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.

Multifunction Integrated Nanocomposites and Their Industrial Applications

Niihara K.,Kusunose M.,Nakayama T.,Sekino T.,Hayashi Y. 한국분말야금학회 2003 한국분말야금학회 학술대회논문집 Vol.2003 No.1

Multifunction Integrasted Ceramic Based Nanocomposites

Niihara Koichi,Nakayama Tadachika,Suematsu Hisayuki,Sekino Tohru,Kusunose Takafumi 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

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.

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.

Sn 산화물 나노입자 형성에 미치는 대류 가스의 영향

이광민,정우남,양상선,K. Niihara 한국분말야금학회 2002 한국분말재료학회지 (KPMI) Vol.9 No.1

In the present study of IGC (Inert Gas Condensation) evaporation-condensation processing study, the effects of IGC convection gas on the crystallographic structure, size and shape of tin oxide nanoparticles were investigated. In addition, the phase transformation of tin oxide nanoparticles was studied after heat treatment. IGC processing was conducted at 1000℃ for 1 hr. The mixture gas of oxygen and helium was used as a convection gas. Metastable tetragonal SnO nanoparticles were obtained at a lower convection gas pressure, whereas amorphous tin oxide nanoparticles were obtained at a higher one. The formation of amorphous phase could be explained by the rapid quenching of the vaporized atoms. The resultant nanoparticles size was about 10 nm with a rounded shape. The tin oxide nanoparticles prepared by IGC were almost transformed to the stable tetragonal SnO₂ after heat treatment.

$Al_2O_3$/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.

Thermal Residual Stress Relaxation Behavior belated with Interface Structure of Oxide Based Nanocomposites

Choa,Y.H.,Niihara,K. 국립경상대학교 공과대학 부설 첨단소재연구소 1998 尖端素材 Vol.8 No.-

Plastic deformation as thermal residual stress relaxation was observed by TEM around interface of intragranular SiC particles in the Al₂O₃matrix for Al₂O₃/SiC nanocompo site system. The dislocations are generated at selected planes and there is a tendency far the dislocations to form a subgrain boundary structure with low-angle grain bound aries and networks. In this experiment, dislocation generated in the Al₂O₃matrix during down from sintering temperatures by the highly localized thermal stresses within and/or around SiC particles caused from the thermal expansion mismatch between Al₂O₃matrix and SiC particle was observed. In monolithic Al₂O₃and Al₂O₃/SiC microcomposite system, however, the dislocation formation was not observed compared to Al₂O₃/SiC nanocompo site system. These phenomena is closely related to the plastic relaxation of the elastic stress and strain energy associated with both thermal misfitting inclusions and creep behaviors. The plastic relaxation behavior was explained by combination of yield stress and internal stress.

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.

Optical, Mechanical and Tribological Properties of Boronnitride Dispersed Silicon Nitride Ceramics

Joshi, Bhupendra,Fu, Zhengyi,Niihara, Koichi,Lee, Soo-Wohn Materials Research Society of Korea 2010 한국재료학회지 Vol.20 No.8

Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline $Si_3N_4$ ceramics were affected by the density, ${\alpha}:{\beta}$-phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of $\alpha-Si_3N_4$, AlN, MgO, and h-BN at $1850^{\circ}C$. The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped $Si_3N_4$ ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.