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

A Development of super radiation-hardened power electronics using silicon carbide semiconductors; Toward MGy-class radiation resistivity

Hijikata, Yasuto*; Mitomo, Satoshi*; Matsuda, Takuma*; Murata, Koichi*; Yokoseki, Takashi*; Makino, Takahiro; Takeyama, Akinori; Onoda, Shinobu; Okubo, Shuichi*; Tanaka, Yuki*; et al.

Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.130 - 133, 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.

Tolerance of spin-Seebeck thermoelectricity against gamma ray irradiation

Okayasu, Satoru; Takeyama, Akinori*; Oshima, Takeshi*; Harii, Kazuya*; Ieda, Junichi; Ishida, Masahiko*; Saito, Eiji

no journal, , 

We are investigating the applications of spintronics devices in atomic fields. We reported the Tolerance of spin-Seebeck thermoelectricity against heavy swift ion irradiation previously. The tolerance of spin-Seebeck thermoelectricity against gamma ray irradiation will be reported at this conference. The spin thermoelectric properties after gamma ray irradiation up to 1MGy at room temperature and at 150C will be reported.

Stability of silicon carbide membrane prepared from polymer precursor in steam

Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito

no journal, , 

Precursor-derived silicon carbide (SiC) membrane has been a promising candidate as a membrane for hydrogen separation in harsh condition. In this report, SiC membrane was exposed to steam and its gas permeances were measured. Polymer precursor, polycarbosilane (PCS) film was coated on a porous support.Subsequently, it was cured and cross-linked by an electron beam irradiation in helium atmosphere followed by the pyrolysis at 973 K or 1073 K. A series of preparation procedure was repeated three times to layer SiC film. Prepared membrane was exposed to steam at 773 K for 10 hours. Water vapor pressure was about 47 kPa. H permeance of as-prepared membrane prepared via pyrolysis at 1073 K followed Arrhenius plot against the reciprocal temperature. This meanes H permeated through the membrane by molecular sieving mechanism. H permeance still followed Arrhenius plot after the exposure to steam. H permeance of as-prepared membrane prepared via pyrolysis at 973 K also followed Arrhenius plot. However, the membrane was subject to oxidation by steam, consequently large sized pores for Knudsen diffufion of H were formed in the membrane after the exposure.

Swelling of radiation-cured polycarbosilane by formation of nanometer sized pores during pyrolysis

Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito

no journal, , 

The conversion of polymer precursor, polycarbosilane (PCS) into polymer derived silicon carbide (SiC) by pyrolysis is accompanied by evolution of decomposed gas and volume shrinkage/expansion of PCS. It has been known thermally cured PCS powder is monotonically shrank, however, electron-beam cured PCS powder is expanded at the pyrolysis temperature of around 723 K. We aimed at clarifying why volume of PCS film is expanded by characterizing pyrolyzed powders cured by those methods by measuring the weight change, density and nitrogen isotherm. From the curve of weight decrease during the pyrolysis, it was observed thermally cured PCS evolved larger amount of gases in the temperature range from 673 to 923 K. In the same temperature range, larger total volume of pores formed in pyrolyzed powders was observed for thermally cured PCS powder. It indicates PCS powders were swelled when decomposed gases were evolved. In particular, for electron-beam cured powders, it was observed increase of total pore volume at 723 K even though hardly gases were evolved and the conversion took place, which attributed volume expansion of the PCS powder without shrinkage usually accompanied by the conversion.

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.