• Journal of Powder Materials
• /
• v.10 no.5
• /
• pp.337-343
• /
• 2003

Nanostructured Cu-$Al_2O_3$ composite powders were synthesized by thermochemical process. The synthesis procedures are 1) preparation of precursor powder by spray drying of solution made from water-soluble copper and aluminum nitrates, 2) air heat treatments to evaporate volatile components in the precursor powder and synthesis of nano-structured CuO + $Al_2O_3$, and 3) CuO reduction by hydrogen into pure Cu. The suggested procedures stimulated the formation of the gamma-$Al_2O_3$, and different alumina formation behaviors appeared with various heat treating temperatures. The mean particle size of the final Cu/$Al_2O_3$ composite powders produced was 20 nm, and the electrical conductivity and hardness in the hot-extruded bulk were competitive with Cu/$Al_2O_3$ composite by the conventional internal oxidation process.

• Journal of Powder Materials
• /
• v.9 no.5
• /
• pp.322-328
• /
• 2002

Fe-Co nanocomposite powders with different composition were prepared by chemical vapor condensation (CVC) process and their characterizations were studied by means of X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer. The particles having the mean size of 5~25 nm consisted of metallic cores and oxide shells. The Co contents and particle size increased with increasing the carrier gas flow rate of Co precursor. The saturation magnetization and coercivity increased with increasing Co content. and the saturation magnetization maximized at the 40 wt.%Co. The Fe-Co nanocomposite powder oxidized at $400^{\circ}C$ showed the maximum coercivity of 1739 Oe.

• Journal of Powder Materials
• /
• v.7 no.2
• /
• pp.93-101
• /
• 2000

In order to clarify the enhanced sintering behavior of nanostructured(NS) W-Cu powder prepared by mechaincal alloying, the sintering behavior during heating stage was analysed by a dilatometry with various heating rates. The sintering of NS W-Cu powders was characterized by the densification of two stages, having two peaks in shrinkage rate curves. The temperature at which the first peak appear was much lower than Cu melting point, and dependent on heating rate. On the basis of the shrinkage rate curves and the microstructural observation, the coupling effect of nanocrystalline W-grain growth and the liquid-like behavior of Cu phase was suggested as a possible mechanism for the enhanced sintering of NS W-Cu powder in the state.

• Journal of Powder Materials
• /
• v.9 no.4
• /
• pp.273-279
• /
• 2002

In this study, the WC-10 wt.%Co nanopowders doped by grain growth inhibiter were produced by three different methods based on the spray conversion process. Agglomerated powders with homeogenous distribution of alloying elements and with internal particles of about 100-200 nm in diameter were synthesized. The microstructural changes and sintering behavior of hardmetal compacts were compared with doping method and sintering conditions. The microstructure of hardmetals was very sensitive to doping methods of inhibitor. Nanostructured WC-Co hardmetal powder compacts containing TaC/VC doped by chemical method instead of ball-milling shown superior sintering densification, and the microstructure maintained ultrafine scale with rounded WC particles.

• Resources Recycling
• /
• v.16 no.1 s.75
• /
• pp.28-36
• /
• 2007

Nano-sized ITO powders with the average particle size below 50 nm were synthesized from complex acid solution dissolved the ITO target into hydrochloric acid by a spray pyrolysis process, and the influences of reaction factors as reaction temperature and concentration of raw material solution were investigated. As the reaction temperature increases from 800 to $1000^{\circ}C$, the average particle size of the ITO powder increases from 40 nm to 100 nm, the microstructure gradually becomes solid, individual particles independently appear with the shape of polygon, the particle size distribution becomes increasingly irregular, the XRD peak intensity gradually increases and the specific surface area decreases. As the concentration of the raw material solution increases from 50g/l to 400g/l, the average particle size of ITO powder gradually increases, yet the particle size distribution appears more irregular. When the concentration is at 50 g/l, the average particle size of ITO powder is below 30 nm and the particle size distribution appears comparatively uniform. Nevertheless, when the concentration reaches 400 g/l, which is close to e saturated concentration, the particle size distribution appears extremely irregular, and the particles with the size ranging from 20 nm to 100 nm coexist. Along with the concentration rise, the XRD peak intensity gradually increases, yet the specific surface area decreases.

• Journal of the Korean Magnetics Society
• /
• v.21 no.2
• /
• pp.77-82
• /
• 2011

The use of soft magnetic materials have been increasing in the various industrial fields according to the increasing demand for high performance, automatic, miniaturing equipments in the recent our life. In this study, we investigated the effect of factors on the core loss and magnetic properties of electrical steel and soft magnetic composites. Furthermore, we reviewed the major efforts to reduce the core loss and improve the soft magnetic properties in the two main soft magnetic materials. Domain purification which results from reduced density of defects in cleaner electrical steels is combined with large grains to reduce hysteresis loss. The reduced thickness and the high electrical conductivity reduce the eddy current component of loss. Furthermore, the coating applied to the surface of electrical steel and texture control lead to improve high permeability and low core loss. There is an increasing interest in soft magnetic composite materials because of the demand for miniaturization of cores for power electronic applications. The SMC materials have a broad range of potential applications due to the possibility of true 3-D electromagnetic design and higher frequency operation. Grain size, sintering temperature, and the degree of porosity need to be carefully controlled in order to optimize structure-sensitive properties such as maximum permeability and low coercive force. The insulating coating on the powder particles in SMCs eliminates particle-to-particle eddy current paths hence minimizing eddy current losses, but it reduces the permeability and to a small extent the saturation magnetization. The combination of new chemical composition with optimum powder manufacturing processes will be able to result in improving the magnetic properties in soft magnetic composite materials, too.

• Composites Research
• /
• v.28 no.4
• /
• pp.226-231
• /
• 2015

Various characteristics(thermal expansion, microstructure, etc.) and mechanical properties of CNT-aluminum nano composites manufactured by volume production system were evaluated. Also, formability and durability were evaluated for potential applications in automotive parts, via compared with high-elasticity material (A390) and the current commercial product. As a result, this composite has excellent mechanical properties and formability, therefore, to verity its potential for application as light and high strength materials in automobile part.

• Proceedings of the KWS Conference
• /
• v.43
• /
• pp.109-111
• /
• 2004

20 vol.$\%$ SiC를 포함한 두 층간의 $Si_{3}N_{4}/SiC$ 나노 복합재료는$\alpha$ $-Si_3N_4$,13 nm 크기의 나노탄소 분말 그리고 $5\;wt$\%\;Y_2O_3$의 분말로 두 단계 소결을 통하여 제작된다. $Si_3N_4$ 입계 사이의 결합은 소결 후 변하지 않고 남은 compact와 $51\~62\%$의 기공으로 얻어진 표면적 사이의 반응에 의해 생성된다. 이 연구에서는 Ti 합금을 SiC 층에 브레이징을 이용하여 제작하고 기계적 특성을 연구하였다. 다양한 변형율과 결합물의 강도, 변형율 증가에 따른 층간 변화를 연구하였다. 층간 파괴 형태는 금속과 브레이징 합금 사이의 파괴, 세라믹과 브레이징 합금 사이의 파괴, 그리고 세라믹 내부에서의 파괴를 보였다.

• Journal of the Society of Cosmetic Scientists of Korea
• /
• v.29 no.1
• /
• pp.169-184
• /
• 2003

비타민 C(L-ascorbic acid)는 강한 항산화성, 피부에 대한 높은 안전성으로 인해 피부의 노화방지, 미백, 주름 개선 등의 기능성 화장품 원료로써 많은 관심이 있는 물질이지만, 화학적으로 매우 불안정하여 쉽게 산화, 분해되므로 화장품 제형으로 포함시키는데 곤란한 문제가 있다. 본 연구에서는 비타민 C 의 안정성에 대한 단점을 보완하기 위하여 생체 및 피부 친화성이 우수한 무기물을 사용하여 비타민 C 를 캡슐화(encapsulation)한 분말상의 유-무기 복합물질 Vitabrid-C 를 합성하고, 이를 함유하는 피부 미백용 트윈케익 파우더를 개발하였다. 우선 Vitabrid-C 는 수용액상에서 비타민 C 를 수화된 산화아연(ZnO)으로 1 차 캡슐화하여 나노입자를 형성시키고, 그 표면을 실리카(silica)나노 입자로 한번 더 코팅하여 표면의 껍질이 다공특성을 갖는 분말을 제조함으로써 완성하였다. 이렇게 제조된 Vitabrid-C는 순수 비타민 C 에 비해 우수한 안정성을 보였으며, 캡슐 내 비타민 C 가 서서히 방출되는 서방특성을 발휘하였다. 또한 Vitabrid-C는 입자의 크기가 미세하고 균일하여 트윈케익 처방에 용이하게 적용할 수 있었다. Vitabrid-C와 순수 비타민 C의 생화학적 동등성에 대한 평가는 tyrosinase 억제능(L-DOPA oxidase 억제) 및 DPPH항산화 실험을 통하여 비교하였다. 트윈 케익 처방에 적용된 Vitabrid-C 에서 비타민 C 의 피부 투과경향을 Franz diffusion cell 법을 이용하여 확인하였다 또한 Vitabrid-C가 포함된 트윈케익을 건강한 피부를 가진 25 세 이상되는 여성의 전박에 색소 침착을 유도한 후 피부색 개선 효과 평가를 통해 임상적 효능을 평가하였다.

• Journal of Powder Materials
• /
• v.12 no.2 s.49
• /
• pp.122-130
• /
• 2005

Layered silicate was synthesized at hydrothermal condition from silica adding to various materials. Nano-clay was synthesized by intercaltion of various amine compounds into synthetic layered silicate. The products were analysed by XRD, SEM, and FT-IR in order to examine the condition of synthesis and intercalation. From the results, it was confirmed that kaolinite was synthesized from precipitated silica and gibbsite at $220^{\circ}C$ during 10 days, and hetorite was synthesized from silica sol at $100^{\circ}C$ during 48 h. Na-Magadiite was synthesized from silica gel at $150^{\circ}C$ during 72 h, and Na-kenyaite was synthesized from silica gel at $160^{\circ}C$ during 84 h. Nano-clay was prepared using synthetic layered silicate intercalated with various amine compounds. Kenyaite was easily intercalated by various organic compounds, and has the highest basal-spacing value among other layered silicates. Basal-spacing was changed according to the length of alkyl chain of amine comopounds. Polymer can be easily intercalated by dispersion with large space of interlayer. Finally, epoxy/nano-clay nanocomposite can be easily prepared.