研究者詳細 - 山下　誠司

論文 - 山下　誠司

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Novel Sodium Chloride/Aluminum Oxide Powder-Composite Structure with High Shape-Retention Performance for the Encapsulation of a High-Temperature Phase-Change Material 査読有り国際共著

Processes 12 巻 ( 3 ) 頁： 465 - 479 2024年12月

Study on the Repair of Irregular and Deep Cracks Induced by Thermal Shock Using Al-Cu-O Reactions in Al<inf>2</inf>O<inf>3</inf> Ceramics 査読有り Open Access

Bao F., Yamashita S., Kita H.

Processes 12 巻 ( 11 ) 2024年11月

担当区分：責任著者記述言語：英語出版者・発行元：Processes

The irregular and deep cracks induced by thermal shock in Al2O3 ceramics were repaired by applying Cu powder layer on their surface and heating at 1200 °C under an atmosphere of air. The Al-Cu-O liquid phase formed at 1200 °C by the reaction of molten Cu, oxygen, and Al2O3 phases penetrate deep into the narrow cracks, and the precipitation phases of Cu2O and CuAlO2 densely fill the crack interior. Our observation and analysis of the filled cracks and the surrounding areas of the repaired cracks, as well as the microstructural analysis results obtained through SEM-EDS and TEM observation, suggested the aforementioned crack repair mechanism. The bending strength of the coated surface after repairing the cracks is 301.8 MPa (ΔT = 300 °C), which is twice as strong as the specimen after thermal shock and 10% higher than the original strength of the base material.

DOI： 10.3390/pr12112606

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

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

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

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 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

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

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–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

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

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

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

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