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published : vol. 126, no.4, April 2018
Koichi KAJIHARA, Ryo TAKAHASHI, Hirohiko KATO and Kiyoshi KANAMURA
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Deca-dodecasil 3R (DDR) was synthesized hydrothermally from essential reagents, i.e., silica source (fumed silica), water, and 1-adamantanamine, without employing seed particles or any special treatments, such as microwave or ultrasonic irradiation. The variations in synthesis time, size, and morphology of DDR particles with reagent composition, fluorine addition, and hydrothermal temperature were examined. At 160°C DDR was synthesized in 15–20 d. Rhombohedral, star-like, and hexagonal plate-like particles were obtained and their crystallographic orientations were determined. The morphology changes in this order are caused by twinning and suppression of growth along the [0001] direction, and simultaneous increase in the average particle size is attributed to the suppression of nucleation. Similar morphology changes were also caused by adding F ions to the precursor mixture or increasing hydrothermal temperature. An increase in hydrothermal temperature to 200°C enabled a reduction of synthesis time in 5 d whereas the average particle size increased and hexagonal plate-like particles were formed dominantly. The rhombohedral particles synthesized at 160°C exhibited the largest micropore volume. The smaller micropore volumes for the hexagonal plate-like particles synthesized at 180 and 200°C are probably due to twinning and resultant narrowing and disruption of the microporous channels. In all samples high-resolution nitrogen adsorption isotherms exhibited two adsorption steps at relative pressures of ∼3 × 10−5 and ∼0.03, respectively attributed to the initial adsorption in micropores and the densification of adsorbates in micropores.
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published : vol. 126, no.4, April 2018
Jiannan HSING, Yoshikazu KAMESHIMA, Shunsuke NISHIMOTO and Michihiro MIYAKE
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In this paper, the photocatalytic activity of nitrogen-doped TiO2/montmorillonite composite (NTM) was successfully enhanced by modification with carbon. NTM was made by mixing a swelling clay solution with an N-doped TiO2 solution prepared by hydrolysis of titanium tetraisopropoxide with urea. Carbon-modified N-doped TiO2/montmorillonite composite (CNTM) was obtained by grinding the dried NTM with EtOH for 1 h, followed by calcination at 250°C in the air for 2 h. Both NTM and CNTM exhibited visible light absorption in the UV–vis spectrum in the same way as commercial N–TiO2 powder. Additionally, CNTM greatly extended the absorption edges to the visible light region. The photocatalytic performance of NTM and CNTM was evaluated using a degradation of bisphenol-A under visible light (>420 nm) radiation. Although the commercial TiO2 powder showed less photocatalytic activity under visible light radiation, NTM, CNTM and commercial N–TiO2 powder showed high photocatalytic activity. The order of degradation performance was as follows: CNTM > commercial N–TiO2 powder > NTM. Since the TiO2 content of CNTM is ca. 30 mass % by energy dispersive spectrum analysis, it was suggested that CNTM has extremely high visible light activity.
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published : vol. 126, no.4, April 2018
Seung-Kyu CHOI, Hyun-Hak JUNG and Sung-Man KANG
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This study investigated the correlation between the surge energy capability and Bi2O3 volatilization in ZnO varistors by analyzing the volatilization phenomenon of Bi2O3. A ZnO varistor is composed mainly of Sb2O3, Bi2O3. Bi2O3 has the lowest vapor pressure among these components. Bi2O3 play an important role, moreover, in forming it grain boundaries. These grain boundaries have low conductivity in the leakage current region, but, becomes higher in the region. It also determines the surge energy capability of the varistors. Bismuth oxide has four phases, each with intrinsic ion-conductivity. Formation of the bismuth oxide phase depends on the amount of bismuth at the grain boundary. Volatilization of Bi2O3 should therefore be prevented when developing ZnO varistors was conducted using with high energy capabilities. Analysis of the volatilization phenomenon of Bi2O3 X-ray analysis methods such as X-ray fluorescence, X-ray photoelectron spectroscopy and X-ray diffraction. The results confirmed a close correlation among them. Sealed sintering methods were proposed to prevent the volatilization of Bi2O3 by ZnO varistors.
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published : vol. 126, no.4, April 2018
Ming XIANG, Youfu ZHOU, Wentao XU, Xiaoqiang LI, Kun WANG and Wei PAN
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Transparent aluminum nitride (AlN) ceramics were sintered by the hot-pressing (HP) method. Comparison has shown that AlN ceramics fabricated using as-prepared nanopowders exhibit relatively high transparency, while AlN ceramics prepared using commercial micro-powders seem almost opaque. The influences of different sintering additives on the phase composition, densification behavior, microstructure, transparency and thermal conductivity of AlN ceramics were investigated. X-ray diffraction and scanning electron microscope analyses revealed that AlN ceramics with fluoride additives exhibited the pure AlN phase, while secondary phases were observed when using oxide additives. The microstructure, especially the distribution of secondary phases and porosity, played an important role, moreover in the transparency and thermal conductivity. Thus, the transmittance and thermal conductivity of ceramics with a 3 wt % CaF2 additive were higher than others.
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published : vol. 126, no.4, April 2018
Shin’ichi ARATANI
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High-speed photo-elastic color photography was introduced to a study of dynamic crack propagation in zone-tempered glass using recent photo-processing technologies. The study had a special focus on the value of stress σCR generated at the propagating crack front. It was recognized that the crack connection phenomenon could be explained using the stress σCR. The values of stress σCR were estimated at about 5 MPa in zone 1 and 3–4 MPa in zone 2 utilizing the color change of the stress field when propagating at terminal velocity. A slant-propagating crack was observed, which could be explained by a generation mechanism involving the stress σCR and the stress release, and propagation in the same way as other general crack propagation based on the maximum normal stress criterion.
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published : vol. 126, no.4, April 2018
Weiqi HE, Lixin CHEN, Tingting XU and Fei PENG
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A single source precursor of borazine derivative (B{NH[Si(CH3)2CH=CH2]}NH)3 (TSAB) was designed for electronic applications. The result of thermo gravimetric analysis combined with mass spectrometry shows a ceramic yield of 60.7%. The X-ray photo-electron spectroscopy confirms that the siliconboron carbonitride (SiBCN) ceramic is obtained. The powder X-ray diffraction pattern and Raman spectra show that the graphite and a little hexagonal BN are formed after pyrolysis at 1500°C. The room temperature conductivity increases with the pyrolysis temperature, the highest is approximately 10−4 (Ω·cm)−1 for SiBCN ceramic from cured TSAB pyrolyzed at 1500°C. Photoluminescence is observed in the visible range. The peaks appear at 417, 466, 498, and 593 nm (2.97, 2.66, 2.49, and 2.09 eV, respectively).
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published : vol. 126, no.4, April 2018
Terukazu KONDO, Yuta MATSUSHIMA, Keigo MATSUDA and Hidero UNUMA
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Herein, we report that δ-MnO2 thin films wet-chemically deposited on electro-conductive substrates exhibited good sensing abilities toward hydrogen peroxide and glucose without the assistance of immobilized enzymes, as well as the excellent supercapacitic performance described in our previous paper. High-sensitivity values of 380 mA/(M·cm2) (H2O2) and 300 mA/(M·cm2) (glucose) were attained with low detection limits of 0.7 µmol/dm3 (H2O2) and 0.6 µmol/dm3 (glucose). The good sensitivities and low detection limits were attributed to the large surface area of accumulated MnO2 nanosheets and their firm adhesion to the substrates. The method presented herein can be used for facile film deposition with good controllability and reproducibility.