• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.166-171
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• 2007

The characterization of monolithic SiC and SiCf/SiC composite materials fabricated by NITE and RS processes was investigated in conjunction with the detailed analysis of their microstructure and density. The NITE-SiC based materials were fabricated, using a SiC powder with average size of 30 nm. RS- SiCf/SiC composites were fabricated with a complex slurry of C and SiC powder. In the RS process, the average size of starting SiC particle and the blending ratio of C/SiC powder were $0.4\;{\mu}m$ and 0.4, respectively. The reinforcing materials for /SiC composites were BN-SiC coated Hi-Nicalon SiC fiber, unidirectional or plain woven Tyranno SA SiC fiber. The characterization of all materials was examined by the means of SEM, EDS and three point bending test. The density of NITE-SiCf/SiC composite increased with increasing the pressure holding time. RS-SiCf/SiC composites represented a great decrease of flexural strength at the temperature of $1000\;^{\circ}C.$

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.245-249
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• 2000

Consolidation of amorphous powders is emerging as a route for synthesis of high strength composite materials. Diffusion processes necessary for consolidation are expected to be more rapid in amorphous state(SRO) than in the crystalline state(LRO). A new synthesis technique of exploiting polymeric ceramic precursors(polysilazane and polyborosilazane) is derived for Si$_3$N$_4$/SiC and boron-modified nanocomposites for extremely high temperature applications up to 200$0^{\circ}C$. The characterization methods include thermal analysis of DTA, and XRD, NMR, TEM, after pyrolysis, as a function of time and temperature.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1996년도 추계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.6-6
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• 1996

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 $Al_2O_3$/SiC, $Al_2O_3$/$Si_3N_4$, MgO/SiC, mullite/SiC, $Si_3N_4/SiC, $Si_3N_4$/B, $Al_2O_3$/W, $Al_2O_3$/Mo, $Al_2O_3$/Ni and $ZrO_2$/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 $Al_2O_3$/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.

• Corrosion Science and Technology
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• 제21권1호
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• pp.41-52
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• 2022

Herein, we report polyvinyl butyral composites coatings containing various loadings of 72-h bath sonicated hexagonal boron nitride particles (5 ㎛) to enhance barrier properties of coatings. Barrier properties of coatings were determined in 3.5 wt% NaCl after different time periods of immersion via electrochemical techniques such as open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization test. Coatings containing sonicated hexagonal boron particles exhibited improved corrosion resistance for longer periods of immersion compared to neat coating. We also discussed effects of hexagonal boron nitride on healing properties of polyvinyl butyral. Coatings containing 1.0 wt% loading of sonicated hexagonal boron nitride showed improved long-term barrier properties than coatings with other compositions. The presence of hexagonal boron nitride also affected the healing properties of polyvinyl butyral coatings besides their barrier properties. Such improved barrier properties of composites coatings were attributed to the high aspect ratio, plate-like shape, and electrically insulated nature of the filler.

• 한국세라믹학회지
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• 제47권6호
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• pp.498-502
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• 2010

Aluminium titanate($Al_2TiO_5$) has extremely anisotropic thermal expansion properties in single crystals, and polycrystalline material spontaneously microcracks in the cooling step after sintering process. These fine intergranular cracks limit the strength of the material, but provide an effective mechanism for absorbing strain energy during thermal shock and preventing catastrophic crack propagation. Furthermore, since machinable BN-ceramics used as an insulating substrate in current micro-electronic industry are very expensive, the development of new low-cost machinable substrate ceramics are consistently required. Therefore, cheap $Al_2TiO_5$-machinable ceramics was studied for the replacement of BN ceramics. $Al_2O_3-Al_2TiO_5$ ceramic composite was fabricated via in-situ reaction sintering. $Al_2O_3$ and $TiO_2$ powders were mixed with various mol-ratio and sintered at 1400 to $1600^{\circ}C$ for 1 h. Density, hardness and strength of sintered ceramics were systematically measured. Phase analysis and microstructures were observed by XRD and SEM, respectively. Machinability of each specimens was tested by micro-hole machining. The results of research showed that the $Al_2TiO_5$-composites could be used for low-cost machinable ceramics.

• 한국염색가공학회지
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• 제28권1호
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• pp.48-56
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• 2016

Improvement of heat sink technology related to the continuous implementation performance and extension of device-life in circumstance of easy heating and more compact space has been becoming more important issue as multi-functional integration and miniaturization trend of electronic gadgets and products has been generalized. In this study, it purposed to minimize of decline of the heat diffusivity by gluing polymer through compounding of inorganic particles which have thermal conductive properties. We used NH-9300 as base resin and used inorganic fillers such as silicon carbide(SiC), aluminum nitride(AlN), and boron nitride(BN) to improve heat diffusivity. After making film which was made from 100 part of acrylic resin mixed hardener(1.0 part more or less) with inorganic particles. The film was matured at $80^{\circ}C$ for 24h. Diffusivity were tested according to sorts of particles and density of particles as well as size and structure of particle to improve the effect of heat sink in view of morphology assessing diffusivity by LFA(Netzsch/LFA 447 Nano Flash) and adhesion strength by UTM(Universal Testing Machine). The correlation between diffusivity of pure inorganic particles and composite as well as the relation between density and morphology of inorganic particles has been studied. The study related morphology showed that globular type had superior diffusivity at low density of 25% but on the contarary globular type was inferior to non-globular type at high density of 80%.