Sinterização de aço inoxidável reforçado com partículas nanométricas dispersas de carbeto de nióbio - NbC

Metal powder sintering appears to be promising option to achieve new physical and mechanical properties combining raw material with new processing improvements. It interest over many years and continue to gain wide industrial application. Stainless steel is a widely accepted material because high corrosion resistance. However stainless steels have poor sinterability and poor wear resistance due to their low hardness. Metal matrix composite (MMC) combining soft metallic matrix reinforced with carbides or oxides has attracted considerable attention for researchers to improve density and hardness in the bulk material. This thesis focuses on processing 316L stainless steel by addition of 3% wt niobium carbide to control grain growth and improve densification and hardness. The starting powder were water atomized stainless steel manufactured for Höganäs (D 50 = 95.0 μm) and NbC produced in the UFRN and supplied by Aesar Alpha Johnson Matthey Company with medium crystallite size 16.39 nm and 80.35 nm respectively. Samples with addition up to 3% of each NbC were mixed and mechanically milled by 3 routes. The route1 (R1) milled in planetary by 2 hours. The routes 2 (R2) and 3 (R3) milled in a conventional mill by 24 and 48 hours. Each milled samples and pure sample were cold compacted uniaxially in a cylindrical steel die (Ø 5 .0 mm) at 700 MPa, carried out in a vacuum furnace, heated at 1290°C, heating rate 20°C stand by 30 and 60 minutes. The samples containing NbC present higher densities and hardness than those without reinforcement. The results show that nanosized NbC particles precipitate on grain boundary. Thus, promote densification eliminating pores, control grain growth and increase the hardness values

Síntese e caracterização de espinélios a base de Cu, Fe e Cr para pigmentos cerâmicos

Inorganic pigment comprises a host lattice, which is part of the chromophore component (usually a transition metal cation) and possible components modifiers, which stabilize, add or restate the properties pigments. Among the materials with spinel, ferrites, and the chromite stand out, because they have broad technological importance in the area of materials, applicability, pigments, catalytic hydrogenation, thin film, ceramic tiles, among others. The present work, pigments containing CuFe2O4, CuCr2O4,e CuFeCrO4, were synthesized by a method that makes use of gelatin as organic precursor using their application to ceramic pigments. The pigments were characterized by X-ray diffraction (XRD), Infrared spectroscopy, scanning electron microscopy (SEM) spectroscopy in the UV-visible and Colorimetry. The results confirmed the feasibility of the synthetic route used, with respect to powders synthesized, there is the formation of spinel phase from 500°C, with an increase in crystallinity and the formation of other phases. The pigments were shown to be crystalline and the desired phases were obtained. The copper chromite have hues ranging from green to black according to the calcination temperature, while the copper chromite doped with iron had brownish. The ferrites showed copper color and darker brown to black, which may indicate an interesting factor because of the importance of black pigment

Estudo e desenvolvimento de um capacitor eletrolítico de nióbio

It seeks to find an alternative to the current tantalum electrolytic capacitors in the market due to its high cost. Niobium is a potential substitute, since both belong to the same group of the periodic table and because of this have many similar physical and chemical properties. Niobium has several technologically important applications, and Brazil has the largest reserves, around 96%. There are including niobium in reserves of tantalite and columbite in Rio Grande do Norte. These electrolytic capacitors have high capacitance specifies, ie they can store high energy in small volumes compared to other types of capacitors. This is the main attraction of this type of capacitor because is growing demand in the production of capacitors with capacitance specifies increasingly high, this because of the miniaturization of various devices such as GPS devices, televisions, computers, phones and many others. The production route of the capacitor was made by powder metallurgy. The initial niobium powder supplied by EEL-USP was first characterized by XRD, SEM, XRF and laser particle size, to then be sieved into three particle size, 200, 400 e 635mesh. The powders were then compacted and sintered at 1350, 1450 and 1550°C using two sintering time 30 and 60min. Sintering is one of the most important parts of the process as it affects properties as porosity and surface cleaning of the samples, which greatly affected the quality of the capacitor. The sintered samples then underwent a process of anodic oxidation, which created a thin film of niobium pentóxido over the whole porous surface of the sample, this film is the dielectric capacitor. The oxidation process variables influence the performance of the film and therefore the capacitor. The samples were characterized by electrical measurements of capacitance, loss factor, ESR, relative density, porosity and surface area. After the characterizations was made an annealing in air ate 260ºC for 60min. After this treatment were made again the electrical measurements. The particle size of powders and sintering affected the porosity and in turn the specific area of the samples. The larger de area of the capacitor, greater is the capacitance. The powder showed the highest capacitance was with the smallest particle size. Higher temperatures and times of sintering caused samples with smaller surface area, but on the other hand the cleaning surface impurities was higher for this cases. So a balance must be made between the gain that is achieved with the cleaning of impurities and the loss with the decreased in specific area. The best results were obtained for the temperature of 1450ºC/60min. The influence of annealing on the loss factor and ESR did not follow a well-defined pattern, because their values increased in some cases and decreased in others. The most interesting results due to heat treatment were with respect to capacitance, which showed an increase for all samples after treatment

Obtenção de polímeros de LCC para aplicação como antioxidante de biodiesel de soja

Biodiesel is a fuel obtained from vegetable oils, such as soy, castorbean, among others. The monoester of fatty acid of these oils have chains with mono, di and tri double connections. The presence of these insaturations are susceptible to oxidization. Antioxidants are substances able to prevent oxidization from oils, fats, fat foods, as well as esters of Alquila( biodiesel). The objective of this work is to summarize a new antioxidant from the Cashew Nut Shell Liquid (CNSL) using the electrolysis technique. A current of 2 amperes was used in a single cell of only one group and two eletrodos of stainless steel 304 in a solution of methanol, together with the eletrolits: acetic acid, sodium chloride and sodium hydroxide, for two hours of agitation. The electrolysis products are characterized by the techniques of cromatography in a thin layer, spectroscopy of infrared and gravimetric analysis. The material was submitted to tests of oxidative stability made by the techniques of spectropy of impendancy and Rancimat (EN 14112). The analyses of characterization suggest that the polimerization of the electrolytic material ocurred. The application results of these materials as antioxidants of soy biodiesel showed that the order of the oxidative stability was obtained by both techniques used

Síntese e caracterização de cerâmicas nanométricas para produção de gás de síntese

In this work, ceramic powders belonging to the system Nd2-xSrxNiO4 (x = 0, 0.4, 0.8, 1.2 and 1.6) were synthesized for their use as catalysts to syngas production partial. It was used a synthesis route, relatively new, which makes use of gelatin as organic precursor. The powders were analyzed at several temperatures in order to obtain the perovskite phase and characterized by several techniques such as thermal analysis, X-rays diffraction, Rietveld refinement method, specific surface area, scanning electron microscopy, energy dispersive spectroscopy of X-rays and temperature programmed reduction. The results obtained using these techniques confirmed the feasibility of the synthesis method employed to obtain nanosized particles. The powders were tested in differential catalytic conditions for dry reforming of methane (DRM) and partial oxidation of methane (POM), then, some systems were chosen for catalytic integrals test for (POM) indicating that the system Nd2-xSrxNiO4 for x = 0, 0.4 and 1.2 calcined at 900 °C exhibit catalytic activity on the investigated experimental conditions in this work without showing signs of deactivation

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

Caracterização microestrutural e elétrica de La(FexNi1-x)O3 sintetizado pelo método da gelatina

The present work deals with the synthesis of materials with perovskite structure with the intention of using them as cathodes in fuel cells SOFC type. The perovskite type materials were obtained by chemical synthesis method, using gelatin as the substituent of citric acid and ethylene glycol, and polymerizing acting as chelating agent. The materials were characterized by X-ray diffraction, thermal analysis, spectroscopy Fourier transform infrared, scanning electron microscopy with EDS, surface area determination by the BET method and Term Reduction Program, TPR. The compounds were also characterized by electrical conductivity for the purpose of observing the possible application of this material as a cathode for fuel cells, solid oxide SOFC. The method using gelatin and polymerizing chelating agent for the preparation of materials with the perovskite structure allows the synthesis of crystalline materials and homogeneous. The results demonstrate that the route adopted to obtain materials were effective. The distorted perovskite structure have obtained the type orthorhombic and rhombohedral; important for fuel cell cathodes. The presentation material properties required of a candidate cathode materials for fuel cells. XRD analysis contacted by the distortion of the structures of the synthesized materials. The analyzes show that the electrical conductivity obtained materials have the potential to act as a cell to the cathode of solid oxide fuel, allowing to infer an order of values for the electrical conductivities of perovskites where LaFeO3 < LaNiO3 < LaNi0,5Fe0,5O3. It can be concluded that the activity of these perovskites is due to the presence of structural defects generated that depend on the method of synthesis and the subsequent heat treatment

Comportamento da adição do carbeto de nióbio (nBC) na matriz metálica do aço ferrítico 15kH2mfa

The 15Kh2MFA steel is a kind of Cr-Mo-V family steels and can be used in turbines for energy generation, pressure vessels, nuclear reactors or applications where the range of temperature that the material works is between 250 to 450°C. To improve the properties of these steels increasing the service temperature and the thermal stability is add a second particle phase. These particles can be oxides, carbides, nitrites or even solid solution of some chemical elements. On this way, this work aim to study the effect of addition of 3wt% of niobium carbide in the metallic matrix of 15Kh2MFA steel. Powder metallurgy was the route employed to produce this metallic matrix composite. Two different milling conditions were performed. Condition 1: milling of pure 15Kh2MFA steel and condition 2: milling of 15Kh2MFA steel with addition of niobium carbide. A high energy milling was carried out during 5 hours. Then, these two powders were sintered in a vacuum furnace (10-4torr) at 1150 and 1250°C during 60 minutes. After sintering the samples were normalized at 950°C per 3 minutes followed by air cooling to obtain a desired microstructure. Results show that the addition of niobium carbide helps to mill faster the particles during the milling when compared with that steel without carbide. At the sintering, the niobium carbide helps to sinter increasing the density of the samples reaching a maximum density of 7.86g/cm³, better than the melted steel as received that was 7,81g/cm³. In spite this good densification, after normalizing, the niobium carbide don t contributed to increase the microhardness. The best microhardness obtained to the steel with niobium carbide was 156HV and to pure 15Kh2MFA steel was 212HV. It happened due when the niobium carbide is added to the steel a pearlitic structure was formed, and the steel without niobium carbide submitted to the same conditions reached a bainitic structure

Síntese e caracterização de ferrita ni-zn pelo método dos precursores poliméricos calcinada por energia de microondas

Magnetic ceramics have been widely investigated, especially with respect to intrinsic and extrinsic characteristics of these materials. Among the magnetic ceramic materials of technological interest, there are the ferrites. On the other hand, the thermal treatment of ceramic materials by microwave energy has offered various advantages such as: optimization of production processes, high heat control, low consumption of time and energy among others. In this work were synthesized powders of Ni-Zn ferrite with compositions Ni1- xZnxFe2O4 (0.25 ≤ x ≤ 0.75 mols) by the polymeric precursor route in two heat treatment conditions, conventional oven and microwave energy at 500, 650, 800 and 950°C and its structural, and morphological imaging. The materials were characterized by thermal analysis (TG/ DSC), X-ray diffraction (XRD), absorption spectroscopy in the infrared (FTIR), scanning electron microscopy (SEM), X-ray spectroscopy and energy dispersive (EDS) and vibrating sample magnetometry (VSM). The results of X-ray diffraction confirmed the formation of ferrite with spinel-type cubic structure. The extrinsic characteristics of the powders obtained by microwave calcination and influence significantly the magnetic behavior of ferrites, showing particles ferrimagnéticas characterized as soft magnetic materials (soft), is of great technological interest. The results obtained led the potential application of microwave energy for calcining powders of Ni-Zn ferrite

Síntese de nanopartículas de magnetita via decomposição térmica em meio não-aquoso

This work aims at obtaining nanoparticles of iron oxide, the magnetite one (Fe3O4), via synthesis by thermal decomposition through polyol. Thus, two routes were evaluated: a simple decomposition route assisted by reflux and a hydrothermal route both without synthetic air atmosphere using a synthesis temperature of 260ºC. In this work observed the influence of the observe of surfactants which are generally applied in the synthesis of iron oxide nanoparticles decreasing cluster areas. Further, was observed pure magnetite phase without secondary phases generally found in the iron oxide synthesis, a better control of crystallite size, morphology, crystal structure and magnetic behavior. Finally, the introduction of hydroxyl groups on the nanoparticles surface was analyzed besides its employment in the polymer production with OH radicals. The obtained materials were characterized by XRD, DLS, VSM, TEM, TG and DSC analyses. The results for the magnetite obtainment with a particle size greater than 5 nm and smaller than 11 nm, well defined morphology and good magnetic properties with superparamagnetic behavior. The reflux synthesis was more efficient in the deposition of the hydroxyl groups on the nanoparticles surface

Síntese e caracterização do poli(ácido láctico) para potencial uso em sistemas de liberação controlada de fármacos

With the advances in medicine, life expectancy of the world population has grown considerably in recent decades. Studies have been performed in order to maintain the quality of life through the development of new drugs and new surgical procedures. Biomaterials is an example of the researches to improve quality of life, and its use goes from the reconstruction of tissues and organs affected by diseases or other types of failure, to use in drug delivery system able to prolong the drug in the body and increase its bioavailability. Biopolymers are a class of biomaterials widely targeted by researchers since they have ideal properties for biomedical applications, such as high biocompatibility and biodegradability. Poly (lactic acid) (PLA) is a biopolymer used as a biomaterial and its monomer, lactic acid, is eliminated by the Krebs Cycle (citric acid cycle). It is possible to synthesize PLA through various synthesis routes, however, the direct polycondensation is cheaper due the use of few steps of polymerization. In this work we used experimental design (DOE) to produce PLAs with different molecular weight from the direct polycondensation of lactic acid, with characteristics suitable for use in drug delivery system (DDS). Through the experimental design it was noted that the time of esterification, in the direct polycondensation, is the most important stage to obtain a higher molecular weight. The Fourier Transform Infrared (FTIR) spectrograms obtained were equivalent to the PLAs available in the literature. Results of Differential Scanning Calorimetry (DSC) showed that all PLAs produced are semicrystalline with glass transition temperatures (Tgs) ranging between 36 - 48 °C, and melting temperatures (Tm) ranging from 117 to 130 °C. The PLAs molecular weight characterized from Size Exclusion Chromatography (SEC), varied from 1000 to 11,000 g/mol. PLAs obtained showed a fibrous morphology characterized by Scanning Electron Microscopy (SEM)

Efeitos do potencial probiótico Enterococcus faecium 32 e de sua associação com o extrato da alga marinha Caulerpa mexicana no tratamento de colite experimental murina

Ulcerative colitis comprising an inflammatory bowel disease, whose most severe consequence is the development of intestinal neoplasia. The drugs currently used to treat the disease trigger a variety of serious adverse effects and are not effective in many cases. Recent studies demonstrated the effectiveness of natural products for the treatment of inflammatory processes. Seaweed extracts and their purified products have shown protective effects in models of inflammation and the association of traditional therapies with probiotics has significantly improved the clinical symptoms of ulcerative colitis. Therefore, the aims of this study include evaluating the potential effects of the use of probiotic strain Enterococcus faecium 32 (Ef32), the methanolic extract of the green seaweed Caulerpa mexicana (M.E.) and their concomitant administration in a murine model of colitis induced by dextran sodium sulfate (DSS). Accordingly, C57BL /6 mice were pretreated orally with Ef32 (109 CFU/ml) for seven days. In the seven days following, the colitis was induced by administration of 3% DSS (w/v) diluted in the animals drinking water. During this period, animals were treated daily with Ef32 and the M.E. (2.0 mg/kg) every other day by intravenous route. The development of colitis was monitored by the disease activity index (DAI), which takes into account the loss of body weight, consistency and presence of blood in stools. After euthanasia, the colon was removed, its length measured and tissue samples were destined for histological analysis and culture for cytokine quantification. The levels of cytokines in the culture supernatant of the colon were measured by ELISA. The treatments with the probiotic Ef32 or the M.E. alone or the combination of these two substances provoked significant improvement as to weight loss and DAI, and prevented the shortening of the colon in response to DSS. The isolated treatments triggered a slight improvement in intestinal mucosal tissue damage. However, their combination was able to completely repair the injury triggered by DSS. The association was also able to reduce the levels of all the cytokines analyzed (IFN-γ, IL-4, IL-6, IL-12, IL-17A and TNF-α). On the other hand, the treatment with Ef32 did not interfere with the levels of TNF-α, whereas treatment with M.E. did not alter the levels of IL-6. Moreover, the treatment with Ef32 not interferes in TNF-α levels, whereas treatment with M.E. did not alter the levels of IL-6. Therefore, the potential probiotic Ef32 and M.E. and especially when these samples were associated proved promising alternatives in the treatment of ulcerative colitis as demonstrated in an experimental model because of its beneficial effects on morphological and clinical parameters, and by reducing the production of proinflammatory cytokines of Th1, Th2 and Th17

Saída compulsória do estrangeiro do território nacional à luz dos direitos humanos: análise de casos

This paper aims to review traditional concepts inherent to the general theory of the state and human rights, relating to the legal situation of foreign, understood as the subject of rights, especially when the is case of compulsory legal imposition of exit from national territory. After the serious violations during the Second World War and the importance acquired by the International Law of Human Rights, values as dignity, justice and equality are enshrined in the legal system and its respect required beyond the boundaries of any country. The creation of an international community, which is governed by rules that its members are subordinated, without distinction, as well as state - based on volunteerism, become inspired by one principled nature of these new concepts required of Global Society, as well as the adoption, influenced by neoconstitutionalism, to the model of State Constitutional rule of law, are opposed to the idea of state sovereignty connected to a superiority, absolute and unlimited power which recognizes no other above it, not even the basic principles or axioms that must govern the relationships internally. So looks for a concept of state that includes all the requirements of a democratic society, that have the people as the power holder, understanding that state element has undergone a relativization, because had to adapt to the contemporary values applicable to the individual, inserting in its concept, the indispensable obligation to protect the inalienable rights of citizens, regardless of with whom he have legal and political bond of nationality. It happens that, to consecrate these privileges to individuals, which, because they contain reference to values with supranational characteristics, are very abstract and are in constant collision course with internal rules, making it difficult to reconcile, it will use hermeneutics of human rights, due mainly to international courts, correlated with constitutional exegesis, in particular, legal principiologia, using, among others, the principles of reasonableness and proportionality, the systematic interpretation of the Constitution and international legal standards. Thus, it seek to enshrine the common foundation of all law , the link between the systems, namely, the dignity of human beings. Finally, it will see if Brazilian jurisdiction, through case studies, is tuned in line with these new paradigms, and in line with the International Bill of Human Rights, the Federal Constitution, the values and principles she hired

Proposta de localização de uma unidade de tratamento de óleo e gordura residual de fritura na cidade do Natal/RN para produção de biodiesel

This work addresses biodiesel by transesterification from the use of waste frying oil as a possible technological alternative for both reducing greenhouse gas emissions and by presenting themselves as an environmental call to designate a rational use of oil when no longer played in the environment to become renewable energy. It has proposed location of a residual oil and fat treatment plant to produce biodiesel, using models of Location and Routing for the improvement of routes. To achieve the goal, questionnaires were administered in establishments that use oil or vegetable fat in their productive activities in order to quantify the residue, to analyze actions and environmental perception of people who work directly with the residue on the destination you are being given to oil and fat used. It has indicated using of two single setup location, the method of Center of Gravity and the model of Ardalan, a geographical point that minimizes the costs of transporting waste to the treatment plant. Actions have been proposed for the improvement of collection routes this residue using the Routing Method of Scanning, as an illustration. The results demonstrated the lack of knowledge of the people who deal directly with large amounts of waste, on the environmental impacts caused by their incorrect disposal. The models used were uniform since point out to neighborhoods in similar regions. The neighborhoods of Lagoa Nova / Morro Branco (Ardalan) and Nova Descoberta (Center of Gravity) as ideal for the installation of treatment plant. However, it is suggested to be tested other models that take into account new variables than those used (supply of waste and the distance between points). The routing through the method of scanning has shown that it is possible, in a simple way to optimize routes in order to reduce distances and therefore the logistics costs in the collection of such waste. Introducing a route as a test to gather the twenty largest oil suppliers used in sample frying, using as a main factor time 8 hour of working shift every day

Proposta de integração das redes de comunicação da COSERN como uma solução de contigêncvia em caso de falhas nos enlaces do backbone de automação

T'his dissertation proposes alternative models to allow the interconnectioin of the data communication networks of COSERN Companhia Energética do Rio Grande do Norte. These networks comprise the oorporative data network, based on TCP/IP architecture, and the automation system linking remote electric energy distribution substations to the main Operatin Centre, based on digital radio links and using the IEC 60870-5-101 protoco1s. The envisaged interconnection aims to provide automation data originated from substations with a contingent route to the Operation Center, in moments of failure or maintenance of the digital radio links. Among the presented models, the one chosen for development consists of a computational prototype based on a standard personal computer, working under LINUX operational system and running na application, developesd in C language, wich functions as a Gateway between the protocols of the TCP/IP stack and the IEC 60870-5-101 suite. So, it is described this model analysis, implementation and tests of functionality and performance. During the test phase it was basically verified the delay introduced by the TCP/IP network when transporting automation data, in order to guarantee that it was cionsistent with the time periods present on the automation network. Besides , additional modules are suggested to the prototype, in order to handle other issues such as security and prioriz\ation of the automation system data, whenever they are travesing the TCP/IP network. Finally, a study hás been done aiming to integrate, in more complete way, the two considered networks. It uses IP platform as a solution of convergence to the communication subsystem of na unified network, as the most recente market tendencies for supervisory and other automation systems indicate