• 전기학회논문지
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• 제56권9호
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• pp.1602-1608
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• 2007

The composites were fabricated, respectively, using 61[vol.%] SiC-39[vol.%] $TiB_2$ and using 61[vol.%] SiC-39[vol.%] $ZrB_2$ powders with the liquid forming additives of 12[wt%] $Al_2O_3+Y_2O_3$ by hot pressing annealing at $1650[^{\circ}C]$ for 4 hours. Reactions between SiC and transition metal $TiB_2$, $ZrB_2$ were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H, 3C), $TiB_2$, $ZrB_2$ and $YAG(Al_5Y_3O_{12})$ crystal phase on the Liquid-Phase-Sintered(LPS) $SiC-TiB_2$, and $SiC-ZrB_2$ composite. $\beta\rightarrow\alpha-SiC$ phase transformation was occurred on the $SiC-TiB_2$ and $SiC-ZrB_2$ composite. The relative density, the flexural strength and Young's modulus showed the highest value of 98.57[%], 249.42[MPa] and 91.64[GPa] in $SiC-ZrB_2$ composite at room temperature respectively. The electrical resistivity showed the lowest value of $7.96{\times}10^{-4}[\Omega{\cdot}cm]$ for $SiC-ZrB_2$ composite at $25[^{\circ}C]$. The electrical resistivity of the $SiC-TiB_2$ and $SiC-ZrB_2$ composite was all positive temperature coefficient resistance (PTCR) in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$. The resistance temperature coefficient of composite showed the lowest value of $1.319\times10^{-3}/[^{\circ}C]$ for $SiC-ZrB_2$ composite in the temperature ranges from $100[^{\circ}C]$ to $300[^{\circ}C]$ Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites.

• Journal of Electrical Engineering and Technology
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• 제6권4호
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• pp.543-550
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• 2011

Conductive SiC-$ZrB_2$ composites were produced by subjecting a 40:60 (vol%) mixture of zirconium diboride (ZrB2) powder and ${\beta}$-silicon carbide (SiC) matrix to spark plasma sintering (SPS). Sintering was carried out for 5 min in an argon atmosphere at a uniaxial pressure and temperature of 50 MPa and $1500^{\circ}C$, respectively. The composite sintered at a heating speed of $25^{\circ}C$/min and an on/off pulse sequence of 12:2 was denoted as SZ12L. Composites SZ12H, SZ48H, and SZ10H were obtained by sintering at a heating speed of $100^{\circ}C$/min and at on/off pulse sequences of 12:2, 48:8, and 10:9, respectively. The physical, electrical, and mechanical properties of the SiC-$ZrB_2$ composites were examined and thermal image analysis of the composites was performed. The apparent porosities of SZ12L, SZ12H, SZ48H, and SZ10H were 13.35%, 0.60%, 12.28%, and 9.75%, respectively. At room temperature, SZ12L had the lowest flexural strength (286.90 MPa), whereas SZ12H had the highest flexural strength (1011.34 MPa). Between room temperature and $500^{\circ}C$, the SiC-$ZrB_2$ composites had a positive temperature coefficient of resistance (PTCR) and linear V-I characteristics. SZ12H had the lowest PTCR and highest electrical resistivity among all the composites. The optimum SPS conditions for the production of energy-friendly SiC-$ZrB_2$ composites are as follows: 1) an argon atmosphere, 2) a constant pressure of 50 MPa throughout the sintering process, 3) an on/off pulse sequence of 12:2 (pulse duration: 2.78 ms), and 4) a final sintering temperature of $1500^{\circ}C$ at a speed of $100^{\circ}C$/min and sintering for 5 min at $1500^{\circ}C$.

• 한국재료학회지
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• 제18권9호
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• pp.475-481
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• 2008

Positive temperature coefficient of resistivity (PTCR) characteristics of (1-x)$BaTiO_3-x(Bi_{0.5}K_{0.5})TiO_3$ ceramics doped with $Nb_2O_5$ were investigated in order to develop the Pb-free PTC thermistor available at high temperatures of > $120^{\circ}C$. The PTCR characteristics appearing in the ($B_{i0.5}K_{i0.5})TiO_3$ (< 5 mol%) incorporated $BaTiO_3$ ceramics, which might be mainly due to $Bi^{+3}$ ions substituting for $Ba^{+2}$ sites. The 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics showed good PTCR characteristics of a low resistivity at room temperature (${\rho}_r$) of $31{\Omega}{\cdot}cm$ a high ${\rho}_{max}/{\rho}_{min}$ ratio of $5.38{\times}10^3$, and a high resistivity temperature factor (${\alpha}$) of $17.8%/^{\circ}C$. The addition of $Nb_2O_5$ to 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics further improved the PTCR characteristics. Especially, 0.025 mol% $Nb_2O_5$ doped 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics exhibited a significantly increased ${\rho}_{max}/{\rho}_{min}$ ratio of $8.7{\times}10^3$ and a high ${\alpha}$ of $18.6%/^{\circ}C$, along with a high $T_c$ of $148^{\circ}C$ despite a slightly increased ${\rho}_r$ of $31{\Omega}{\cdot}cm$.

• 한국전기전자재료학회논문지
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• 제23권12호
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• pp.929-935
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• 2010

$(1-x)BaTiO_3-x(Bi_{0.5}Na_{0.5})TiO_3$ ($0.01{\leq}x{\leq}0.10$) ceramics were fabricated with muffled sintering by a modified synthesis process. Their positive temperature coefficient of resistivity (PTCR) characteristics were investigated systematically. All specimen showed a perovskite structure with a tetragonal symmetry. Both the lattice parameter of a and c axes were slightly decreased with increasing $(Bi_{0.5}Na_{0.5})TiO_3$ (BNT) content. Grain growth was achieved when the incorporated BNT was increased to 6 mol% and the inhibition of grain growth is considered to be due to the appearance of Ba vacancy ($V^{"}_{Ba}$) in the $(1-x)BaTiO_3-x(Bi_{0.5}Na_{0.5})TiO_3$ ($0.08{\leq}x$). With 4 mol% BNT addition, room temperature resistivity decreased to $48 \Omega{\cdot}cm$ and a resistivity jump ($\rho_{max}/\rho_{min}$) was as high as $1.1{\times}10^4$, respectively. Curie temperature was also increased to $171^{\circ}C$ with increasing BNT content.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 전자세라믹스 센서 및 박막재료 반도체재료 일렉트렛트 및 응용기술
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• pp.72-75
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• 2000

The effect of $Al_2O_3+Y_2O_3$ additives on fracture toughness of ${\beta}-SiC-TiB_2$ composites by hot-pressed sintering were investigated, The ${\beta}-SiC-TiB_2$ ceramic composites were hot-presse sintered and annealed by adding 4, 8, 12wt% $Al_2O_3+Y_2O_3$(6 : 4wt%) powder as a liquid forming additives at low temperature($1800^{\circ}C$) for 4h. In this microstructures, the relative density is over 97% of the theoretical density and the porosity increased with increasing $Al_2O_3+Y_2O_3$ contents because of the increasing tendency of pore formation. But the fracture toughness showed the highest of $7.0MPa{\cdot}m^{1/2}$ for composites added with 12wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity showed the lowest of $1.59\times10^{-3}\Omega{\cdot}cm$ for composite added with 8wt% $Al_2O_3+Y_2O_3$ additives at room temperature and is all positive temperature coefficient resistance(PTCR} against temperature up to $700^{\circ}C$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 C
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• pp.479-481
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• 2000

The effect of $Al_{2}O_{3}+Y_{2}O_{3}$ additives on fracture toughness of $\beta-SiC-TiB_2$ composites by hot-pressed sintering were investigated. The f$\beta-SiC-TiB_2$ ceramic composites were hot-presse sintered and annealed by adding 16, 20, 24wt% $Al_{2}O_{3}+Y_{2}O_{3}$(6 : 4wt%) powder as a liquid forming additives at low temperature($1800^{\circ}C$) for 4h. In this microstructures, the relative density is over 95.88% of the theoretical density and the porosity increased with increasing $Al_{2}O_{3}+Y_{2}O_{3}$ contents because of the increasing tendency of pore formation. The fracture toughness showed the highest of $5.88MPa{\cdot}m^{1/2}$ for composites added with 20wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature. The electrical resistivity showed the lowest of $5.22{\times}10^{-4}\Omega{\cdot}cm$ for composite added with 20wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature and is all positive temperature coefficient resistance (PTCR) against temperature up to $700^{\circ}C$.

• 마이크로전자및패키징학회지
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• 제28권4호
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• pp.73-77
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• 2021

신체 착용 및 부착이 가능한 웨어러블 기기용 유연 전극은 외력에 대한 기계적/전기적 내구성을 확보하고 동시에, 다양한 기능성을 부여하는 방향으로 연구가 활발히 진행되고 있다. 본 연구는 Carbon black를 전도성 필러로 적용하여 Carbon/PDMS 기반 유연 복합체를 제조하고 carbon black의 함량에 따른 복합체의 유연전극, 온도 센서 및 히터용 소재로서의 적용 가능성에 대해 고찰해 보았다. Carbon black의 함량 증가에 따른 비저항 감소를 관찰하였고, 반복인장에 따른 전기저항 변화율 실험을 통해 유연전극으로서의 적용 가능성을 확인하였다. 온도 변화에 따른 carbon/PDMS 복합체의 전기적 특성 평가를 통해 온도센서로서 적용이 가능한 정온도계수 특성을 관찰하였고, carbon black 함량에 따라 정온도계수 특성 조절이 가능함을 확인할 수 있었다. 전압 인가에 따른 Carbon/PDMS 복합체의 발열 특성 관찰을 통해 히터용 소재로서의 적용가능성 역시 확인할 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.1474-1476
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-Sic-$ZrB_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_{2}O_{3}+Y_{2}O_{3}$. Phase analysis of composites by XRD revealed $\alpha$-SiC(6H), $ZrB_2$, and YAG($Al_{5}Y_{3}O_{12}$). The relative density of composites were increased with increasing $Al_{2}O_{3}+Y_{2}O_{3}$ contents. The flexural strength showed the highest value of 390.6MPa for composites added with 20wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature. Owing to crack deflection, crack bridging. phase transition and YAG of fracture toughness mechanism. the fracture toughness showed the highest value of 6.3MPa${\cdot}m^{1/2}$ for composites added with 24wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance (PTCR) in the temperature range of 25$^{\circ}C$ to 900$^{\circ}C$.

• 한국재료학회지
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• 제20권12호
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• pp.654-660
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• 2010

The influences of Na and K content on the crystal phase, the microstructure and the electrical property of $BaTiO_3$-based thermistors was found to show typical PTC effects. The crystal phase of powder calcined at $1000^{\circ}C$ for 4hrs showed a single phase with $BaTiO_3$, and the crystal structure was transformed from tetragonal to cubic phase according to added amounts of Na and K. In XRD results at $43^{\circ}\sim47^{\circ}$, the $(Ba_{0.858}Na_{0.071}K_{0.071})(Ti_{0.9985}Nb_{0.0015})O_{3-\delta}$ showed (002) and (200) peaks but the $(Ba_{0.762}Na_{0.119}K_{0.119})(Ti_{0.9975}Nb_{0.0025})O_{3-\delta}$ showed (002), (020) and (200) peaks. In sintered bodies, those calcined at $600^{\circ}C$ rather than at $1000^{\circ}C$ were dense, and for certain amounts of Na and K showed rapid decreases in grain size. In relative permittivity, the curie temperature due to the transformation of ferroelectric phase rose with added Na and K but decreased in terms of relative permittivity. In the result of the R-T curve, the sintered bodies have curie temperatures of about $140^{\circ}C$ and the resistivity of sintered bodies have scores of $\Omega{\cdot}cm$; the jump order of sintered bodies was shown to be more than $10^4$ in powder calcined at $1000^{\circ}C$.

• 한국결정성장학회지
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• 제9권5호
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• pp.498-503
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• 1999

La가 혼입된 $BaTiO_3$를 균일침전법으로 제조하여 La의 혼입량 및 입자의 크기 변화에 따른 전기적 특성을 관찰하였다. 온도변화에 따른 저항을 측정한 결과 란탄의 농도가 0.6 mol%일 때 그리고 입자의 크기가 1.0 $\mu\textrm{m}$으로 작을 때 가장 큰 PTCR 효과를 나타내었다. 상전이온도($(T_c)$) 이상에서 온도와 1/$\varepsilon_m$(T)의 관계를 나타낸 도시에 의하면 유전상수의 변화가 Curie-weiss 법칙에 잘 다름을 알 수 있었다. 측정한 비저항과 유전상수로부터 계산한 전위장벽의 높이도 란탄의 농도가 0.6 mol%일 때 입자의 크기가 1.0$\mu\textrm{m}$으로 작을 때 가장 큰 전위장벽을 나타내었다.