• Journal of the Korean Ceramic Society
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• v.33 no.3
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• pp.285-292
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• 1996

The effect of AlN on the thermal conductivity of aluminum oxide pressurelessly sintered at nitrogen atmos-phere was investigated. Increasing aluminium nitride content up to 1~10 mol% the thermal conductivity of $Al_{2}O_{3}$-AlN system was singnificantly decreased and was constant with adding 20 and 25 mol% aluminium nitride. The thermal conuctivity of $Al_{2}O_{3}$ containing 1~10 mol% the thermal conductivity of $Al_{2}O_{3}$-AlN system was singificantly decreased and was constant with adding 20 and 25mol% aluminum nitride. The thermal conctivity of $Al_{2}O_{3}$ containing 1~10 mol% AlN showed a maximum at $1700^{\circ}C$ and decrea-sed with increasing sintering tempertures. This phenomenon was attributed to $\alpha$-$Al_{2}O_{3}$ and ALON formed by reacting $Al_{2}O_{3}$ with AlN up to $1700^{\circ}C$ and the secondary phases such as ${\gamma}$-ALON ($9Al_{2}O_{3}$.AlN)and $\Phi$($5Al_{2}O_{3}$.AlN) phase above $1750^{\circ}C$ The thermal conductivity of $Al_{2}O_{3}$ containing 20 and 25 mol% AlN showed maximum value at $1800^{\circ}C$ Both $\alpha$-$Al_{2}O_{3}$ and ALON existed up to $1600^{\circ}C$ value at $1800^{\circ}C$ Both $\alpha$-$Al_{2}O_{3}$ and ALON existed up to $1600^{\circ}C$ while only AlON phase existed above $1650^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1035-1040
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• 2011

This research was performed on a microfilter made of a hybrid material (ceramic + metal) that was coated with ceramics on the metal-filter surface by using the thermal spray method. The ceramic powders used were $Al_2O_3+40TiO_2$ powder with a particle size of $20{\mu}m$ and $Al_2O_3$ (98%+)powder with a particle size of $45{\mu}m$. The metal filters were filter-grade $20{\mu}m$, $30{\mu}m$, and $50{\mu}m$ sintered metal powder filters (SIKA-R 20 IS, 30 IS, 50 IS; Sinter Metals Filters) and filter-grade $75{\mu}m$ sintered mesh filter with five layers. Ceramic-coated filters that were coated using the thermal spray method had a great influence on powder material, particle size, and coating thickness. However, these filters showed a fine performance when used as micro-filters.

• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.954-960
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• 2003

To develop mobile phone antenna modules, glass-ceramics composites that are 20∼80 dielectric constant materials which has been fabricated. The glass-ceramics composites were based in the BNT (BaO-Nd$_2$O$_3$-TiO$_2$), and properties-a sintering and dielectric property-were investigated in its composites according to the $K_2$O-CaO-P$_2$O$_{5}$ system glass frits. The prepared ceramics were sintered at 900∼120$0^{\circ}C$ with the glass frit contents ranging from 10 to 40 wt%. The shrinkage and relative density grew into increasing glass frits and sintering temperature. Sintered composites showed the tendency that the dielectric constant ($\varepsilon$$_{r}$) and quality factor (Q${\times}$f) decreased in increasing glass frits and sintering temperature.

• Journal of the Korean Ceramic Society
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• v.36 no.3
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• pp.325-331
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• 1999

SrWO4가 첨가된 (Sr1-xBax)(Mg1/3Nb2/3)O3의 마이크로파 유전특성에 관하여 조사하였다. 관찰된 조성영역에서 Sr(Mg1/3Nb2/3)O3과 Ba(Mg1/3Nb2/3)O3은 (Sr1-xBax)(Mg1/3Nb2/3)O3고용체를 형성하고 SrWO4의 첨가는 고용체의 소결성을 향상시켜 소결온도 155$0^{\circ}C$에서 상대밀도 97% 이상을 얻었다. 소결한 시편의 EDS분석결과, SrWO4의 첨가량이 많은 시편에서 2차상이 존재하는 것을 알수 있었다. 순수한 Sr(Mg1/3Nb2/3)O3에 SrWO4를 0.01 mole첨가하여 1550~1$600^{\circ}C$에서 소결한 시편의 유전특성은 $\varepsilon$r 30, Q$\times$fo$\geq$55000,$ au$f -23 ppm/$^{\circ}C$이었다. 0.01 mole SrWO4가 첨가된 (Sr1-xBax)(Mg1/3Nb2/3)O3 고용체의 유전율과 온도계숙가 x에 따라 점차적으로 계속 증가하였고 Q$\times$fo는 x$\leq$0.25에서 x에 따라 감소하고 x$\geq$0.3에서 다시 증가하였다. (Sr0.65Ba0.35)(Mg1/3Nb2/3)O3+0.01SrWO4의 조성을 갖는 시편에서 $\varepsilon$r 34.4, Q$\times$fo$\geq$55000,$\tau$f 0 ppm/$^{\circ}C$이었다.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.45-50
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• 2002

Effect of sintering additives on the densification behavior of reaction-bonded silicon nitride prepared by using coarse Si powders is discussed. Sintering additives such as 6 wt% $Y_2O_3$+1wt% $A1_2O_3$ (6YlA) did not give rise to full densification, while full densification was obtained by using the sintering additives such as 6wt% $Y_2O_3$+3 wt% $A1_2O_3$+ 2wt% $SiO_2$ (6Y3A2S) and 9wt% $Y_2O_3$+ 1.5wt% $A1_2O_3$+ 3wt% $SiO_2$ (9Yl.5A3S). In the case of 6Y3A2S addition, high fracture strength of 960 MPa and the fracture toughness of $6.5 MPa.m^{1/2}$ were obtained.

• Journal of the Korean Ceramic Society
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• v.39 no.11
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• pp.1083-1089
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• 2002

Densification and grain growth behavior of MgO and -doped alumina ceramics were investigated. MgO was found to inhibit grain growth and to promote densification, but acted to promote grain growth more than densification. The density which showed the maximum shrinkage rate was investigated in the plot of shrinkage rate versus density. The data suggests that the maximum shrinkage rate separates the two kinetic regimes, below the density of maximum shrinkage, the regime associated with densification and above the maxima, the regime associated with the grain growth. The plot exhibits a maximum which shifts to higher temperatures with MgO doping and to lower with doping.

• Journal of the Korean Ceramic Society
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• v.34 no.3
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• pp.281-288
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• 1997

The effects of 0 to 6 mol% excess 91PbO-9WO3 addition on the microstructure and the dielectric pro-perties in 40Pb(Mg1/3Nb2/3)O3-30PbTiO3-30Pb(Mg1/2W1/2)O3 ternary system were investigated. Excess 91PbO-9WO3 addition enhanced densification at relatively lower temperature due to the formation of liquid phase. The dielectric constant of the specimen with standard composition was 16,400 and that of specimen with 1 mol% excess additive was the maximum of 18,500. And more than 2 mol% excess addition decreased dielec-tric constant. Specimens with 2~4 mol% 91PbO-9WO3 addition showed dual peak maxima in the tem-perature dependence of dielectric constant. In the specimens which have more than 5 mol% excess addition a new phase with W-rich composition was formed at grain boundary.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.205-205
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• 2008

PZT 세라믹은 우수한 유전 및 압전특성을 갖고 있어 변압기, 센서 및 엑츄에이터 등에 널리 응용되고 있다. 그러나, 우수한 특성에도 불구하고 PZT세라믹스의 소결시 PbO의 높은 유독성 및 휘발로 인하여 환경오염을 야기 시킨다. 그러므로 PbO로 구성된 세라믹을 대체하기 위한 우수한 압전특성을 가진 비납계 세라믹스 개발이 연구의 주류를 이루고 있다. 그 중 비납계 NKN와 BZT는 대체물질로 많이 관심을 받고 있다. 이는 일반적인 NKN조성은 우수한 압전성과 높은 큐리온도를 가지고 있을 뿐만 아니라, BZT조성의 Zr성분이 큐리온도를 낮추거나 유전특성을 졸게 하여 유전율 곡선을 완화하게 하는 특징이 있다. 하지만 NKN은 $1140^{\circ}C$이상의 소결온도에서 K의 휘발특성으로 인해 소성 후에도 주변의 수분을 흡수하는 조해성이 발생하는 문제가 발생한다. 그래서 본 연구에서는 낮은 온도에서 NKN계 세라믹스의 밀도를 증가시킬 뿐만 아니라, 우수한 유전 및 압전특성을 갖는 세라믹스를 제조하고자 비납계 $0.94(K_{0.5}Na_{0.5})NbO_3-0.06Ba(Zr_{0.05}Ti_{0.95})O_3$ (NKN-BZT)의 조성을 사용하였고 소결조제로는 $MnO_2$, NiO, $Bi_2O_3$, ZnO, $Li_2CO_3$, CuO등을 변화주어 유전 및 압전 특성을 알아보았다.

• Journal of the Korean Ceramic Society
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• v.35 no.5
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• pp.499-504
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• 1998

ZnO varistors having a composition of 98.0 mol% ZnO 1.0 mol% $Bi_2O_3$ 0.5 mol% $MnO_2$ were prepared by the Pechini process and the sintering behavior and electrical characteristics were studied. ZnO varis-색 powder with $1.5\mu\textrm{m}$ mean diameter and narow particle size distribution was obtained using the Pechni pro-cess. Typical intermediate stage grain growth of liquid phase sintering was observed by sintering at $1100^{\circ}C$ At this temperature ZnO varistors having uniform grain size and Bi-rich liquid phase distributed uniformly along grain boundaries were prepared. The nonlinear coefficients of the ZnO varistors were in the range of 40-60 The breakdown voltages of the varistors were nearly inversely propeortional to the grain size which reflects that ZnO varistors prepared by the Pechini process have uniform distribution of Bi-rich liquid phase along grain boundaries It is believed that the microstructures of ZnO varistors can be controlled effectively by using the Pechini process which makes the control of the electrical properties of ZnO varistors possible.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.7-14
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• 1999

TiZrB2 solid solution was synthesized using fine powders of Ti, Zr and B by SHS microwave process. The characterization of the synthesized powder and sintered bodies ws investigated. The combustion temperature and rate were increased with increasing the mole ratio of Zr in temperature profile, and showed the maximum combustion temperature and velocity values of 285$0^{\circ}C$ and 14.6mm/sec in Ti0.2Zr0.8B2 composition. Phase separation has been occured into a composite with TiB2 and ZrB2 phases from TiZrB2 solid solution, which was hot pressed sintering at 30 MPa for an hour at 190$0^{\circ}C$. At the composition of Ti0.8Zr0.2B2 the best properties has been obtained in relative density, bending strength, fracture toughness and hardness, with 99%, 680 MPa, 7.3MPa.m1/2 and 2750 Kg/$\textrm{mm}^2$ respectively.