• Journal of the Korean Ceramic Society
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• v.42 no.1
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• pp.33-36
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• 2005

Effect of heating rate was studied on consolidation of the low-temperature-sinterable PMN-PT-BT powder by varying the heating rate from 5, 10, to $20^{circ}C/min$. Slow rate of $5^{circ}C/min$ showed more homogeneous microstructure than high rate of 10 or $20^{circ}C/min$ due to low PbO (m.p. $886^{circ}C$) evaporation at 850^{circ}C$. It showed sintered density of $7.93 g/cm^{3}$, room temperature dielectric constant of 15300, and dissipation factor of $0.92\%$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.97-103
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• 2005

In this paper, effects on the heat transport limitation of heat pipe by the wick structural factors were theoretically analyzed for the sintered-copper wick heat pipe. Uniformity of particle size and sintering process were acted as dominant factors on the pore distribution and wick porosity, and small deviations of the wick thickness and the pore size greatly affected the heat transport limitations of the heat pipe. Especially, slight variations of the wick thickness, mean particle radius and capillary radius along the vapor temperatures and inclination angles remarkably changed the capillary limitation of the heat pipe.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.6
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• pp.246-251
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• 2001

The $[(Pb_{1-x}$La_{2x/3})TiO_3$, X=0.2] powder was synthesized by the hydrothermal method, and their sintering and dielectric properties according to Mn additive were examined. The relative density of sintered PLT specimen at $1150^{\circ}C$ for 5 hrs with Mn 0.02 mol% additive was 96.7%. The dielectric properties of sintered PLT specimen were changed by content of Mn and increacement of sintering temperature. Dissipation factor was improved by increasing of measuring temperature. Curie temperature of sintered PLT specimens was decreased with increasing of Mn additive.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.1
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• pp.43-48
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• 2006

In this Part 2, the grain growth processes of $Al_2O_3$ ceramics is numerically simulated using Monte Carlo method (MCM) and finite element method (FEM) and the pore sizes are analyzed. As the green ceramics whose thermal conductivities in high temperatures are generally low are sintered by the plasma heat and are rapidly cooled, the grain growth of the sintered body in the center is different from that in the outer. Also, even in the same sintering temperature, the pore size differs according to the pressing pressure. In order to prove the difference, the temperature distribution of the sintered body was analyzed using the finite element method and then the grain growth process associated with pressing pressures and relative densities was simulated using Monte Carlo method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.280-281
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• 2006

Cordierite 결정상을 LTCC공정 적용온도에서 소결하기 위한 glass 조성을 조사하였다. 상용의 glass중 Pb-B-Si-O계, Na-Zn-B-O계 glass를 선택하였고 LTCC용 기판소재로서의 가능성을 확인하기 위하여 저온 동시소성이 가능한 소결온도인 $850^{\circ}C$와 $1000^{\circ}C$ 사이에서 소재의 소결실험을 진행하였다. 소결조건에 따른 상변화, 유전특성을 확인한 결과 glass상, 결정상, 용융에 의한 glass상으로 상의 변화가 있음을 확인 할 수 있었으며, LTCC 소결 조건에서 Pb-B-Si-O계 glass의 경우 2.9~3.7의 낮은 유전율과 0.0027의 우수한 dielectric loss, 내전압 특성을 가지고 있음을 확인하였다.

• Korean Journal of Materials Research
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• v.7 no.3
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• pp.251-264
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• 1997

공진 주파수 온도 계수($\tau$$_{f}$)가 큰 음의 값을 가지는 (Li$_{1}$2Nd$_{1}$2)TiO$_{3}$(LNT) 고주파 유전체를 125$0^{\circ}C$에서 140$0^{\circ}C$까지의 온도에서 2시간동안 소결을 하였고 소결후에는 소결온도보다 약간 낮은 120$0^{\circ}C$에서 5시간 동안 annealing을 실시를 하였다. 그리고 열처리에 의한 상, 미세구조의 변화를 X-ray, SEM을 통해서 분석하였으며, 열처리가 고주파 유전물성에 대해 미치는 영향에 대해서도 고찰하였다. 130$0^{\circ}C$에서 135$0^{\circ}C$ 근방에서 소결시킨 재료는 Annealing효과에 의해 소결체에 균일한 입도 분포가 증진되었고 체적 밀도가 향상되었으며, 열처리 효과에 의해 품질계수(Q)값이 향상되었고 유전상수($\varepsilon$$_{r}$)는 약간 감소하였으며 공진주파수 온도계수($\tau$$_{f}$)는 더 큰 음의 값을 가지게 되었다. 그러나 135$0^{\circ}C$이상에서 소결한 경우에는 비정상적인 입자 성장에 의해 밀도가 감소되며, 이에 따라 고주파 유전특성이 전반적으로 저하되었다.었다.

• Composites Research
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• v.22 no.4
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• pp.50-53
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• 2009

This paper mainly describes the armor materials, especially the ceramic materials for the personal protection. In the ceramic armor materials, B4C ceramics and SiC ceramics are the most popular materials. The $B_4C$ ceramics which consists of 4 atoms of boron and I atom of carbon is very light and strong. It is usually used to personal protection armor and chair protection in the helicopter. This material must be sintered at very high temperature because it melts at $2400^{\circ}C$. In order to have a good armor property, it must have very high density which is achieved by hot press or subsidiary sintering aid methods such as reducing the particle size of raw materials or mixing the sintering agents to the raw materials.

• Journal of the Korean Ceramic Society
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• v.39 no.11
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• pp.1108-1112
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• 2002

pellets were fabricated as a reactor control material by the powder process. Sinterability of $Dy_2O_3+TiO_2$ mixtures and phases of solid solutions were analyzed by using TMA and XRD, respectively. The thermal conductivity of pellet was determined from the measurement data of the specific heat and the thermal diffusivity of the pellet. The sinterability and the sintered density varied as a function of Dy content in $Dy_xTi_yO_z$. The pellet of $3\;g\;Dy/cm^3\;Dy_xTi_yO_z$ melted in the sintering temperature of $1580{\circ}C$. There were two phases of $Dy_2TiO_5+Dy_2Ti_2O_7$ and a single phase of $Dy_2TiO_5$ for the pellet that has the Dy content of and , respectively. The thermal conductivity of $Dy_xTi_yO_z$ was nearly constant in the temperature range of $25~600{\circ}$. It was 1.69~1.78 W/mK for the pellet sintered in and 1.49~1.55 W/mK for the pellet sintered in $1550{\circ}$.

• Journal of the Korean Ceramic Society
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• v.39 no.11
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• pp.1074-1082
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• 2002

Nanocomposite PMN-PT-BT/Ag/MgO was prepared by sintering at $950{\circ}C$ with addition of $AgNO_3$ and MgO sol to the PMN-PT-BT powder sinterable at $1200{\circ}C$. The low-temperature-sinterable PMN-PT-BT/Ag powder prepared by the modified mixed oxide method was calcined at $600{\circ}C$ for 1h and surface modified with the MgO sol of 0-10 wt% and then subjected to consolidation at $850-950{\circ}C$ for 4h under a flowing oxygen. The nanocomposite PMN-PT-BT/Ag/MgO(0.5wt%) sintered at $950{\circ}C$ showed the microstructure with grains of $1-3{\mu}m$, the second phase of MgO of $0.1-0.3{\mu}m$ by SEM and Ag of << $1{\mu}m$ qualitatively by SIMS. It showed the sintered relative density of 99%, the room temperature dielectric constant of 17200, the dielectric loss of 2.1% and the specific resistivity of $5.46{\times}10^{12}{\Omega}{\cdot}cm$. But the PMN-PT-BT/Ag/MgO(0 wt%) nanocomposite sintered at $950{\circ}C$ showed a little better properties : the sintered relative density of 99.5%, the room temperature dielectric constant of 19500, the dielectric loss of 2.1% and the specific resistivity of $7.30{\times}10^{12}{\Omega}{\cdot}cm$.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.97-105
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• 1999

In the binary system of SiC and carbon, porosity and pore size distribution of green body was controlled by varying pH, by the addition of polyelectrolyte dispersants, and by using different particle size of starting powders. The preforms having different green microstructure were fabricated by slip casting from suspensions having different dispersion condition. The reaction bonding process was carried out for these preforms. The condition of reaction bonding was 1600$^{\circ}C$ and 20 min. under vacuum atmosphere. The analyses of optical and SEM were studied to investigate the effect of green microstructure on that of reaction bonded silicon carbide and subsequently the mechanical properties of sintered body was investigated. Different green microstructures were obtained from suspensions having different dispersion condition. It was found that the pore size could be remarkably reduced for a fine SiC(0.5$\mu\textrm{m}$). The bimodal microstructure was not found in the present study, which is frequently observed in the typical reaction bonded silicon carbide. It is considered that the ratio between SiC and C was responsible for the formation of bimodal microstructure. For the preform fabricated from the well dispersed suspension, the 3-point bending strength of reaction-bonded silicon carbide was 310${\pm}$40 MPa compared to the specimen fabricated from relatively agglomerated particles having lower value 260${\pm}$MPa.