• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.443-446
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• 2006

Carbon-supported Platinum (Pt) is the potential electro-catalyst material for anodic and cathodic reactions in fuel cell. Catalytic activity of the metal strongly depends on the particle shape, size and distribution of the metal in the porous supportive network. Conventional preparation techniques based on wet impregnation and chemical reduction of the metal precursors often do not provide adequate control of particle size and shape. We have proposed a novel route for preparing nano sized Pt colloidal particles in solution by oxidation of ethylene glycol. These Pt nano particles were deposited on large surface area carbon support. The process of nano Pt colloid formation involves the oxidation of solvent ethylene glycol to mainly glycolic acid and the presence of its anion glycolate depends on the solution pH. In the process of colloidal Pt formation glycolate actsas stabilizer for the Pt colloidal particle and prevents the agglomeration of colloidal Pt particles. These mono disperse Pt particles in carbon support are found uniformly distributed in nearly spherical shape and the size distribution was narrow for both supported and unsupported metals. The average diameter of the Pt nano particle was controlled in the range off to 3 nm by optimizing reaction parameters. Transmission electron microscopy, CV and RRDE experiments were used to compliment the results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.753-759
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• 2000

Photoelectric charging is a very efficient way of charging small particles. This method can be applied to combustion measurement, electrostatic precipitator, metal separation and control of micro-contamination. To understand the photoelectric charging mechanism, particle charging of silver by exposure to ultraviolet is investigated in this study. Average charges and charge distributions are measured at various conditions, using two differential mobility analyzers, a condensation nucleus counter, and an aerosol electrometer. The silver particles are generated in a spark discharge aerosol generator. After that process, the generated particles are charged in the photoelectric charger using low-pressure mercury lamp that emits ultraviolet having wavelength 253.7 nm. The results show that ultra-fine particles are highly charged by the photoelectric charging. The average charges linearly increase with increasing particle size and the charge distribution change with particle size. These results are discussed by comparison with previous experiments and proposed equations. It is assumed that the coefficient of electron emission probability is affected by initial charge. The results also show that the charge distribution of a particle is dependent on initial charge. Single changed particle, uncharged particle and neutralized particle are compared. The differences of charge distribution in each case increase with increasing particle size.

• Journal of the Korean Applied Science and Technology
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• v.30 no.3
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• pp.387-393
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• 2013

The crystallization of polypropylene (PP) particles in PP/decalin solution was conducted using the thermally induced phase separation(TIPS). During the control of particles sizes followed by the cooling of PP/decalin solution, particles were formed controllably, the concentrated PP resulted in an increase in the average diameter of PP particles. The effects of surfactants changes on particles sizes were investigated by using a field emission scanning electron microscope (FE-SEM). The PP crystals showed spherical shapes with a diameter 5~18 ${\mu}m$. Additionally, as an effect of concentration of PP, the size distribution of the PP particles became broad with higher concentration of PP in the solution.

• Korean Journal of Materials Research
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• v.12 no.10
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• pp.803-808
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• 2002

Nickel powders were prepared from nickel chloride solution by wet reduction process, and the size control of the particles was investigated with reactant concentration, dispersant agent, and the addition of ethanol as an organic solvent in NiCl$_2$ aqueous solution. The size of the particle decreased with the increase of nickel chloride concentration. Their average particle size were 1.9$\mu\textrm{m}$, 1.6$\mu\textrm{m}$ and $1.5\mu\textrm{m}$ with 0.5M, 0.8M and 1.0M of nickel chloride concentration respectively. The spherical particle was easily controlled by the addition of ethanol as an organic solvent. Especially, in 30 vol% of ethanol, the average particle size and specific surface area were about 0.2$\mu\textrm{m}$ and 8.98m$^2$/g, respectively.

• Polymer(Korea)
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• v.31 no.3
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• pp.215-220
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• 2007

The control of the surface energy by electrohydrodynamic force provides electrospraying with various potential advantages such as simple particle size control, mono-dispersity, high recovery, and mild processing conditions. The advantages are quite helpful to improve the stability of protein drug and control its release. Herein, the nano-encapsulation of protein drugs using electrospraying was investigated. Albumin as a model protein was processed using uniaxial and co-axial electrospraying, and chitosan, polycaporlactone (PCL), and poly (ethylene glycol) (PEG) were used as encapsulation materials. The major processing parameters such as the conductivity of spraying liquids, flow rate, the distance of electrical potential gradient, etc were measured to obtain the maximum efficiency. In the chitosan systems, mean particles size decreases as flow rate and the distance between nozzle and the collecting part decreases. In the uniaxial technique of the PCL systems, mean particles size decreases as flow rate decreases. In the coaxial technique of the PCL systems, it was found that the particles size gets larger under the application of the higher ratio of inner-to-outer liquid flow rates. The primary particles formed out of an electrospraying nozzle showed narrow particle size distribution, but once they arrived to the collecting part, aggregation behavior was observed obviously. Efficient nano-encapsulation of albumin with PCL, PEG, and chitosan was conveniently achieved using electrospraying at above 12 kV.

• Applied Chemistry for Engineering
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• v.22 no.4
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• pp.444-446
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• 2011

Nanosized polystyrene (PS) particles with the narrow size distribution were synthesized from styrene monomer at the presence of the surfactant (polyvinylpyrrolidone, PVP), the solvent of 95 % alcohol, and the initiator of benzoyl peroxide (BPO). Since the emulsion polymerization method was applied, many factors could have effects on the size of PS particles during polymeric process. Aside from the concentration of monomer, surfactant and initiator, the factors such as the stirring speed and the ultrasonic radiation were mainly studied. By adjusting the radiating time, PS particles with their size of about 400 nm were synthesized.

• Journal of Powder Materials
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• v.17 no.5
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• pp.379-384
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• 2010

In the present work, bismuth nanopowders with various particle size distributions were synthesized by controlling argon (Ar) gas flow rate and chamber pressure of a gas condensation (GC) apparatus. From the analyses of transmission electron microscopy (TEM) images and nitrogen gas adsorption results, it was found that as Ar gas flow rate increased, the specific surface area of bismuth increased and the average particles size decreased. On the other hand, as the chamber pressure increased, the specific surface area of bismuth decreased and the average particles size increased. The optimum gas flow rate and chamber pressure for the maximized electrochemical active surface area were determined to be 8 L/min and 50 torr, respectively. The bismuth nanopowders synthesized at the above condition exhibit 13.47 $m^2g^{-1}$ of specific surface area and 45.6 nm of average particles diameter.

• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.710-714
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• 2006

Barium titanate nanoparticles were synthesized under N$_2$ atmosphere by the hydrolysis and condensation of barium hydroxide octahydrate and titanium (IV) isopropoxide. The synthesized particles were aggregates of nanosized primary particles. The primary particles of about 20-50 nm in diameter became building blocks of larger secondary particles, which are in most cases spherical in shape. The size and morphological evolution of secondary particles are strongly related to the precursor concentration. The observations suggest that formation and control of secondary particles is an essential step in the alkoxidehydroxide sol-precipitation process to obtain monodispersed barium titanate nanopowders.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.67-72
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• 2003

Graphite powders were coated with ZrO₂ by the controlled hydrolysis of a DI water, ethanol and DI water+ethanol solutions. The hydrolysis process was carried out with temperature control because of the low wettability of Zr ions to the surface of the graphite. PVA was added to the solution for the enhancement of metal ion adsorption. The surface of the graphite powders coated with ZrO₂ was observed by SEM and TEM. There are two types of ZrO₂ particles with the condition of ZrOCl₂°§8H₂O aqueous solutions were used; (a) primary particles a few nm in size and (b) secondary particles with ∼0.1 ㎛ size were obtained. The graphite powders coated in 50% ethanol-50% DI water solution of Zr(SO₄)₂ㆍ4H₂O have the relatively uniform coating layer and the starting temperature of oxidation was 100℃ higher than the raw graphite.

• 제어로봇시스템학회:학술대회논문집
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• 1999.10a
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• pp.270-273
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• 1999

Circular dynamic stereo has special advantages as it enables a 3-D measurement using a single TV camera and also enables a high accurate measurement without a cumbersome calibration. Annular particle streaks are recorded using this system and the size of annular streaks directly concerns to the depth from TV camera. That is, the size of annular streaks is inversely proportional to the depth from the TV camera and the depth can be measured automatically by image processing technique. Overlapped streaks can be processed also by our method. The flow measurement in a water tank is one of the applications of our system. Tracer particles are introduced into the water in a flow measurement. Since the tracer particles flow with water, three-dimensional velocity distributions in the water tank can be obtained by measuring the all movement of tracer particles. Experimental results demonstrate the feasibility of our method.