Papers by Author: Atsushi Nakahira

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Authors: Atsushi Nakahira, Y. Fujita, T. Kubo, S. Eguchi, S. Nishida, Toshiyuki Isshiki
Abstract: By the usage of the hydrolysis of Ti alkoxide, various types of TiO2 were obtained through the addition of catalyst (HCl, NH4OH, and CH3COONH4) and some additives into Ti alkoxide solution at room temperature. In special, the effect of two additives, diethylene glycol (DEG) and hexamethylphospheric triamide (HMPA), on hydrolysis behaviors and microstructure with various catalyst for hydrolysis of Ti-tetraisopropoxide was in detail investigated. In case of TiO2 powder with HMPA as an additive, the crystallinity of TiO2 except with NH4OH as a catalyst decreased in XRD patterns, compared to those of products with no additive and with DEG as an additive. The addition of HMPA prohibited the growth of TiO2 and led to fine TiO2 with the average particle size of approximately 10nm.
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Authors: Atsushi Nakahira, K. Shiba, S. Yamaguchi, K. Kijima
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Authors: M. Hussain, Atsushi Nakahira, S. Nishijima, Koichi Niihara
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Authors: S. Yamada, M. Nagasaka, T. Natsume, Koichi Niihara, Atsushi Nakahira
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Authors: Koichi Niihara, K. Izaki, Atsushi Nakahira
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Authors: Atsushi Nakahira, M. Tamai, Keisuke Eguchi, Satoshi Nakamura, Kimihiro Yamashita
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Authors: Atsushi Nakahira, Mitsuhiko Ohta, T. Murakami, T. Kudo
Abstract: 12 mol%CeO2 based composites were fabricated by a pressureless sintering technique and post-HIP treatments. The mixture of 12CeO2-ZrO2/3Y2O3-ZrO2 (= 80 wt%/20 wt%) powders from various methods were prepared by a ball milling technique and consequently sintered at 1400 in air atmosphere and post-HIP treatment at 1350. The 12Ce-ZrO2/Y-ZrO2 composites sintered from mixture of 12CeO2-ZrO2 powder and 3Y2O3-ZrO2 powders possessed the high strength over 1300 MPa and also high fracture toughness over 11 MPam1/2. Furthermore, the significant inhibition of the ZrO2 phase transformation of tetragonal to monoclinic phase under an aqueous hydrothermal condition at 150 was obtained for these 12Ce-ZrO2/Y-ZrO2 composites prepared from this method. Microstructural observation was in detail performed by TEM and EDS.
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Authors: Mitsuhiko Ohta, Masahiko Tajika, Atsushi Nakahira
Abstract: In this study, porous hydroxyapatite (HAp) bodies were prepared by the simple process. We fabricated porous fibers consisting of polyacrylonitrile (PAN) and HAp by an extrusion method of the mixture of PAN and HAp in dimethylformamide (DMF) solution. Fibers obtained by this extrusion method were chopped and molded. Subsequently, these compactions from chopped fibers consisting of HAp and PAN were sintered at various temperatures in air atmosphere. The sintered HAp bodies had high porosity and a number of pores with diameter some hundreds μm. These porous HAp bodies can be used as a scaffold in the body.
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Authors: S. Takezoe, Kazuyuki Hosoi, Masahiko Tajika, Yuki Yamasaki, Atsushi Nakahira
Abstract: Synthesis of bulky Y-zeolite was attempted by a hydrothermal hot-pressing (HHP) method. These bulky products synthesized under hydrothermal conditions were identified as Y-zeolite single phase. Especially, bulky Y-zeolite having translucency, high density and large surface area was obtained by HHP treatment at 423K for 2h with 17wt% of 5M-NaOH solution. This solidified zeolite like single-crystal was considered to be made by dissolution and precipitation mechanism. High-density bulky zeolites can be expected as novel molecular sieves and catalysts with high activity.
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Authors: Masato Tsujiguchi, Tadashi Kobashi, Junji Kanbara, Yasuhiko Utsumi, Nobuaki Kakimori, Atsushi Nakahira
Abstract: Zeolite is a microporous aluminosilicate material with uniform pore size of less than 2 nm and chemical, mechanical, and thermal stability. In general zeolite is synthesized from silica, alumina, mineralizer (alkali metal hydroxide and fluoride) and water. Recently it has been reported that various zeolites is synthesized from soda-lime glass, slag and coal fly ash as silica and alumina source. On the other hand, the production volume of various kinds of high-quality glass which are utilized for high-tech products such as liquid crystal displays and plasma displays is rapidly increasing. The purpose in this study is to synthesize a zeolite from crushed aluminoborosilicate glasses which is used as LCD panels glass substrate. According to the XRD analysis, it was found that the synthesized sample had zeolite related structure. And the results of SEM observation of the products suggest that the zeolite structure was obtained as well as XRD results. It was thought that zeolite was successfully synthesized from the glass by this synthetic processing.
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