Papers by Author: Hayao Imamura

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Authors: Hayao Imamura, Kazuki Yoshihara, Mika Yoo, Ichiro Kitazawa, Yoshihisa Sakata, Shinji Ooshima, Takeshi Kataoka
Abstract: The hydrogen desorption of Sn/MgH2 nanocomposite which is formed by ball milling of MgH2 and tin compounds (Sn, Sn(C4H9)4 or SnCl2), has been studied. The hydrogen desorption properties (desorption temperature and enthalpy of dehydriding) were significantly improved as a result of a Sn/MgH2 nanocomposite formation. TDS (thermal desorption spectrometry), TG (thermogravimetry) and DSC (differential scanning calorimeter) measurements exhibited the existence of at least two types of hydrogen species in the Sn/MgH2 nanocomposite resulting from ball milling of MgH2 with Sn; the one was hydrogen in the newly formed Sn/MgH2 nanocomposite and the other hydrogen derived from MgH2 remaining in Sn/MgH2.
Authors: Hayao Imamura, Naotaka Shimomura, Keisuke Watanabe, Kenichi Tanaka, Fumiya Nakamura, Yoshihisa Sakata
Abstract: Hydrogen storage by calcium nitride or magnesium nitride has been undertaken by the use of ammonia, in which the possibility of ammonia as a vector for hydrogen carriers has been studied. When the calcium imide ornitride obtained by thermal decomposition of calcium amide dispersed on active carbon (AC) was brought into contact with ammonia gas (300 Torr) at room temperature, NH3 uptake readily occurred. When the sample after NH3 uptake was heated, the absorbed ammonia was released in the form of hydrogen and nitrogen. The ammonia is possibly absorbed in the form of the decomposed state in the imide ornitride. This type of hydrogen storage has been extensively studied and characterized.For magnesium nitride, ammonia was absorbed and desorbed without the decomposition.
Authors: Asuka Kozu, Hirotaka Fujimori, Ki Young Kim, Kazunori Oshiro, Setsuo Yamamoto, Yoshihisa Sakata, Hayao Imamura
Abstract: Sr2Ta2O7, a layered perovskite compound, has been reported to possess most excellent photocatalytic properties among the layered perovskite materials. Recently, we have successfully demonstrated that Ba5Ta4O15 that was prepared under Ta rich atmosphere has high photocatalytic performance as well as Sr2Ta2O7. In this study, several amount of Ba was doped into Sr2Ta2O7, and the photocatalyst samples with a mol ratio of Sr: Ba: Ta = (1-x): x: 1 were prepared by the polymerized complex method to investigate the effect of Ba substitution for the Sr site on photocatalytic activity. The maximum photocatalytic performance was obtained for x = 0.2 near the solid solubility limit, which is three times as high as that of undoped Sr2Ta2O7 and is in the highest level in a series of tantalum photocatalysts reported so far. The increase of photocatalytic activity would be caused by crystal distortion due to doping of Ba ion.
Authors: Kiyoshi Hirao, Hayao Imamura, Koji Watari, Manuel E. Brito, Motohiro Toriyama, Shuzo Kanzaki
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