Papers by Keyword: Magnetic Pulsed Compaction (MPC)

Abstract: Highly dense Y2O3 ceramics have been fabricated by a magnetic pulsed compaction (MPC) which is capable of reaching a sufficiently high pressure (~1GPa) in a very short duration (a few microseconds), and a subsequent pressureless sintering at 1600°C. The Y2O3 green bodies with a relative density of about 68% were achieved by the application of the MPC process due to the effect of an enhanced rearrangement and a high speed movement of the particles, without the help of ceramic binder. Those compacts showed densities greater than 95%, which is very close to the theoretical density, after the subsequent pressureless sintering process at 1600 oC. The shrinkage rates of the diameter for the samples compacted by the MPC process were markedly reduced, when compared to those for the ones by the conventional compaction (CC) process.

Abstract: The effect of MPC pressure on the density, microstructure, mechanical properties, and electrical property of MPCed and sintered bulk was investigated. A detail characterization of the MPCed and sintered bulk has been performed using XRD, SEM, TEM, Vickers hardness tester, and breakdown voltage tester. The alumina powder used in this research has a size of 50-200 nm, a smooth surface and elliptical shape. The obtained density of MPCed and sintered bulk is increased with increasing MPC pressure from 0.5 to 1.25 GPa. The highest density of 92% in this research is obtained in the MPCed at 1.25 GPa and sintered bulk, while it is 90 % in the MPCed at 0.5 GPa. The different Vickers hardness with MPC pressure is associated with the different density and grain size of bulks. The maximum breakdown voltage of 47 kV/cm is achieved in the bulk MPCed at 1.25 GPa due to the higher density than that of others. In addition, the fracture mechanism of MPCed and sintered bulk is discussed.

Abstract: In this study the nanostructured α-Al2O3 ceramics has been fabricated by the combined application of magnetic pulsed compaction (MPC) and spark plasma sintering (SPS), and their density and hardness properties were investigated. The α-Al2O3 prepared by the combined processes showed an increase of 8.4 % in density, approaching a value close to the theoretical density, a enhancement by 210∼400 Hv in hardness, compared to those for the ones by the MPC or static compaction method followed by a sintering treatment. Its grain size was almost equivalent to or slightly higher than the size of the starting Al2O3 powder, suggesting that the grain growth was remarkably reduced during the MPC and SPS processes.

Abstract: Fabrication of dense YSZ electrolytes and porous LSM cathodes in the shape of tubes using a radial magnetic pulsed compaction of multilayered tubular blanks of powder tapes has been investigated. The tapes were prepared with butyral resin binder. The multilayered blanks were compacted magnetically. Magnetic pressures of 0.2-0.3 GPa in amplitude, sintering temperatures as low as 1100-1300 °C (in air) with holding time of 20-540 min have been used. Cathode tubes of 0.2-1.0 mm thick exhibited the reproducible open porosity up to 45 %. YSZ electrolyte tubes with the wall of 100-450 microns thick had near full relative density, 0.97-0.99, and were characterized with grains of 200-500 nm in size on the average depending on the sintering temperature. The electrochemical cells built up of as-prepared tubular electrolytes and traditional research electrodes were tested under the air-hydrogen fuel cell conditions. The specific output power, 0.6 W cm-2, was realized at temperature of 885 °C.

Abstract: An influence of aggregation degree of alumina nanopowder and of radial magnetic pulsed compaction conditions on the powder densification and on the density distribution inside compacts has been investigated experimentally. The usage of radial magnetic pulsed compaction allows to compact alumina nanopowders up to high densities at low degree of aggregation. The compacts homogeneity is attained by appropriate compaction pulse duration and by the usage of powder packing prior to compaction until the condition with high local sound speed is achieved.

Abstract: Magnetic Pulse Compaction (MPC), as a dynamic compaction, can be possible to reach higher relative density of nano metallic compacts owing to sufficiently high pressure and adiabatic heating in very short duration of an order of µsec. The present work is concerned with the magnetic pulsed compaction of the nano-sized aluminum powders, which particle size was a range of 50 ~ 100 nm passivated in air. The compaction pressure was 1.5 GPa for 300 µsec in the temperature range from 20°C to 500°C. The grain size of compacts was maintained less than 50 nm, which was analyzed by X-ray diffraction (XRD) using Scherrer method. From the calculation of adiabatic heat and of pressure induced by thermal expansion, and the observation by transmission electron microscopy (TEM), it was found that Al₂O₃ could be broken and dispersed with a few nano-meter sizes in the Al matrix and that the ultra fine and uniform bulk structure was maintained up to 400°C of compaction temperature.e