Síntese e caracterização de nanopartículas magnéticas de Co e Ni com aplicação em magneto hipertermia

Nanoparticles are importante for the study of new phenomena and for the development of new applications. Metallic magnetic nanoparticles like Cobalt and Nickel are important for their applications in nanoscience and nanotechnology. In this work, we report on the synthesis and characterization of Ni and Co nanoparticles. The nanoparticles were prepared by the modi- ed sol-gel method and were formed in the pore-network of the biopolymer quitosan. The reduction occurred in absence of H2 ux. The metallic particles and their monoxides have a face-centered- cubic structure. The metallic particles sizes ranged from 59 to 77 nm and from 19 to 50 nm for Ni and Co, respectively. Their monoxides chemically passivated the metallic cores, and after several weeks we have not observed further increase in oxidation. The synthesis method was tuned to obtain mainly the ferromagnetic phase. The system behaves like a core/shell structure with a ferromagnetic core and an antiferromagnetic shell. Exchange bias e ect was observed at temperatures below the Néel temperature. Both systems were submitted to an alternated magnetic eld and the heat released by the particles increased the temperature to 140°C in an interval of 5 min. Similar studies in samples dispersed in water increased the temperatures to 40-59°C, these results suggest that these materials are candidates for magnetic hyperthermia.

Efeito da adição de WC e Co na sinterização e propriedades mecânicas da alumina

Composites based on alumina (Al2O3), tungsten carbide (WC) and cobalt (Co) exhibit specific properties such as low density, high oxidation resistance, high melting point and high chemical inertia. That composite shows to be a promising material for application in various fields of engineering. In this work, the mechanical properties of the composite (Al2O3 – WC – Co), particularly density and hardness, were evaluated according to the effects of the variables of powder processing parameters, green compact and sintered. Powder composites with the composition of 80 wt% Al2O3, 18 wt% WC and 2 wt% Co were processed by high energy ball milling in a planetary mill for 50 hours as well as mixed by manual mixing in a glass vessel with the same proportion. Samples were collected (2, 10, 20, 30, 40 and 50 hours) during the milling process. Then, the powders were compacted in a cylindrical die with 5 mm in diameter in a uniaxial press with pressures of 200 and 400 MPa. The sintering was in two stages: first, the solid phase sintering was performed at 1126 and 1300 °C for 1 hour with a heating rate of 10 °C/min in a resistive furnace under argon atmosphere for green samples compacted in 200 and 400 MPa; the second sintering was performed on dilatometer in solid phase at 1300 °C for green sample compacted in 200 MPa, another sintering also was performed on dilatometer, this time in liquid phase at 1550 °C for green samples compacted in 200 and 400 MPa, with the same parameters used in resistive furnace. The raw materials were characterized by X – ray diffraction (XRD), X – ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and laser particlemeter. The sintered samples were subjected to microhardness testing. The results showed that high energy milling achieved to the objectives regarding the particle size and the dispersion of composite phases. However, the hardness did not achieve to significant results, this is an indication that the composite has low fracture toughness.

Efeito da adição de WC e Co na sinterização e propriedades mecânicas da alumina

Composites based on alumina (Al2O3), tungsten carbide (WC) and cobalt (Co) exhibit specific properties such as low density, high oxidation resistance, high melting point and high chemical inertia. That composite shows to be a promising material for application in various fields of engineering. In this work, the mechanical properties of the composite (Al2O3 – WC – Co), particularly density and hardness, were evaluated according to the effects of the variables of powder processing parameters, green compact and sintered. Powder composites with the composition of 80 wt% Al2O3, 18 wt% WC and 2 wt% Co were processed by high energy ball milling in a planetary mill for 50 hours as well as mixed by manual mixing in a glass vessel with the same proportion. Samples were collected (2, 10, 20, 30, 40 and 50 hours) during the milling process. Then, the powders were compacted in a cylindrical die with 5 mm in diameter in a uniaxial press with pressures of 200 and 400 MPa. The sintering was in two stages: first, the solid phase sintering was performed at 1126 and 1300 °C for 1 hour with a heating rate of 10 °C/min in a resistive furnace under argon atmosphere for green samples compacted in 200 and 400 MPa; the second sintering was performed on dilatometer in solid phase at 1300 °C for green sample compacted in 200 MPa, another sintering also was performed on dilatometer, this time in liquid phase at 1550 °C for green samples compacted in 200 and 400 MPa, with the same parameters used in resistive furnace. The raw materials were characterized by X – ray diffraction (XRD), X – ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and laser particlemeter. The sintered samples were subjected to microhardness testing. The results showed that high energy milling achieved to the objectives regarding the particle size and the dispersion of composite phases. However, the hardness did not achieve to significant results, this is an indication that the composite has low fracture toughness.

Avaliação da adaptação marginal de diferentes tipos de restaurações obtidas por CAD/CAM e métodos convencionais

The past few decades have brought many changes to the dental practice and the technology has become ready available. The result of a satisfactory rehabilitation treatment basically depends on the balance between biological and mechanical factors. The marginal adaptation of crowns and prosthetic structures is vital factor for long-term success. The development of CAD / CAM technology in the manufacture of dental prostheses revolutionized dentistry, this technology is capable of generating a virtual model from the direct digital scanning from the mouth, casts or impressions. It allows the planning and design of the structure in a computered software. The virtual projects are obtained with high precision and a significant reduction in clinical and laboratory time. Thus, the present study (Chapters 1, 2 and 3) computed microtomography was used to evaluate, different materials, different CAD/CAM systems, different ways of obtaining virtual model (with direct or indirect scanning), and in addition, also aims to evaluate the influence of cementing agent in the final adaptation of crowns and copings obtained by CAD / CAM. Furthermore, this study (Chapter 4, 5 and 6) also aims to evaluate significant differences in vertical and horizontal misfits in abutment-free frameworks on external hexagon implants (HE) using full castable UCLAs, castable UCLAs with cobalt-chromium pre-machined bases and obtained by CAD / CAM with CoCr or Zirconia by different scanning and milling systems. For this, the scanning electron microscopy and interferometry were used. It was concluded that the CAD / CAM technology is capable to produce restorations, copings and screw-retained implant-supported frameworks in different materials and systems offering satisfactory results of marginal accuracy, with significative reduction in clinical and laboratory time.

Nanoestruturas multicomponentes de CoFe2O4/Ag visando aplicações biológicas

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

Deficiencias minerales en bovinos para carne: diagnóstico, caracterización y control

La demanda de una producción de alimentos cada vez mayor a nivel mundial sumado a la tecnificación y al ritmo acelerado del progreso de las explotaciones agropecuarias actuales hacen que el ganado deba soportar elevadas presiones de producción aumentando los requerimientos de nutrientes. Este es el caso de los minerales considerados actualmente elementos esenciales para los animales, aunque tradicionalmente fueron definidos como los nutrientes pobres de la nutrición y alimentación animal. Actualmente se ha demostrado con evidencia clínica y productiva, el importante rol metabólico de los minerales en el animal sano y productivo, como también se ha definido qué elemento mineral y porcentaje del mismo es requerido para el normal funcionamiento del organismo. Los macro-minerales (calcio, magnesio, fósforo, sodio, potasio, cloro y azufre) y los oligo-minerales (cobre, zinc, hierro, selenio, cobalto, iodo, manganeso, molibdeno y cromo) son elementos esenciales y necesarios para transformar la proteína y la energía de los alimentos en componentes del organismo o en productos animales como leche, carne, crías, piel, lana. Además, ayudan al organismo a combatir las enfermedades, manteniendo al animal en buen estado de salud. Se ha considerado a los minerales como el tercer grupo limitante en la nutrición animal, siendo a su vez, el que mayor potencial y menor costo tiene para incrementar la producción del ganado. Los minerales desempeñan funciones tan importantes como ser constituyentes de la estructura ósea y dental, de tejidos blandos y líquidos corporales. Están involucrados en el funcionamiento celular, siendo activadores de más de trescientas enzimas, constituyentes esenciales de vitaminas, hormonas y pigmentos respiratorios y facilitando la actividad de los microorganismos del rumen. Cuando el aporte de minerales en la ración no es el adecuado en calidad y/o cantidad se originan las deficiencias minerales, encuadradas dentro de las enfermedades metabólicas o enfermedades de la producción. Estas han sido informadas en casi todo el mundo y son responsables de importantes pérdidas económicas en los rodeos de bovinos para carne. Las deficiencias y/o desequilibrios minerales pueden causar los siguientes trastornos en los animales: bajo porcentaje de parición, mayor número de servicios por concepción, abortos, retenciones placentarias, incremento del intervalo entre partos, baja producción de leche, menor peso al nacimiento y al destete, menor porcentaje de destete, menor ganancia de peso, mayor incidencia de enfermedades infecciosas, fracturas espontáneas, diarrea, deformación de huesos y mortandad. Así cobra importancia el diagnóstico mediante el análisis de la sangre de los animales, del pasto y el agua que consumen y la caracterización de estas deficiencias en primarias o secundarias con el objetivo de poder realizar un control de las mismas mediante un adecuado plan de suplementación mineral acorde a las necesidades de los distintos establecimientos agropecuarios.

Efeito da moagem de alta energia na microestrutura e nas propriedades magnéticas do compósito wc-10%p.Co

This work a studied the high energy milling effect in microstructure and magnetic properties of the WC-10wt.%Co composite. The composite powders were prepared by mechanical mixed and milled at 2 hours, 100 hours, 200 hours and 300 hours in planetary milling. After this process the composite were compacted in stainless steel die with cylindrical county of 10 mm of diameter, at pressure 200 Mpa and sintered in a resistive furnace in argon atmosphere at 1400 oC for 5 min. The sintered composite were cutted, inlaid, sandpapered, and polished. The microestrutural parameters of the composite was analyzed by X-ray diffraction, scanning electronic microscopy, optical microscopy, hardness, magnetic propriety and Rietveld method analyze. The results shows, with milling time increase the particle size decrease, it possibility minor temperature of sintering. The increase of milling time caused allotropic transformation in cobalt phase and cold welding between particles. The cold welding caused the formation of the particle composite. The X-ray diffraction pattern of composite powders shows the WC peaks intensity decrease with the milling time increase. The X-ray diffraction pattern of the composite sintered samples shows the other phases. The magnetic measurements detected a significant increase in the coercitive field and a decrease in the saturation magnetization with milling time increase. The increase coercitive field it was also verified with decrease grain size with milling time increase. For the composite powders the increase coercitive field it was verified with particle size reduction and saturation magnetization variation is relate with the variation of free cobalt. The Rietveld method analyze shows at milling time increase the mean crystalline size of WC, and Co-cfc phases in composite sintered sample are higher than in composite powders. The mean crystallite size of Co-hc phase in composite powders is higher than in composite sintered sample. The mean lattice strains of WC, Co-hc and Co-cfc phases in composite powders are higher than in composite sintered samples. The cells parameters of the composite powder decrease at milling time increase this effect came from the particle size reduction at milling time increase. In sintered composite the cells parameters is constant with milling time increase

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)

Síntese de pigmentos cerâmicos inorgânicos nanométricos e encapsulados com estrutura core-shell pela rota dos precursores poliméricos

The present work has as objective the development of ceramic pigments based in iron oxides and cobalt through the polymeric precursor method, as well as study their characteristics and properties using methods of physical, chemical, morphological and optical characterizations.In this work was used iron nitrate, and cobalt citrate as precursor and nanometer silica as a matrix. The synthesis was based on dissolving the citric acid as complexing agent, addition of metal oxides, such as chromophores ions and polymerization with ethylene glycol. The powder obtained has undergone pre-ignition, breakdown and thermal treatments at different calcination temperatures (700 °C, 800 °C, 900 °C, 1000 °C and 1100 °C). Thermogravimetric analyzes were performed (BT) and Differential Thermal Analysis (DTA), in order to evaluate the term decomposition of samples, beyond characterization by techniques such as BET, which classified as microporous materials samples calcined at 700 ° C, 800 º C and 900 º C and non-porous when annealed at 1000 ° C and 1100 º C, X-ray diffraction (XRD), which identified the formation of two crystalline phases, the Cobalt Ferrite (CoFe2O4) and Cristobalite (SiO2), Scanning Electron Microscopy (SEM) revealed the formation of agglomerates of particles slightly rounded;and Analysis of Colorimetry, temperature of 700 °C, 800 °C and 900 °C showed a brown color and 1000 °C and 1100 °C violet

Comportamento magnético de compósitos de matriz polimérica com adição de ferritas

Polymer matrix composites offer advantages for many applications due their combination of properties, which includes low density, high specific strength and modulus of elasticity and corrosion resistance. However, the application of non-destructive techniques using magnetic sensors for the evaluation these materials is not possible since the materials are non-magnetizable. Ferrites are materials with excellent magnetic properties, chemical stability and corrosion resistance. Due to these properties, these materials are promising for the development of polymer composites with magnetic properties. In this work, glass fiber / epoxy circular plates were produced with 10 wt% of cobalt or barium ferrite particles. The cobalt ferrite was synthesized by the Pechini method. The commercial barium ferrite was subjected to a milling process to study the effect of particle size on the magnetic properties of the material. The characterization of the ferrites was carried out by x-ray diffraction (XRD), field emission gun scanning electron microscopy (FEG-SEM) and vibrating sample magnetometry (VSM). Circular notches of 1, 5 and 10 mm diameter were introduced in the composite plates using a drill bit for the non-destructive evaluation by the technique of magnetic flux leakage (MFL). The results indicated that the magnetic signals measured in plates with barium ferrite without milling and cobalt ferrite showed good correlation with the presence of notches. The milling process for 12 h and 20 h did not contribute to improve the identification of smaller size notches (1 mm). However, the smaller particle size produced smoother magnetic curves, with fewer discontinuities and improved signal-to-noise ratio. In summary, the results suggest that the proposed approach has great potential for the detection of damage in polymer composites structures

Multifuncionalização de nanopartículas de CoFe2O4 pela incorporação da prata na sua superfície : síntese e caracterização

Tese (doutorado)—Universidade de Brasília, Instituto de Física, 2015.