• 한국세라믹학회지
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• 제32권3호
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• pp.366-370
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• 1995

The ballistic efficiency of alumina tiles with various sizes, shapes, and target configurations was measured by the thick backing plate technique. The ballistic efficiency of square tiles roughly 8 mm thick struck by 12.7mm diameter bullets rapidly increased with tile size up to about 100mm, then tended to saturate. Circular shape tiles had lower ballistic efficiencies than those of square shape tiles for the same width and thickness. Small tiles (50mm) that were recessed in aluminum wells had a significantly higher ballistic efficiency than tiles placed on a flat surface. However, the difference in the ballistic efficiency between the two target configurtions became small at larger tile sizes. All the results could be explained by the effect of reflected waves at edges and the propagation of resulting cracks on the penetration process.

• 한국화재소방학회논문지
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• 제11권3호
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• pp.15-23
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• 1997

In this study, the alumina for gas sensor was prepared by anodic oxidation. It was stable thermally and chemically, and pore diameter and pore distribution was uniform. And the shape of pore was cylinderical. The aluminum plate was carried out by the thermal oxidation, chemical polishing and electropolishing pretreatment. The pore diameter, pore size distribution, pore density and thickness of alumina was observed with the change of reaction temperature, electrolyte concentration and current density. As a results, It was able to use for carrier because alumina which was prepared by anodic oxidationhas uniform pore size distribution.

• 한국세라믹학회지
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• 제52권5호
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• pp.366-373
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• 2015

Sol-gel binder was prepared by hydrolysis and condensation reaction using boehmite sol and methyltrimethoxysilane as a function of aging-time. The coating slurry was composed of a plate-shape alumina in the sol-gel binder for the EPD process, in which particles dispersed in the slurry were deposited on the electrode under an electric field due to the surface charge. We studied the effects of three parameters: the content of boehmite, the aging time, and the applied voltage, on the physical, thermal, and electrical properties of the hybrid composite films by EPD. The amount of boehmite was 10 ~ 20 wt% and the aging time was 0.5 ~ 72, with a fixed amount of plate-shape alumina of 10 wt%. The condition of applied voltage was 5 ~ 30 V with a distance of 2 cm between the electrode during the EPD process. We confirmed that a structure of hybrid composite films of well-ordered plate alumina was deposited on the substrate when the film was prepared using a sol-gel binder composed of 15 wt% boehmite with 1 hr aging time and EPD at 10 V. The process shows a weight loss of 7% at $500^{\circ}C$ in TGA and a breakdown voltage of 8 kV at $87{\mu}m$.

• 한국세라믹학회지
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• 제49권6호
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• pp.592-600
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• 2012

Conventional methods for preparing ceramic bodies, such as cold isostatic pressing, gypsum-mold slip casting, and filter pressing are not completely suitable for fabricating large and thick ceramic plates owing to disadvantages of these processes, such as the high cost of the equipment, the formation of density gradients, and differential shrinkage during drying. These problems can be avoided by employing a pressure-vacuum hybrid slip casting approach that considers not only by the compression of the aqueous slip in the casting room (pressure slip casting) but also the vacuum sucking of the dispersion medium (water) around the mold (vacuum slip casting). We prepared the alumina formed bodies by means of pressure-vacuum hybrid slip casting with stepwise pressure loading up to 0.5 MPa using a slip consisting of 40 vol% solid, 0.6 wt% APC, 1 wt% PEG, and 1 wt% PVA. After drying the green body at $30^{\circ}C$ and 80% RH, the green density of the alumina bodies was about 56% RD. The sintered density of an alumina plate created by means of sintering at $1650^{\circ}C$ for 4 h exceeded 99.8%.This method enabled us to fabricate a $110{\times}110{\times}20$ mm alumina plate without cracks and with a homogeneous density, thus demonstrating the possibility of extending the method to the fabrication of other ceramic products.

• 한국세라믹학회지
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• 제41권7호
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• pp.513-517
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• 2004

기공크기와 형태를 제어하여 열전도도 이방성을 나타내기 위해 판상의 기공이 배향된 다공질 알루미나 소결체의 제조방법을 연구하였다. 속이 가스로 차있는 열가소성 고분자 microsphere를 알루미나 분말과 혼합한 후 일축 가압 열변형 방법을 이용하여 15 MPa의 압력으로 가압한 상태에서 20$0^{\circ}C$까지 승온하여 microsphere를 판상으로 변형시킨 후, 1,00$0^{\circ}C$에서 1시간동안 소결하였다. Microsphere의 함량이 10wt%인 경우 45.3%의 기공율을 나타내었으며, 44 MPa의 꺾임강도 값을 나타내었다. 미세구조를 살펴본 결과 판상기공이 압축방향과 수직방향으로 배향되었으며, 열전도도를 측정한 결과 압축방향으로 3.803 W/mK, 측면방향으로는 7.818 W/mK로서 두 값의 비는 2 이상이었다.

• 한국세라믹학회지
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• 제27권6호
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• pp.729-734
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• 1990

The microstructural dependence of thermal conductivity of a high-alumina (ca. 70%) heat-insulating frebricks(ca. 75%porosity) was investigated under special consideration of the tailored-pore shape effects. Pores different shape could be incorporated into the insulators through pore formers : Styrofoam produces spherical pores while saw dust results in parallel plate pores. Concerning the pore-shape effectiveness of thermal insulation, the specimen with irregular plate pores showed much lower values of heat conductivity than those with spherical pores, the values being 0.31 to 0.38 at $600^{\circ}C$ and 0.35 to 0.47 at 100$0^{\circ}C$, respectively. On the contrary, however, other material properties such as strength and softening temeprature under load were turned out to be better in the case of the spherical pores.

• Korean Chemical Engineering Research
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• 제53권5호
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• pp.603-608
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• 2015

일반적으로 결정은 계면에 따라 그 성장속도가 다르기 때문에 계면의 성장을 제어함으로써 다양한 형태의 결정입자를 얻는 것이 가능하다. 알루미나의 경우 산업적 이용범위가 다양해지고 있어, 다양한 크기 또는 종횡비가 다른 다양한 형상의 분말이 요구되기도 한다. 용융염(molten-salt)을 이용하여 세라믹 입자를 성장시킬 경우, $800{\sim}900^{\circ}C$ 이상에서 용융되는 salt의 조건을 변화함으로써 세라믹 입자의 결정 성장 방향을 제어할 수 있는데, 알루미나의 경우 주로 판상형으로 입자가 성장하게 되며, 이때 salt의 ionic strength에 따라 판상형으로 성장하는 결정의 성장 속도를 제어하는 것이 가능하다. 본 연구에서는 NaCl, $Na_2SO_4$, $Na_3PO_4$를 이용하여 ionic strength가 다른 다양한 salt 조건에서 알루미나 입자를 성장시켰으며, 이들이 알루미나 결정 성장에 미치는 영향과 온도, 농도 변화에 따라 형성되는 알루미나의 크기 및 형상의 변화에 관하여 연구하였다.

• 한국세라믹학회지
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• 제50권2호
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• pp.142-148
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• 2013

Conventional cold isostatic pressing, slip casting, and filter pressing are not completely suitable for fabricating large plates because of disadvantages such as the high cost of equipment and formation of density gradient. These problems could be avoided by employing pressure-vacuum hybrid slip casting (PVHSC). In the PVHSC, the consolidation occurs not only by the compression of the slip in casting room, but also by vacuum sucking of the dispersion medium around the mold. We prepared the alumina bodies by the PVHSC in a static- or stepwise-pressure manner for loading up to 0.5 MPa using an aqueous slip. The green bodies were dried at $30^{\circ}C$ with 40 ~ 80% relative humidity. Under static pressure, casting induced a density gradient in the formed body, resulting in cracking and distortion after the firing. However, the stepwise pressure loading resulted in green bodies with homogeneous density, and the minimization of the appearance of those defects in final products. Desirable drying results were obtained from the cast bodies dried with 80% RH environment humidity. When sintered at $1650^{\circ}C$ for 4 h, the alumina plate made by stepwise-pressure casting reached full density (> 99.7% relative density).

• 한국세라믹학회지
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• 제50권6호
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• pp.460-465
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• 2013

Plate-shaped inorganic particles are coated onto a stainless steel substrate by the electrophoretic deposition of a precursor slurry which includes the inorganic particles of $Al_2O_3$ and polymer resin in mixed solvents to mimic the abalone shell structure, which is a composite of plate-shaped inorganic particles and organic interlayer binding materials with a layered orientation. The process parameters of the electrophoretic deposition include the voltage, coating time, and conductivity of the substrate. In addition, the suspension parameters are the particle size, concentration, viscosity, conductivity, and stability. We prepared an organic-inorganic composite coating with a high inorganic solid content by arraying the plate-shaped $Al_2O_3$ particles and electrophoretic resin via an electrophoretic deposition method. We analyzed the effect of the slurry composition and the electrophoretic deposition process parameters on the physical, mechanical and thermal properties of the coating layer, i.e., the thickness, density, particle orientation, Young's modulus and thermogravimetric analysis results.

• 공업화학
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• 제9권4호
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• pp.481-485
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• 1998

마이크로파 열원을 이용하여 황산 용액에서 카올린을 가열 반응시켜 무기고분자인 수화 황산 알루미늄을 합성하였다. 하소된 카올린으로부터 알루미나의 최대 추출율은 재래식 열공정 ($80^{\circ}C$, 1 M 및 240분)에서 72.8%이었고, 마이크로파 공정 ($90^{\circ}C$, 1 M 및 60분)에서 99.9%이었다. 재래식 열공정에서와는 달리 마이크로파 공정에서 추출 합성된 수화 황산 알루미늄 시료는 빠른 결정립 성장에 의해 거대 크기의 판상으로 이루어진 층상구조로 존재하였다. 마이크로파와 재래식 열공정에서 합성하여, $1100^{\circ}C$에서 하소된 시료들을 모두 구형으로 응집된 분말상의 ${\gamma}-Al_2O_3$ 존재하였고, 이 시료들의 비표면적은 각각 113.5와 $106.6m^2/g$이었고, 입자의 평균 입경은 각각 46.5와 $26.3{\mu}m$이었다.