Engenharia de Materiais
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/17
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Resultados da Pesquisa
Artigo de evento 1 Citação(ões) na Scopus Carbon nanotubes experiment in microgravity(2011-10-03) LA NEVE, A.; BELLODI, M.; MELO, M. A. A.; FERREIRA, M.; CASTRO, R. H. R.; PEREIRA, A. N.; F. S. OrtegaCarbon Nanotubes (CNTs) nanostructures are an interesting focus of research, due to their unique electrical and mechanical properties, including high specific surface area and electrical conductivity. These characteristics make them potential components for applications in microelectronics, field emitters and catalysts, among others. The purpose of this experiment is to obtain CNT homogeneous films on aluminum substrates both in microgravity and on earth, in order to study the real effect of gravity in the deposits organization. This experiment was carried out in microgravity, during a period of 4 minutes, aboard a VSB-30 Brazilian sounding rocket. To perform the experiment, it was developed an equipment, called CADEN, which consists of 3 sets of 4 reaction chambers, each one containing an aluminum substrate (in a total of 12), in addition to embedded electronics, responsible for the system control, data acquisition and monitoring of electric currents in each chamber. The chambers were loaded with a CNT solution in different concentrations, 0.1 mg/ml and 0.5 mg/ml; in each of them an electrolytic current flew according to the electrical potential applied to the aluminum plates, which acted as anode and cathode. In order to provide for a wide range of possibilities, which might be useful in further analysis, different DC voltages were applied to each pair of chambers, which were loaded with different CNT concentrations. On receiving the microgravity signal, on flight, the control system applies a different bias on each of the three sets. From this moment on, each pair of chambers will be active for 2 or 4 minutes time, accordingly to their programming. While the experiment is running, the electric currents that flow through all chambers, along with temperature and other variables, are periodically read and stored in the internal memory, and are also transmitted by telemetry. The launching and payload rescue were successful, and so was the equipment functioning. Electrodes electrical characterization was performed, focusing on the plates surface resistivity, and it was observed a significant increase in electrical conductivity. Additional analyses include plate surfaces electron microscopy, to verify both CNT deposition morphology and the nanotubes orientation on the surface. The results were compared with data obtained on earth under similar conditions, to identify the influence of microgravity and the role of the other variables in the experiment. The electrical resistance of plates with CNT deposited in microgravity was, in general, lower than that of plates with CNT deposited on Earth. Copyright ©2010 by the International Astonautical Federation. All rights reserved.- Aisi 310 stainless steel formed by gelcasting: An alternative manufacturing method(2020-10-05) RODRIGUES, O. L. F.; NEVEZ, M. D. M.; F. S. Ortega© 2020 Trans Tech Publications Ltd, Switzerland.This work evaluates the microstructure and the yield strength under compression at room temperature and at 800°C of specimens prepared with AISI 310 stainless steel powder (D50 = 10 µm), manufactured by gelcasting. Parts were vacuum sintered in a single batch at 1280°C. At room temperature, specimens presented average yield strength of 270 MPa, and at 800°C, 105 MPa. Microstructure analysis involved the measurement of grain size along the vertical axis of cylindrical specimens, with special attention to the effect of particles settling, and was conducted using scanning electron and optical microscopy, and X-ray diffraction. Settling effect was assessed considering the position where the specimen was taken and was negligible: both density and yield strength did not vary significantly along the vertical axis.
- AISI 310 Stainless Steel Formed by Gelcasting: An Alternative Manufacturing Method(2020-10-05) OLIVEIRA, LOUISE FERNANDA RODRIGUES; NEVES, MAURÍCIO DAVID MARTINS DAS; F. S. OrtegaThis work evaluates the microstructure and the yield strength under compression at room temperature and at 800°C of specimens prepared with AISI 310 stainless steel powder (D50 = 10 μm), manufactured by gelcasting. Parts were vacuum sintered in a single batch at 1280°C. At room temperature, specimens presented average yield strength of 270 MPa, and at 800°C, 105 MPa. Microstructure analysis involved the measurement of grain size along the vertical axis of cylindrical specimens, with special attention to the effect of particles settling, and was conducted using scanning electron and optical microscopy, and X-ray diffraction. Settling effect was assessed considering the position where the specimen was taken and was negligible: both density and yield strength did not vary significantly along the vertical axis.
- Effects of Milling pH and Hydrothermal Treatment on Formation of Nanostructured Boehmite Binder for Alumina Extrusion(2017-07-05) LIMA, M. B.ATISTA DE; TERCINI, M. B.; SANTOS, S. F.; F. S. Ortega; YOSHIMURA, HUMBERTO NAOYUKIThe in situ formation of nanostructured aluminum hydroxides on the surface of alumina particles, which can work as inorganic binder, was reported in this paper.Theeffect of the suspension pH during milling of alumina powder and subsequent hydrothermal treatment for the hydroxide formation and microstructure was depicted. Under acidic pH condition, the formation of hydroxides was not observed.When the pH of suspension changed fromacidic to basic during milling, bayerite [Al(OH)3] nanoparticles were formed, but only a fraction of this hydroxide was converted to boehmite (AlOOH) during subsequent hydrothermal treatment. The aluminum hydroxide and oxyhydroxide formed in this condition improved the smoothness of extruded rods and the strength of presintered segments. For the powder milled under basic pH condition, themechanochemically formed bayerite was completely converted into boehmite nanoparticles during the hydrothermal treatment. The presence of boehmite nanoparticles contributed to improving plasticity during extrusion, which allowed the reduction of organic binder and increased the strength of presintered alumina rods.