Papers by Author: Minoru Takahashi

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Authors: Minoru Takahashi, Y. Kataoka, C.-S. Chieh, M. Oya, Masayoshi Fuji
Authors: C. Takai, Masayoshi Fuji, Minoru Takahashi
Abstract: The control of particle dispersion is essential to the fabrication of highly designed ceramics. In this study, a direct observation technique was employed to characterize the heterocoagulation of particles in two-component slurry. TEM observation of solidified slurry composed of alumina and silica particles was attempted to evaluate heterocoagulation. At 10 mass% solid loading, the TEM showed the aggregation of silica with dispersed alumina particles at acidic region. A large scale of aggregation caused by attractive force among alumina and silica particles was observed on the TEM images at neutral region. At basic region, the aggregation of alumina with dispersed silica particles was observed. The measurements of zeta potential and viscosity were conducted to explain the results of the TEM observations.
Authors: Gunawan Hadiko, Yong Sheng Han, Masayoshi Fuji, Minoru Takahashi
Abstract: Hollow calcium carbonate (CaCO3) particles were synthesized by bubbling CO2 in the solution of calcium chloride (CaCl2) with the presence of ammonia at room temperature. In this method, CO2 bubble, besides as reactant, has an important role as a template for forming hollow particles. The precipitation was carried out by controlling the precipitation condition, such as pH, flow rate and additives. Hollow calcium carbonate particles were precipitated with the major crystal phase of vaterite. An interesting finding is that magnesium ion (Mg2+) can suppress the transformation of vaterite to calcite by inhibiting the growth of the calcite.
Authors: Hideo Watanabe, Masayoshi Fuji, Atsuko Tada, Minoru Takahashi
Abstract: Nobel metal particles with nanometer size have attracted keen interest because of, for example, their high catalytic activity to be applied for industrial applications. In this study, nano-sized gold particles were deposited onto a graphite carbon plate by two approaches: 1) electrophoresis of colloidal gold nanoparticles, 2) electrolysis of chlorauric acid. For former case, commercially-available gold nanoparticle and anionic mercapto ligand-stabilized gold nanoparticles, synthesized by citric acid reduction of chlorauric acid, were used. Size and morphology of the gold particles deposited were characterized by scanning electron microscopy. Electrolytic deposition resulted in larger gold particles around tens to hundreds nm in size. Electrophoretic deposition accomplished particle sizes smaller than 15 nm, which basically reflected the size of colloidal gold particles used.
Authors: Hideo Watanabe, Hideki Matsushima, Masayoshi Fuji, Minoru Takahashi
Abstract: Layered clay has been of great interest because of their nano-sized layer structure and hence intercalation and ion-exchange capacity to be used as a host material of composite with polymers and/or metals. In this study, smectite as a silicate-layered clay was easily exfoliated and dispersed into purified water, and was deposited onto a cupper plate for which dc voltage ranging from + 1.0 V to + 6.0 V was applied with respect to a counter platinum plate electrode. The cupper plate was pre-treated by chemical and chemical mechanical polishing (CP and CMP) prior to the electrophoretic deposition (EPD). The surface roughness of the substrate as well as the smectite film formed was characterized by an atomic force microscope (AFM). The thickness of smectite layer was estimated using an X-ray fluorescence (XRF) analysis as well as a scanning electron microscope (SEM) observation. The layer thickness can be described as a function of operational parameters such as applied voltage and operating time. Smooth smectite film with thickness ranging from 100 nm to 10 μm has been successfully fabricated onto the CMP cupper plate by the EPD method in this study.
Authors: J. Takahashi, M. Natsuisaka, Shoich Shimada, H. Itoh, Minoru Takahashi, T. Nishikawa
Authors: Minoru Takahashi, Koichiro Adachi, Ruben L. Menchavez, Masayoshi Fuji
Abstract: In this study, we propose a new process to fabricate electrically conductive alumina by gelcasting and reduction sintering. The process used the conventional gelcasting method except for varying amounts of monomer at 2.8, 5.5, and 8.0 wt.% relative to the weight of the slurry. In the plastic mould, the slurry was under in situ solidification for 3 hrs at 25oC to achieve gelation. The freshly gelled bodies were demolded, carefully dried, and then sintered at 1100oC, 1300oC, and 1550oC in nitrogen atmosphere. The holding times at 1100oC and 1300oC was 2 hours, while at 1550oC were 2, 4, and 6 hrs. The sintered alumina body was characterized by electrical property, X-ray diffraction, and scanning electron microscopy. Results showed that monomer additions and sintering schedule significantly affect in lowering electrical resistance. The low value was 3.6×106 +cm at 8.0wt.% monomer addition and sintering at 1550oC for 2 hrs. The effect of physical properties on electrical conductivity and the corresponding reaction mechanism were discussed in details.
Authors: Gunawan Hadiko, Yong Sheng Han, Masayoshi Fuji, Minoru Takahashi
Abstract: Hollow calcium carbonate (CaCO3) particles were synthesized by bubbling CO2 in the solution of calcium chloride (CaCl2) with the presence of ammonia at room temperature. Hollow calcium carbonate is a potential component to be used as pharmaceuticals, agrochemicals, and catalysis. This paper investigated the effect of additive on the hollow structure. In this study was used vanadate ion as additive agent. Physical characteristics of precipitate were evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD).
Authors: Ruben L. Menchavez, Masayoshi Fuji, Tomohiro Yamakawa, Takeshi Endo, Minoru Takahashi
Abstract: This study investigates the phase compositions in gelcast dense alumina and porous alumina that were sintered in an inert atmosphere. Both materials were gelcasted using identical slurry composition except for adding surfactant to slurry intended for porous shaping. The resulting gelcasted samples were dried and then sintered in argon gas at 1700oC. The X-ray photoelectron analysis was used for identifying the phase compositions in sintered samples, which was supported with TG/DTA and electrical measurements. Results showed that, in addition to alumina and carbon phases, the dense sample yielded Al4C3 and Al, while porous sample yielded aluminum oxycarbides. The formation of these phases reduced the carbon content through different chemical reactions to a limited extent because they formed a protective layer on alumina grains, which prevented the direct contact between alumina and carbon. Subsequent measured electrical resistivities of dense and porous alumina were, respectively, 0.20 and 0.32 ,-cm, indicating that the carbon networks are preserved in both materials.
Authors: Hisao Suzuki, Hidetoshi Miyazaki, Junichi Takahashi, Shirou Shimada, Toshitaka Ota, Minoru Takahashi, Yasuo Hikichi
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