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RISS 인기검색어
- 검색키워드
- 저자 : Junichi Tatami (검색결과 4 건)
- 무료
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LEE, Hyun Min,TATAMI, Junichi,KIM, Do Kyung CERAMIC SOC OF JAPAN 2016 JOURNAL- CERAMIC SOCIETY JAPAN Vol.124 No.8
<P>Microstructural evolution of Si3N4 ceramics and thermal/mechanical properties were investigated with respect to the initial alpha-to-beta ratios of the starting powders. The fast growth of elongated beta-grains was observed in the alpha powder, while the growth of relatively equiaxed grains occurred in the beta powder. In the cases where alpha/beta mixed raw powder was used, exaggerated bimodal microstructural evolution occurred as a result of the abnormal grain growth. These microstructural variations of the Si3N4 had a significant influence on the mechanical and thermal properties, such as strength, fracture toughness and thermal conductivity. The bimodal microstructure, which consisted of large elongated grains surrounded by fine matrix grains, resulted in both high flexural strength and high fracture toughness. Controlling the microstructural evolution, resulted in a high thermal conductivity of 86W/mK, a high flexural strength of 912 MPa, and a high fracture toughness of 7.88 MPa. m(1/2) from alpha/beta mixed raw powder. The achievement of both high thermal and mechanical properties of Si3N4 ceramics was highly essential for thermal management applications. (C) 2016 The Ceramic Society of Japan. All rights reserved.</P>
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Matsuoka, Mitsuaki,Yoshio, Sara,Tatami, Junichi,Wakihara, Toru,Komeya, Katsutoshi,Meguro, Takeshi The Korean Ceramic Society 2012 한국세라믹학회지 Vol.49 No.4
The study to give electrical conductivity by dispersing carbon nanotubes (CNT) into silicon nitride ($Si_3N_4$) ceramics has been carried out in recent years. However, the density and the strength of $Si_3N_4$ ceramics were degraded and CNTs disappeared after firing at high temperatures because CNTs prevent $Si_3N_4$ from densification and there is a possibility that CNTs react with $Si_3N_4$ or $SiO_2$. In order to suppress the reaction and the disappearance of CNTs, lower temperature densification is needed. In this study, $HfO_2$ and $TiO_2$ was added to $Si_3N_4-Y_2O_3-Al_2O_3$-AlN system to fabricate CNT-dispersed $Si_3N_4$ ceramics at lower temperatures. $HfO_2$ promotes the densification of $Si_3N_4$ and prevents CNT from disappearance. As a result, the sample by adding $HfO_2$ and $TiO_2$ fired at lower temperatures showed higher electrical conductivity and higher bending strength. It was also shown that the mechanical and electrical properties depended on the quantity of the added CNTs.
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Development of CNT-dispersed Si3N4 Ceramics by Adding Lower Temperature Sintering Aids
Mitsuaki Matsuoka,Sara Yoshio,Junichi Tatami,Toru Wakihara,Katsutoshi Komeya,Takeshi Meguro 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.4
The study to give electrical conductivity by dispersing carbon nanotubes (CNT) into silicon nitride (Si3N4) ceramics has been carried out in recent years. However, the density and the strength of Si3N4 ceramics were degraded and CNTs disappeared after firing at high temperatures because CNTs prevent Si3N4 from densification and there is a possibility that CNTs react with Si3N4 or SiO2. In order to suppress the reaction and the disappearance of CNTs, lower temperature densification is needed. In this study, HfO2 and TiO2 was added to Si3N4-Y2O3-Al2O3-AlN system to fabricate CNT-dispersed Si3N4 ceramics at lower temperatures. HfO2 promotes the densification of Si3N4 and prevents CNT from disappearance. As a result, the sample by adding HfO2 and TiO2 fired at lower temperatures showed higher electrical conductivity and higher bending strength. It was also shown that the mechanical and electrical properties depended on the quantity of the added CNTs.
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Takashi Yokoyama,Masaru Nakamura,Junichi Tatami,Toru Wakihara,Takeshi Meguro 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.5
Preparation of cubic spinel-type oxides, Mn(1.75−1.25X)Co2.5XNi1.25(1−X)O4 (0 ≤X≤ 0.6), and their electrical properties were investigated. The starting oxides, containing metals with a prescribed molar ratio, were heated to 1400℃ and held for 3 h in argon. The sintered bodies were cooled to 800 oC and then oxidized for 48 h in air to convert them into a cubic spinel structure. The electrical conductivities of the sintered bodies were confirmed to increase exponentially with an increase in the temperature, indicating that they have intrinsic NTC thermistor characteristics. In the region of 0 ≤ X≤ 0.4, the electrical conductivity increased with an increase in X and decreased with an increase in X in the region of 0.4 < X ≤ 0.6. The concentration of Mn4+ in the octahedral sites of the spinel structure was considered to be larger than that of Mn3+ because the sintered bodies were n-type semiconducting. The electrical conduction of the oxides prepared in this study was concluded to be controlled by a small polaron hopping mechanism. Preparation of cubic spinel-type oxides, Mn(1.75−1.25X)Co2.5XNi1.25(1−X)O4 (0 ≤X≤ 0.6), and their electrical properties were investigated. The starting oxides, containing metals with a prescribed molar ratio, were heated to 1400℃ and held for 3 h in argon. The sintered bodies were cooled to 800 oC and then oxidized for 48 h in air to convert them into a cubic spinel structure. The electrical conductivities of the sintered bodies were confirmed to increase exponentially with an increase in the temperature, indicating that they have intrinsic NTC thermistor characteristics. In the region of 0 ≤ X≤ 0.4, the electrical conductivity increased with an increase in X and decreased with an increase in X in the region of 0.4 < X ≤ 0.6. The concentration of Mn4+ in the octahedral sites of the spinel structure was considered to be larger than that of Mn3+ because the sintered bodies were n-type semiconducting. The electrical conduction of the oxides prepared in this study was concluded to be controlled by a small polaron hopping mechanism.
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