Papers by Author: Masaki Yasuoka

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Authors: Tatsuzo Nagai, Hae Jin Hwang, Masaki Yasuoka, Mutsuo Sando, Koichi Niihara
Authors: Masaki Yasuoka, Takashi Shirai, Yutsuki Nisimura, Takaaki Nagaoka, Koji Watari
Abstract: The drying and sintering processes require large quantities of energy. If this energy could be used more efficiently, less would be consumed. In this research, the effect of the microwave on the manufacturing process of ceramics where heat was needed was examined. We obtained the following results when oxide ceramics were dried and sintered by microwave technique: In drying process, slip cast bodies were dried rapidly by microwave drying and compared with those dried by conventional drying techniques. In sintering process, power consumption and efficiency were lower with the time-control method than with the power-control method. The power-control method gave more precise temperature control under our experimental conditions.
Authors: Shoichi Kume, Masaki Yasuoka, Naoki Omura, Koji Watari
Abstract: The effects of sintering additives on dielectric loss tangent of AlN ceramics were explored. Different amounts of Y2O3 and TiO2 were respectively added as sintering additives to AlN powders and pressureless sintering was performed in a nitrogen flow atmosphere at 1850 °C or 1900 °C for 2 hours. The resulted AlN ceramics became denser when TiO2 addition was more than 0.5 mol%, and a dense sinter with a relative density of 0.987 could be obtained. Tan δ decreased when TiO2 content was more than 0.5 mol% and a tan δ value of as low as 1.0 x 10-3 could be attained.
Authors: Shoichi Kume, Masaki Yasuoka, Koji Watari
Abstract: The effect of sintering additives on dielectric loss tangent and microstructure of AlN ceramics have been investigated. Different amounts of Y2O3 and La2O3 were added as sintering additives to AlN powder and pressureless sintering was performed at 1900 °C for 2 h in a flowing nitrogen atmosphere. Bulk densities of sintered AlN were found to be 3.27 and 3.32 Mg·m-3 when Y2O3 contents were 0.5 and 1 mol%, respectively. The bulk densities of AlN-Y2O3 increased with increasing La2O3 content. Densities of 3.41 and 3.42 Mg·m-3 were obtained for 0.5 mol%Y2O3-1 mol%La2O3-AlN and 1 mol%Y2O3-1 mol%La2O3-AlN ceramics respectively. A decrease in tan δ was observed with increase in La2O3 content and a minimum value of 1.3 x 10-3 was obtained for 0.5 mol%La2O3-1 mol%Y2O3-AlN ceramic in the present study.
Authors: Manuel E. Brito, Kiyoshi Hirao, Masaki Yasuoka, Shuzo Kanzaki
Authors: Masaki Yasuoka, Mutsuo Sando, Koichi Niihara
Authors: Yutsuki Nishimura, Masaki Yasuoka, Takaaki Nagaoka, Yoshiaki Kinemuchi, Koji Watari
Abstract: Microwave sintering is a process in which target materials absorb microwaves and heat themselves from the inside. When microwave energy is effectively absorbed by the material, energy consumption for the sintering can be reduced. Our study is focused on the microwave sintering of BaTiO3 to more rapidly obtain dense ceramics with specific characteristics. For BaTiO3-based electronic components, the sintering temperature is too high for manufacture, so various additives are used to decrease the sintering temperature without undue worsening of the electrical characteristics. In this work, during microwave sintering, BaCO3, H3BO3, BaB2O4 and LiF were added to form a liquid. The effects of the amount of liquid phase on density and dielectric properties were investigated. BaTiO3 sintered with BaCO3 and H3BO3 showed dielectric properties, whereas BaTiO3 sintered with BaB2O4 had semiconducting properties with PTCR characteristics. Also, LiF-added BaTiO3 indicated a dielectric constant in which the peak shifts to lower temperatures with higher LiF concentrations.
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