Papers by Author: Ricardo Mendes Leal Neto

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Authors: Rodrigo Estevam Coelho, Ricardo Mendes Leal Neto, Priscilla Alves Camargo, Ambrozio Filho Francisco
207
Authors: Cláudio José da Rocha, Ricardo Mendes Leal Neto, Valéria S. Gonçalves, L.L. Carvalho, Francisco Ambrozio Filho
144
Authors: Railson Bolsoni Falcão, Edgar Djalma Campos Carneiro Dammann, Cláudio José da Rocha, Ricardo Mendes Leal Neto
Abstract: This work reports the efforts to obtain TiFe intermetallic compound by high-energy ball milling of Ti and Fe powder mixtures. This process route has been used to provide a better hydrogen intake in this compound. Milling was carried out in a SPEX mill at different times. Strong adherence of material at the vial walls was seen to be the main problem at milling times higher than 1 hour. Attempts to solve this problem were accomplished by adding different process control agents, like ethanol, stearic acid, low density polyethylene, benzene and cyclohexane at variable quantities and keeping constant other milling parameters like ball to powder ration and balls size. Better results were attained with benzene and cyclohexane, but with partial formation of TiFe compound even after a heat treatment (annealing) of the milled samples.
329
Authors: Ricardo Mendes Leal Neto, Cláudio José da Rocha, Francisco Ambrozio Filho
156
Authors: Fabiana Buracovas, Valéria S. Gonçalves, Cláudio José da Rocha, Ricardo Mendes Leal Neto
Abstract: In this work shake milling were used to mechanically activate Nb – Al powder mixtures at different relative proportions (Nb80Al, Nb65Al, Nb54Al e Nb42Al). All milling process parameters were unchanged, e.g., powders mass, ball/powder mass ratio, balls diameter, quantity and kind of process control agent. Uniaxially compacted cylindrical pellets of milled powders were vacuum reacted. After a two-step degassing treatment (290°C for 0.5 h and 400°C for 4 h), samples were heated at 30°C/min. Ignition and combustion temperatures were measured by a thermocouple inserted in a hole drilled into the pellets. The microstructure of milled powders and reacted pellets were characterized by X-ray diffraction and SEM analysis. Bulk density of the pellets was measured by water immersion (Archimedes). The results showed a decrease of both ignition and combustion temperature with mechanical activation as seen by comparison with reacted pellets of the same composition not mechanically activated (simple mixtures). By increasing the heating hate the completeness of the reactions were improved. The lower the aluminum contents the lower the ignition and combustion temperatures and also the densification. The decrease on ignition temperature was caused by a more effective dispersion (and so more activation) attained by samples with lower aluminum content.
152
Authors: Ricardo Mendes Leal Neto, P.Í. Ferreira
271
Authors: Ricardo Mendes Leal Neto, Cláudio José da Rocha
567
Authors: Michelangelo Durazzo, Cláudio José da Rocha, José Mestnik-Filho, Ricardo Mendes Leal Neto
Abstract: For the last 30 years high uranium density dispersion fuels have been developed in order to accomplish the low enrichment goals of the Reduced Enrichment for Research and Test Reactors (RERTR) Program. Gamma U-Mo alloys, particularly with 7 to 10 wt% Mo, as a fuel phase dispersed in aluminum matrix, have shown good results concerning its performance under irradiation tests. Thats why this fissile phase is considered to be used in the nuclear fuel of the Brazilian Multipurpose Research Reactor (RMB), currently being designed. Powder production from these ductile alloys has been attained by atomization, mechanical (machining, grinding, cryogenic milling) and chemical (hydriding-dehydriding) methods. This work is a part of the efforts presently under way at IPEN to investigate the feasibility of these methods. Results on alloy fabrication by induction melting and γ-stabilization of U-10Mo alloys are presented. Some results on powder production and characterization are also discussed.
362
Authors: Edval G. de Araújo, Ricardo Mendes Leal Neto, M.F. Pillis, Francisco Ambrozio Filho
128
Authors: Cláudio José da Rocha, Valéria S. Gonçalves, Ricardo Mendes Leal Neto
203
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