研究者詳細 - 山下　誠司

Development of rice husk composite ceramic sphere with enhanced radiation heat transfer for rapid heat storage and release at high temperature 査読有り

Liao S., Zhou X., Chen X., Bao F., Zhang H., Yamashita S., Kita H.

Ceramics International 50 巻 ( 20 ) 頁： 38051 - 38062 2024年10月

担当区分：責任著者記述言語：英語出版者・発行元：Ceramics International

Regenerative burner systems have recently garnered increasing attention in the field of high-temperature thermal storage, the development of thermal storage materials that feature rapid heat storage and release rates along with high infrared absorptivity is significant for enhancing the efficiency of regenerative burner systems. This study innovatively uses rice husk ash as the raw material to develop a rice husk composite ceramic (RHC) sphere thermal storage material, which is simple to prepare, has a greatly reduced cost and compared with conventional thermal storage materials used in commercial regenerative burner systems, such as SiC and Al2O3 ceramic spheres, RHC demonstrates comparable rapid heat storage and release rates to SiC and is significantly faster than Al2O3. In addition, RHC exhibits an impressive radiation absorptivity of 0.93 in the 600–1200 °C range, which is higher than the 0.85 of SiC ceramic spheres and 0.25 of Al2O3 ceramic spheres. The distribution of high radiation absorptivity carbon and SiC particles within RHC is a key factor for its strong radiation properties, as the temperature increases, radiation heat transfer becomes the dominant mode of heat transfer. RHC achieves rapid overall heat storage and release rates due to its excellent radiation heat transfer performance. After 30 cycles of testing, RHC demonstrated good stability and long-term durability. RHC shows a high heat storage capacity of 2183 J/cm3 and 822 J/g in the furnace for 3 min. This study is poised to significantly enhance efficiency in the field of high-temperature rapid heat storage and release applications.

DOI： 10.1016/j.ceramint.2024.07.167

A time-domain nuclear magnetic resonance (TD-NMR) as a tool to characterize affinity between partially hydrophobic silica nanoparticles and ethanol/hexane mixtures 査読有り

Teramae A., Takai-Yamashita C., Ikeda J., Yamashita S., Sugiura M., Kato A., Ohya Y., Kinyanjui Kimani P.

Advanced Powder Technology 35 巻 ( 9 ) 2024年9月

記述言語：英語出版者・発行元：Advanced Powder Technology

Affinity between partially hydrophobic silica nanoparticles and organic solvents (ethanol and hexane) as dispersing medium has been characterized with change in the relaxation time obtained by a time-domain nuclear magnetic resonance (TD-NMR). Different chain lengths (denoted as C3, C6, and C12) were utilized as surface modifiers for the particles and the modification ratio was controlled. For ethanol, the longer chain length and higher modification ratio showed the higher affinity while for hexane, vice versa even though a quite poor affinity appeared in whole conditions. We hypothesize that the ethanol molecules could be attracted to residual silanol groups among long-chain length-functional groups. In order to prove, affinity of the partially hydrophobic silica nanoparticles with ethanol/hexane mixture has been investigated. In the range from 60 to 80 vol% of hexane, relaxation time of the C12-modified silica nanoparticles (modification ratio was 1.4 /nm2) quickly decreased. When the residual silanol was additionally modified with C3, the corresponding decrease disappeared. The TD-NMR has an effective tool to detect the change in the surface affinity of the partially hydrophobic nanoparticles even if they showed the same hydrophobicity.

DOI： 10.1016/j.apt.2024.104593

Microstructure modification of alumina prepared by water-stabilized plasma spraying method using Al-Cu-O reaction 査読有り

Bao F., Yamashita S., Daki H., Nakagawa K., Kita H.

Journal of the European Ceramic Society 44 巻 ( 10 ) 頁： 6113 - 6123 2024年8月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the European Ceramic Society

To improve the strength of Al2O3 specimens produced using the water-stabilized plasma spraying technique (WSPSAO), this study investigates the effect of structural modification on the mechanical properties of WSPSAO using the Al-Cu-O reaction between the metal, atmospheric oxygen, and base material. A Cu-powder layer is applied to the specimen surface, melted, and oxidized at high temperatures. It penetrates into the specimen, resulting in significant microstructural modification deep in the specimen. After modification, uniaxial Al2O3, CuO, Cu2O, and CuAl2O4 are formed in the specimen, resulting in a denser and more uniform structure than that of the original material. The bending strength of the coated surface is 145 MPa, and that on the opposite side of the coated surface is 118 MPa, which is 130%–180% higher than the original strength of the base material.

DOI： 10.1016/j.jeurceramsoc.2024.03.016

Development of Macro-Encapsulated Phase-Change Material Using Composite of NaCl-Al<inf>2</inf>O<inf>3</inf> with Characteristics of Self-Standing 査読有り国際共著 Open Access

Liao S., Zhou X., Chen X., Li Z., Yamashita S., Zhang C., Kita H.

Processes 12 巻 ( 6 ) 2024年6月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Processes

Developing thermal storage materials is crucial for the efficient recovery of thermal energy. Salt-based phase-change materials have been widely studied. Despite their high thermal storage density and low cost, they still face issues such as low thermal conductivity and easy leaks. Therefore, a new type of NaCl-Al2O3@SiC@Al2O3 macrocapsule was developed to address these drawbacks, and it exhibited excellent rapid heat storage and release capabilities and was extremely stable, significantly reducing the risk of leakage at high temperatures for industrial waste heat recovery and in concentrated solar power systems above 800 °C. Thermal storage macrocapsules consisted of a double-layer encapsulation of silicon carbide and alumina and a self-standing core of NaCl-Al2O3. After enduring over 1000 h at a high temperature of 850 °C, the encapsulated phase-change material exhibited an extremely low weight loss rate of less than 5% compared with NaCl@Al2O3 and NaCl-Al2O3@Al2O3 macrocapsules, for which the weight loss rate was reduced by 25% and 10%, respectively, proving their excellent leakage prevention. The SiC powder layer, serving as an intermediate coating, further prevented leakage, while the use of Al2O3 ceramics for encapsulation enhanced the overall mechanical strength. It was innovatively discovered that the Al2O3 particles formed a network structure around the molten NaCl, playing an important role in maintaining the shape and preventing leakage of the composite thermal storage phase-change material. Furthermore, the addition of Al2O3 significantly enhanced the rapid heat storage and release rate of NaCl-Al2O3 compared to pure NaCl. This encapsulated phase-change material demonstrated outstanding durability and rapid heat storage and release performance, offering an innovative approach to the application of salt phase-change materials in the field of high temperature rapid heat storage and release and encapsulating NaCl as a high-temperature thermal storage material in a packed bed system. Compared with conventional salt-based phase-change materials, the developed product is expected to significantly improve the reliability and thermal efficiency of thermal storage systems.

DOI： 10.3390/pr12061123

Development of redox-type thermochemical energy storage module: A support-free porous foam made of CuMn<inf>2</inf>O<inf>4</inf>/CuMnO<inf>2</inf> redox couple 査読有り Open Access

Chen X., Kubota M., Kobayashi N., Lin S., Deng L., Li J., Yamashita S., Kita H.

Chemical Engineering Journal 485 巻 2024年4月

記述言語：英語出版者・発行元：Chemical Engineering Journal

In this study, we developed a CuMn2O4/CuMnO2-based porous foam thermochemical energy storage (TCES) module, which is free from any supporting materials. The raw material of CuMn2O4/CuMnO2 was synthesized using co-precipitation method which is different with the Pechini method we have used in the previous study, aiming to a large-scale synthesis. The porous foam modules were prepared using polyurethane (PU) foam replica method. We investigated the sintering temperature and holding time as critical parameters affecting the module's mechanical strength, chemical reactivity, and durability. The optimal condition for CuMn2O4/CuMnO2-based porous foam TCES module were identified as 1100 ℃ and 6 h. Our findings suggests that these modules are promising for the fixed-bed reactors in redox-type TCES systems.

DOI： 10.1016/j.cej.2024.149540

Novel Sodium Chloride/Aluminum Oxide Powder-Composite Structure with High Shape-Retention Performance for the Encapsulation of a High-Temperature Phase-Change Material Open Access

Microstructure modification of alumina prepared by water-stabilized plasma spraying method using Al-Cu-O reaction 査読有り

Fuhai Bao, Seiji Yamashita, Hajime Daki, Keita Nakagawa, Hideki Kita,

Journal of the European Ceramic Society 2024年3月

Yamashita S., Fuhai B., Shenghao L., Kita H., Hong F.

Processes 12 巻 ( 3 ) 2024年3月

出版者・発行元：Processes

Inorganic phase-change materials (PCMs) with high melting points have great potential for thermal energy storage systems. Sodium chloride (NaCl) has a high melting point (801 °C) and high latent-heat-storage density (482 kJ/kg). However, it is difficult to encapsulate NaCl using a sintered ceramic shell because of its good wettability against ceramics and high volume-expansion capacity during melting. In this study, a novel NaCl/Al2O3 powder-composite structure was developed as highly stable PCM core material for highly stable encapsulation. The shape-retention performance and the mechanism of NaCl/Al2O3 powder-composite structure during melting were investigated. We have successfully fabricated a NaCl/Al2O3 powder-composite structure, which has a higher NaCl volume ratio of 80 vol% than conventional techniques. The gel-like network structure of Al2O3 particles in molten NaCl was a key structure to keep the shape of the composite ball and to prevent the evaporation of molten NaCl.

DOI： 10.3390/pr12030465

Enhanced radiation heat transfer performance of Alumina-Spinel composite sphere with hollow structure for rapidly ultra-high temperature thermal storage/release process

Zhou X., Liao S., Yamashita S., Kubota M., Takeuchi A., Gao P., Liu M., Li R., Zhang C., Kita H.

Chemical Engineering Journal 479 巻 2024年1月

出版者・発行元：Chemical Engineering Journal

Heat storage technologies for high temperatures have recently been gaining increasing attention. For heat storage applications at high temperatures, such as industrial regenerative burner systems, the impact of radiant heat transfer on the efficiency of rapid heat storage and release cannot be ignored. Hence, the development of heat storage materials with high infrared radiation absorption is of great significance for energy saving and CO2 emission reduction. Consequently, this study innovatively proposes an advanced composite heat storage material, composited by alumina and a Fe-Co-Mn-Al spinel, with the aim of improving absorptivity. A medium-entropy approach is employed to improve IR absorptivity of alumina. Through the strategic adding of various transition metal oxides, the radiative absorptivity of the alumina material in the 600–1200 °C range increased from an initial 0.2 to an impressive 0.8, provided that doping additives remain below 10 wt%. The high-temperature heat storage material balances cost, heat recovery efficiency and thermal stability. In addition, the heat storage material is prepared as a hollow sphere to further enhance the heat storage density of rapid heat storage/release and reduce cost. Multi-scale numerical simulations are carried out to reveal the heat transfer enhancement mechanisms of modified materials and hollowing. radiative modification can significantly increase the heat storage and release capacity, especially at ultra-high temperatures above 1000 °C. Experimental evaluations using an actual regenerative burner further confirmed the heat recovery performance of this novel heat storage sphere. Comparing with conventional regenerative burner system, heating power remarkably increased by 24.6 %, and the heat storage density of packed bed improved by 16.7 %. This study promises to significantly improve the efficiency of rapid heat recovery at high temperature.

DOI： 10.1016/j.cej.2023.147381

An in-depth oxidation kinetic study of CuCr<inf>x</inf>Mn<inf>1-x</inf>O<inf>2</inf> (x = 0, 0.1, 0.3) for thermochemical energy storage at medium-high temperature

Chen X., Kubota M., Kobayashi N., Yamashita S., Kita H.

Solar Energy Materials and Solar Cells 260 巻 2023年9月

出版者・発行元：Solar Energy Materials and Solar Cells

In this study, we investigated the effect of Cr doping on CuMn2O4/CuMnO2 and established an oxidation (heat release) kinetic model for CuCrxMn1-xO2 (x = 0, 0.1, 0.3) as an extension of our previous research on developing medium-high temperature (500–1000 °C) redox-type thermochemical energy storage materials. Our objective is to develop a reliable model for predicting the heat release power at constant temperature conditions. The as-prepared samples were characterized using XRD Rietveld refinement, SEM-EDS, and XPS analysis to obtain a more precise crystal structure and elemental states. The oxidation kinetic model was established using an isothermal oxidation method which differs from the method (non-isothermal) used in the previous study. Additionally, the pressure term was also taken into consideration. The reaction models and kinetic parameters of CuMnO2, CuCr0.1Mn0.9O2 and CuCr0.3Mn0.7O2 were determined using master plots and Arrhenius plots. Among all sample, CuCr0.1Mn0.9O2 exhibited the smallest oxidation activation energy of 29.932 kJ/mol, which was significantly lower than the previous value obtained using the non-isothermal method. Combining the reaction rate and heat release, CuCr0.1Mn0.9O2 showed the highest instantaneous power output of 4.69 kW/kg at the oxygen partial pressure of 0.5.

DOI： 10.1016/j.solmat.2023.112495

Macro encapsulated Cu-based phase change material for high temperature heat storage with characteristic of self-sealing and high durability

Zhou X., Yamashita S., Kubota M., Zhang C., Hong F., Kita H.

Applied Thermal Engineering 229 巻 2023年7月

出版者・発行元：Applied Thermal Engineering

The objective of this research is to develop encapsulated phase change materials with applications exceeding 1000 °C that can be applied to concentrated solar power systems and industrial waste heat recovery. In this study, a macro-encapsulation phase change storage material with a copper-based core and an alumina-based shell was developed by slip-casting method and filling mixture of copper beads and Cu-40 %Al powder. The capsule was able to achieve self-sealing by local oxidation reaction at the entrance without leakage. After aging tests at 1100 °C for up to 1000 h, no leakage or damage was found and mass increase of the encapsulate phase change material was only 4.5 %, confirming the superior durability and oxidation resistance of the encapsulated phase change material. The heat storage density of the copper-based phase change material was evaluated as high as 147 J/g. The heat storage capacity did not decrease after 1000 h and ten cycles of aging. The mechanism of its high durability was explored by morphological observations and Raman spectroscopy. In the original material, a small amount of aluminum was oxidized with priority to alumina which significantly enhanced the durability of the capsules. This macro-encapsulated phase change material exhibits excellent thermal storage performance, as well as self-sealing and durability properties, which are of great significance for improving the efficiency of thermal energy recovery above 1000 °C.

DOI： 10.1016/j.applthermaleng.2023.120491

Water Vapor Adsorption Behavior of Thermosensitive Polymers for Desiccant Humidity Control Systems Open Access

Kubota M., Nakai R., Yamashita S., Kita H., Tokuyama H.

ＩＳＩＪ　Ｉｎｔｅｒｎａｔｉｏｎａｌ 62 巻 ( 12 ) 頁： 2536 - 2541 2022年12月

記述言語：英語出版者・発行元：一般社団法人日本鉄鋼協会

Desiccant humidity control systems have been garnering considerable attention in the attempt to achieve highly efficient utilization of low-temperature heat exhausted from various industries at temperatures less than 373 K. We have focused on thermosensitive polymers as new desiccants because a large amount of dehumidified water would be expected in the system because of their thermosensitivity. Our previous study focused on the water adsorption behavior of poly(N-isopropylacrylamide) (poly(NIPA)), which has a low critical solution temperature (LCST) of 306 K. In this study, poly(N-isopropylmethacrylamide) (poly(NIPMA)) and poly(2-(dimethylamino)ethyl methacrylate) (poly(DMAEMA)) cross-linked with N,N'-methylenebisacrylamide (MBAA) were investigated. These polymers are known to exhibit thermosensitivity in the temperature range of 313-319 K in water, which is a higher LCST than that of poly(NIPA). Poly(NIPMA) adsorbed water vapor linearly with increasing relative humidity. It was also observed that poly(NIPMA) prepared at MBAA concentrations of 200 mol/m3 exhibited a thermosensitivity in the temperature range of 303-313 K in water vapor adsorption. Meanwhile, poly(DMAEMA) adsorbed little water vapor up to a relative humidity (RH) of 40%; however, it exponentially adsorbed water at RH levels higher than 40%. From the estimation results of effective water adsorptivity, we found that poly(DMAEMA) is applicable in desiccant humidity control systems when the dehumidification process is performed at high RH.

DOI： 10.2355/isijinternational.isijint-2022-204

マハラノビス－タグチ（MT）法を用いたカブトムシ三齢幼虫糞形状による雌雄判別 Open Access

高井（山下）千加, 山下誠司, 馬渕裕也, 寺前敦史, 松山拓矢, 田口裕己, 虫鹿太賀, 和田雄也, Shinta Fitria Novasari, 大矢豊

粉体工学会誌 59 巻 ( 12 ) 頁： 620 - 627 2022年12月

記述言語：日本語出版者・発行元：一般社団法人粉体工学会

The Mahalanobis-Taguchi system (MTS) is one of the multi-variate analyses which can classify data by correlations among multi-variables. The MTS has significant advantage of applying a cause analysis which provides effective variable combinations to upgrade the accuracy of the classification. In this study, droppings, which were extruded from Japanese rhinoceros beetle larva were selected to classify into male/female based on their shape-related features using the MTS. Based on the cause analysis, the projected area/Feret's diameter (A/F) and solidity were the best variable combination which all the larval droppings were classified into male/female. Both the variable has surface roughness-related factors with size effect (A/F) without size effect (solidity). The MTS has the great ability to classify from the powders' minor difference and will be an effective tool for particle design in the near future.

DOI： 10.4164/sptj.59.620

Low-Temperature Joining of B<inf>4</inf>C Ceramics Using Cold-Sprayed Al-8wt%Si Alloy and Microstructure of the Vicinity of the Joint Interface Open Access

Low-Temperature Joining of B4C Ceramics Using Cold-Sprayed Al-8wt%Si Alloy and Microstructure of the Vicinity of the Joint Interface 招待有り査読有り

10 巻 ( 12 ) 2022年12月

Kita H., Gou R., Yamashita S.

Processes 10 巻 ( 12 ) 2022年12月

出版者・発行元：Processes

A series of studies were conducted to demonstrate the feasibility of low-temperature bonding by the forming and heating an Al-8wt%Si alloy thick film on a B4C surface by cold spraying. The results show that: (1) The cracks near the joining interface are closed by the Al alloy by the process studied in this study, and a joining strength of about 220 and 240 MPa is achieved by low temperature joining of 580 °C and 600 °C, respectively.; (2) The amount of weak intermetallic compounds at the joining interface is reduced; (3) It is assumed that the reduction in the amount of Al-B-C compounds is due to the formation of the β phase during the solidification process of the Al-Si alloy, which hinders the growth of the compounds.; (4) On the primary joint surface, a continuous void group is formed in the vicinity of the β phase that surrounds the α phase, causing a decrease in the joining strength.

DOI： 10.3390/pr10122573

Aluminum Electrodeposition on the Surface of Boron Carbide Ceramics by Use EMIC–AlCl<inf>3</inf> Ions Liquid Open Access

Aluminum Electrodeposition on the Surface of Boron Carbide Ceramics by Use EMIC–AlCl3 Ions Liquid 査読有り

Roujia Gou,Jae-Hyeok Park , Seiji Yamashita, Takeshi Hagio, Ryoichi Ichino and Hideki Kita

Coatings 12 巻 2022年10月

Gou R., Park J.H., Yamashita S., Hagio T., Ichino R., Kita H.

Coatings 12 巻 ( 10 ) 2022年10月

出版者・発行元：Coatings

Coating technology is decisively important for metallization of ceramic materials and ceramic metal sealing technology. Previous studies have shown that the network-like structure after penetration of molten aluminum can significantly improve the strength of joint components. However, the direct aluminum coating method is limited by the shape of the substrate. To obtain a dense aluminum film on the surface of B4C, in this study, aluminum was deposited by pulse electroplating in EMIC–AlCl3 ionic liquid. The deposited metals were observed and analyzed by SEM–EDS and XRD. A Vickers hardness tester was adopted as an auxiliary equipment to clarify the film quality. The results show that frequency and duty cycle have significant effects on crystal orientation. The content of oxides in the contact gap reduces the bonding strength of the deposited metal, which provides experimental basis for metal electrodeposition on B4C.

DOI： 10.3390/coatings12101535

Storage and heat dissipation behavior of a heat storage ball with an Al–xSi alloy core and alumina ceramic shell Open Access

Zhou X., Bao F., Yamashita S., Kubota M., Kita H.

Journal of Energy Storage 52 巻 2022年8月

出版者・発行元：Journal of Energy Storage

Regenerative thermal storage systems are becoming increasingly popular for recycling large amounts of waste heat generated in industrial furnaces every year. In order to improve the efficiency of regenerative burners, encapsulated phase change material consisting of an Al–Si alloy core sealed in a spherical ceramic shell has been proposed as a promising heat storage material. This is due to its melting temperature of 850 K, high heat storage density, and high heat storage rate under high-temperature operating conditions (over 773 K) with a short burner switch time. This study conducted rapidly heat storage simulation based on finite element method, heating and cooling tests and microstructural analysis to compare the properties of conventional solid alumina heat storage balls with those of the proposed core–shell heat storage ball with different Si concentrations. It was confirmed that the core–shell ball can store latent heat and is superior to the conventional solid alumina ball in terms of heat storage rate and heat storage density. The eutectic composition of Al–12.2% Si was determined as the optimal core composition for rapid high-temperature heat storage owing to its high heat phase change rate and density over a short time.

DOI： 10.1016/j.est.2022.104955

Effect of Cr Addition on Cu−Mn Spinel/Delafossite Redox Couples for Medium-High Temperature Thermochemical Energy Storage Open Access

Storage and heat dissipation behavior of a heat storage ball with an Al–xSi alloy core and alumina ceramic shell 査読有り

Xin Zhou, Fuhai Bao, Seiji Yamashita, Mitsuhiro Kubota Hideki Kita

Journal of Energy Storage 52 巻 2022年8月

Chen X., Kubota M., Kobayashi N., Yamashita S., Kita H.

ACS Applied Energy Materials 5 巻 ( 5 ) 頁： 5811 - 5821 2022年5月

出版者・発行元：ACS Applied Energy Materials

In this study, we developed Cu(CrxMn1−x)2O4/ CuCrxMn1−xO2 (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) redox couples for medium-high temperature (500−1000 °C) redox-type thermochemical energy storage systems. Structural characterization, redox behavior, reoxidation behavior and kinetic analysis, heat storage capacity, and cyclability were investigated using SEM-EDS, XRD, TGA, and DSC, respectively. When x = 0−0.5, samples exhibited decreasing operating temperatures with increasing amounts of Cr, whereas they lost their reversibility when x > 0.5. R-CuCr0.1Mn0.9 and R-CuCr0.3Mn0.7 showed a faster reaction rate than R-CuMn because samples with small amounts of Cr required a lower activation energy (Ea) for reoxidation. The DSC results showed that a small amount of Cr improved the heat storage capacity of materials. In the cyclability test, the introduction of a small amount of Cr did not cause the deterioration of cyclic properties.

DOI： 10.1021/acsaem.2c00178

Effect of Counterbody on Friction and Wear Properties of Copper-MgP-Graphite Composites Prepared by Powder Metallurgy Open Access

Li R., Yamashita S., Yoshida K., Kita H.

Processes 10 巻 ( 5 ) 2022年5月

出版者・発行元：Processes

The purpose of this study was to investigate the influence of different counterbodies against Cu/magnesium phosphate treated graphite (Cu-MgPG) composite materials to find the best material combination in terms of friction coefficient and specific wear amount. A Cu matrix composite reinforced with 10 vol% magnesium phosphate treated graphite and pure Cu powder were prepared by powder metallurgy techniques under the same consolidation processing condition. The friction and wear properties of the composites were investigated at 10 N using a pin-on-disc tribometer on Al2O3, SiC and SUJ2 bearing steel counterbodies. The Cu-MgPG/Al2O3 pair showed the lowest friction coefficient, but the specific wear rate tended to increase slightly when compared with Cu/Al2O3 pair. On the other hands, the Cu-MgPG/SUJ2 pair showed about the same specific wear rate as the Cu/SUJ2 pair, but the friction coefficient was significantly reduced. These phenomena are thought to be due to the fact that the added graphite acts as a solid lubricant during sliding and also suppresses the oxidation behavior of the sliding material.

DOI： 10.3390/pr10050804

Sex determination of Japanese rhinoceros beetles, Trypoxylus dichotomus (Coleoptera: Scarabaeidae), based on their dropping shape Open Access

Takai-Yamashita C., Yamashita S., Mabuchi Y., Teramae A., Matsuyama T., Taguchi Y., Mushika T., Wada Y., Novasari S.F., Ikeda J., Ohya Y.

Advanced Powder Technology 33 巻 ( 5 ) 2022年5月

出版者・発行元：Advanced Powder Technology

The Mahalanobis-Taguchi system (MTS) is one of the multi-variate analyses which can classify by correlations among multi-variables. It has a significant advantage of applying a cause analysis which provides effective variable combinations to upgrade the accuracy of the classification. In this study, droppings, which were extruded from Japanese rhinoceros beetle larva (called Kabutomushi in Japanese) were classified into male/female based on their shape-related features using the MTS. Their droppings have a spheroid shape of approximately 10 mm in their long axis. Seven features (i.e., variables) were obtained from digital micrographic images using image analysis software, such as height/width (H/M), major/minor (Ma/Mi), perimeter/Feret diameter (P/F), projected area/Feret diameter (A/F), roundness, circularity, and solidity. Although an abnormality rate, which shows how the correlation pattern of one larval dropping is far from any standard ones, has a boundary in order to classify into male/female from 18 larval droppings, 3 larva were judged as the opposite sex. Based on the cause analysis, the A/F and solidity were the best variable combination which all the larval droppings were completely classified into male/female. Why these variables were affected by the sex most seemed to be caused by the gut components, as determined by time-domain nuclear magnetic resonance (TD-NMR). MTS has the great ability to classify from the powders’ minor difference and will be an effective tool for particle design in the near future.

DOI： 10.1016/j.apt.2022.103552

Effect of Counterbody on Friction and Wear Properties of Copper-MgP-Graphite Composites Prepared by Powder Metallurgy 招待有り査読有り

Ruoxuan Li , Seiji Yamashita, Katsumi Yoshida and Hideki Kita

Processes 10 巻頁： 804 2022年4月

Microstructural analysis of network-like crack structure formed at Al–B4C interface 招待有り査読有り

Roujia Gou, Seiji Yamashita, Kiyoto Sekine, Hideki Kita

Journal of the European Ceramic Society 41 巻 ( 14 ) 頁： 6962 - 6970 2022年3月

Encapsulated Copper-Based Phase-Change Materials for High-Temperature Heat Storage 招待有り査読有り Open Access

Zhou X., Yamashita S., Kubota M., Kita H.

ACS Omega 7 巻 ( 6 ) 頁： 5442 - 5452 2022年2月

記述言語：英語出版者・発行元：ACS Omega

In this study, a copper-based capsule, encapsulated by a black alumina shell using a simple method, was developed for higherature heat storage over 1000 °C. The shell was filled with copper beads (diameter = ∼3 mm), the copper-aluminum (Cu-Al) atomized powder (particle size = 150 μm) was filled in the gap, and then it was heat-treated. This eventually formed a high-density, aluminum-rich network around the Cu beads in the shell. Morphological observations indicated that the corrosion of copper oxide (CuO) on the alumina shell was significantly reduced by mixing Al with Cu. When heat-treated in air at 1100 °C, Cu became CuO, which reacted with Al2O3 to form a new compound, CuAl2O4. Owing to this two-step reaction, the area around the hole provided at the top of the spherical shell gets sealed, thereby suppressing the flow of oxygen into the shell (self-sealing function). The mechanism of in situ sealing was detected using X-ray diffraction and scanning electron microscopy analyses. The Cu-(5-10%) Al capsule could endure a 400 h air exposure test at 1100 °C without leakage or cracking. A low weight increase ratio of 3.5% after the exposure revealed good oxidation resistance of the capsule, whereas the slight damage load change of the capsule after the exposure showed good mechanical stability. The results concluded that a Cu-(5-10%) Al capsule for higherature heat storage applications above 1000 °C can be fabricated by a simple process, and it demonstrates excellent durability during the long-term air exposure test. The data obtained in this study can be used as a reference for the design of packed beds in the future.

DOI： 10.1021/acsomega.1c06751

Frictional characteristics of carbide ceramics in water

PubMed

Zhang W., Chen X., Yamashita S., Kubota M., Kita H.

Journal of Tribology 144 巻 ( 1 ) 2022年1月

出版者・発行元：Journal of Tribology

Frictional characteristics of carbide ceramics (SiC, B4C-SiC, and B4C) sliding against SiC balls in water were measured over a wide range of test conditions. Carbide ceramics can obtain hydrodynamic lubrication with low friction coefficients at 20 and 40 N; however, carbide ceramics cannot obtain hydrodynamic lubrication with low friction coefficients at 5 N. Carbide ceramics exhibit lower friction coefficients at 20 and 40 N than those at 5 N in each lubrication regime. Carbide ceramics can exhibit a wider application range with low friction at high loads (20 and 40 N). The low friction of carbide ceramics is achieved by the combination of hydrodynamic lubrication and tribochemical reactions. The products of tribochemical reactions of carbide ceramics improve the viscosity of water at or near the worn surfaces of carbide ceramics, promoting the hydrodynamic lubrication for carbide ceramics. B4C ceramic shows lower friction coefficients than those of SiC and B4C-SiC ceramics in boundary lubrication and mixed lubrication at 20 and 40 N.

DOI： 10.1115/1.4050732

Effects of Additional Mullite Micro-Powder on Rheological Behavior of Highly Concentrated Aqueous Silicon Slurry

Himoto I., Kita H., Shenghao L., Yamashita S.

Journal of Chemical Engineering of Japan 54 巻 ( 11 ) 頁： 586 - 592 2021年11月

記述言語：英語出版者・発行元：公益社団法人化学工学会

Low-thermal-conductive reaction-bonded silicon nitride (RBSN), with a thermal conductivity of 8.08 W/(m · K), was developed by the addition of mullite micro-powder as a rare-earth-free oxide sintering agent to silicon nitride. This addition was expected to generate a glassy grain boundary as well as a solid solution of oxygen across the microstructure of the RBSN, which leads to low thermal conductivity. During the fabrication of a heat-insulating component with a hollow structure made of the RBSN via slip casting and subsequent reaction sintering, it was found that the viscosity of aqueous silicon-mullite slurries decreased evidently by the addition of the mullite micro-powder with ammonium polycarboxylate as a dispersant. The viscosity decreased even though the pH (7–8) of the slurries were maintained, and the particle size distributions did not vary significantly. At the effective mullite content when the viscosity decrease was attained, the ratio of the number of particles of mullite to silicon was approximately 1. Therefore, the viscosity decrease in Si slurry (50 vol%) was primarily caused by the steric hindrance due to the adsorption of dispersant by the mullite particles, preventing the direct contact among the silicon particles, rather than by electrostatic repulsions among the silicon particles. This was also explained through the modality of bimodal dispersion. Thus, it was found that the mullite not only acts as a sintering agent but also facilitates viscosity decrease of highly concentrated aqueous Si slurry, which successfully enables the integration of the slip casting and reaction sintering processes.

DOI： 10.1252/jcej.20we173

Microstructural analysis of network-like crack structure formed at Al–B<inf>4</inf>C interface Open Access

Gou R., Yamashita S., Sekine K., Kita H.

Journal of the European Ceramic Society 41 巻 ( 14 ) 頁： 6962 - 6970 2021年11月

出版者・発行元：Journal of the European Ceramic Society

The morphology and structure of microcracks extending toward B4C were investigated from a joint obtained by sandwiching Al foil between two B4C ceramic plates and heat-treating at 1000 °C in vacuum. Network-like structures of cracks were seen, and Al penetrated the extremely narrow part at the tip. The molten Al penetrated a narrow area within the cracks and filled them. Several compounds were produced in the primary junction area because of reactions between Al and B4C. However, only pure Al was present within the cracks. Atoms moved easily in a wide joint interface, and a reaction occurred accordingly, whereas in a narrow region inside the micro crack, atoms moved with difficulty even if molten Al penetrated the crack. The fact that the reaction is unlikely to occur inside the crack is consistent with the permeation of Al into the inside of the elongated crack.

DOI： 10.1016/j.jeurceramsoc.2021.06.043

7-2-3　エクセルギー解析グラフツールの開発とその生産プロセスへの適用

北英紀, 山下誠司, 窪田光宏

日本エネルギー学会大会講演要旨集 30 巻 ( 0 ) 頁： 166 - 167 2021年7月

Exploring Cu-Based Spinel/Delafossite Couples for Thermochemical Energy Storage at Medium-High Temperature Open Access

Chen X., Kubota M., Yamashita S., Kita H.

ACS Applied Energy Materials 4 巻 ( 7 ) 頁： 7242 - 7249 2021年7月

出版者・発行元：ACS Applied Energy Materials

Cu-based spinel/delafossite couples with Mn and Fe as second cations were synthesized using the Pechini method for medium-high temperature thermochemical energy storage. Physicochemical properties of each sample were investigated. Only CuMn2O4/CuMnO2exhibited favorable redox behavior in the range of 500-1000 °C. Cu-based delafossite can reoxidize at a lower temperature (∼600 °C), which may be related to the existence of a MO6octahedra structure. Through the isothermal oxidation method, CuMn2O4/CuMnO2couple showed a larger oxidation enthalpy of 258.32 ± 15.31 kJ/kg (1402.68 ± 83.13 kJ/L) than 190.35 ± 4.81 kJ/kg (1048.83 ± 26.50 kJ/L) of CuFe2O4/CuFeO2couple. CuMn2O4was chosen for further cyclability test with 20 cycles; the depth of reduction increased gradually and stabilized at 4% change in mass after 13 cycles.

DOI： 10.1021/acsaem.1c01352

Effect of Water Temperature on Tribological Performance of B<inf>4</inf>C-SiC Ceramics under Water Lubrication

Effects of Additional Mullite Micro-Powder on Rheological Behavior of Highly Concentrated Aqueous Silicon Slurry 招待有り査読有り

Iori Himoto, Hideki Kita, Liao Shenghao, Seiji Yamashita

JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 54 巻 ( 11 ) 頁： 586 - 592 2021年7月

Zhang W., Chen X., Yamashita S., Kubota M., Kita H.

Tribology Letters 69 巻 ( 2 ) 2021年6月

出版者・発行元：Tribology Letters

Abstract: The tribological performance of B4C-SiC ceramics under water lubrication at different water temperatures was studied. The wear mechanisms of B4C-SiC ceramics sliding in water are expected to be mechanical wear and tribochemical wear. There is only SiO2 film on the wear surfaces of B4C-SiC discs after sliding under different loads, and there is no boron oxide or hydroxide on the wear surfaces of B4C-SiC discs when the water temperature varied between room temperature and 60 °C. The tribochemical reaction of B4C in B4C-SiC ceramics is discovered. The products of tribochemical reaction of B4C in B4C-SiC ceramics are H3BO3 and C, and the residual carbon will be left on the wear surface. B4C-SiC/SiC tribopairs can obtain the lowest friction coefficients and systematic wear rates as sliding in water at water temperature between 40 and 60 °C, which is attributed to the promoted tribochemical reaction of SiC in B4C-SiC ceramics, rather than the tribochemical reaction of B4C in B4C-SiC ceramics. More SiO2 film is gradually formed on the wear surfaces as the sliding distance increases, which can cover or protect more B4C grains. The formation of more SiO2 film results in the reduced friction coefficient, tribochemical wear, and mechanical wear for B4C-SiC ceramics. Graphical Abstract: [Figure not available: see fulltext.].

DOI： 10.1007/s11249-021-01406-0

Investigating the chemical bonding state of graphite powder treated with magnesium(II) phosphate through EELS, TEM, and XPS analysis

Investigation of Sr-based perovskites for redox-type thermochemical energy storage media at medium-high temperature 招待有り査読有り

XiaoyuChen MitsuhiroKubota SeijiYamashita HidekiKita

Journal of Energy Storage 2021年6月

Li R., Yamashita S., Kita H.

Diamond and Related Materials 116 巻 2021年6月

出版者・発行元：Diamond and Related Materials

Graphite is often used as a solid lubricant owing to its unique layered structure. However, graphite powder is susceptible to oxidation at high temperatures. In this study, graphite powder was treated with magnesium(II) phosphate solution to obtain graphite powder with excellent oxidation resistance at high temperatures while retaining its lubricating properties. The oxidation resistance of the obtained graphite powder and original graphite was evaluated at temperatures ranging from room temperature (RT) to 1000 °C. The results show that the initial temperature of graphite oxidation increased by nearly 170 °C. Furthermore, this study confirmed that the treated powder still retains the unique layered structure of graphite, which contributes to its lubricating properties. In addition, to clarify the mechanism of using magnesium(II) phosphate to treat graphite for improving its oxidation resistance, the chemical bonding state was specifically analyzed using electron energy loss spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Therefore, the magnesium(II) phosphate-treated graphite maintains the graphite-based interlayer structure and magnesium(II) phosphate forms a C–O–P chemical bond on the graphite defect to cover the reaction site of graphite, which allows the treated graphite to improve oxidation resistance.

DOI： 10.1016/j.diamond.2021.108423

Investigation of Sr-based perovskites for redox-type thermochemical energy storage media at medium-high temperature Open Access

Chen X., Kubota M., Yamashita S., Kita H.

Journal of Energy Storage 38 巻 2021年6月

出版者・発行元：Journal of Energy Storage

Thermochemical heat storage system exhibits extraordinary properties compared with sensible or latent heat storage system. Owing to the versatility of perovskite, Sr-based perovskites were investigated for redox-type thermochemical energy storage at medium-high temperature. In this study, SrCoO3-δ, SrFeO3-δ and SrMnO3-δ were prepared via a modified Pechini method. The oxidation enthalpy of each sample was measured using a combination of tubular furnace and DSC. Composition analysis, redox and cyclability tests revealed that SrFeO3-δ possesses favorable behavior validating the design principles.

DOI： 10.1016/j.est.2021.102501

A study of B<inf>4</inf>C-SiC composite for self-lubrication

Zhang W., Yamashita S., Kita H.

Journal of the American Ceramic Society 104 巻 ( 5 ) 頁： 2325 - 2336 2021年5月

出版者・発行元：Journal of the American Ceramic Society

A B4C-SiC composite without annealing and two B4C-SiC composites followed by annealing at 1000℃ and 1200℃ for 1 hour in air, respectively, were prepared. The tribological properties of the three composites were evaluated by sliding against SiC balls at room temperature under unlubricated conditions. The B4C-SiC composite can obtain lower friction coefficient by annealing at 1000℃, whereas the friction coefficient of B4C-SiC composite annealed at 1200℃ was significantly increased. The cause for this difference was ascribed to different surface compositions after annealing. The mechanism of self-lubrication of the B4C-SiC composite was the formation of H3BO3 layer.

DOI： 10.1111/jace.17584

B<inf>4</inf>C-SiC Ceramics with Interfacial Nanorelief Morphologies and Low Underwater Friction and Wear

Investigating the chemical bonding state of graphite powder treated with magnesium(II) phosphate through EELS, TEM, and XPS analysis 招待有り査読有り

RuoxuanLi SeijiYamashita HidekiKita

Diamond and Related Materials 2021年4月

Zhang W., Chen X., Yamashita S., Kubota M., Kita H.

ACS Applied Nano Materials 4 巻 ( 3 ) 頁： 3159 - 3166 2021年3月

出版者・発行元：ACS Applied Nano Materials

The tribological properties of carbide ceramics (SiC, B4C-SiC, and B4C) sliding against SiC balls in water at a normal load of 20 N in ambient conditions were investigated. Compared with traditional SiC ceramics used as mechanical seal materials, B4C-SiC ceramics exhibit lower friction and wear under water lubrication. The lower coefficient of friction of B4C-SiC ceramics is caused by the nanorelief with a depth of 12 nm formed on their friction surfaces. The water stored in the valleys of nanorelief can provide continuous lubrication to the B4C-SiC ceramic friction surfaces, and the good load carrying capacity makes B4C-SiC ceramics exhibit lower COF under higher load (20 N). In situ formed nanorelief can show beneficial influence on the frictional property of materials under water lubrication. The formation of nanorelief on B4C-SiC ceramics is the result of competition between mechanical wear and tribochemical wear under water lubrication. B4C-SiC ceramics with better tribological properties are expected to replace traditional SiC ceramics as mechanical seal materials under water lubrication. A design idea that using the microhardness difference between the two phases of composite ceramics to in situ prepare relief on the composite ceramic surface to improve the frictional property under water lubrication has been proposed in this study.

DOI： 10.1021/acsanm.1c00375

Tribological behaviour of B<inf>4</inf>C-SiC composite ceramics under water lubrication: influence of counterpart

Zhang W., Chen X., Yamashita S., Kubota M., Kita H.

Materials Science and Technology (United Kingdom) 37 巻 ( 9 ) 頁： 863 - 876 2021年

出版者・発行元：Materials Science and Technology (United Kingdom)

The tribological tests under water lubrication have been made on B4C-SiC composite ceramics in contact with different counterparts (Si3N4, Al2O3, and SUJ2 (high carbon chromium steel)). When the B4C-SiC discs slide against different counterparts in water, similar coefficients of friction are obtained, except against SUJ2 counterpart at 40 N. The B4C-SiC discs show the highest wear rate when sliding against Si3N4 counterpart, followed by Al2O3 counterpart, and lastly SUJ2 counterpart. The wear of B4C-SiC disc when sliding in water mainly depends on the nature of counterparts, followed by the hardness of counterparts. As a whole, B4C-SiC/Al2O3 tribo-couple shows better tribological properties when sliding in water as compared to B4C-SiC/Si3N4 tribo-couple and B4C-SiC/SUJ2 tribo-couple.

DOI： 10.1080/02670836.2021.1961365

Self lubrication of pressureless sintered SiC ceramics Open Access

Zhang W., Yamashita S., Kita H.

Journal of Materials Research and Technology 9 巻 ( 6 ) 頁： 12880 - 12888 2020年11月

出版者・発行元：Journal of Materials Research and Technology

The self lubrication of SiC ceramics prepared by pressureless sintering was investigated by annealing at different temperatures in air. It was found that low coefficient of friction can be obtained for SiC ceramics by annealing, and the coefficient of friction of SiC ceramics decreased with the increase of annealing temperature. The SiC ceramics with annealing at 1500 °C revealed the best self lubricating property, with the coefficient of friction of 0.4, while the coefficient of friction of SiC ceramics without annealing was as high as 0.7. The SiC ceramics with annealing at 1000 °C can show self lubrication over a long sliding distance without increasing wear. The formation of α-cristobalite on the annealed SiC ceramics can further lubricate SiC ceramics and shorten run in period. Self lubrication mechanism of SiC ceramics with annealing is considered that on the one hand, the formation of silicon oxide layers after annealing can reduce the number of SiC grains directly exposed to the sliding interface in the early stage of the sliding, decreasing the number of hard SiC wear particles formed on the sliding interface; and on the other hand, silicon oxide wear particles generated by the wear of the silicon oxide layers formed by annealing can be used as solid lubricant.

DOI： 10.1016/j.jmrt.2020.09.022

Effect of counterbody on tribological properties of B<inf>4</inf>C–SiC composite ceramics

Zhang W., Yamashita S., Kita H.

Wear 458-459 巻 2020年10月

出版者・発行元：Wear

Pressureless sintered B4C–SiC composite ceramics were subjected to dry sliding friction and wear against Al2O3, Si3N4 and SUJ2 bearing steel counterbodies at 5 N, 10 N and 20 N. Friction coefficient and specific wear rate were measured, and wear mechanisms were studied. For the B4C–SiC composite ceramics, both the friction coefficient and specific wear rate were dependent on counterbody materials. However, the influence of counterbody materials on friction coefficient and systematic specific wear rate of B4C–SiC composite ceramics was not obvious at high load, which was attributed to the formation of a number of compaction layers on all the worn surfaces of B4C–SiC composite ceramics against Al2O3, Si3N4 and SUJ2 counterbodies. At the same loads, the wear of B4C–SiC composite ceramics sliding against different counterbodies at low load was mainly controlled by the chemical similarity of counterbody, whereas the wear of B4C–SiC composite ceramics sliding against different counterbodies at intermediate and high loads was mainly controlled by the hardness of counterbody.

DOI： 10.1016/j.wear.2020.203418

Tribological Properties of B<inf>4</inf>C Ceramics Prepared by Pressureless Sintering and Annealed at Different Temperatures

7-12　人工物製造プロセスのエクセルギー解析

北英紀, 山下誠司, 窪田光宏

日本エネルギー学会大会講演要旨集 29 巻 ( 0 ) 頁： 188 - 189 2020年7月

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Kita H.

Tribology Transactions 63 巻 ( 4 ) 頁： 672 - 682 2020年7月

出版者・発行元：Tribology Transactions

B4C ceramics were fabricated by pressureless sintering, and the tribological behaviors of B4C ceramics without and with a postannealing treatment at different temperatures were investigated. It was found that the pores of B4C ceramics prepared by pressureless sintering might cause large fluctuations in the coefficient of friction but did not increase the coefficient of friction. A B2O3 layer was not formed on the B4C ceramics after annealing at 700 °C, whereas an H3BO3 layer was formed on the B4C ceramics after annealing at 1000 and 1200 °C, respectively. B4C ceramics obtained a favorable self-lubricating property after annealing at 1000 or 1200 °C because of the formation of an H3BO3 layer during the annealing treatment. B4C ceramics annealed at 1200 °C exhibited the best self-lubricating properties, with the lowest coefficient of friction of approximately 0.08. The friction and wear mechanisms of B4C ceramics without and with a postannealing treatment are discussed in detail.

DOI： 10.1080/10402004.2020.1734705

Effects of load on tribological properties of B<inf>4</inf>C and B<inf>4</inf>C-SiC ceramics sliding against SiC balls Open Access

Zhang W., Yamashita S., Kita H.

Journal of Asian Ceramic Societies 8 巻 ( 3 ) 頁： 586 - 596 2020年7月

出版者・発行元：Journal of Asian Ceramic Societies

Pressureless sintered B4C and B4C-SiC ceramics were subjected to tests of dry sliding against SiC balls at 5 N, 10 N and 20 N. The effects of load on the respective tribological properties of B4C and B4C-SiC ceramics were studied. Meanwhile, the tribological properties and friction, wear mechanisms of B4C and B4C-SiC ceramics at different loads were compared. Both the friction coefficient and wear rate of B4C ceramics first decreased and then increased with increases in load, while both the friction coefficient and wear rate of B4C-SiC ceramics increased with increases in load. At low load, the B4C-SiC ceramics showeda lower friction coefficient and wear rate. At intermediate load, the B4C ceramics showed a lower friction coefficient, and no difference between the wear rates of B4C and B4C-SiC ceramics was apparent. At high load, the B4C ceramics showed a lower friction coefficient, while the B4C-SiC ceramics showed a lower wear rate. With increases in load from 5 N to 20 N for the B4C ceramics, the wear mechanism changed from adhesive wear to delamination and spalling of tribofilm; for the B4C-SiC ceramics, meanwhile, the wear mechanism changed from surface polishing and mild abrasion to micro-fracture.

DOI： 10.1080/21870764.2020.1769819

Tribological properties of SiC-B<inf>4</inf>C ceramics under dry sliding condition

Zhang W., Yamashita S., Kita H.

Journal of the European Ceramic Society 40 巻 ( 8 ) 頁： 2855 - 2861 2020年7月

出版者・発行元：Journal of the European Ceramic Society

SiC-B4C ceramic composites with different ratios of SiC to B4C were produced. The relative density, mechanical properties, initial surface characteristics, dry sliding tribological properties against SiC ball and worn surface characteristics of the SiC-B4C ceramics were studied. Results of dry sliding tribological tests showed that, 40 wt. % SiC-60 wt. % B4C ceramic composite had the best tribological properties in SiC-B4C ceramic composites. A relief structure with height difference of 10−30 nm between B4C grains and SiC grains is formed after dry sliding. This relief structure, on the one hand, can reduce real contact area on interface, decreasing adhesion effect, and on the other hand, can fix or trap the wear pieces formed on sliding interface during the dry sliding process, reducing the abrasive wear. However, there is a limit to the beneficial influence of decreased adhesion effect and reduced abrasive wear, and an optimum proportion of relief structure. Pores can also fix or trap some wear pieces, reducing the abrasive wear. Under the condition of strong bonding between SiC grains and B4C grains, the SiC-B4C ceramic composites with higher porosity can obtain better tribological properties. In addition, it is observed by AFM that the depth of scratch on B4C grains is shallower than that on SiC grains. Hence, it is demonstrated by micro scale measurement that the wear rate of B4C is lower than that of SiC in this study.

DOI： 10.1016/j.jeurceramsoc.2020.02.062

Study on friction behavior of SiC-B<inf>4</inf>C composite ceramics after annealing

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Kita H.

Industrial Lubrication and Tribology 72 巻 ( 5 ) 頁： 673 - 679 2020年6月

出版者・発行元：Industrial Lubrication and Tribology

Purpose: This study aims to investigate the friction behavior of SiC-B4C composite ceramics treated by annealing in air sliding against SiC balls. Design/methodology/approach: The dry sliding tests were performed with a ball-on-disk tribometer in ambient air condition. Analysis of friction coefficient, phase compositions of the surfaces, morphologies of worn surfaces of disks and wear scars of balls and surface profiles of wear tracks for disks were carried out using Raman spectroscope, microscope and surface profilometer. Findings: The results show that a self-lubricating layer with the main composition of H3BO3 was successfully fabricated on the surface of SiC-B4C composite ceramics by the annealing treatment in air. When the mass fraction of SiC is more than that of B4C, SiC-B4C composite ceramics show higher friction coefficients, the values of which are 0.38 for 80 Wt.%SiC-20 Wt.%B4C and 0.72 for 60 Wt.%SiC-40 Wt.%B4C, respectively. SiC-B4C composite ceramics show lower friction coefficients when the mass fraction of B4C is more than that of SiC. The low friction coefficients of 40 Wt.%SiC-60 Wt.% B4C composite ceramics (0.16) and 20 Wt.%SiC-80 Wt.% B4C composite ceramics (0.20) are attributed to the formation of a sufficient amount of H3BO3 layer, rather than the layer of silicon oxides. Originality/value: This study will help to understand the friction behavior of SiC-B4C composite ceramics with different ratios of SiC to B4C treated by annealing in air.

DOI： 10.1108/ILT-08-2019-0350

Progress in tribological research of SiC ceramics in unlubricated sliding-A review Open Access

Zhang W., Yamashita S., Kita H.

Materials and Design 190 巻 2020年5月

出版者・発行元：Materials and Design

Silicon carbide ceramics have many excellent properties, such as high melting point, high strength, high thermal conductivity, high hardness, high stiffness, good chemical resistance, good electrical conductivity and remarkable wear resistance. Therefore, SiC ceramics are useful for various tribological applications. Nevertheless, SiC ceramics usually exhibit poor friction characteristics under unlubricated sliding contacts, which can greatly deteriorate the durability and reliability of a tribosystem. In this work, the tribological research progress of SiC ceramics was summarized based on microstructural characteristics, self-lubrication methods, surface characteristics and external factors. First, tribological performance of SiC ceramics can be improved by controlling microstructural characteristics, such as reducing grain size of SiC ceramics, acquiring elongated SiC grains, reducing the content of grain boundary/intergranular phase, crystallizing amorphous grain boundary phases, hardening intergranular phases, controlling cracks propagation way. Second, good self-lubrication property for SiC ceramics can be obtained by annealing heat treatment, adding the secondary phase or producing porous SiC ceramics. Third, tribological performance of SiC ceramics can be improved by proper surface processing or surface modification, such as proper roughness, surface texture or coating technology. Fourth, tribological performance of SiC ceramics is affected by various external factors. Besides, the research trends of SiC ceramic tribology in future were proposed. This work aims to provide some reference for the design of SiC ceramics with high wear resistance and low friction.

DOI： 10.1016/j.matdes.2020.108528

Water vapor adsorption on poly(N-isopropylacrylamide) gel cross-linked with N, N′-methylenebisacrylamide

Kubota M., Mochizuki T., Yamashita S., Kita H., Tokuyama H.

Materials Today Communications 22 巻 2020年3月

出版者・発行元：Materials Today Communications

Water vapor adsorption characteristics and the thermosensitivity for vapor adsorption of poly(N-isopropylacrylamide) gel (NIPA gel) cross-linked with N, N′-methylenebisacrylamide (MBAA) (cross-linked NIPA gel) were investigated for application in desiccant humidity control systems. The cross-linked NIPA gels were prepared via copolymerization of NIPA monomers and MBAA monomers, which were used as crosslinkers, at various reagent concentrations and polymerization temperatures in the range of 283–323 K. The water vapor adsorption isotherms of NIPA homopolymer, MBAA homopolymer, and cross-linked NIPA gels were obtained at adsorption temperatures in the range of 298–323 K using a volumetric gas adsorption apparatus. The water vapor adsorptivity of the cross-linked NIPA gel increased with increasing MBAA monomer concentration and decreasing NIPA monomer concentration. NIPA homopolymer under dry conditions showed weak thermosensitivity for water vapor adsorption between 298 and 313 K. Meanwhile, MBAA homopolymer showed almost no change in water vapor adsorptivity above adsorption temperatures of 298 K. The cross-linked NIPA gels had a similar thermosensitivity to NIPA homopolymer, but its sensitivity might be shifted to higher temperature than NIPA homopolymer. Thermosensitivity of the cross-linked NIPA gel was effective in improving polymer water adsorptivity, necessary for desiccant humidity control systems; however, the adsorption performance of the polymer gel systems investigated require further improvements before practical application will be possible.

DOI： 10.1016/j.mtcomm.2019.100804

A study on formation mechanisms of relief structure formed in situ on the surface of ceramics

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Norimatsu W., Kita H.

Ceramics International 45 巻 ( 17 ) 頁： 23143 - 23148 2019年12月

出版者・発行元：Ceramics International

The formation mechanisms of relief structure formed in situ on the surface of B4C–SiC ceramics were studied. The hardness difference between B4C and SiC is one of the formation conditions of relief structure. SiC grains are subjected to a preferential wearing owing to their lower hardness as compared to B4C grains, resulting in the difference of wear rates between B4C grains and SiC grains. Clean, no gap grain boundary in the B4C–SiC ceramics, which can make B4C grains and SiC grains bond firmly protecting them from pulling out, is another formation condition of relief structure.

DOI： 10.1016/j.ceramint.2019.08.008

Effect of nanorelief structure formed in situ on tribological properties of ceramics in dry sliding

Influence of surface roughness parameters and surface morphology on friction performance of ceramics Open Access

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Kita H.

Journal of the Ceramic Society of Japan 127 巻 ( 11 ) 頁： 837 - 842 2019年11月

記述言語：英語出版者・発行元：公益社団法人日本セラミックス協会

Influence of both surface roughness and surface morphology on frictional behavior of ceramics during run-in period under dry sliding was investigated simultaneously. Similar average surface roughness (Ra = 0.01-0.02 μm) was produced for the three ceramics: monolithic boron carbide ceramics, boron carbide-silicon carbide composite ceramics and monolithic silicon carbide ceramics. Surface roughness parameters show some influence on friction processes, however, surface morphology is considered as a more important competitive factor. Lower friction coefficient during run-in period and shorter sliding distance up to the steady state condition were observed for the B4C-SiC composite ceramics, which has a different surface morphology from those of monolithic B4C ceramics and monolithic SiC ceramics.

DOI： 10.2109/jcersj2.19124

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Kita H.

Ceramics International 45 巻 ( 11 ) 頁： 13818 - 13824 2019年8月

出版者・発行元：Ceramics International

Nanorelief structure formed on the surface of B 4 C–SiC ceramics by an in-situ method is reported. The nanorelief structure formed by the in-situ method, which differs from the relief structure produced by laser treatment, results from preferential wearing of SiC particles, which have lower hardness, by free diamond particles and mixed wear particles of B 4 C and SiC during polishing and sliding, respectively. The effect of the nanorelief structure formed by the in-situ method on the sliding dry friction against a SiC ball is examined using a pin-on-disk tribometer. A comparison of dry sliding of the B 4 C–SiC composite ceramics with nanorelief structure to that of SiC ceramics without nanorelief structure reveals that B 4 C–SiC composite ceramics have a lower coefficient of friction and a significantly lower specific wear rate than the SiC ceramics. Worn surface analysis indicates that the nanorelief structure does not disappear after a dry sliding test. The depth of the nanorelief structure formed by the in-situ method ranges from 10 to 40 nm. The friction and wear results are associated with the nanorelief structure formed by the in-situ method.

DOI： 10.1016/j.ceramint.2019.04.078

Progress in pressureless sintering of boron carbide ceramics–a review

P-7-1 廃棄物を利用したグリーンコンポジットの作製ならびにエクセルギー解析に基づく環境負荷評価

鶴見和幸, 山下誠司, 窪田光宏, 北英紀

日本エネルギー学会大会講演要旨集 28 巻 ( 0 ) 頁： 286 - 287 2019年7月

Zhang W., Yamashita S., Kita H.

Advances in Applied Ceramics 118 巻 ( 4 ) 頁： 222 - 239 2019年5月

出版者・発行元：Advances in Applied Ceramics

Boron carbide (B4C) ceramics has many outstanding performance, such as extremely high hardness, low density, high melting point, high elastic modulus, high thermoelectromotive force, high chemical resistance, high neutron absorption cross section, high impact and excellent wear resistance. Therefore, B4C ceramics can be used in various industrial applications, such as lightweight ceramic armour, high temperature thermocouples, neutron absorber, reactor control rods in nuclear power engineering, polishing media for hard materials, abrasive media for lapping and grinding, and wear resistant components (blasting nozzles, die tips and grinding wheels). Pressureless sintering is the method with industrialised application value for B4C ceramics, however, it is impossible to sinter pure B4C ceramics to high densities without additives by pressureless sintering. So sintering additives must be used to promote the densification of B4C ceramics. The different sintering additives used to promote the densification of boron carbide will be described in this review, including carbon additives, metallic additives, oxide additives, non-oxide additives, combined additives and rare earth oxide additives. Finally, the recent research trends for sintering methods and sintering additives of B4C ceramics will also be proposed.

DOI： 10.1080/17436753.2019.1574285

Heat press molding of open-celled porous Si-SiC ceramics consisting of skeletal strut via gelcasting with flexible and thermosetting polyurethane resin

Fracture analysis of porous SiSiC ceramics with anisotropic three-dimensional network structure Open Access

Himoto I., Yamashita S., Kita H.

Journal of the Ceramic Society of Japan 127 巻 ( 5 ) 頁： 295 - 303 2019年5月

記述言語：英語出版者・発行元：公益社団法人日本セラミックス協会

The fracture mechanism and reliability of typical dense ceramics can be statistically analyzed using a Weibull distribution as a basis for device design. However, it is not understood if the Weibull distribution can even be applied to highly porous ceramics. In this study, porous Siliconized Silicon Carbide (SiSiC) ceramics with anisotropic three-dimensional network structures in a porosity range of 7192% were fabricated and subjected to a fracture analysis using the results of three-point bending tests. Observations of fracture behavior during the bending tests were conducted using a high-speed camera, image analysis of stress distribution, and observation of crack distribution inside the partially damaged specimens using X-ray computed tomography. The results indicate non-linear behavior with multiple peaks in the loaddisplacement curves. In this regard, the fracture mechanism of the porous SiSiC ceramics was intrinsically different from the brittle fracture of dense ceramics and did not appear to be based on the weakest-link model. However, the Weibull distribution was found to be applicable to the bending strength of the porous ceramics with a confidence coefficient of 0.90. This was because although strain and cracks were generated sporadically during loading, the catastrophic fracture of the porous SiSiC ceramic specimens occurred with a macroscopic crack opening at the bottom of the test specimens, almost the same as a Mode I crack opening in dense ceramics. Furthermore, graded three-layer structures can be formed integrally using the proposed novel replication method with uniaxial pressing, taking the plateau of the stressstrain curve of the template polyurethane foam into account, providing a kind of damage tolerance owing to the sporadic generation and sequential propagation of cracks, manifested as the multiple peaks shown in the loaddisplacement curves.

DOI： 10.2109/jcersj2.18209

P-5-1 異形シェル型セラミック蓄熱体の開発とコンパクト蓄熱システムへの適合性評価

赤埴達也, 山下誠司, 窪田光宏, 北英紀

日本エネルギー学会大会講演要旨集 27 巻 ( 0 ) 頁： 292 - 293 2018年8月

P-6-1 中空セラミックス構造体の活用によるコンパクト蓄熱槽の開発

関井裕哉, 赤埴達也, 山下誠司, 窪田光宏, 北英紀

日本エネルギー学会大会講演要旨集 26 巻 ( 0 ) 頁： 314 - 315 2017年

Design of Heat Emission Controlled Spherical Container Constructed with Skeletal Ceramic Units Based on Heat Transfer Analysis 査読有り

Iori Himoto, Seiji Yamashita, Hideki Kita

JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 49 巻 ( 9 ) 頁： 850-863 2016年9月

Himoto I., Yamashita S., Kita H.

Advanced Powder Technology 27 巻 ( 3 ) 頁： 948 - 958 2016年5月

出版者・発行元：Advanced Powder Technology

A novel powder processing method for the fabrication of thin open-celled porous siliconized silicon carbide (Si-SiC) ceramic substrates is reported. Green SiC-carbon (C) substrate is first formed via a newly developed gelcasting method, using an organic-solvent-based slurry comprised of submicron SiC and nanometer C powders, along with a flexible and thermosetting polyurethane resin, based on the replica method with polyurethane foam as a template. Subsequently, the flexible semi-wet green substrate is uniaxially compressed under heating for molding to a set thickness; this is possible because of its thermosetting property (heat press molding). Although the slurry viscosity is highly sensitive to fine fluctuations in the powder volume concentration (PVC; 0.45-0.48), the PVC criterion for homogeneous powder solidification and improvement in the green SiC-C strut quality is determined to be 0.46. At 0.48 PVC, it is confirmed that the formed green SiC-C struts reproduce the template morphologically with a high correlation coefficient of 0.96 for the average strut thickness. As regards the open-celled sintered Si-SiC substrate (thickness: 6 mm), the Si-SiC strut appears to be skeletal with a triangular vertical cross-section, which can be successfully warped or twisted without cracking; furthermore, the mechanical strength is evidently improved via the heat press molding.

DOI： 10.1016/j.apt.2016.02.031

Design of heat emission controlled spherical container constructed with skeletal ceramic units based on heat transfer analysis

Heat Press Molding of Open-celled Porous Si-SiC Ceramics Consisting of Skeletal Strut via Gelcasting with Flexible and Thermosetting Polyurethane Resin 査読有り

Iori HIMOTO, Seiji YAMASHITA and Hideki KITA

Advanced Powder Technology 27 巻 ( 3 ) 頁： 948-958 2016年

Himoto I., Yamashita S., Kita H.

Journal of Chemical Engineering of Japan 49 巻 ( 9 ) 頁： 850 - 863 2016年

記述言語：英語出版者・発行元：公益社団法人化学工学会

Authors have been developing a spherical container having an inner wall constructed with skeletal ceramic units for transporting molten aluminum. This container is expected to provide innovative weight reduction and higher heat retaining property compared with current cylindrical containers having an inner wall made of castable refractory. In this study, a spherical inner wall with a combinative structure was designed: molten contacting part of the inner wall was constructed with skeletal unit made of reaction bonded silicon nitride (RBSN), while the non-contacting part with molten was constructed with skeletal unit made of aluminum titanate (AT). The quantity of heat emission from the container, temperature drop of molten in the container and thermal stress at the inner wall, while holding the molten, were simulated by heat transfer analysis. As a result, the spherical container reduced the quantity of heat emission compared with an inner wall constructed with only the RBSN unit, and was more reliable compared with that with only the AT unit. Thus, the new inner wall which enables a combination of light weight, high heat retaining property and reliability was proposed.

DOI： 10.1252/jcej.15we122

層状金属水酸化物を利用したヘテロ凝集構造体の作製とその充填層に関する研究

山下誠司

ホソカワ粉体工学振興財団年報 24 巻 ( 0 ) 頁： 129 - 132 2016年

記述言語：日本語出版者・発行元：公益財団法人ホソカワ粉体工学振興財団

粘土鉱物などに代表される層状金属水酸化物粒子は，その結晶構造に由来した特異的な電荷構造を有しており，水溶液中でpHなどの条件により結晶面によって異なる電荷を持つことから通常の粒子とは異なる凝集構造を形成することが知られている．本研究では，特異な表面電荷を利用し層状金属水酸化物粒子の異なる結晶面に金属酸化物微粒子を部分的に吸着させることで得られるヘテロ凝集体を作製し，それらの充填層について評価を行った．本研究室で新規化学蓄熱材料として合成しているMg系層状水酸化物粒子を用いて，Al2O3微粒子とヘテロ凝集体を作製した複合粒子について化学蓄熱システムへの適用を想定し，充填層における脱水－水和反応性について評価を行うことで，部分的ヘテロ凝集構造を用いた充填層の優位性を明らかにした．

DOI： 10.14356/hptf.14122