研究者詳細 - 山下　誠司

論文 - 山下　誠司

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

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

Open Access

Scopus

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

Open Access

Scopus

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

Open Access

Scopus

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

Open Access

Scopus

PubMed

Frictional characteristics of carbide ceramics in water

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

Scopus

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

Scopus

CiNii Research

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

Scopus

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

Open Access

Scopus

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

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

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

Web of Science

Scopus

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

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

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

Scopus

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

Open Access

Scopus

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

Web of Science

Scopus

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

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

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

Scopus

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

Scopus

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