最新コンテンツ

Full Paper
published : vol. 126, no.12, December 2018
Masaya FUJIOKA, Naoki KUBO, Masanori NAGAO, Robin MSISKA, Naoki SHIRAKAWA, Satoshi DEMURA, Hideaki SAKATA, Hideo KAIJU and Junji NISHII
MORE
Ag+ ions were intercalated into the transition-metal dichalcogenide TaS2 using the recently developed method of proton-driven ion introduction. Single-crystalline Ag0.58TaS2 with a stage 1 structure and Ag0.21TaS2 with a stage 2 structure were prepared using this method. The stage 2 structure of Ag0.21TaS2 was formed by exploiting the differences in ion diffusion properties among the polytypes of TaS2. Furthermore, our intercalation method can forcibly insert Ag+ ions into interlayers by applying a high voltage at low temperature (100°C), resulting in the formation of thermodynamically metastable phase. Such a synthesis approach offers a potential route for diversifying intercalation compounds with different stage structures. The first observations of superconductivity in AgxTaS2 were demonstrated in this study. The onset of superconductivity of AgxTaS2 was estimated to be 0.4 and 1.7 K in the samples with x = 0.58 and x = 0.21, respectively. Some anomalies, which were speculatively attributed to charge density wave order, were confirmed in the resistivity measurements of AgxTaS2. The results suggested that the anomalies were closely correlated with the superconducting transition temperature.
The 72th CerSJ Awards for Academic Achievements in Ceramic Science and Technology: Review
Special Article
published : vol. 126, no.12, December 2018
Hideki HYUGA
MORE
This study reviews the development of fabrication processes for silicon nitride ceramics with excellent mechanical properties, such as high fracture strength and fracture toughness. Silicon nitride ceramics with high wear resistance and thermal conductivity have been produced by tuning their composition and utilizing highly efficient processing techniques. The nitridation behavior of silicon powder in the presence of Zr compounds has been studied in order to assess the nitridation enhancement effect of zirconium during formation of reaction bonded silicon nitride. Thermogravimetric analysis has revealed that the addition of ZrO2 to Si powder reduces the temperature of the main nitridation reaction. It is possible to produce reaction-bonded silicon nitride using a rapid nitridation technique with a heating rate of over 5 °C/min, which is 80 times higher than that for the conventional reaction bonding process. A nitridation enhancement effect has also been observed with the addition of some rare-earth oxides. The reaction bonding process has been used to fabricate high-thermal-conductivity silicon nitride ceramics with a relatively short processing time. Si3N4/carbon fiber composites have been developed using randomly dispersed high-tensile-modulus carbon fibers. The aligned silicon nitride grains and short carbon fibers in the composites result in both high fracture strength and toughness and a low friction coefficient under dry and water sliding conditions. The mechanical properties of the composites are anisotropic with respect to the grain alignment, with both strength and toughness being highest parallel to the extrusion direction. In this direction, the seeded specimen, with both silicon nitride grains and carbon fibers aligned, has higher fracture toughness and higher fracture strength than those of the non-seeded specimen, with only fibers aligned.
Full Paper
published : vol. 126, no.12, December 2018
Feng WANG, Xiangcheng LI, Pingan CHEN, Girish Madhav KALE and Boquan ZHU
MORE
In this paper, the morphology of CA6 was adjusted by changing the particle sizes of alumina powders (D50 = 7.26, 5.33 and 2.37 µm), and the effect of this on the thermo-mechanical properties of corundum based high temperature composites was investigated. The results indicated that when the alumina particle size was decreased from 7.26 to 2.37 µm, the morphology of calcium hexaluminate (CA6) transformed from equiaxial to platy shape. The microstructure changes of CA6 may be due to differences in CA6 nuclei numbers and the contact area between alumina and calcium dialuminate. This transformation process can proceed without liquid. Because of the transformation of the CA6 morphology, the hot modulus of rupture and residual cold modulus of rupture of corundum composites fired at 1600°C increased by 143 and 192%, respectively. The loop areas of in-situ elastic modulus also increased by 20%. The fracture ways of composites were transformed from intergranular to transgranular. Therefore, corundum-based composites with excellent properties including room temperature and high temperature properties can be obtained by adjusting the microstructure of CA6.
Full Paper
published : vol. 126, no.12, December 2018
Yusuf TIJJANI, Faizah MOHD YASIN, Mohd Halim S. ISMAIL and Azmah Hanim MOHAMED ARIFF
MORE
Monolithic refractory ceramic materials have outstanding heat resistant properties at elevated temperature and possess high stiffness but are generally brittle. To toughen a typical matrix of natural traditional monolithic quartz ceramic, functionalized multiwalled carbon nanotubes (FMWNTs) were added to the matrix as filler for the first time and processed by a wet method using conventional powder processing; involving consolidation by pressureless sintering technique, to obtain the novel nanocomposite. The effect of the varied amount of carbon nanotubes (0.01, 0.1, 0.5, 1 & 4 wt.%) on densification and mechanical properties of the composites were studied. 1 wt.% FMWNTs/quartz (QF-1) possesses moderate tensile and compressive strengths, modest Young’s modulus and toughness, and high fracture strain in tension. Good combination of strengths and toughness in QF-1 nanocomposite, suggest the possibility of using 1 wt.% FMWNTs as an additive in the preparation of silica/silica-based refractory mixture for optimum mechanical properties.
Full Paper
published : vol. 126, no.12, December 2018
Kohei FUKUMI, Naoyuki KITAMURA, Hiromitsu KOZUKA and Shinji KOHARA
MORE
The coordination structure around Bi atoms has been studied in Li2O–Bi2O3–B2O3 glasses by X-ray diffraction method. It was found that Bi atoms were coordinated by five or six oxygen atoms. The number of Bi atoms around a Bi atom through Bi–O–Bi bonds increased with an increase in Bi/O ratio. It was inferred that BiOx polyhedra were clumped in the glasses, although BiOx polyhedra were more clumped in Li2O–Bi2O3–B2O3 glasses than in Bi2O3–B2O3 glasses.
Full Paper
published : vol. 126, no.12, December 2018
Masahiro SHIMIZU, Shohei HOSOYA, Takeyuki KATO, Jun MATSUOKA, Hiroshi KATO, Masayuki NISHI, Kazuyuki HIRAO, Yasuhiko SHIMOTSUMA and Kiyotaka MIURA
MORE
The Soret effect or thermodiffusion is temperature-gradient-driven diffusion in a multicomponent system. A physical model to accurately predict the Soret coefficient of oxide melts has not yet been proposed. Here, for the first time, we report a quantitative comparison between experiment and theory concerning the Soret coefficient in binary glass-forming oxide melts. We measured the Soret coefficient of 11Na2O–89B2O3 (mol %) after 90- and 180-h heat treatment under a temperature gradient near 1200 K and estimated the Soret coefficient for the steady state. We used a vertical furnace to reduce the effect of natural convection on the Soret effect by heating the sample from the top side. The Soret coefficient estimated for the steady state near 1200 K was 5.12 × 10−3 K−1, whereas that obtained by the adjusted Kempers model, in which we adjusted the original Kempers thermodynamic model for binary oxide melts, was 6.09 × 10−3 K−1. The sign and order of magnitude were consistent, which suggests that the adjusted Kempers model is a promising model to explain the Soret effect and that the equilibrium thermodynamic parameters of partial molar volume, partial molar enthalpy, and chemical potential are important factors in the phenomenon.
Full Paper
published : vol. 126, no.12, December 2018
Yo YAMAMOTO, Withanage Isuru Udakara WITHANAGE, Takahiro TAKEI, Sayaka YANAGIDA, Nobuhiro KUMADA and Hisanori YAMANE
MORE
Hydrothermal reactions of a hydrated sodium bismuth oxide, NaBiO3·1.4H2O were performed with transition-metal salts MCl2, M(NO3)2 and MSO4 (M: Co, Ni, Cu). The common identified products from nitrate and chloride solutions were (Bi,M)2O2(OH)NO3 and (Bi,M)OCl, respectively and every product contained a small amount of unknown impurity phases. Various unknown phases also appeared in the products from the sulfate solutions, and no common crystalline phases were observed. During the course of these hydrothermal reactions, a new bismuth sulfate, BiOHSO4 was found by using a H2SO4 solution, and its crystal structure was clarified by using single-crystal X-ray diffraction data. No photocatalytic activity for the phenol degradation of BiOHSO4 was observed under ultraviolet and visible light irradiation.
Technical Report
published : vol. 126, no.12, December 2018
Tetsufumi KOMUKAI and Masato KAKIHANA
MORE
In this study, the particle size control of (Ba,Sr)2SiO4:Eu2+, a green-emitting phosphor, was evaluated via reduction firing using various flux agents. Phosphor particles grown to ∼10–50 µm in diameter and having high internal quantum efficiency of 77.3% were obtained via reduction firing at 1473 K using 10 wt % BaCl2 as a flux. To reduce the particle size, the reduction firing temperature was lowered to 1223 and 1273 K respectively and the amount of BaCl2 was increased to 20 wt %. The diameter of phosphor particles significantly reduced; however, fibrous fine particles were formed and the internal quantum efficiency decreased to 60.7%. Using BaCl2–KCl and BaCl2–CsCl mixed fluxes to increase the amount of molten flux while suppressing the dissolution of (Ba,Sr)2SiO4 into the molten flux, a phosphor with fewer fibrous fine particles was obtained. In particular, the phosphor obtained via reduction firing at 1273 K using a 10 wt % BaCl2–10 wt % CsCl mixed flux had an improved internal quantum efficiency of 73.4%. The ionic radius of Cs+ (0.167 nm for CN = 6) is considerably larger than that of Ba2+ (0.135 nm for CN = 6) and Sr2+ (0.118 nm for CN = 6); therefore, high-quality host crystals with few defects could be possibly obtained without the substitution of Cs+ for Ba2+ and Sr2+ during reduction firing. To control the particle size of phosphor while maintaining a high internal quantum efficiency, the solubility of the host crystal into the molten flux as well as the substitution of the cation between the flux and host must be considered.
Note
published : vol. 126, no.12, December 2018
Nobuaki TERAKADO, Yuudai YOKOCHI, Kouki WATANABE, Yoshihiro TAKAHASHI and Takumi FUJIWARA
MORE
Materials with high thermal conductivity have attracted considerable attention for thermal management of electronic devices. Therefore, focusing on formability and anisotropic heat transfer, we fabricated glass-ceramics containing the spin-chain compound SrCuO2 and demonstrated its high thermal conductivity in the previous work, where SrCuO2 is known to exhibit high thermal conductivity owing to the presence of quasiparticles, i.e., spinons. In this study, we attempt to confirm the presence of spinons by analyzing temperature dependence of specific heat and investigate relationship between spinons and thermal properties.
The 72th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 126, no.10, October 2018
Kotaro FUJII and Masatomo YASHIMA
MORE
This article provides the first critical review on the discovery and development of BaNdInO4. Exploring a new structure family of ionic conductors is an important task to develop ceramic ionic conductors. Since some A2BO4 compositions exhibit high oxide-ion conductivities, we investigated ABCO4 compositions to explore new oxide-ion conductors with A/B/C cation-ordered structures. Here A, B and C are cations [ionic radii: r(A) ≥ r(B) ≥ r(C)]. In 2014, we discovered a new material BaNdInO4 which belongs to a new structure family of perovskite-related structures. This BaNdInO4-type structure (monoclinic, P21/c) consists of alternative stacking of the A rare earth oxide unit and perovskite unit with a b c tilt system. We also discovered new materials BaRInO4 (R = Sm, Y, Ho, Er, Yb) having the BaNdInO4-type structure, and report their lattice parameters and anisotropic chemical expansion. Electrical conductivity of BaNdInO4 was higher than those of BaRInO4 (R = Sm, Y, Er). Oxide-ion conduction was dominant for BaNdInO4 in the P(O2) region from 3.8 × 10−22 to 5.5 × 10−9 atm at 858°C. Oxide-ion conductivities of Ba1.1Nd0.9InO3.95, BaSr0.1Nd0.9InO3.95 and BaCa0.2Nd0.8InO3.9 were higher than that of BaNdInO4. Structure analyses of Ba1.1Nd0.9InO3.95 and BaSr0.1Nd0.9InO3.95 indicated that the excess Ba and doped Sr cations were partially substituted for Nd cation and that there existed oxygen vacancies, leading to the increase of the carrier concentration and higher oxide-ion conductivity. Following the discovery of BaNdInO4, BaRScO4 (R = Nd, Eu, Y, Yb) and SrYbInO4 were reported as new ABCO4 materials. BaYScO4 and BaYbScO4 have the BaNdInO4-type structure. BaNdScO4 and BaEuScO4 crystallize into the space group Cmcm, which has a higher symmetry than P21/c for BaNdInO4. SrYbInO4 is the first example of pure oxide-ion conductors with CaFe2O4-type structure. Further investigations of ABCO4 compositions and BaNdInO4 related materials will lead to development of materials science and solid state ionics.
Full Paper
published : vol. 126, no.10, October 2018
Jang-Hoon HA, Sujin LEE, Syed Zaighum Abbas BUKHARI, Jongman LEE, In-Hyuck SONG, Seung Jun LEE and Jaeho CHOI
MORE
Porous ceramic membranes have received increasing attention for decades. Due to their excellent thermal and chemical properties. Because their pore sizes of as-sintered silicon carbide supports are within the microfiltration range, silicon carbide membranes have been actively investigated by many researchers and industries. For example, silicon carbide supports by themselves (average pore size of 1–10 µm) and microfiltration layer-coated silicon carbide supports (average pore size of 0.1–1 µm) can be easily prepared. However, there is insufficient data concerning the combination of ultrafiltration layer-coated silicon carbide supports (average pore size of below 0.1 µm). Therefore, the authors first prepared typical microfiltration layer-coated silicon carbide supports, and then deposited ultrafiltration layers on them. Furthermore, the authors characterized the membrane properties of the ultrafiltration layer-coated silicon carbide supports. In addition, the possibility of reducing the average pore size of microfiltration layer-coated silicon carbide supports below 0.1 µm was investigated, and improving the water permeability of ultrafiltration layer-coated silicon carbide supports by controlling processing conditions such as the heat-treatment temperature, dip-coating conditions, and composition of the alumina coating slurry was explored.
Full Paper
published : vol. 126, no.10, October 2018
Yoshiteru ITAGAKI, Jian CUI, Naoto ITO, Hiromichi AONO and Hidenori YAHIRO
MORE
Samaria-doped ceria, (SmO1.5)0.2(CeO2)0.8 (SDC), containing nickel (Ni) was prepared as the anode of solid oxide fuel cell fueled with 6% ammonia (NH3). The Ni-free SDC powders prepared by the reverse co-precipitation method exhibited poor catalytic activities for NH3 decomposition in 6% NH3/Ar. Impregnation of Ni onto the SDC powders significantly enhanced its catalytic activity. The catalytic activity was highest at 10 wt % Ni–SDC, but it decreased with an increase in the Ni content. Contrary to expectation, the anodic performances were similar between 10 and 40 wt % of Ni loading and the highest maximum power densities were 98.8 and 96.5 mW·cm−2 at 900°C, respectively. Impedance analysis of the anodes revealed that the anodic performance was rate-controlled by the similar process in 4%H2 fuel and that was electrochemical oxidation and diffusion processes.

Special Call for Papers

Specially Scheduled Issue “Cutting edge researches on electroceramics, 2018”PDF
Posted Deadline:March 31, 2019
Posted schedule No.:2019. October issue
Specially Scheduled Issue “the 57th Symposium on Basic Science of Ceramics”PDF
Posted Deadline:March 31, 2019
Posted schedule No.:2019. October issue