• 한국재료학회지
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• 제27권8호
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• pp.422-430
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• 2017

Al/expanded graphite was successfully synthesized through a facile method including ultrasonic and heat treatment. In the well-designed three dimensional structure, expanded graphite(EG) works as a conductive matrix to support coated Al particles. The effects of the fabrication parameters on the microstructures and thermal conductivities of these composites were investigated. As a result, it was found that composites with graphite volume fraction of 17.4-69.4 % sintered at $600^{\circ}C$/45MPa exhibit in-plane thermal conductivities of 380-940 W/mK, over 90 % of the predictions by rule of mixture. According to the non-destructive analysis results, the synergistic enhancement was caused by the formation of efficient thermally conductive pathways due to the hybrid of the differently sized EG. The structure integrates the advantages of expanded graphite as a conductive support, preserving the electrode activity and integrity and improving the electrochemical performance.

• 항공우주기술
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• 제7권2호
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• pp.131-143
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• 2008

KSLV-I의 상단부 킥모터의 정확한 성능예측을 위해서 슬래그 적층량을 예측하였다. 수치해석의 타당성을 확인하기 위해 KM 4호기의 질유량에 대한 시험값을 비교하였다. 비행중 KM 슬래그 적층해석을 위해 각 시점별 내부유동 현상을 해석하였다 알루미늄 액적의 궤적을 통해 슬래그가 모터 내부에 적층되는 현상을 나타내었다. 유동현상 및 액적의 적층현상을 Flunet 6.3을 사용해서 수치해석을 수행하였다. 슬래그 적층량을 예측하는데 비행중의 가속도, 액적 출발점 위치, 액적의 크기 등에 대한 영향을 분석하였고 이를 고려하여 총 슬래그 양을 예측하였다. 이 예측값을 지상시험 결과를 이용해서 예측되는 슬래그양과 비교하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.145-148
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• 2006

Cold gas dynamic spray is a relatively new coating process by which coatings can be produced without significant heating during the process. Cold gas dynamic spray is conducted by powder sprayed by supersonic gas jet, and generally called the kinetic spray or cold-spray. Cold-spray was developed in Russia in the early 1980s to overcome the defect of thermal spray method. Its low process temperature can minimize thermal stress and also reduce the deformation of the substrate. Most researches on cold-spray have focused on micro scale coating, but our research team tried to apply this method to macro scale deposition. The macro scale deposition causes deformation of a thin substrate which is usually convex to the deposited side. In this research, the main cause of the deformation was investigated using 6061-T6 aluminum alloy and properties of deposited aluminum layer such as coefficient of thermal expansion, Elastic modulus, hardness, electric conductivity were measured. From the result of the analysis, it was concluded that compressive residual stress was the main reason of substrate deformation while CTE had little effect.

• 한국세라믹학회지
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• 제33권10호
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• pp.1138-1146
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• 1996

Al2TiO5 powder was prepared by the sol-gel processing from th metal alkoxides ; aluminium sec-butoxide (Al(OC4H9)3 and tetraethyl orthotitanate (Ti(OC2H5)4) The particles of Al2TiO5 produced from alkoxides were measured to be below $1.5mutextrm{m}$ and mre than 90% weere below 1 ${\mu}{\textrm}{m}$ however those from commercial alumina and titania were over 0.5-7${\mu}{\textrm}{m}$ and only 60% were below 1${\mu}{\textrm}{m}$ and 90% were below 2.5${\mu}{\textrm}{m}$ Therefore Al2TiO5 powder produced from alkoxides had the narrower distributionin size than that produced from the commercial alumina and titania powders. The addition of mullite or Al2O3 powder to the prepared aluminum titanate inhibited the grain growth and this resulted in decreased and increase in density.

• 한국분말재료학회지
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• 제14권2호
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• pp.145-149
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• 2007

Nanocrystalline transient aluminas (${\gamma}$-alumina) were coated on core particles (${\gamma}$-alumina) by a carbonate precipitation and thermal-assisted combustion, which is environmentally friend. The ammonium aluminum carbonate hydroxide (AACH) as a precursor for coating of transient aluminas was produced from precipitation reaction of ammonium aluminum sulfate and ammonium hydrogen carbonate. The crystalline size and morphology of the synthetic, AACH, were greatly dependent on pH and temperature. AACH with a size of 5 nm was coated on the core alumina particle at pH 9. whereas rod shape and large agglomerates were coated at pH 8 and 11, respectively. The AACH was tightly bonded coated on the core particle due to formation of surface complexes by the adsorption of carbonates, hydroxyl and ammonia groups on the surface of the core alumina powder. The synthetic precursor successfully converted to amorphous- and ${\gamma}$-alumina phase at low temperature through decomposition of surface complexes and thermal-assisted phase transformation.

• 한국표면공학회지
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• 제43권5호
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• pp.230-237
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• 2010

FTMP(friction thermo-mechanical process) is an adaptation of friction stir welding, and can be used as a generic process to modify the microstructure at selective locations. In this study, in order to analyze characteristics of surface modification of ACA4 castings by FTMP, change of rotating speed(R/S) and traveling speed(T/S) of tool were applied as conditional parameter. Analysis of microstructure, hardness, surface roughness and depth of modified zone(MZ) were searched. The best condition were obtained at R/S 600 rpm and T/S 100 mm/min. At this time, hardness was 82 HV, the surface roughness was 0.07 mm and the depth at MZ was 1.72 mm. Free defects microstructure and fine Si particles formation and strong forging effects were analyzed at MZ.

• 한국재료학회지
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• 제8권2호
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• pp.126-130
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• 1998

카올린을 용해시킨 황산용액을 에탄올에 주입함으로써 알루미늄황산염의 침전물, $AI_{2}(SO_{4})_{3}\cdot18H_{2}O$을 제조하고, 그것의 열분해거동을 검토하였다. 합성된 고순도의 침전물은 약 $2\mu\textrm{m}$크기의 판상형태의 입자들로 구성되어져 있었다. 에탄올속으로 카올린을 용해시킨 황산용액의 주입속도를 증가시킴에 따라서 생성된 침전물의 결정사 크기는 감소하였다. 침전물의 탄수 및 탄황산에 대한 겉보기 활성화에너지는 각각 $11.9Kcal mol^{-1}$ 과 $48.2kcal mol^{-1}$ 이었다.

• 한국추진공학회지
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• 제13권4호
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• pp.1-8
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• 2009

킥모터의 정확한 성능 예측을 위해서 슬래그 적층량을 구하였다. 수치해석의 타당성을 확인하기 위해 KM 4호기의 질유량 시험값을 비교하였다. 비행 중 KM 슬래그 적층해석을 위해 각 시점별 내부유동 현상을 분석하였다. 알루미나 액적의 궤적을 통해 슬래그가 모터 내부에 적층되는 현상을 나타내었다. Fluent 6.3을 사용해서 유동현상 및 액적의 적층현상에 대한 수치해석을 수행하였다. 슬래그 적층량을 예측하기 위해 비행중의 가속도, 액적 출발점 위치, 액적의 크기 등에 대한 영향을 분석하였고 이를 고려하여 총 슬래그 양을 예측하였다.

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1962-1966
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• 2012

Boehmite sols have been prepared by crystallization of amorphous aluminum hydroxide gel obtained by hydrolysis and peptization of aluminum using acetic acid. The size of the boehmite crystallites could be controlled by Al molar concentration in amorphous gel by means of controlling grain growth at nucleation stage. The size of boehmite increases as a function of Al molar concentration. With increasing boehmite crystallite size, the $d_{(020)}$ spacing and the specific surface area decreases, whereas the pore volume increases along with pore size. Especially, the pore size of the boehmite sol particles is comparable to the crystallite size along the b axis, suggesting that the fibril thickness along the b axis among the crystallite dimensions of the boehmite contributes to the pore size. Therefore, the physical properties of boehmite sols can be determined by the crystallite size controlled as a function of initial Al concentration.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.617-621
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• 2017

본 연구에서는 Al 입자가 함유된 고폭약의 성능 특성을 2 상 모델(two-phase model)을 이용하여 수치 해석을 수행하였다. Al 입자의 점화와 연소시간은 고폭약에 비해 상대적으로 긴 시간이 요구되기 때문에, Al 입자연소에 의한 에너지 발산은 고폭약의 데토네이션 후방에서 이루어진다. Al 입자를 함유하는 고폭약은 Al 함유량이 증가함에 따라 데토네이션 속도의 감소와 고폭약 데토네이션 후방에서 Al 입자 연소가 일어나며 이중 데토네이션이 관찰되는 특징이 있다. 본 연구에서는 Al 입자가 함유된 HMX의 데토네이션 특성을 재현하기 위해 최대 Al 함유량 50%를 갖는 confined rate stick이 고려되었으며, 수치해석 결과는 5-25% 함유량에 대한 실험결과와 비교되었다.