• 한국세라믹학회지
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• 제34권5호
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• pp.467-472
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• 1997

Porous silicon was prepared by an anodic etching. The pore size was about 10 nm at an etching time of 20 sec and a current density of 20 mA/$\textrm{cm}^2$. The porous layer was composed of an micro-porous layer (0.6 ${\mu}{\textrm}{m}$) and a macro-porous layer (10 ${\mu}{\textrm}{m}$). Room temperature PL with maximum peak 6700$\AA$ appeared. The peak disappeared by an oxidation reaction when the porous silicon was heated to 100~20$0^{\circ}C$ in atmosphere. In order to avoid the oxidation a heat treatment was done in H2 atmosphere. The micro-pore and Si column, which formed quantum well, were collapsed by the high temperature. The PL maximum peak of heated sample was gradually red-shifted and showed about 300$\AA$ red-shift at 50$0^{\circ}C$. The intensity of PL was maintained to high temperatures in lower pressures. The porous Si was carbonized in C2H2+H2 gas in order to increase thermal stability. The carbonization of the porous Si prevented red-shift of the maximum PL peak caused by sintering effect at high temperatures, and the carbonized porous Si showed Pl signal at higher temperatures by above 20$0^{\circ}C$ than the sample in H2 atmosphere.

• 한국세라믹학회지
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• 제35권2호
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• pp.172-179
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• 1998

Valve lifter namely tappet is supported by lifter hole which is located upper side of camshaft in cylinder block transforms rotatic mvement of camshaft into linear movement and helps to open and shut the en-gine valve as an engine parts. The face of valve lifter which is continuously contacting with camshaft brings about abnormal wears such as unfair wear and early wear because it is severely loaded in the valve train system. These wears act as a defect like over-clearance and cause imperfect combustion of fuel during the valve lifting in the combustion chamber. Consequently this imperfect combustion makes the engine out-put decrease and has cause on air pollution. To prevent these wears therefore The valve lifter cast in me-tal developed into SiC ceramics valve lifter which has an excellence in wear and impact resistance As a results the optimum process conditions like injection condition mixture ratio and debonding process could be established. After sintering fine-sinered dual microstructure in which prior ${\alpha}$-SiC matches well with new SiC(${\beta}$-SiC) produced by reaction among the ${\alpha}$-SiC carbon and silicon was obtained. Based on the study it is verified that mechanical properties of SiC valve lifter are excellent in Vickers hardness 1100-1200 bending strength (300-350 Pa) fracture toughness(1.5-1.7 Mpa$.$m1/2) Through engine dynamo test-ing SiC valve lifter and metal valve lifter are examined and compared into abnormal phenomena such as early fracture unfair and early wear. It is hoped that this research will serve as an important springboard for the future study of heavy duty diesel engine parts developed by ceramics which has a good wear resis-tance relaibility and lightability.

• 한국재료학회지
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• 제9권6호
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• pp.577-582
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• 1999

전도성 $Si_3N_4$-TiN 세라믹 복합재료를 제조하기 위해 성형체를 $1450^{\circ}C$에서 20시간 질화처리한 후 $1950^{\circ}C$에서 3.5시간 가스압소결 기술에 의해 후소결하였다. 초기 분말로 약 $10\mu\textrm{m}$로 된 상용 Si분말, 100mesh와 325mesh로된 Ti분말, 그리고 미세한 $\2.5mu\textrm{m}$ TiN분말을 사용하였다. Ti분말울 사용한 $Si_3N_4$-TiN 소결체에서 상대밀도 및 파괴인성값은 다량의 조대한 기공의 존재로 인하여 낮은 값을 보였다. 그러나 TiN분말을 사용한 $Si_3N_4$-TiN 복합체에서 파괴인성, 파괴강도 및 전기저항은 각각 $5.0MPa{\cdot}m^{1/2}$, 624MPa 그리고 $1400{\omega}cm$였다. 복합체에서 TiN 업자의 분산은 $Si_3N_4$ 업자의 조대한 봉상형태로의 성장올 방해하며 $Si_3N_4$/TiN 계면에 강한 변형장울 만든다. $Si_3N_4$-TiN 복합체의 전기전도도 및 기계적 특성을 향상시키기 위해 TiN 업자가 균일하게 분산 된 미세조직 제어가 요망된다.

• The Korean Journal of Ceramics
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• 제4권4호
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• pp.279-285
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• 1998

The $UO_2$ pellets are usually sintered under hydrogen gas atmosphere. Hydrogen gas may cause unexpected early failure of the refractory bricks in the sintering furnace. In this work, nitrogen was mixed with hydrogen to investigate the effect of nitrogen gas on a failure machanism of the refractory bricks and on the microstructure of the $UO_2$ pellet. The hydrogen-nitrogen mixed gas experiments show that the larger nitrogen the mixed gas contains, the less the refractory materials are reduced by hydrogen. The weight loss measurements at $1400^{\circ}C$ for fire clay and chamotte refractories containing high content of $SiO_2$ indicate that the weight loss rate for the mixed gas is about half of that for the hydrogen gas. Based on the thermochemical analyses, it is proposed that the weight loss is caused by hydrogen-induced reduction of free $SiO_2$ and/or $SiO_2$ bonded to $Al_2O_3$ in the fire clay and chamotte refractories. However, the retardation of the hydrogen-induced $SiO_2$ reduction rate under the mixed gas atmosphere may be due to the reduction of the surface reaction rate between hydrogen gas and refractory materials in proportion to volume fraction of nitrogen gas in the mixed gas. On the other hand, the mixed gas experiments show that the test data for $UO_2$ pellet still meet the related specification values, even if there exists a slight difference in the pellet microstructural parameters between the cases of the mixed gas and the hydrogen gas.

• 한국재료학회지
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• 제17권7호
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• pp.366-370
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• 2007

Silicon nitride ($Si_3N_4$) ceramics have been considered for various components of nuclear power plants such as the mechanical seal of a reactor coolant pump (RCP), the guide roller for a control rod drive mechanism (CRDM), and a seal support, etc. Corrosion behavior of $Si_3N_4$ ceramics in a high-temperature and high-pressure water must be elucidated before they can be considered as components for nuclear power plants. In this study, the corrosion behaviors of $Si_3N_4$ ceramics containing MgO and $Al_2O_3$ as sintering aids were investigated at a hydrothermal condition ($300^{\circ}C$, 9.0 MPa) in pure water and 35 ppm LiOH solution. The corrosion reactions were controlled by a diffusion of the reactive species and/or products through the corroded layer. The grain-boundary phase was preferentially corroded in pure water whereas the $Si_3N_4$ grain seemed to be corroded at a similar rate to the grain-boundary phase in LiOH solution. Flexural strengths of the $Si_3N_4$ ceramics were significantly degraded due to the corrosion reaction. Results of this study imply that a variation of the sintering aids and/or a control (e.g., crystallization) of the grain-boundary phase are necessary to increase the corrosion resistance of $Si_3N_4$ ceramics in a high-temperature water.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2000년도 추계학술대회
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• pp.42-42
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• 2000

반응소결 탄화규소는 소결체 내에 잔존 실리콘이 남아 있어 고온강도의 감소를 초래하는 단점이 있어 고온 구조재료로서의 사용이 제한되어 왔다. 따라서 이러한 문제점을 해결하기 위한 방법으로 Si 단독으로 용응침투시키는 대신 Si-MoSi₂를 침투시키는 방법이 시도되고 있으며, 이외에도 TiC 성형체에 Co, Ni 등의 금속, ZrB₂ 성형체에 Zr 금속 등을 용융, 침투시켜 성능향상을 유도하는 연구가 진행되고 있다. 본 연구에서는 반응소결에 대한 기본이론과 응용분야, 반응소결 비산화물계 세라믹스의 제조공정 및 이들 소결체의 미세구조와 기계적 특성 등을 소개하고자 한다.

• 한국세라믹학회지
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• 제45권9호
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• pp.561-566
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• 2008

Carbon fiber fabric-silicon carbide composites were fabricated by liquid silicon infiltration (LSI) process. The porous two-dimensional carbon fiber fabric performs were prepared by 13 plies of 2D-plain-weave fabric in a three laminating method, [0/90], [${\pm}45$], [$0/90/{\pm}45$] lay-up, respectively. Before laminating, a thin pyrolytic carbon (PyC) layer deposited on the surface of 2D-plain weave fabric sheets as interfacial layer with $C_3H_8$ and $N_2$ gas at $900^{\circ}C$. A densification of the preforms for $C_f-Si-SiC$ matrix composite was achieved according to the LSI process at $1650^{\circ}C$ for 30 min. in vacuum atmosphere. The bending strength of the each composite were measured and the microstructural consideration was performed by a FE-SEM.

• 한국분말재료학회지
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• 제12권6호
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• pp.447-452
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• 2005

The synthesis and consolidation of titanium silicide by electro-discharge-sintering has been investigated. As-received Ti powder was in flaky shape and the mean particle size was $45.0{\mu}m$, whereas the mean particle size of the pre-milled Si powder with angular shape was $8.0{\mu}m$. Single pulse of 2.5 to 5.0 kJ/0.34g-elemental Ti and pre-milled Si powder mixture with the composition of $Ti-37.5at.\%$ Si was applied using $300{\mu}F$ capacitor. The solid with $Ti_5Si_3$ phase has been successfully fabricated by the discharge with the input energy more than 2.5kJ in less than $129{\mu}sec.$ Hv values were found to be higher than $1000kgf/mm^2$. The formation of $Ti_5Si_3$ occurred through a fast solid state diffusion reaction.

• 한국세라믹학회지
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• 제41권11호
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• pp.797-803
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• 2004

마이크로파 가열장치를 이용하여 마이크로파 조사에 따른 SiC와 MO$_2$ 시료에 대한 발열실험을 수행하였고, 이 실험에서 얻은 발열특성 결과들을 고려하여 $UO_2$+5wt% CeO$_2$ 성형체에 대한 산화소결 실험을 수행하였다. 그리고 마이크로파와 전기로에서 각각 소결된 MO$_2$ 소결체의 특성변화를 비교분석하였다 마이크로파 조사에 따른 MO$_2$시료의 발열온도는 입력전력의 증가에 따라서 급속히 증가하였으며, 출력전력은 주로 보조가열재인 SiC와 MO$_2$ 시료가 마이크로파와 반응하는 정도에 따라서 변하였다. 마이크로파에 의하여 소결된 소결체의 밀도는 전기로에서 동일한 조건으로 소결된 소결체의 밀도보다 약 2% T.D. 낮았다. 소결체의 미세조직은 전기로에서 제조된 소결조직에 비하여 마이크로파에 의해 제조된 소결체의 기공분포가 불규칙적이었으나, 평균결정립 크기는 크게 나타났다.

• 한국결정성장학회지
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• 제15권2호
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• pp.68-74
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• 2005

지정 폐기물인 electrical arc furnace(EAF) 더스트에는 액상을 형성하는 fluk 성분이 많이 포함되어있어, 점토와 혼합하면 시편의 소결온도를 낮춰주고 기계적 강도를 향상시키는 장점이 있다. 그러나 더스트-점토 계 벽돌 제조시 더스트 첨가량을 증가시키면 소결과정에서 과도한 액상이 생성되어 제품 불량률이 높아진다. 점토-더스트 계 시편의 소결공정 중에 발생하는 액상을 제어하기 위하여 $Al_2O_3$를 첨가하고 물리적 특성 변화를 분석하였다. $Al_2O_3$가 첨가된 더스트-점토계 소결체는 기공크기가 감소되면서 미세구조가 균일해졌다. 이에 따라 기계적 강도가 증가되었고 동시에 최대강도가 나타나는 온도가 높아졌다. 또한 겉보기 밀도가 증가되었고 흡수율은 감소하였다. 첨가된 $Al_2O_3$는 mullite($3Al_2O_3{\cdot}2SiO_2$)를 생성함으로서, 액상형성에 참여할 $SiO_2$을 소모시키고 동시에 액상의 점도를 높여, 소결체의 내화도를 증진시키고 따라서 소결과정에서 시편 불량률을 낮출 것으로 분석되었다.