• 한국세라믹학회지
• /
• 제44권5호
• /
• pp.173-178
• /
• 2007

The microstructure and microwave dielectric properties of dolomite type borates, $CaZr(BO_3)_2$ ceramics prepared by conventional mixed oxide method were explored. The sintering temperature of $CaZr(BO_3)_2$ ceramics could be reduced from $1150^{\circ}C\;to\;925^{\circ}C$ with little amount of sintering additives. Microwave dielectric properties of 3 wt% $Bi_2O_3-CuO$ added $CaZr(BO_3)_2$ ceramics sintered at $925^{\circ}C$ were $K{\approx}10.4,\;Q{\times}f{\approx}80,000GHz\;and\;TCF{\approx}+2ppm/^{\circ}C$. Thus obtained LTCC tape was co-fired with Ag paste for compatibility test and revealed no sign of Ag reaction with the ceramics. Therefore, $CaZr(BO_3)_2$ ceramics is considered as a possible candidate material for low temperature co-fired multilayer devices.

• 한국세라믹학회지
• /
• 제52권5호
• /
• pp.374-379
• /
• 2015

Mullite-matrix and $Al_2O_3$-matrix composites were fabricated with 30 wt% hydroxyapatite (HA) and tricalcium phosphate (TCP), respectively, as additives to give bioactivity. A diphasic gel process was employed to lower the densification temperature of the mullite matrix to $1320^{\circ}C$. A polymer complexation process was used to synthesize a TCP powder that was fully densified at $1250^{\circ}C$, for application to the matrix. For the HA/mullite composite, HA decomposed during sintering by reactions with the matrix components of $Al_2O_3$ and $SiO_2$, resulting in a mixture of $Al_2O_3$, TCP, and other minor phases with a low densification of less than 88% of the theoretical density (TD). In contrast, the TCP/$Al_2O_3$ composite was highly densified by sintering at $1350^{\circ}C$ to 96%TD with no reaction between the components. Different from the TCP monolith, the TCP/$Al_2O_3$ composite also showed a fine microstructure and intergranular fracture, both of which characteristics are advantageous for strength and fracture toughness.

• 한국전기전자재료학회논문지
• /
• 제15권5호
• /
• pp.406-411
• /
• 2002

Ni-Zn ferrite is required to have predominant and stable characteristics in the range of high frequency for the power line communication, so that microstructures and magnetic properties such as power loss and initial permeability in $Ni_{0.8}Zn_{0.2}Fe_2O_4$ were investigated in terms of variable $Bi_2O_3,CaO$ and $V_2O_5$ contents. $Bi_2O_3$ and $V_2O_5$ liquid phase created during sintering process promoted sintering and grain growth but much of the closed pore existed in the grains. The grain size of the specimens with $V_2O_5$ of over 0.5 wt% decreased as the result of "pinning effect"and the resonance frequency increased with CaO of 0.3we%. The high initial permeability of 81.52%, resonance frequency of 17.05 MHz and low power loss of 17,858 kW/$\textrm{m}^3$ were obtained from the samples with $Bi_2O_3$ of 0.5, CaO of 0.3, and $V_2O_5$ of 0.7 wt%.

• Journal of Electrical Engineering and Technology
• /
• 제9권5호
• /
• pp.1719-1723
• /
• 2014

In this study, the microwave dielectric properties of nano spheroidization glass powders added $Ba(Zn_{1/3}Ta_{2/3})O_3$ ceramics prepared by solid state reaction have been investigated. Adding $(Ba_{0.4}Ca_{0.6})SiO_3$ nano spheroidization glass powders could effectively promote the densification even in the case of decreasing the sintering temperature. When the glass frit is 0.3 wt% and sintering is carried out at a temperature of $1500^{\circ}C$ for 6 hr, a temperature stable microwave dielectric ceramic could be obtained, which has a dielectric constant (${\varepsilon}_r$) of 30.2, a quality factor ($Q{\times}f_0$) of 124,000 GHz and a temperature coefficient of resonance frequency (${\tau}_f$) of $2ppm/^{\circ}C$.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2007년도 제38회 하계학술대회
• /
• pp.1289-1290
• /
• 2007

The composites were fabricated 61Vo.% ${\beta}$-SiC and 39Vol.% $TiB_2$ powders with the liquid forming additives of 12wt% $Al_{2}O_{3}+Y_{2}O_{3}$ as a sintering aid by pressure or pressureless annealing at $1650^{\circ}C$ for 4 hours. The present study investigated the influence of annealed sintering on the microstructure and mechanical of SiC-$TiB_2$ electroconductmive ceramic composites. Reactions between SiC and transition metal $TiB_2$ were not observed in the microstructure and the phase analysis of the SiC-$TiB_2$ electroconductive ceramic composites. Phase analysis of SiC-$TiB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $TiB_2$, and In Situ YAG($Al_{5}Y_{3}O_{12}$). The relative density, the flexural strength, the Young's modulus showed the highest value of 86.69[%], 136.43[MPa], 52.82[GPa] for pressure annealed SiC-$TiB_2$ ceramic composites.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
• /
• pp.279-282
• /
• 2003

For the millimeter-wave dielectrics, Forsterite-based ceramics were produced. Pure forsterite ceramics($Mg_2SiO_4$) shows porous micro-structure and very low Q*f values, which is not suitable for the dielectrics for the millimeter-wave band. Several sintering aids including $Al_2O_3$, $Li_2CO_3$, $Li_2SiO_4$, were added to the forsterite ceramics in order to produce dense low-loss dielectrics. Among these additives, $Li_2CO_3$ is the most effective sintering aids. Several sub-components including NiO, ZnO, $SnO_2$, $TiO_2$, were added to enhance the microwave dielectric properties. $TiO_2$ is the most effective additive to enhance the dielectric properties at microwave bands. The simultaneous addition of $TiO_2$ and $Li_2CO_3$ increases Q*f value over 170,000, which can be used as dielectrics in millimeter-wave bands.

• 한국세라믹학회지
• /
• 제38권12호
• /
• pp.1155-1161
• /
• 2001

YIG 페라이트는 마이크로파 RF 대역 통신 시스템, 이동통신, 위성방송 등의 정보산업과 각종 계측기기 등에 없어서는 안될 중요한 전자부품인 서큘레이터/아이솔레이터의 핵심소자로서 널리 사용되고 있다. 본 연구에서는 소결온도와 치환원소에 따른 서큘레이터/아이솔레이터용 YIG 페라이트의 미세구조와 전자기적 특성을 고찰하고자 하였다. Ca, V, In을 치환시킨 YIG 페라이트를 분무건조기를 사용하여 준구형 과립상태로 만들고, 일반적인 세라믹 제조 공정에 따라 125$0^{\circ}C$, 1275$^{\circ}C$, 130$0^{\circ}C$, 13$25^{\circ}C$에서 각각 소결하였다. 소결체는 XRD를 이용하여 상분석을 실시하였고, SEM을 이용하여 미세구조를 관찰하였으며, 전자기적 특성을 측정하기 위하여 VSM을 이용한 포화자화값 (4$\pi$ $M_{s}$) 측정과 FMR(Ferromagnetic Resonance)실험을 통한 자기공명반치폭($\Delta$H) 측정을 실시하였다. $Y_{1.6}$C $a_{1.4}$F $e_4$ $V_{0.7}$I $n_{0.3}$ $O_{12}$ 조성의 YIG 페라이트에 대한 전자기적 특성 측정 결과 130$0^{\circ}C$에서 소결한 YIG 페라이트가 높은 포화자화(4$\pi$ $M_{s}$) 값과 낮은 자기공명반치폭($\Delta$H)을 지닌 우수한 전자기적 특성을 나타내었다.다.을 나타내었다.다.

• 한국세라믹학회지
• /
• 제41권12호
• /
• pp.893-899
• /
• 2004

Nitrided Pressureless Sintering(NPS) 공정에 의한 질화규소 세라믹스의 기계적 특성, 미세구조 및 열적 특성을 세 가지조성을 갖는 $Al_{2}O_3,\;Y_{2}O_3$ 소결조제의 변화에 따라 조사하였다. 또한 각 조성에서 금속 실리콘의 첨가량을 0, 5, 10, 15, 그리고 $20wt\%$로 변화를 주어 실리콘의 첨가효과를 조사하였다. $5wt\%\;Al_{2}O_3,\;5wt\%\;Y_{2}O_3$, 그리고 $5wt\%$ Si 조성에서 질화규소 소결체의 치밀화가 진행되었으며, 4점 꺽임강도와 상대밀도는 각각 500 MPa과 $98\%$를 나타내었다. 또한 상온에서 열팽창계수와 열전도도는 각각 $2.89{\times}10^{-6}/^{\circ}C$와 $28W/m^{\circ}C$를 나타내었으며, 20,000회의 열충격 싸이클을 반복한 후, 꺽임강도를 측정한 결과, 초기 500MPa의 강도를 유지하고 있었다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제55권9호
• /
• pp.434-441
• /
• 2006

The effect of pressureless-sintered temperature on the densification behavior, mechanical and electrical properties of the $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at temperatures in the range of $1,750{\sim}1,900[^{\circ}C]$, with an addition of 12[wt%] of $Al_2O_3+Y_2O_3$(6:4 mixture of $Al_2O_3\;and\;Y_2O_3$) as a sintering aid. The relative density and mechanical properties are increased markedly at temperatures in the range of $1,850{\sim}1,900[{^\circ}C]$. The relative density, flexural strength, vicker's hardness and fracture toughness showed the highest value of 81.1[%], 230[MPa], 9.88[GPa] and $6.05[MPa\;m^{1/2}]$ for $SiC-ZrB_2$ composites of $1,900[{^\circ}C]$ sintering temperature at room temperature respectively. The electrical resistivity was measured by the Pauw method in the temperature ranges from $25[{^\circ}C]\;to\;700[{^\circ}C]$, The electrical resistivity showed the value of $1.36{\times}10^{-4},\;3.83{\times}10^{-4},\;3.51{\times}10^{-4}\;and\; 3.2{\times}10^{-4}[{\Omega}{\cdot}cm]$ for SZ1750, SZ1800, SZ1850 and SZ1900 respectively at room temperature. The electrical resistivity of the composites was all PTCR(Positive Temperature Coefficient Resistivity). The resistance temperature coefficient showed the value of $4.194{\times}10^{-3},\;3,740{\times}10^{-3},\;2,993{\times}10^{-3},\;3,472{\times}10^{-3}/[^{\circ}C}$ for SZ1750, SZ1800, SZ1850 and SZ1900 respectively in the temperature ranges from $25[{\circ}C]\;to\;700[{\circ}C]$, It is assumed that because polycrystallines such as recrystallized $SiC-ZrB_2$ electroconductive ceramic composites, contain of porosity and In Situ $YAG(Al_5Y_3O_{12})$ crystal grain boundaries, their electrical conduction mechanism are complicated. In addition, because the condition of such grain boundaries due to $Al_2O_3+Y_2O_3$ additives widely varies with sintering temperature, electrical resistivity of the $SiC-ZrB_2$ electroconductive ceramic composites with sintering temperature also varies with sintering condition. It is convinced that ${\beta}-SiC$ based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제55권10호
• /
• pp.467-474
• /
• 2006

The effect of pressureless-sintered temperature on the densification behavior, mechanical and electrical properties of the $SiC-TiB_2$ electroconductive ceramic composites was investigated. The $SiC-TiB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at temperatures in the range of $1,750{\sim}1,900[^{\circ}C]$, with an addition of 12[wt%] $Al_2O_3+Y_2O_3(6:4\;mixture\;of\;Al_2O_3\;and\;Y_2O_3)$ as a sintering aid. The relative density, flexural strength, vicker's hardness and fracture toughness showed the highest value of 84.92[%], 140[MPa], 4.07[GPa] and $3.13[MPa{\cdot}m^{1/2}]$ for $SiC-TiB_2$ composites of $1,900[^{\circ}C]$ sintering temperature at room temperature respectively. The electrical resistivity was measured by the Pauw method in the temperature ranges from $25[^{\circ}C]\;to\;700[^{\circ}C]$. The electrical resistivity showed the value of $5.51{\times}10^{-4},\;2.11{\times}10^{-3},\;7.91{\times}10^{-4}\;and\;6.91{\times}10^{-4}[\Omega{\cdot}cm]$ for ST1750, ST1800, ST1850 and ST1900 respectively at room temperature. The electrical resistivity of the composites was all PTCR(Positive Temperature Coefficient Resistivity). The resistance temperature coefficient showed the value of $3.116{\times}10^{-3},\;2.717{\times}10^{-3},\;2.939{\times}10^{-3},\;3.342{\times}10^{-3}/[^{\circ}C]$ for ST1750, ST1800, ST1850 and ST1900 respectively in the temperature ranges from $25[^{\circ}C]\;to\;700[^{\circ}C]$. It is assumed that because polycrystallines, such as recrystallized $SiC-TiB_2$ electroconductive ceramic composites, contain of porosity and In Situ $YAG(Al_5Y_3O_{12})$ crystal grain boundaries, their electrical conduction mechanism are complicated. In addition, because the condition of such grain boundaries due to $Al_2O_3+Y_2O_3$ additives widely varies with sintering temperature, electrical resistivity of the $SiC-TiB_2$ electroconductive ceramic composites with sintering temperature also varies with sintering condition. It is convinced that ${\beta}-SiC$ based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.