• Journal of Mechanical Science and Technology
• /
• 제20권2호
• /
• pp.227-233
• /
• 2006

Engineering ceramics have many unique characteristics both in mechanical and physical properties such as high temperature hardness, high thermal, chemical and electrical resistance. However, its machinability is very poor in conventional machining due to its high hardness and severe tool wear. In the current experimental study, alumina $(Al_2O_3)$ was ultrasonically machined using SiC abrasives under various machining conditions to investigate the material removal rate and surface quality of the machined samples. Under the applied amplitude of 0.02mm, 27kHz frequency, three slurry ratios of 1:1, 1:3 and 1:5 with different tool shapes and applied static pressure levels, the machining was conducted. Using the mesh number of 240 abrasive, slurry ratio of 1:1 and static pressure of $2.5kg/cm^2$, maximum material removal rate of $18.97mm^3/min$ was achieved. With mesh number of 600 SiC abrasives and static pressure of $3.0kg/cm^2$, best surface roughness of $0.76{\mu}m$ Ra was obtained.

• 마이크로전자및패키징학회지
• /
• 제3권2호
• /
• pp.27-38
• /
• 1996

Lithium fluorhectorite 결정상을 함유한 glass ceramics 분말의 형성과 제조된 glass ceramics 분말을 이용한 저온 소결기판의 특성평가를 하였다. Li2O-MgO-MgF2-SiO2 계 유 리로 핵형성 및 결정 성장을 실시하여 lithium fluorhectorite 결정상을 지닌 glass ceramics 를 제조하였다. 유리시편의 핵형성 온도는 46$0^{\circ}C$였고 결정성장온도는 600, 640, 110$0^{\circ}C$에서 나타났다. $600^{\circ}C$에서의 결정상으 Li2.4LiSi4O10F2가 나타났다. Li2.4Mg8LiSi4와 Li2.8Mg0.6SiO4은 lithium fluorhectorite 결정상으로 되기 위한 중간상임을 확인할수 있었다. 64$0^{\circ}C$에서 열처리 후 110$0^{\circ}C$에서 재열처리하여 형성된 결정은 lithium fluorhectorite 와 tridymite가 최종 결정 상으로 나타났다. 이것은 수중에서 water swelling 현상에 의하여 분말화할 수 있었다, 기판 제조용 slurry를 제조하기 위해 glass ceramics 분말에 Al2O3분말을 0,25,50wt%로 혼합한것 과 glass ceramics 분말에 potashborosilica-te glass 분말을 15, 30, 45, 60 wt% 로 배합하 여 doctor blade 법으로 green sheet를 제조하였다. green sheet 는 950~150$0^{\circ}C$로소성하여 기판의 특성을 평가하였다. 겉보기 기공율은 3.06~19,14%이었고, 전기적 특성으로 유전상수 는 3~5(100KHz)를 나타내었다.

• 한국입자에어로졸학회지
• /
• 제5권4호
• /
• pp.189-197
• /
• 2009

Wet-type particulate removal system is employed in most of ironmaking processes. These de-dusting systems require additional downstream aggregates for treatment of water and for drying of the collected slurry. Thus dried slurry can be pressed in shape of briquettes and recycled in the steelmaking process. Different from the wet-type, the dry-type particulate removal systems generate no slurry. A high-temperature, high-pressure de-dusting system with inertial inlet was developed. The target application of this system was to remove particulate matter generated from the novel ironmaking process and other steelmaking processes. In this study we conducted tests with this newly developed system to evaluate the performance of the silica-carbide (SiC) ceramic filters. In addition, for purpose of comparison, we also conducted tests with a unit which has conventional direct inlet. Fe-Particles collected from the novel ironmaking process were used in our tests as test dusts. The temperature and the pressure were kept constant at their respective values $800^{\circ}C$ and $3kg_f/cm^2$.

• Composites Research
• /
• 제36권3호
• /
• pp.180-185
• /
• 2023

본 논문에서는 스프레딩된 SiC 섬유를 적용해 SiC_f/SiC를 제조하였을 경우, 섬유의 분산도가 복합소재의 내부구조 및 기계적 강도에 어떠한 영향을 주는지를 연구하였다. Spread SiC 섬유를 적용한 시편의 섬유 체적비는 non-spread 시편 대비 9%p 감소하였으며, 수지 슬러리가 섬유 사이로 더 원활히 함침되어 기지내 기공도 거의 발견되지 않았다. 각 시편의 섬유 분산도를 비교하기 위해, 복합소재 내 섬유간 이격거리를 수치화하고 평가하는 방법을 제안하였다. 그 결과 spread 시편의 섬유간 중심거리는 non-spread 시편 대비 2.23 ㎛ 증가하였으며, 섬유 표면 사이 거리는 42.6%로 대폭 증가하였다. 3점 굽힘시험을 통해 spread 시편의 굽힘강도가 non-spread 시편 대비 49.3% 가량 높으며, 시험 데이터의 편차도 더 균일함을 확인하였다. 따라서 복합소재 기지내 SiC 섬유의 분산도 향상이 SiC_f/SiC의 균일한 기지상 치밀화와 기계적 강도 증가에 매우 큰 영향을 미친다는 점을 알 수 있다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1997년도 고액공존금속의 성형기술 심포지엄
• /
• pp.160-173
• /
• 1997

Microstructure of hypereutectic Al-17wt.% Si alloy, fabricated by mechanical stirring and by reheating at semi-solid state, was investigated by optical microscope. Flow behavior semi-solid metal also was investigated at diffentent mould temperatures 280$^{\circ}C$, 290$^{\circ}C$ and 300$^{\circ}C$. Size of silicon particles were increased over 100$\mu\textrm{m}$ during solidification as a result of stirring. It is considered as microstructural coarsening by bonding between neighbouring primary silion particles during stirring of slurry. In case of reheating at semi-solid state, however, primary silicon particle was not increased at size of 40$\mu\textrm{m}$ and nearly spherical aluminum solde particle also could be obtained uniformly in distribution. The fludity of Al-17wt.% Si alloys at semi-solid state was improved when solid fraction was 0.7 at mould temperature of 300$^{\circ}C$ than other conditions.

• 한국디지털건축인테리어학회논문집
• /
• 제11권3호
• /
• pp.35-42
• /
• 2011

The exterior system of buildings, which is the typical curtain wall, has been made with glass and metal. Theses materials, however, have weaknesses such as inadequate insulating quality, short durability, combustibility and toxic substance. On the other hand, Autoclaved Aerated Concrete(AAC) or Autoclaved Lightweight Concrete(ALC) possess the great energy efficiency and the superb insulating quality as substitute of existing exterior system materials. In this research, strength characteristics and bubble dispersion of hydrothermal synthesis process of AAC based on CaO/$SiO_2$(C/S) ratio are analyzed. C/S ratio is determinated and bubble distribution and compressive strength are studied through the test of varied water-to-solid mineral ratio(W/S). In hydrothermal synthesis program, final C/S ratio is determined as 0.7 consider of the manufacturing process and hydrothermal synthesis is done at $180^{\circ}C$ for 7 hours. The analysis shows slurry has about 2,300cP viscosity and 0.56 specific gravity therefore it is expected AAC has the appropriate facility in the manufacturing process and Hydrates of AAC's Expansion.

• 한국결정성장학회지
• /
• 제29권6호
• /
• pp.383-388
• /
• 2019

개선된 열탄소환원법으로 합성된 금속불순물함량 1 ppm 이하의 고순도 SiC 미립 분말을 이용하여 2,100℃ 이상고온의 RF 가열 PVT 장치에서 SiC 단결정을 성장시켰으며, In-situ x-ray 이미지 분석을 통해 성장과정 중 분말의 승화거동 및 단결정 성장거동을 관찰하였다. SiC 분말은 단결정 성장의 공급원으로 온도가 높은 외곽 부분부터 소진되고 graphite 잔여물이 남았다. 성장 중 원료의 흐름은 가운데 부분으로 집중되었으며 SiC 단결정의 성장거동에도 영향을 미쳤는데, 이는 미립분말로 인한 도가니 내부 온도분포 차이가 원인으로 예상되었다. 단결정 성장이 완료된 후, 단결정 잉곳을 1 mm 두께의 단결정 기판으로 절단하고 또한, 잉곳에서 얻어진 단결정 기판은 전반적으로 짙은 황색의 4H -SiC가 관찰되었으며, 외곽에 일부 발생한 다결정은 시드결정을 시드홀더에 부착하는 과정에서 혼입된 기포층과 같은 불순물 혼입이 원인으로 사료된다.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
• /
• pp.110.1-110.1
• /
• 2010

A bench scale slurry bubble column reactor (SBCR) with active-Fe based catalyst was developed for the Fischer-Tropsch synthesis (FTS) reaction. Considering the highly exothermic reaction heat generated in the bench scale SBCR, an effective cooling system was devised consisting of a U-type dip tube submerged in the reactor. Also, the physical and chemical properties of the catalyst were controlled so as to achieve high activity for the CO conversion and liquid oil ($C_{5+}$) production. Firstly, the FTS performance of the FeCuK/$SiO_2$ catalyst in the SBCR under reaction conditions of $265^{\circ}C$, 2.5 MPa, and $H_2/CO=1$ was investigated. The CO conversion and liquid oil ($C_{5+}$) productivity in the reaction were 88.6% and 0.226 $g/g_{cat}-h$, respectively, corresponding to a liquid oil ($C_{5+}$) production rate of 0.03 bbl/day. To investigate the FTS reaction behavior in the bench scale SBCR, the effects of the space velocity and superficial velocity of the synthesis gas and reaction temperature were also studied. The liquid oil production rate increased upto 0.057 bbl/day with increasing space velocity from 2.61 to 3.92 $SL/h-g_{Fe}$ and it was confirmed that the SBCR bench system developed in this research precisely simulated the FTS reaction behavior reported in the small scale slurry reactor.

• 한국재료학회지
• /
• 제9권9호
• /
• pp.865-871
• /
• 1999

지르콘 쉘 몰드를 제조하여 소결 온도 및 시간에 따른 소결거동이 기계적특성에 미치는 영향을 관찰하였다. $1000^{\circ}C$에서 1.5시간동안 소결 한 쉘 몰드의 1차 코팅 표면층에서 미세균열의 크기 및 수가 극대화되었으며 소결온도 및 시간이 증가할수록 상온강도와 기공의 비표면은 감소하였다. 1차 소결 후 $1500^{\circ}C$에서 4시간동안 소결 처리한 주형의 고온변형거동은 백업층과 하중의 역방향으로 스터코와 지르콘 슬러리의 경계면을 따라 변형이 발생하였다. 1차 코팅층에서 알루미나 스터코와 지르콘 슬러리의 열팽창계수 차이와 백업 코팅층에서 지르콘 슬러리간의 입도 차이가 고온변형시험 중 역변형을 일으킨 것으로 판단된다.

• 한국주조공학회지
• /
• 제15권5호
• /
• pp.483-493
• /
• 1995

The microstructural changes during semi-solid state processing of hypereutectic Al-Si alloy has been investigated in the present study. Stirring of semi-solid slurry results in the morphological changes of the primary Si particles, i.e. from angular rod shape to near-spherical shape. Besides the spherodization of primary Si particles, the average particle size increases, especially, at much higher rate in the final stage than that in the early stage of stirring. Various microstructure characterization techniques, such as anisotropic etching, SEM imaging and ECP analysis, reveal that the spherodization of primary Si particles occurs by the combinations of the mechanisms of coalescence, fracture, and wear of the individual particles. Isothermal shearing of hypereutectic Al-Si at $580^{\circ}C$ shows that spherical ${\alpha}-Al$ particles are formed by the dissociation of Al-Si eutectic structure at the early stage of isothermal shearing. The spherical ${\alpha}-Al$ particles gradually grow by the mechanisms of Ostwald ripening and coalescence of the particles.