• 한국분말재료학회지
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• 제11권1호
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• pp.43-49
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• 2004

The electrical and thermal conductivity of W-Cu composites were investigated as a function of the W-particle size and W-W contiguity. Powder mixtures were prepared by ball milling or mechanical alloying process, and then sintered at various temperatures. The electrical conductivity of sintered composite was increased with decreasing W grain size. Dependence of electrical conductivity on the W grain size was explained by the W-W contiguity concept. The thermal conductivity was increased with increasing the temperature up to $600^{\circ}C$ but decreased at the temperature above $600^{\circ}C$ Also, thermal conductivity value was influenced by the W particle size. Change of thermal conductivity in W-Cu composites was discussed based on the observed microstructural characteristics and theoretical considerations.

• 한국응용과학기술학회지
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• 제23권1호
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• pp.1-11
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• 2006

The W/O emulsion was formed by mixing hydrophobic nonion surfactants of span 80 and tween 60 with kerosine, and by adding sodium silicate aqueous solution. Precipitating the W/O emulsion by sodium bicarbonate resulted in spherical silica particles. Shape and size distribution of silica particles were observed. The particles were spherical and they have narrow size distribution. Particle sizes were 9.29, 7.39 and $5.73\;{\mu}m$ at homogenizer speed of 2500, 3000, and 3500 rpm, respectively. The particle size was decreased by increasing agitation speed due to the formation of emulsion droplet. At fixed agitation speed, absorbed paraffin oil weight were measured and the $SiO_2/Na_2O$ mole ratio effects on particle size were investigated. Particle size was decreased by increasing the mole ratio of $SiO_2/Na_2O$.

• 한국세라믹학회지
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• 제31권10호
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• pp.1159-1168
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• 1994

We powders were synthesized from W powders in differnet particle sizes by Self-propagating High-temperature Synthesis process (SHS) using a chemical furnace. The effects of the mole ratio of chemical fuel content, pellet thickness and the mole ratio between carbon and tungsten (C/W Ratio) on synthesis were investigated with the tungsten powders have different particle size each other. Compositional and structural characterization of these powders was carried out by scanning electron microscope (SEM0 and x-ray diffractometer. Powder characterization was carried out by the measurement of particle size distribution with laser-particle size analyzer. The amounts of WC obtained by SHS process depend very much on the particle size of tungsten powder and heat contents given in a product, i.e. as the particle size of W powder is smaller, the amounts of WC produced increase. Also the more heat contents is given, the more amounts of WC increase. By optimizing the synthesis conditions, it is possible to fabricate WC powders which have little secondary phases (W2C, C).

• 대한기계학회논문집
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• 제13권4호
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• pp.689-696
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• 1989

본 실험에서는 종래와는 달리 먼저 입출구 부분에서 입자분포 측정장치를 이용하여 실험함으로써 여러 가지 입자크기에 대하여 동시에 효율을 구할 수 있는 장치를 구성하고 앞에서 열거한 여러 가지 실험인자중 레이놀즈수와 S/W를 변화시키면 서 일단 슬릿 임팩터(one-stage slit impactor)의 효율을 .root.Stk에 따라 구하여 일단 임팩터 뿐만 아니라 다단 임팩터(multistage impactor)에 대한 설계기초자료를 마련하 고자 한다.

• Journal of Pharmaceutical Investigation
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• 제31권4호
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• pp.241-256
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• 2001

Alginate microspheres, containing fluorescein isothiocyanate-bovine serum albumin (FITC-BSA) or green fluorescent protein (GFP) were prepared and used as a model drug to develop the oral vaccine delivery system. The alginate microspheres were coated with poly-L-lysine or chitosan. Two methods, w/o-emulsion and spray, were used to prepare alginate microspheres. To optimize preparation conditions, effects of several factors on the particle size and particle morphology of microsphere, and loading efficiency of model antigen were investigated. In both preparation methods, the particle size and the loading efficiency were enhanced when the concentration of sodium alginate increased. In the w/o-emulsion preparation method, as the concentration of Span 80 was increased from 0.5% to 2%, the particle size was decreased, but the loading efficiency was increased. The higher the emulsification speed was, the smaller the particle size and loading efficiency were. The concentration of calcium chloride did not show any effect on the particle size and loading efficiency. In the spray preparation method, the particle size was increased as the nozzle pressure $(from\;1\;kgf/m^2\;to\;3\;kgf/m^2)$ and spray rate was raised. Increasing calcium chloride concentration (<7%) decreased the particle size, in contrast to no effect of calcium chloride concentration on the w/o-emulsion preparation method. Alginate microspheres prepared by two methods were different in the particle size and loading efficiency, the particle size of microspheres prepared by the spray method was about $2-6\;{\mu}m$, larger than that prepared by the w/o emulsion method $(about\;2{\mu}m)$, and the loading efficiency was also higher with spray method. Furthermore, drying process for the microspheres prepared by the spray was simpler and easier, compared with the w/o emulsion preparation. Therefore, the spray method was chosen to prepare alginate microspheres for further experiments. Release pattern of FITC-BSA in alginate microspheres was evaluated in simulated intestinal fluid and PBS (phosphate buffered saline). Dissolution rate of FITC-BSA from alginate/chitosan microsphere was lower than that from alginate microsphere and alginate/poly-L-lysine microsphere. By confocal laser scanning microscope, it was revealed that alginate/FITC-poly-L-lysine microspheres were present in close apposition epithelium of the Peyer's patches of rabbits following inoculation into lumen of intestine, which proved that microspheres could be taken up by Peyer's patch. In conclusion, it is suggested that alginate microsphere prepared by spray method, showing a particle size of & $10\;{\mu}m$ and a high loading efficiency, can be used as a model drug for the development of oral vaccine delivery system.

• KSBB Journal
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• 제29권5호
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• pp.385-391
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• 2014

In this study, the emulsion dispersion stability of optimizing storage temperature was investigated. The system was based on oil/water (O/W) emulsions. In order to evaluate the stability, mean diameter of droplet was measured as a function of temperature with various mixed hydrophilic lipophilic balance (HLB). In addition, the correlations between phase inversion temperature (PIT) and the optimum storage temperature were probed. In this system, majority of the smallest droplet was shown at temperature of $20^{\circ}C$ below PIT. Whether the temperature was increased or decreased from the optimum, size of the droplet increased. According to the mixed HLB, the particle size and optimum storage temperature were also affected. As the concentrations of surfactant were increased, the size of particle decreased with lower optimum temperature for storage. If the surfactant (4 wt%) were mixed with HLB, the optimum storage temperature was $21^{\circ}C$ for maintaining the size of smallest droplet at 108.3 nm in diameter. At above optimum condition, increased size of particle was observed approximately 4 % increases from 108.2 nm to 112.3 nm after 600 hours. The size of particle in emulsion was maintained stably without any considerable effect of Ostwald ripening phenomena at the optimum storage temperature with low polydispersity index.

• 한국주조공학회지
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• 제5권2호
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• pp.85-96
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• 1985

In order to investigate the effect of particle size and distribution of silica sand on the characteristics of investment, W/P ratio, setting time, temperature change during setting, setting expansion, thermal expansion and compressive strength of the investments were measured. In this experiment, magnesia clinker and mono ammonium phosphate were used as binder, and particle size and distribution of silica sand were classified for convinence into 10 categories. The main results obtained from this investigation were summerized as follows. 1. W/P ratio decreased with increase of particle size and evenness in distribution of sand grain. 2. Setting time decreased with increase of evenness in distribution of sand grain, and temperature during setting increased with evenness in distribution of sand grain. 3. Setting expansion decreased with increase of particle size, while it increased with evenness in distribution of sand grain. 4. Thermal expansion decreased with increase of particle size. 5. Compressive strength increased with increase of particle size and evenness in distribution of sand grain. From above results, G.F.N. 250 sand which contains 30% of 50-100 mesh could be recommended for investment casting.

• 약학회지
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• 제12권3_4호
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• pp.41-49
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• 1968

The optimum reaction conditions for the preparation of the precipitated calcium carbonate of an average particle size of 0.05.mu. in diameter was set in which the Box-Wilson Plan was applied. The reaction conditions are as follows; 1) concentration of milk of lime; 6.56% w/w 2) temperature; 14.24.deg. C #) velocity of carbon dioxide introducing; 1.95l/min. The crystal form was found that of calcite in X-ray diffraction analysis. The particle size was determined by the sedimentation volume measurement. The shape was identified by the elctron micro-diffraction pattern and the electron microscopic photographs.

• 한국식품저장유통학회지
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• 제14권4호
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• pp.364-368
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• 2007

가공이나 저장 중 쉽게 산화되는 특성을 갖는 비타민 C의 안정성과 가공적성을 향상시키고자 Zein-DP와 HPMC-FCC를 코팅제로 한 유동층 코팅법을 이용하여 코팅한 비타민 C 분말의 품질 특성에 대하여 조사하였다. 유동층 코팅은 비타민 C의 입자크기($80{\sim}100\;mesh,\;100{\sim}140\;mesh$)와 코팅액의 혼합비(1:1.6, 1:2.5, 1:3(w/w))를 달리하여 실시하였다. 코팅효율은 $80{\sim}100\;mesh$의 경우가 $100{\sim}140\;mesh$보다 높았고 코팅액의 혼합량이 많을수록 감소함을 보였다. 코팅된 필름의 두께는 $80{\sim}100\;mesh$의 경우가 $100{\sim}140\;mesh$보다 두꺼웠으며, 코팅된 입자의 입도분포도는 코팅액 혼합비 1:3에서 가장 좁았다. 코팅분말의 DPPH 소거능은 코팅 전 입자크기와 코팅액 혼합비에 따른 큰 차이를 보이지 않았다. 상기의 코팅된 분말의 품질 특성에 코팅물질의 종류는 거의 영향을 미치지 않았다. 이로써 비타민 C의 유동층 코팅에 적합한 조건으로 비타민 C의 입자크기는 $80{\sim}100\;mesh$, 비타민 C와 코팅 액의 혼합비는 1:3(w/w)으로 판단된다.

• Journal of Pharmaceutical Investigation
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• 제14권2호
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• pp.62-69
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• 1984

Three-ply walled microcapsules containing furosemide and reserpine were prepared from multiple emulsion, and the the appearance of multiple emulsion, the particle size distribution and the drug contents of microcapsules were studied. The microcapsule consisted of alternating three layer of acacia/ethyl cellulose/acacia, and the surface of microcapsules was not porous but wrinkles and had relatively elaborate structure and the particle size range is $4{\mu}m$ to $64{\mu}m$.