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노명훈,김영욱,김원중,Toshiyuki Nishimura,서원선,고신일,이상진 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.6
Two different SiC ceramics, one with 10 vol.% AlN-Sc2O3 in a 2:3 molar ratio, and the other with 20 vol.% of the same additives with the same ratio, were fabricated by hot-pressing at 1900 °C for 1 h and subsequent annealing at 2000 °C for 6 h in nitrogen. The grain boundary structures of both materials were observed by using high-resolution transmission electron microscopy. The results showed that both materials had clean boundaries without any amorphous films. Although both samples exhibited the same boundary structure, the sample with the higher AlN-Sc2O3 content contained more junction phases. The SiC ceramic with 10 vol.% AlN-Sc2O3 maintained its room-temperature strength up to 1400 °C, whereas the SiC ceramic with 20 vol.% AlN-Sc2O3 showed a gradual decrease in strength at above 900 °C. The present results suggest that the hightemperature strength is dependent on the amount of junction phase, as well as the characteristics of the intergranular phase. Two different SiC ceramics, one with 10 vol.% AlN-Sc2O3 in a 2:3 molar ratio, and the other with 20 vol.% of the same additives with the same ratio, were fabricated by hot-pressing at 1900 °C for 1 h and subsequent annealing at 2000 °C for 6 h in nitrogen. The grain boundary structures of both materials were observed by using high-resolution transmission electron microscopy. The results showed that both materials had clean boundaries without any amorphous films. Although both samples exhibited the same boundary structure, the sample with the higher AlN-Sc2O3 content contained more junction phases. The SiC ceramic with 10 vol.% AlN-Sc2O3 maintained its room-temperature strength up to 1400 °C, whereas the SiC ceramic with 20 vol.% AlN-Sc2O3 showed a gradual decrease in strength at above 900 °C. The present results suggest that the hightemperature strength is dependent on the amount of junction phase, as well as the characteristics of the intergranular phase.
Consideration of the Formation Mechanism of an Al2O3-HfO2 Eutectic Film on a SiC Substrate
Kyosuke Seya,Shunkichi Ueno,Toshiyuki Nishimura,Byung-Koog Jang 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.1
An Al2O3-HfO2 eutectic EBC film was prepared on a SiC substrate by using the electric furnace heating and the optical zone melting methods. All of Al2O3 phase disappeared during the heating step at a temperature below the melting point, and all of the HfO2 phase reacted with the carbon and boron, which are included in SiC bulk as sintering agents, during the heating step at a temperature below the melting point. The thermal decomposition of the SiC phase, the reduction reaction of Al2O3 phase, the vaporization of the Al2O3 component, the reduction reaction of HfO2 and the formation of the HfC phase occurred at a temperature below the melting point. However, a highly dense HfC phase was formed on the SiC substrate. A rapid heating process becomes possible by using the optical zone melting method. A solidified film that was composed of a highly dense HfC layer as the intermediate layer and the Al2O3-HfO2 eutectic structure layer as the top coat was obtained by using the optical zone melting method.
Fabrication of Heat-Resistant Silicon Carbide Ceramics by Controlling Intergranular Phase
Kim, Young Wook,Lee, Sung Hee,Nishimura, Toshiyuki,Mitomo, Mamoru,Lee, Je Hun,Kim, Doh Yeon Trans Tech Publications, Ltd. 2005 Key engineering materials Vol.287 No.-
<P>The effect of glassy-phase, using AlN and Lu2O3 as sintering additives, on the microstructure and mechanical properties of liquid-phase-sintered, and subsequently annealed SiC ceramics was investigated. The microstructure was strongly influenced by the sintering additive composition, which determines the intergranular phase (IGP). The average thickness of SiC grains increased with increasing the Lu2O3 /(AlN + Lu2O3) ratio, whereas the average aspect ratio decreased with increasing the molar ratio. The homophase and heterophase boundaries of the SiC ceramics were completely crystalline in all specimens. The room temperature (RT) strength decreased with increasing the molar ratio whereas the RT toughness showed a minimum at the molar ratio of 0.6. The best results at RT were obtained when the molar ratio was 0.2. The flexural strength and fracture toughness of the ceramics were >700 MPa and ~6 MPa.m1/2 at RT. The high temperature strength was critically affected by the chemistry, especially the content of Al in the IGP. The best strength at temperatures ³ 1500oC was obtained when the molar ratio was 0.5. Flexural strengths of the ceramics at 1500oC and 1600oC were 610 ± 80 MPa and 540 ± 30 MPa, respectively. The beneficial effect of the new additive compositions (Lu2O3-AlN) on high-temperature strength of SiC ceramics was attributed to the crystallization or removal of IGP and introduction of Al into SiC, i.e., removal or reduction of Al content from the IGP, resulting in an improved refractoriness of the IGP.</P>
Seo, Yu-Kwang,Kim, Young-Wook,Nishimura, Toshiyuki,Seo, Won-Seon Elsevier 2016 Journal of the European Ceramic Society Vol.36 No.15
<P><B>Abstract</B></P> <P>The high-temperature strength of a thermally conductive SiC ceramic sintered with 1vol% equimolar Y<SUB>2</SUB>O<SUB>3</SUB>–Sc<SUB>2</SUB>O<SUB>3</SUB> additives (thermal conductivity=234W (mK)<SUP>−1</SUP>) was investigated at temperatures up to 1800°C. Observation of the ceramic using high resolution transmission electron microscopy (HRTEM) exhibited both clean and crystallized SiC/SiC boundaries, as well as clean SiC/junction phase boundaries with a fully crystallized junction phase. No microstructural or polytype changes after flexural testing at 1800°C were observed using scanning electron microscopy and phase analysis with the Rietveld method. The ceramic maintained 93% of its room temperature (RT) strength up to 1600°C, and showed rapid degradation at 1700°C and 1800°C. Degradation at temperatures above 1600°C was due to softening of the grain boundary phase, as evidenced by the nonlinear behavior of load-displacement curves. Flexural strengths of the highly thermally conductive SiC ceramic at RT and 1800°C were 536MPa and 345MPa, respectively.</P>
Synthesis and Sinterability of Hydroxyapatite from Fishery by-products
Wibisono, Yusuf,Dwijaksara, Ni Luh Bella,Widayatno, Wahyu Bambang,Wismogroho, Agus Sukarto,Amal, Muhamad Ikhlasul,Rochman, Nurul Taufiqu,Nishimura, Toshiyuki,Noviyanto, Alfian The Korean Ceramic Society 2018 한국세라믹학회지 Vol.55 No.6
Hydroxyapatites (HAps) were synthesized using the powdered waste of fishery products, i.e., fish scales and crab shells, as starting materials. HAp was synthesized by a wet-chemistry method followed by calcination at 600 and $800^{\circ}C$. Calcined crabshell powder revealed a single HAp phase and fine powder, while calcined fish-scale powder showed a ${\beta}-TCP$ secondary phase, even at the higher calcination temperature. Dense HAp pellets were obtained from the crab-shell powder by spark plasma sintering at $1000^{\circ}C$ for 10 min under applied pressures of 40 and 80 MPa in a vacuum state, giving sample densities of 2.93 and $3.06g/cm^3$, respectively. The estimated grain size of HAp was $448{\pm}96$ and $283{\pm}59nm$ for applied pressures of 40 and 80 MPa, respectively. In contrast, the HAp obtained using the pressureless sintering technique showed excessive grain growth without further densification.
OCIAD2 activates γ-secretase to enhance amyloid β production by interacting with nicastrin
Han, Jonghee,Jung, Sunmin,Jang, Jiyeon,Kam, Tae-In,Choi, Hyunwoo,Kim, Byung-Ju,Nah, Jihoon,Jo, Dong-Gyu,Nakagawa, Toshiyuki,Nishimura, Masaki,Jung, Yong-Keun Springer-Verlag 2014 Cellular and molecular life sciences Vol.71 No.13