100 resultados para Síntese química


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The research and development of nanostructured materials have been growing significantly in the last years. These materials have properties that were significantly modified as compared to conventional materials due to the extremely small dimensions of the crystallites. The tantalum carbide (TaC) is an extremely hard material that has high hardness, high melting point, high chemical stability, good resistance to chemical attack and thermal shock and excellent resistance to oxidation and corrosion. The Compounds of Tantalum impregnated with copper also have excellent dielectric and magnetic properties. Therefore, this study aimed to obtain TaC and mixed tantalum oxide and nanostructured copper from the precursor of tris (oxalate) hydrate ammonium oxitantalato, through gas-solid reaction and solid-solid respectively at low temperature (1000 ° C) and short reaction time. The materials obtained were characterized by X-ray diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), Spectroscopy X-Ray Fluorescence (XRF), infrared spectroscopy (IR), thermogravimetric (TG), thermal analysis (DTA) and BET. Through the XRD analyses and the Reitiveld refinement of the TaC with S = 1.1584, we observed the formation of pure tantalum carbide and cubic structure with average crystallite size on the order of 12.5 nanometers. From the synthesis made of mixed oxide of tantalum and copper were formed two distinct phases: CuTa10O26 and Ta2O5, although the latter has been formed in lesser amounts

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Synthetic inorganic pigments are the most widely used in ceramic applications because they have excellent chemical and thermal stability and also, in general, a lower toxicity to man and to the environment. In the present work, the ceramic black pigment CoFe2O4 was synthesized by the polymerization Complex method (MPC) in order to form a material with good chemical homogeneity. Aiming to optimize the process of getting the pigment through the MPC was used a fractional factorial design 2(5-2), with resolution III. The factors studied in mathematical models were: citric acid concentration, the pyrolysis time, temperature, time and rate of calcination. The response surfaces using the software statistica 7.0. The powders were characterized by thermal analysis (TG/DSC), x-ray diffraction (XRD), scanning electron microscopy (SEM) and spectroscopy in the UV-visible. Based on the results, there was the formation of phase cobalt ferrite (CoFe2O4) with spinel structure. The color of the pigments obtained showed dark shades, from black to gray. The model chosen was appropriate since proved to be adjusted and predictive. Planning also showed that all factors were significant, with a confidence level of 95%

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In recent decades have seen a sharp growth in the study area of nanoscience and nanotechnology and is included in this area, the study of nanocomposites with self-cleaning properties. Since titanium dioxide (TiO2) has high photocatalytic activity and also antimicrobial, self-cleaning surfaces in your application has been explored. In this study a comparison was made between two synthesis routes to obtain TiO2 nanoparticles by hydrothermal method assisted by microwave. And after analysis of XRD and SEM was considered the best material for use in nanocomposites. It was deposited nanocomposite film of poly (dimethyl siloxane) (PDMS) with 0.5, 1, 1.5 and 2% by weight of nanoparticles of titanium dioxide (TiO2) by the spraying method. The nanocomposite was diluted with hexane and the suspension was deposited onto glass substrate, followed by curing in an oven with forced air circulation. The photocatalytic activity of the nanocomposite impregnated with methylene blue was evaluated by UV- vis spectroscopy from the intensity variation of absorption main peak at 660nm with time of exposure to the UV chamber. Changes in the contact angle and microhardness were analyzed before and after UV aging test. The effect of ultraviolet radiation on the chemical structure of the PDMS matrix was evaluated by spectrophotometry Fourier transform infrared (FTIR).The results indicated that the addition of TiO2 nanoparticles in the coating PDMS gave high photocatalytic activity in the decomposition of methylene blue, an important characteristic for the development of self-cleaning coatings

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The refractory metal carbides have proven important in the development of engineering materials due to their properties such as high hardness, high melting point, high thermal conductivity and high chemical stability. The niobium carbide presents these characteristics. The compounds of niobium impregnated with copper also have excellent dielectric and magnetic properties, and furthermore, the Cu doping increases the catalytic activity in the oxidation processes of hydrogen. This study aimed to the synthesis of nanostructured materials CuNbC and niobium and copper oxide from precursor tris(oxalate) oxiniobate ammonium hydrate through gas-solid and solid-solid reaction, respectively. Both reactions were carried out at low temperature (1000°C) and short reaction time (2 hours). The niobium carbide was produced with 5 % and 11% of copper, and the niobium oxide with 5% of copper. The materials were characterized by X-Ray Diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), X-Ray Fluorescence Spectroscopy (XRF), infrared spectroscopy (IR), thermogravimetric (TG) and differential thermal analysis (DTA , BET and particle size Laser. From the XRD analysis and Rietveld refinement of CuNbC with S = 1.23, we observed the formation of niobium carbide and metallic copper with cubic structure. For the synthesis of mixed oxide made of niobium and copper, the formation of two distinct phases was observed: CuNb2O6 and Nb2O5, although the latter was present in small amounts

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For the chemical method of synthesis of co-precipitation were produced ferrite powders manganese-cobalt equal stoichiometric formula Mn (1-x) Co (x) Fe2O4, for 0 < x < 1, first reagent element using as the hydroxide ammonium and second time using sodium hydroxide. The obtained powders were calcined at 400 ° C, 650 ° C, 900 ° C and 1150 ° C in a conventional oven type furnace with an air atmosphere for a period of 240 minutes. Other samples were calcined at a temperature of 900 ° C in a controlled atmosphere of argon, to evaluate the possible influence of the atmosphere on the final results the structure and morphology. The samples were also calcined in a microwave oven at 400 ° C and 650 ° C for a period of 45 minutes possible to evaluate the performance of this type of heat treatment furnace. It was successfully tested the ability of this group include isomorphic ferrite with the inclusion of nickel cations in order to evaluate the occurrence of disorder in the crystalline structures and their changes in magnetic characteristics.To identify the structural, morphological, chemical composition and proportions, as well as their magnetic characteristics were performed characterization tests of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDX), thermogravimetric (TG), vibrating sample magnetometry (MAV) and Mössbauer spectroscopy. These tests revealed the occurrence of distortion in the crystal lattice, changes in magnetic response, occurrence of nanosized particles and superparamagnetism

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Nowadays, composite resins are the direct restorative materials more important in dental clinical performance, due to their versatility and aesthetic excellence. Bis-GMA (2,2-bis[4(2-hydroxy-3-metacryloxypropoxy)phenil]propane) is the base monomer more frequently used in restorative composite resins. However, this monomer presents some disadvantages, such as high viscosity and two aromatic rings in its structure that can promote allergic reactions to the humans. In this work, the main purpose was to synthesize new monomers from glycidyl methacrylate to use in dental restorative materials. Structural characterization of the monomers was carried out through FTIR and NMR 1H, and eight composites were produced from the new monomers, by addition of silane-treated alumino silicate particles (inorganic filler) and a photocuring system (camphorquinone and ethyl 4-dimethylaminebenzoate). The composites were analyzed by environmental scanning electronic microscopy and the water sorption and solubility, compressive strength and elastic modulus were determined. A commercial composite resin [Z100 (3M)] was used to comparison effect. The new composites presented general characteristics similar to the commercial ones; however, they didn t present the properties expected. This behavior was attributed to the lower degree of monomer reaction and to the granulometry and size distribution of the mineral filler in the polymeric matrix

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Sugar esters are substances which possess surfactant, antifungical and bactericidal actions and can be obtained through two renewable sources of raw materials: sugars and vegetable oils. Their excellent biodegradability, allied to lhe fact that they are non toxic, insipid, inodorous, biocompatible, no-ionic, digestible and because they can resist to adverse conditions of temperature, pH and salinity, explain lhe crescent use of these substances in several sections of lhe industry. The objective of this thesis was to synthesize and characterize surfactants and polymers containing sugar branched in their structures, through enzymatic transesterification of vinyl esters and sugars, using alkaline protease from Bacillus subtilis as catalyst, in organic medium (DMF).Three types of sugars were used: L-arabinose, D-glucose and sucrose and two types of vinyl esters: vinyl laurate and vinyl adipate. Aiming to reach high conversions from substrates to products for a possible future large scale industrial production, a serie of variables was optimized, through Design of Experiments (DOE), using Response Surface Methodology (RSM).The investigated variables were: (1) enzyme concentration; (2) molar reason of substrates; (3) water/solvent rale; (4) temperature and (5) time. We obtained six distinct sugar esters: 5-0-lauroyl L-arabinose, 6-0-lauroyl D-glucose, 1'-O-lauroyl sucrose, 5-0-vinyladipoyl L-arabinose, 6-0-vinyladipoyl D-glucose and 1 '-O-vinyladipoyl sucrose, being lhe last three polymerizable. The progress of lhe reaction was monitored by HPLC analysis, through lhe decrease of sugar concentration in comparison to lhe blank. Qualitative analysis by TLC confirmed lhe formation of lhe products. In lhe purification step, two methodologies were adopted: (1) chromatographic column and (2) extraction with hot acetone. The acylation position and lhe chemical structure were determined by 13C-RMN. The polymerization of lhe three vinyl sugar esters was possible, through chemical catalysis, using H2O2 and K2S2O8 as initiators, at 60°C, for 24 hours. IR spectra of lhe monomers and respective polymers were compared revealing lhe disappearance of lhe vinyl group in lhe polymer spectra. The molar weights of lhe polymers were determined by GPC and presented lhe following results: poly (5-0-vinyladipoyl L-arabinose): Mw = 7.2 X 104; PD = 2.48; poly (6-0-vinyladipoyl D-glucose): Mw = 2.7 X 103; PD = 1.75 and poly (1'-O-vinyladipoyl sucrose): Mw = 4.2 X 104; PD = 6.57. The six sugar esters were submitted to superficial tension tests for determination of the critical micelle concentrations (CMC), which varied from 122 to 167 ppm. Finally, a study of applicability of these sugar esters, as lubricants for completion fluids of petroleum wells was' accomplished through comparative analysis of lhe efficiency of these sugar esters, in relation to three commercial lubricants. The products synthesized in this thesis presented equivalent or superior action to lhe tested commercial products

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Ionic liquids (ILs) are organic compounds liquid at room temperature, good electrical conductors, with the potential to form as a means for electrolyte on electrolysis of water, in which the electrodes would not be subjected to such extreme conditions demanding chemistry [1]. This paper describes the synthesis, characterization and study of the feasibility of ionic liquid ionic liquid 1-methyl-3(2,6-(S)-dimethyloct-2-ene)-imidazole tetrafluoroborate (MDI-BF4) as electrolyte to produce hydrogen through electrolysis of water. The MDI-BF4 synthesized was characterized by thermal methods of analysis (Thermogravimetric Analysis - TG and Differential Scanning Calorimetry - DSC), mid-infrared spectroscopy with Fourier transform by method of attenuated total reflectance (FTIR-ATR), nuclear magnetic resonance spectroscopy of hydrogen (NMR 1H) and cyclic voltammetry (CV). Where thermal methods were used to calculate the yield of the synthesis of MDI-BF4 which was 88.84%, characterized infrared spectroscopy functional groups of the compound and the binding B-F 1053 cm-1; the NMR 1H analyzed and compared with literature data defines the structure of MDI-BF4 and the current density achieved by MDI-BF4 in the voltammogram shows that the LI can conduct electrical current indicating that the MDI-BF4 is a good electrolyte, and that their behavior does not change with the increasing concentration of water

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Nowadays generation ethanol second, that t is obtained from fermentation of sugars of hydrolyses of cellulose, is gaining attention worldwide as a viable alternative to petroleum mainly for being a renewable resource. The increase of first generation ethanol production i.e. that obtained from sugar-cane molasses could lead to a reduction of lands sustainable for crops and food production. However, second generation ethanol needs technologic pathway for reduce the bottlenecks as production of enzymes to hydrolysis the cellulose to glucose i.e. the cellulases as well as the development of efficient biomass pretreatment and of low-cost. In this work Trichoderma reesei ATCC 2768 was cultivated under submerged fermentation to produce cellulases using as substrates waste of lignocellulosic material such as cashew apple bagasse as well as coconut bagasse with and without pretreatment. For pretreatment the bagasses were treated with 1 M NaOH and by explosion at high pressure. Enzyme production was carried out in shaker (temperature of 27ºC, 150 rpm and initial medium pH of 4.8). Results showed that T.reesei ATCC 2768 showed the higher cellulase production when the cashew apple bagasse was treated with 1M NaOH (2.160 UI/mL of CMCase and 0.215 UI/mL of FPase), in which the conversion of cellulose, in terms of total reducing sugars, was of 98.38%, when compared to pretreatment by explosion at high pressure (0.853 UI/mL of CMCase and 0.172 UI/mL of Fpase) showing a conversion of 47.39% of total reducing sugars. Cellulase production is lower for the medium containing coconut bagasse treated with 1M NaOH (0.480 UI/mL of CMcase and 0.073 UI/mL of FPase), giving a conversion of 49.5% in terms of total reducing sugars. Cashew apple bagasse without pretreatment showed cellulase activities lower (0.535 UI/mL of CMCase and 0,152 UI/mL of FPase) then pretreated bagasse while the coconut bagasse without pretreatment did not show any enzymatic activity. Maximum cell concentration was obtained using cashew nut bagasse as well as coconut shell bagasse treated with 1M NaOH, with 2.92 g/L and 1.97 g/L, respectively. These were higher than for the experiments in which the substrates were treated by explosion at high pressure, 1.93 g/L and 1.17 g/L. Cashew apple is a potential inducer for cellulolytic enzymes synthysis showing better results than coconut bagasse. Pretreatment improves the process for the cellulolytic enzyme production

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The nanostructures materials are characterized to have particle size smaller than 100 nm and could reach 1 nm. Due to the extremely reduced dimensions of the grains, the properties of these materials are significantly modified relatively when compared with the conventional materials. In the present work was accomplished a study and characterization of the molybdenum carbide, seeking obtain it with particles size in the nanometers order and evaluate its potential as catalyst in the reaction of partial methane oxidation. The method used for obtaining the molybdenum carbide was starting from the precursor ammonium heptamolybdate of that was developed in split into two oven, in reactor of fixed bed, with at a heating rate of 5ºC/min, in a flow of methane and hydrogen whose flow was of 15L/h with 5% of methane for all of the samples. The studied temperatures were 350, 500, 600, 650, 660, 675 and 700ºC and were conducted for 0, 60, 120 and 180 minutes, and the percent amount and the crystallite size of the intermediate phases were determined by the Rietveld refinement method. The carbide obtained at 660ºC for 3 hours of reaction showed the best results, 24 nm. Certain the best synthesis condition, a passivating study was accomplished, in these conditions, to verify the stability of the carbide when exposed to the air. The molybdenum carbide was characterized by SEM, TEM, elemental analysis, ICP-AES, TG in atmosphere of hydrogen and TPR. Through the elemental analysis and ICP-AES the presence carbon load was verified. TG in atmosphere of hydrogen proved that is necessary the passivating of the molybdenum carbide, because occur oxidation in room temperature. The catalytic test was accomplished in the plant of Fischer-Tropsch of CTGAS, that is composed of a reactor of fixed bed. Already the catalytic test showed that the carbide presents activity for partial oxidation, but the operational conditions should be adjusted to improve the conversion

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The main goal of this work was to produce nanosized ceramic materials of the family of the tungstates (tungstates of cerium and strontium), and test them for their catalytic activity in processes involving the transformation of methane (CH4). The methodology used for the synthesis of the ceramic powders involved the complexation combining EDTA-citrate. The materials characterization was performed using simple and differential thermogravimetry, x-ray diffraction, transmission electron microscopy, and energy dispersive spectroscopy (EDS). The microstructure analysis was performed using the refinement by the Rietveld method, and the crystallite size and distribution of the materials was elucidate by the Scherrer and Williamson-Hall methods. The conditions of the synthesis process for the three envisaged materials (SrWO4, SrWO4 using tungsten oxide concentrate as raw material, and Ce2(WO4)3) were adjusted to obtain a single phase crystalline material. The catalytic tests were carried out in the presence of methane and synthetic air, which is composed of 21% O2 and 79% N2. The analysis of the conversion of the reaction was done with the aid of an fourier transform infrared device (FTIR). The analysis showed that, structurally, the SrWO4 produced using raw materials of high and poor purity (99% and 92%, respectively) are similar. The ideal parameters of calcination, in the tested range, are temperature of 1000 °C and time of calcination 5 hours. For the Ce2(WO4)3, the ideal calcination time and are temperature 15 hours and 1000°C, respectively. The Williamson-Hall method provided two different distributions for the crystallite size of each material, whose values ranged between the nanometer and micrometer scales. According to method of Scherrer, all materials produced were composed of nanometric crystallites. The analyses of transmission electron microscopy confirmed the results obtained from the Williamson- Hall method for the crystallite size. The EDS showed an atomic composition for the metals in the SrWO4 that was different of the theoretical composition. With respect to the catalytic tests, all materials were found to be catalytically active, but the reaction process should be further studied and optimized.

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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

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Metabolic flux analysis (MFA) is a powerful tool for analyzing cellular metabolism. In order to control the growth conditions of a specific organism, it is important to have a complete understanding of its MFA. This would allowed us to improve the processes for obtaining products of interest to human and also to understand how to manipulate the genome of a cell, allowing optimization process for genetic engineering. Streptomyces olindensis ICB20 is a promising producer of the antibiotic cosmomycin, a powerful antitumor drug. Several Brazilian researchers groups have been developing studies in order to optimize cosmomycin production in bioreactors. However, to the best of our knowledge, nothing has been done on metabolic fluxes analysis field. Therefore, the aim of this work is to identify several factors that can affect the metabolism of Streptomyces olindensis ICB20, through the metabolic flux analysis. As a result, the production of the secondary metabolite, cosmomycin, can be increased. To achieve this goal, a metabolic model was developed which simulates a distribution of internal cellular fluxes based on the knowledge of metabolic pathways, its interconnections, as well as the constraints of microorganism under study. The validity of the proposed model was verified by comparing the computational data obtained by the model with the experimental data obtained from the literature. Based on the analysis of intracellular fluxes, obtained by the model, an optimal culture medium was proposed. In addition, some key points of the metabolism of Streptomyces olindensis were identified, aiming to direct its metabolism to a greater cosmomycin production. In this sense it was found that by increasing the concentration of yeast extract, the culture medium could be optimized. Furthermore, the inhibition of the biosynthesis of fatty acids was found to be a interesting strategy for genetic manipulation. Based on the metabolic model, one of the optimized medium conditions was experimentally tested in order to demonstrate in vitro what was obtained in silico. It was found that by increasing the concentration of yeast extract in the culture medium would induce to an increase of the cosmomycin production

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The current natural gas production of 52 Mm3d-1 and the large projects for its expansion has been setting new boundaries for the Brazilian industry of oil and gas. So far, one of the biggest challenges regards to the logistics for gas transportation from offshore fields. Therefore, the transformation of natural gas into gasoline, diesel and/or olefins via Fischer-Tropsch synthesis would be an alternative to this matter. In this work, the production of hydrocarbons by Fischer-Tropsch synthesis in a slurry reactor was investigated and a perovskite-type catalyst (LayCu0,4Fe0,6O3 ± d) was used with y varying from 0 to 1 on a molar basis. In addition, Nb2O5 support was also applied in order to observe the selectivity of the produced hydrocarbons by the Fischer-Tropsch process. It is shown that the hydrogen conversion was influenced by the support as well as the different phases of the samples. The kinetic results for the CO2 production suffered great influence with the introduction of the Nb2O5 support throughout the series of samples studied. The catalysts allowed obtaining welldefined cuts of hydrocarbons in the range of C1-C6 and C17-C28, and these results were clearly influenced by the support and the lanthanum content. The higher olefin/paraffin ratio obtained was 1.8 when using a non-supported perovskite with y equal to 0.8. This would indicate the suitability of using this material for the production of olefins

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Discussions about pollution caused by vehicles emission are old and have been developed along the years. The search for cleaner technologies and frequent weather alterations have been inducing industries and government organizations to impose limits much more rigorous to the contaminant content in fuels, which have an direct impact in atmospheric emissions. Nowadays, the quality of fuels, in relation to the sulfur content, is carried out through the process of hydrodesulfurization. Adsorption processes also represent an interesting alternative route to the removal of sulfur content. Both processes are simpler and operate to atmospheric temperatures and pressures. This work studies the synthesis and characterization of aluminophosphate impregnate with zinc, molybdenum or both, and its application in the sulfur removal from the gasoline through the adsorption process, using a pattern gasoline containing isooctane and thiophene. The adsorbents were characterized by x-ray diffraction, differential thermal analysis (DTG), x-ray fluorescence and scanning electron microscopy (SEM). The specific area, volume and pore diameter were determined by BET (Brunauer- Emmet-Teller) and the t-plot method. The sulfur was quantified by elementary analysis using ANTEK 9000 NS. The adsorption process was evaluated as function of the temperature variation and initial sulfur content through the adsorption isotherm and its thermodynamic parameters. The parameters of entropy (ΔS), enthalpy variation (ΔH) and free Gibbs energy (ΔG) were calculated through the graph ln(Kd) versus 1/T. Langmuir, Freundlich and Langmuir-Freundlich models were adjusted to the experimental data, and the last one had presented better results. The thermodynamic tests were accomplished in different temperatures, such as 30, 40 and 50ºC, where it was concluded the adsorption process is spontaneous and exothermic. The kinetic of adsorption was studied by 24 h and it showed that the capability adsorption to the adsorbents studied respect the following order: MoZnPO > MoPO > ZnPO > AlPO. The maximum adsorption capacity was 4.91 mg/g for MoZnPO with an adsorption efficiency of 49%.