• 한국세라믹학회지
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• 제35권6호
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• pp.610-618
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• 1998

Alumina were added to ceria based ceramic powders upto 9.7 vol% and composite powders were sprayed by plasma spraying process in order to improve the mechanical properties such as hardness fracture tough-ness and thermal shock resistance. The ceria based coating sprayed without alumina has the typical colum-nar and lamellar structure. Alumina addition has lowered the amount of columnar and lamellar sturcture Added alumina was segreagated in the grain boundary and grain of ceria based crystal accompanied with pore. The maximum value of density and the minimum value of porosity were observed at the sprayed coating with 4.8 vol% alumina. The hardness fracture toughness and thermal shock resistance were increased with alumina addition. The improvement of mechanical properties of plasma sparyed ceria based coatings result-ed from the disapperance of the columnar and lamellar sturcture by addition of alumina.

• 한국세라믹학회지
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• 제53권5호
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• pp.548-556
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• 2016

Recently, porous alumina-based ceramics have been extensively applied in the semi-conductor and display industries, because of their high mechanical strength, high chemical resistance, and high thermal resistance. However, the high electrical resistance of alumina-based ceramics has a negative effect in many applications due to the generation of static electricity. The low electrical resistance and high air permeability are key aspects in using porous alumina-based ceramics as vacuum chucks in the semi-conductor industry. In this study, we tailored the pore structure of porous alumina-based ceramics by adjusting the mixing ratio of the starting alumina, which has different particle sizes. And the electrical resistance was controlled by using chemical additives. The characteristics of the specimens were studied using scanning electron microscopy, mercury porosimetry, capillary flow porosimetry, a universal testing machine, X-ray diffraction, and a high-resistance meter.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.412-415
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• 2017

본 연구에서는 금속을 담지한 alumina bead 촉매를 이용하여 ammonium dinitramide (ADN)기반 단일액상추진제 분해 성능 분석을 수행하였다. Alumina bead를 $1200^{\circ}C$에서 소성한 후, 회전 증발기를 이용하여 과량 용액 함침법 (Excess water impregnation)으로 alumina bead에 Pt 및 Cu 를 담지하였다. 자체 제작한 batch 반응기에서 ADN기반 단일액상추진제 분해 온도($T_{dec}$)를 측정하였다. Cu/$Al_2O_3$ 촉매가 Pt/$Al_2O_3$ 촉매에 비해 분해 온도가 더 낮게 나타났으며, $T_{dec}$ 는 약 $130^{\circ}C$이었다.

• 세라미스트
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• 제9권6호
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• pp.49-55
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• 2006

Intra-type alumina-based nanocomposites, in which second-phase nanoparticles are embedded within alumina grains, use dislocation activities to enhance strength and fracture toughness. The dislocations are generated around the nanoparticles by residual stresses during cooling process. In this paper, first, we explain strengthening and toughening mechanisms of alumina-based nanocomposites based on dislocation activities. Second, we propose a soaking method to construct the intra-type nanostructure and fabricate alumina/nickel and alumina/silver nanocomposites. The nanocomposites are then annealed in order to enhance the fracture toughness of the materials. Finally, we discuss the relation between the strength, fracture toughness, and critical frontal process zone size of the materials.

• 동력기계공학회지
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• 제17권2호
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• pp.78-86
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• 2013

In this research, dilute colloidal suspension alumina nanofluids were prepared by dispersing alumina nanoparticles in DI water and ethylene glycol as base fluids. Particle size analyzer and TEM test results revealed that the size of the alumina nanofluids(3wt% and 5wt%) with dispersion time 3hrs were 46nm and 60nm respectively. Thermal conductivity of these alumina nanofluids was measured by means of hot wire technique using a LAMBDA system. For water based alumina nanofluids, thermal conductivity enhancement was from 2.29% to 3.06% with 5wt% alumina at temperatures ranging from 15 to $40^{\circ}C$. Whereas in case of ethylene glycol based alumina nanofluids under the same temperature range, thermal conductivity enhancement was from 9.6% to 10% with 5wt% alumina. An enhancement of 37% average convective heat transfer was achieved with 5wt% alumina nanofluids at Re of 1,100.

• 한국세라믹학회지
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• 제54권4호
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• pp.331-339
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• 2017

Porous alumina-based ceramics are of special interest due to their outstanding mechanical properties and their thermal and chemical stability. Nevertheless, the high electrical resistance of alumina-based ceramics, due to the generation of static electricity, leads to difficulty in applying a vacuum chuck in the semi-conductor process. Therefore, development of alumina-based ceramics for applications with vacuum chucks aims to have primary properties of low electrical resistance and high air permeability. In this study, we tailored the electrical resistance of porous alumina-based ceramics by adjusting the amount of $MnO_2$ (with $TiO_2$ fixed at an amount of 2 wt%) and by using coarse alumina powder for high air permeability. The characteristics of the specimens were studied using scanning electron microscopy, mercury porosimeter, capillary flow porosimetry, universal testing machine, X-ray diffraction and high-resistance meter.

• 한국세라믹학회지
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• 제36권10호
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• pp.1123-1131
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• 1999

Alumina-glass composites which are considered as the material of the choice for all dental crown was prepared by aqeous-based tape casting and sintering for 2h at 1120$^{\circ}C$ followed by glass infiltration for 2h at 1100$^{\circ}C$ Biaxial strength and fracture toughness of the composites were evaluated to determine the optimum composition of the tape as a function of the amount of constituent such as alumina binder and plasticizer. The strength and the fracture toughness of the alumina tape increased with increasing the contents of alumina and binder. These observations are consistent with in fluence of the constituents on mean alumuna particle distance in tapes suggesting that high strength of the glass infiltrated alumina composites is related to toughening by crack bowing. The biaxial strength and the fracture toughness of the composite containing the optimum constituent composition were 523 MPa and 3.3 MPa$.$1/2 respectively.

• 한국산학기술학회논문지
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• 제11권3호
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• pp.853-858
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• 2010

본 논문은 알루미늄의 양극산화를 통하여 알루미나(Alumina, $Al_2O_3$)를 형성함으로써 알루미나 및 알루미늄의 적층 구조 DRAM 패키지 기판을 구현하였다. 전송선 기반의 설계를 적용하기 위해 2차원 전자장 시뮬레이션을 수행하였다. 분석 결과를 바탕으로 새로운 기판에 적용할 신호선의 폭 및 간격과 알루미나 두께 등의 설계인자를 최적화하였다. 테스트 패턴 제작 및 측정을 통해 설계인자를 검증하였으며, 이를 바탕으로 설계 룰(Design rule)을 정하고 패키지의 개념 설계 및 상세 설계를 진행하여 DDR2 DRAM 패키지 기판을 성공적으로 제작하였다.

• Macromolecular Research
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• 제17권12호
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• pp.1032-1038
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• 2009

A polypyrrole (PPy)/alumina composite filler prepared via in-situ polymerization of pyrrole on alumina particles was incorporated into $Nafion^{(R)}$ to improve the performance of ionic polymer-metal composite (IPMC) actuators. The IPMCs with the pristine PPy without alumina support did not show bending displacements superior to that of the bare Nafion-based IPMC, except at a high PPy content of 4 wt%. This result was attributed to the low redox efficiency of the PPy alone in the IPMC and may have also been related to the modulus of the IPMC. However, at the optimized filler contents, the cyclic displacement of the IPMCs bearing the PPy/alumina filler was 2.2 times larger than that of the bare Nafion-based IPMC under an applied AC potential of 3 Vat 1 Hz. Even under a low AC potential of 1.5 V at 1 Hz, the displacement of the PPy/alumina-based IPMCs was a viable level of performance for actuator applications and was 2.7 times higher than that of the conventional Nafion-based IPMC. The generated blocking force was also improved with the PPy/aiumina composite filler. The greatly enhanced performance and the low-voltage-operational characteristic of the IPMCs bearing the PPy/alumina filler were attributed to the synergic effects of the neighboring alumina moiety near the PPy moiety involving electrochemical redox reactions.

• 한국세라믹학회지
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• 제38권11호
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• pp.1060-1066
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• 2001

세라믹 인공치관으로 응용을 위해 생체친화적이며 용매에 용해가 잘되고 연소 후 잔류물이 남지 않는 결합제인 PVP로 수계용 알루미나 테이프를 제조하였다. 알루미나 테이프의 인장강도는 결합제(b)와 가소제(p)의 비(b/b+p))에 의해, 그리고 소결체 수축과 밀도는 알루미나(a)와 유기물(o)의 비 (a/(a+o))에 의해 영향을 받았다. 소결된 가공성 알루미나 테이프에 유리를 침투시켜 강화된 세라믹 인공치관용 복합체의 강도는 소결밀도가 증가할수록 높은 값을 보였다.