• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1230-1231
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• 2008

The effect of content of $Al_2O_3+Y_2O_3$ sintering additives on the densification behavior, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at 1,700[$^{\circ}C$] temperatures with an addition of $Al_2O_3+Y_2O_3$(6:4 mixture of $Al_2O_3$ and $Y_2O_3$) as a sintering aid in the range of 8${\sim}$20[wt%]. Phase analysis of $SiC-ZrB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $ZrB_2$ and In Situ YAG($Al_5Y_3O_{12}$). The relative density, flexural strength, Young's modulus and vicker's hardness showed the highest value of 89.01[%], 81.58[Mpa], 31.437[GPa] and 1.34[GPa] for $SiC-ZrB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature respectively. Abnormal grain growth takes place during phase transformation from ${\beta}$-SiC into ${\alpha}$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites. In this paper, it is convinced that ${\beta}$-SiC based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1091-1092
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• 2006

Silicon nitride - silicon carbide composite was developed by using an abrasive SiC powders as a raw material. The composites were prepared by mixing abrasive SiC powder with silicon, pressing and sintering at $1400^{\circ}C$ under nitrogen atmosphere in atmosphere controlled vacuum furnace. The proportion of silicon in the initial mixtures varied from 20 to 50 wt%. After sintering, crystalline phases and microstructure were characterized. All composites consisted of ${\alpha}-Si_3N_4$ and ${\beta}-Si_3N_4$ as the bonding phases in SiC matrix. Their physical and mechanical properties were also determined. It was found that the density of the obtained composites increased with an increase in the $Si_3N_4$ content formed in the reaction.

• 한국세라믹학회지
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• 제35권10호
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• pp.1020-1029
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• 1998

The reaction-bonded TiC-Ni/Si/Co composites were prepared by the melt infiltration of Co, Si, and Ni me-tal into the TiC preforms. The miocrostructure reaction composition and mechanical properties were in-vestigated. In the case of the melt infiltrated with Co and Ni TiC grain shape was changed from angular to spherical shape with the average grain size of ∼5$\mu\textrm{m}$. In the case of the melt infiltrated with Co/Si or Ni/Si, Si was reacted with TiC particles and formed SiC particles. The bending strength of both specimens which have atomic ratio of 3 were 710 MPa and 515 MPa respectively. In the case of the melt infiltrated with Ni/Si/Co,. nonstoichiometric TiC was formed and its bending strength decreased to 420 MPa.

• 한국세라믹학회지
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• 제31권4호
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• pp.399-406
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• 1994

The SiC/MoSi2 composite material was prepared by infiltration with the mixture of metal Si and MoSi2 into the preform of $\alpha$-SiC and graphite under the vacuum atmosphere of 10-1 torr. The mechanical properties, phases and microstructural characteristics have been investigated by employing an universal testing machine, scanning electron microscope and X-ray diffractometer. With the increase of MoSi2/Si mixing content, the quantity of the residual silicon phase was decreased and the hardness and fracture toughness of composite materials were increased. Also, as the infiltration temperature increased, a lot of fine-grained $\beta$-SiC phases, which were produced from the reaction of graphite and liquid silicon melt, were transformed to $\alpha$-SiC phases.

• 한국세라믹학회지
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• 제35권4호
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• pp.311-318
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• 1998

The reaction bonded alumina ceramics with reinforced particles which have low shrinkage were pro-duced by blending of SiC or TiC or ZrO2 powders to the mixture of Al metal and Al2O3 powder. The powd-ers were attrition milled isostantically pressed and preheated tio 110$0^{\circ}C$ with a heating rate of $1.5^{\circ}C$/min The specimens were then sintered at the temperature range 1500 to 1$600^{\circ}C$ for 5 hours with a heating rate of 5$^{\circ}C$/min. The specimens showed 5-9% weight gain and 2-9% dimensional expansion through the complete oxidation of Al after preheating up to 11--$^{\circ}C$ the overall dimensional change of the specimens after the reaction sintering at 1500-1$600^{\circ}C$ was 6-12% The maximum densities were 92% theoretical. The fine grain-ed(average grain size :0.4 ${\mu}{\textrm}{m}$) microstructure were observed in the specimen with ZrO2 and SiC. But the microstructure of specimen with TiC was relatively coarse.(average grain size : 2.1 ${\mu}{\textrm}{m}$) The mullite phase was formed by the reaction of Al2O3 and SiO2 in a specimen with SiC. In the TiC contained specimen TiC was oxidized into TiO2 and finally reacted with Al2O3 to form Al2TiO5 during sintering.

• 전기학회논문지
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• 제57권5호
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• pp.808-815
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• 2008

The composites were fabricated 61[vol.%] ${\beta}$-SiC and 39[vol.%] $TiB_2$ powders with the liquid forming additives of 8, 12, 16[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid by pressureless annealing at 1650[$^{\circ}C$] for 4 hours. The present study investigated the influence of the content of $Al_2O_3+Y_2O_3$ sintering additives on the microstructure, mechanical and electrical properties of the pressureless annealed SiC-$TiB_2$ electroconductive ceramic composites. Reactions between SiC and transition metal $TiB_2$ were not observed in the microstructure and the phase analysis of the pressureless annealed SiC-$TiB_2$ electroconductive ceramic composites. Phase analysis of SiC-$TiB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), ${\beta}$-SiC(3C), $TiB_2$, and In Situ YAG($Al_2Y_3O_{12}$). The relative density of SiC-$TiB_2$ composites was lowered due to gaseous products of the result of reaction between SiC and $Al_2O_3+Y_2O_3$. There is another reason which pressureless annealed temperature 1650[$^{\circ}C$] is lower $300{\sim}450[^{\circ}C]$ than applied pressure sintering temperature $1950{\sim}2100[^{\circ}C]$. The relative density, the flexural strength, the Young's modulus and the Vicker's hardness showed the highest value of 82.29[%], 189.5[Mpa], 54.60[Gpa] and 2.84[Gpa] for SiC-$TiB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature. Abnormal grain growth takes place during phase transformation from ${\beta}$-SiC into ${\alpha}$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. The electrical resistivity showed the lowest value of 0.0117[${\Omega}{\cdot}cm$] for 16[wt%] $Al_2O_3+Y_2O_3$ additives at 25[$^{\circ}C$]. The electrical resistivity was all negative temperature coefficient resistance (NTCR) in the temperature ranges from $25^{\circ}C$ to 700[$^{\circ}C$]. The resistance temperature coefficient of composite showed the lowest value of $-2.3{\times}10^{-3}[^{\circ}C]^{-1}$ for 16[wt%] additives in the temperature ranges from 25[$^{\circ}C$] to 100[$^{\circ}C$].

• 한국세라믹학회지
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• 제31권4호
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• pp.443-447
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• 1994

Compacts of mixed SiO2-Si powder were liquid phase sintered at 145$0^{\circ}C$ for up to 60 min in a hydrogen atmosphere. In contrast to the conventional microstructures of liquid phase sintered materials, the specimens showed that the solid phase of SiO2 formed a matrix while the liquid phase of Si was the dispersed in the solid matrix. The dispersion of liquid Si pockets was attributed to the high wetting angle of liquid Si on solid SiO2. Because of relatively high solubility of SiO2 in liquid Si at 145$0^{\circ}C$, SiO2 particles accommodated their shape via a solution-reprecipitation process. The liquid Si pockets grew by coalescing with their neighbour pockets. In the latter stage of the sintering, plate-shape grains appeared in the liquid Si pockets. The grains were SiO2 phase precipitated from the liquid Si which was oversaturated with oxygen during cooling to room temperature. By the formation and subsequent removal of the gaseous SiO phase due to the reaction between SiO2 and Si, the specimens became porous.

• 한국세라믹학회지
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• 제53권1호
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• pp.99-104
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• 2016

High purity Si-C (99.999%) powder prepared by mechanical alloying was added to a commercial SiC powder as a sintering additive. Reaction bonded silicon carbide balls and jars with high purity (99.98%) were used for the mechanical alloying. As a result, the purity of the sintered Si-C was higher than 99.99%. When sintered at $2200^{\circ}C$ under 50 MPa pressure for 1 h, SiC containing 10 wt% of high purity Si-C showed a relative density of 95.3%, similar to the relative density of commercial SiC (95%). However, the relative density of SiC decreased to 90.6% without the additive when the applied pressure decreased to 40 MPa. In contrast, the relative density was nearly unaffected by the decrease of the pressure when using the Si-C additive. Therefore, the addition of Si-C powder promoted the densification of SiC above $2000^{\circ}C$ under 40 MPa pressure.

• 한국재료학회지
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• 제8권7호
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• pp.596-600
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• 1998

반응결합 알루미나(RBAO)-SiC 세라믹스를 AI금속분말/$AI_2O_3$/SiC 분말혼합체로부터 제조하였다. 하소알루미나와 용융알루미나를 알루미나 분말공급원으로 사용하였다. 출발원료는 단일구경(3mm)또는 혼합구경(3mm+5mm)의 $ZrO_2$볼로 어트리션 밀링 하였다. 정수압 성형한 시편을 $1100^{\circ}C$까지$ 1.5^{\circ}C$/mim로 1차소성한 다음,$ 1500^{\circ}C$~$1600^{\circ}C$까지 $5^{\circ}C$/mim으로 2차소성하였다. 용융알루미나와의 분말혼합체가 하소알루미나와의 분말혼합체보다 분쇄가 더욱 잘 되었다. 또한 단일구가 혼합구보다 분쇄에 더욱 효율적이었다. $AI_2O_3$ 형태에 따른 반응소결거동에는 별 차이가 없었다.

• 한국세라믹학회지
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• 제39권1호
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• pp.45-50
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• 2002

평균입경 25$\mu m$의 Si조대분말에 소결조제의 조성과 양을 변화시켜 질화반응 질화규소 (RBSN)세라믹스를 제조할 때 나타나는 치밀화 거동, 미세구조의 발달 및 기계적 특성에 대하여 고찰하였다. 6wt% $Y_2O_3$ + 1wt% $Al_2O_3$(6YlA)의 소결조제를 첨가한 경우에는 치밀화를 이루지 못하였으나, 6wt% $Y_2O_3+3\;wt%\;Al_2O_3+2\;wt%\;SiO_2(6Y3A2S)$와 9wt% $Y_2O_3$+1.5wt% $A1_2O_3$+ 3w% $SiO_2$(9Yl.5A3S)의 소결조제를 첨가하여 이론밀도에 가까운 치밀화를 이루었다. $1900^{\circ}C$에서 소결한 6Y3A2S시편의 경우, 960MPa의 높은 파괴강도값과 $6.5MPa.m^{1/2}$의 파괴인성값을 얻었다.