Síntese de pigmentos cerâmicos inorgânicos nanométricos pela rota dos precursores poliméricos

Considering the constant evolution of technology in growth and the need for production techniques in the ceramics area to move forward together, we sought in this study, the research and development of polymeric precursor method to obtain inorganic ceramic pigments. Method that provides quality to obtain the precursor powders of oxides and pigments at the same time, offers time and cost advantages, such as reproducibility, purity and low temperature heat treatment, control of stoichiometry. This work used chromium nitrate and iron nitrate as precursors. The synthesis is based on the dissolution of citric acid as a complexing agent, addition of metal oxides, such as ion chromophores; polymerization with ethylene glycol and doping with titanium oxide. Passing through precalcination, breakdown, thermal treatments at different temperatures of calcination (700 to 1100 oC), resulting in pigments: green for chromium oxide deposited on TiO2 (CrTiO3) and orange for iron oxide deposited on TiO2 ( FeTiO3). Noticing an increase of opacity with increasing temperature. Were performed thermal analysis (TG and ATD) in order to evaluate its thermodecomposition. The powders were also characterized by techniques such as XRD, revealing the formation of crystalline phases such as iron titanate (FeTiO3) and chrome titanate (CrTiO3), SEM, demonstrating formation of rounded particles for both oxides and Spectroscopy in the UV-Visible Region, verifying the potential variation and chromaticity os pigments. Thus, the synthesized oxides were within the requirements to be applied as pigments and shown to be possible to propose its use in ceramic materials

Mecanismos de desgaste de poliuretano em ensaios de microabrasão

Wear mechanisms and thermal history of two non-conforming sliding surfaces was investigated in laboratory. A micro-abrasion testing setup was used but the traditional rotative sphere method was substituted by a cylindrical surface of revolution which included seven sharp angles varying between 15o to 180o. The micro-abrasion tests lead to the investigation on the polyurethane response at different contact pressures. For these turned counterfaces with and without heat treatment. Normal load and sliding speeds were changed. The sliding distance was fixed at 5 km in each test. The room and contact temperatures were measured during the tests. The polyurethane was characterized using tensile testing, hardness Shore A measurement, Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Thermomechanical Analyze (TMA). The Vickers micro-hardness of the steel was measured before and after the heat treatment and the metallographic characterization was also carried out. Worn surface of polyurethane was analysed using Scanning Electron Microscope (SEM) and EDS (Electron Diffraction Scanning) microanalyses. Single pass scratch testing in polyurethane using indenters with different contact angles was also carried out. The scar morphology of the wear, the wear mechanism and the thermal response were analyzed in order to correlate the conditions imposed by the pressure-velocity pair to the materials in contact. Eight different wear mechanisms were identified on the polyurethane surface. It was found correlation between the temperature variation and the wear scar morphology.

Caracterização e análise das propriedades da fibra de Macambira (Bromelia Laciniosa)

Concern for the environment and the exploitation of natural resources has motivated the development of research in lignocellulosic materials, mainly from plant fibers. The major attraction of these materials include the fact that the fibers are biodegradable, they are a renewable natural resource, low cost and they usually produce less wear on equipment manufacturing when compared with synthetic fibers. Its applications are focused on the areas of technology, including automotive, aerospace, marine, civil, among others, due to the advantageous use in economic and ecological terms. Therefore, this study aims to characterize and analyze the properties of plant fiber macambira (bromelia laciniosa), which were obtained in the municipality of Ielmo Marino, in the state of Rio Grande do Norte, located in the region of the Wasteland Potiguar. The characterization of the fiber is given by SEM analysis, tensile test, TG, FTIR, chemical analysis, in addition to obtaining his title and density. The results showed that the extraction of the fibers, only 0.5% of the material is converted into fibers. The results for title and density were satisfactory when compared with other fibers of the same nature. Its structure is composed of microfibrils and its surface is roughened. The cross section has a non-uniform geometry, therefore, it is understood that its diameter is variable along the entire fiber. Values for tensile strength were lower than those of sisal fibers and curauá. The degradation temperature remained equivalent to the degradation temperatures of other vegetable fibers. In FTIR analysis showed that the heat treatment may be an alternative to making the fiber hydrophobic, since, at high temperature can remove the hemicellulose layer, responsible for moisture absorption. Its chemical constitution is endowed with elements of polar nature, so their moisture is around 8.5% which is equivalent to the percentage of moisture content of hydrophilic fibers. It can be concluded that the fiber macambira stands as an alternative materials from renewable sources and depending on the actual application and purpose, it may achieve satisfactory results

Avaliação, identificação e atividade enzimática de bactérias psicotróficas presentes no leite cru refrigerado

Extended storage of refrigerated milk can lead to reduced quality of raw and processed milk, which is a consequence of the growth and metabolic activities of psychrotrophic bacteria, able to grow under 7oC or lower temperatures. Although most of these microorganisms are destroyed by heat treatment, some have the potential to produce termoresistant proteolytic and lipolytic enzymes that can survive even UHT processing and reduce the processed products quality. Recently, the IN 51 determineds that milk should be refrigerated and stored at the farm what increased the importance of this group of microorganisms. In this work, psychrotrophic bacteria were isolated from 20 communitarian bulk tanks and 23 individual bulk tanks from dairy farms located at Zona da Mata region of Minas Gerais State and from southeastern Rio de Janeiro. Selected milk dilutions were plated on standard agar and after incubation for 10 days at 7oC, five colonies were isolated, firstly using nutrient agar and after using McConkey agar for 24 hours at 21oC. The isolates were identified by morphology, Gram stain method, catalase production, fermentative/oxidative metabolism and by API 20E, API 20NE, API Staph, API Coryne or API 50 CH (BioMerieux). In order to ensure reproductibility, API was repeated for 50% of the isolates. Species identification was considered when APILAB indexes reached 75% or higher. 309 strains were isolated, 250 Gram negative and 59 Gram positive. 250 Gram negative isolates were identified as: Acinetobacter spp. (39), Aeromonas spp. (07), A. Hydrophila (16), A. sobria (1), A. caviae (1), Alcaligenes feacalis (1), Burkholderia cepacia (12), Chryseomonas luteola (3), Enterobacter sp. (1), Ewingella americana(6), Hafnia alvei (7), Klebsiella sp. (1), Klebsiella oxytoca (10), Yersinia spp. (2), Methylobacterium mesophilicum (1), Moraxella spp. (4), Pantoea spp. (16), Pasteurella sp. (1), Pseudomonas spp. (10), P. fluorescens (94), P. putida (3), Serratia spp. (3), Sphigomonas paucomobilis (1). Five isolates kept unidentified. Pseudomonas was the predominant bacteria found (43%) and P. fluorescens the predominant species (37.6%), in accordance with previous reports. Qualitative analysis of proteolytic and lipolytic activity was based on halo formation using caseinate agar and tributirina agar during 72 hours at 21oC and during 10 days at 4°C, 10oC and 7°C. Among 250 Gram negative bacteria found, 104 were identified as Pseudomonas spp. and 60,57% of this group showed proteolytic and lipolytic acitivities over all four studied temperatures. 20% of Acinetobacter, Aeromonas, Alcaligenes, Burkholderia, Chryseomonas, Methylobacterium, Moraxella presented only lipolytic activity. Some isolates presented enzymatic activity in one or more studied temperatures. Among Gram positive bacteria, 30.51% were proteolytic and lipolytic at 10oC, 8.47% were proteolytic at 7oC, 10oC, and 21oC, 8.47% were proteolytic at all studied temperatures (4oC, 7oC, 10oC and 21oC) and 3.38% were proteolytic only at 21oC. At 4oC, only one isolate showed proteolytic activity and six isolates were lipolytic. In relation to Gram negative microorganisms, 4% were proteolytic and lipolytic at 7oC, 10oC and 21oC, 10% were proteolytic at 10oC and 4.4% were lipolytic at 4oC, 7oC, 10oC and 21oC, while 6.4% of all isolates were proteolytic and lipolytic at 10oC and 21oC as well as lipolytic at 4oC and 7oC. These findings are in accordance with previous researches that pointed out Pseudomonas as the predominant psycrotrophic flora in stored refrigerated raw milk

Estudo dos óxidos A2B2O7 e ABO3 a base de terras raras, para aplicações térmicas e catalíticas a altas temperaturas

Rare earth elements have recently been involved in a range of advanced technologies like microelectronics, membranes for catalytic conversion and applications in gas sensors. In the family of rare earth elements like cerium can play a key role in such industrial applications. However, the high cost of these materials and the control and efficiencies associated processes required for its use in advanced technologies, are a permanent obstacle to its industrial development. In present study was proposed the creation of phases based on rare earth elements that can be used because of its thermal behavior, ionic conduction and catalytic properties. This way were studied two types of structure (ABO3 and A2B2O7), the basis of rare earths, observing their transport properties of ionic and electronic, as well as their catalytic applications in the treatment of methane. For the process of obtaining the first structure, a new synthesis method based on the use of EDTA citrate mixture was used to develop a precursor, which undergone heat treatment at 950 ° C resulted in the development of submicron phase BaCeO3 powders. The catalytic activity of perovskite begins at 450 ° C to achieve complete conversion at 675 ° C, where at this temperature, the catalytic efficiency of the phase is maximum. The evolution of conductivity with temperature for the perovskite phase revealed a series of electrical changes strongly correlated with structural transitions known in the literature. Finally, we can establish a real correlation between the high catalytic activity observed around the temperature of 650 ° C and increasing the oxygen ionic conductivity. For the second structure, showed clearly that it is possible, through chemical processes optimized to separate the rare earth elements and synthesize a pyrochlore phase TR2Ce2O7 particular formula. This "extracted phase" can be obtained directly at low cost, based on complex systems made of natural minerals and tailings, such as monazite. Moreover, this method is applied to matters of "no cost", which is the case of waste, making a preparation method of phases useful for high technology applications

Síntese, caracterização e aplicação de MCM-41 funcionalizado com diisopropilamina no processo de adsorção do dióxido de carbono

Emissions of CO2 in the atmosphere have increased successively by various mechanisms caused by human action, especially as fossil fuel combustion and industrial chemical processes. This leads to the increase in average temperature in the atmosphere, which we call global warming. The search for new technologies to minimize environmental impacts arising from this phenomenon has been investigated. The capture of CO2 is one of the alternatives that can help reduce emis ions of greenhouse gases. The CO2 can be captured through the process of selective adsorption using adsorbents for this purpose. Were synthesized by hydrothermal method, materials of the type MCM-41 and Al-MCM-41 in the molar ratio Si / Al equal to 50. The synthesis of gels were prepared from a source of silicon, sodium, water and aluminum in the case of Al-MCM-41. The period of synthesis of the materials was 5 days in autoclave at 100°C. After that time materials were filtered, washed and dried in greenhouse at 100 º C for 4 hours and then calcined at 450 º C. Then the calcined material was functionalized with the Di-isopropylamine (DIPA) by the method of wet impregnation. We used 0.5 g of material mesopores to 3.5 mL of DIPA. The materials were functionalized in a closed container for 24 hours, and after this period were dried at brackground temperature for 2 hours. Were subsequently subjected to heat treatment at 250°C for 1 hour. These materials were used for the adsorption of CO2 and were characterized by XRD, FT-IR, BET / BJH, SEM, EDX and TG / DTG. Tests of adsorption of CO2 was carried out under the following conditions: 100 mg of adsorbent, temperature of 75°C under flow of 100 mL/min of CO2 for 2 hours. The desorption of CO2 was carried out by thermogravimetry from ambient temperature to 900ºC under flow of 25 mL min of He and a ratio of 10ºC/min. The difratogramas X-ray for the synthesized samples showed the characteristic peaks of MCM-41, showing that the structure of it was obtained. For samples functionalized there was a decrease of the intensities of these peaks, with a consequent reduction in the structural ordering of the material. However, the structure was preserved mesopores. The adsorption tests showed that the functionalized MCM-41 is presented as a material promising adsorbent, for CO2 capture, with a loss of mass on the desorption CO2 of 7,52%, while that in Al-MCM- 41 functionalized showed no such loss

Avaliação da síntese e caracterização de zeólita ZSM-5 ausente de direcionador orgânico estrutural

The catalytic processes play a vital role in the worldwide economy, a business that handles about US$ 13 billion per year because the value of products depends on the catalytic processes, including petroleum products, chemicals, pharmaceuticals, synthetic rubbers and plastics, among others. The zeolite ZSM-5 is used as catalyst for various reactions in the area petrochemical, petroleum refining and fine chemicals, especially the reactions of cracking, isomerization, alkylation, aromatization of olefins, among others. Many researchers have studied the hydrothermal synthesis of zeolite ZSM-5 free template and they obtained satisfactory results, so this study aims to evaluate the hydrothermal synthesis and the physicochemical properties of ZSM-5 with the presence and absence of template compared with commercial ZSM-5. The methods for hydrothermal synthesis of zeolite ZSM-5 are of scientific knowledge, providing the chemical composition required for the formation of zeolitic structure in the presence and absence of template. Samples of both zeolites ZSM-5 in protonic form were obtained by heat treatment and ion exchange, according to procedures reported in the literature. The sample of commercial ZSM-5 was acquired by the company Sentex Industrial Ltda. All samples were characterized by XRD, SEM, FTIR, TG / DTG / DSC, N2 adsorption and desorption and study of acidity by thermo-desorption of probe molecule (n-butylamine), in order to understand their physicochemical properties. The efficiency of the methods applied in this work and reported in the literature has been proved by well-defined structure of ZSM-5. According as the evaluation of physicochemical properties, zeolite ZSM-5 free template becomes promising for application in the refining processes or use as catalytic support, since its synthesis reduces environmental impacts and production costs

Síntese, caracterização e estudo das propriedades magnéticas de ortoferritas de lantânio dopadas com manganês

Orthoferrites AFeO3 (A = rare earth) are an important class of perovskite oxides that exhibit weak ferromagnetism. These materials find numerous applications as chemical sensors, cathodes for fuel cells and catalysis, which make them interesting from the standpoint of science and technology. Their structural, electrical and magnetic properties are dependent on many factors such as the preparation method, heat treatment conditions, chemical composition and replacement of cations in sites A and/or B. In this paper, LaFe1-xMnxO3 (0 ≤ x ≤ 1) orthoferrites-type was prepared by Pechini method and Microwave-assisted combustion reaction in order to evaluate the influence of synthesis route on the formation of oxide, as well as the effect of parcial replacement of iron by manganese and heat treatment on the magnetic properties. The precursor powders were calcined at 700°C, 900°C, 1100°C and 1300°C for 4 hours and they were characterized by the techniques: Thermogravimetric analysis (TGA), X ray diffraction (XRD), Refinement by Rietveld method, Scanning electron microscopy (SEM), Reduction temperature programmed (RTP) and Magnetic hysteresis measurements performed at room temperature. According to the XRD patterns, the formation of perovskite phase with orthorhombic structure was observed for the systems where 0 ≤ x ≤ 0.5 and rhombohedral for x = 1. The results also showed a decrease of lattice parameters with the parcial replacement of iron by manganese and consequently a reduction in cell volume. The hysteresis curves exhibited weak ferromagnetism for the systems prepared by both synthesis methods. However, a dependence of magnetization as a function of dopant content was observed for samples produced by Pechini method. As for the systems prepared by combustion reaction, it was found that the secondary phases exert a strong influence on the magnetic behavior

Síntese hidrotérmica e caracterização estrutural de titanatos nanotubulares para aplicação na captura do dióxido de carbono

Nanostructured materials have been spreading successfully over past years due its size and unusual properties, resulting in an exponential growth of research activities devoted to nanoscience and nanotechnology, which has stimulated the search for different methods to control main properties of nanomaterials and make them suitable for applications with high added value. In the late 90 s an alternative and low cost method was proposed from alkaline hydrothermal synthesis of nanotubes. Based on this context, the objective of this work was to prepare different materials based on TiO2 anatase using hydrothermal synthesis method proposed by Kasuga and submit them to an acid wash treatment, in order to check the structural behavior of final samples. They were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), adsorption/desorption of N2, thermal analysis (TG/DTA) and various spectroscopic methods such as absorption spectroscopy in the infrared (FT-IR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). All the information of characterizations confirmed the complete conversion of anatase TiO2 in nanotubes titanates (TTNT). Observing the influence of acid washing treatment in titanates structure, it was concluded that the nanotubes are formed during heat treatment, the sample which was not subjected to this process also achieved a complete phase transformation, as showed in crystallography and morphology results, however the surface area of them practically doubled after the acid washing. By spectroscopy was performed a discussion about chemical composition of these titanates, obtaining relevant results. Finally, it was observed that the products obtained in this work are potential materials for various applications in adsorption, catalysis and photocatalysis, showing great promise in CO2 capture

Síntese, caracterização de ferritas espinélio com propriedades magnéticas e absorvedoras de microondas

Were synthesized spinel-type ferrites with general formula Ni0,8Mg0.2-xMxFe2O4, where M represents the doping Mn, Co or Mn + Co simultaneously, x ranges for the values 0.02, 0.05 and 0.1. The value of x was divided by 2 in cases where M equals Mn and Co conjugates. We used the citrate precursor method and heat treatment to obtain the phases at 1100°C. The materials were characterized by XRD, TGA/ DTGA, SEM, MAV and reflectivity measurements by the method of waveguide. Powders to 350°C/3.5 h were crystalline and nanosized. According to the results this temperature all powders have a percentage of ferrite phase over 90%. The composition had the addition of Mn and Co simultaneously showed a higher percentage of secondary phase NiO, 5.8%. The TGA/DTGA curves indicate that this sample reached phase (s) crystalline (s) at lowest temperatures. The X-ray diffractograms of the samples calcined at 350°C and 1100°C were treated with the Rietveld refinament technique. The powders calcined at 1100 °C/3h in air show to be 100% except spinel phase composition with 0.02 doping. The micrographs show clusters of particles with sizes smaller than 1 μm in calcination temperature of 1100°C which agreed with the result of Rietveld refinement. In the compositions doped with Mn were higher values of magnetization (45.90 and 53.20 Am2/kg), which did not cause high microwave absorption. The theoretical calculation of magnetization (MT) was consistent with the results, considering that there was agreement between the increase of magnetization experimental and theoretical. It was observed that there was the interrelation of the final effect of absorption with the thickness of MARE, the composition of ferrimagnetic materials and in particular the specific values of frequency. The analysis shows that the reflectivity increases in the concentration of cobalt increased the frequency range and also for absorption 10.17 GHz and 84%, respectively. The best result of chemical homogeneity and the value of 2.96 x 10-2 tesla coercive field were crucial for high performance ferrite absorber with 0.1 cobalt. The Cobalt has high magnetocrystalline anisotropy, it is associated with an increased coercive field, Hc. Therefore, this property improves the results of reflectivity of spinel ferrites

Desenvolvimento de uma rota química alternativa de síntese de SrCo0,8Fe0,2O3- e LaNi0,3Co0,7O3- para aplicação na reação de oxidação do CO

This thesis focuses on the coprecipitation synthesis method for preparation of ceramic materials with perovskite structure, their characterization and application as catalytic material in the reaction of converting CO to CO2 developing a methodological alternative route of synthesis from the middle via oxalate coprecipitation material SrCo0,8Fe0,2O3-d. In order to check the influence of this method, it was also synthesized using a combined citrate - EDTA complexing method. The material was characterized by: X-ray diffraction (XRD), Rietveld refinement method, thermogravimetry and differential thermo analysis (TG / DTA), scanning (SEM) and transmission (TEM) electron microscopy, particle size distribution and surface analysis method BET. Both methods led to post-phase synthesis, with pH as a relevant parameter. The synthesis based on the method via oxalate coprecipitation among particles led to the crystalline phase as those obtained using a combined citrate - EDTA complexing method under the same conditions of heat treatment. The nature of the reagent used via oxalate coprecipitation method produced a material with approximately 80 % lower than the average size of crystallites. Moreover, the via oxalate coprecipitation method precursors obtained in the solid state at low temperature (~ 26 oC), shorter synthesis, greater thermal stability and a higher yield of around 90-95 %, maintaining the same order of magnitude the crystallite size that the combined citrate - EDTA complexing method. For purposes of comparing the catalytic properties of the material was also synthesized by the using a combined citrate - EDTA complexing method. The evaluation of catalytic materials SrCo0,8Fe0,2O3-d LaNi0,3Co0,7O3-d was accompanied on the oxidation of CO to CO2 using a stainless steel tubular reactor in the temperature range of 75-300 oC. The conversion CO gas was evaluated in both materials on the results shaved that the firm conversion was loves for the material LaNi0,3Co0,7O3-d

Síntese e caracterização estrutural e magnética da ferrita de cálcio

The calcium ferrite (Ca2Fe2O5) has a perovskite-type structure with oxygen deficiency and is used as a chemical catalyst. With the advent of nanoscience and nanotechnology, methods of preparation, physical and chemical characterizations, and the technological applications of nanoparticles have attracted great scientific interest. Calcium nanostructured ferrites were produced via high-energy milling, with subsequent heat treatment. The milling products were characterized by X-ray diffraction, magnetization and Mössbauer spectroscopy. Samples of the type Ca2Fe2O5 were obtained from the CaCO3 and Fe2O3 powder precursors, which were mixed stoichiometrically and milled for 10h and thermally treated at 700ºC, 900ºC and 1100ºC. The Mössbauer spectra of the treated samples were adjusted three subespectros: calcium ferrite (octahedral and tetrahedral sites) and a paramagnetic component, related to very small particles of calcium ferrite, which are in a superparamagnetic state. For samples beats in an atmosphere of methyl alcohol, there is a significant increase in area associated with the paramagnetic component. Hysteresis curves obtained are characteristic of a weak ferromagnetic-like material

Propriedades magnéticas e magnetorresistência em filmes finos de Ni81Fe19

The ferromagnetic materials play an important role in the development of various electronic devices and, have great importance insofar as they may determine the efficiency, cost and, size of the devices. For this reason, many scientific researches is currently focused on the study of materials at ever smaller scales, in order to understand and better control the properties of nanoscale systems, i.e. with dimensions of the order of nanometers, such as thin film ferromagnetic. In this work, we analyze the structural and magnetic properties and magnetoresistance effect in Permalloy-ferromagnetic thin films produced by magnetron sputtering. In this case, since the magnetoresistance effect dependent interfaces of thin films, this work is devoted to the study of the magnetoresistance in samples of Permalloy in nominal settings of: Ta[4nm]/Py[16nm]/Ta[4nm], Ta[4nm]/Py[16nm]/O2/Ta[4nm], Ta[4nm]/O2/Py[16nm]/Ta[4nm], Ta[4nm]/O2/Py[16n m]/O2/Ta[4nm], as made and subjected to heat treatment at temperatures of 160ºC, 360ºC e 460ºC, in order to verify the influence of the insertion of the oxygen in the layer structure of samples and thermal treatments carried out after production of the samples. Results are interpreted in terms of the structure of the samples, residual stresses stored during deposition, stresses induced by heat treatments and magnetic anisotropies