Síntese citrato-hidrotermal e caracterização eletroquímica de LSCF para aplicação como catodo em célula a combustível de temperatura intermediária

The lanthanum strontium cobalt iron oxide (La1-xSrxCo1-yFeyO3 LSCF) is the most commonly used material for application as cathode in Solid Oxide Fuel Cells (SOFCs), mainly due to their high mixed ionic electronic conductivity between 600 and 800ºC. In this study, LSCF powders with different compositions were synthesized via a combination between citrate and hydrothermal methods. As-prepared powders were calcined from 700 to 900°C and then characterized by X-ray fluorescence, X-ray diffraction, thermal analyses, particle size analyses, nitrogen adsorption (BET) and scanning electronic microscopy. Films of composition La0,6Sr0,4Co0,2Fe0,8O3 (LSCF6428), powders calcined at 900°C, were screen-printed on gadolinium doped ceria (CGO) substrates and sintered between 1150 and 1200°C. The effects of level of sintering on the microstructure and electrochemical performance of electrodes were evaluated by scanning electronic microscopy and impedance spectroscopy. Area specific resistance (ASR) exhibited strong relation with the microstructure of the electrodes. The best electrochemical performance (0.18 ohm.cm2 at 800°C) was obtained for the cathode sintered at 1200°C for 2 h. The electrochemical activity can be further improved through surface activation by impregnation with PrOx, in this case the electrode area specific resistance decreases to values as low as 0.12 ohm.cm2 (800°C), 0.17 ohm.cm2 (750°C) and 0.31 ohm.cm2 (700°C). The results indicate that the citrate-hydrothermal method is suitable for the attainment of LSCF particulates with potential application as cathode component in intermediate temperature solid oxide fuel cells (IT-SOFCs)

Descarga em barreira dielétrica: construção de um reator DBD e caracterização mediante análises ópticas e elétricas do plasma produzido

The plasma produced by Dielectric Barrier Discharge (DBD) is a promising technique for producing plasma in atmospheric pressure and has been highlighted in several areas, especially in biomedical and textile industry, this is due to the fact that the plasma generated by DBD not reaches high temperatures, enabling use it for thermally sensitive materials. But still it is necessary the development of research related to understanding of the chemical, physical and biological interaction between the non-thermal plasma at atmospheric pressure with cells, tissues, organs and organisms. This work proposes to develop equipment DBD and characterize it in order to obtain a better understanding of the process parameters of plasma production and how it behaves under the parameters adopted in the process, such as distance, frequency and voltage applied between electrodes. For this purpose two techniques were used to characterize distinct from each other. The first was the method of Lissajous figures, this technique is quite effective and accurately for complete electrical characterization equipment DBD. The second technique used was Optical Emission Spectroscopy (EEO) very effective tool for the diagnosis of plasma with it being possible to identify the excited species present in the plasma produced. Finally comparing the data obtained by the two techniques was possible to identify a set of parameters that optimize the production when combined DBD plasma atmosphere in the equipment was built precisely in this condition 0.5mm-15kV 600Hz, giving way for further work

Estudo do aproveitamento do rejeito da mineração de esmeraldas na produção de refratários conformados isolantes

Emerald mining is an important area of the economy in Brazil, country which is in second place among the exporting nations of this gem. Due to the process of extraction, a great amount of reject is generated. Since there is no appropriate destination, the reject is abandoned around the mining industries, contributing to environment degradation. Nowadays, some of the most relevant things to an industry in general are: energy conservation, cost reduction, quality and productivity enhancement. The production of isolating, transformed refractory materials achieves the sustainability dimension when protection of the environment is incorporated to such process. This work investigates the use of emerald mining rejects in the ceramic body of refractory materials, aiming at obtaining a product whose characteristics are compatible with commercial products and, at the same time, allow the use of such rejects to solve the environmental issue caused by its disposal in nature. X-ray fluorescence analysis show that the emerald reject obtained after the flotation to extract molybdenum and mica has 70% of silica and alumina (SiO2+Al2O3) and 21% of a basic oxides and alkaline metals and earthy alkaline mixture (Na2O, K2O, CaO e MgO). Because of the significant amount of silica and alumina present in the reject, four refractory ceramic bodies were prepared. Samples with a rectangular shape and dimensions 100x50x10 mm were pressed in a steel mold at 27,5 MPa and sintered at 1200ºC for 40 min. under environment atmosphere in a resistive oven. The sintered samples were characterized in relation to the chemical composition (FRX), mineralogical composition (DRX), microstructure (MEV) and physical and mechanical properties. The results indicate that the mixture with 45% of reject, 45% of alumina and 10% of kaolin presents a refractory quality of 1420ºC, dimensional linear variation below 2.00%, apparent specific mass of 1,56 g/cm3 and porosity of 46,68%, which demonstrates the potential use of the reject as raw material for the industry of isolating transformed refractory materials

Desenho e Construção de um protótipo gerador de jato de plasma frio a pressão atmosférica para aplicações biomédicas

Research for better performance materials in biomedical applications are constants. Thus recent studies aimed at the development of new techniques for modification of surfaces. The low pressure plasma has been highlighted for its versatility and for being environmentally friendly, achieving good results in the modification of physic chemical properties of materials. However, it is requires an expensive vacuum system and cannot able to generate superficial changes in specific regions. Furthermore, it is limits their use in polymeric materials and sensitive terms due to high process temperatures. Therefore, new techniques capable of generating cold plasma at atmospheric pressure (APPJ) were created. In order to perform surface treatments on biomaterials in specific regions was built a prototype capable of generating a cold plasma jet. The prototype plasma generator consists of a high voltage source, a support arm, sample port and a nozzle through which the ionized argon. The device was formed to a dielectric tube and two electrodes. This work was varied some parameters such as position between electrodes, voltage and electrical frequency to verify the behavior of glow discharges. The disc of titanium was polished and there was a surface modification. The power consumed, length, intensity and surface modifications of titanium were analyzed. The energy consumed during the discharges was observed by the Lissajous figure method. To check the length of the jets was realized with Image Pro Plus software. The modifications of the titanium surfaces were observed by optical microscopy (OM ) and atomic force microscopy (AFM ). The study showed that variations of the parameters such as voltage, frequency and geometric position between the electrodes influence the formation of the plasma jet. It was concluded that the plasma jet near room temperature and atmospheric pressure was able to cause modifications in titanium surface

Obtenção de ferrita de cobalto através de dois métodos de síntese: método de complexação combinando EDTA/Citrato e método hidrotérmico

In this work it was synthesized and characterized the cobalt ferrite (CoFe2O4) by two methods: complexation combining EDTA/Citrate and hydrothermal investigating the influence of the synthesis conditions on phase formation and on the crystallite size. The powders were mainly characterized by x-ray diffraction. In specific cases, it was also used scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray fluorescence (XRF) and isotherms of adsorption and desorption of nitrogen (BET method). The study of the crystallite size was based on the interpretation of x-ray diffractograms obtained and estimated by the method of Halder-Wagner-Scherrer and Langford. An experimental design was made in order to assist in quantifying the influence of synthesis conditions on the response variables. The synthesis parameters evaluated in this study were: pH of the reaction medium (8, 9 and 10), the calcination temperature (combined complexation method EDTA/Citrate 600°C, 800°C and 1000°C), synthesis temperature (hydrothermal method 120°C, 140°C and 160°C), calcination time (combined complexation method EDTA/Citrate - 2, 4 and 6 hours) and time of synthesis (hydrothermal method 6, 15 and 24 hours). By the hydrothermal method was possible to produce mesoporous powders with high purity, with an average crystallite size up to 7 nm, with a surface area of 113.44 m²/g in the form of pellets with irregular morphology. By using the method of combined complexation EDTA/Citrate, mesoporous powders were produced with greater purity, crystallite size up to 22nm and 27.95 m²/g of surface area in the form of pellets with a regular morphology of plaques. In the experimental design was found that the hydrothermal method to all the studied parameters (pH, temperature and time) have significant effect on the crystallite size, while to the combined complexation method EDTA/Citrate, only temperature and time were significant

Metais pesados do solo após aplicação de biossólido: I - Fracionamento

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Formulação de novos combustíveis base diesel: avaliação de desempenho e emissões

The industry, over the years, has been working to improve the efficiency of diesel engines. More recently, it was observed the need to reduce pollutant emissions to conform to the stringent environmental regulations. This has attached a great interest to develop researches in order to replace the petroleum-based fuels by several types of less polluting fuels, such as blends of diesel oil with vegetable oil esters and diesel fuel with vegetable oils and alcohol, emulsions, and also microemulsions. The main objective of this work was the development of microemulsion systems using nonionic surfactants that belong to the Nonylphenols ethoxylated group and Lauric ethoxylated alcohol group, ethanol/diesel blends, and diesel/biodiesel blends for use in diesel engines. First, in order to select the microemulsion systems, ternary phase diagrams of the used blends were obtained. The systems were composed by: nonionic surfactants, water as polar phase, and diesel fuel or diesel/biodiesel blends as apolar phase. The microemulsion systems and blends, which represent the studied fuels, were characterized by density, viscosity, cetane number and flash point. It was also evaluated the effect of temperature in the stability of microemulsion systems, the performance of the engine, and the emissions of carbon monoxide, nitrogen oxides, unburned hydrocarbons, and smoke for all studied blends. Tests of specific fuel consumption as a function of engine power were accomplished in a cycle diesel engine on a dynamometer bench and the emissions were evaluated using a GreenLine 8000 analyzer. The obtained results showed a slight increase in fuel consumption when microemulsion systems and diesel/biodiesel blends were burned, but it was observed a reduction in the emission of nitrogen oxides, unburned hydrocarbons, smoke index and f sulfur oxides

Estudo da remoção de Ba2+, Ni2+, Cd2+, Cu3+, Cr3+, Sr2+, Zn2+ por eletrocoagulação em água associada à produção de petróleo

Among the waste generated in the petrochemical industry water associated with oil production is the most important. It is considered one of the great challenges due to the presence of considered toxic chemicals present in this composition. The presence of these substances difficult to reuse the water associated with the enhanced recovery processes, so that prior to their reuse or disposal, treatment is necessary. This paper aimed to study the removal efficiency of chemical species: Ba2+, Ni2+, Cd2+, Cu2+, Cr3+, Sr2+ and Zn2+, present in the composition of the water associated with oil production by electrocoagulation. The evaluation of removal of these chemical species was performed by laboratory tests using electrochemical batch reactors and continuous flow. Initial tests were performed with electrocoagulation of synthetic wastewater in batch reactor using iron electrode. Results of removal of Zn2+ and Ni2+ were 78 % and 59 % respectively. While the percentage of removed Ba2+ was 19 % by 30 minutes of treatment and by applying current of 1.10 A. The tests were performed on effluent batch reactor applying the electrochemical technique with stainless steel electrodes 304, the objective was to remove part of the dispersed oil and also of organic compounds in the effluent. Under the experimental conditions used, the maximum result was obtained TOG was 60 % and TOC was approximately 50 % compared to the initial concentration. In the experiments carried out in continuous reactor, with effluent semisynthetic, have been used electrodes of iron and aluminum and the results were 100 % removal of Cd2+, Cu2+, Cr3+ and Zn2+ and 77 % of Sr2+. These percentages were only attainable through the use of the iron electrode. However, when the electrode was replaced by aluminum, there was a reduction in the percentage of removal to 65 %, using the same flow rate and current. Therefore according to the results obtained using the iron electrode was more effective in removing these metals and the conditions of lower current and lower flow rate was satisfactory, as observed in the experimental design adopted

Novas alternativas de remoção de enxofre do óleo diesel utilizando tensoativos e microemulsões

The diesel combustion form sulfur oxides that can be discharged into the atmosphere as particulates and primary pollutants, SO2and SO3, causing great damage to the environment and to human health. These products can be transformed into acids in the combustion chamber, causing damage to the engines. The worldwide concern with a clean and healthy environment has led to more restrictive laws and regulations regulating the emission levels of pollutants in the air, establishing sulfur levels increasingly low on fuels. The conventional methods for sulfur removal from diesel are expensive and do not produce a zero-level sulfur fuel. This work aims to develop new methods of removing sulfur from commercial diesel using surfactants and microemulsion systems. Its main purpose is to create new technologies and add economic viability to the process. First, a preliminary study using as extracting agent a Winsor I microemulsion system with dodecyl ammonium chloride (DDACl) and nonyl phenol ethoxylated (RNX95) as surfactant was performed to choose the surfactant. The RNX95 was chosen to be used as surfactant in microemulsioned systems for adsorbent surface modification and as an extracting agent in liquid-liquid extraction. Vermiculite was evaluated as adsorbent. The microemulsion systems applied for vermiculite surface modification were composed by RNX95 (surfactant), n-butanol (cosurfactant), n-hexane (oil phase), and different aqueous phases, including: distilled water (aqueous phase),20ppm CaCl2solution, and 1500ppm CaCl2solution. Batch and column adsorption tests were carried out to estimate the ability of vermiculite to adsorb sulfur from diesel. It was used in the experiments a commercial diesel fuel with 1,233ppm initial sulfur concentration. The batch experiments were performed according to a factorial design (23). Two experimental sets were accomplished: the first one applying 1:2 vermiculite to diesel ratio and the second one using 1:5 vermiculite to diesel ratio. It was evaluated the effects of temperature (25°C and 60°C), concentration of CaCl2in the aqueous phase (20ppm and 1500ppm), and vermiculite granule size (65 and 100 mesh). The experimental response was the ability of vermiculite to adsorb sulfur. The best results for both 1:5 and 1:2 ratios were obtained using 60°C, 1500ppm CaCl2solution, and 65 mesh. The best adsorption capacities for 1:5 ratio and for 1:2 ratio were 4.24 mg sulfur/g adsorbent and 2.87 mg sulfur/g adsorbent, respectively. It was verified that the most significant factor was the concentration of the CaCl2 solution. Liquid-liquid extraction experiments were performed in two and six steps using the same surfactant to diesel ratio. It was obtained 46.8% sulfur removal in two-step experiment and 73.15% in six-step one. An alternative study, for comparison purposes, was made using bentonite and diatomite asadsorbents. The batch experiments were done using microemulsion systems with the same aqueous phases evaluated in vermiculite study and also 20ppm and 1500 ppm BaCl2 solutions. For bentonite, the best adsorption capacity was 7.53mg sulfur/g adsorbent with distilled water as aqueous phase of the microemulsion system and for diatomite the best result was 17.04 mg sulfur/g adsorbent using a 20ppm CaCl2solution. The accomplishment of this study allowed us to conclude that, among the alternatives tested, the adsorption process using adsorbents modified by microemulsion systems was considered the best process for sulfur removal from diesel fuel. The optimization and scale upof the process constitutes a viable alternative to achieve the needs of the market

Engenharia de microestrutura em varistor à base de ZnO: evidências de homogeneidade e correlação com reações químicas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Síntese e caracterização estrutural do niobato de potássio e estrôncio com estrutura tipo Tetragonal Tungstênio Bronze TTB

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Propriedades física de molécilas orgânicas e compostos do tipo perovskita CdSiO3 e CaPbO3

In the first part of this work our concern was to investigate the thermal effects in organic crystals using the theory of the polarons. To analyse such effect, we used the Fröhlich s Hamiltonian, that describes the dynamics of the polarons, using a treatment based on the quantum mechanics, to elucidate the electron-phonon interaction. Many are the forms to analyzing the polaronic phenomenon. However, the measure of the dielectric function can supply important information about the small polarons hopping process. Besides, the dielectric function measures the answer to an applied external electric field, and it is an important tool for the understanding of the many-body effects in the normal state of a polaronic system. We calculate the dielectric function and its dependence on temperature using the Hartree-Fock decoupling method. The dieletric function s dependence on the temperature is depicted by through a 3D graph. We also analyzed the so called Arrhenius resistivity, as a functionof the temperature, which is an important tool to characterize the conductivity of an organic molecule. In the second part we analyzed two perovskita type crystalline oxides, namely the cadmium silicate triclinic (CdSiO3) and the calcium plumbate orthorhombic (CaPbO3), respectively. These materials are normally denominated ABO3 and they have been especially investigated for displaying ferroelectric, piezoelectric, dielectrics, semiconductors and superconductors properties. We found our results through ab initio method within the functional density theory (DFT) in the GGA-PBE and LDA-CAPZ approximations. After the geometry optimization for the two structure using the in two approximations, we found the structure parameters and compared them with the experimental data. We still determined further the angles of connection for the two analyzed cases. Soon after the convergence of the energy, we determined their band structures, fundamental information to characterize the nature of the material, as well as their dielectrics functions, optical absorption, partial density of states and effective masses of electrons and holes

Sistemas Nanoestruturados: Heteroestruturas Quasi-Periódicas de Nitretos e Cálculos Ab initio em Polimorfos CaCO3

The physical properties and the excitations spectrum in oxides and semiconductors materials are presented in this work, whose the first part presents a study on the confinement of optical phonons in artificial systems based on III-V nitrides, grown in periodic and quasiperiodic forms. The second part of this work describes the Ab initio calculations which were carried out to obtain the optoeletronic properties of Calcium Oxide (CaO) and Calcium Carbonate (CaCO3) crystals. For periodic and quasi-periodic superlattices, we present some dynamical properties related to confined optical phonons (bulk and surface), obtained through simple theories, such as the dielectric continuous model, and using techniques such as the transfer-matrix method. The localization character of confined optical phonon modes, the magnitude of the bands in the spectrum and the power laws of these structures are presented as functions of the generation number of sequence. The ab initio calculations have been carried out using the CASTEP software (Cambridge Total Sequential Energy Package), and they were based on ultrasoft-like pseudopotentials and Density Functional Theory (DFT). Two di®erent geometry optimizations have been e®ectuated for CaO crystals and CaCO3 polymorphs, according to LDA (local density approximation) and GGA (generalized gradient approximation) approaches, determining several properties, e. g. lattice parameters, bond length, electrons density, energy band structures, electrons density of states, e®ective masses and optical properties, such as dielectric constant, absorption, re°ectivity, conductivity and refractive index. Those results were employed to investigate the confinement of excitons in spherical Si@CaCO3 and CaCO3@SiO2 quantum dots and in calcium carbonate nanoparticles, and were also employed in investigations of the photoluminescence spectra of CaCO3 crystal

Efeitos da eletroestimulação percutânea na incontinência urinária e qualidade de vida pós-prostatectomia: registro de seis casos

Introduction: Radical prostatectomy surgery is the best treatment currently adopted by detecting prostate cancer. The urinary incontinence is one more common and difficult to treat postoperative complications, which causes a negative impact on quality of life of the individual prostatectomy . The surface electrical nerve stimulation involves the transmission of electrical impulses from an external stimulator for peripheral nerve through surface electrodes attached to skin. It is an easy and efficient technique, widely used for pain relief, rehabilitation and muscle strengthening. Objective: To analyze the effect of T10-L2 percutaneous electrical stimulation, in individuals with urinary incontinence who underwent radical prostatectomy by the laparoscopic technique. Methods: Six patients had previously undergone radical prostatectomy were submitted to 20 sections of surface electrical stimulation with frequency of 4 Hz, pulse width of 1ms during 20 minutes. All subjects fillid a quality of life - International Consultation on Incontinence Questionnaire- Short FormI - ICIQ-SF questionnaire evaluating. Results: Results showed reduction in the use of the number of pads, number of leaks before and after treatment, and reduced voiding frequency and consequent improvement in quality of life. No side effects were reported. Conclusion: Percutanous electrical stimulation in T10-L2 may be an effective technique to treat urinary incontinence (UI) after radical prostatectomy video laparoscopy

Mobilidade de oxigênio intersticial em cerâmicas SmBa2Cu3O7-delta

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)