• Title/Summary/Keyword: fine powders

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The effects of starting precursor conditions on the phase formation and transport properties of Bi-2223/Ag tapes

  • Chunhai Jiang;Jaimoo Yoo;Jaewoong Ko;Kim, Haidoo;Hyungsik Chung
    • Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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    • 2002.02a
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    • pp.343-345
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    • 2002
  • The influence of starting precursor powders on the phase formation and transport properties of Bi-2223/Ag tapes has been studied. The experimental results show that the average particle size of precursors as fine as 1.64 ${\mu}{\textrm}{m}$ and 1.51 ${\mu}{\textrm}{m}$ can still increase the transport properties. The J$_{c}$-B behavior is also enhanced in tapes fabricated with powders in finer particle sizes. However, at higher magnetic fields, J$_{c}$ of tape started from the powder with the finest particles drops rapidly at the direction of H//c, which is possibly attributed to the small grain sizes and weak flux pinning ability that due to the short induction period at the initial stage of phase formation as the result of fine particles in precursor powder.der.

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A Study on the Ultrasonic In-Process Dressing Method of CBN Grinding Wheel (CBN 연삭숫돌의 초음파 인프로세스 드레싱 기법)

  • 이석우;정해도;최헌종
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.2
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    • pp.43-50
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    • 2000
  • A CBN wheel was used for the highly efficient and precision grinding of the mold material(STD11). The grinding form accuracy by a CBN wheel is very excellent due to its low wheel wear, but grinding fragments resemble fine powders rather chips. A fine powders by this fragmentation can easily get attached to the wheel surface and therefore causing a loading. In order to prevent this fragmentation phenomena, the alumina stick is use to processing. Because the dressing with alumina stick should be interrupted for a processing, the automation of the processing and high productivity was very difficult. The investigation on the effect of Ultrasonic In-Process Dressing(ULID) on the grinding characteristics focuses in this Paper. This ULID method is that ultrasonic vibration in my Position of wheel is used to remove impurities on the wheel surface. Finally, the rate of surface roughness change in grinding by the ULID method was less than grinding without ultrasonic vibration. Loading phenomena by the ULID method were more prevented than grinding without ultrasonic vibration.

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Development of Superior Fe-Si Sintered Magnetic Cores Equivalent to Wrought Si-steels

  • Hamano, Aya;Isihara, Chio;Asaka, Kazuo
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09b
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    • pp.799-800
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    • 2006
  • Wrought Si-steels are generally used for electromagnetic valves, which are needed good response. To date, Hitachi Powdered Metals Co., Ltd. have produced Fe-Si base sintered magnetic material, EU-52, which shows a magnetic flux density of more than 1.25T at 2000A/m and a maximum permeability of more than 3500. However these magnetic properties are lower than that of wrought Si-steels. Because EU-52 has a low density of $7.2Mg/m^3$. For improving the magnetic properties, it is necessary to increase the density of sintered cores. To increase density, a new mixing method of coating fine Si powders on atomized iron powders was developed, for avoiding the Kirkendall effect. As the result, developed P/M Fe-Si magnetic cores shows higher density of $7.38Mg/m^3$, higher magnetic flux density of 1.48T at 2000A/m and higher maximum permeability of 6800.

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Effect of Initial Silicon Scrap Size on Powder Refining Process During High Energy Ball Milling (HEBM) (폐실리콘의 고에너지 밀링 과정에서 초기 입자 크기가 분말의 미세화에 미치는 효과)

  • Song, Joon-Woo;Kim, Hyo-Seob;Kim, Sung-Shin;Koo, Jar-Myung;Hong, Soon-Jik
    • Journal of Powder Materials
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    • v.17 no.3
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    • pp.242-250
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    • 2010
  • In this research, the optimal manufacturing conditions of fine Si powders from Si scrap were investigated as a function of different initial powder size using the high-energy ball milling equipment, which produces the fine powder by means of an ultra high-energy within a short duration. The morphological change of the powders according to the milling time was observed by Scanning electron microscopy (SEM). With the increasing milling time, the size of Si powder was decreased. In addition, more energy and stress for milling were required with the decreasing initial powder size. The refinement of Si scrap was rapidly carried out at 10min ball milling time. However, the refined powder started to agglomerate at 30 min milling time, while the powder size became uniform at 60 min milling time.

Synthesis and Properties of La1-xSrxMnO3 System as Air Electrode for Solid Oxide Fuel Cell (고체산화물 연료전지의 공기극으로서 La1-xSrxMnO3 계의 합성 및 특성)

  • Lee, You-Kee;Lee, Young-Ki
    • Korean Journal of Materials Research
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    • v.22 no.9
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    • pp.470-475
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    • 2012
  • $La_{1-x}Sr_xMnO_3$(LSM,$0{\leq}x{\leq}0.5$) powders as the air electrode for solid oxide fuel cell were synthesized by a glycine-nitrate combustion process. The powders were then examined by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The as-formed powders were composed of very fine ash particles linked together in chains. X-ray maps of the LSM powders milled for 1.5 h showed that the metallic elements are homogeneously distributed inside each grain and in the different grains. The powder XRD patterns of the LSM with x < 0.3 showed a rhombohedral phase; the phase changes to the cubic phase at higher compositions($x{\geq}0.3$) calcined in air at $1200^{\circ}C$ for 4 h. Also, the SEM micrographs showed that the average grain size decreases as Sr content increases. Composite air electrodes made of 50/50 vol% of the resulting LSM powders and yttria stabilized zirconia(YSZ) powders were prepared by colloidal deposition technique. The electrodes were studied by ac impedance spectroscopy in order to improve the performance of a solid oxide fuel cell(SOFC). Reproducible impedance spectra were confirmed using the improved cell, which consisted of LSM-YSZ/YSZ. The composite electrode of LSM and YSZ was found to yield a lower cathodic resistivity than that of the non-composite one. Also, the addition of YSZ to the $La_{1-x}Sr_xMnO_3$ ($0.1{\leq}x{\leq}0.2$) electrode led to a pronounced, large decrease in the cathodic resistivity of the LSM-YSZ composite electrodes.

A Study on Polyamide-6 Sintering and Effect by $CO_2$ Laser ($CO_2$ Laser에 의한 Polyamide-6 소결과 그 영향에 관한 연구)

  • Bae S.W.;Kim D.S.;Ahn Y.J.;Kim H.I.;Choi K.S.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2006.05a
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    • pp.197-198
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    • 2006
  • In the solid freeform fabrication (SFF) system using selective laser sintering (SLS), polyamide-12 powder is currently recognized as general material. In this study, some kinds of polyamide-6 powders with different shape and particlesize were fabricated to investigate the formability, the microstructure and mechanical properties. Also, to develop a more elaborate and rapid system, this study employs a new SLS device with a 3-axis dynamic focusing scanner system instead of the existing fe lens used in commercial SLS. Polyamide-6 powders having the average size of 100 m were treated thermally in order to keep the spherical symmetry in shape. These polyamide-6 powders were mixed with polyamide-12 powders having the average size of 50 m to give the bimodal distribution of size. These mixed powders showed the better fabrication in the selective laser sintering process because the smaller particles of polyamide-11 played an important role in the compact packing of powders by filling the void space between the large particles of polyamide-6. Also, Experiments have performed to evaluate the effect of a scanning path and sintering parameters by fabricating the various 3D objects.

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A Synthesis of $(Ba_{1-x}Sr_x)TiO_3$ Powders by Sol-Gel Route (졸-겔법을 이용한$(Ba_{1-x}Sr_x)TiO_3$분말합성)

  • Kim, Young-Seok;Kim, Duk-Jun;Kim, Hwan
    • Korean Journal of Materials Research
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    • v.2 no.2
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    • pp.151-156
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    • 1992
  • Using $Ba(OH)_2{\cdot}8H_2O, \;Sr(OH)_2{\cdot}8H_2O$ and $Ti(i-OC_3H_7)_4$, fine $(Ba_{1-x}, \;Sr_{x})TiO_3$ powders were synthesized through sol-gel process. The particle size of the powders calcined at $700^{\cric}C$ proved to be 20-40nm by the observation of TEM micrographs and measurement of BET specific surface area. The analysis of XRD patterns showed that the phase of the powders was cubic, and it was identified with the lattice parameters determined through XRD patterns and the shift of (112) peaks that the solid solution powders were synthesized. It was expected through the analysis of relative ratio of cations and the uniformity of compositions in the powders examined by EDAX analysis and relative dielectric constant measurements for sintered body that the distribution of cations was uniform in particle unit.

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Preparation and Characterization of Fine $TiO_2$ Powders by Vapor-Phase Hydrolysis of TiCl4 (사염화티타늄의 기상가수분해반응에 의한 $TiO_2$ 미분의 제조 및 입자특성)

  • 염선민;김광호;신동원;박찬경
    • Journal of the Korean Ceramic Society
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    • v.29 no.7
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    • pp.525-532
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    • 1992
  • TiO2 fine powder was synthesized in the gas phase by chemical vapor deposition using hydrolysis of TiCl4. Content of rutile phase in the powder was investigated. Powder characteristics such as size, crystallinity and morphology were also studied by means of TEM, SEM and XRD. Rutile phase in TiO2 powder started to be formed from 100$0^{\circ}C$ and the content increased with the reaction temperature and TiCl4 concentration. As the temperature increased from 80$0^{\circ}C$ to 140$0^{\circ}C$, the primary particle size increased while secondary particle size decreased. Spherical secondary particle with fine primary crystals agglomerated was produced at low temperature of 80$0^{\circ}C$ whereas the grown primary particle being final particle size was produced at higher temperature of 140$0^{\circ}C$. Other effects of TiCl4 and H2O partial pressures on particle size were also reported in this study.

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Microwave Absorption of Ferrite Powders by Wet-Direct Synthesis (습식직접합성 Ferrite 분말의 전파흡수능)

  • 남경호;이경희;이병하
    • Journal of the Korean Ceramic Society
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    • v.28 no.11
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    • pp.843-850
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    • 1991
  • There is a growing demend for absorptive electromagentic shielding materials for wide band frequency application. In this study, the absorber which consists of a rubber plus Ni-Zn ferrite which have been prepared by direct-wet method. A rubber ferrite composite for electromagnetic shielding, it is most importan facter the homogeneous ultra fine size and high dispersitive ferrite powder. Direct-wet method and solid-solid reaction method for preparing of ultra fine ferrite powder was used. It has been experimentally verified that the powder which prepared by direct-wet method was very fine and almost same size spherical powder, the composite ferrite have excellent electromagnetic wave absorption in X-band.

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Y-TZP Fine Powder Preparation by Ultrasonic Spray Pyrolysis (초음파 분무 열분해법에 의한 Y-TZP 미립자의 합성)

  • 이정형;김복희;최의석;황재석
    • Journal of the Korean Ceramic Society
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    • v.30 no.4
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    • pp.325-331
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    • 1993
  • Aqueous solutions of metallic salts, ZrO(NO3)2.2H2O and Y(NO3)3.5H2O were used as raw materials to synthesize crystalline submicron spherical powders of Zr0.94Y0.06O1.97 with tetragonal crystal phase. Each aqueous solution was mixed on the magnetic stirrer to homogenize for 12 hours. The concentration of the mixed solutionwas changed from 0.01mol/$\ell$ to 0.1mol/$\ell$ calculated as the concentration of Zr0.94Y0.06O1.97. Ultrafine droplets of starting mixed solution were sprayed by the ultrasonic vibrator and carried into the furnace kept at 55$0^{\circ}C$, $650^{\circ}C$, 75$0^{\circ}C$ and 85$0^{\circ}C$ using carrier gas of air (10$\ell$/min) and pyrolysed to form Y-TZP fine powders. The results of this exeriment were as follows. 1) Synthesized powders were nonagglomerated and spherical type. 2) Particle size distribution was narrow between 0.1${\mu}{\textrm}{m}$ and 1${\mu}{\textrm}{m}$. 3) Forming reaction Y-TZP was finished above synthetic temperature 75$0^{\circ}C$. 4) As the synthetic temperature rised from 55$0^{\circ}C$ to 85$0^{\circ}C$, the mean particle size decreased from 0.35${\mu}{\textrm}{m}$ to 0.22${\mu}{\textrm}{m}$ in the concentration of starting solution with 0.02mol/$\ell$. 5) At 75$0^{\circ}C$ of synthetic temperature, the concentration changes of starting solution from 0.01mol/$\ell$ to 0.1mol/$\ell$ increased the mean particle size from 0.24${\mu}{\textrm}{m}$ to 0.38${\mu}{\textrm}{m}$. 6) Chemical compositions of each synthesized particle were homogeneous nearly.

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