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Feature: Porous Ceramics: From Innovative Processing to Advanced Applications and Functionalities
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published : vol. 128, no.9, September 2020
Akihiro SHIMAMURA, Manabu FUKUSHIMA, Naoki KONDO and Mikinori HOTTA
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Direct foaming is one of the most widely used fabrication processes for macro porous ceramics. We previously reported on direct foaming using phenolic resin as both the thermal foaming agent and the binder. This study investigates the effect of the heating rate during thermal foaming on the porous structure of an alumina/resin foamed body. In this process, a ceramic compact is prepared by mixing alumina powder with phenolic resin powder, and it is followed by press molding. The ceramic compact is then heated at different heating rates of up to the thermal foaming temperature of the phenolic resin. The effect of the heating rate on the thermal foaming behavior of the ceramic compact is examined using differential scanning calorimeter-thermogravimetry. After thermal foaming, the effect of heating rate on the porous structure of the foamed body is characterized via morphological observations using a scanning electron microscope, optical microscope imaging, porosity measurements, and pore size measurements. The foamed body is finally debound and sintered to obtain a sintered porous alumina.
Feature: Porous Ceramics: From Innovative Processing to Advanced Applications and Functionalities
Full Paper
published : vol. 128, no.9, September 2020
Manabu FUKUSHIMA and Yu-ichi YOSHIZAWA
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Thermal insulators were fabricated by freezing and drying gelatin gels containing calcined kaolinite with various amounts of hexagonal alumina platelets, followed by sintering. Unidirectional macroscopic porosity was created via the freezing process, with accompanying pore walls composed of the platelet grains microscopically longitudinally oriented. The relationship among different platelet contents, microstructure, compressive strength, and thermal conductivity was examined. Varying the platelet content in the initial gels enabled effective control of the porosity and properties of the resultant insulators. The use of a gel with a high content of platelets led to a larger porosity because of reduced shrinkage during sintering, resulting in decreased thermal conductivity and strength. The overall morphology and properties of the insulators prepared by gelation–freezing were investigated.
Feature: Porous Ceramics: From Innovative Processing to Advanced Applications and Functionalities
Full Paper
published : vol. 128, no.9, September 2020
Hua CHENG, Jian-Feng YANG and Nan-Long ZHANG
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With phenolic resin as carbon source, ethylene glycol as solvent and pore-forming agent, and silicon monoxide as pore-forming agent and silicon source, a kind of light hierarchical porous silicon carbide (SiC) ceramics with adjustable pores was prepared by gelcasting, carbonization and carbothermal reduction. With the addition of silicon monoxide in the green body from 13 to 49%, the porosities increased from 66 to 89%, the densities and thermal conductivity are as low as 0.36 g·cm−3 and 0.29 W·m−1·K−1. The macropores are mainly determined by the addition of silica particle size, which increases from 9.2 to 39.5%, while the micropores and mesopores, ranging from 56.8 to 49.5%, are mainly determined by the pyrolysis of resin carbon source. When the porosity of porous SiC is 75%, the compressive strength of 7.83 MPa can be reached. The prepared porous SiC ceramics possessed light, good thermal insulation and other properties, which can be further improved by changing the shape and size of the added SiO particles. In addition, different from using polycarbosilane as preceramic polymer, the porous SiC ceramics with complex shape and uniform microstructure can be prepared via gelcasting, which will reduce the production costs and broaden its application.
Feature: Porous Ceramics: From Innovative Processing to Advanced Applications and Functionalities
Full Paper
published : vol. 128, no.9, September 2020
Marco PELANCONI, Ehsan REZAEI and Alberto ORTONA
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We present in this work a review on the developments of computer aided design (CAD) for ceramic cellular architectures. From the first attempts in using CAD to explain by finite element modelling the behaviour of ceramic foams, this practice became a fundamental step with the newcomer ceramic additive manufacturing (AM) technique. Suddenly AM allowed the realization of such complex structures. End users requirements in several industrial fields could be satisfied thanks to the combination of CAD, simulation and AM. As structures became more complex, new tools were developed in order to solve multi-physical tasks. We first developed a tool to generate and crop periodic and random architectures. Digitally connecting the boundary struts allowed then to increase their mechanical strength. Further tools were developed to obtain periodic and random architectures with variable porosity and pore sizes. We also present an innovative tool, inspired from the atoms patterns within the grain boundaries, which allows to create a solution of continuity between two different periodic architectures. The final chapter presents a set of real components which were produced and tested in different industrial fields.
Feature: Porous Ceramics: From Innovative Processing to Advanced Applications and Functionalities
Full Paper
published : vol. 128, no.9, September 2020
Wai Kian TAN, Keita TSUZUKI, Atsushi YOKOI, Go KAWAMURA, Atsunori MATSUDA and Hiroyuki MUTO
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Porous ceramics possess many unique properties that are used for multifunctional applications. This study reports on a feasible formation of Al2O3–SiO2 composite ceramics using an electrostatic assembly technique without any use of pore former. Homogeneously SiO2-particles-decorated Al2O3 composites were first obtained using electrostatic assembly. The amount of SiO2 added was varied at 12 and 40 vol.%. The Al2O3–SiO2 composite powders were then pressed into green bodies and sintered at different temperatures from 1300 to 1600 °C. The morphologies, open porosity and crystallinity as well as the mechanical properties of the Al2O3–SiO2 composite ceramics were systematically characterized. The microstructural observation demonstrated that the porosity was altered by changing the amount of SiO2 added as well as sintering temperature. A mullite phase was observed after sintering at 1600 °C. The elastic modulus and yield stress were found to correlate with the open porosity of the Al2O3–SiO2 composites.
Feature: Porous Ceramics: From Innovative Processing to Advanced Applications and Functionalities
Full Paper
published : vol. 128, no.9, September 2020
Zhuguo LI and Ko IKEDA
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Besides natural gypsum, byproduct gypsum is always discharged from the desulfurization process in power plants and the neutralization process in chemical industry. In this study, a porous lightweight material was studied in order to develop a fundamental technology for recycling byproduct gypsum. First of all, several kinds of byproduct gypsums were converted to hemihydrate type gypsums by heating at 150 °C overnight, and their bending strengths were tested. Then, as next step, using one of the hemihydrates, porous materials were prepared at ambient temperature by the aid of an organic foaming agent and water. Two types of lightweight materials were obtained through adjusting the amounts of water and the forming agent. One is ordinary porous monolith having 96–183 kg/m3 of bulk density and 0.043–0.069 W/m K of thermal conductivity. Another is granule, of which bulk density was 69–137 kg/m3 and thermal conductivity was 0.047–0.050 W/m K. Hence, it is concluded that even using byproduct gypsum, high-performance porous heat-insulators could be produced, if the counterpart nonporous monolith has over 3 MPa of bending strength.
Feature: Porous Ceramics: From Innovative Processing to Advanced Applications and Functionalities
Technical Report
published : vol. 128, no.9, September 2020
Shuko AKAMINE
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Conventional industrial thermal insulating materials have a porous structure and provide resistance to thermal conduction. However, this structure permits heat transfer through radiation. Hence, they exhibit high thermal conductivity at temperatures higher than 1000 °C. To achieve high total-thermal-insulation efficiency, we recently developed new insulating materials, called THERMOSCATTTM, which greatly suppress radiation heat transfer. Their thermal conductivity was measured to be less than 0.3 W/(m·K) at 1500 °C. These insulating materials consist of porous MgAl2O4 ceramics having 1–5 µm pores which restrain heat transfer through radiation, which was consistent with the Mie scattering theory. From the thermal emissivity estimated from reflectance measurements, the porous MgAl2O4 ceramics had near-zero hemispherical spectral emissivity values in the wavelength range of 0.35–5 µm. Mixing these powdered porous MgAl2O4 ceramics with a conventional commercial insulating castable ceramics is shown to successfully reduce heat transfer through radiative Mie scattering. This report describes the experimental result of the powdered porous MgAl2O4 ceramics mixed into the commercial insulating castable.
The 73rd CerSJ Awards for Academci Achievements in Ceramic Science and Technology: Review
Special Article
published : vol. 128, no.9, September 2020
Takashi TANIGUCHI
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Boron nitride (BN) is a III–V compound positioned in the upper row of the Periodic Table, and is used in a diverse range of applications. Hexagonal boron nitride (hBN) is known for practical applications such as heat insulation and heat-resistant materials. On the other hand, cubic boron nitride (cBN), which has a sphalerite crystal structure similar to diamond, can be obtained by converting hBN to a high density phase under high pressure and high temperature. Recent some activities studied on BN polymorphic phase transformation and synthesis of high purity cBN as well as hBN single crystals resulted in some new trends such as super-hard materials, wide-band gap materials with deep ultraviolet emission nature and substrate for 2D materials.
The 74th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 128, no.9, September 2020
Kenji OKADA
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This review briefly describes recent advances on the fabrication methods affording macroscopically controlled orientation and aggregation of one-dimensional (1D) metal hydroxide nanomaterials and the structuralization-driven functional applications. A special attention is focused on the functionalization based on two approaches: 1) superhydrophobic adhesive surface, and monolithic cation-exchangers and photocatalysts by controlled orientation and aggregation of titanate nanotubes, 2) a supported catalyst, electrothermal sensor and switchable fluorescence film by the structuralization of metal organic framework (MOF) derived from orientation/aggregation-controlled copper hydroxide nanotubes/nanobelts.
Full Paper
published : vol. 128, no.9, September 2020
Hirotaka SONE, Shuhei YOSHIDA, Manabu TANAKA and Takayuki WATANABE
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Synthesis of lithium nickel manganese oxide (LNMO) nanoparticles was performed by induction thermal plasmas. The change in the crystal structure of the LNMO nanoparticles was confirmed with the substitution of a part of Mn of the lithium nickel oxide nanoparticles with Ni. The formation mechanism of the nanoparticle crystal structure was investigated based on nucleation theory and thermodynamic considerations. The synthesized LNMO nanoparticles formed two crystal structures of cubic rock salt type Li0.4Ni1.2Mn0.4O2 (space group Fm3m) of non-stoichiometry and cubic spinel type LiNi0.5Mn1.5O4 (space group Fd3m). The cubic rock salt structure nanoparticles are easily formed when the molar ratio of Mn and (Ni + Mn) is taken as 0.25. The cubic spinel structure nanoparticles are easily formed when the Mn/(Ni + Mn) molar ratio is 0.875. The formation mechanism of the LNMO was generated by condensation of MnO and Li2O after nucleation of NiO. This report investigated the effect of the crystal structure and formation mechanism of the LNMO nanoparticles by varying the molar ratio of Ni and Mn formed by induction thermal plasma.
Full Paper
published : vol. 128, no.9, September 2020
Fumika TSUJI, So YUBUCHI, Atsushi SAKUDA, Masahiro TATSUMISAGO and Akitoshi HAYASHI
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Solid electrolytes have become important materials for improving the performance of next-generation all-solid-state sodium rechargeable batteries. Therefore, sodium vacancy doping for Na3SbS4 electrolytes was performed by partially substituting Cl for S. Na3−xSbS4−xClx electrolytes were prepared using a mechanochemical process and consecutive heat treatment. The structures, ionic conductivities, and air safety of the prepared Na3−xSbS4−xClx electrolytes were evaluated via X-ray diffraction and impedance, air stability, and electrochemical tests. The Na2.9375SbS3.9375Cl0.0625 electrolyte showed a higher room-temperature ionic conductivity of 2.9 × 10−3 S cm−1 than that of the Na3SbS4 electrolyte. An all-solid-state Na15Sn4/Na2.9375SbS3.9375Cl0.0625/TiS2 cell showed a reversible capacity of approximately 100 mA h g−1 at room temperature. Thus, the Na2.9375SbS3.9375Cl0.0625 solid electrolyte has the potential for application as a solid electrolyte in all-solid-state batteries.
Technical Report
published : vol. 128, no.9, September 2020
Taro ASAHI, Riho KISHIDA, Susumu NAKAYAMA and Noriyuki WADA
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Herein, coloration in sodium borate glasses containing sulfur were investigated and sulfur species in the glasses were determined using ultraviolet–visible (UV–vis), Raman, and fluorescence spectroscopy. Sample coloration varied from blue to brown and depended on alkali content and glass matrix composition. Using UV–vis spectroscopy, several absorption bands were detected at 280, 380, and 580 nm. It was anticipated that the sulfur species, such as S2, S2, and S3, will be formed in the glass samples and will influence sample coloration. Raman spectroscopy suggested that the absorption band at approximately 580 nm was due to the S3 anion species, whereas fluorescence spectroscopy suggested that the absorption band at approximately 380 nm was due to S2 anion species. The ratio of these sulfur anion species varied with matrix glass compositions and had a strong effect on the sample coloration. Herein, the origin of these color centers is discussed from the viewpoint of the redox of the melt and borate glass network.
Note
published : vol. 128, no.9, September 2020
Kei SHIMAMOTO, Atsushi SAKUDA, Akitoshi HAYASHI and Masahiro TATSUMISAGO
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Composite quasi-solid electrolytes comprising Li3PS4 (LPS) glass and various organic carbonates were prepared, and the effects of these carbonates on the glass were investigated. Compared to LPS glass, the conductivity decreased for composites with highly dielectric cyclic carbonates and increased slightly for composites with a poorly dielectric linear carbonate. Scanning electron microscopy observations indicated that the addition of a poorly dielectric linear carbonate slightly improved the formability of LPS glass.
Note
published : vol. 128, no.9, September 2020
Koki CHOJIN, Masahiro SHIMIZU, Yasuhiko SHIMOTSUMA and Kiyotaka MIURA
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In glasses, the cooling-rate dependence of thermal conductivity has not been sufficiently studied and has not been microscopically interpreted. In this study, we investigate the cooling-rate dependence of thermal conductivity in 33.3Na2O–66.7SiO2 (mol.%) glasses with molecular dynamics (MD) simulations. We simulated the glasses by changing the cooling rate in the range of 0.01 to 10 K/ps, and then we calculated thermal conductivity using non-equilibrium MD. The calculated thermal conductivity was approximately 1.58 W/mK, which shows good agreement with the experimental value (1.02 W/mK). When the cooling rate was decreased, the thermal conductivity monotonically increased. To investigate the correlation between the thermal conductivity and the change in the glass structure, we defined the degree of relaxation using the Qn distribution and checked the correlation. Consequently, a clear positive correlation with a correlation coefficient of 0.492 is obtained, suggesting that the dependence of the thermal conductivity on the cooling rate is attributable to the rearrangement of the medium-range structure.
Note
published : vol. 128, no.9, September 2020
Md SAIDUZZAMAN, Khandaker Monower HOSSAIN, Nobuhiro KUMADA, Sayaka YANAGIDA, Takahiro TAKEI, Yuji HANADA, Masanori NAGAO and Masaki AZUMA
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A pyrochlore-type strontium bismuthate, (Sr0.75Bi0.25)2Bi2O6.83 was synthesized by a hydrothermal method using NaBiO3·nH2O as a starting material. The crystal structure was refined using synchrotron powder X-ray diffraction data. The final R-factors were Rwp = 8.07 % and Rp = 5.87 %, and the lattice parameter was a = 11.0195 (2) Å. This compound had a mixed bismuth valence state involving Bi3+ and Bi5+, where Bi3+ partially occupied the A-site (Sr2+) as well as the B-site (Bi5+) in the pyrochlore-type structure. Moreover, the present compound was found to be a diamagnetic semiconductor with electrical resistivity of ∼90 Ωm at room temperature.