• 분석과학
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• 제20권4호
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• pp.302-307
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• 2007

$TiO_2$ 나노분말 제조시 HCl과$NH_4OH$의 첨가량에 따른 반응양상과 pH의 영향을 고찰하였다. Titanium tetra-isopropoxide의 가수분해 반응을 이용하여 nanosize의 $TiO_2$ 분말를 합성하였고, 촉매로 HCl과$NH_4OH$를 사용하였다. 촉매의 첨가량에 따른 반응양상과 생성된 $TiO_2$ 분말의 특성 변화를 조사하였다. 염기성 촉매인$NH_4OH$를 사용하였을 경우에 균질한 형상의 분말 형태의 $TiO_2$를 합성할 수 있었으며, 산성 촉매인 HCl을 사용하여 pH가 5.04 이하일 경우에는 괴상이나 과립의 형태로 생성되었다. 사용한 촉매의 종류와 양에 따라 저온의 결정상인 anatase의 생성속도와 보다 안정한 rutile 상으로의 상전이 속도가 영향을 받았다.

• 한국재료학회지
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• 제22권4호
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• pp.174-179
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• 2012

In this study, we demonstrated a simple and eco-friendly method, including mechanical polishing and attrition milling processes, to recycle sputtered indium tin oxide targets to indium tin oxide nanopowders and targets for sputtered transparent conductive films. The utilized indium tin oxide target was first pulverized to a powder of sub- to a few- micrometer size by polishing using a diamond particle coated polishing wheel. The calcination of the crushed indium tin oxide powder was carried out at $1000^{\circ}C$ for 1 h, based on the thermal behavior of the indium tin oxide powder; then, the powders were downsized to nanometer size by attrition milling. The average particle size of the indium tin oxide nanopowder was decreased by increasing attrition milling time and was approximately 30 nm after attrition milling for 15 h. The morphology, chemical composition, and microstructure of the recycled indium tin oxide nanopowder were investigated by FE-SEM, EDX, and TEM. A fully dense indium tin oxide sintered specimen with 97.4% of relative density was fabricated using the recycled indium tin oxide nanopowders under atmospheric pressure at $1500^{\circ}C$ for 4 h. The microstructure, phase, and purity of the indium tin oxide target were examined by FE-SEM, XRD, and ICP-MS.

• 한국분말재료학회지
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• 제24권3호
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• pp.223-228
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• 2017

Nanopowders provide better details for micro features and surface finish in powder injection molding processes. However, the small size of such powders induces processing challenges, such as low solid loading, high feedstock viscosity, difficulty in debinding, and distinctive sintering behavior. Therefore, the optimization of process conditions for nanopowder injection molding is essential, and it should be carefully performed. In this study, the powder injection molding process for Fe nanopowder has been optimized. The feedstock has been formulated using commercially available Fe nanopowder and a wax-based binder system. The optimal solid loading has been determined from the critical solid loading, measured by a torque rheometer. The homogeneously mixed feedstock is injected as a cylindrical green body, and solvent and thermal debinding conditions are determined by observing the weight change of the sample. The influence of the sintering temperature and holding time on the density has also been investigated. Thereafter, the Vickers hardness and grain size of the sintered samples have been measured to optimize the sintering conditions.

• International Journal of Precision Engineering and Manufacturing
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• 제9권3호
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• pp.22-26
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• 2008

The use of electrical discharge machining (EDM) for micro-machining applications requires particular attention to the machined surface roughness and discharge gap distance, as these factors affect the geometrical accuracy of micro-parts. Previous studies of conventional EDM have shown that selected types of semi-conductive and non-conductive powder suspended in the dielectric reduced the surface roughness while ensuring a limited increase in the gap distance. Based on this, an extension of the technique to micro-EDM was studied Such work is necessary since the introduction of nanopowders suspended in the dielectric is not well understood. The experimental results showed that a statistically significant reduction in the surface roughness value was achieved at particular concentrations of the powder additives, depending on the powder material and the machining input energy setting. The average reduction in surface roughness using a powder suspended dielectric was between 14-24% of the average surface roughness generated using a pure dielectric. Furthermore, when these additive concentrations were used for machining, no adverse increase in the gap distance was observed.

• Journal of Magnetics
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• 제14권2호
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• pp.75-79
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• 2009

Nickel (Ni) and ferrite ($Fe_3O_4$, $NiFe_2O_4$) nanoparticles were synthesized by LGC using both wire feeding (WF) and micron powder feeding (MPF) systems. Phase evolution and magnetic properties were then investigated. The Ni nanopowder included magnetic-ordered phases. The LGC synthesis yielded spherical particles with large coercivity while the abnormal initial magnetization curve for Ni indicated a non-collinear magnetic structure between the core and surface layer of the particles. Since the XRD pattern cannot actually distinguish between magnetite ($Fe_3O_4$) and maghemite (${\gamma}-Fe_2O_3$) as they have a spinel type structure, the phase of the iron oxide in the samples was unveiled by $M{\ddot{o}}ssbauer$ spectroscopy. The synthesized Ni-ferrite consisted of single domain particles, including an unusual ionic state. The synthesized nanopowder bore an active surface due to the defects that affected abnormal magnetic properties.

• 한국분말재료학회지
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• 제23권6호
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• pp.409-413
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• 2016

Electrical wire explosion in liquid media is a promising method for producing metallic nanopowders. It is possible to obtain high-purity metallic nanoparticles and uniform-sized nanopowder with excellent dispersion stability using this electrical wire explosion method. In this study, Ni-Fe alloy nanopowders with core-shell structures are fabricated via the electrical explosion of Ni-Fe alloy wires 0.1 mm in diameter and 20 mm in length in de-ionized water. The size and shape of the powders are investigated by field-emission scanning electron microscopy, transmission electron microscopy, and laser particle size analysis. Phase analysis and grain size determination are conducted by X-ray diffraction. The result indicate that a core-shell structured Ni-Fe nanopowder is synthesized with an average particle size of approximately 28 nm, and nanosized Ni core particles are encapsulated by an Fe nanolayer.

• 대한금속재료학회지
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• 제49권1호
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• pp.32-39
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• 2011

The present investigation was performed on the die compaction and sintering behavior of Fe micro-nano mixed powder with a mixed binder for powder injection molding. Warm die compaction of the feedstock for simulation of the static injection molding process was conducted using a cylindrical mold of 10 mm diameter at $100^{\circ}C$ under 4MPa. The die compaction of the micro-nanopowder feedstock underwent a uniform molding behavior showing a homogeneous distribution of nanopowders among the micropowders without porosity and distortion. After debinding, the powder compact maintained a uniform structure without crack and distortion, leading to a high green density of 64.2% corresponding to the initial powder loading of 65%. The sintering experiment showed that the micro-nanopowder compact underwent a near full and isotropic densification process during sintering. It was observed that the nanopowders effectively suppressed the growth of micropowder grains during densification process. Conclusively, the use of nanopowder for PIM feedstock might provide a new concept for processing a full density PIM parts with fine microstructure.

• 한국결정성장학회지
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• 제27권6호
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• pp.309-312
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• 2017

세리아 분말은 Ce 이온의 산화, 환원 반응을 통한 산소저장능력(OSC)이 뛰어나 배기가스를 정화하는 자동차의 삼원촉매에 대표적인 재료로 사용된다. 그러나 일반적으로 세리아는 고온에서 열적 안정성이 떨어지기 때문에 금속이온을 도핑시켜 열적 안정성을 향상시켜 사용한다. 따라서 본 연구에서는 Zr 이온을 세리아 분말에 도핑시켰고, 도핑으로 인해 입자크기가 감소하면서 비 표면적 증가로 인해 그 특성은 더욱 향상되었다. 그리고 본 연구에서는 세리아 및 Zr 이온이 도핑된 세리아를 나노 크기로 합성하기 위해 수열반응법을 이용하여 합성하였다. 수열합성 조건은 pH = 11, 반응온도는 $200^{\circ}C$에서 6시간 동안 합성하였다. 수열합성법을 이용하여 합성된 세리아 및 Zr 도핑 $CeO_2$ 나노 분말의 평균 입자 크기는 약 20 nm 이하였다. 합성된 세리아 나노분말의 비표면적은 $52.03m^2/g$, Zr 이온이 도핑된 $CeO_2$ 분말의 비 표면적 $132.27m^2/g$이었다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2001년도 춘계학술강연 및 발표대회
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• pp.25-25
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• 2001

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2000년도 춘계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.21-22
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• 2000