• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.36-46
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• 2001

Finite element analyses of the ceramic drying process are performed. The heat and moisture movements in green ceramics caused by temperature gradient, moisture gradient, conduction, convection and evaporation are considered. The finite element formulation for solving the temperature and moisture distributions which not only change the volume but also induce the hygro-thermal stress is carried out. In order to verify the formulation, the drying process of a ceramic electric insulator is simulated. Temperature distribution, moisture distribution, and hygro-thermal stress are compared with those of other researcher. Good agreements are achieved.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1996.10a
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• pp.52-57
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• 1996

Conductive Ceramic Matrix Composite(CMC) of TIC/Al2O3 and Metal Matrix Composite (MMC) of SiC/Al were experienced by the die sinking Electrical Discharge Machining(EDM) for different current and duty factor according to negative polarity. Inthis experimental study Material Removal Rate(MRR) maximum surface roughness four point bending stress distribution and Scanning Electron Microscopy(SEM) Photographs were analysed. the higher MRR was obtained for CMC than MMC but slowly decreased around duty factor of 0.67 for MMC and better surface morphology was found CMC than MMC. The SEM photographs of discharge traces for CMC showe uniform shape about 100 to 200${\mu}{\textrm}{m}$ in diameter but MMC showed irregular shape.

• Journal of the Korean Ceramic Society
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• v.38 no.1
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• pp.34-38
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• 2001

Hot filament CVD 방법에서 가스압을 증가시키는 방법을 사용하여 nanocrystalline 다이아몬드 막을 합성하였다. 메탄-수소 혼합가스를 사용하고 메탄함량, 유량, 기판온도합성시간은 각각 4%, 100sccm, 110$0^{\circ}C$, 10시간으로 일정하게 유 였다. 합성 변수로서 가스압을 40 Torr에서 300 Torr 구간에서 변화시켰다. High-resolution SEM으로 막 표면의 형상을 관찰하고, TEM, XRD, micro-Raman spectroscopy를 사용하여 합성된 막의 구조 및 특성을 분석하였다. 합성된 다이아몬드 막은 압력이 높아짐에 따라 mocrocrystalline 다이아몬드 막에서 점진적으로 nanocrystalline 다이아몬드 막으로 변화해갔으며, 가스압에 다라 비다이아몬드 상의 량이 증가하였다. 증착속도는 microcrystalline 다이아몬드 막이 형성되는 구간에서는 압력에 따라 1.1~1.3 $\mu\textrm{m}$/h까지 증가하다가 nanocrystalline 다이아모느 막이 형성되는 구간에서는 압력에 따라 감소하였다. 감소하였다.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.846-852
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• 1995

The multiply reinforced mullite-zirconia composites were prepared with addition of Al2O3 particles, platelets, and fibers. The sinter-HIP specimens (presintered at 1$700^{\circ}C$ and hipped at 1$600^{\circ}C$) showed that the fracture toughness of Al2O3 fiber reinforcement (4.4 MPa.{{{{ SQRT {m} }}) was higher than those of platelet (4.0 MPa.{{{{ SQRT {m} }}) and of particle (3.9MPa.{{{{ SQRT {m} }}) reinforcement, whereas the fracture strength of Al2O3 particle reinforcement (304 MPa) was higher than those of platelet (293MPa) and of fiber (248MPa) reinforcement.

• Journal of the Korean Ceramic Society
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• v.35 no.3
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• pp.239-244
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• 1998

Iron complexes were prepared using ferric nitrate and ethylene glycol as starting materials and the ul-trafine ${\alpha}-Fe_2O_3$ particles with the sizes smaller than 200nm were obtained by the pyrolysis of iron com-plexes at over $350^{\circ}C$ In addition the decomposition mechanism of the synthesized iron complexes was in-vestigated by differential scanning calorimeter X-ray diffractometer and IR spectrometer. Transmission electron microscopy and BET method were performed to analyze the effects of ferric nitrate contents and reaction temperatures on the size and shape of the particles.

• Journal of the Korean Ceramic Society
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• v.26 no.4
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• pp.539-549
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• 1989

Polycrystalline TiO2 thin films were deposited on Si and Al2O3 substrates by CVD method. Ethyl titanate, Ti(OC2H5)4, was used as a source material for Ti and O, and Ar was used for carrier gas. In the surface chemical reaction controlled deposition condition, the apparent activation energy of 6.74 Kcal/mole was obtained, and the atomic adsorption on substrate surface was proved to be governed by Rideal-Elley mechanism. In the mass transfer controlled deposition condition, the deposition rate was in a good agreement with the result which was calculated by the simple boundary layer theory. It was also observed that TiO2 thin films show different surface morphology according to the different deposition mechanism, which was fixed by deposition conditions. This phenomenon could be well explained by the surface perturbation theory.

• Journal of the Korean Ceramic Society
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• v.37 no.12
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• pp.1135-1139
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• 2000

본 연구에서는 Pt/Sn $O_2$박막의 CO 감지특성을 향상시키기 위하여 표면 형상을 제어하였다. Pt/Sn $O_2$계 박막센서의 최적 동작온도는 175$^{\circ}C$이었다. Pt가 12초 동안 증착된 Sn $O_2$가 200ppm의 CO 가스에 대하여 1.23의 최대감도를 나타내었고, 그 이상의 Pt 증착시간 증가에 따라 Sn $O_2$위의 Pt의 coverage가 증가하여 센서의 감도를 감소시켰다. 다층박막(multi-layer thin film)의 단층의 Pt/Sn $O_2$복합체 위에 다시 Sn $O_2$및 Pt의 cluster 층들을 연속적으로 증착함으로서 제작되었다. 단지 하나의 Pt 층만을 증착한 Sn $O_2$막보다 다층의 Pt/Sn $O_2$막이 더욱 우수한 감도( $R_{air}$/ $R_{co}$=1.72, CO: 200 ppm)를 나타내었다. Pt/Sn $O_2$다층박막의 우수한 감도의 원인은 Pt와 Sn $O_2$사이의 계면적 증대 때문인 것으로 생각되어 진다.다.

• Journal of the Korean Ceramic Society
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• v.36 no.4
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• pp.372-379
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• 1999

Hihg-toughened ceria-stabilized tetragonal zirconia ceramics with irregular grain shape and undulated grain boundary was prepared by ceria doping. Irregularity of grain shapes was increased with the amount of doped ceria. But in case of the large amount of doped ceria grain boundary was migrated to the reverse direction of DIGM. Ceria-stabilized zirconia ceramics annealed at 1650$^{\circ}C$ for 2h after twice dippings into cerium nitrate solu-tion of 0.2M and sintering at 1500$^{\circ}C$ for 2h showed the highest grain boundary length with a value of 23.6$\mu\textrm{m}$ Ceria concentration difference between convex and concave sides in irregular grains was observed over 1 mol% but not observed in normal grains, Specimens with normal grain shape showed intergranular fracture mode whereas the specimens with irregular grain shape showed transgranular fracture mode.

• The Journal of the Acoustical Society of Korea
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• v.17 no.8
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• pp.48-57
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• 1998

본 논문에서는 순수 압전세라믹에 비해 동등이상의 압전특성을 가지면서도 음향임 피던스가 월등히 낮은 1-3형 압전복합체를 이용한 탐촉자의 개발에 관해 연구하였다. 압전 복합재료 탐촉자는 그 자체만으로 측정대상체와의 음향임피던스 차를 최소화하여 별도의 정 합층을 필요로 하지 않는 특징을 가진다. 이를 위하여 본 연구에서는 복합재료에 사용되는 고분자 재료의 물성값 설계와, 압전세라믹과의 적절한 배합구조와 형상의 결정에 설계의 주 안점을 두었다. 그 결과를 바탕으로 압전복합체 초음파 트랜스듀서 시작품을 제작하고 그 성능을 분석하였으며, 이론적인 시뮬레이션 결과와의 비교를 통해 설계이론의 타당성을 검 증하였다. 본 연구에서는 수립되어진 압전복합체 트랜스듀서의 설계 및 제작기법은 향후, 측 정대상체와의 정합을 위해 정합층에 대해 복잡한 설계 및 제작공정을 거쳐야하는 다양한 탐 촉자 개발에 유용하게 활용될 수 있을 것이다.

• Journal of the Korean Ceramic Society
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• v.37 no.8
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• pp.739-744
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• 2000

YAG(Y3Al5O12) as host material of YAG:Tb3+ was studied via hydrothermal synthesis of metal hydroxides. We changed the kind of mineralizer, the concentrations and process conditions in hydrothermal synthesis. As a result, we found, acicular YAG powders were obtained by the use of KOH as a mineralizer, the concentration of KOH affected the shape and size of YAG powder. Fine grained YAG were perpared by the use of NH4OH as a mineralizer and the concentration of NH4OH affected crystal phases but did not affect particle size. We could finally get the spherical looking YAG powder at 8 M NH4OH and at 35$0^{\circ}C$ for 12h. The average particle size was about 0.2${\mu}{\textrm}{m}$.