Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.
Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03
Times Cited Count：44 Percentile：97.1(Astronomy & Astrophysics)Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 
C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.
Kumada, Takayuki; Oba, Yojiro; Motokawa, Ryuhei; Morooka, Satoshi; Tominaga, Aki; Tanida, Hajime; Shobu, Takahisa; Konno, Azusa; Owada, Kenji*; Ono, Naoko*; et al.
Journal of Nuclear Materials, 528, p.151890_1 - 151890_7, 2020/01
Times Cited Count：1 Percentile：11.8(Materials Science, Multidisciplinary)We have developed an anomalous small-angle X-ray scattering (ASAXS) diffractometer in SPring-8 to investigate irradiation-induced nanostructural change in ion-beam irradiated stainless steel. A thermally-aged MA956 stainless steel sample displays power-law scattering that follows the Porod law at the magnitude of scattering vector, Q, below 0.5 nm
and an overlapped shoulder around 0.7 nm. After the ion-beam irradiation, the intensity of the shoulder remained unchanged, whereas that of the power-law scattering nearly doubled. This result indicates that none of the structural parameters of the Cr-rich nanoprecipitates, such as the number density, size, and interface roughness, were changed by the irradiation.
Nara, Yoshitaka*; Kato, Masaji*; Niri, Ryuhei*; Kono, Masanori*; Sato, Toshinori; Fukuda, Daisuke*; Sato, Tsutomu*; Takahashi, Manabu*
Pure and Applied Geophysics, 175(3), p.917 - 927, 2018/03
Times Cited Count：14 Percentile：57.88(Geochemistry & Geophysics)Information on the permeability of rock is essential for various geoengineering projects. It is especially important to investigate how fractures and pores influence the physical and transport properties of rock. Infiltration of groundwater through the damage zone fills fractures in granite with fine-grained minerals. However, the permeability of rock possessing a fracture naturally filled with fine-grained mineral grains has yet to be investigated. In this study, the permeabilities of granite samples, including a macro-fracture filled with clay and a mineral vein, are investigated. The permeability of granite with a fine-grained mineral vein agrees well with that of the intact sample, whereas the permeability of granite possessing a macro-fracture filled with clay is lower than that of the macro-fractured sample. The decrease in the permeability is due to the filling of fine-grained minerals and clay in the macro-fracture. It is concluded that the permeability of granite increases due to the existence of the fractures, but decreases upon filling them with fine-grained minerals.
Kodaira, Takahide*; Ikeda, Ayumi*; Oura, Kotone*; Ono, Ryuhei*; Matsuyama, Emi*; Sawada, Shinichi; Yamaki, Tetsuya; Nomura, Mikihiro*
no journal, ,
no abstracts in English
Ikeda, Ayumi*; Ono, Ryuhei*; Matsuyama, Emi*; Nomura, Mikihiro*; Tanaka, Nobuyuki; Kubo, Shinji
no journal, ,
In the IS process, the improvement of efficiency and the downsizing can be achieved if equilibrium inversion rate of HI decomposition is improved by using membrane reactor with hydrogen separation membrane. In this paper, the application to the silica hybrid membrane prepared by counter diffusion CVD method was investigated. As a result, we can obtain the H
/HI permeation rate, 6820 and the H permeance, 5.0
10
mol m
s
Pa at 400 C, indicating that this membrane can be applied to this system. In addition, relation between SF
and HI permeance of membrane was investigated and verified to show the positive correlation. This result indicates that HI permeance of membrane can be evaluated by using SF permeance, which can be easily treated.
Kodaira, Takahide*; Oura, Kotone*; Ikeda, Ayumi*; Ono, Ryuhei*; Matsuyama, Emi*; Nomura, Mikihiro*; Sawada, Shinichi; Yamaki, Tetsuya; Tanaka, Nobuyuki; Kubo, Shinji
no journal, ,
Bunsen reactor in the IS process has a potential of the downsizing and the improvement of efficiency by using redox type reactor with an ion exchange membrane. The key to the performance of redox reactor is the development of the high performance ion exchange membrane. In this paper, we investigated the performance (proton transport number (t
) and water permeation factor (
)) of Nafion 212, which is the reference. As a result, t and were 0.63 and 2.82, respectively, indicating that not only H
but also I
and water permeate through the membrane. The permeation of these components might cause the precipitation of sulfur and the rising of the voltage. Aftertime, we must new ion exchange membrane which can restrict the permeation of I and water.
Nagai, Takayuki; Kaneko, Koji; Motokawa, Ryuhei; Okamoto, Yoshihiro; Haga, Yoshinori; Kobayashi, Hiromi*; Homma, Masanobu*; Hatakeyama, Kiyoshi*; Hirono, Kazuya*
no journal, ,
no abstracts in English
Konno, Azusa; Yamashita, Shinichiro; Kumada, Takayuki; Oba, Yojiro; Motokawa, Ryuhei; Morooka, Satoshi; Ukai, Shigeharu*; Hashimoto, Naoyuki*; Ono, Naoko*; Shobu, Takahisa; et al.
no journal, ,
Duplex stainless steels is composed by austenite and ferrite phases, offering superior toughness, high strength properties, good weldability, and corrosion-resistance. It has been used as the heat exchanger components for the chemical industrial plants and pipes for the Pressurized light-Water Reactors (PWR). However, the duplex stainless steels is also known to suffer from the embrittlement due to the phase separation into the Cr-rich phase and Fe-rich one when it is annealed at longer time at the temperature over 300 degrees. In this study, we focused on the Anomalous Small-Angle X-ray Scattering (A-SAXS) technique that can analyze "arbitrary element" by using absorption edge of a specific element and estimated the chromium separation quantitatively by utilizing the A-SAXS method, considering the availability of this new technique as the quantitative and non-destructive analysis method for microstructure in metallic material.
Konno, Azusa; Oba, Yojiro; Tominaga, Aki; Morooka, Satoshi; Ono, Naoko*; Hashimoto, Naoyuki*; Ukai, Shigeharu; Owada, Kenji*; Motokawa, Ryuhei; Kumada, Takayuki; et al.
no journal, ,
An ODS alloy is one of the promising candidate materials applicable to the fusion reactor because of its high-temperature creep strength and irradiation resistance. However, the ODS ferritic stainless steel with high Cr content sometimes suffers from the embrittlement related to phase separation below 748 K for a long term using in the reactor. It is, therefore, an important issue to understand embrittlement phenomena from not only macrostructural viewpoint but also microstructural one. Anomalous Small Angle X-ray Scattering (A-SAXS) is a unique and potential evaluation method that can analyze complex microstructure. This method can extract the signal only from an element of interest to implant the X-ray of the wavelength near orbit electron of the element. In this study, we performed both the A-SAXS analysis and TEM observation for high Cr-ODS alloy in order to assess the applicability of the A-SAXS technique as a microstructure determination and compared the A-SAXS signal with the TEM micrograph. The specimen of the commercial MA956 (Fe-20Cr-4.8Al-0.4Ti-0.02C-0.4YO
(mass%)) were thermally-aged at 748 K for 1, 10, 100 and 1000 hrs, and measured using the A-SAXS diffractometer at BL22XU in SPring-8 and a TEM. The A-SAXS data reveal that the average size of Cr precipitations increases with increasing the aging time. Also, using the A-SAXS profiles, it was estimated that there were two cases; one is the case that the microstructure does have a distinct interface between the matrix and Cr precipitate. The other case is the microstructure does not have the distinct interface. On the other hand, in TEM observation, the periodic modulated structure was observed for 10 hrs thermally-aged sample, and the sphere precipitation was confirmed for 100 hrs thermally-aged sample. It was suggested that there would be a crucial phase separation mode from spinodal decomposition to nucleation-growth between 10 and 100 hrs.
Nagai, Takayuki; Okamoto, Yoshihiro; Kaneko, Koji; Motokawa, Ryuhei; Kobayashi, Hiromi*; Homma, Masanobu*; Hirono, Kazuya*
no journal, ,
To understand the structural property of borosilicate glass frit for vitrification of radioactive wastes, we prepared the glass frit samples which coordinated alkaline component and BO amount and measured the Si-O bridge structure of those samples by using Raman spectrometer. Moreover, we made the simulated waste glass samples which added non-radioactive nitrate solution to those frit and observed a change of Raman spectra by glass composition.
