• 한국분말재료학회지
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• 제22권4호
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• pp.283-288
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• 2015

Two sintering methods of a pressureless sintering and a spark-plasma sintering are tested to densify the Fe-TiC composite powders which are fabricated by high-energy ball-milling. A powder mixture of Fe and TiC is prepared in a planetary ball mill at a rotation speed of 500 rpm for 1h. Pressureless sintering is performed at 1100, 1200 and $1300^{\circ}C$ for 1-3 hours in a tube furnace under flowing argon gas atmosphere. Spark-plasma sintering is carried out under the following condition: sintering temperature of $1050^{\circ}C$, soaking time of 10 min, sintering pressure of 50 MPa, heating rate of $50^{\circ}C$, and in a vacuum of 0.1 Pa. The curves of shrinkage and its derivative (shrinkage rate) are obtained from the data stored automatically during sintering process. The densification behaviors are investigated from the observation of fracture surface and cross-section of the sintered compacts. The pressureless-sintered powder compacts show incomplete densification with a relative denstiy of 86.1% after sintering at $1300^{\circ}C$ for 3h. Spark-plasma sintering at $1050^{\circ}C$ for 10 min exhibits nearly complete densification of 98.6% relative density under the sintering pressure of 50 MPa.

• 한국분말재료학회지
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• 제24권6호
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• pp.444-449
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• 2017

Aluminum nitride (AlN) powder specimens are treated by high-energy bead milling and then sintered at various temperatures. Depending on the solvent and milling time, the oxygen content in the AlN powder varies significantly. When isopropyl alcohol is used, the oxygen content increases with the milling time. In contrast, hexane is very effective at suppressing the oxygen content increase in the AlN powder, although severe particle sedimentation after the milling process is observed in the AlN slurry. With an increase in the milling time, the primary particle size remains nearly constant, but the particle agglomeration is reduced. After spark plasma sintering at $1400^{\circ}C$, the second crystalline phase changes to compounds containing more $Al_2O_3$ when the AlN raw material with an increased milling time is used. When the sintering temperature is decreased from $1750^{\circ}C$ to $1400^{\circ}C$, the DC resistivity increases by approximately two orders of magnitude, which implies that controlling the sintering temperature is a very effective way to improve the DC resistivity of AlN ceramics.

• 한국세라믹학회지
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• 제24권1호
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• pp.9-16
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• 1987

Physical and electrical properties of ${\beta}$-Al2O3 were investigated as function of Na2O content from 6.67 wt.% to 13.19 wt.%. The majority phase is ${\beta}$-Al2O3 and the small amount of ${\beta}$"-Al2O3 exists in the specimens sintered at 1600$^{\circ}$for 30 mins. In the case of specimens with 8.54 wt.% Na2O sintered at 1600$^{\circ}C$, the relative amount of ${\beta}$-Al2O3 phase increases and that of ${\beta}$"-Al2O3 phase decreases with increasing sintering time, and then ${\beta}$"-Al2O3 phase does not exist if sintering time is over 8 hrs. As the Na2O content is increased, the 3-Point MOR and the resistivity are decreased. However, density and 3-Point MOR with increasing sintering time are decreased due to increasing the enclosed pore trapped inside of the exaggerated grains. As the sintering time is increased, the average grain size and the duplexity of microstructure are increased, and the resistivity is slightly decreased.

• 세라미스트
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• 제23권2호
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• pp.114-131
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• 2020

Fracture in the titanium carbonitride-metal composites occurs by crack propagation through the carbonitride grains or in the interfaces. Thus, intrinsic properties of the carbonitride need to be enhanced and the interfaces should be also modified to coherent structure to strengthen the composites. Especially, interfacial structure can be the main factor to determine the mechanical properties of titanium carbonitride-metal composites because the interfaces between carbonitride grains and metallic phase are weak parts due to heterogeneous nature of carbonitride and metallic phase. In this paper, methodologies for improving the interfacial structure of titanium carbonitride-metal composites are suggested. Total area of the interfaces can be reduced using solid solution type carbonitrides as raw materials instead of a mixture of various carbonitrides in the composites. Also, synthesis of titanium carbonitride-metal composite powders and the low-temperature sintering of the composite powders for short time can be the way for formation of coherent interfaces. The sintering of the composite powders for short time at low temperature can reduce the potential of formation of interfaces by dissolution and precipitation of carbonitride in the liquid metal. As a result of formation of coherent boundaries due to low-temperature and short-time sintering, interfaces between titanium carbonitride grains and metallic phase have the favorable structure for the enhanced fracture toughness. It is believed that the low-temperature sintering of solid solution type composite powders for short time can be the way to improve the low toughness of the titanium carbonitride-metal composites.

• 한국세라믹학회지
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• 제39권3호
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• pp.259-264
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• 2002

본 연구에서는 석탄회로 제조된 인공경량골재에 석회석을 첨가하였을 때 소성온도 및 시간에 따른 소성특성을 관찰하였다. 소성온도의 증가에 따라 quartz($SiO_2$)가 감소한 반면 mullite($3Al_2O_3{\cdot}2SiO_2$)가 증가되었으며, 석회석의 첨가에 의해 clinoptiolite와 pagioclase와 같은 소성에 의한 소성광물이 생성되었다. 석탄회 및 석회석으로 제조된 경량골재의 소성성은 주로 소성시간보다는 소성온도에 의해서 좌우되는 것으로 확인되었다. 또한 소성온도 및 시간의 증가는 골재내 형성된 거대기공의 미세화 및 폐기공의 형성으로 전체 기공부피를 축소시키는 경향을 나타냈다. 1000$^{\circ}$C에서 5분가 소성시킨 경량골재의 표면은 용융 슬래그 층의 융착현상에 의해 개기공이 거의 없었으나 내부는 발포가스에 의해 수 ${\mu}$의 미세기공이 폐기공 형태로 균일하게 분포하였다. 이로부터 석회석이 첨가된 소성 경량골재의 적정 소성조건은 소성온도는 약 1000$^{\circ}$C, 소성시간은 5분이 바람직한 것으로 나타났다.

• 한국분말재료학회지
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• 제23권1호
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• pp.1-7
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• 2016

Cu-Mn compacts are fabricated by the pulsed current activated sintering method (PCAS) for sputtering target application. For fabricating the compacts, optimized sintering conditions such as the temperature, pulse ratio, pressure, and heating rate are controlled during the sintering process. The final sintering temperature and heating rate required to fabricate the target materials having high density are $700^{\circ}C$ and $80^{\circ}C/min$, respectively. The heating directly progresses up to $700^{\circ}C$ with a 3 min holding time. The sputtering target materials having high relative density of 100% are fabricated by employing a uniaxial pressure of 60 MPa and a sintering temperature of $700^{\circ}C$ without any significant change in the grain size. Also, the shrinkage displacement of the Cu-Mn target materials considerably increases with an increase in the pressure at sintering temperatures up to $700^{\circ}C$.

• 한국분말재료학회지
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• 제22권5호
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• pp.356-361
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• 2015

Fe-30 wt% TiC composite powders are fabricated by in situ reaction synthesis after planetary ball milling of (Fe, $TiH_2$, Carbon) powder mixture. Two sintering methods of a pressureless sintering and a spark-plasma sintering are tested to densify the Fe-30 wt% TiC composite powder compacts. Pressureless sintering is performed at 1100, 1200 and $1300^{\circ}C$ for 1-3 hours in a tube furnace under flowing argon gas atmosphere. Spark-plasma sintering is carried out under the following condition: sintering temperature of $1050^{\circ}C$, soaking time of 10 min, sintering pressure of 50 MPa, heating rate of $50^{\circ}C/min$, and in a vacuum of 0.1 Pa. The curves of shrinkage and its derivative (shrinkage rate) are obtained from the data stored automatically during sintering process. The densification behaviors are investigated from the observation of fracture surface and cross-section of the sintered compacts. The pressureless-sintered powder compacts are not densified even after sintering at $1300^{\circ}C$ for 3 h, which shows a relative denstiy of 66.9%. Spark-plasma sintering at $1050^{\circ}C$ for 10 min exhibits nearly full densification of 99.6% relative density under the sintering pressure of 50 MPa.

• 한국세라믹학회지
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• 제35권4호
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• pp.413-419
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• 1998

${\beta}$-silicon carbides with yttrium aluminum garnet of 2,5,10 mol% were prepared by a liquid--phase sint-ering and the microstructural evolution and phase transformation were investigated during sintering as functions of liquid-phase amount and sintering time. The rate of grain growth decreases with the addition of the amount of yttrium aluminum garnet (YAG) in the SiC starting powder however the apparent density and the aspect ratio of grains in sintered body increase. The phase transformation from ${\beta}$-SiC to ${\alpha}$-SiC were dependent on the liquid-phase amount and sintering time.

• 한국세라믹학회지
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• 제36권6호
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• pp.655-661
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• 1999

${\beta}$-SiC formation mechanism in Si melt-C-SiC system with varying in size of carbon source was investigated. A continuous reaction sintering process using Si melt infiltration method was adopted to control the reaction sintering time effectively. It was found that ${\beta}$-SiC formation mechanism in Si melt-C-SiC system was directly affected by the size of carbon source. In the Si melt-C-SiC system with large carbon source ${\beta}$-SiC formation mechanism could be divided into two stages depending on the reaction sintering time: in early stage of reaction sintering carbon dissolution in Si melt and precipitation of ${\beta}$-SiC was occurred preferentially and then SIC nucleation and growth was controlled by diffusion of carbon throughy the ${\beta}$-SiC layer formed on graphite particle. Furthmore a dissolution rate of graphite particles in Si melt could be accelerated by the infiltration of Si melt through basal plane of graphite crystalline.

• 한국세라믹학회지
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• 제32권1호
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• pp.51-56
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• 1995

Variation of sintered density of BaTiO3 powder calcined at 120$0^{\circ}C$ and 135$0^{\circ}C$ was investigated with respect to the grain growth behavior. It was found that BaTiO3 powder, which was calcined at 120$0^{\circ}C$, showed abnormal grain growth behavior during sintering process. At initial stage of sintering process, the densification rate of specimen was accelerated with rapid grain growth caused by the abnormal grain growth. But with the increase of sintering time, abnormally grown grain met each other and the density of specimen decreased drastically due to coalescence of pores located in triple junction. On the contrary, BaTiO3 powder calcined at 135$0^{\circ}C$ showed normal grain growth behavior and gradually densified with the increase of sintering time.