• 한국분말재료학회지
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• 제8권3호
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• pp.186-191
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• 2001

Several fabrication processes, corresponding nanostructural features and multifunctionality as well has been investigated for oxide ceramic based nanocomposites with metal nanodispersion (i.e., ceramic/metal nanocomposites). Transition metal (Ni, Co, etc) dispersed alumina and zirconia based nanocomposites have been synthesized by reducing and hot-press sintering of ceramic and metal oxide mixtures prepared by several method. Improved fracture strength (1.1 and 1.9 GPa for $Al_2O_3/Ni$ and $ZrO_2/Ni$ nanocomposites, respectively) of these composites have been achieved according to their nanostructures. In addition, ferromagnetic characteristic has been kept. The variation of magnetization with an applied stress has found to be more sensitive as smaller as the magnetic metal dispersion is. This result thus suggests the possibility of fracture and/or stress sensing of the composites by simple magnetic measurement.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.327-328
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• 2006

We have demonstrated that textured $Al_2O_3-mullite-SiC$ nanocomposites can be fabricated by slip casting followed by partial oxidation - reaction sintering of mixed suspensions of $Al_2O_3$ and SiC powders in a high magnetic field. The sintered density was changed by the degree of oxidation at 1200C and 1300C. The degree of orientation of alumina in the nanocomposite was examined on the basis of the X-ray diffraction patterns and scanning electron micrographs. It is confirmed that alumina-oriented nanocomposites were fabricated. The three-point bending strength at room temperature was observed for the nanocomposites.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.455-456
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• 2006

We have demonstrated that textured $Al_2O_3-mullite-SiC$ nanocomposites can be fabricated by slip casting followed by partial oxidation. reaction sintering of mixed suspensions of $Al_2O_3$ and SiC powders in a high magnetic field. The sintered density was changed by the degree of oxidation at 1200C and 1300C. The degree of orientation of alumina in the nanocomposite was examined on the basis of the X-ray diffraction patterns and scanning electron micrographs. It is confirmed that aluminaoriented nanocomposites were fabricated. The three-point bending strength at room temperature was observed for the nanocomposites.

• 한국자기학회지
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• 제20권6호
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• pp.216-221
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• 2010

본 연구에서는 dimethylacetamide(DMAc)와 toluen을 용매로 사용하여 만들어진 양친매성 urethan acrylate nonionomer(UAN) 선구고리를 기초로 하는 양친매성 고분자 망상구조 복합체에 철산화물을 주입시킨 나노복합체의 구조와 자기적성질 그리고 나노복합체에 존재하는 Fe 이온의 원자가 상태를 알아보기 위하여 전계방출주사전자현미경(FESEM)과 X-ray diffraction 그리고 Mossbauer spectrum을 측정하였다. 결과로부터 나노복합체 시료 내에 존재하는 모든 Fe이온은 $Fe^{3+}$의 상태로 존재하고 $Fe_2O_3$의 결정구조를 갖고 있음을 알 수 있으며, 시료 내에 철산화물 나노복합체가 형성되어 있음을 알 수 있었다. 그리고 urethan acrylate nonionomer(UAN) 선구 고리를 기초로 하는 양친매성 고분자 망상구조 복합체를 형성시키는 경우 용매로 DMAc를 이용하는 경우가 toluen을 이용한 경우 보다 더 미세한 나노구조를 형성함을 알 수 있으며, 시료들의 자기적 성질이 상온에서 상자성을 나타내는 것은 나노크기의 단일자구형성에 따른 초상자성효과에 의한 것임을 알 수 있었다.

• The Korean Journal of Ceramics
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• 제5권4호
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• pp.395-399
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• 1999

MgO/metal nanocomposite powder mixtures were prepared by solution chemical processes to obtain suitable structure for ceramic/metal nanocomposites. Nickel or cobalt nitrate, as a source of metal dispersion, was dissolved into alcohol and mixed with magnesia powder. After calcined in air, these powders were reduced by hydrogen. Densified nanocomposites were successively obtained by Pulse Electric Current Sintering (PECS) process. The dispersed metal partical size depended on temperature and time in calcination and reduction processes. The phase analyses in the synthesized powders as a functioni of temperature were tracked using a dynamic high temperature X-ray diffractioni (HTXRD) system. Phase and crystallite size analyses were done using X-ray diffractioni and TEM. The MgO/metal nanocomposites were successfully fabricated, and ferromagnetic responses with enhanced coercive force were also investigated for these composites.

• Journal of Magnetics
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• 제8권1호
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• pp.18-23
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• 2003

In our previous work, microstructure and magnetic properties of two-phase exchange-coupled $Sm_2Fe_{15}Ga_2C_{x}$/$\alpha$-Fe nanocomposites have been investigated by means of x-ray diffraction, transmission electron microscopy and magnetization measurement. It was found the exchange coupling between the magnetically hard phase $Sm_2Fe_{15}Ga_2C_{x}$ and the magnetically soft one ${\alpha}$-Fe results in an enhancement of the remanence. The sizes of crystallites of both phases are, however much larger than the Block domain-wall width of the magnetically hard phase. This microstructure gives rise to a concave demagnetization curve and consequently reduces the maximum energy Product. In order to improve their magnetic properties, a few Percent of Zr, which may be effective to refine the microstructure through rapid quenching, was introduced into the nanocomposites. The addition of Zr was found to improve the magnetic properties significantly, Under optimum heat-treatment conditions, the remanence, coercivity and maximum energy Product increase from 0.65 T, 0.48 T and 50 kJ/$m^{3}$ for the Zr-free sample to 0.72 T, 0.77 T and 71.6 kJ/$m^{3}$ for the 1 at.% Zr-containing one, respectively, The improvements of magnetic properties are due to the refinement of microstructure by the addition of Zr.

• Journal of Microbiology and Biotechnology
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• 제29권6호
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• pp.913-922
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• 2019

Magnetic $Ni_{0.7}Co_{0.3}Fe_2O_4$ nanoparticles that were prepared via the rapid combustion process were functionalized and modified to obtain magnetic $Ni_{0.7}Co_{0.3}Fe_2O_4@SiO_2-CHO$ nanocomposites, on which penicillin G acylase (PGA) was covalently immobilized. Selections of immobilization concentration and time of fixation were explored. Catalytic performance of immobilized PGA was characterized. The free PGA had greatest activity at pH 8.0 and $45^{\circ}C$ while immobilized PGA's activities peaked at pH 7.5 and $45^{\circ}C$. Immobilized PGA had better thermal stability than free PGA at the range of $30-50^{\circ}C$ for different time intervals. The activity of free PGA would be 0 and that of immobilized PGA still retained some activities at $60^{\circ}C$ after 2 h. $V_{max}$ and $K_m$ of immobilized PGA were 1.55 mol/min and 0.15 mol/l, respectively. Free PGA's $V_{max}$ and $K_m$ separately were 0.74 mol/min and 0.028 mol/l. Immobilized PGA displayed more than 50% activity after 10 successive cycles. We concluded that immobilized PGA with magnetic $Ni_{0.7}Co_{0.3}Fe_2O_4@SiO_2-CHO$ nanocomposites could become a novel example for the immobilization of other amidohydrolases.

• 한국분말재료학회지
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• 제15권4호
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• pp.320-330
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• 2008

On the base of experience in development of Magnetic Powder Composites, and particularly Soft Magnetic Composites, authors are trying to systematize classification and indicate possible development prospective of Magnetic Nanocomposites (MN) technology and their applications in electrical converters. Clear classification and systematization, at an early stage of any materials and technology development, are essential and lead for better understanding and communication between researchers and industry involved. This concern MN as well and it seems to be the right time to make it at present stage of their development. Presented proposal of classification distinguishes various types of MN by their magnetic properties and area of possible applications. It is not a close set of types, and can be extended due to increase of knowledge concern these nanocomposites.

• Journal of Magnetics
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• 제11권1호
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• pp.30-35
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• 2006

A thorough study about the influences of Mn substitution for Fe on the microstructure and magnetic characteristics of $Fe_{73.5-x}Mn-{x}Si_{13.5}B_{9}Nb_{3}Cu_1$ (x = 1, 3, 5) alloys prepared by the melt-spinning technique has been performed. Nanocomposites composed of nanoscale $(Fe,Mn)_{3}Si$ magnetic phase embedded in an amorphous matrix were obtained by annealing their amorphous alloys at $535^{\circ}C$ for 1 hour. The addition of Mn causes a slight increase in the mean grain size. The Curie temperatures of the initial amorphous phase and of the nanocrystals phase decreased, while the Curie temperature of the remaining amorphous phase remained nearly constant with increasing Mn content. Soft magnetic properties of the crystallized samples have been significantly improved by a proper thermal treatment. Accordingly, the giant magnetoimpedance effect is observed and ascribed to the increase of the magnetic permeability, and the decrease of the coercivity of the samples. The increased magnetic permeability is resulted from a decrease in the magnetocrystalline anisotropy and saturation magnetostriction.

• Carbon letters
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• 제24권
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• pp.103-110
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• 2017

Carbon-based magnetic nanostructures in several instances have resulted in improved physicochemical and catalytic properties when compared to multi-wall carbon nanotubes (MWCNTs) and magnetic nanoparticles. In this study, magnetic MWCNTs with a structure of $Ni_xZn_xFe_2O_4/MWCNT$ as peroxidase mimics were fabricated by the one-pot hydrothermal method. The structure, composition and morphology of the nanocomposites were characterized with X-ray diffraction (XRD), Fourier transform infrared spectroscopy and transmission electron microscopy. The magnetic properties were investigated with a vibrating sample magnetometer. The peroxidase-like catalytic activity of the nanocomposites was investigated by colorimetric and electrochemical tests with 3,3',5,5'-tetramethylbenzidine (TMB) and $H_2O_2$ as the substrates. The results show that the synthesis of the nanocomposites was successfully performed. XRD analysis confirmed the crystalline structures of the $Ni_xZn_xFe_2O_4/MWCNT$ nanohybrids and MWCNTs. The main peaks of the $Ni_xZn_xFe_2O_4/MWCNT$s crystals were presented. The $Ni_{0.25}Zn_{0.25}Fe_2O_4/MWCNT$ and $Ni_{0.5}Zn_{0.5}Fe_2O_4/MWCNT$ nanocatalysts showed nearly similar physicochemical properties, but the $Ni_{0.5}Zn_{0.5}Fe_2O_4/MWCNT$ nanocatalyst was more appropriate than the $Ni_{0.25}Zn_{0.25}Fe_2O_4/MWCNT$ nanocatalyst in terms of the magnetic properties and catalytic activity. The optimum peroxidase-like activity of the nanocatalysts was obtained at pH 3.0. The $Ni_{0.5}Zn_{0.5}Fe_2O_4/MWCNT$ nanocatalyst exhibited a good peroxidase-like activity. These magnetic nanocatalysts can be suitable candidates for future enzyme-based applications such as the detection of glucose and $H_2O_2$.