propiedades fotocatalíticas de los materiales obtenidos en la degradación de rodamina B. Las pruebas fotocatalíticas se realizaron en un reactor tipo Batch, utilizando una lámpara de Xenón de 6000 K. El estudio fotocatalítico finalizó con el cálculo de parámetros cinéticos tales como la constante de velocidad aparente (k) y tiempo de vida media (t1/2). Los resultados mostraron que el BaBiO3 sintetizado por reacción de estado sólido presentó la mayor eficiencia fotocatalitica. Para incrementar la eficiencia fotocatalitica de los materiales sintetizados se adicionaron superficialmente partículas de NiO en porcentajes de 3, 5 y 10 % al bismutato de estroncio y bario, utilizando para ello el método de impregnación. Los materiales fueron caracterizados y probados en la degradación de rodamina B. Por otro lado, para conocer el grado de eficiencia de los materiales se realizó el estudio fotoelectroquímico para determinar la posición de las bandas de conducción y valencia de cada uno de ellos. El grado de mineralización de la rodamina B se analizó mediante análisis de Carbón Orgánico Total (COT) y adicionalmente se realizaron pruebas de reproducibilidad para determinar la estabilidad de los materiales ante la exposición de ciclos sucesivos de irradiación. Contribuciones y conclusiones: Se lograron obtener los Bismutatos de Estroncio y Bario mediante la reacción en estado sólido a 800 y 900 °C. Mientras que por el método de hidrotermal se obtuvieron los materiales a 130, 150 y 170°C, seguido de un tratamiento térmico a 700°C. Los resultados de electroquímica mostraron que el material de Sr2Bi2O5 es apto para generar procesos de oxidación y reducción. La adición de NiO no proporcionó mejora en la eficiencia fotocatalítica, lo que se atribuyó a las aglomeraciones de partículas sobre la superficie de los materiales. Los materiales obtenidos por estado sólido presentaron la mayor actividad fotocatalítica en degradación de rodamina B, comparados con los obtenidos por el método de hidrotermal, por lo que el factor que domina la actividad fotocatalítica de estos materiales fue principalmente la cristalinidad. Además los materiales presentaron buena estabilidad ante ciclos sucesivos de irradiación y mostraron un buen grado de mineralización de la rodamina B.

Caracterização de compósitos Nb-20%cu obtidos por moagem de alta energia e sinterizados por fase líquida

In this work, was studied the formation of a composite of the refractory metal niobium with copper, through the process of high-energy milling and liquid phase sintering. The HEM can be used to synthesize composite powders with high homogeneity and fine size particle distribution. It may also produce the solid solubility in immiscible systems such as Nb-Cu, or extend the solubility of systems with limited solubility. Therefore, in the immiscible system Cu-Nb, the high-energy milling was successfully used to obtain the composite powder particles. Initially, the formation of composite particles during the HEM and the effect of preparation technique on the microstructure of the material was evaluated. Four loads of Nb and Cu powders containing 20%wt Cu were synthesized by MAE in a planetary type ball mill under different periods of grinding. The influence of grinding time on the metal particles is evaluated during the process by the withdrawal of samples at intermediate times of milling. After compaction under different forces, the samples were sintered in a vacuum furnace. The liquid phase sintering of these samples prepared by HEM produced a homogeneous and fine grained. The composite particles forming the sintered samples are the addition of a hard phase (Nb) with a high melting point, and a ductile phase (Cu) with low melting point and high thermal and electrical conductivities. Based on these properties, the Nb-Cu system is a potential material for many applications, such as electrical contacts, welding electrodes, coils for generating high magnetic fields, heat sinks and microwave absorbers, which are coupled to electronic devices. The characterization techniques used in this study, were laser granulometry, used to evaluate the homogeneity and particle size, and the X-ray diffraction, in the phase identification and to analyze the crystalline structure of the powders during milling. The morphology and dispersion of the phases in the composite powder particles, as well the microstructures of the sintered samples, were observed by scanning electron microscopy (SEM). Subsequently, the sintered samples are evaluated for density and densification. And finally, they were characterized by techniques of measuring the electrical conductivity and microhardness, whose properties are analyzed as a function of the parameters for obtaining the composite

Síntese e impregnação de peneiras moleculares Fe MCM-41 derivada de sílica da casca do arroz

The mesoporous molecular sieves of the MCM-41 and FeMCM-41 type are considered promissory as support for metals used as catalysts in oil-based materials refine processes and as adsorbents for environmental protection proposes. In this work MCM-41 and FeMCM41 were synthesized using rice husk ash - RHA as alternative to the conventional silica source. Hydrothermal synthesis was the method chosen to prepare the materials. Pre-defined synthesis parameters were 100°C for 168 hours, later the precursor was calcinated at 550°C for 2 hours under nitrogen and air flow. The sieves containing different proportions of iron were produced by two routes: introduction of iron salt direct synthesis; and a modification post synthesis consisting in iron salt 1 % and 5% impregnation in the material followed by thermal decomposition. The molecular sieves were characterized by X ray diffraction XRD, Fourier transform infrared spectroscopy FT-IR, X ray fluorescence spectroscopy XFR, scanning electronic microscopy SEM, specific surface area using the BET method, Termogravimetry TG. The kinetic model of Flynn Wall was used with the aim of determining the apparent activation energy of the surfactant remove (CTMABr) in the MCM- 41 porous. The analysis made possible the morphology characterization, identifying the presence of hexagonal structure typical for mesoporous materials, as well as observation of the MCM41 and iron of characteristic bands.

Degradação do PMMA através da reação despolimerização uitlizando catalisadores de óxidos mistos

In this work, mixed oxides were synthesized by two methods: polymeric precursor and gel-combustion. The oxides, Niquelate of Lanthanum, Cobaltate of Lanthanum and Cuprate of Lanthanum were synthesized by the polymeric precursor method, and treated at 300 º C for 2 hours, calcined at 800 º C for 6h in air atmosphere. In gel-combustion method were produced and oxides using urea and citric acid as fuel, forming for each fuel the following oxides Ferrate of Lanthanum, Cobaltato of Lanthanum and Ferrato of Cobalt and Lanthanum, which were submitted to the combustion process assisted by microwave power maximum of 10min. The samples were characterized by: thermogravimetric analysis, X-ray diffraction; fisisorção of N2 (BET method) and scanning electron microscopy. The reactions catalytic of depolymerization of poly (methyl methacrylate), were performed in a reactor of silica, with catalytic and heating system equipped with a data acquisition system and the gas chromatograph. For the catalysts synthesized using the polymeric precursor method, the cuprate of lanthanum was best for the depolymerization of the recycled polymer, obtaining 100% conversion in less time 554 (min), and the pure polymer, was the Niquelate of Lanthanum, with 100% conversion in less time 314 (min). By gel-combustion method using urea as fuel which was the best result obtained Ferrate of Lanthanum for the pure polymer with 100% conversion in less time 657 (min), and the recycled polymer was Cobaltate of Lanthanum with 100 % conversion in less time 779 (min). And using citric acid to obtain the best result for the pure polymer, was Ferrate of Lanthanum with 100% conversion in less time 821 (min and) for the recycled polymer, was Ferrate of Lanthanum with 98.28% conversion in less time 635 (min)

Design of functional hybrid coatings with anti-biofouling, self-cleaning and anti-reflecting applications

263 p.

Síntese de catalisadores do tipo LaNixFe1-xO3 como precursores catalíticos para reação oxidação parcial do metano

Nickel-bases catalysts have been used in several reform reactions, such as in the partial oxidation of methane to obtain H2 or syngas (H2 + CO). High levels of conversion are usually obtained using this family of catalysts, however, their deactivation resulting from carbon deposition still remains a challenge. Different approaches have been tested aiming at minimizing this difficulty, including the production of perovskites and related structures using modern synthesis methods capable of producing low cost materials with controlled microstructural characteristics at industrial scale. To establish grounds for comparison, in the present study LaNixFe1-xO3 (x=0, 0.3 or 0.7) perovskites were prepared following the Pechini method and by microwave assisted self-combustion. All samples were sub sequently calcined at 900 °C to obtain the target phase. The resulting ceramic powders were characterized by thermogravimetric analysis, infrared spectroscopy, X ray diffraction, specific area and temperature programmed reduction tests. Calcined samples were also used in the partial oxidation reaction of methane to evaluate the level of conversion, selectivity and carbon deposition. The results showed that the calcined samples were crystalline and the target phase was formed regardless of the synthesis method. According to results obtained by Rietveld refinement, we observed the formation of 70.0% of LaNi0.3Fe0.7O3 and 30.0% of La2O3 for samples LN3F7-900- P, LN3F7-900-M and 41,6% of LaNi0.7Fe0.3O3, 30.7% of La2NiO4 and 27.7% of La2O3 for samples LN7F3-900-P and LN7F3-900-M.Temperature-programmed profiles of the LaNiO3 sample revealed the presence of a peak around 510 °C, whereas the LaFeO3 sample depicted a peak above 1000°C. The highest l evel of methane conversion was obtained for LaNiO3 synthesized by the Pechini method. Overall, catalysts prepared by the Pechini method depicted better conversion levels compared to those produced by microwave assisted self-combustion

Preparação de óxidos mistos de níquel e zinco nanoparticulados a partir de combustíveis alternativos

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

Métodos no convencionales para la preparación de polímeros de coordinación porosos. Una aproximación económica, medioambientalmente amigable y escalable

293 p. El contenido del capítulo 5 está sujeto a confidencialidad

Influência do método de síntese e caracterização de pós compósitos de NiO- Ce1-xEuxO2-δ para anodos catalíticos de células a combustível

Fuel cells are electrochemical devices that convert chemical energy into electricity. Due to the development of new materials, fuel cells are emerging as generating clean energy generator. Among the types of fuel cells, categorized according to the electrode type, the solid oxide fuel cells (SOFC) stand out due to be the only device entirely made of solid particles. Beyond that, their operation temperature is relatively high (between 500 and 1000 °C), allowing them to operate with high efficiency. Another aspect that promotes the use of SOFC over other cells is their ability to operate with different fuels. The CeO2 based materials doped with rare earth (TR+3) may be used as alternatives to traditional NiO-YSZ anodes as they have higher ionic conductivity and smaller ohmic losses compared to YSZ, and can operate at lower temperatures (500-800°C). In the composition of the anode, the concentration of NiO, acting as a catalyst in YSZ provides high electrical conductivity and high electrochemical activity of reactions, providing internal reform in the cell. In this work compounds of NiO - Ce1-xEuxO2-δ (x = 0.1, 0.2 and 0.3) were synthesized from polymeric precursor, Pechini, method of combustion and also by microwave-assisted hydrothermal method. The materials were characterized by the techniques of TG, TPR, XRD and FEG-SEM. The refinement of data obtained by X-ray diffraction showed that all powders of NiO - Cex-1EuxO2-δ crystallized in a cubic phase with fluorite structure, and also the presence of Ni. Through the characterizations can be proved that all routes of preparation used were effective for producing ceramics with characteristics suitable for application as SOFC anodes, but the microwave-assisted hydrothermal method showed a significant reduction in the average grain size and improved control of the compositions of the phases