Swelling of radiation-cured polymer precursor powder for silicon carbide by pyrolysis

Takeyama, Akinori; Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito

Journal of Asian Ceramic Societies (Internet), 3(4), p.402 - 406, 2015/12

https://doi.org/10.1016/j.jascer.2015.08.003

Effect of humidity and temperature on the radiation response of SiC MOSFETs

Takeyama, Akinori; Matsuda, Takuma; Yokoseki, Takashi; Mitomo, Satoshi; Murata, Koichi; Makino, Takahiro; Onoda, Shinobu; Tanaka, Yuki*; Kandori, Mikio*; Yoshie, Toru*; et al.

Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.134 - 137, 2015/11

Development of the RAQM2 aerosol chemical transport model and predictions of the Northeast Asian aerosol mass, size, chemistry, and mixing type

Kajino, Mizuo*; Inomata, Yayoi*; Sato, Keiichi*; Ueda, Hiromasa*; Han, Z.*; An, J.*; Katata, Genki; Deushi, Makoto*; Maki, Takashi*; Oshima, Naga*; et al.

Atmospheric Chemistry and Physics, 12(24), p.11833 - 11856, 2012/12

https://doi.org/10.5194/acp-12-11833-2012

A new aerosol chemical transport model, Regional Air Quality Model 2 (RAQM2), was developed to simulate Asian air quality. We implemented a simple version of a modal-moment aerosol dynamics model and achieved completely dynamic solution of a gas-to-particle mass transfer over a wide range of aerosol diameters from 1 nm to super micro m. To consider a variety of atmospheric aerosol properties, a category approach is utilized: aerosols are distributed into 4 categories, Aitken, accumulation, soot aggregates, and coarse mode. A regional-scale simulation was performed for the entire year of 2006, covering Northeast Asian region. Statistical analysis showed the model reproduced the regional-scale transport and transformation of the major inorganic anthropogenic and natural air constituents within factors of 2 to 5. Modeled size distributions of total weight and chemical components were consistent with the observations, indicating simulations of aerosol mixing types were successful.

Photocatalytic activity of Sulfur-doped TiO fiber under visible light illumination (Joint research)

Takeyama, Akinori; Yamamoto, Shunya; Yoshikawa, Masahito; Hasegawa, Yoshio*; Awatsu, Satoshi*

JAEA-Research 2007-012, 29 Pages, 2007/03

JAEA-Research-2007-012.pdf:3.77MB

The Sol-Gel derived precursor fiber was annealed under hydrogen disulfeid (HS) following oxygen atmosphere, Sulfer-doped titanium dioxide (TiO) fiber was obtained. Crystal structure of the fiber was identified as anatase phase of TiO. The energy band gap of the fiber was narrower by about 0.06 eV than that of anatase, which showed that it could absorb visible light. The fiber contains about 0.58 atomic % of Sulfer, and they located at the oxygen lattice site of TiO. Under visible light illumination, the fiber degraded Trichroloethylen (TCE) and produced carbon dioxide (CO). This shows Sulfer-doped TiO fiber has the photocatalytic activity under visible light illumination.

Characterization of sulfur-doped TiO films by RBS/C

Yamamoto, Shunya; Takeyama, Akinori; Yoshikawa, Masahito

Nuclear Instruments and Methods in Physics Research B, 242(1-2), p.377 - 379, 2006/01

https://doi.org/10.1016/j.nimb.2005.08.077

no abstracts in English

Formation of Cu precipitates by ion implantation and thermal annealing for the growth of oxide nanorods

Takeyama, Akinori; Yamamoto, Shunya; Ito, Hiroshi; Yoshikawa, Masahito

Nuclear Instruments and Methods in Physics Research B, 232(1-4), p.333 - 337, 2005/05

https://doi.org/10.1016/j.nimb.2005.03.068

Cu precipitates were formed on Si(100) by 200 keV Cu ion implantation and subsequent annealing at 773 K. The shape of the Cu precipitates evolved from a large rectangle to a small elongated pyramid with increasing annealing time. This shape evolution seemed to result from the epitaxial formation of Cu precipitates to minimize the interfacial energy between the precipitate and the Cu implanted substrate. The average density of Cu precipitates monotonously increased and the average diameter of Cu precipitates decreased with increasing annealing time up to 1 h. These indicate that the morphology, size and average density of Cu precipitates can be controlled by varying annealing time, and that Cu ion implantation and subsequent annealing were effective in producing a substrate dispersed with catalytic particles for oxide nanorods growth.

Swelling of radiation-cured polycarbosilane during pyrolysis

Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito

no journal, , 

Inorganic membrane prepared from thermally stable precursor-derived silicon carbide (SiC) has been paid attention for the use of hydrogen or carbon dioxide separation. For preventing formation of defects called as pinholes or cracks in the membrane, volume shrinkage of polymer precursor, polycarbosilane (PCS) should be as small as possible when PCS is converted into SiC. We aim at revealing mechanism for prevention of the volume shrinkage of PCS powder during pyrolysis. With increasing the pyrolysis temperature from 673 K to 823 K, density of pyrolyzed PCS powder was decreased, whilst calculated volume change was increased, indicating PCS powder swelled. Furthermore, increased amount of total pore volume compared with that of un-pyrolyzed powder was observed in the same temperature range. We found volume shrinkage of PCS powder was relieved by swelling.

Single photon source in silicon carbide annealed at high temperature

Oshima, Takeshi; Lohrmann, A.*; Johnson, B. C.*; Castelletto, S.*; Onoda, Shinobu; Makino, Takahiro; Takeyama, Akinori; Klein, J. R.*; Bosi, M.*; Negri, M.*; et al.

no journal, , 

no abstracts in English

Structural evolution of polymer precursor of silicon carbide ceramics during pyrolysis

Takeyama, Akinori; Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito

no journal, , 

In order to prepare crack-free silicon carbide hydrogen separation membrane, how volume shrinkage or expansion of polymer precursor, polycarbosilne (PCS) take places when it is converted into silicon carbide ceramics during pysolysis was investigated. PCS powder cured by electron beam irradiation with several dose of 12,16,18,24 MGy in helium atmosphere was pysolysed at 923 K to convert them into SiC ceramic powder. As the dose was increased, ceramic yield was gradually increased, indicating amount of decomposed gas evolved during pyrolysis was decreased. Density of obtained SiC ceramic powders was decreased with increasing dose. By electron beam irradiation, network structure of PCS was developed and decomposition gas seemed to be easily accumulated in the network structure. It follows that PCS powder swelled as decomposition gas was accumulated and swelling was lowered density of SiC ceramic powders. Furthermore, surface area of SiC ceramic powder was increased from 0 m/g for 12 MGy to 0.6 m/g for 24 MGy by swelling. Consequently, swelling suppressed volume shrinkage of PCS powder during pyrolysis.

Gas permeation characteritics of silicon carbide membranes prepared with an immersion of a precursor film

Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito

no journal, , 

Silicon carbide (SiC) films as a hydrogen separation membrane were prepared using a novel preparation technique. The films were obtained by a coating of precursor films on porous alumina supports followed by an immersion into cycohexane, curing in an inert atmosphere and pyrolisis. A selectivity of the film, which is defined as the ratio of the amount of hydrogen (H) to nitrogen (N) which passed thorough the membrane, was increased up to 6.1 as increasing the immersion time. This is supposed that precursor in pores is dissolved by cyclohexane and pores are filled with the precursor solution, which leads to a decrease of the pore diameter and an improvement of the selectivity.