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The 70th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 126, no.7, July 2018
Tetsuo KISHI
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Surface-tension molding (StM) and localized-laser heating (LLH) techniques were developed for on-chip fabrication of micrometer-size super-hemispherical glass (µ-SSG), which has a truncated spherical shape, and spherical glass. The optical functionalities of these glasses as solid immersion lenses (SILs) and whispering gallery mode (WGM) optical resonators were demonstrated. In the StM method, glass particles on a glassy carbon substrate were heat-treated under an H2/N2 atmosphere and the glass particles were melted and deformed into super-hemispherical shapes that were determined by the wetting property of glass melt on the substrate. The contact angle of the droplet ranged from 120 to 167° depending on the glass composition. We found that the shape of a µ-SSG with a composition of 20Na2O–10CaO–70SiO2 (in mol %) satisfied the optical condition of a SIL and demonstrated super-resolution for µ-SSG fabricated by StM. The LLH technique enables us to make a nearly perfect sphere on a substrate. A micrometer-size Nd3+-doped tellurite glass particle on a transparent substrate was irradiated by a continuous-wave (CW) laser with a wavelength near 810 nm and a power of more than 150 mW, and only the particle was heated and melted into a spherical shape on a transparent substrate at room temperature. The obtained spherical glass had a very smooth spherical surface with high sphericity. The Nd3+-doped microsphere showed WGM resonances to free-space direct pumping of the CW laser with a wavelength of 790–820 nm, and laser emissions were observed with a threshold of a few-milliwatts. Effects of add-on structures, e.g., a terrace or a bubble, on the laser characteristics of the microsphere were also investigated. Both structures acted as an entrance for pumping light and resulted in laser thresholds lower than 1 mW. The terrace structure reduced the emission modes and showed quasi-single mode laser emission. The bubble-containing microsphere laser realized broad excitation spectra due to the modified WGM. These results indicate that a spherical glass with a smooth surface formed from a molten glass droplet on a chip has excellent potential in the field of optics and photonics.
Full Paper
published : vol. 126, no.7, July 2018
Zhiwu JIANG, Peizhong FENG, Xiaohong WANG, Hanzhu ZHANG and Yanan LIU
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MoSi2–ZrB2–SiC ceramics were synthesized using Mo, Zr, Si and B4C powders by self-propagating high-temperature synthesis and densifying by spark plasma sintering. The effects of MoSi2 content on the combustion synthesis process, microstructure, and mechanical properties of the ceramics were investigated. The results showed that combustion synthesis is an unstable mode, spiral combustion. The Gibbs calculations and combustion temperature curves indicate there are two reactions occurring at the same time. The volume fraction of the four different phases and their relative densities were also measured and calculated. Compared to pure MoSi2, the 1.0MoSi2–0.2ZrB2–0.1SiC (M10) ceramic exhibits excellent mechanical properties with its maximum Vickers hardness and fracture toughness being 14.0 GPa and of 5.5 MPa m1/2, respectively. The hardness is in agreement with the rule of mixture. The morphology of indentation cracks reveals that the fracture toughness improves as a result of toughening mechanisms such as crack bridge, crack deflection, and microcracks.
Full Paper
published : vol. 126, no.7, July 2018
Zhiwu JIANG, Peizhong FENG, Xiaohong WANG, Hanzhu ZHANG and Yanan LIU
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Catalytic effect of in-situ formed La2O3 nanoparticles (NPs) on the nitridation of Si powders was studied by X-ray diffraction, field emission-scanning electron microscopy and transmission electron microscope. Thermodynamic analysis and the effects of various processing parameters such as addition of catalyst and firing temperature on the nitridation of Si powders were respectively investigated. The results showed that: 1) The La2O3 NPs significantly promoted the nitridation rate of Si powders, and complete nitridation was achieved at 1623 K by using 1 wt % La2O3 NPs as catalyst 2) Numerous Si3N4 whiskers of 20–300 nm in diameter and tens of microns in length were fabricated in the final product. The Si3N4 whiskers which was believed to be governed by vapor-vapor–solid mechanism were verified to have single-crystal nature, growing along [101] direction.
Full Paper
published : vol. 126, no.7, July 2018
Li LONGBIAO
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In this paper, the damage development and lifetime prediction of fiber-reinforced ceramic-matrix composites subjected to the dwell-fatigue loading at elevated temperatures in oxidizing atmosphere have been investigated using the micromechanics approach. Considering the damage mechanisms of matrix multicracking, fiber/matrix interface debonding, interface wear and interface oxidation and fibers fracture, the damage evolution of the fatigue hysteresis dissipated energy, fatigue hysteresis modulus, fatigue peak strain and broken fibers fraction have been analyzed. The relationships between the fatigue hysteresis-based damage parameters and the internal damage development of matrix multicracking, fiber/matrix interface debonding and sliding and fibers fracture have been established. The experimental dwell-fatigue damage development and fatigue lifetime curves of cross-ply Nicalon™–SiC/MAS and 2D Sylramic™–SiC/SiC composites subjected to the dwell-fatigue loading at elevated temperatures in air and in steam conditions have been predicted.
Full Paper
published : vol. 126, no.7, July 2018
Dieni XIE, Lina YANG, Lingyu LI, Wenjie WANG, Jiachen LIU, Haiyan DU and Xiaoxia HU
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The influences of different fibers and F ions on the formation mechanism of hierarchical structure were investigated. This study was undertaken to better understand how fibers affect the growth of mullite whisker and how the fluoride influences the transition of new phases. In this work, three networks with different fibers and the same active powder were prepared to investigate the effect of fibers on the mullite nucleation. The scanning electron microscope, X-ray diffraction and thermal gravity analysis and differential scanning calorimetry were employed to investigate the morphology, phase and weight changes during the fabrication process. The results showed that mullite fibers did not only decrease the reaction temperature but also promote mullite whiskers to grow on the fiber surface preferentially. Moreover, it was also certified that topaz was not the necessary intermediate to form mullite whisker. The investigation of AlF3 illustrated it departed at about 600°C largely lower than the evaporation temperature of AlF3 to react with Al and Si.
Full Paper
published : vol. 126, no.7, July 2018
Gopal Prasad KHANAL, Sangwook KIM, Minsu KIM, Ichiro FUJII, Shintaro UENO and Satoshi WADA
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BaTiO3 ceramics with grain sizes of 4.7–26.1 µm were fabricated using 100 and 300 nm BaTiO3 powders by employing a two-step sintering (TSS) or conventional one-step sintering (CS) method. Polished and cut BaTiO3 samples were annealed for the recovery and relaxation of mechanical-processing-induced surface damage and lattice strain, and the piezoelectric properties were investigated. TSS-BaTiO3 ceramics annealed at 1000°C for 1 h with a grain size of 4.9 µm exhibited an excellent piezoelectric property of d33 = 529 pC/N, while the d33 value of CS-BaTiO3 ceramics annealed at 1200°C for 8 h with a grain size of 26.1 µm was 272 pC/N. Besides the excellent piezoelectric properties of the fine-grained BaTiO3 ceramics, the performance of the coarse-grained ceramics was higher than previously reported. The observed superior piezoelectric and electromechanical properties in annealed samples despite the increase in grain size suggested that the effect of annealing was more crucial than that of grain size.
Full Paper
published : vol. 126, no.7, July 2018
Minsu KIM, Piyush SAPKOTA, Gopal Prasad KHANAL, Sangwook KIM, Ichiro FUJII, Shintaro UENO, Takahiro TAKEI, Tohru S. SUZUKI, Tetsuo UCHIKOSHI and Satoshi WADA
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We fabricated thick and dense green ceramics consisting of the powders of (Bi0.5Na0.5)TiO3 (BNT) and hexagonal BaTiO3 (BT) with a molar ratio of 0.85:0.15 by electrophoretic deposition (EPD) in the suspension of iso-propanol of 200 ml with the mixed powders of 20 g, and investigated the effect of the ball-milling time and the surfactant (polyethylenimine, PEI) content for the suspension on the deposition weight and density of the green ceramics. When the ball-milling time was changed from 2 to 30 h with the PEI content of 0.2 g, the deposition weight was maximized at the ball-milling time of 15 h while the density monotonically increased with increasing ball-milling time for the EPD process of 1 h. When the PEI content was increased from 0.1 g to 0.2 and 0.3 g at the ball-milling time of 20 h, the deposit weight and density were increased. At the PEI content of 0.3 g, after the first EPD process was carried out and the cathode where the green ceramics were deposited was replaced without changing the suspension, the second green ceramics could be fabricated for the suspension ball-milled for 20 h, but not for the suspension ball-milled for 3 h. These results were explained by the size of the powders and the amount of PEI attached to the powders.
Full Paper
published : vol. 126, no.7, July 2018
Geun-Hyoung LEE
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The morphology of tin oxide (SnO2) crystals, which were formed by thermal evaporation of SnO2/graphite powder mixture, was changed with the ratio of graphite to SnO2 powder in the source material. The synthesis process was performed in air at atmospheric pressure and no catalysts and substrates were used, which makes the process very simple and low cost. At the low ratios of graphite to SnO2 powder in the source material, the SnO2 crystals had a spherical shape with nanometer dimensions. With increasing the ratio of graphite to SnO2 powder, the morphology of SnO2 crystals changed from particle to belt. The belt-shaped SnO2 crystals had the widths in the range of 1.2–3.1 µm and the lengths of several tens of micrometers. X-ray diffraction analysis showed that all the SnO2 crystals had a rutile tetragonal crystal structure. Visible emission band with the wavelength in the range of 400–600 nm was observed in the cathodoluminescence spectra of the SnO2 crystals.
Full Paper
published : vol. 126, no.7, July 2018
Ryo IKESHITA, Tomokatsu HAYAKAWA, Masato ISOGAI, Yuji IWAMOTO, Jean René DUCLÈRE, Fabien RÉMONDIÈRE, Philippe THOMAS and André LECOMTE
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In this study, Eu3+-doped ZrO2 nanophosphors were obtained by a sol–gel method with HNO3 as a catalyst, which led to white powders of small ZrO2 nanocrystals after low temperature calcination. However, exothermic reactions of NO3 were observed during the heat-treatment leading to ZrO2 crystallization. To avoid such reactions and to understand the initial crystallization of ZrO2 doped with Eu3+ ions, we developed an original route in which the xerogel powders were pre-washed in ethanol before immersing them in Eu3+ solution to remove NO3. The effects of heat-treatment on the Eu3+ photoluminescence (PL), crystallization of ZrO2 xerogels, and Eu3+ localization were studied with PL spectroscopy, thermogravimetric analysis and powder X-ray diffraction. It was found that the amorphous ZrO2 xerogels crystallized in a tetragonal structure, with a small amount of monoclinic ZrO2 also being precipitated after longer calcination periods. Finally, the Eu3+ ions on the surface of the ZrO2 xerogels were found to diffuse into higher symmetric Zr substitutional sites in the tetragonal ZrO2 matrix after heat-treatment.
Full Paper
published : vol. 126, no.7, July 2018
Jae-Young SHIN, Jaemin CHA and Bong-Ki RYU
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Lead-free low-melting sealing materials are needed in many fields, especially in organic light-emitting diode and Vacuum-Insulated Glass applications. Accordingly, V2O5–P2O5–TeO2 (VPTe) glass systems have been invested in as lead-free low-melting sealing materials because of their low coefficient of thermal expansions (CTE) and glass transition temperature (Tg). However, these glasses are vulnerable to moisture. This problem can be overcome by adding bismuth oxide to the VPTe glass system. The addition of 9 mol % of Bi2O3 improves water resistance, and causes changes in the Tg increased about 40°C and the CTE decreased about 14 (×10−7/K) that may reflect the structural changes. As a result, the glasses, which are doped with Bi2O3, maintain their low-temperature properties, and they are improved their water resistance about 1.2 × 10−5 (g/cm2/min).
Full Paper
published : vol. 126, no.7, July 2018
Chiharu AKATSUKA, Tsuyoshi HONMA and Takayuki KOMATSU
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Crystallization behavior of bulk Na2FeP2O7 glass produced by a melt-quenching method was examined. The valence state of iron is 76% Fe2+ in glass matrix by using Fe(II)O and carbon crucible during glass melting. After mirror polishing crystallization was performed. Surface crystallization of triclinic Na2FeP2O7 was confirmed by heat-treatment of the bulk sample in a nitrogen atmosphere. The outermost surface of crystallized sample have no crystal orientation but, strong (122) and (133) orientation was confirmed by X-ray diffraction of surface crystalized glass obtained after polish 10 µm thick. This technique may be effective to control ionic conductive channel in phosphate derived active material for secondary batteries.
Full Paper
published : vol. 126, no.7, July 2018
Yusaku SUTO, Yuta FUJII, Akira MIURA, Nataly Carolina ROSERO-NAVARRO, Mikio HIGUCHI and Kiyoharu TADANAGA
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Submicron-sized NiPS3 particles were synthesized by heating fine Ni powder (&lt 100 nm), red phosphorus, and sulfur at 673 K for 48 h, and their electrochemical properties as cathodes in sulfide-based all-solid-state lithium batteries were investigated using discharge/charge measurements, X-ray diffraction (XRD) measurements, electrochemical impedance spectroscopy, and X-ray absorption near-edge structure spectroscopy (XANES). Batteries using submicron-sized NiPS3 as a cathode active material exhibited a 10th discharge capacity of 147 mAh g−1, which was larger than that obtained with 10–100 micron-sized NiPS3 (∼90 mAh g−1). The XRD patterns of the composite cathode before and after discharge/charge suggested that Li4P2S6 was formed irreversibly (2NiPS3 + 4Li+ + 4e → Li4P2S6 + 2Ni), and this irreversible reaction would reduce the capacity of the cathode. The XANES spectra suggested the oxidation/reduction of Ni during discharge–charge cycles, but the change in the spectra during the cycles was considerably small if one assumed the oxidation/reduction of Ni2+/Ni0.
Full Paper
published : vol. 126, no.7, July 2018
Isao KAGOMIYA, Yuki SUGIYAMA and Ken-ichi KAKIMOTO
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We propose Pd–Al2O3 matrix composites as hydrogen separators instead of pure Pd films. The Pd–Al2O3 is lower cost, more stable at higher temperatures as well as higher mechanical strength. The plasma electronic sintering method was effective for preparing 25(30) vol % Pd–Al2O3. The hydrogen permeation flux (JH2) or total electrical conductivity (σt) of the 30 vol % Pd[with polyvinylpyrrolidinone (PVP)]–Al2O3 was one order of magnitude higher than that of the 25 vol % Pd(with PVP)–Al2O3, suggesting percolation conductions of 30 vol % Pd. The 30 vol % Pd(with no PVP)–Al2O3 was further higher than that of the 30 vol % Pd(with PVP)–Al2O3, because of connections among larger Pd grains for the sample with no PVP. The σt or JH2 of the 30 vol % Pd(with no PVP)–Al2O3 was one magnitude lower than that of Pd films.
Full Paper
published : vol. 126, no.7, July 2018
Michiyuki YOSHIDA, Simone FALCO and Richard I. TODD
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Flash sintering is a newly developed technique to quickly densify conductive ceramics in the presence of an electric field. At a critical combination of field and temperature, densification takes place in a few seconds. This paper investigates the electrical resistivity during flash sintering of 3YSZ by the four-terminal method in combination with numerical modelling of electrical heating and temperature distributions. Densification rates were similar to those observed previously in specimens rapidly heated by methods not involving direct electrical heating. Temperature gradients caused by heat loss from the surface and non-uniform electrical heating led to differential sintering, specimen distortion and non-uniform grain size. The four point measurements revealed significant contact resistance at the power supply electrodes and allowed accurate measurement of the resistivity under the high current conditions of flash sintering. The specimen resistivity was lower for a given temperature under high current conditions and this was attributed to electronic conduction. Concurrent sintering led to a progressive reduction of resistivity during heating causing an increase in the apparent activation energy for electrical conduction. When the effect of sintering on resistivity was accounted for, the onset conditions for the “flash event” were accurately predicted on the basis of thermal runaway.
Note
published : vol. 126, no.7, July 2018
Natsuumi TAKAHASHI, Masanori NAGAO, Akira MIURA, Satoshi WATAUCHI, Kiyoharu TADANAGA, Yoshihiko TAKANO and Isao TANAKA
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The layered compound Bi2(O,F)S2 is synthesized by NaF treatment. Heat treatment of Bi2OS2 with different amounts of NaF powder at 400°C produces Bi2(O,F)S2 superconductors. NaF is low-cost and stable fluorination sources when it is compared with other sources. NaF treatment increased the a-axis of Bi2(O,F)S2. Maximum superconducting transition temperature of obtained Bi2(O,F)S2 is 4.7 K.
Express Letter
published :
Miyuri TERASAWA, Tsuyoshi HONMA, Takayuki KOMATSU
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Optically transparent and electrically conductive glass-ceramics have been successfully prepared from 1Na2O–0.5MnO–0.5FeO–1SiO2 (Na2Mn0.5Fe0.5SiO4) glass by heat-treatment. Crystallization tendency was sensitive to the valence state of transition metal oxide. The as-quenched glass melted at 1400°C for 15 min, exhibited two exothermic peaks in the differential thermal analysis. Optically transparent glass-ceramics obtained at 493°C for 3 h showed simple X-ray diffraction pattern, which could be assigned to a cubic phase with a lattice constant of 0.74511 nm. A monoclinic Na2MSiO4 (M = Mn, Fe) phase appeared with the heat treatment above 610°C, suggesting that the crystal phase precipitated in the low temperature region was thermodynamically metastable. The transparent glass-ceramics showed an order of magnitude higher electrical conductivity than that of glass and the monoclinic phase.