999 resultados para Isoterma de Curie


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Na avicultura algumas integrações têm a prática de estocar as dietas por vários dias dentro da granja e muitas vezes, essas são submetidas a condições inadequadas de armazenamento. Os dados relacionados aos fatores ambientais, especialmente temperatura e umidade relativa do ambiente, tempo de estocagem e principalmente atividade de água (aw) do alimento, são fatores importantes que influenciam o crescimento fúngico e produção de micotoxinas no substrato, tornando-se importantes para o estabelecimento de um programa de prevenção e controle deste agente (ORRIS, 1999). Este trabalho objetivou analisar a atividade de água em dietas animais para verificar o potencial de crescimento fúngico e a forma de armazenamento do produto. Desta forma, foi estudada a atividade de água da dieta comercial de empresa de integração avícola no Rio Grande do Sul, antes da entrega ao criador e no último dia de armazenamento, nas diferentes estações do ano. Assim, buscou-se contribuir para a verificação das condições de conservação do alimento e dos possíveis riscos de contaminação, contribuindo para a prevenção de fungos e toxinas de importância avícola e com reflexos na saúde pública, avaliando o potencial de crescimento de microrganismos no alimento, com a possibilidade de se fornecer uma ferramenta de monitoramento das rações armazenadas, dentro de um programa com critérios fundamentados de prevenção e controle. Também foi determinada a umidade e a isoterma de adsorção destes alimentos, para auxiliar na compreensão sobre a forma de armazenamento. Pelos resultados encontrados ficou confirmado o aumento da atividade de água após o período de armazenamento da dieta, correspondendo ao valor de 0.681 de aw na fábrica e 0.693 de aw na granja. No entanto, os valores de atividade de água não estavam inseridos nos limites mínimos de crescimento fúngico (0.78 de aw) e produção de aflatoxinas (0.86 de aw). Houve correlação linear positiva entre atividade de água e umidade da ração, tanto na fábrica quanto na granja. A isoterma de adsorção apresentou aumento da umidade com o aumento da atividade de água. Não houve correlação entre atividade de água e ppb de aflatoxina encontrados nas dietas.

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Ta-Cu bulk composites combine high mechanical resistance of the Ta with high electrical and thermal conductivity of the Cu. These are important characteristics to electrical contacts, microwave absorber and heat skinks. However, the low wettability of Ta under Cu liquid and insolubility mutual these elements come hard sintering this composite. High-energy milling (HEM) produces composite powders with high homogeneity and refines the grain size. This work focus to study Ta-20wt%Cu composite powders prepared by mechanical mixture and HEM with two different conditions of milling in a planetary ball mill and then their sintering using hydrogen plasma furnace and a resistive vacuum furnace. After milling, the powders were pressed in a steel dye at a pressure of 200 MPa. The cylindrical samples pressed were sintered by resistive vacuum furnace at 10-4torr with a sintering temperature at 1100ºC / 60 minutes and with heat rate at 10ºC/min and were sintered by plasma furnace with sintering temperatures at 550, 660 and 800ºC without isotherm under hydrogen atmosphere with heat rate at 80ºC/min. The characterizations of the powders produced were analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and laser granulometry. After the sintering the samples were analyzed by SEM, XRD and density and mass loss tests. The results had shown that to high intense milling condition produced composite particles with shorter milling time and amorphization of both phases after 50 hours of milling. The composite particles can produce denser structure than mixed powders, if heated above the Cu melting point. After the Cu to arrive in the melting point, liquid copper leaves the composite particles and fills the pores

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In this study barium hexaferrite was (general formulae BaFe12O19) was synthesized by the Pechini method under different conditions of heat treatment. Precursors like barium carbonate and iron nitrate were used. These magnetic ceramic, with magnetoplumbite type structure, are widely used as permanent magnet because of its excellent magnetic properties, such as: high Curie temperature, good magnetic anisotropy, high coercivity and corrosion resistance. The samples were characterized by thermal analysis (DTA and TG), X- ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) end Vibrating sample Magnetometer (VSM). The results confirm the expected phase, which was reinforced according to our analysis. A single phase powder at relatively high temperatures with particle sizes around 100 nm was obtained. The characteristic magnetic behavior one of the phases has been noted (probably superparamagnetic material), while another phase was identified as a ferrimagnetic material. The ferrimagnetic phase showed vortex configuration with two central and slightly inclined plateaus. In general, increase of heat treatment temperature and time, directly influenced the technological properties of the samples

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In building, during the implementation process of major or even minor works, there is a considerable waste of plaster in the steps of coating, making it is a negative factor because of the loss of these processes constructive remains incorporated into buildings, as component, whose final dimensions are higher than those projected. Another negative factor is the disposal of waste gypsum in inappropriate places, thus contributing to the degradation of environmental quality, due to the leaching of this waste and may trigger the formation of sulfuric acid. Therefore, based on this picture, processing and reuse of waste coating, combined with the ceramics industry, which is a strong potential in the reuse of certain types of waste, promote mutual benefits. Thus the overall objective of this work is to conduct a search with scientific and technological aspects, to determine the effect of the incorporation of the residue of plaster for coating, from the building, the formulation of bodies for red ceramic. The residue of plaster coating was collected and characterized. They were also selected raw materials of two ceramic poles of the state of Rio Grande do Norte and formulations have been made with the intention of obtaining those with the best physical and mechanical properties, the residue was added the percentage of 5%, 10%, 15%, 20%, 25% and 30%, in the best formulation of ceramic industry 1 and, according the properties analyses, 5%, 10% and 15% as the best results of ceramic industry 2. The samples were sintered at temperatures of 850 ºC, 950 °C and 1050 °C, the heating rate of 5 ºC / min with isotherm of two hours. They were submitted to testing technology, such as lineal shrinkage, water absorption, apparent porosity, apparent density and bending resistence. The residue incorporation best results in the formulations of mass in red ceramic, were observed between the temperatures of 850 ºC and 950 ºC, in those formulations that have illite clays and medium plastic in their composition, in the range of 0% to 15% residue incorporated

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This masther dissertation presents a contribution to the study of 316L stainless steel sintering aiming to study their behavior in the milling process and the effect of isotherm temperature on the microstructure and mechanical properties. The 316L stainless steel is a widely used alloy for their high corrosion resistance property. However its application is limited by the low wear resistance consequence of its low hardness. In previous work we analyzed the effect of sintering additives as NbC and TaC. This study aims at deepening the understanding of sintering, analyzing the effect of grinding on particle size and microstructure and the effect of heating rate and soaking time on the sintered microstructure and on their microhardness. Were milled 316L powders with NbC at 1, 5 and 24 hours respectively. Particulates were characterized by SEM and . Cylindrical samples height and diameter of 5.0 mm were compacted at 700 MPa. The sintering conditions were: heating rate 5, 10 and 15◦C/min, temperature 1000, 1100, 1200, 1290 and 1300◦C, and soaking times of 30 and 60min. The cooling rate was maintained at 25◦C/min. All samples were sintered in a vacuum furnace. The sintered microstructure were characterized by optical and electron microscopy as well as density and microhardness. It was observed that the milling process has an influence on sintering, as well as temperature. The major effect was caused by firing temperature, followed by the grinding and heating rate. In this case, the highest rates correspond to higher sintering.

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This research studies the sintering of ferritic steel chips from the machining process. Were sintered metal powder obtained from machining process chips for face milling of a ferritic steel. The chip was produced by machining and characterized by SEM and EDS, and underwent a process of high energy mill powder characterized also by SEM and EDS. Were constructed three types of matrixes for uniaxial compression (relation l / d greater than 2.5). The differences in the design of the matrixes were essentially in the direction of load application, which for cylindrical case axial direction, while for the rectangular arrays, the longer side. Two samples were compressed with different geometries, a cylindrical and rectangular with the same compaction pressure of 700 MPa. The samples were sintered in a vacuum resistive furnace, heating rate 20 °C / min., isotherm 1300 °C for 60 minutes, and cooling rate of 25 °C / min to room temperature. The starting material of the rectangular sample was further annealed up to temperature of 800 ° C for 30 min. Sintered samples were characterized by scanning electron microscopy, optical microscopy and EDS. The sample compressed in the cylindrical matrix did not show a regular density reflecting in the sintered microstructure revealed by the irregular geometry of the pores, characterizing that the sintering was not complete, reaching only the second phase. As for the specimen compacted in the rectangular array, the analysis performed by scanning electron microscopy, optical microscopy and EDS indicate a good densification, and homogeneous microstructure in their full extent. Additionally, the EDS analyzes indicate no significant changes in chemical composition in the process steps. Therefore, it is concluded that recycling of chips, from the processed ferritic steel is feasible by the powder metallurgy. It makes possible rationalize raw material and energy by manufacture of known properties components from chips generated by the machining process, being benefits to the environment

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Extractivism mineral is considered an activity highly degrading, due to the large volume of material that he moves in the form of ore and residues. The vast majority of mining companies do not show any technology or economically viable application that will allow the recycling of mineral residue, these being launched in areas receiving located the "open skies" degrade the environment. In Rio Grande do Norte to the production of ceramic red restricts their activities to the production of products such as: solid bricks, ceramic blocks, tiles, among others. Seeking to unite experiences and technical information that favor sustainable development, with important benefits to the construction sector and civil society in general, the present work studies the incorporation of the residue of scheelite in ceramic matrix kaolinitic, coming from the municipality of Boa Saúde - RN, in percentage of 5 %, 10 %, 20 %, 30% 40% and 50 %, by evaluating its microstructure, physical properties and formulation. The raw materials were characterized through the trials of X ray fluorescence, Diffraction of X rays, Differential Thermal Analysis and Termogravimetric Analysis. The samples were formed and fired at temperatures of 850o, 900o, 1000o, 1050o, 1100o, 1150o and 1200 oC, with isotherm of 1 hour and heating rate of 10 oC/min. Assays were performed technological of loss to fire, Water Absorption, Apparent Porosity, Apparent Density, Mass Loss in Fire and Bending Resistance; in addition to the Scanning Electron Microscopy, analyzing their physical and mechanical properties. The use of residue of scheelite in ceramic mass kaolinitic provided a final product with technological properties that meet the technical standards for the production of bricks and roofing tiles, with the percentage of 20% of waste that showed the best results

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Actually in the oil industry biotechnological approaches represent a challenge. In that, attention to metal structures affected by electrochemical corrosive processes, as well as by the interference of microorganisms (biocorrosion) which affect the kinetics of the environment / metal interface. Regarding to economical and environmental impacts reduction let to the use of natural products as an alternative to toxic synthetic inhibitors. This study aims the employment of green chemistry by evaluating the stem bark extracts (EHC, hydroalcoholic extract) and leaves (ECF, chloroform extract) of plant species Croton cajucara Benth as a corrosion inhibitor. In addition the effectiveness of corrosion inhibition of bioactive trans-clerodane dehydrocrotonin (DCTN) isolated from the stem bark of this Croton was also evaluated. For this purpose, carbon steel AISI 1020 was immersed in saline media (3,5 % NaCl) in the presence and absence of a microorganism recovered from a pipeline oil sample. Corrosion inhibition efficiency and its mechanisms were investigated by linear sweep voltammetry and electrochemical impedance. Culture-dependent and molecular biology techniques were used to characterize and identify bacterial species present in oil samples. The tested natural products EHC, ECF and DCTN (DMSO as solvent) in abiotic environment presented respectively, corrosion inhibition efficiencies of 57.6% (500 ppm), 86.1% (500 ppm) and 54.5% (62.5 ppm). Adsorption phenomena showed that EHC best fit Frumkin isotherm and ECF to Temkin isotherm. EHC extract (250 ppm) dissolved in a polar microemulsion system (MES-EHC) showed significant maximum inhibition efficiency (93.8%) fitting Langmuir isotherm. In the presence of the isolated Pseudomonas sp, EHC and ECF were able to form eco-compatible organic films with anti-corrosive properties

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A retenção de Se pelos colóides do solo constitui importante processo para a manutenção da sanidade ambiental. A informação sobre a adsorção de Se em solos altamente intemperizados é restrita e existem poucos padrões quantitativos disponíveis para a definição de estratégias de remediação de áreas contaminadas. Quantidades crescentes de Se (5, 10, 25, 50, 100 e 250 mg L-1), na forma de Na2SeO3, foram adicionadas a amostras de dez Latossolos brasileiros [três Latossolos Vermelho-Amarelos (LVA-1, LVA-2 e LVA-3), dois Latossolos Vermelhos (LV-1 e LV-2), um Latossolo Vermelho eutroférrico (LVef), um Latossolo Vermelho acriférrico (LVwf), dois Latossolos Amarelos (LA-1 e LA-2) e um Latossolo Amarelo acriférrico (LAwf)]. Isotermas de adsorção foram construídas e foi verificado o ajuste dos resultados experimentais aos modelos de Langmuir e de Freundlich. A equação de Langmuir ajustou melhor os resultados de adsorção de Se do que a isoterma de Freundlich. Todas as isotermas apresentaram o formato tipo-L (exponencial), com exceção daquelas obtidas para o LVA-1 e para o LVA-2, que apresentaram comportamento tipo-C (linear). Valores de adsorção máxima (Ads máx), estimada pelo modelo de Langmuir, variaram de 135 (LVA-3) a 2.245 mg kg-1 (LA-1), enquanto os coeficientes de afinidade (K L) estiveram entre 0,002 (LVA-2) e 0,326 (LVA-3). A constante de afinidade estimada pelo modelo de Freundlich (Kf) variou de 13,7 (LVA-2) a 180,1 (LAwf). A adsorção máxima de Se foi mais elevada no LVef e nos Latossolos ácricos (LAwf e LVwf), enquanto os maiores valores de Kf foram encontrados no LV-2, LVef, LVA-3 e LVwf. Não houve correlação entre os atributos dos solos e as constantes de Langmuir. Valores de Kf correlacionaram-se com os teores de argila (r = 0,42*) e com a capacidade de troca de ânions (r = 0,64*).

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The production of roof tiles in the state of Rio Grande do Norte accounts for around 60% of the total of ceramic pieces produced. There is a need for investment to improve quality and productivity, thereby promoting technological innovations. Accordingly, the aim of this study is to determine the effect of kaolin, potassium feldspar and quartz in two standard formulations, as well as the effect of sintering temperature on the technological properties of linear firing shrinkage, water absorption and bending rupture stress, by fitting the statistical model and using multiple linear regression to assess the relationship between technological properties and independent variables. The raw materials were characterized using the following techniques: X-ray fluorescence (XRF), X-ray diffraction (XRF), rational analysis (RA), differential thermal analysis (DTA) and granulometric analysis (GA). The test specimens were compacted by uniaxial pressure (25 MPa), dried in a stove at 110 ºC for 24 hours and sinterized at 850 ºC, 950 ºC and 1050 ºC and held isothermal for 30 minutes. The results obtained indicate that the addition of kaolin to two standard formulations (M and R) promoted a reduction in water absorption values and an increase in bending rupture stress values. The sintering temperatures for group M that resulted in the lowest linear firing shrinkage and water absorption values were 850 ºC and 950 ºC, respectively, and the highest bending rupture stress values were reached at a temperature of 950 ºC. In the case of group R, the sintering temperature that obtained the lowest water absorption and linear firing shrinkage values was 850 ºC, and the highest bending rupture stress values were attained at a temperature of 1050 ºC. This work explains the statistical approach used to fit the model that describes the relationship between the technological properties and percentage of kaolin, quartz and feldspar, as well as the models that enable predictions, provided that the lower and upper limits of the percentage of clay minerals, flux and quartz used in this study are respected. Statistica 6 software was used and results were obtained by stepwise forward regression

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The State Bahia, Brazil, presents different geological sites it with a very expressive variety minerals. It is situated among the very important States which produces minerals for industries, such as pointed aggregate, ornamentals stones and ceramics raw materials. Nowadays only four companies producting ceramics tiles. Porcelainized stoneware tiles is one of the noblest ceramics, depicting low water absorption (typically below of 0,5%), in addition to excellent staining resistance and mechanical strength. The present work aims at investigating the potential of local raw materials for the production of porcelainized stoneware tiles. For this purpose, these materials were characterized by X-ray fluorescence, X-ray diffraction, particle size analysis, thermal gravimetric analysis, thermal differential analysis and dilatometric analysis. Admixtures containing different compositions were prepared and fired at four temperatures, 1100 ºC, 1150 ºC, 1200 ºC and 1250 ºC with isotherm for 60 minute and heathing rate of 5 oC/min. After firing the samples, they were characterized by water absorption tests, linear retraction, analysis, apparent porosity, apparent specific mass, flexural strength, and microstructural analysis by X-ray diffraction and scanning electron microscopy . The results revealed three ceramics with porcelainized stoneware tiles characteristics and porcelain tile will be produce from raw materials originated in the State of Bahia

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The sector of civil construction is strongly related to the red ceramic industry. This sector uses clay as raw material for manufacturing of various products such as ceramic plates. In this study, two types of clay called clay 1 and clay 2 were collected on deposit in Ielmo Marinho city (RN) and then characterized by thermogravimetric analysis (TG/DTG), differential thermal analysis (DTA), X-ray diffraction (XRD), X-ray fluorescence (XRF), rational analysis and particle size distribution and dilatometric analyses. Ceramic plates were manufactured by uniaxial pressing and by extrusion. The plates obtained by pressing were produced from the four formulations called 1, 2, 3 and 4, which presented, respectively, the following proportions by mass: 66.5% clay 1 and 33.5% clay 2, 50% clay 1 and 50% clay 2, 33.5% clay 1 and 66.5% clay 2, 25% clay 1 and 75% clay 2. After firing at 850, 950 and 1050 °C with heating rate of 10 °C/min and soaking time of 30 minutes, the following technological properties were determined: linear firing shrinkage, water absorption, apparent porosity, apparent specific mass and tensile strength (3 points). The formulation containing 25% clay 1 produced plates with most satisfactory results of water absorption and mechanical resistance, because of that it was chosen for manufacturing plates by extrusion. A single firing cycle was established for these plates, which took place as follow: heating rate of 2 °C/min up to 600 ºC with soaking time of 60 minutes, followed by heating using the same rate up to 1050 ºC with soaking time of 30 minutes. After this cycle, the same technological properties investigated in the plates obtained by pressing were determined. The results indicate (according to NRB 13818/1997) that the plates obtained by pressing from the mixture containing 25 wt% clay 1, after firing at 1050 °C, reach the specifications for semi-porous coating (BIIb). On the other hand, the plates obtained by extrusion were classified as semi-stoneware (group AIIa)

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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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The generation of effluent from the finishing process in textile industry is a serious environmental problem and turned into an object of study in several scientific papers. Contamination with dyes and the presences of substances that are toxic to the environment characterize this difficult treatment effluent. Several processes have already been evaluated to remove and even degrade such pollutants are examples: coagulation-flocculation, biological treatment and advanced oxidative processes, but not yet sufficient to enable the recovery of dye or at least of the recovery agent. An alternative to this problem is the cloud point extraction that involves the application of nonionic surfactants at temperatures above the cloud point, making the water a weak solvent to the surfactant, providing the agglomeration of those molecules around the dyes molecules by affinity with the organic phase. After that, the formation of two phases occurred: the diluted one, poor in dye and surfactant, and the other one, coacervate, with higher concentrations of dye and surfactants than the other one. The later use of the coacervate as a dye and surfactant recycle shows the technical and economic viability of this process. In this paper, the cloud point extraction is used to remove the dye Reactive Blue from the water, using nonionic surfactant nonyl phenol with 9,5 etoxilations. The aim is to solubilize the dye molecules in surfactant, varying the concentration and temperature to study its effects. Evaluating the dye concentration in dilute phase after extraction, it is possible to analyze thermodynamic variables, build Langmuir isotherms, determine the behavior of the coacervate volume for a surfactant concentration and temperature, the distribution coefficient and the dye removal efficiency. The concentration of surfactant proved itself to be crucial to the success of the treatment. The results of removal efficiency reached values of 91,38%, 90,69%, 89,58%, 87,22% and 84,18% to temperatures of 65,0, 67,5, 70,0, 72,5 and 75,0°C, respectively, showing that the cloud point extraction is an efficient alternative for the treatment of wastewater containing Reactive Blue