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RISS 인기검색어
- 검색키워드
- 저자 : Hirotaka Fujimori (검색결과 6 건)
- 무료
- 기관 내 무료
- 유료
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${29}^Si$ MAS NMR Study on Quantitative Analysis of the Amorphous Phase in a $Si_3N_4$ Powder
Fujimori, Hirotaka,Kitahara, Hiromoto,Ioku, Koji,Goto, Seishi,Nakayasu, Tetsuo,Yamada, Tetsuo The Korean Ceramic Society 2000 The Korean journal of ceramics Vol.6 No.2
NMR study has been used for measuring precise quantity of the amorphous phase in the $Si_3N_4$powder. Care must be taken to allow the $^{29}$Si nuclear spin system to fully relax between pulses in order to make the signals proportional to the number of nuclei in each phase. $^{29}$Si MAS spectrum was decomposed into the three spectra of $\alpha$-, $\beta$-, and amorphous $Si_3N_4$assuming pseudo-Voigt function. Moreover, the Rietveld analysis of the powder X-ray diffraction data was performed to measure quantity of crystalline phases as $\alpha/\beta$ ratio.
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Photocatalytic Performance of Barium-doped Strontium Tantalate
Kozu Asuka,Fujimori Hirotaka,Kim Ki-Young,Oshiro Kazunori,Yamamoto Setsuo,Sakata Yoshihisa,Imamura Hayao 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Sr2Ta2O7, a layered perovskite compound, has been reported to possess most excellent photocatalytic properties among the layered perovskite materials. Recently, we have demonstrated that Ba5Ta4O15 that was prepared under a mol ratio of Ba: Ta=1:1 has high photocatalytic performance as well as Sr2Ta2O7. In this study, the photocatalyst samples with a mol ratio of Sr: Ba: Ta = (1-x): x: 1 were prepared. The maximum photocatalytic performance was obtained for x= 0.2, which is three times as high as that of undoped Sr2Ta2O7.
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Application of DV-X$\alpha$ Method to ${\gamma}$-2CaO.SiO$_2$
Yamaguchi, Norio,Fujimori, Hirotaka,Ioku, Koji,Goto, Seishi,Nakayasu, Tetsuo The Korean Ceramic Society 2000 The Korean journal of ceramics Vol.6 No.4
In the present study, we attempted to apply DV-X$\alpha$ method to expressing the reactivity of materials. The expression of reactivity was discussed by comparison between ${\gamma}$-C$_2$G having hydraulic activity and ${\gamma}$-C$_2$S not having hydraulic activity at normal conditions. It was found that the model cluster used for calculation can finely reproduce the bulk and surface states using with and without point charge, respectively. The hydration state was also represented by placing OH￣ on the surface of the cluster. It was calculated that the bond strength of the first layer (as surface) was bigger than that of inner layers (as bulk) for ${\gamma}$-C$_2$S while that of the first layer for ${\gamma}$-C$_2$G was smaller than that of inner layers. Subsequently a model in which OH￣ is coordinated on Ca at the surface was also calculated. The bond strength with OH￣ was stronger than that without OH￣, while for ${\gamma}$-C$_2$G the bond strength with OH￣ was weaker than that without OH￣. From these results, it is concluded that the hydraulic activity depends on whether the bond strength for hydrated state becomes weaker than that unhydrated state or not.
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In Vitro Reaction for Calcium Phosphate Ceramics
Ioku, Koji,Toya, Hiroyuki,Fujimori, Hirotaka,Goto, Seishi The Korean Ceramic Society 2000 The Korean journal of ceramics Vol.6 No.3
Hydroxyapatite (HA) and $\beta$-tricalcium phosphate ($\beta$-TCP) are bio-compatible materials with bones and teeth. HA has been widely applied as bone substitutes because of chemical stability in vivo, while $\beta$-TCP has higher resorbability than HA when the material is implanted in a bone defect. In the present study, both HA and $\beta$-TCP porous ceramics were soaked in the simulated body fluid in order to investigate the reaction between the materials and the fluid. After the soaking test, carbonate hydroxyapatite was formed on HA surface at 1 week, and then the amount of precipitates increased with increasing period of the soaking test. While $\beta$-TCP was not dissolved in the fluid, carbonate hydroxyaopatite was also formed on $\beta$-TCP surface after 12 weeks, and the amount of precipitates was less than that on HA. In vitro behavior of HA was similar to that in vivo, but in vitro behavior of $\beta$-TCP was not similar to that in vivo.
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Microsotructure Designed Porous Apatite Ceramics Prepared by Hydrothermal Method
Ioku, Koji,Fukuhara, Michiko,Fujimori, Hirotaka,Goto, Seishi The Korean Ceramic Society 1999 The Korean journal of ceramics Vol.5 No.2
Microsotructure designed porous ceramics of calcium hydroxyapatite $(Ca_{10}(PO_4)_6(OH)_2)$ were prepared by hydrothermal method. The particle size, shape, and the micro-pore size of the porous hydroxyapatite ceramics could becontrolled. The hydroxyapatite was non-stoichiometric apatite with calcium deficient compositions (Ca/P ratio < 1.67). The composition of non-stoichiometric hydroxyapatite ceramics could be controlled from 1.50 to 1.63 in Ca/P ratio. The hydroxyapatite ceramics preparedc at $105^{\circ}C$ under the saturated vapor pressure for 20h were composed of rod-shaped crystals with about 10$\mu\textrm{m}$ in length with the mean aspect ratio of 40. The porous ceramics of calcium deficient hydroxyapatite had about 45% porosity with the inter-connecting pore structure. Porous hydroxyapatite ceramics prepared hydrothermally had the compressive strength of about 10 to 30 MPa. In addition, porous ceramics of $\beta$-tricalcium phosphate ($\beta-Ca_3(PO_4)_2$) were prepared from the calcium deficient hydroxyapatite.
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Koichi Shigeno,Haruka Nishijima,Takeshi Souma,Hirotaka Fujimori 한국전기전자재료학회 2023 Transactions on Electrical and Electronic Material Vol.24 No.1
In this study, a single-phase quadruple perovskite oxide powder, Cu 3.21 Ti 1.16 Nb 2.63 O 12 , was synthesized, and the novel coexistence of Cu 2+ and Cu + was confirmed via X-ray photoelectron spectroscopy. We produced a dense, sintered body with a relative density of 96% by firing at 885 °C in air. The sintered body exhibited an electrical conductivity of 2.2 S/cm, a Seebeck coefficient of -280 μV/K, a thermal conductivity of 2.4 W/m K at 730 °C, and a relatively low dimensionless figure of merit ( ZT ) of approximately 0.006. The main reason for the low ZT was the low electrical conductivity, which was approximately 1/100 of that of Na 0.7 CoO 2 , which is a typical thermoelectrical oxide. However, the obtained ZT value was higher than that of similar CaCu 3 Ti 4 O 12 -based oxides, indicating the significant potential of the as-prepared perovskite oxide as a thermoelectric material. The electrical conductivity exhibited an Arrhenius-type temperature dependence above room temperature, and its activation energy was 0.1 eV, which was equivalent to that of CuO hopping conduction. This suggested that hopping conduction between Cu + and Cu 2+ plays a signifi cant role in the electrical conduction of this system. This study provides important insights for the development of new quadruple perovskite oxide thermoelectric materials.
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