• 한국전기전자재료학회논문지
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• 제27권6호
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• pp.399-406
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• 2014

Thermal batteries are used for military power sources that require robustness and long storage life such as missiles and torpedoes. $FeS_2$ powder is currently used for cathode materials because of its high specific energy density, environmental non-toxicity and low cost. However, large particle size of conventional $FeS_2$ has been deterred its possible application for higher power thermal batteries. In order to improve the power density, high energy ball milling of $FeS_2$ has been introduced to crush the micron-sized $FeS_2$. Discharge characteristics of the single cells fabricated with nano-materials and conventional $FeS_2$ powder were evaluated.

• Macromolecular Research
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• 제15권5호
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• pp.403-411
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• 2007

Monodisperse micron-sized polystyrene (PS) spheres were successfully obtained using a single stage soap-free emulsion method in aqueous media mixed with ethanol (co-solvent) containing NaCI as the electrolyte. The optimum conditions for preparing the monodisperse PS microspheres, using soap-free emulsion polymerization in a water/ethanol mixture with an electrolyte, were studied. The presence of the co-solvent and electrolyte controlled the particle dispersion stability during the polymerization. The microspheres formed using PS, with a weight-average diameter of $2.6{\mu}m$, coefficient of variation of 5.3% and zeta potential of -15.1 eV, were successfully obtained in the presence of 0.1 wt% NaCI, 10 wt% monomer, 0.1 wt% initiator and 95/5 (g/g) of a water/ethanol mixture reacted at $70^{\circ}C$ for 24 h.

• 한국분말재료학회지
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• 제8권3호
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• pp.151-156
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• 2001

MgO based nanocomposite powder including ferromagnetic iron particle dispersions, which can be available for the magnetic and catalytic applications, was fabricated by the spray pyrolysis process using ultra-sonic atomizer and reduction processes. Liquid source was prepared from iron (Fe)-nitrate, as a source of Fe nano-dispersion, and magnesium (Mg)-nitrate, as a source of MgO materials, with pure water solvent. After the chamber were heated to given temperatures (500~$^800{\circ}C$), the mist of liquid droplets generated by ultrasonic atomizer carried into the chamber by a carrier gas of air, and the ist was decomposed into Fe-oxide and MgO nano-powder. The obtained powders were reduced by hydrogen atmosphere at 600~$^800{\circ}C$. The reduction behavior was investigated by thermal gravity and hygrometry. After reduction, the aggregated sub-micron Fe/MgO powders were obtained, and each aggregated powder composed of nano-sized Fe/MgO materials. By the difference of the chamber temperature, the particle size of Fe and MgO was changed in a few 10 nm levels. Also, the nano-porous Fe-MgO sub-micron powders were obtained. Through this preparation process and the evaluation of phase and microstructure, it was concluded that the Fe/MgO nanocomposite powders with high surface area and the higher coercive force were successfully fabricated.

• Advances in materials Research
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• 제1권3호
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• pp.169-182
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• 2012

In this paper the intrinsic influence of micron-sized nickel particle reinforcements on microstructure, micro-hardness tensile properties and tensile fracture behavior of nano-alumina particle reinforced magnesium alloy AZ31 composite is presented and discussed. The unreinforced magnesium alloy (AZ31) and the reinforced nanocomposite counterpart (AZ31/1.5 vol.% $Al_2O_3$/1.5 vol.% Ni] were manufactured by solidification processing followed by hot extrusion. The elastic modulus and yield strength of the nickel particle-reinforced magnesium alloy nano-composite was higher than both the unreinforced magnesium alloy and the unreinforced magnesium alloy nanocomposite (AZ31/1.5 vol.% $Al_2O_3$). The ultimate tensile strength of the nickel particle reinforced composite was noticeably lower than both the unreinforced nano-composite and the monolithic alloy (AZ31). The ductility, quantified by elongation-to-failure, of the reinforced nanocomposite was noticeably higher than both the unreinforced nano-composite and the monolithic alloy. Tensile fracture behavior of this novel material was essentially normal to the far-field stress axis and revealed microscopic features reminiscent of the occurrence of locally ductile failure mechanisms at the fine microscopic level.

• International Journal of Vascular Biomedical Engineering
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• 제1권2호
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• pp.30-35
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• 2003

Flow characteristics of blood flow in a micro channel were investigated experimentally using a micro-PIV (Particle Image Velocimetry) velocity field measurement technique. The main objective of this study was to understand the real blood flow in micron-sized blood vessels. The Reynolds number based on the hydraulic diameter of micro-channel for deionized (DI) water was about Re=0.34. For each experimental condition, 100 instantaneous velocity fields were captured and ensemble-averaged to get the spatial distributions of mean velocity. In addition, the motion of RBC (Red Blood Cell) was visualized with a high-speed CCD camera. The captured flow images of nano-scale fluorescent tracer particles in DI water were clear and gave good velocity tracking-ability. However, there were substantial velocity variations in the central region of real blood flow in a micro-channel due to the presence of red blood cells.

• 한국수소및신에너지학회논문집
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• 제18권3호
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• pp.238-243
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• 2007

The composite powder of Cu and YSZ was synthesized for a high temperature electrolysis cathode by mechanical milling. The average Cu particle size was reduced to 5 micro-meter from 48 micro-meter after the mechanical ball milling. The composite powder showed that Cu particles were uniformly covered with finer YSZ particles. Sub-micron sized pores were uniformly dispersed in the Cu/YSZ composit. Homogeneously-dispersed fine YSZ in the composite is expected to the increase in triple phase boundaries, thereby leading the enhanced performance of cathode.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.488-491
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• 2005

Abrasive Jet Micromachining (AJM) is a process that uses high pressure air with micron-sized particles to erode a substrate. It has been considered as the most economic and appropriate technique to pattern glass surfaces for the flat panel applications. To accelerate the industrialization of AJM, it is necessary to understand the erosion mechanisms thoroughly. Thus, this paper introduces a new method to model the erosion mechanism in AJM. The model is developed by using the concept of the accumulation of the microdeformation caused by each particle. And this paper proposes the model added the effects of second impact. The developed model is used to simulate the erosion profile, and is compared with the model considered only first impact. It can be concluded that the proposed model predicts the erosion profile more accurately.

• Macromolecular Research
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• 제17권10호
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• pp.750-756
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• 2009

Stable, spherical, polystyrene particles were synthesized in ab initio dispersion polymerization by using the poly(methacrylic acid)[PMAA] macro-RAFT agent. The presence of the PMAA macro-RAFT agent on the polystyrene (PS) particles was confirmed by NMR and FTIR spectroscopy. The PS particle size was influenced by the concentration of the RAFT agent and monomer due to the initial nucleation. When the concentration of the PMAA macro-RAFT agent was increased from 2 to 10 wt% relative to the monomer, the average particle size decreased from 2.31 to 1.36 ${\mu}m$, the conversion decreased from 93.3 to 88.9%, the weight-average molecular weight increased from 46,300 to 150,200 g $mol^{-1}$ and the PDI decreased from 2.79 to 1.94, respectively. In particular, the incorporation of 10 wt% of PMAA macro-RAFT agent produced monodisperse PS spheres of 1.36 ${\mu}m$ with a coefficient of variation (CV) of 6.44%. Thus, the PMAA macro-RAFT agent worked as a reactive steric stabilizer providing monodisperse, micron-sized, PS particles.

• 열처리공학회지
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• 제29권2호
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• pp.51-55
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• 2016

The P/M processing of titanium aluminide using amorphous TiAl is developed by which it is possible to overcome inherent fabricability problems and to obtain a fine microstructure. A high quality amorphous TiAl powder produced by reaction ball milling shows clear glass transition far below a temperature at the onset of crystallization in differential scanning calorimetry above a heating rate of 0.05 K/s. We obtained a fully dense compact of amorphous TiAl powders, encapsulated in a vacuumed can, via viscous flow by hot isostatic pressing (HIP). Isothermally annealing of HIP'ed amorphous compact under a pressure of 196 MPa shows a progressive growth of ${\gamma}-TiAl$ phase with ${\alpha}2$ ($Ti_3Al$), which is characterized by increasing sharpness of X-ray peaks with temperature. Fully dense HIP'ed compact of titanium aluminide TiAl shows a high hardness of 505 Hv, suggesting strengthening mechanisms by sub-micron sized grain of ${\gamma}-TiAl$ and particle-dispersion by second phase constituent, ${\alpha}2$.

• Korean Chemical Engineering Research
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• 제45권5호
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• pp.493-499
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• 2007

본 연구에서는 UV photo-lithography 방식의 particle replication in non-wetting templates(PRINT) 법을 이용하여 약물 전달에 운반체로 사용되는 $3{\mu}m{\times}3{\mu}m{\times}2{\mu}m$ 사이즈의 균일한 고분자 하이드로젤 입자를 제조하였다. 몰드(mold)와 기재(substrate)는 PRINT 방식을 통하여 탄성을 지닌 perfluoropolyethers(PFPE)로 제작하였으며 이를 반복적으로 사용할 수 있도록 하였다. 제작된 입자는 점착성이 있는 수용성 고분자를 이용하여 회수하였다. 입자의 주요 성분은 생분해성 고분자인 poly(ethylene glycol) diacrylate(PEG-diA)이며, 세포 uptake에 적합하도록 aminoethylacrylate(AEM)와 2-acryloxyethyltrimethyl ammonium chloride(AETMAC)를 첨가하였다. 본 연구를 통해 균일하고 원하는 크기의 생체분해성 고분자 입자를 제작하는 PRINT 기술이 약물 전달 및 유전자 전달에 필요한 수송체인 비바이럴 벡터를 제작하기 위한 효과적인 기술임을 제시하였다.