• 한국재료학회지
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• 제9권12호
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• pp.1170-1175
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• 1999

반도체 폐 Si슬러지를 이용하여 질화반응 및 post-sintering을 통해 제조된 질화규소세라믹의 미세조직 및 기계적 특성을 광학현미경, SEM 및 XRD를 이용하여 연구하였다. 상당량의 $SiO_2$ 비정질상을 포함하는 폐 Si분말에서 많은 microcracks이 관찰되었다. 폐 슬러지를 사용한 Si 성형체의 질화율은 상용되고 있는 Si분말을 이용한 성형체의 값에 비해 낮은 값을 보였다. 그러나 질화온도가 증가함에 따라 질화율은 증가하였으며 1470$^{\circ}C$에서 질화율은 98%를 보였다. 반응소결체내에 존재하는 $Si_3N_4$의 결정은 ${\alpha}$와 ${\beta}$상으로 혼재되어 있으며 상당량의 산질화규소상이 검출되었다. 1950$^{\circ}C$에서 후처리된 시료의 최대파괴인성 및 파괴강도 값은 각각 5.6 $^MPa{\cdot}m^{1/2}$과 497 MPa로 H. C. Starck사의 Si을 이용한 것에 비해 낮은 값을 보였으며 이는 산질화규소 형성에 기인한 것으로 사료된다.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1093-1101
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• 2002

Continuous fiber ceramic composites (CFCCs) have advantages over monolithic ceramics : Silicon Nitride composites are not well used for application because of their low fracture toughness and fracture strength, but CFCCs exhibit increased toughness for damage tolerance, and relatively high stiffness in spite of low specific weight. Thus it is important to characterize the fracture resistance and properties of new CFCCs materials. Tensile and flexural tests were carried out for mechanical properties and the fracture resistance behavior of a SCS6 fiber reinforced Si$_3$N$_4$ matrix CFCC was evaluated. The results indicated that CFCC composite exhibit a rising R curve behavior in flexural test. The fracture toughness was about 4.8 MPa$.$m$\^$1/2 , which resulted in a higher value of the fracture toughness because of fiber bridging. Mechanical properties as like the elastic modulus, proportional limit and the ultimate strength in a flexural test are greater than those in a tensile test. Also a numerical modeling of failure process was accomplished for a flexural test. This numerical results provided a good simulation of the cumulative fracture process of the fiber and matrix in CFCCs.

• 한국세라믹학회지
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• 제20권4호
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• pp.305-314
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• 1983

In order to enhance the rate of th nitridation and to give the high density of reaction-bonded silicon nitride MgO powder as nitriding aid were added to silicon powders and the mixture was pressed isostatically into compacts which were nitrided in the furnace of 1, 35$0^{\circ}C$ where 95% $N_2$-5% $H_2$ gases were flowing. As the other nitriding aid $Mg(NO_3)_2 6H_2O$ was selected, A slip made of magnesium nitrate solution and fine silicon particles was spray-dried and then decomposed at 30$0^{\circ}C$. Magnesium oxide-coated silicon powders were formed into compacts prior to the nitridation on the same condition as the former. Magnesium nitrate (MgO, produced from the decomposition of magnesium nitrate) was more effective for the formation of the $\beta$-phase in the initial stage of the nitridation probably due to the easy formation of $MgO-SiO_2$-metal oxide eutectic melt. It has been confirmed that forsterite was formed as a result of the reaction between MgO and $SiO_2$ film of silicon surface. It was considered that MgO produced from magnesium nitrate may be finer more reactive and more uniformly distributed on the surface of silicon particles than original MgO. The higher the forming pressure was the more the $\beta$-phase was formed.

• 한국세라믹학회지
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• 제43권8호
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• pp.472-478
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• 2006

The effect of compositional and processing variables on a nitriding reaction of silicon powder compact and subsequent post sintering of RBSN (Reaction-Bonded Silicon Nitride) was investigated. The addition of a nitriding agent enhanced nitridation rate substantially at low temperatures, while the formation of a liquid phase between the nitriding agent and the sintering additives at a high temperature caused a negative catalyst effect resulting in a decreased nitridation rate. A liquid phase formed by solely an additive, however, was found to have no effect on nitridation for the additive amount used in this research. The original site of a decomposing pore former was loosely filled by a reaction product ($Si_3N_4$), which provided a specimen with nitriding gas passage. For SRBSN (Sintered RBSN) specimens of high porosity, only a marginal dimensional change was measured after post sintering. Its engineering implication for near-net shaping ability is discussed.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.97.1-97.1
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• 2012

Porous ceramics are widely used for applications such as catalysis supports, gas distributors and filters such as DPF. For these purpose, it is important to have proper porosity controlling pore structure while maintaining mechanical and thermal properties. In this work, we have prepared the porous ceramic structures made of reaction bonded silicon nitride with hierarchical pore structures. Uni-directionally aligned pore channels, which are mostly filled with ${\beta}$-Si3N4 whiskers, were achieved by an ice-templating method. The structures of the pore channels and the walls are controllable by the processing conditions, such as solid concentration, freezing rate of the slurry, and additives. We have investigated and characterized the influences of the conditions on the microstructures and the properties, such as porosity, pore size distribution, lamellar thickness, wavelength, and orientations. The compressive strength test and flow test was performed to determine the structural integrity and air permeability.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.15-15
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• 2011

As you know, boron compounds, borax ($Na_2B_4O_5(OH)_4{\cdot}8H_2O$) etc. were known thousands of years ago. As for natural boron, it has two naturally occurring and stable isotopes, boron 11 ($^{11}B$) and boron 10 ($^{10}B$). The neutron absorption $^{10}B$ is included about 19~20% with 80~81% $^{11}B$. Boron is similar to carbon in its capability to form stable covalently bonded molecular networks. The mass difference results in a wide range of ${\beta}$ values between the $^{11}B$ and $^{10}B$. The $^{10}B$ isotope, stable with 5 neutrons is excellent at capturing thermal neutrons. For example, it is possible to decrease a thermal neutron required for the nuclear reaction of uranium 235 ($^{235}U$). If $^{10}B$ absorbs a neutron ($^1n$), it will change to $^7Li+^1{\alpha}$ (${\alpha}$ ray, like $^4He$) with prompt ${\gamma}$ ray from $^{11}B$ $^{11}B$ (equation 1). $$^{10}B+^1n\;{\rightarrow}\;^{11}B\;{\rightarrow}\; prompt \;{\gamma}\;ray (478 keV), \;^7Li+4{\alpha}\;(4He)\;\;\;\;{\cdots}\; (1)$$ If about 1% boron is added to stainless steel, it is known that a neutron shielding effect will be 3 times the boron free steel. Enriched boron or $^{10}B$ is used in both radiation shielding and in boron neutron capture therapy. Then, $^{10}B$ is used for reactivity control and in emergency shutdown systems in nuclear reactors. Furthermore, boron carbide, $B_4C$, is used as the charge of a nuclear fission reaction control rod material and neutron cover material for nuclear reactors. The $B_4C$ powder of natural B composition is used as a charge of a control material of a boiling water reactor (BWR) which occupies commercial power reactors in nuclear power generation. The $B_4C$ sintered body which adjusted $^{10}B$ concentration is used as a charge of a control material of the fast breeder reactor (FBR) currently developed aiming at establishment of a nuclear fuel cycle. In this study for new boron compound, silicon boride ceramics for capturing thermal neutrons, preparation and characterization of both silicon tetraboride ($SiB_4$) and silicon hexaboride ($SiB_6$) and ceramics produced by sintering were investigated in order to determine the suitability of this material for nuclear power generation. The relative density increased with increasing sintering temperature. With a sintering temperature of 1,923 K, a sintered body having a relative density of more than 99% was obtained. The Vickers hardness increased with increasing sintering temperature. The best result was a Vickers hardness of 28 GPa for the $SiB_6$ sintered at 1,923K for 1 h. The high temperature Vickers hardness of the $SiB_6$ sintered body changed from 28 to 12 GPa in the temperature range of room temperature to 1,273 K. The thermal conductivity of the SiB6 sintered body changed from 9.1 to 2.4 W/mK in the range of room temperature to 1,273 K.