• 한국세라믹학회지
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• 제41권7호
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• pp.541-547
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• 2004

일반적으로 혼합분말의 소결에서 작은 입자에 큰 입자의 첨가는 소결성의 저하를 가져온다. 본 연구에서는 이러한 원리를 이용하여 작은 SiC 입자에 큰 SiC 휘스커 또는 큰 SiC 입자를 첨가하여 소결성을 저하시키고, YAG(Y$_3$A1$_{5}$O$_{12}$)상을 소결 첨가제로 사용함으로서 다공질 SiC 세라믹스를 제조하였다. 제조된 다공질 SiC 세라믹스의 기공율은 큰 입자의 함량과 소결 압력을 제어함으로서 0.3-39% 범위에서 제어할 수 있었다. 기공율은 큰 입자의 함량이 증가함에 따라 증가하였고, SiC 휘스커를 첨가하는 것이 큰 SiC 입자를 첨가하는 것 보다 기공율을 높이는데 효과적이었다. 제조된 다공질 세라믹스에서 기체의 통기성은 기공율이 증가함에 따라 증가하였고, 굽힘강도는 기공율이 증가함에 따라 감소하였다. 기공율이 18% 이상인 다공질 SiC 세라믹스의 경우에 주목할 만한 변형율이 관찰되었다.

• The Korean Journal of Ceramics
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• 제1권3호
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• pp.147-151
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• 1995

Porous composite of $Al_2O_3$ and AIN based mullite and SiC can be prepared by alumium reaction synthesis and atmosphere controllied sintering in order to improve the durability of a gas filter body. The porous $Al_2O_3$-AIN-mullite, which has a strength of 168 kg/$\textrm{cm}^2$ and porosity of 51.59%, could be obtained by stmospheric firing at $1600^{\circ}C$ and the porous $Al_2O_3$-AIN-SiC with a porosity of 33% and strength of 977 kg/$\textrm{cm}^2$, could also be prepared. The average pore size has been changed from 0.2$\mu\textrm{m}$ in a reduction atmosphere and to 2$\mu\textrm{m}$ in an air atmosphere, respectively.

• 한국세라믹학회지
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• 제55권3호
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• pp.285-289
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• 2018

We synthesized silicon carbide (${\beta}-SiC$) nanowires with nano-scale diameter (30 - 400 nm) and micro-scale length ($50-200{\mu}m$) on a porous body using low-grade silica and carbon black powder by carbothermal reduction at $1300-1600^{\circ}C$. The SiC nanowires were formed by vapor-liquid-solid deposition with self-evaporated Fe catalysts in low-grade silica. We investigated the characteristics of the SiC nanowires, which were grown on a porous body with Ar flowing in a vacuum furnace. Their structural, optical, and electrical properties were analyzed with X-ray diffraction (XRD), transmission electron microscopy (TEM), and selective area electron diffraction (SAED). We obtained high-quality SiC single crystalline nanowire without stacking faults that may have uses in industrial applications.

• 한국재료학회지
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• 제16권3호
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• pp.188-192
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• 2006

The microstructures and mechanical properties of continuously porous $SiC-Si_3N_4$composites fabricated by multi-pass extrusion were investigated at different Si levels added. Si-powder with different weight percentages (0%, 5%, 10%, 15%, 20%) was added to the SiC powder to make the raw mixture powders, with $6wt%Y_2O_3-2wt%Al_2O_3$ as sintering additives, carbon ($10-15{\mu}m$) as a pore-forming agent, ethylene vinyl acetate as a binder and stearic acid ($CH_3(CH_2)_{16}COOH$) as a lubricant. In the continuously porous $SiC-Si_3N_4$ composites, $Si_3N_4$ whiskers like the hairs of nostrils were frequently observed on the wall of the pores. In this study, the morphology of the $Si_3N_4$ whiskers was investigated with the silicon addition content. In the composites containing of 10 wt% Si, a large number of $Si_3N_4$ whiskers was found at the continuous pore regions. In the sample to which 15 wt% Si powder was added, maximum values of about 101 MPa bending strength and 57.5% relative density were obtained.

• 한국세라믹학회지
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• 제49권6호
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• pp.625-630
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• 2012

Highly porous silicon carbide (SiC) ceramics were fabricated from polysiloxane, SiC and carbon black fillers, AlN-$Y_2O_3$ additives, and poly (ether-co-octene) (PEOc) and expandable microsphere templates. Powder mixtures with a fixed PEOc content (30 wt%) and varying SiC filler contents from 0-21 wt% were compression-molded. During the pyrolysis process, the polysiloxane was converted to SiOC, the PEOc generated a considerable degree of interconnected porosity, and the expandable microspheres generated fine cells. The polysiloxane-derived SiOC and carbon black reacted and synthesized nano-sized SiC with a carbothermal reduction during a heat-treatment. Subsequent sintering of the compacts in a nitrogen atmosphere produced highly porous SiC ceramics with porosities ranging from 78 % to 82 % and a flexura lstrength of up to ~7 MPa.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2004년도 춘계학술발표대회 및 제6회 신소재 심포지엄
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• pp.44-44
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• 2004

• 통합자연과학논문집
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• 제3권3호
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• pp.153-156
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• 2010

Oxidation behaviors of porous silicon were investigated by the measurement of area of $SiO_2$ vibrational peaks in FT-IR spectra during thermal oxidation of porous silicon at corresponding temperatures. Visible photoluminescent porous silicon samples were obtained from an electrochemical etch of n-type silicon of resistivity between 1-10 ${\Omega}/cm$. The etching solution was prepared by adding an equal volume of pure ethanol to an aqueous solution of HF. The porous silicon was illuminated with a 300 W tungsten lamp for the duration of etch. Etching was carried out as a two-electrode galvanostatic procedure at applied current density of 200 $mA/cm^2$ for 5 min. The porosity of samples prepared was about 80%. After formation of porous silicon, the samples were thermally oxidized at $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$, and $400^{\circ}C$, respectively. The growth rate of $SiO_2$ layer of porous silicon was investigated by using FT-IR spectroscopy. The effect of oxidation of porous silicon was presented.

• 한국세라믹학회지
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• 제27권3호
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• pp.412-422
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• 1990

Porous SiC ceramics were proposed to be promising materials for high-temperature thermoelectric energy conversion. Throughthe thermoelectric property measurements and microstructure observations on the porous alpha SiC and the mixture of $\alpha$-and $\beta$-SiC, it was experimentally clarified that elimination of stacking faults and twin boundaries by grain growth is effective to increase the seebeck coefficient and increasing content of $\alpha$-SiC gives rise to lower electrical conductivity. Furthermore, the effects of additives on the thermoelectric properties of 6H-SiC ceramics were also studied. The electrical conductivity and the seebeck coefficient were measured at 35$0^{\circ}C$ to 105$0^{\circ}C$ in argon atmospehre. The thermoelectric conversion efficiency of $\alpha$-SiC ceramics was lower than that of $\beta$-SiC ceramics. The phase homogeneity would be needed to improve the seebeck coefficient and electrical conductivity decreased with increasing the content of $\alpha$-phase. In the case of B addition, XRD analysis showed that the phase transformation did not occur during sintering. On the other hand, AlN addiiton enhanced the reverse phase transformation from 6H-SiC to 4H-SiC, and this phenomenon had a great effect upon the electrical conductivity.

• 한국산학기술학회논문지
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• 제20권3호
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• pp.29-34
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• 2019

SiC는 큰 에너지 밴드 갭을 갖고, 불순물 도핑에 의해 p형 및 n형 전도의 제어가 용이해서 고온용 전자부품 소재로 활용이 가능한 재료이다. 특히 $N_2$ 분위기, $2000^{\circ}C$에서 ${\beta}-SiC$ 분말로부터 제조한 다공질 n형 SiC 반도체의 경우, $800{\sim}1000^{\circ}C$에서의 도전율 값이 단결정 SiC와 비교해서 비슷하거나 오히려 높은 값을 나타내었으며, 반면에 열전도율은 치밀한 SiC 세라믹스와 비교시 1/10~1/30 정도로 낮은 값을 나타내었다. 본 연구에서는 소결온도를 낮추기 위해 n형 ${\beta}-SiC$에 함침 시킨 polycarbosilane (PCS)의 열분해에 의한 반응소결 공정 ($1400{\sim}1600^{\circ}C$)으로 다공질 소결체를 제작하였다. 함침 및 소결공정($N_2$ 분위기, $1600^{\circ}C$, 3시간)을 반복함에 따라 상대밀도는 크게 증가하지 않았지만 Seebeck 계수 및 도전율은 크게 증가하였다. 본 연구에서의 열전변환 효율을 반영하는 power factor는 고온에서 상압소결 공정으로 제작한 다공질 SiC 반도체에 비해 1/100~1/10 정도 작게 나타났지만, 미세구조 및 캐리어 밀도를 정밀하게 제어하면, 본 연구에서의 반응소결 공정으로 제작한 SiC 반도체의 열전물성은 크게 향상될 것으로 판단된다.

• 한국세라믹학회지
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• 제47권4호
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• pp.308-311
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• 2010

Porous SiC samples were prepared with three types of wood (poplar, pine, big cone pine) by simply embedding the wood charcoal in a powder mixture of Si and $SiO_2$ at 1600 and $1700^{\circ}C$. The basic engineering properties such as density, porosity, pore size and distribution, and strength were characterized. The samples showed full conversion to mostly $\beta$-SiC with good retention of the cellular structure of the original wood. More rigid SiC struts were developed for $1700^{\circ}C$. They showed similar bulk density ($0.5{\sim}0.6\;g/cm^3$) and porosity (81~84%) irrespective of the type of wood. The poplar sample showed three pore sizes (1, 8, $60\;{\mu}m$) with a main size of $60\;{\mu}m$. The pine sample showed a single pore size ($20\;{\mu}m$). The big cone pine sample showed two pore sizes (10, $80\;{\mu}m$) with a main size of $10\;{\mu}m$. The bend strength was 2.5 MPa for poplar, 5.7 MPa for pine, 2.8 MPa for big cone pine, indicating higher strength with pine.