Papers by Author: Tohru Sekino

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Authors: H. Takano, Takafumi Kusunose, Tohru Sekino, Rajagopalan Ramaseshan, Koichi Niihara
Abstract: 6061 aluminum alloy composite reinforced with α-alumina and aluminum borate is fabricated by casting method. The above mentioned composite has been compared to a similar composite without aluminum borate reinforcement for their machinability. The aluminum borate filler was controlled up to (2.5, 5.0 and 30vol %) on the surface of α-alumina. The reaction zone between alumina and the matrix in both the systems are analyzed with the help of TEM micrographs as well as X-ray diffraction profiles. At the reaction zone between alumina and the aluminum alloys, some spinel-like compounds (MgAl2O4) are identified. Finally, machinability was analyzed with the single point tool machining.
Authors: Young Ik Seo, Kyung Ho Min, Young Jung Lee, Kyu Hwan Lee, Tohru Sekino, Young Do Kim
Abstract: Compressive behavior of 7xxx series Al metal matrix composite (MMC) powders with different ceramic contents and different particle size were investigated. As a starting powder of the experiments, ceramic contents of each starting powder were 5 and 10 wt.% and ceramic particle size of starting powder were 20 and 100 ㎛, respectively. And 7xxx Al blended powder was used for comparison. The powders were uniaxially cold-compacted using cylindrical die with a compacting pressure 250 MPa and sintered at 620oC in a dry N2 atmosphere for 60 min with heating rate of 20oC/min. In case of heat treatment condition, sintered parts were solution treated at 475oC and aged at 175oC. To reveal the effect of Al2O3 particle content and particle size on the mechanical properties of composites, compression test were conducted with constant strain rate of 1×10-3/s using sub-size cylindrical samples of 9 mm diameter. Compression test was performed 5 times and its average value was used. Then fractography analysis was conducted using scanning electron microscope.
Authors: Takafumi Kusunose, Tohru Sekino, P.E.D. Mogan, Koichi Niihara
Abstract: The Si3N4/YSiO2N composite in which crystalline YSiO2N was formed as grain boundary phase was fabricated by hot-pressing the mixture of SiO2, Si3N4 and Y2O3. The fracture toughness of this composite was significantly improved, compared to the Si3N4 composites containing Y5Si3O12N or Y2Si3O3N4 as a grain boundary phases. To clarify the toughening mechanism, the microstructure and the crack propagation profiles were observed.
Authors: Yamato Hayashi, Hirotsugu Takizawa, Yoshitaka Saijo, Tohru Sekino, Katsuaki Suganuma, Koichi Niihara
Abstract: Nano-sized metal particles have recently attracted considerable interest owing to their application potential. Such particles can be synthesized using physical and chemical methods. In this study, nano-sized noble metals were synthesized through the reaction of metal oxides by ultrasonic. This means that the chemical reactions which take place under conventional conditions can be accelerated by ultrasonic cavitations. In general, the chemical effects of ultrasonic irradiation fall into three areas: homogeneous sonochemical efffects of liquids, heterogeneous sonochemical effects of liquid-liquid or liquid-solid systems, and sonocatalytic effects. It has been proposed that liquid-liquid systems are used for the fabrication of nano-metal particles in the past. In this study, the fabrication of nano-metal particles and supported composites was investigated for the liquid-solid system from a viewpoint of economy and ecology. By choosing suitable conditions, it is reasonable to expect that these simple ultrasonic processes can be extended to obtain nano-sized metal particles. Thus applications by using these reactions were investigated to prepare the nano-sized metal particle supported materials, and mechanisms were investigated.
Authors: Ari T. Hirvonen, Yoo Yamamoto, Tohru Sekino, Roman Nowak, Koichi Niihara
Abstract: Ceramic nanocomposites became nowadays an important ingredient of many structural and electronic ceramics, as well as ceramic coatings. The same applies to chemically processed and environmental related ceramics. The performance and characteristics of ceramic components are considerably influenced by the characteristics of precursor powder. The outstanding properties possessed by advanced nanoceramics are achieved through exceptional composition and microstructure that require very careful control throughout the successive stages of the applied processing.
Authors: Youn Gyu Han, Tomonori Shibata, Rajagopalan Ramaseshan, Tohru Sekino, Koichi Niihara
Abstract: A novel organic/inorganic composite material which can work as a pressure sensor has been synthesized. This composite basically contains nano-sized carbon particles as conductive filler into an elastomer matrix to achieve pressure sensitive function. The superior pressure sensitive effect was showed at 0.88vol% of carbon particles while in the previous study the micro-sized carbon particle was required above 30vol%. In addition, nano-sized silica particles were added to reinforce electrical insulation properties and to improve the pressure sensing reliability of the composite. The addition of the surface modified silica improved better both the sensing performance and the mechanical strength than the composite containing non-modified silica particles. These polymer-based sensors have economical advantage due to low cost production regardless of the high performance.
Authors: Hao Wang, Wei Min Wang, Zheng Yi Fu, Tohru Sekino, Koichi Niihara
Abstract: Mullite-based nanocomposites with embedded FeCr alloy nanoparticles were synthesized by reduction of sol-gel prepared Al5.4(Fe0.8Cr0.2)0.6Si2O13 solid solution in hydrogen. The feature of the formation of FeCr alloy is characterized by XRD analysis. Structural characterization revealed that the intragranular FeCr alloy nanoparticles along with inter-granular iron grains were obtained in as reduced sample. After acid washing, the intergranular metal grains were eliminated. The static magnetic properties of nanocomposite powders were studied using Magnetic Property Measurement System. It is found that part of the intra-granular metal nanoparticles have superparamagnetic behavior at room temperature.
Authors: C.L. Li, Doh Hyung Riu, Tohru Sekino, Koichi Niihara
Authors: Yoshifumi Konishi, Takafumi Kusunose, P.E.D. Morgan, Tohru Sekino, Koichi Niihara
Authors: Toshiyuki Takagi, Yong Ho Choa, Tohru Sekino, Koichi Niihara
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