• 한국해양공학회지
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• 제23권5호
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• pp.32-38
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• 2009

Silicon nitride samples with aligned whisker seeds were prepared with different amounts of yttria and alumina as the sintering additives. Their sintering behaviors and the microstructural developments between $1850^{\circ}C$ and $2050^{\circ}C$ were examined. The sample with larger amount of the sintering additives showed faster densification and grain growth. Even though addition of the aligned whisker seeds slightly retarded densification of silicon nitride, it improved the flexural strength and the fracture toughness. Both the flexural strength and the fracture toughness of silicon nitride with the aligned whisker seeds were increased as the amount of the sintering additives was increased.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 센서 박막재료 반도체 세라믹
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• pp.282-286
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• 2003

We investigated the effects of calcination temperature and sintering additives on the sintering behaviors and microwave dielectric properties of $(Zn_{0.8}Mg_{0.2})TiO_3$. Highly densified samples were obtained at the sintering temperatures below $1000^{\circ}C$ with additions of 0.45 wt.% $Bi_2O_3$ and 0.55 wt.% $V_2O_5$. From the examination of the existing phases and microstructures before and after sintering of $(Zn_{0.8}Mg_{0.2})TiO_3$ system calcined at the various temperatures ranging from $800^{\circ}C$ to $1000^{\circ}C$, it was found that high $Q{\times}f_o$ values were obtained when unreacted or second phases in calcined body were reduced. When calcined at $1000^{\circ}C$ and sintered at $900^{\circ}C$, it consists of hexagonal as a main phase with uniform microstructure and exhibits $Q{\times}f_o$ value of 42,000 GHz and dielectric constant of 22.

• 대한기계학회논문집A
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• 제32권11호
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• pp.1003-1009
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• 2008

In this study, liquid phase sintered SiC (LPS-SiC) materials were made by hot pressing method. The particle size of nano-SiC powder was 30nm. Alumina ($Al_2O_3$), yttria ($Y_2O_3$) and silica ($SiO_2$) were used for sintering additives. To investigate effects of $SiO_2$, ratios of $SiO_2$ contents were changed by five kinds. Materials have been sintered for 1 hour at $1760^{\circ}C$, $1780^{\circ}C$ and $1800^{\circ}C$ under the pressure of 20MPa. The system of sintering additives which affects a property of sintering as well as the influence depending on compositions of sintering additives were investigated by measurement of density, mechanical properties such as flexural strength, vickers hardness and sliding wear resistance were investigated to make sure of the optimum condition which is about matrix of $SiC_f$/SiC composites. The abrasion test condition apply to load of 20N at 100RPM for 20min. Sintered density, flexural strength of fabricated LPS-SiC increased with increasing the sintering temperature. And in case of LPS-SiC with low $SiO_2$, sliding wear resistance has very excellent. Monolithic SiC $1800^{\circ}C$ sintering temperatures and 3wt% have excellent wear resistance.

• 한국세라믹학회지
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• 제30권10호
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• pp.829-837
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• 1993

Chemically and geometrically homogeneous mixing of Si3N4 powders with sintering additives(YAG, 3Y2O3$.$5Al2O3) was attempted via coprecipitation method. X-ray dot maps for the additive elements(Al and Y) showed that the additives are evenly distributed in the powder mixture prepared by coprecipitation method(CP). TEM observation of the coprecipittion-treated Si3N4 powders revealed that they are covered with extremely fine crystallites of additive. The shift in isoelectric point(IEP) of Si3N4 powders from pH 6.7 to pH 7.9 after coprecipitation mixing gave another evidence for coating of Si3N4 powders with YAG additives. SIMS analysis for composition on the surface and in the matrix of mixed powders showed that the YAG additives are highly enriched on the surface of coprecipitation-treated Si3N4 powders. Especially when a small amount of additive was used, the effect of homogeneous additive distribution on densification was preceptible: After pressureless-sintering of powder compacts containing 5 mol% YAG at 1800$^{\circ}C$ for 0.5h, a sintered density of 96.5% theoretical was obtained from the specimens prepared bycoprecipitation in comparison with 93.8% from the mechanically-mixed one.

• 한국해양공학회지
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• 제20권5호
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• pp.77-81
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• 2006

In this study, monolithic liquid phase sintered SiC (LPS-SiC) was made by the hot pressing method with nano-SiC powder, whose particle size is 30 nm and less on the average. Alumina ($Al_{2}O_{3}$), yttria ($Y_{2}O_{3}$), and silica ($S_{i}O_{2}$) were used for sintering additives. To investigate the effects of $S_{i}O_{2}$, the $Al_{2}O_{3}/Y_{2}O_{3}$ composition was fixed and the ratio of $S_{i}O_{2}$ was changed, with seven different ratios tested. And to investigate the effects of the sintering temperature, the sintering temperature was changed, with $1760^{\circ}C,\;1780_{\circ}C$, and $1800_{\circ}C$ being used with a $S_{i}O_{2}$ ratio of 3 wt%. The materials were sintered for 1 hour at $1760^{\circ}C,\;1780^{\circ}C$ and $1800^{\circ}C$ under a pressure of 20 MPa. The effects on sintering from the sintering system used, as well as from the composition of the sintering additives, were investigated by density measurements. Mechanical properties, such as flexural strength, were investigated to ensure the optimum conditions for a matrix of SiCf/SiC composites. Sintered densityand the flexural strength of fabricated LPS-SiC increased with an increase in sintering temperature. Particularly, the relative density of a sintered body at $1800^{\circ}C$ with a non-content of $S_{i}O_{2}$, a specimen of AYSO-1800, was 95%. Also, flexural strength was about 750MPa.

• 한국세라믹학회지
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• 제49권4호
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• pp.342-346
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• 2012

This work deals with the preparation of dense SiC based ceramics with high electrical conductivity without oxide sintering additives. SiC samples with different content of conductive Ti-NbC phase were hot pressed at $1850^{\circ}C$ for 1 h in Ar atmosphere under mechanical pressure of 30 MPa. The conductive phase is a mixture of Ti-NbC in weight ratio of Ti/NbC 1:4. Composite with 50% of conductive Ti-NbC phase showed the highest electrical conductivity of $30.6{\times}10^3\;S{\cdot}m^{-1}$, while the good mechanical properties of SiC matrix were preserved (fracture toughness 4.5 $MPa{\cdot}m^{1/2}$ and Vickers hardness 18.7 GPa). The obtained results show that use of NbC and Ti as sintering and also electrically conductive additives is appropriate for the preparation of SiC-based composite with sufficient electrical conductivity for electric discharge machining.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.439-442
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• 2004

The effects of sintering additives on the low-temperature sintering and microwave dielectric properties of $Mg_4Nb_2O_9$ dielectric ceramics were studied. When $3{\sim}20wt%$ of $0.242Bi_2O_3-0.758V_2O_5$ was added, the sintering temperature decreased from $1100{\sim}1300^{\circ}C$ to $950^{\circ}C$ and high density was obtained. When $Mg_4Nb_2O_9$ was sintered at $950^{\circ}C$ with 10wt% of sintering additive, the microwave dielectric properties of $Q{\times}f_0\;=\;80.035GHz,\;\epsilon_r\;=\;13.3\;and\;\tau_f\;=\;-12.9\;ppm/^{\circ}C$ were obtained.

• 한국세라믹학회지
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• 제25권6호
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• pp.609-614
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• 1988

This study was carried out to investigate the effects of B4C or Y2O3 additives on the tendency of sintering, $\beta$-SiC synthesis and mineral phase changes by reaction bonding of SiC at 145$0^{\circ}C$. At the sintering temperature of 145$0^{\circ}C$, the additives such as B4C or Y2O3 did not improved porosity and bending strength. Added more than 1.5% of Y2O3, 0.5-0.3% of B4C, the formation of $\beta$-SiC was increased. At higher temperature above 145$0^{\circ}C$, it seems that the bodies added B4C, contained 3C form of SiC were denser than that of Y2O3 added. Because the transition of 3Clongrightarrow4Hlongrightarrow6H promoted sintering.

• 자연과학논문집
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• 제8권1호
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• pp.53-59
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• 1995

Alumina 세라믹스의 기계적 물성 증진을 위하여 SiC whisker로 강화시키고 소결 조제 및 소결 온도의 영향을 고찰하였다. Whiker의 소결억제 효과로 인하여 고상소결을 촉진하는 MgO나 $TiO_2$를 소결조제로 사용한 경우에서는 치밀한 소결체를 얻을 수 없었으나, 액상을 형성하는 $Y_2O_3$를 2wt% 첨가한 경우에 양호한 소결밀도를 얻을 수 있었다. whisker 첨가에 의한 기지의 기계적 물성의 증진 효과도 함께 얻을 수 있었다. 강화 효과는 보강재인 whiker 자체의 보강 효과와 함께 입성장 억제 효과가 복합적으로 작용한 것으로 판단되었다. 소결체를 HIP 처리한 경우에는 거의 이론 밀도까지 이르는 아주 치밀한 소결체의 제조가 가능하였으며, 기계적 물성은 상압소결 후의 결과에 비하여 향상됨을 확인할 수 있었다.

• 한국결정성장학회지
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• 제29권1호
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• pp.1-5
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• 2019

산화물을 포함한 세라믹 재료의 물성은 소재 치밀도에 크게 영향을 받는다. 따라서 소재 치밀도를 높이기 위한 다양한 노력들이 진행되어왔다. 이중 많이 사용되는 전략으로 재료 소결 시 소결조제를 첨가하는 것이다. 기존의 소결조제는 3차원 구조를 갖는 구형의 분말이었다. 본 연구에서는 차별화 전략으로 세륨산화물의 소결 밀도를 높이기 위해 2차원 층상구조를 갖는 소결조제를 첨가하였다. 실제로 2차원 층상구조의 조결조제에 의해 소결밀도가 증가되는 것을 확인할 수 있었다. 2차원 층상구조 소재로 초나노 두께(~1 nm)를 갖는 $TiO_x$와 $MnO_x$ 나노쉬트가 이용되었다.