• Journal of the Korean Ceramic Society
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• v.38 no.6
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• pp.582-586
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• 2001

방전 플라즈마 소결법을 이용하여 ZrB$_2$-ZrC 복합체를 소결하여 소결 거동과 미세구조에 대하여 조사하였다. 소결 조제로서 란타늄을 첨가하였을 경우에 첨가하지 않았을 경우보다 더 낮은 온도에서 소결 수축이 시작되었으며, 180$0^{\circ}C$에서 거의 치밀화가 완성되었다. 란타늄은 방전플라즈마 소결시 초기 분말 간 액상 형성으로 물질이동을 가속화하여 ZrB$_2$-ZrC 복합체의 치밀화에 커다란 기여를 하며, 냉각 시에 재결정화하여 결정립계와 결정립 삼중점에 란타늄이 포함된 이차상을 형성하는 것으로 확인되었다. 또한 ZrB$_2$-ZrC는 강한 공유결합성 재료임에도 불구하고 미세 구조 내에 잘 발달된 전위 구조를 형성하고 있음을 확인하였다.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1512-1515
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• 1996

Dense $SiC-ZrB_2$ electro-conductive ceramic composites were obtained by hot pressing for high temperature structural application. The influences of the $ZrB_2$ additions an the mechanical and electrical properties of $SiC-ZrB_2$ composites were investigated. Samples were prepared by adding 15, 30, 45 vol.% $ZrB_2$ particles as a second phase to a SiC matrix. Sintering of monolithic SiC and $SiC-ZrB_2$ composites were achieved by hot pressing under a $10^{-4}$ torr vacuum atmosphere from 1000 to $2000^{\circ}C$ with a pressure of 30 MPa and held for 60 minutes at $2000^{\circ}C$. SiC and $SiC-ZrB_2$ samples obtained by hot pressing were fully dense with the relative densities over 99%. Flexural strength and fracture toughness of the samples were improved with the $ZrB_2$ contents. In the case of SiC sample containing 30vol.% $ZrB_2$, the flexural strength and fracture toughness showed 45% and 60% increase, respectively compared to those of monolithic SiC sample. The electrical resistivities of $SiC-ZrB_2$ composites were measured utilizing the four-point probe method and they decreased significantly with Increasing $ZrB_2$ contents. The resistivity of SiC-30vol.% $ZrB_2$ showed $6.50{\times}10^{-4}{\Omega}{\cdot}cm$.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.342-351
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• 2010

The SiC-$ZrB_2$ composites were fabricated by combining 30, 35, 40, 45 and 50 vol. % of zirconium diboride ($ZrB_2$) powders with silicon carbide (SiC) matrix. The SiC-$ZrB_2$ composites and the sintered compacts were produced through spark plasma sintering (SPS) under argon atmosphere, and its physical, electrical, and mechanical properties were examined. Also, the thermal image analysis of the SiC-$ZrB_2$ composites was examined. Reactions between $\beta$-SiC and $ZrB_2$ were not observed via x-ray diffraction (XRD) analysis. The apparent porosity of the SiC+30vol.%$ZrB_2$, SiC+35vol.%$ZrB_2$, SiC+40vol.%$ZrB_2$, SiC+45vol.%$ZrB_2$ and SiC+50vol.%$ZrB_2$ composites were 7.2546, 0.8920, 0.6038, 1.0981, and 10.0108%, respectively. The XRD phase analysis of the sintered compacts demonstrated a high phase of SiC and $ZrB_2$. Among the $SiC+ZrB_2$ composites, the SiC+50vol.%$ZrB_2$ composite had the lowest flexural strength, 290.54MPa, the other composites had more than 980MPa flexural strength except the SiC+30vol.%$ZrB_2$ composite; the SiC+40vol.%$ZrB_2$ composite had the highest flexural strength, 1011.34MPa, at room temperature. The electrical properties of the SiC-$ZrB_2$ composites had positive temperature coefficient resistance (PTCR). The V-I characteristics of the SiC-$ZrB_2$ composites had a linear shape in the temperature range from room to $500^{\circ}C$. The electrical resistivities of the SiC+30vol.%$ZrB_2$, SiC+35vol.%$ZrB_2$, SiC+40vol.%$ZrB_2$ SiC+45vol.%$ZrB_2$ and SiC+50vol.%$ZrB_2$ composites were $4.573\times10^{-3}$, $1.554\times10^{-3}$, $9.365\times10^{-4}$, $6.999\times10^{-4}$, and $6.069\times10^{-4}\Omega{\cdot}cm$, respectively, at room temperature, and their resistance temperature coefficients were $1.896\times10^{-3}$, $3.064\times10^{-3}$, $3.169\times10^{-3}$, $3.097\times10^{-3}$, and $3.418\times10^{-3}/^{\circ}C$ in the temperature range from room to $500^{\circ}C$, respectively. Therefore, it is considered that among the sintered compacts the SiC+35vol.%$ZrB_2$, SiC+40vol.%$ZrB_2$ and SiC+45vol.%$ZrB_2$ composites containing the most outstanding mechanical properties as well as PTCR and V-I characteristics can be used as an energy friendly ceramic heater or ohmic-contact electrode material through SPS.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.4
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• pp.770-776
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• 2009

The composites were fabricated by adding 0, 15, 30, 45[vol.%] $ZrB_2$ powders as a second phase to SiC matrix. The physical, mechanical and electrical properties of electroconductive SiC ceramic composites by spark plasma sintering(SPS) were investigated. Reactions between ${\beta}$-SiC and $ZrB_2$ were not observed in the XRD and the phase analysis of the electroconductive SiC ceramic composites. The relative density of mono ${\beta}$-SiC, ${\beta}$-SiC+15[vol.%]$ZrB_2$, ${\beta}$-SiC+30[vol.%]$ZrB_2$ and ${\beta}$-SiC+45[vol.%]$ZrB_2$ composites are respectively 99.24[%], 87.53[%], 96.41[%] and 98.11[%] Phase analysis of the electroconductive SiC ceramic composites by XRD revealed mostly of ${\beta}$-SiC, $ZrB_2$ and weakly of $ZrO_2$ phase. The flexural strength showed the lowest of 114.44[MPa] for ${\beta}$-SiC+15[vol.%]$ZrB_2$ powders and showed the highest of 210.75[MPa] for composite no added with $ZrB_2$ powders at room temperature. The trend of the mechanical properties of the electroconductive SiC ceramic composites is accorded with the trend of the relative density. The electrical resistivity of the electroconductive SiC ceramic composites decreased with increased $ZrB_2$ contents. The electrical resistivity of mono ${\beta}$-SiC, ${\beta}$-SiC+15[vol.%]$ZrB_2$, ${\beta}$-SiC+30[vol.%]$ZrB_2$ and ${\beta}$-SiC+45[vol.%]$ZrB_2$ composites are respectively $4.57{\times}10^{-1},\;2.13{\times}10^{-1},\;2.68{\times}10^{-2}\;and\;1.99{\times}10^{-2}[{\Omega}{\cdot}cm]$ at room temperature. The electrical resistivity of mono ${\beta}$-SiC and ${\beta}$-SiC+15[vol.%]$ZrB_2$ are negative temperature coefficient resistance(NTCR) in temperature ranges from $25[^{\circ}C]\;to\; 100[^{\circ}C]$. The electrical resistivity of ${\beta}$-SiC+30[vol.%]$ZrB_2$ and ${\beta}$-SiC+45[vol.%]ZrB_2$ are positive temperature coefficient resistance(PTCR) in temperature ranges from $25[^{\circ}C]\;to\;100[^{\circ}C]$. It is convinced that ${\beta}$-SiC+30[vol.%]$ZrB_2$ composites by SPS for heater or ignitors can be applied.

• Journal of Powder Materials
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• v.16 no.6
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• pp.442-448
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• 2009

$ZrB_2$-based composites are candidate materials for ultra-high temperature materials (UHTMs). $ZrB_2$ has become an indispensable ingredient in UHTMs, due to its high melting temperature, relatively low density, and excellent resistance to thermal shock or oxidation. $ZrB_2$ powders are usually synthesized by solid state reactions such as carbothermal, borothermal, or combined carbothermal reaction. SiC is added to this system in order to enhance the oxidation resistance of $ZrB_2$. In this study, $ZrB_2$?based composites were successfully synthesized and densified through two different processing paths. $ZrB_2$ or $ZrB_2$ 25 vol.%SiC was fully synthesized from oxide starting materials with reducing agents after heat treatment at 1400$^{\circ}C$. Besides, $ZrB_2$?20 vol.%SiC was fully densified with $B_4C$ as a sintering additive after hot pressing at 1900$^{\circ}C$. The synthesis mechanism and the effect of sintering additives on densification of $ZrB_2$ ?SiC composites were also discussed.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.400-403
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• 1999

The mechanical and electrical properties of hot-pressed and annelaed $\beta$-SiC+39vol.% $ZrB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of $Al_2O_3+Y_2O_3$(6:4 wt%). In this microstructures, no reactions and elongated $\alpha$-SiC grains with equiaxed $ZrB_2$ grains were observed between $\beta$-SiC and $ZrB_2$. The properties of the $\beta$-SiC+39vol.%$ZrB_2$ composites with 4wt% $Al_2O_3+Y_2O_3$ at R.T. are as follows: fracture toughness is 6.37 MPa.m1/2, electical resistivity is $1.51\times10^{-4}\Omega \cdot\textrm{cm}$ and the relative density is 98.6% of the theoretical density. The fracture toughness of the $\beta$-SiC+39 vol.% $ZrB_2$ composites were weakly decreased with increasing amount of $Al_2O_3+Y_2O_3$ additives. Internal stresses due to the difference of $\beta$-SiC and $ZrB_2$ thermal expansion coefficient and elastic modulus mismatch appeared to contribute to fracture toughening in $\beta$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composites.

• Journal of the Korean Ceramic Society
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• v.34 no.11
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• pp.1165-1172
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• 1997

ZrB2 powders were prepared from a mixture of ZrO2, B2O3 and Mg by self-propagating high temperature synthesis method. The combustion product was successfully obtained from a mixture of ZrO2:B2O3:Mg=1:2:8.5 molar ratio. By-product, MgO was effectively removed by leaching with 1M HCl solution at 9$0^{\circ}C$ for over 5hours. After leaching, the Mg content was 0.86~1.42 wt%, and the mean particle size was 4.72${\mu}{\textrm}{m}$. The addition of 7.5 wt%(14Ni:1.0C) as a sintering aid greatly densified ZrB2 bodies compared with that of only Ni. The ZrB2 sintered bodies containing 7.5 wt%(14Ni:1.0C) was 94.3% of the theoretical density. In this case, ZrB2 existed as a major phase and had a bend strength of 300 MPa and a vickers hardness of 2000 kg/$\textrm{mm}^2$.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05a
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• pp.219-224
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• 1996

노심설계에서 현재 사용되는 일체형 가연성 흡수봉인 Gd, ZrB$_2$ 그리고 Er의 한국표준형 원전 노심 설계에의 타당성을 노심 F$\Delta$H 제어, 저누출 장전모형 설계, 농축도/주기길이 그리고 주기말의 잔존 페널티 등의 측면에서 분석하였다. 초기노심의 경우는 영광 3호기 1주기 장전모형에 동일 연료집합체를 사용한 Gd/ZrB$_2$/Er의 경우와 ZrB$_2$/Er 최적장전모형에 동일 연료집합체를 사용한 경우에 대하여 분석하였다. 평형노심은 Gd/ZrB$_2$/Er 모두 동일한 장전모형을 사용한 18개월 주기길이의 노심에 대하여 동일한 농축도에서의 주기길이차이와 동등 주기길이를 내는데 필요한 농축도 요구량에 대하여 분석하였다. 초기노심 평형노심 모두 F$\Delta$H 제어에는 ZrB$_2$/Er가 Gd보다 유리하였으며, 저누출 장전모형의 설계에도 ZrB$_2$와 Er가 Gd보다 유리하였다. 평형노심에서 동일한 주기길이를 내는데 요구되는 농축도는 ZrB$_2$에 비하여 Er는 0.182 w/o Gd는 0.063 w/o 높게 나타났으며 동일 농축도를 사용할 경우 주기길이는 ZrB$_2$에 비하여 Gd는 165 MWD/MTU 그리고 Er은 575 MWD/MTU가 짧게 나타났다. 따라서, F$\Delta$H 제어와 저누출 장전모형은 설계에는 ZrB$_2$와 Er가 Gd보다 유리하였으나 Er의 경우 주기말에서의 잔존 페널티가 매우 크다는 단점이 있다.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.8-13
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• 1999

$ZrB _2$ was prepared from a mixture of $ZrO_2$, $B_2$$O_3$and Mg by SHS method. The combustion products were successfully obtained from a mixture of $Zro_2$:$B_2$$O_3$:Mg=1:2.0:8.5(molar ratio). MgO, by-product, was removed to 92.7% by leaching with 1M HCl solution at 9$0^{\circ}C$, for 10 hours. After leaching, the mean particle size of the resultant $ZrB_2$powders was 23.6$\mu\textrm{m}$. $ZrB_2$-ZrC composite was suitably obtained from a mixture of C/Zr=1.2 molar ratio by arc-melting method. The density of arc-melted specimen increased by adding excess zirconium content(x). The bulk density was 6.17g/㎤ for x=0, and 6.37g/㎤ x=4. Vickers hardness of arc-melted specimen was /$1290kg\textrm{mm}^2$ for x=0, and fracture toughness increased to 4.2MPa.m\ulcornerforx=4 compared to 3.4MPa.m\ulcornerfor x=0.

• Journal of Powder Materials
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• v.26 no.6
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• pp.455-462
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• 2019

ZrB₂ ceramic and ZrB₂ ceramic composites with the addition of SiC, WC, and SiC/WC are successfully synthesized by a spark plasma sintering method. During high-temperature oxidation, SiC additive form a SiO₂ amorphous outer scale layer and SiC-deplete ZrO₂ scale layer, which decrease the oxidation rate. WC addition forms WO₃ during the oxidation process to result in a ZrO₂/WO₃ liquid sintering layer, which is known to improve the anti-oxidation effect. The addition of SiC and WC to ZrB₂ reduces the oxygen effective diffusivity by one-fifth of that of ZrB₂. The addition of both SiC and WC shows the formation of a SiO₂ outer dense glass layer and ZrO₂/WO₃ layer so that the anti-oxidation effect is improved three times as much as that of ZrB₂. Therefore, SiC- and WC-added ZrB₂ has a lower two-order oxygen effective diffusivity than ZrB₂; it improves the anti-oxidation performance 3 times as much as that of ZrB₂.