Papers by Author: Koji Watari

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Authors: Koji Watari, Manuel E. Brito, Takaaki Nagaoka, Motohiro Toriyama, Shuzo Kanzaki
Authors: Yoshiaki Kinemuchi, H. Morimitsu, H. Ishiguro, Shoji Uchimura, Koji Watari
Abstract: Co-firing of multiple materials results in the formation of internal stress due to the difference in shrinkage behavior. This internal stress causes retardation of sintering, crack formation and/or de-lamination at the interface. To reduce internal stress in layered structures, homogeneous pressing via centrifuge has been attempted. The effect of centrifugal pressing was demonstrated by film sintering, in which crack suppression and void removal by the present process were revealed. Owing to the homogeneous microstructure, the thermal stability of the film was significantly improved.
Authors: Yoshiaki Kinemuchi, Hirohide Ishiguro, Shoji Uchimura, Koji Watari
Abstract: Centrifugal sintering is a novel process for the preparation of thick films. In this process, high gravity such as 104g is applied at high temperatures. Because of the distinctive measure of pressing by the centrifugal force, gradient of pressure arises in the specimen, resulting in the graded porous structure during the progress of sintering. After the sintering, highly densified thick films are obtained. Furthermore, crack formation was suppressed by this process.
Authors: Koji Watari, Yoshiaki Kinemuchi, Kiminori Sato, Shoji Uchimura
Authors: Yoshiaki Kinemuchi, Shoji Uchimura, Koji Watari
Authors: Shoichi Kume, Saruhan Saklar, Koji Watari
Abstract: Attempts have been made to sinter hexagonal boron nitride (h-BN) by pressureless-sintering in air. In order to achieve this purpose, feldspar has been selected as a sintering aid to produce sintered compacts at a temperature above the melting point of feldspar. Even though h-BN was not wetted by the molten feldspar in nitrogen, the wettability was significantly improved in air. Through the heating process, the h-BN powder disappeared owing to the oxidation of the powder followed by sublimation of the boron oxide. The decomposition of BN was prevented effectively by the presence of molten feldspar in the h-BN/feldspar (30 vol.%) compact. It was shown that h-BN/feldspar composite can be sintered in air under normal pressure, although the bulk density of h-BN/feldspar composites (1.40 to 1.51 g/cm3) was not satisfactory enough.
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: Weiwu Chen, Shoichi Kume, Cihangir Duran, Koji Watari
Abstract: In the present work, effects of different salts (NaCl, 0.5NaCl-0.5KCl and KCl) on molten-salt-synthesized Sr0.5Ba0.5Nb2O6 (SBN50) powder were explored. A variety of particle morphology, compositions and lattice parameters of SBN50 were investigated. The results showed that SBN50 particles synthesized in NaCl salt have the finest diameter (0.1-0.2μm) and the highest aspect ratio (around 10), while the particles from 0.5NaCl-0.5KCl salt show the coarsest diameter (0.2-0.3μm) and the lowest aspect ratio (around 5). If only using KCl salt, trace Sr2Nb2O7 normally co-exists with SBN50 phase. In addition, Na+ and K+ cations from salts are easily incorporated with SBN structure and reach a very high content.
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.
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