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Express Letter
published : Advance online publication
Hyoung-Won SON, Philipp SAUERSCHNIG, David BERTHEBAUD and Takao MORI
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Dense YB22C2N samples were directly synthesized from powder mixtures via reactive spark plasma sintering. The gas/solid reaction step was applied to introduce nitrogen into the mixture during heating. The sample reactively sintered at 1700 °C for 10 min after the gas/solid reaction step at 1200 °C for 30 min consisted of YB22C2N with small amounts of secondary phases. The thermoelectric behavior shifted toward n-type behavior with increasing amount of YB22C2N phase. This newly developed synthesis technique could facilitate the rapid and cost-effective preparation of complex borocarbonitrides.
Full Paper
published : vol. 128, no.2, February 2020
Naoki KAWANO, Daisuke NAKAUCHI, Fumiya NAKAMURA and Takayuki YANAGIDA
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We synthesized a Dy-doped CaF2 translucent ceramic by the spark plasma sintering method, and investigated its scintillation and dosimetric properties compared with those of the single crystal. Both the samples showed sharp peaks across 480–670 nm due to the 4f–4f transitions of Dy3+, and a broad peak approximately at 300 nm due to the self-trapped excitons. The decay time constants of both the samples in scintillation were approximately 5 ms, which was close to those for the 4f–4f transitions of Dy3+. Regarding thermally-stimulated luminescence, the translucent ceramic exhibited higher sensitivity than the single crystal, and the dynamic range was at least 0.01–100 mGy. In addition, both the samples showed optically stimulated luminescence due to the 4f–4f transitions of Dy3+ during 590 nm stimulation light, but the lowest detection limit of both the samples was approximately 10 mGy.
Express Letter
published : vol. 128, no.2, February 2020
Jiazhuo PENG, Heping LI and Sen LIN
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High-pressure sintering method was used to prepare the proton conductor based on BaZr0.7Ce0.2Y0.1O3−δ for the first time, and a comparative research of traditional pressureless sintering and high-pressure sintering methods was carried out. High-pressure sintering accelerated the sintering densification and greatly lowered the sintering temperature, resulting in high performance BaZr0.7Ce0.2Y0.1O3−δ product which was expected to be used as solid electrolyte to fabricate a sensor for measuring hydrogen in high-pressure hydrothermal systems.
Full Paper
published : vol. 128, no.2, February 2020
Zhanjiang LI, Chenglong ZHU, Bingjie CAI, Fa CHANG, Xiaoqiang LIU, Muhammad Zeeshan NAEEM and Pinqiang DAI
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Composite cermets with different mass ratios of Ti (C,N)/TiB2 and 10 wt % FeCoCrNiAl high-entropy alloys (HEAs) binder were fabricated by mechanical alloying and vacuum hot press sintering. The effect of the TiB2 content on the microstructure and mechanical properties of the Ti (C,N)–TiB2–HEAs cermets was systematically examined and is discussed in detail. The microstructure was analyzed by X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The results of this study show that a small amount of Fe2B phase was detected in the XRD patterns besides the Ti(C,N) and TiB2 phase. The TEM observation shows the presence of a HEAs binder phase, which was tightly bound to Ti(C,N) and TiB2 phases. The grain size of the composite cermets gradually decreased with increasing TiB2 content increased from 0 to 45 wt %. The relative density of the composite cermets first increased and then decreased with increasing TiB2 content from 11.25 to 45 wt %. When the TiB2 content reached 22.5 wt %, the composite cermets exhibited excellent comprehensive performance. The grain size, relative density, and hard phase of the composite cermets were the dominating factors that determined the mechanical properties with increasing TiB2 content. The relative density, Vickers hardness, bending strength, and fracture toughness of the Ti (C,N)–22.5 wt % TiB2–10 wt % HEAs composite cermets reached 98.86 ± 0.20%, 1954.4 ± 20 HV10, 727 ± 20 MPa, and 7.9 ± 0.1 MPa m1/2, respectively.
Full Paper
published : vol. 128, no.2, February 2020
Chika MATSUNAGA, You ZHOU, Dai KUSANO, Hideki HYUGA and Kiyoshi HIRAO
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Sintering of reaction-bonded silicon nitride (SRBSN) is a method of preparing Si3N4 ceramics with high thermal conductivity and good mechanical properties. In the present study, by using a high purity silicon powder as the starting material and 2 mol % of Y2O3 and 5 mol % of MgO as sintering additives, the phenomena including phase transformation, grain growth, densification, and pore size evolution occurred in the SRBSN process were studied. It was found that the α- to β-Si3N4 phase transformation could complete at 1700°C. Obvious grain growth started at around 1700°C. Substantial densification took place at temperatures between 1800 and 1900°C. When sintered at 1900°C for 30 min, not only the total number of pores drastically decreased as a result of the shrinkage of the compact, but also a fraction of open pores turned to be closed pores due to microstructural changes such as grain growth and pore coalescence.
Full Paper
published : vol. 128, no.2, February 2020
Miho AKO, Jun-ichi FUJISAWA and Minoru HANAYA
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Formation of solid solutions was examined in a wide miscibility gap system of Ba1−xCaxZrO3 by preparing film samples having amorphous structures with the help of rf magnetron sputtering and then annealing the amorphous film samples at a moderate temperature condition. Ba1−xCaxZrO3 solid solutions were successfully formed as monophasic products over the entire Ca composition range, indicating the usefulness of the method for the formation of solid solutions in perovskite-type oxides, and Ca composition dependence of the permittivity was revealed in the solid-solution system.
Full Paper
published : vol. 128, no.2, February 2020
Takuya EHIRO, Kazuaki KATAGIRI, Shimpei YAMAGUCHI and Yayoi YOSHIOKA
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MgO-modified mesoporous silicas (MgO/SBA-15) were prepared in a one-pot synthesis method. In the present study, a silica precursor was rapidly hydrolyzed and condensed together with a Mg source under mild conditions without a hydrothermal treatment. It was confirmed that N2 adsorption–desorption isotherms of the prepared MgO/SBA-15s were classified as type IV, which is characteristic of SBA-15. The X-ray diffraction (XRD) patterns at low diffraction angle also indicated that MgO/SBA-15s retained the ordered mesoporous structure of SBA-15, in spite of a high Mg content. On the other hand, no diffraction peaks due to Mg species were confirmed in the XRD patterns at high diffraction angle, suggesting that Mg species were dispersed on mesopores. After MgO/SBA-15s were impregnated with Co and Mo, the obtained CoMo/MgO/SBA-15 catalysts were tested for ammonia decomposition. It was revealed that the MgO content greatly influenced the catalytic activities of the CoMo-based catalysts. Although a small or large additive amount of MgO decreased the catalytic activity of CoMo/SBA-15, the modification of SBA-15 with 15 wt % of MgO resulted in the highest catalytic performance for ammonia decomposition. Moreover, the present one-pot synthesis method was more favorable for the enhancement of the catalytic activity, compared with the conventional impregnation method.
Technical Report
published : vol. 128, no.2, February 2020
Isao SAKAGUCHI
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We studied on the oxygen diffusion in two kinds of Al implanted ZnO samples (100 keV, 4 × 1014 ions/cm2). Parts of samples were annealed to diffuse simultaneously Al and Li impurity, and then same concentration distribution of Al and Li were observed. Through the oxygen diffusion experiments, the feature of bulk diffusion in the pre-annealed samples was separated at 950°C so that the large activation energy for bulk diffusion was observed below the pre-annealing temperature. Oxygen diffusion feature was explained as result from interaction between Al and Li for the pre-annealing.
Technical Report
published : vol. 128, no.2, February 2020
Taro UTSUMI, Toshiharu TERASAWA, Isamu KUDO, Tsuneo SUZUKI, Tadachika NAKAYAMA, Hisayuki SUEMATSU and Toru OGAWA
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A method to control the millimeter-sized open porosity in geopolymer foam was attempted to produce hydrogen recombining supports for radioactive waste canisters. The raw materials were mixed with silicon powder as a foaming agent. Geopolymer foams with open porosities as high as 81% were obtained by a water bath treatment before pouring the slurry into the mold. The increase in the open porosity of geopolymer foam was observed by an increase in the water bath treatment time. It was thought that the viscosity of slurry increase induced the pores trapped inside the geopolymer foam and connected to form millimeter-sized and open pores. It was concluded that a simple method with a foaming agent and a water bath treatment to prepare geopolymer foams with high open porosity was developed.