Centro de Tecnologia
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Artigo Influência do método de síntese sobre propriedades da peneira molecular SAPO-11(Associação Brasileira de Química, 1997) Medeiros, Gilson Gomes de; Cardoso, DilsonSamples of SAPO-11 were synthesized by hydrothermal crystallization, with the objective of investigating the influence of the method of synthesis on the properties such as crystallinity, morphology, and catalytic activity. Solid products were analyzed by X-ray diffraction, scanning electronic microscopy and plasma emission spectroscopy. Catalytic evaluation of the samples in ethylbenzene disproportionation was realized using a continuous flow fixed bed reactor connected on-line with a gas cromatograph. The results with regard to percentual conversion of ethylbenzene and para-selectivity are givenArtigo Fator de encobrimento e seletividade no transporte: análise do fenônemo e estudo experimental(Associação Brasileira de Recursos Hídricos (ABRHidro), 1998-03) Moreira, Lúcio Flávio Ferreira; Marin, Eduardo MartínezEstudou-se o grau de seletividade no transporte de misturas de sedimento arenoso mediante a realização de ensaios utilizando um canal equipado com um sistema de alimentação de sedimentos. Para isso, foram utilizadas 4 diferentes misturas, com diâmetros que variam entre 0,59 mm e 1,91 mm. O método do transporte de referência idealizado por Parker et al. (1982) foi adotado para determinar a tensão crítica do início do transporte. No desenvolvimento do estudo, as misturas M1 e M2, com granulometria aproximadamente uniforme, foram representadas pelos seus diâmetros medianos D50 e submetidas a uma análise geral do transporte da mistura. As misturas M3 e M4, por sua vez, apresentaram uma granulometria com distribuição logarítmica e foram submetidas à análise do transporte das frações que compõem a mistura. Além disso, M2 e M4 têm o mesmo diâmetro mediano. Os valores obtidos dos parâmetros da função de encobrimento refletem uma condição de igualdade no transporte das frações. As tensões de cisalhamento críticas obtidas para M2 e M4 confirmam o parâmetro D50 como representativo da mistura. Os resultados obtidos permitem concluir que a tensão crítica (tc50) determinada a partir da análise geral do transporte, pode ser suficiente para expressar o valor médio de tensão crítica que atua em cada fração da misturaArtigo A survey of control architectures for autonomous mobile robots(Journal of the Brazilian Computer Society, 1998-04) Medeiros, Adelardo Adelino Dantas deArtigo Neutron diffraction and finite-element analysis of thermal residual stresses on diffusion-bonded silicon carbide–molybdenum joints(Wiley, 1999) Martinelli, Antonio Eduardo; Drew, Robin A.L.; Fancello, Eduardo A; Rogue, Ronald; Root, John H.Various approaches can be used to minimize residual stresses in ceramic–metal joining, such as a refractorymetal interlayer in a hot-pressed joint. Nonetheless, it is still necessary to characterize the stresses at and near the interface between the interlayer and the ceramic, as a function of the hot-pressing parameters. This study combines two techniques to assess the stress distribution of hotpressed silicon carbide–olybdenum joints: neutron diffraction and finite-element (FEM) analysis. The results demonstrate that the joining temperature greatly influences the final stress distribution, and that significant stress accommodation is achieved by controlling the cooling rate of the diffusion couples. FEM analysis provides a broad view of stress distribution profiles, whereas experimental stress values that are obtained via neutron diffraction allow a better assessment of the effects of parameters that are not easily reproduced using a mathematical modelArtigo The use of design methods within production machinery companies(SAGE Publications, 1999-03-01) Gouvinhas, Reibson Pereira; Corbett, J.This paper presents a review of how production machinery companies typically develop their products and also investigates the perceived views of typical designers within this sector with regard to the utilization of formal design methods. This analysis is based on an extended visit to a production machinery company and a series of one day visits to other companies followed by an extensive questionnaire survey. The results have indicated that production machinery companies tend to control their product development process through regular design review meetings and, in general, the level of awareness and utilization of formal design methods is very low. A series of ‘roadblocks’ that are responsible for the avoidance of more widespread use of formal design methods within these particular companies has also been identified. The subject of ‘formal design methods’ created much interest from a significant number of those who responded to the questionnaire. It is concluded that there is a demand within production machinery companies for training and the development and implementation of new and/or existing design procedures that are specifically applicable for production machinery companiesArtigo Microstructure and mechanical strength of diffusion-bonded silicon nitride–molybdenum joints(Elsevier, 1999-10) Martinelli, Antonio Eduardo; Drew, Robin A.L.Solid-state bonding of reactive systems, such as Si3N4–Mo often results in the formation of excessively thick intermetallic layers that can be detrimental to the final strength of the joint. The objective of this work was to study the microstructural evolution of Si3N4–Mo interfaces, aiming at maximum joint strength via a balance between the fraction of bonded material and the amount of interfacial reaction. Joining was carried out under vacuum or nitrogen atmosphere for temperatures between 1100 and 1800°C. Microstructural analyses of the interfaces revealed the presence of Mo3Si and Mo5Si3 along with residual pores. The results from shear strength tests revealed a strong relationship between the microstructure of the interface and the mechanical strength of the jointArtigo Brazing Al2O3 to sintered Fe-Ni-Co alloys(Springer, 1999-12) Nascimento, Rubens Maribondo do; Martinelli, Antonio Eduardo; Bushinelli, Augusto José de Almeida; Klein, A. N.Active metal brazing has been widely used to join ceramics to metals, as sound joints are usually achieved in a single step process without special equipment. However, residual stresses may be a potential problem especially upon joining ceramics to alloys with relatively high thermal expansion coefficients. This work investigates the brazing behavior of Alumina (Al2O3) to a sintered Fe-Ni-Co alloy, specially designed to match its coefficient of thermal expansion to that of the ceramic counterpart. The results indicate the presence of an interfacial zone whose microstructure depends on the filler alloy employed. A relationship was established between the microstructure of the interface and the flexural strength of the jointsArtigo The effect of pulse width on the microstructure of d.c.-plasma-nitrided layers(Elsevier, 1999-12-15) Alves Júnior, Clodomiro; Rodrigues, José de Anchieta; Martinelli, Antonio EduardoModern ion nitriding equipment are powered by pulsed sources in order to prevent arcing and overheating. In industrial applications, the pulse frequency is usually adjusted to set the working temperature. However, frequency variations may drastically affect the plasma species population, and consequently, the microstructure of the final nitrided layer. In this study, AISI-409 steel was nitrided in a mixture of 20% N2–80% H2 using a d.c power source. The depth and microstructure of the nitrided layer were assessed as a function of the time that the voltage was off, toff, in the range of 1–4 ms during a 10 ms pulse cycle. The results suggested that both the microstructure and mechanical behavior of the nitrided layer were affected by toff. Long toff values imply a deleterious effect on the mechanical properties of the nitrided layersArtigo Growth of nitrided layers on Fe–Cr alloys(Elsevier, 2000-02-29) Alves Júnior, Clodomiro; Rodrigues, José de Anchieta; Martinelli, Antonio EduardoChromium is an important alloying element present in numerous commercial steels. A systematic study on the nitriding behavior of Fe–Cr alloys is helpful in predicting the properties of nitrided Cr-alloyed steels. Aspects such as microstructural evolution, growth kinetics, and mechanical properties should be particularly emphasized. Fe–Cr alloys containing 5, 10, and 20 wt.% Cr have been arc melted and subsequently plasma nitrided under a N2–80% H2 atmosphere. The microstructure of the resulting nitrided layers was characterized and the microhardness profiles evaluated. Thicker layers developed on low chromium alloys. Differences in hardness profiles were also observed as a function of chromium contents. Nitriding Fe–5% Cr alloys resulted in two discrete fronts, refereed to as the diffusion front and the transformation front. Transformed regions sustained a decrease in hardness from 1000 down to 600 HV, associated with the conversion of homogeneously dispersed fine precipitates into coarser needle like particles immersed in the ferritic matrix. Similar behavior was not observed for the other alloys, where both fronts developed simultaneouslyArtigo Effect of Y2O3 addition on the densification and mechanical properties of alumina±niobium carbide composites(Elsevier, 2000-04-21) Acchar, Wilson; Greil, P.; Martinelli, Antonio Eduardo; Vieira, F. A.; Bressiani, A. H. A.; Bressiani, José CarlosAlumina-based composites reinforced with refractory carbides are potential cutting tool materials. They exceed the capabilities of cemented carbides with respect to hot hardness and thermal stability, resulting in faster cutting speeds. Liquid-phase sintering of Al2O3±NbC composites was investigated as an alternative to pressure-assisted processes. Al2O3 reinforced by NbC (5±40 wt.%) was sintered with 3 wt.% Y2O3. In order to assess the e ect of the formation of a liquid phase on the properties of the composites, sintering was carried out either below or above the Al2O3±Y2O3 eutectic temperature, at 1650 and 1800 C, respectively. Density, hardness, fracture toughness and wear resistance of the composite materials were evaluated. Liquid phase sintering did not affect the fracture toughness, but improved both the density and the hardness of the material, regardless of its NbC contents. Higher concentrations of NbC increased the wear resistance of the compositeArtigo Sintering behaviour of alumina–tungsten carbide composites(Elsevier, 2000-05-31) Acchar, Wilson; Martinelli, Antonio Eduardo; Vieira, F. A.; Cairo, Carlos Alberto AlvesAlumina reinforced with tungsten carbide has been investigated as an alternative material for metalworking, combining resistance to high service temperatures and improved toughness. Pressureless sintered and hot-pressed Al2O3–WC composites were manufactured and characterised. The use of Y2O3 as a sintering additive has also been evaluated. Additions of up to 30 wt.% WC resulted in limited grain boundary pinning and corresponding high densification. Although the addition of Y2O3 improved sintering, the presence of a residual grain boundary phase (YAG) was harmful to the fracture toughness of the composites, as it affected the effectiveness of the crack deflection mechanism that takes place at the interfaces between Al2O3 and WC grains. Hot-pressing resulted in hardness ∼17.5 GPa and fracture toughness ∼7 MPa m−1/2, which is an improvement compared to alumina reinforced by other refractory carbidesArtigo Preparartion and characterization of terbium over paligorsquite clay as acid catalyst(Elsevier, 2000-08-01) Melo, Marcus Antônio de Freitas; Ruiz, Juan Alberto Chavez; Melo, Dulce Maria de Araújo; Vitor Sobrinho, Eledir; Schmall, M.Palygorskite clays containing 5% and 10% terbium (W/W) were prepared by ion exchange from acid-leached naturalclay. Samples were calcined at 523, 573, 623 and 673 K to verify the e ect of the temperature over the physical±chemicalproperties. Characterization was using X-ray di raction, infrared spectroscopy (n-butylamine adsorption), UV±visibledi use reØectance spectroscopy and N2adsorption. Isopropyl alcohol (IPA) transformation was also performed inorder to improve the acid behavior. TB3áintroduction does not change the palygorskite structure, albeit leading to anincrease in the surface area and generation of Lewis acid sites. Results from the DRS spectra along with a decrease inthe catalytic activity suggested the formation of terbium oxide for relatively high TB3ácontentsArtigo Reinforcing Al2O3 with W–Ti mixed carbide(Elsevier, 2000-11) Acchar, Wilson; Martinelli, Antonio Eduardo; Cairo, Carlos Alberto AlvesRecent advances in high-speed cutting materials have focused on reinforcing alumina with different carbides and nitrides in order to improve hardness and fracture toughness. However, data on mixed carbides is still scarce. The potential use of this type of material for cutting tool applications has yet to be determined. The present study reports some preliminary results obtained reinforcing Al2O3 with WTiC in the range of 5–30 wt.%. The material was hot-pressed at 1650°C for 30 min and then characterized. Vicker's microhardness (HV) and fracture toughness (KIC) were evaluated by the indentation method. The addition of WTiC did not result in any significant change in the fracture toughness of alumina, however hardness values in excess of 22 GPa were obtainedArtigo A mixed formulation for general triangular isoparametric shell elements based on the degenerated solid approach(Elsevier, 2000-11) Bucalem, Miguel Luiz; Nóbrega, Selma Hissae Shimura daA mixed formulation to construct general shell elements based on the degenerated solid approach is presented. This mixed formulation can be understood as a modification of the discrete potential energy of the shell in which the membrane and shear energy terms are obtained as a combination of the usual terms, i.e., directly obtained from the displacement and geometry interpolation assumptions, and membrane and shear terms obtained from assumed strain fields. This energy splitting idea was first introduced in the context of the Naghdi shell theory by Arnold and Brezzi. This mixed formulation is used to study quadratic general triangular shell elements based on the degenerated solid approach. Although considerable success has been achieved in the formulation of reliable, free of locking, general quadrilateral shell elements, the attempts of formulating general triangular shell elements have not yet produced an element that satisfies the locking free requirements. Therefore, there is a great interest in investigating new approaches, as the one discussed in this paper, that can lead to triangular elements that do not suffer from locking difficulties. We present in this paper the formulation of specific elements and their numerical assessment through the use of well established benchmark shell problemsArtigo Avaliação química e sensorial de linguiças de pescado tipo frescal(Boletim Centro de Pesquisa de Processamento de Alimentos, 2001) Correia, Roberta Targino Pinto; Mendonça, Silvana Correia de; Lima, Maria Lucilda; Silva, Priscilla Diniz daA presente pesquisa teve por objetivo caracterizar quimicamente e investigar a aceitabilidade de três tipos de lingüiça preparadas a partir da associação dos seguintes ingredientes cárneos: camarão e peixe, camarão e bacon, camarão, bacon e peixe. As análises químicas incluíram determinação do teor de umidade, gordura, proteína e cinzas, enquanto a análise sensorial envolveu os testes de aceitabilidade e de preferência. A composição química mostrou-se adequada, com teores de umidade, cinzas e proteína similares a de produtos existentes no mercado e percentual lipídico reduzido, configurando produto cárneo com baixo teor de gordura. Todas as preparações analisadas tiveram boa aceitação e a formulação obtida a partir de camarão e bacon foi considerada a preferida pelo painel sensorial.Artigo α Function for a series of hydrocarbons to peng−robinson and van der waals equations of state(ACS Publications, 2001) Chiavone Filho, Osvaldo; Amaral Filho, Pedro G.; Silva, Douglas do Nascimento; Terron, Luiz RobertoThis paper reports estimated coefficients for the α function based on vapor pressure data to a series of 438 components, mainly hydrocarbons, for both van der Waals and Peng−Robinson equations of state (EoS). The α function utilized for the attractive term is the one proposed by Mathias and Copeman in 1983, and it improves the cubic EoS calculations. Accurate vapor-pressure correlations and critical data required for the estimation of the constants were retrieved from two databases, i.e., AIChE DIPPR and the Reid et al. (The Properties of Gases and Liquids; McGraw-Hill: New York, 1987) reference book. The method of calculation is described, and the constants are tested with respect of their representation of thermodynamic properties, mainly in terms of the vapor-pressure deviations. The behavior of density and enthalpy EoS predictions is also evaluated. The estimated coefficients for the α function are reported in the Supporting Information and may be applied as a data bank in a simulator, providing more accurate thermodynamic property calculations in the recommended temperature range, as demonstratedArtigo Transportes no Brasil: que história contar?(ANPET - Associação Nacional de Pesquisa e Ensino em Transportes, 2001) Aragão, Joaquim José Guilherme de; Lima Neto, Oswaldo; Brasileiro, Anísio; Santos, Enilson Medeiros dos; Senna, José Menezes; Orrico Filho, Rômulo DanteO presente trabalho se propõe a desenvolver uma abordagem historiográfica com vistas a contribuir para o entendimento da história dos transportes no Brasil. Inicialmente, desenham-se considerações gerais sobre o ofício de historiar os transportes, de modo a que possam ser úteis para a compreensão das origens e do desenvolvimento do setor. Em seguida, tentamos demonstrar a complexidade dos transportes enquanto fenômeno histórico, e que pontes devem ser colocadas entre a história dos transportes e a história política, econômica e social mais abrangente, sobretudo no que concerne ao desenvolvimento espacial da sociedade. A partir dessa discussão metodológica, apresenta-se uma metodologia aplicada à historiografia dos transportes. Em seguida, aplica-se a metodologia através da definição de uma tipologia de fatos históricos relevantes, com vistas a dotar a análise historiográfica de uma maior consistência analíticaArtigo Effect of workpiece geometry on the uniformity of nitrided layers(Elsevier, 2001-05-01) Alves Júnior, Clodomiro; Silva, Eronildes Felisberto da; Martinelli, Antonio EduardoThe growth behavior of plasma-nitrided layers on workpieces with complex geometry was systematically investigated. AISI 316 stainless steel pellets with different heights were nitrided under a mixture of N2–80% H2 at different temperatures (673, 773 and 843 K) and pressures (100 and 500 Pa). Significant differences in thickness and hardness of the resulting nitrided layers were observed as a function of nitriding parameters. The thickness of nitrided layers increased with sample height, excepted those nitrided at 843 K. The diameter of eroded rings, commonly observed on nitrided samples, varied with coupon height. Changes in both layer thickness and eroded ring diameter are presently addressed based on the thermal balance and charge density that take place near the edges of the samplesArtigo Avaliação de risco como instrumento de gestão ambiental(Universidade Federal de Santa Catarina, 2001-10) Araújo, Francisco José Costa; Adissi, Paulo José; Macedo, Rose Meire Penha Rovoredo de; Rocha, Sayonara Sonnaly; Marques Filho, SérgioEnvironmental quality and its risks are major concerns for modern society. Such priority is motivated by the potential impact of developing technologies, changes in lifestyle and an increased consciousness of potential risks these changes have on health and security. The meticulous examination of environmental impact has become a worldwide challenge. Concepts and instruments which allow for precise analysis of the ecosystem and its repercussions have been the object of investigation at numerous universities and research centers. The incorporation of better methods of evaluation of environmental impacts takes on another dimension when Brazilian businesses seek ISO 14000 certification. The goal of this research paper is to offer information for a better understanding of the technoscientific knowledge which accompanies the discussions concerning the risks involved in environmental management of electrical energy transmission systems. A method is proposed for defining the level of risk of environmental impact occasioned by an electrical energy transmission system; a method based on a preliminary analysis of risksArtigo Spectral power distributions for the CIE stimuli(Wiley Periodicals, LLC, 2001-10-08) Bezerra, Clovis de Medeiros; Hawkyard, C. J.The CIE reference colour stimuli, X, Y, and Z, were derived by constructing a triangle outside the R,G,B triangle and outside the area bounded by the spectrum locus and the purple line. By this means, all colours, including monochromatic ones, have positive tristimulus values. The colour-matching functions are the relative quantities of these stimuli required to be mixed additively to match the equal energy monochromatic colours. The stimuli are not realizable as light sources, and the CIE has not specified their spectral power distributions. There is an infinite num ber of spectral power distributions whose properties meet the prerequisites for X (X 5 100, Y 5 0, Z 5 0), Y (0, 100, 0), and Z (0, 0, 100), and two possible sets have been calculated by different methods. These curves could be used as primary red, green, and blue lights in additive mixing to produce synthetic reflectance curves, which are useful in the specification of on-screen colours, and as a means of pro ducing colour constant standards