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NANO-SIZED COMPOSITE MATERIALS WITH HIGH PERFORMANCE
Niihara N.,Choa H.Y.,Sekino T. 한국분말야금학회 1996 한국분말야금학회 학술대회논문집 Vol.1996 No.1
Ceramic based nanocomposite, in which nano-sized ceramics and metals were dispersed within matrix grains and/or at grain boundaries, were successfully fabricated in the ceramic/cerarnic and ceramic/metal composite systems such as /SiC, /, MgO/SiC, mullite/SiC, /SiC, /B, /W, /Mo, /Ni and /Mo systems. In these systems, the ceramiclceramic composites were fabricated from homogeneously mixed powders, powders with thin coatings of the second phases and amorphous precursor composite powders by usual powder metallurgical methods. The ceramiclmetal nanocomposites were prepared by combination of H2 reduction of metal oxides in the early stage of sinterings and usual powder metallurgical processes. The transmission electron microscopic observation for the /SiC nanocomposite indicated that the second phases less than 70nm were mainly located within matrix grains and the larger particles were dispersed at the grain boundaries. The similar observation was also identified for other cerarnic/ceramic and ceramiclmetal nanocornposites. The striking findings in these nanocomposites were that mechanical properties were significantly improved by the nano-sized dispersion from 5 to 10 vol% even at high temperatures. For example, the improvement in hcture strength by 2 to 5 times and in creep resistance by 2 to 4 orders was observed not only for the ceramidceramic nanocomposites but also for the ceramiclmetal nanocomposites with only 5~01%se cond phase. The newly developed silicon nitride/boron nitride nanocomposites, in which nano-sized hexagonal BN particulates with low Young's modulus and fracture strength were dispersed mainly within matrix grains, gave also the strong improvement in fracture strength and thermal shock fracture resistance. In presentation, the process-rnicro/nanostructure-properties relationship will be presented in detail. The special emphasis will be placed on the understanding of the roles of nano-sized dispersions on mechanical properties.
Microarray Analysis of Oral Mucosal Epithelial Cell Sheet
Fawzia Bardag-Gorce,Joan Oliva,Hope Niihara,Andrew Makalinao,Sean Sabino,Derek Pan,Jacquelyn Thropay,Hiroyuki Sota,Yutaka Niihara,Andrew Wood 한국조직공학과 재생의학회 2013 조직공학과 재생의학 Vol.10 No.6
Corneal epithelium regeneration using autologous oral mucosal epithelial cell sheet is a successful new approach in corneal therapy. In the present study, gene expression profiling was performed to characterize engi-neered cell sheets. Cell sheets were obtained by culturing isolated rabbit oral mucosal epithelial cells on a thermo-responsive cultureware (UpCell®, CellSeed Inc. Japan). H&E staining of cell sheets showed a multistratified epi-thelium, similar to corneal epithelium. DeltaN-p63 stained positive in the basal cells, indicating that cell sheets have renewal capacity. Microarray analysis of these cell sheets showed that only 160 genes out of 43,000 rabbit probes listed on the microarray chip were identified. We first identified the extracellular matrix group of genes and found that matrix metalloproteinase MMP-1, MMP-3 and MMP-12, known to promote angiogenesis, were down regu-lated, while MMP-13 and collagen type VIII alpha 1 (COL8A1), proteins involved in wound healing, were up reg-ulated. Tissue inhibitors of metalloproteinase TIMP-1 and TIMP-3, anti-angiogenic factors, were also identified. Gap junction protein A7 (GJA7 or Connexin 45) was found up regulated, indicating that cell sheets have developed well preserved cell-cell interactions. Alcohol dehydrogenase 5 (ADH class III) and aldehyde dehydrogenase (ALDH1A1), involved in protecting the cornea against oxidative stress induced by UV radiation, were also found up regulated. In conclusion, microarray analysis has led us to identify new target molecules and their subsequent biochemical analysis indicated how the composite cell sheets are advantageous to the original isolated cells in terms of the integrity and potency of corneal epithelial grafts without any scaffolds.
Fabrication of Nanocomposite Powders by Sonochemical Method
Hayashi, Yamato,Sekino, Tohru,Niihara, Koichi The Korean Powder Metallurgy Institute 2001 한국분말재료학회지 (KPMI) Vol.8 No.3
Nano particles have recently been a major research interest, motivated by their unusual physical and chemical properties. Such particles can be synthesized using physical and chemical methods. The physical methods need expensive installation like vacuum induction furnace, whereas in chemical methods the process in generally very simple and low cost. In this study, simple and new fabrication process by using ultrasound was investigated to prepare the nano-sized metal particles on various powders at room temperature.
Structural modifications of SiOx/DLC films by thermal annealing
Won Jae Yang,Koichi Niihara,Keun Ho Auh 한양대학교 세라믹연구소 2004 Journal of Ceramic Processing Research Vol.5 No.3
SiOx/DLC films were deposited on Si substrates using CH4/(C2H5O)4Si/Ar gas mixtures by PECVD. The films deposited were identified as atomic-scale composite networks consisting mainly of diamond-like a-C:H and silica-like a-Si:O structures with a smaller contribution of Si-C and C-O bonds. Structural modifications of SiOx/DLC films were monitored under thermal annealing in an Ar atmosphere. The structural transitions of the amorphous carbon matrix in the SiOx/DLC films were investigated by a Raman spectrometer. The relationships between the microstructural modifications and mechanical properties are discussed.
Multifunctionality in Ceramic/Metal Nanocomposites
Sekino, Tohru,Kondo, Hiroki,Niihara, Koichi The Korean Powder Metallurgy Institute 2001 한국분말재료학회지 (KPMI) Vol.8 No.3
Several fabrication processes, corresponding nanostructural features and multifunctionality as well has been investigated for oxide ceramic based nanocomposites with metal nanodispersion (i.e., ceramic/metal nanocomposites). Transition metal (Ni, Co, etc) dispersed alumina and zirconia based nanocomposites have been synthesized by reducing and hot-press sintering of ceramic and metal oxide mixtures prepared by several method. Improved fracture strength (1.1 and 1.9 GPa for $Al_2O_3/Ni$ and $ZrO_2/Ni$ nanocomposites, respectively) of these composites have been achieved according to their nanostructures. In addition, ferromagnetic characteristic has been kept. The variation of magnetization with an applied stress has found to be more sensitive as smaller as the magnetic metal dispersion is. This result thus suggests the possibility of fracture and/or stress sensing of the composites by simple magnetic measurement.
$Al_2O_3$/5vo1%Cu 나노복합재료의 제조 및 기계적특성
오승탁,이재성,Koichi Niihara 한국분말야금학회 2000 한국분말재료학회지 (KPMI) Vol.7 No.4
An optimum route to fabricate the $Al_2O_3/Cu$ nanocomposites with sound microstructure and improved mechanical properties was investigated. Microstructural investigations for the composites prepared using $Al_2O_3/Cu$-nitrate showed that fine Cu particles with average size of 150 nm were homogeneously distributed within the $Al_2O_3$ matrix grains and at the grain boundaries. Fracture strength of 953 MPa and toughness of 4.8 Mpa(equation omitted)m were measured for the composite. The strengthening and toughening of the composites are explained by the refinement of the microstructure and the crack bridging/deflection, respectively.
Characterization of 3YSZ/LaPO4 composites coatings made by an atmospheric plasma spraying method
김성호,ZhenbgYi Fu,Koichi Niihara,이수완 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.2
3YSZ/LaPO4 composites applied for thermal barrier coatings (TBC) were deposited by an atmospheric plasma spraying (APS)method. The residual stresses and thermal conductivity of 3YSZ/LaPO4 composite coating samples were investigated. The thickness of the APS coating layer on the substrate metal was about 115 to 130 μm. Residual stresses of APS coating samples were observed to be both compressive and tensile. Residual stresses of APS coating samples were changed by the amount of LaPO4. As the amount of LaPO4 increased, the compressive residual stresses of APS coating samples were increased. The differences of the residual stress of APS coating samples were increased from 49.44MPa of 3YSZ/10 vol% LaPO4 to 305.9 MPa of 3YSZ/40 vol% LaPO4. The thermal conductivity of the 3YSZ/LaPO4 composite coating layer was calculated by utilizing APS coating layer on the substrate metal. The calculated value of the thermal conductivity of coating layers ranges from 0.11to 0.19 W/m·K.
김성호,ZhengYi Fu,Koichi Niihara,이수완 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.3
To apply a thermal barrier coating, the coating materials must satisfy the basic requirements. This paper explains composite powder processing and the characterization of sintered materials. The composite powders were prepared by two types of method: conventional ball-milling and chemical precipitation. The morphology of the powder differed with the processing method. In chemically precipitated powder, the surface of zirconia was coated with LaPO4. The samples were fabricated from these powders, using the PECSed method. The flexural strength of the nanocomposites was decreased with an increase in the amount of LaPO4 due to its poor mechanical properties. However, the thermal properties, such as thermal conductivity and high temperature stability, were lower and more stable than that of the monolith.