• 한국분말재료학회지
• /
• 제20권6호
• /
• pp.411-424
• /
• 2013

In this study, the synthesis of nickel nanoparticles and copper nanospheres for the potential applications of MLCC electrode materials has been studied by plasma arc evaporation method. The change in the broad distribution of the size of nickel and copper nanopowders is successfully controlled by manifesting proper mixture of gas ambiance for plasma generation in the size range of 20 to 200 nm in diameter. The factors affecting the mean diameter of the nanopowder was studied by changing the composition of reactive gases, indicating that nitrogen enhances the formation of larger particles compared to hydrogen gas. The morphologies and particle sizes of the metal nanoparticles were observed by SEM, and ultrathin oxide layers on the powder surface generated during passivation step have been confirmed using TEM. The metallic FCC structure of the nanoparticles was confirmed using powder X-ray diffraction method.

• 한국재료학회지
• /
• 제17권1호
• /
• pp.50-55
• /
• 2007

Ultra-fine Copper powder for a conductive paste in electric-electronic field have been synthesized by chemical reduction of aqueous $CuSO_4$ with hydrazine hydrate $(N_2H_4{\cdot}H_2O)$ as a reductor. The effect of reaction conditions such as dispersant and reaction temperature on the particle size and shape for the prepared Cu powders was investigated by means of XRD, SEM, TEM and TGA. Experiments showed that type of dispersant and reaction temperature were affected on the particle size and morphology of the copper powder. When the carboxymethyl cellulose (CMC) was added as a dispersant the relative mono-dispersed and spherical Cu powder was obtained. Cu powders with particle size of approximately 140nm and narrow particle size distribution were obtained from 0.3M $CuSO_4$ with adding of 0.03M CMC and 40ml $N_2H_4{\cdot}H_2O$ at a reaction temperature of $70^{\circ}C$.

• 한국응용과학기술학회지
• /
• 제22권2호
• /
• pp.175-181
• /
• 2005

The spherical particles of $CeO_2/SiO_2$ composite powder with narrow-size distribution and pure phase particles were synthesized by ultrasonic spray pyrolysis method from aqueous cerium sulfate solution. The resulting composite powder was characterized by X-ray diffraction, scanning electron microscopy, transmittance electron microscopy, in-vitro sun protect factor, and BET surface area analysis. The concentration of cerium sulfate was tested to vary the particle size from $3.40{\times}10^{-3}$ to $1.02{\times}10^{-2}mol/cm^3$ to study concentration effect of starting material. The average particle size from the $3.40{\times}10^{-3}mol/cm^3$ concentration was found to be slightly smaller than that from the $1.02{\times}10^{-2}mol/cm^3$ concentration, because of the relation between the droplet size and the concentration of the starting material solution.

• 보존과학회지
• /
• 제32권2호
• /
• pp.261-271
• /
• 2016

굴 패각 분말의 입자분포가 채색시의 작업성과 채색도막의 내구성에 미치는 영향을 연구하기 위하여 입도분포와 입자형태(구형, 타원형, 길쭉한 막대형, 부정형)의 분포가 각각 다른 3종의 패각분말을 제조하여 연구에 이용하였다. 채색시의 작업성의 척도로서 발림성과 도막의 균일성을 평가하였으며, 도막내구성의 척도로서 도막의 밀착성과 표면경도를 평가하였다. 그 결과 작업성과 내구성은 입자크기보다는 입자형태에 의해 더 큰 영향을 받으며, 특히 길쭉한 막대형 입자의 구성비율이 높을수록 작업성은 떨어지는 반면 내구성이 향상되는 것으로 확인되었다. 이것은 단청 등 회화문화재 보존에 있어 중요한 고려사항인 내구성에 영향을 주는 중요인자를 확인한 결과로서, 단청문화재 보존 및 복원재료의 선정과 품질기준 마련뿐만 아니라 향후 이러한 특성이 제어된 고품질의 전통재료 생산에 중요한 근거자료가 될 수 있을 것으로 기대된다.

• 한국분말재료학회지
• /
• 제13권4호
• /
• pp.256-262
• /
• 2006

The amorphous $Fe_{73}Si_{16}B_7Nb_3Cu_1$ alloy strip was pulverized to get a flake-shaped powder after annealing at $425^{\circ}C$ for 90 min and subsequently ground to obtain finer flake-shaped powder by using a ball mill. The powder was mixed with polyimide-based binder of $0.5{\sim}3wt%$, and then the mixture was cold compacted to make a toroidal powder core. After crystallization treatment for 1 hour at $380{\sim}600^{\circ}C$, the powder was transformed from amorphous to nanocrystalline with the grain size of $10{\sim}15nm$. Soft magnetic characteristics of the powder core was optimized at $550{\sim}600^{\circ}C$ with the insulating binder of 3wt%. As a result, the powder core showed the outstanding magnetic properties in terms of core loss and permeability, which were originated from the optimization of the grain size and distribution of the insulating binder.

• 한국재료학회지
• /
• 제23권2호
• /
• pp.89-97
• /
• 2013

The study of grinding behavior characteristics on aluminum powders and carbon nano tubes (CNTs) has recently gained scientific interest due to their useful effect in enhancing advanced nano materials and components, which significantly improves the property of new mechatronics integrated materials and components. We performed a series of dry grinding experiments using a planetary ball mill to systematically investigate the grinding behavior during Al/CNTs nano composite fabrication. This study focused on a comparative study of the various experimental conditions at several variations of rotation speeds, grinding time and with and without CNTs. The results were monitored for the particle size distribution, median diameter, crystal structure from XRD pattern and particle morphology at a given grinding time. It was observed that pure aluminum powders agglomerated with low rotation speed and completely enhanced powder agglomeration. However, Al/CNTs composites were achieved at maximum experiment conditions (350 rpm, 60 min.) of this study by a mechanical alloy process for Al/CNTs mixed powders because the grinding behavior of Al/CNTs composite powder was affected by addition of CNTs. Indeed, the powder morphology and crystal size of the composite powders changed more by an increase of grinding time and rotation speed.

• 한국식품영양과학회지
• /
• 제32권3호
• /
• pp.370-374
• /
• 2003

홍삼 분쇄의 신 가공 기술로서 비충격 분쇄방식인 cell cracker의 공장 적용 가능성을 제시하고 홍삼분말의 품질고급화에 기초자료로 활용하고자, 기존의 hammer mill(충격분쇄방식)과 cell cracker에 의한 분쇄방식으로 홍삼분말을 제조한 후 물성, 표면구조적 특성 및 관능적 특성을 측정하였다. 입도분석에서 sieve shaker로 분석한 결과, 100 mesh 이상은 모두 95%수준으로 비슷한 분포를 나타냈고 120 mesh 이상은 hammer mill로 분쇄한 홍삼분말이 높았으며 그 밖의 각 mesh별 입도분포는 큰 차이를 나타내지 않았다. Laser scattering analyzer로 분석한 결과 hammer mill로 분쇄한 홍분말의 입도분포는 최소 0.77$\mu\textrm{m}$에서 최대 128.07$\mu\textrm{m}$으로, cell cracker로 분쇄한 홍삼분말 4.24~180.07$\mu\textrm{m}$보다 분포가 넓었으며, 평균 입자 크기는 cell cracker로 분쇄한 홍삼분말이 크고 표준편차는 hammer mill로 분쇄한 홍삼분말이 크게 나타났다. 비표면적은 hammer mill로 분쇄한 홍삼분말이 1.42 $m^2$/g로 cell cracker로 분쇄한 홍삼분말 0.59 $m^2$/g보다 높게 나타났고, 표면구조적 특성은 hammer mill로 분쇄한 홍삼분말은 크고 작은 입자가 불균일하게 분포하고 있으며, 개별입자의 형태는 부등형의 거칠게 연마된 돌 모양에 가깝고 표면은 작고 부드러운 솜털모양을 하고 있는 반면에, cell cracker로 분쇄한 홍삼분말은 입자크기가 상대적으로 고르게 분포하고 있으며 개별입자의 형태는 부등형의 조각난돌 모양의 형태로 관찰되었다.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
• /
• pp.250-251
• /
• 2006

It is known that powder characteristics including particle size and distribution, particle shape, and chemical composition are important parameters which influence direct laser sintering of metal powders. In this paper, we introduce a first order kinetics model for densification of steel powders during laser sintering. A densification coefficient (K) is defined which express the potential of different powders to be laser-sintered to a high density dependent on their particle characteristics.

• 한국분말재료학회지
• /
• 제5권4호
• /
• pp.258-264
• /
• 1998

The initial sintering behaviour of the powder injection molded (PIMed) W-l5wt%Cu nanocomposite powder was investigated. The W-Cu nanocomposite powder was produced by the mechanochemical process consisting of high energy ball-milling and hydrogen reduction of W blue powder-CuO mixture. Solid state sintering of the powder compacts was conducted at $1050^{\circ}C$ for 2~10 hours in hydrogen at mosphere. The sintering behaviour was examined and discussed in terms of microstructural developments such as W-Cu aggregate formation, pore size distribution and W grain growth. The volume shrinkage of PIM specimen was slightly larger than that of PM(conventional PM specimen), being due to fast local densification in the PIM. Remarkable decrease of carbon and oxygen in the PIM enhanced local densification in the early stage of solid state sintering process with eliminating very fine pores less than 10 nm. In addition, such local densiflcation in the PIM is presumably responsible for mitigating of W-grain growth in the initial stage.

• 한국세라믹학회지
• /
• 제52권6호
• /
• pp.521-526
• /
• 2015

$Ce_{0.8}Gd_{0.2}O_{1.9}$(GDC20) powder was prepared from a mixture of submicron-sized $CeO_2$ powder and Gd precipitates using ammonium carbonate $((NH_4)_2CO_3)$ as a precipitant. The mixture was calcined at $700^{\circ}C$ for 4 h followed by ball-milling that resulted in the GDC powder with an average particle size of $0.46{\mu}m$. The powder had a very uniform particle size distribution with particle sizes ranging from $0.3{\mu}m$ to $1{\mu}m$. Sintering of undoped GDC samples did not show a relative density of 99.2% until the temperature was increased to $1500^{\circ}C$, whereas GDC samples doped with 5 mol% CoO exhibited a significant densification at lower temperature reaching a relative density of 97.6% at $1100^{\circ}C$ and of 98.8% at $1200^{\circ}C$.