• 한국표면공학회지
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• 제43권1호
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• pp.36-40
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• 2010

The SiO vapor that was generated from a mixture of Si and $SiO_2$ was reacted at $1350^{\circ}C$ for 2 h under vacuum with carbon nanofibers to produce SiC nanofibers having an average diameter of 100~200 nm. In order to understand the gas corrosion behavior, SiC nanofibers were exposed to air up to $1000^{\circ}C$. SiC oxidized to amorphous $SiO_2$, but its oxidation resistance was inferior unlike bulk SiC, because of high surface area of nanofibers. When SiC nanofibers were exposed to Ar-1% $SO_2$ atmosphere, SiC oxidized to amorphous $SiO_2$, without forming $SiS_2$, owing to the thermodynamic stability of $SiO_2$.

• 한국세라믹학회지
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• 제37권8호
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• pp.805-810
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• 2000

The formation, microstructure and properties of MoSi2/SiC ceramic composites by polymer pyrolysis were investigated for the application of heating element material. Polymethylsiloxanes were mixed with Si, SiC, MoSi2 as filler and ceramic composites prepared by pyrolysis in N2 atmosphere at 1320~145$0^{\circ}C$ were studied. Dimensional change, density variation and phases were analyzed and correlated to the resulting material properties. Microstructures of ceramic composite prepared by polymer pyrolysis were composed of MoSi2, SiC and silicon oxycarbide glass matrix. Depending on the pyrolysis conditions, ceramic composites with a density of 86~90 TD%, a fracture strength of 213~284 MPa, a thermal expansion coefficient of 4~7$\times$10-6 were obtained. The electrical resistivity of the specimen decreased with increasing of temperature up to 50$0^{\circ}C$.

• 한국세라믹학회지
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• 제39권4호
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• pp.413-419
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• 2002

$Al_2O_3$/TiC/SiC, $Al_2O_3$/SiC 및 $Al_2O_3$/TiC 복합체들을 고온가압소결로 제조하여 이들의 균열저항거동과 기계적 성질을 비교해 보았다. $Al_2O_3$에 $0.8{\mu}m$의 TiC가 30vol% 첨가된 $Al_2O_3$/TiC는 단일체 $Al_2O_3$와 비슷한 균열저항거동을 보이며 파괴인성은 전반적으로 10% 이내의 증가를 보이는데 그쳤지만 강도는 약 30% 증가하였다. $Al_2O_3$에 $3{\mu}m$ SiC가 30vol% 첨가된 $Al_2O_3$/SiC는 SiC 입자의 균열 접속으로 인해 증가하는 균열저항거동을 뚜렷이 보이면서 파괴인성이 긴 균열에서 약 75% 증가하였으나 강도는 다소 감소했다. $Al_2O_3$/TiC에 SiC 입자가 30 vol% 첨가된 $Al_2O_3$/TiC/SiC 복합체의 경우 단일체 $Al_2O_3$에 비해 긴 균열 거리에서 파괴인성이 50% 이상 증가된 6.6 MP${\cdot}\sqrt{m}$에 이르렀으며 강도 값도 약 20% 상승하였다. 그러나 큰 SiC 입자의 첨가로 인해 TiC 입자만 첨가된 $Al_2O_3$/TiC 복합체보다는 강도가 다소 낮았다. 또한 SiC 입자만 첨가된 $Al_2O_3$/SiC 복합체보다는 파괴인성이 다소 낮았는데, 이는 작은 TiC 입자들이 SiC 입계를 거칠게 만들어 균열접속을 일으키는 SiC 입자의 뽑힘 현상을 방해하였기 때문이다.

• 센서학회지
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• 제17권5호
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• pp.325-328
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• 2008

This paper describes the electrical properties of poly (polycrystalline) 3C-SiC thin films with different nitrogen doping concentrations. In-situ doped poly 3C-SiC thin films were deposited by APCVD at $1200^{\circ}C$ using HMDS (hexamethyildisilane: $Si_2(CH_3)_6)$) as Si and C precursor, and $0{\sim}100$ sccm $N_2$ as the dopant source gas. The peak of SiC is appeared in poly 3C-SiC thin films grown on $SiO_2/Si$ substrates in XRD(X-ray diffraction) and FT-IR(Fourier transform infrared spectroscopy) analyses. The resistivity of poly 3C-SiC thin films decreased from $8.35{\Omega}{\cdot}cm$ with $N_2$ of 0 sccm to $0.014{\Omega}{\cdot}cm$ with 100 sccm. The carrier concentration of poly 3C-SiC films increased with doping from $3.0819{\times}10^{17}$ to $2.2994{\times}10^{19}cm^{-3}$ and their electronic mobilities increased from 2.433 to $29.299cm^2/V{\cdot}S$, respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.204-209
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• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, $SiC_f/SiC$ composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of $SiC_f/SiC$ composites by hot pressing method. In the present work, Monolithic LPS-SiC was fabricated by hot pressing method in Ar atmosphere at 1760 $^{\circ}C$, 1780 $^{\circ}C$, 1800 $^{\circ}C$ and 1820 $^{\circ}C$ under 20 MPa using $Al_2O_3-Y_2O_3$ system as sintering additives in order to low sintering temperature. The starting powder was high purity ${\beta}-SiC$ nano-powder with an average particle size of 30 nm. Monolithic LPS-SiC was evaluated in terms of sintering density, micro-structure, flexural strength, elastic modulus and so on. Sintered density, flexural strength and elastic modulus of fabricated LPS-SiC increased with increasing the sintering temperature. In the micro-structure of this specimen, it was found that grain of sintered body was grown from 30 nm to 200 nm.

• 한국재료학회지
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• 제12권1호
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• pp.48-53
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• 2002

$Al_2O_3-SiC$ and $Al_2O_3-SiC$-TiC composite powders were prepared by SHS process using $SiO_2,\;TiO_2$, Al and C as raw materials. Aluminum powder was used as reducing agent of $SiO_2,\;TiO_2$ and activated charcoal was used as carbon source. In the preparations of $Al_2O_3-SiC$, the effect of the molar ratio in raw materials, compaction pressure, preheating temperature and atmosphere were investigated. The most important variable affecting the synthesis of $Al_2O_3-SiC$ was the molar ratio of carbon. Unreactants remained in the product among all conditions without compaction. The optimum condition in this reaction was $SiO_2$: Al: C=3: 5: 5.5, 80MPa compaction pressure under Preheating of $400^{\circ}C$ with Ar atmosphere. However there remains cabon in the optimum condition. The effect of $TiO_2$ as additive was investigated in the preparations of $Al_2O_3-SiC$. As a result of $TiO_2$ addition, $Al_2O_3-SiC$-TiC composite powder was prepared. The $Al_2O_3$ powder showed an angular type with 8 to $15{\mu}m$, and the particle size of SiC powder were 5~$10{\mu}m$ and TiC powder were 2 to $5{\mu}m$.

• 한국표면공학회지
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• 제40권6호
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• pp.279-282
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• 2007

Cr-Mo-Si-C-N coatings were deposited on steel and Si wafer by a hybrid system of AIP and sputtering techniques using Cr, Mo and Si target in $Ar/N_2/CH_4$ gaseous mixture. Instrumental analyses of XRD and XPS revealed that the Cr-Mo-Si-C-N coatings must be a composite consisting of fine(Cr, Mo and Si)(C and N) crystallites and amorphous $Si_3N_4$ and SiC. The hardness value of Cr-Mo-Si-C-N coatings significantly increased from 41 GPa of Cr-Mo-C-N coatings to about 53 GPa with Si content of 9.3 at.% due to the refinement of (Cr, Mo and Si)(C and N) crystallites and the composite microstructure characteristics. A systematic investigation of the microstructures and mechanical properties of Cr-Mo-Si-C-N coatings prepared with various Si contents is reported in this paper.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.396-400
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• 2003

A new synthesis process for nano laminating Ti$_3$SiC$_2$ has been developed using TiCx (x=0.67) and Si powder as starting materials by a reaction hot pressing. Bulk Ti$_3$SiC$_2$ was fabricated using a green body consisting of TiCx and Si by a hot pressing under the pressures of 25 MPa at 1420-1550 $^{\circ}C$ for 90 min. The synthesized Ti$_3$SiC$_2$ was consisting of only TiCx and Ti$_3$SiC$_2$. The relative density of sintered bulk Ti$_3$SiC$_2$ was increased as the hot pressing temperature was increased, which was mainly due to the increase in TiCx contents in synthesized Ti$_3$SiC$_2$. The synthesized Ti$_3$SiC$_2$ bulk was consisted of nano sized lamella structure of 20-100 nm in thickness. It was found that TiCx particles in Ti$_3$SiC$_2$ would increase the 3-point bending strength of synthesized Ti$_3$SiC$_2$ bulk. The maximum 3-P. bending strength of synthesized Ti$_3$SiC$_2$ bulk was more than 800 MPa. The Vickers hardness of synthesized Ti$_3$SiC$_2$bulk was as low as 5 Gpa, which was decreased with the indentation load. The quasi-plastic deformation behaviors were observed around indentation mark on Ti$_3$SiC$_2$.

• 한국결정성장학회지
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• 제13권6호
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• pp.290-296
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• 2003

본 연구에서는 열화학기상증착법을 사용하여 6H-SiC 기판 위에 silane($SiH_4$)과 prophane($C_3H_8$)을 사용하여 3C-SiC 이종박막을 성장시키고 이의 성장 특성을 조사하였다. C/Si 유량 비율이 4.0, 운반기체의 유량은 5 slm이고 성장온도가 $1200^{\circ}C$인 경우의 박막성장율은 약 1.8 $\mu$m/h이었다. 성장박막의 Nomarski 표면형상, X-선 회절분광, Raman 산란 특성 및 광발광(PL) 특성 등을 측정하고 성장조건에 따른 결정성을 비교하였다. 이러한 평가를 통하여 성장온도 $1150^{\circ}C$ 이상에서 양질의 결정성 3C-SiC 이종박막이 성장점을 확인하였다.

• 한국세라믹학회지
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• 제34권4호
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• pp.406-412
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• 1997

Al2O3/SiC hybrid-composite has been fabricated by the conventional powder process. The addition of $\alpha$-Al2O3 as seed particles in the transformation of ${\gamma}$-Al2O3 to $\alpha$-Al2O3 provided a homogeneity of the microstructure. The grain growth of Al2O3 are significantly surpressed by the addition of nano-size SiC particles. Dislocation were produced due to the difference of thermal expansion coefficient between Al2O3 and SiC and piled up on SiC particles in Al2O3 matrix, resulting in transgranular fracture. The high fracture strength of the composite was contributed to the grain refinement and the transgranular fracture mode. The addition of SiC platelets to Al2O3/SiC nano-composite decreased the fracture strength, but increased the fracture toughness. Coated SiC platelets with nitrides such as BN and Si3N4 enhanced fracture toughness much more than non-coated SiC platelets by enhancing crack deflection.