• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권2호
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• pp.98-103
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• 1999

The effect of $Al_2O_3$ additives to $\beta-SiC+39vol.%ZrB_2$ electroconductive ceramic composites by pressureless sintering on microstructural, mechanical and electrical properties were investigated. The $\beta-SiC+39vol.%ZrB_2$ ceramic composites were pressureless sintered by adding 4, 8, 12wt.% $Al_2O_3$ powder as a liquid forming additives at $1950^{\cire}C$ for 1h. Phase analysis of composites by XRD revealed mostly of $\alpha-SiC(6H), ZrB_2$ and weakly $\alpha-SiC(4H), \beta-SiC (15R)$ phase. The relative density of composites was lowered by gaseous products of the result of reaction between \beta-SiC and Al_2O_3$, therefore, porosity was increased with increasing $Al_2O_3$ contents, and showed the maximum value of 1.4197MPa.$m^{1/2}$ for composite with 4wt.% $Al_2O_3$ additives. The electrical resistivity of $\beta-SiC+39vol.%ZrB_2$ electroconductive ceramic composite was increased with increasing $Al_2O_3$ contents, and showed positive temperature coefficient resistance (PTCR) in the temperature range of $25^{\cire}C$ to $700^{\cire}C$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.314-314
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• 2010

The SiC-$ZrB_2$ composites were fabricated by combining 40vol.% of Zirconium Diboride(hereafter, $ZrB_2$) powders with Silicon Carbide(hereafter, SiC) matrix. TheSiC+40vol.%$ZrB_2$ composites were manufactured through Spark Plasma Sintering(hereafter, SPS) under argon atmosphere, uniaxial pressure of 50MPa, heating rate of $100^{\circ}C$/min, sintering temperature of $1,500^{\circ}C$ and holding time of 5min. But one on/off pulse sequence(one pulse time: 2.78ms) is 10:9(hereafter, SZ10), and the other is 48:8(hereafter, SZ48). The physical and mechanical properties of the SZ12 and SZ48 were examined. Reactions between $\beta$-SiC and $ZrB_2$ were not observed via X-Ray Diffraction(hereafter, XRD) analysis. The apparent porosity of the SZ10 and SZ48 composites were 9.7455 and 12.2766%, respectively. The SZ10 composite, 593.87MPa, had higher flexural strength than the SZ48 composite, 324.78MPa, at room temperature. The electrical properties of the SiC-$ZrB_2$ composites had Positive Temperature Coefficient Resistance(hereafter, PTCR).

• Progress in Superconductivity
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• 제9권1호
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• pp.68-73
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• 2007

We fabricated the in-situ $MgB_2$ wires using the powder-in-tube method and investigated the effects of sintering temperature and SiC contents on the microstructure and superconducting properties. Pure $MgB_2$ wires and 5, 10, 20 wt.% SiC doped $MgB_2$ wires were sintered at $600-1000^{\circ}C$ for 30 minutes in Ar atmosphere. We found that $MgB_2$ phase was mostly formed at the sintering temperature of $700^{\circ}C$ and above, and the critical temperature ($T_c$) increased with increasing sintering temperature. For the $MgB_2$ sintered at $850^{\circ}C$, the highest critical current density ($J_c$) was obtained to be $3.7{\times}10^5\;A/cm^2$ at 5 K and 1.6 T by a magnetic properties measurement system (MPMS). The addition of SiC to the $MgB_2$ wires changed microstructure and critical properties. SEM observation showed that the $MgB_2$ core had considerable micro-cracks in undoped wire and the density of micro-cracks decreased with increasing SiC contents. The critical temperature decreased as the SiC contents increased, on the other hand, the critical current density of SiC doped $MgB_2$ wires in high magnetic field was enhanced compared to that of undoped $MgB_2$ wires.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 추계학술대회 논문집 학회본부 C
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• pp.847-849
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• 1998

The effect of $Al_{2}O_{3}$ additives on the microstructure, mechanical and electrical properties of ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composites by pressureless sintering were investigated. The ${\beta}$-SiC+39vol.%$ZrB_2$ ceramic composites were pressureless sintered by adding 4, 8, 12wt.% $Al_{2}O_{3}$ powder as a liquid forming additives at $1950^{\circ}C$ for 1h. Phase analysis of composites by XRD revealed mostly of $\alpha$-SiC(6H), $ZrB_2$ and weakly $\alpha$-SiC(4H), $\beta$-SiC(15R) phase. The relative density of composites was lowered by gaseous products of the result of reaction between $\beta$-SiC and $Al_{2}O_{3}$ therefore, porosity was increased with increased $Al_{2}O_{3}$ contents. The fracture toughness of composites was decreased with increased $Al_{2}O_{3}$ contents, and showed the maximum value of $1.4197MPa{\cdot}m^{1/2}$ for composite added with 4wt.% $Al_{2}O_{3}$ additives. The electrical resistivity of ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composite was increased with increased $Al_{2}O_{3}$ contents, and showed positive temperature coefficient resistance (PTCR) in the temperature from $25^{\circ}C$ to $700^{\circ}C$.

• 멤브레인
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• 제14권4호
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• pp.312-319
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• 2004

졸겔법에 의해 Si(OC$_2$$H_5$/)$_4$-($CH_3$O)$_3$B-C$_2$$H_5$OH-$H_2O$계로부터 다공성의 SiO$_2$-B$_2$O$_3$ 막을 제조하였다. SiO$_2$-B$_2$O$_3$막의 특성을 BET, IR spectrophotometer, X-ray diffractometer, SEM 과 TEM을 사용하여 조사하였다. $700^{\circ}C$에서 얻어진 SiO$_2$-B$_2$O$_3$ 막의 평균 기공직경은 0.0048 $\mu\textrm{m}$이고, 표면적은 354.398 $m^2$/g이었으며, 입자의 크기는 7 nm인 무정형의 다공체이었다. SiO$_2$-B$_2$O$_3$ 막의 수소/질소 혼합 기체 분리 특성은 기체분리 압력을 달리하여 조사하였다. $25^{\circ}C$, ΔP 155.15cmHg에서 수소/질소 혼합 기체를 분리하여 본 결과 SiO$_2$-B$_2$O$_3$ 막의 수소에 대한 real separation factor($\alpha$)는 4.68이었다. 그리고 투과셀의 압력차(ΔP)값이 증가할수록 real separation factor($\alpha$), head separation factor($\beta$), tail separation factor((equation omitted))값이 증가하였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권2호
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• pp.104-108
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• 1999

The electrical conductive mechanism and temperature dependence of electrical resistivity of $\alpha-SiC-ZrB_2$ composites with $ZrB_2$ contents were investigated. The electrical resistivity of hot-pressed composites was measured by the Pauw method form $25^{\circ} to 700^{\circ}C$. The electrical resistivity of the composites follow the electrical conduction model for a homogeneous mixture of two kind of particles with different conductivity. Also, the electrical resistivity versus temperature curves indicate the formation of local chains of $ZrB_2$ particles. In case of $\alpha-SiC-ZrB_2$ composites containing above 39vol.% $ZrB_2$ showed positive temperature coefficient resistance(PTCR), whereas the electrical resistivity of $\alpha-SiC-21vol.% ZrB_2$ showed negative temperature coefficient resistance(NTCR).

• 한국재료학회지
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• 제7권10호
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• pp.845-850
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• 1997

수직형 FHD증착법을 사용하여 SiO$_{2}$, SiO$_{2}$-P$_{2}$O$_{5}$, SiO$_{2}$P$_{2}$O$_{5}$-B$_{2}$O$_{3}$-GeO$_{2}$계 실리카 유리미립자를 형성하였으며, SEM, ICP-AES, XRD, TGA-DSC을 사용하여 그 특성을 분석하였다. XRD측정을 통해, 미립자 형성시 사용된 화염온도(130$0^{\circ}C$-150$0^{\circ}C$)와 기판온도(-20$0^{\circ}C$)가 SiO$_{2}$-P$_{2}$O$_{5}$계 미립자를 비정질상태로 형성하였으며, SiO$_{2}$P$_{2}$O$_{5}$-B$_{2}$O$_{3}$와 SiO$_{2}$P$_{2}$O$_{5}$-B$_{2}$O$_{3}$-GeO$_{2}$계 미립자에서는 B$_{2}$O$_{3}$, BPO$_{4}$, GeO$_{2}$의 결정성피크들을 관찰하였다. TGA-DSC 열분석을 통해, SiO$_{2}$와 SiO$_{2}$-P$_{2}$O$_{5}$는 온도변화에 따른 질량변화가 없었으며, SiO$_{2}$P$_{2}$O$_{5}$-B$_{2}$O$_{3}$-GeO$_{2}$계의 경우 질량감소를 동반한 유리전이에 따른 분자이완현상 및 결정화나 회복반응을 나타내고 있다. 질량감소는 미립자가 결정상태일때 가속되는 경향을 나타냈으며, DSC열분석을 통해 SiO$_{2}$, SiO$_{2}$-P$_{2}$O$_{5}$, SiO$_{2}$P$_{2}$O$_{5}$-B$_{2}$O$_{3}$-GeO$_{2}$계 유리미립자들의 고밀화가 시작되는 온도를 각각 1224$^{\circ}C$, 1151$^{\circ}C$, 953$^{\circ}C$, 113$0^{\circ}C$에서 관찰하였다.

• 한국세라믹학회지
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• 제52권6호
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• pp.462-466
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• 2015

This paper reports the microstructure of hot-pressed $ZrB_2$-SiC ceramics with added $B_4C$ as characterized by transmission electron microscopy. $ZrB_2$ has a melting point of $3245^{\circ}C$, a relatively low density of $6.1g/cm^3$, and specific mechanical properties at an elevated temperature, making it a candidate for application to environments with ultra-high temperatures which exceed $2000^{\circ}C$. Due to the non-sinterability of $ZrB_2$-based ceramics, research on sintering aids such as $B_4C$ or $MoSi_2$ has become prominent recently. From TEM investigations, an amorphous layer with contaminant oxide is observed in the vicinity of $B_4C$ grains remaining in hot-pressed $ZrB_2$-SiC ceramics with $B_4C$ as an additive. The effect of a $B_4C$ addition on the microstructure of this system is also discussed.

• The Korean Journal of Ceramics
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• 제5권2호
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• pp.155-161
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• 1999

The tribological behaviour of monolithic SiC as well as SiC-TiC and SiC-TiC-$TiB_2$ particulate composite materials has been investigated in unlubricated oscillating sliding tests against $Al_2O_3$ at temperature in the range from room temperature up to $600^{\circ}C$. At temperatures below $600^{\circ}C$ the wear rate of the systems with the composite materials was up to 20 times lower than the wear of the $Al_2O_3$/SiC system and was dominated by the oxidation of the titanium phases. At $600^{\circ}C$ the oxidation rate of the TiC and -TEX>$TiB_2$ grains becomes predominant resulting in an enhanced wear rate of the composite rate of the TiC and TiB2 grains becomes predominant resulting in an enhanced wear rate of the composite materials. The coefficient of friction shows similar values for all materials of investigation, increasing from 0.25…0.3 at room temperature to 0.7…0.8 $600^{\circ}C$. The wear of the $Al_2O_3$/SiC system is mainly abrasive at temperatures above room temperature and is characterised by an enhanced wear of the alumina ball at $600^{\circ}C$.

• 한국분말재료학회지
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• 제18권6호
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• pp.562-567
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• 2011

This paper reports the effect of sintering processes and additives on the microstructures and mechanical properties of $ZrB_2$-SiC composite ceramics. We fabricated sintered bodies of $ZrB_2$-20 vol.% SiC with or without sintering additive, such as C or $B_4C$, densified by spark plasma sintering as well as hot pressing. While almost full densification was achieved regardless of sintering processes or sintering additives, significant grain growth was observed in the case of spark plasma sintering, especially with $B_4C$. With sintered bodies, mechanical properties, such as flexural strength and Vickers hardness, were also examined.