• Journal of Powder Materials
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• v.11 no.3
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• pp.247-252
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• 2004

Recently, it has been found that mechanical alloying (MA) facilitates the nanocomposites formation of metal-metal oxide systems through solid-state reduction during ball milling. In this work, we studied the MA effect of Fe$_{3}$O$_{4}$-M (M = Al, Ti) systems, where pure metals are used as reducing agents. It is found that composite powders in which $Al_{2}$O$_{3}$ and TiO$_{2}$ are dispersed in $\alpha$-Fe matrix with nano-sized grains are obtained by mechanical alloying of Fe$_{3}$O$_{4}$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the large negative heat associated with the chemical reduction of magnetite by aluminum is responsible for the shorter MA time for composite powder formation in Fe$_{3}$O$_{4}$-Al system. X-ray diffraction results show that the reduction of magnetite by Al and Ti if a relatively simple reaction, involving one intermediate phase of FeAl$_{2}$O$_{4}$ or Fe$_{3}$Ti$_{3}$O$_{10}$. The average grain size of $\alpha$-Fe in Fe-TiO$_{2}$ composite powders is in the range of 30 nm. From magnetic measurement, we can also obtain indirect information about the details of the solid-state reduction process during MA.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.4
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• pp.552-557
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• 1996

Microstructural development of $Si_3N_4$/20 vol% SiC nanocomposites doped 2 wt% $Al_2O_3$ and 6 wt% $Y_2O_3$ as sintering additives were analyzed by sintering interruption. Density of samples was significantly increased between $1500^{\circ}C$ and $1700^{\circ}C$, and near full density was achieved at $1800^{\circ}C$. Transformation rate from $\alpha-Si_3N_4$ to $\betha-Si_3N_4$ was increased at $1700^{\circ}C$ and $1800^{\circ}C$, and then elongated matrix grains were appeared. Small size SiC particles had suppressive effect on densification rate and transformation of $Si_3N_4$ phase.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.04a
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• pp.63-63
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• 2006

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.6
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• pp.309-314
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• 2003

A spark plasma sintering technique has been used for the fabrication of $Al_2O_3$-SiC nanocomposites at the low temperature of $1100^{\circ}C$∼$1500^{\circ}C$. The sintered $Al_2O_3$-SiC composites shows very homogeneous microstructure without any particular abnormal grain growth, indicating that the addition of nano-sized SiC particles is very effective to control grain growth and to induce the residual stress in the $Al_2O_3$ matrix, resulting in the intragranular fracture. These SiC particles are present in the grain boundaries and also intragrain, depending on the sintering condition, and improve remarkably the mechanical properties of $Al_2O_3$-SiC composite through the mechanisms of strengthening and toughening induced by crack diffraction and crack bridging.

• Korean Journal of Materials Research
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• v.11 no.11
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• pp.986-990
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• 2001

An optimum route to fabricate the $A1_2O_3/Fe-Ni$ alloy nanocomposites with sound microstructure and enhanced mechanical properties as well as magnetism was investigated. To prepare homogeneous nanocomposite powders of Fe-Ni alloy and $Al_2O_3$, the solution-chemistry routes using $Al_2O_3 \; Ni(NO_3)_2{\cdot}6H_2O$ and $Fe(NO_3)_3{\cdot}9H_2O$ powders were applied. Microstructural observation of the powder mixture revealed that the Fe-Ni alloy particles of about 20 nm in size were homogeneously surrounded $A1_2O_3$, forming nanocomposite powder. The hot-pressed composite showed improved fracture toughness and magnetic response. These results suggest that the synergy materials with an improved mechanical properties and excellent functionality can be fabricated by controlled powder preparation and consolidation processing.

• Korean Journal of Materials Research
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• v.14 no.10
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• pp.696-700
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• 2004

The reduction behavior of $Al_{2}O_3/CuO$ powder mixtures, prepared from $Al_{2}O_3/CuO$ or $Al_{2}O_3/Cu-nitrate$, was investigated by using thermogravimetry and hygrometry. The powder characteristics were examined by BET, XRD and TEM. Also, the influence of powder characteristics on the microstructure and properties of hot-pressed composites was analyzed. The formation mechanism of nano-sized Cu dispersions was explained based on the powder characteristics and reduction kinetics of oxide powders. In addition, the dependence of the microstructure and mechanical properties of hot-pressed composites on powder characteristics is discussed in terms of the initial size and distribution of Cu particles. The practical implication of these results is that an optimum processing condition for the design of homogeneous microstructure and required properties can be established.

• Journal of Surface Science and Engineering
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• v.35 no.3
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• pp.158-164
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• 2002

Nanocomposites consisting of a nanocrystalline brass matrix (grain size ; 20-100nm) with sub-micron sized Al2O3 particles (60-200nm) were prepared by pulsed current electrodeposition. The microhardness of the nanocomposite with a grain size of 90-100nm was approximately 1.7 times higher than that of a comparable electrodeposit with no particles. However, significant variations in microhardness were not observed between the nanocomposites with grain sizes of 20 nm and the comparable electrodeposit.

• Journal of Powder Materials
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• v.7 no.4
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• pp.237-243
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• 2000

The property and performance of the $Al_2O_3/Ni$ nanocomposites have been known to strongly depend on the structural feature of Ni nanodispersoids which affects considerably the structure of matrix. Such nanodispersoids undergo structural evolution in the process of consolidation. Thus, it is very important to understand the microstructural development of Ni nanodispersoids depending on the structure change of the matrix by consolidation. The present investigation has focused on the growth mechanism of Ni nanodispersoids in the initial stage of sintering. $Al_2O_3/Ni$ powder mixtures were prepared by wet ball milling and hydrogen reduction of $Al_2O_3$ and Ni oxide powders. Microstructural development and the growth mechanism of Ni dispersion during isothermal sintering were investigated depending on the porosity and structure of powder compacts. The growth mechanism of Ni was discussed based upon the reported kinetic mechanisms. It is found that the growth mechanism is closely related to the structural change of the compacts that affect material transport for coarsening. The result revealed that with decreasing porosity by consolidation the growth mechanism of Ni nanoparticles is changed from the migration-coalescence process to the interparticle transport mechanism.

• Advances in materials Research
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• v.1 no.1
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• pp.93-107
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• 2012

Epoxy resin is widely used in high voltage apparatus as insulation. Fillers are often added to epoxy resin to enhance its mechanical, thermal and chemical properties. The addition of fillers can deteriorate electrical performance. With the new development in nanotechnology, it has been widely anticipated that the combination of nanoparticles with traditional resin systems may create nanocomposite materials with enhanced electrical, thermal and mechanical properties. In the present paper we have carried out a comparative study on dielectric properties, space charge and dielectric breakdown behavior of epoxy resin/nanocomposites with nano-fillers of $SiO_2$ and $Al_2O_3$. The epoxy resin (LY556), commonly used in power apparatus was used to investigate the dielectric behavior of epoxy resin/nanocomposites with different filler concentrations. The epoxy resin/nanocomposite thin film samples were prepared and tests were carried out to measure their dielectric permittivity and tan delta value in a frequency range of 1 Hz - 1 MHz. The space charge behaviors were also observed by using the pulse electroacoustic (PEA) technique. In addition, traditional epoxy resin/microcomposites were also prepared and tested and the test results were compared with those obtained from epoxy resin/nanocomposites.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1141-1142
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• 2015

실리콘 고무는 옥외용 폴리머 애자 또는 부싱 등에 주로 사용되고 있으며, 이에 대한 연구가 많이 진행되어 지고 있다. 최근에는 나노 기술이 발달함에 따라 전기 재료에 나노 사이즈의 필러를 첨가하여 재료의 특정 특성들을 향상시키는 연구들이 진행되어 지고 있다. 본 논문에서는 전기적인 성능을 향상시키고자 나노 사이즈의 $Al_2O_3$를 첨가한 상온 경화형 실리콘 고무에 대한 연구를 진행하였으며, DC 전계와 오염 상황 하에서 연면 파괴 강도를 측정하였으며, 접촉각과 표면 저향률을 측정하였다. 실험 결과, 필러 함량이 증가할수록 연면 절연 파괴 강도와 표면 저항률은 증가하였으며 접촉각은 감소하였다. 또한, 일정 함량 이상에서는 연면 절연 파괴 강도와 표면 저항율이 감소하는 것으로 나타났다.