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Express Letter
published :
Shengfang Shi, Tomoyo Goto, Sung Hun Cho, Hideki Hashimoto, Shu Yin, Soo Wohn Lee, Tohru Sekino
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A simple method was used to form one-dimensional (1D) TiO2 nanorod arrays on the surfaces of hot-pressed Ti-dispersed Al2O3 composites by heating. After heating below 600°C, the Ti surface morphologies had changed significantly, while the Al2O3 surfaces remained unchanged. After heating for 5 h above 500°C, vertically grown nanorods were observed on the surfaces of Ti grains among Al2O3/Ti composites, which exhibited a crystalline phase of rutile-type TiO2 doped with a small quantity of aluminum. Nanorod formation was believed to be due to Ti diffusion and its acceleration by Al incorporation. The photocatalytic activity of the heated Al2O3/Ti composites was verified by rhodamine B degradation under ultraviolet light irradiation, although the oxide fraction on the composites was small. The activity was enhanced by 1D TiO2 nanorod growth on the composite surface.
The 72th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 126, no.9, September 2018
Takao SHIMIZU
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Ferroelectric HfO2 film has garnered a lot of attention lately due to unique features that cannot be achieved with conventional ferroelectric materials. The ferroelectricity of HfO2 originates from the metastable orthorhombic phase, which does not appear in the phase transition sequence of HfO2 in ambient pressure. This review introduces our recent research on HfO2-related ferroelectrics. The ferroelectric orthorhombic phase was achieved with Hf0.5Zr0.5O2 metal–organic chemical vapor deposition, and obtained by intermediate thermal treatment conditions with low- and high-thermal budget yield in the tetragonal and monoclinic phases, respectively. Furthermore, ferroelectricity was enhanced with the aid of compressive strain, as elucidated by a study using various substrates with different thermal expansion coefficients. Epitaxial films were successfully grown by quenching of a YO1.5–HfO2 solid solution. This epitaxial film revealed that HfO2-related ferroelectrics are good candidates for future integrated application because their ferroelectric properties are comparable to conventional ferroelectric materials.
The 72th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 126, no.9, September 2018
Atsushi SAKUDA
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All-solid-state batteries show great promise as next-generation batteries with high safety, high power, and long life. In addition to high-performance active electrode materials and solid electrolytes, the properties of the electrode–electrolyte interface and the morphology of the electrode layer are important for the development of high-performance batteries. In this review, current research and future prospects for the design of composite electrodes for all-solid-state batteries are outlined. In order to achieve high-performance all-solid-state batteries, composite electrodes must satisfy a number of requirements. The resistance at the electrode–electrolyte interface must be minimal, the contact area between the electrode and solid electrolyte must be maximized, favorable lithium-ion and electron conducting pathways must be formed in the electrode layer. Maintenance of the formed interface is important to enhance cyclability. In this review, some effective approaches to construct better composite electrodes are demonstrated.
The 72th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 126, no.9, September 2018
Kenji SHINOZAKI
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This article reviews the development of new of new oxyfluoride glass-ceramics designed from the viewpoint of the local fluorine structure and crystallization process. Oxyfluoride glasses often form fluoride crystals, but formation of oxyfluoride crystals with a large fraction of fluorine is rare. We successfully fabricated oxyfluoride crystals of BaAlBO3F2 in glass-ceramics through heat-treatment by controlling the local structure of fluorine. The glass showed highly efficient photoluminescence with Eu3+-doping up to 97%. A reason for this is the high fluorine content and structural similarity to the crystal. Laser-induced crystallization was performed on Ni2+-doped glass as a heating source, and lines composed of a single crystal were fabricated. Birefringence images and transmission electron microscope observations indicate that the growth of highly c-axis oriented BaAlBO3F2 crystals follows the laser scanning direction even if it changes. Notably, the direction of the c-axis of BaAlBO3F2 crystals changes gradually at crossing and bending points. The model of ‘‘self-organized homo-epitaxial growth” is proposed for orientations of single crystal line with crossing and bending shapes.
Full Paper
published : vol. 126, no.9, September 2018
Chika MATSUNAGA, You ZHOU, Dai KUSANO, Hideki HYUGA and Kiyoshi HIRAO
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Dielectric breakdown of silicon nitride substrates was evaluated using alternating current voltage. Two different kinds of Si3N4 ceramics with mainly small and large grains were used. Test specimens were prepared from both Si3N4 ceramics with thicknesses of 0.25, 0.32, and 0.64 mm. Average breakdown strength of 0.25, 0.32 and 0.64-mm-thick Si3N4 specimens with small grains were 36.8, 35.1 and 24.9 kV/mm, and those of Si3N4 specimens with large grains were 29.5, 27.1, and 21.4 kV/mm, respectively. At all thicknesses, average breakdown strengths of Si3N4 specimens with small grains were higher than those of Si3N4 specimens with large grains. Average breakdown strength of both Si3N4 ceramics increased with decreasing thickness. Both the top and bottom surfaces of the Si3N4 ceramics with small and large grains had holes of 50 to 250 µm in diameter after breakdown test. Concentric cracks were observed around the holes. Both Si3N4 ceramics with small and large grains showed a tortuous breakdown channel in the direction of thickness after breakdown test. One or both edges of the tortuous breakdown channel had a crater-like structure where the opening was larger than the channel. The channel openings showed two different types of morphologies. One channel opening had concentric deposits around the channel, and other opening showed bare grains and no deposits.
Full Paper
published : vol. 126, no.9, September 2018
Bo FENG, Guangqiang LI, Zhao PAN, Xiaoming HU, Peihai LIU, Yawei LI, Zhu HE and Xi’an FAN
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Bi1−xCuSeO + x Fe (x = 0, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, and 0.12) ceramics have been prepared by mechanical alloying and resistance pressing sintering process, and the synergistic effects of Bi Deficiencies and magnetic Fe doping on the thermoelectric properties and hardness of BiCuSeO ceramics have been investigated in detail. The results indicate that the band gap of the doped sample has narrowed down, which could be confirmed by the infrared absorption spectra. This leads to the dramatical increase of carrier concentration. The corresponding electrical conductivity increases significantly. The Seebeck coefficient decreases, but maintains high values in the high temperature zone. The maximum power factor of 0.38 m Wm−1 K−2 and ZT of 0.76 were obtained for the Bi0.92CuSeO + 8% Fe sample at 873 K, which was ∼1.4 and ∼1.3 times as that of the pristine BiCuSeO. The hardness of pristine BiCuSeO is up to 200.0 HV, and increases greatly with the increase of x for solid solution strengthening.
Full Paper
published : vol. 126, no.9, September 2018
Napatr TALOEY, Yutaka AIKAWA, Osamu KUBOTA and Etsuo SAKAI
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The reaction process between components in mixed systems consisting of silica fume and low-heat Portland cement was studied by using an extended version of the Tomozawa’s equation that considers particle size distributions. In addition, the relationship between the hydration reaction of the cement and the pozzolanic reaction of silica fume was quantitatively analyzed. In order to determine theoretical porosity of the silica fume containing cements, a special equation including the hydration reaction of the mixed system was described and used to quantify cement porosity as a function of time. The comparison of the simulated porosity results with the measured values revealed that the silica fume reactivity was similar to that of alite.
Full Paper
published : vol. 126, no.9, September 2018
Shigeru SUGIYAMA, Yuto TSUCHIYA, Rayan Hamid Elbakhit GASMALLA, Toshihide HORIKAWA, Masahiro KATOH, Yuka ARAI and Masamori AKAMATSU
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A Si/SiC ceramic filter was used to support a structural palladium catalyst in a continuous fixed-bed flow reactor during a reductive decomposition of nitrite. A previous report described the use of non-porous alumina spheres coated with Pd/C, a carbon monolith impregnated with Pd or a structural catalyst consisting of a polyurethane sponge skeleton impregnated with Pd resulted either in negligible activity or a complete stoppage of the flow by increasing the pressure drop in the flow system. The use of a Si/SiC filter impregnated with palladium, however, overcame the demerits and resulted in an 11% conversion of nitrite in 60 min. The use of a Si/SiC filter coated with a char intermediate followed by impregnation with Pd (Pd/C/Si/SiC) resulted in a structural catalyst that enhanced the activity to yield a 33% conversion of nitrite in 60 min. When five Pd/C/Si/SiC structural catalysts were used, however, the complete decomposition was achieved in the same amount of time. Although improvement was previously observed by using an alumina intermediate, use of the char intermediate resulted in a new factor for activity improvement. The characterization results show that it was the affinity between aqueous nitrite and the intermediate rather than palladium dispersion that contributed the most to the improvement of activity.
Full Paper
published : vol. 126, no.9, September 2018
Atsutaka KATO, Masashi NOSE, Mirai YAMAMOTO, Atsushi SAKUDA, Akitoshi HAYASHI and Masahiro TATSUMISAGO
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Sulfide glasses are considered to be promising electrolytes for all-solid-state batteries because of their high ionic conductivities and favorable mechanical properties. In this paper, comprehensive studies of the mechanical properties of sulfide glasses were carried out based on the Li2S–P2S5 system, and we evaluated the effects of changing the glass former and modifier on the elastic moduli and formability of these glasses. Young’s moduli of Li2S–P2S5 glasses increased when the glass former P was replaced with Ge or Si. Moreover, the Young’s moduli of Li2S–P2S5 glasses also increased when substituting S with O. Irrespective of the glass modifier, the Young’s moduli of RxSy–P2S5 glasses (R = Li, Na, Ag, Mg, or Sn) increased with the increase in content of each modifier. The measured Young’s moduli are correlated with the mean atomic volumes of the glasses. We evaluated the formability of the sulfide glasses in powder-compaction tests at room temperature. Sulfide glasses with lower bonding energy, larger free volume, and more isolated structure exhibited higher densification ability. Pugh’s ratio (B/G) (B is the bulk and G the shear modulus) was used to evaluate the ductile-brittle property of materials. The glasses with a larger B/G ratio, meaning higher ductility, tended to show a higher relative density. It is suggested that plastic deformation contributes to the densification. This study will provide valuable results for glass science, and will be useful for developing all-solid-state batteries.
Technical Report
published : vol. 126, no.9, September 2018
Tsukasa KOYAMA, Akihito KUMAMOTO, Koji MATSUI, Yuichi IKUHARA and Hidehiro YOSHIDA
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Grazing incident-angle X-ray diffraction measurement was performed to observe the initial stage of tetragonal-to-monoclinic (t-m) phase transformation in 3 mol % Y2O3-stabilized tetragonal ZrO2 (3Y-TZP) body exposed to hot water at 140°C, i.e. low temperature degradation (LTD) aging treatment. In the 3Y-TZP body after LTD aging for longer than 15 min, small amount of monoclinic phase was detected, while the as-sintered specimen consisted of tetragonal phase. The monoclinic phase was observed only at the surface portion with the thickness of less than about 100 nm. The t-m transformation in 3Y-TZP in hot water initiated from the surface of the specimen.
Note
published : vol. 126, no.9, September 2018
Masanobu KAMITAKAHARA, Shohei TAKAHASHI, Taishi YOKOI, Chihiro INOUE and Koji IOKU
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Suitable support materials for microorganisms are useful for bioreactors to achieve high efficiencies. Spherical porous hydroxyapatite (HA) granules about 5 mm in diameter composed of rod-like particles were prepared through hydrothermal treatment. The granules with and without pores tens of micrometers in size were prepared. These granules were immersed in a suspension containing microorganisms obtained from the soil, and the adhesion of microorganisms on the granules was examined. The adhesion of microorganisms on the surfaces of the HA granules was observed. The total metabolic activity of the microorganisms adhering onto the granule with pores tens of micrometers in size was higher than that adhering onto the granule without such pores. These results suggested that the HA granules had an affinity for microorganisms, and that granules with pores tens of micrometers in size are expected to be support materials for microorganisms.