• Proceedings of the Korean Magnestics Society Conference
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• 2012.05a
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• pp.99-100
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• 2012

• Proceedings of the Korean Magnestics Society Conference
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• 2016.05a
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• pp.151-152
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• 2016

• Journal of the Korean Magnetics Society
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• v.3 no.1
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• pp.34-40
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• 1993

Nylon 6 based magnetic pellets for injection molding were produced using plasma arc melt-spun $Nd_{10.5}Fe_{79}Co_{2}Zr_{1.5}B_{7}$ powders. Two sorts of bonded magnets made of two different sizes of particles ($38~75\;\mu\textrm{m}$ and $75~150\;\mu\textrm{m}$) were prepared to determine critical volume fraction of magnet powders, and the magnetic prop erties of the magnets were discussed as a function of density. For the nylon fi based Nd-Fe-Co-Zr-B pellets made of $38~75\;\mu\textrm{m}$ particles, the critical volume fraction of powders 0.7 was obtained with the pellet density which is 90% of theoretical density while the magnets of $75~150\;\mu\textrm{m}$ showed the density of 87% of the theoretical value with the same volume fraction. The nylon (i magnets with the addition of 0.5 wt. % silicon oil only exhibited the best magnetic properties to have $_{i}H_{c}=8.8\;kOe,\;B_{r}=5.1\;kG$ and $(BH)_{max}=5.2\;MGOe$ which are of world class. An empirical relationship in predicting the magnet density with a known fraction ($V_s$) of loading powders was obtained such as ${\rho}(g/cm^{3})=1.1+K.V_{s}$ where the K ranges over 5.3~5.6 be ing dependent upon the particle size loaded.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.4
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• pp.292-296
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• 2000

Mechenochemical reaction by planetary type ball mill is applied to prepare $Sm_2$$Fe_{17}$$N_{x}$ permanent magnet powders. Starting from pure samarium and iron powders, the formation process of hard magnetic $Sm_2$$Fe_{17}$$N_{x}$ phase by ball milling and a subsequent solid state reaction were studied. At as-milled stage powders were found to consist of amorphous Sm-Fe and $\alpha$-Fe phases in all composition of $Sm_2$$Fe_{100-x}$(x = 11, 13, 15). The dependence of starting composition of elemental powder on the formation of Sm-Fe intermetallic compound was investigated by heat treatment of as-milled powders. When Sm concentration was 15 at%, heat-treated powder consists of mostly $Sm_2$$Fe_{17}$$N_{x}$single phase. For synthesizing of hard magnetic $Sm_2$$Fe_{17}$$N_{x}$ compound, additional nitriding treatment was carried out under $N_2$gas atmosphere at $450^{\circ}C$. The increase in the coercivity and remanence was parallel to the nitrogen content which increased drastically at first and then gradually as the nitriding time was extended. The ball-milled Sm-Fe-N powders were expected to be prospective materials for synthesizing of permanent magnet with high performance.

• Korean Journal of Materials Research
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• v.11 no.7
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• pp.609-614
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• 2001

This study was carried out to obtain a basic data on the production of the Nd-Fe-B system rare earth anisotropic bonded magnet by R-D & HDDR process. The reduction reaction of Nd$_2$O$_3$by metallic Ca and the diffusion reaction of Nd into Fe-B alloy powder were investigated for the production the Nd-Fe-B alloy powder. We concluded that a proper quantity of metallic Ca was about 1.3 times of theoretical equivalent from the yields of Nd and B after the R-D reaction at 100$0^{\circ}C$ for 1h. In the XRD analysis the diffusion reaction of Nd into the center of Fe-B alloy powder for the completed homogenization was required through about 45min at 110$0^{\circ}C$ for the R-D reaction, and also the maximum efficiency on the yield of Nd was obtained with such a condition. Residual Ca and oxygen contents of the final powder sample after washing were detected in 0.17wt% and 0.42wt% by ICP and oxygen analyzer, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.253-254
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• 2006

초미세립 복합상 영구자석은 연 경자성상의 크기와 분포에 큰 영향을 받는 자성재료이다. 또한, 결정립간 교환상호작용력은 초미세립 복합상 영구자석의 잔류자속밀도에 큰 영향을 미친다. 이에 $Nd_8Fe_{86-x}Nb_xB_6$(x=0, 1, 2, 3) 조성으로 급냉자성 분말을 제조하고, 열처리 후 자기특성을 평가하였다. Nb 첨가에 따른 $Nd_2Fe_{14}B$ 상과 $\alpha$-Fe 상과의 교환상호작용력을 Henkel(${\delta}M$) plot을 통해 평가하고, 각 상의 크기와 분포를 조사하여 자기특성 변화를 합리화하였다. 본 연구에서 얻은 최대 자기특성은 $B_r$ = 9.791 kG, $_iH_c$ = 5.565 kOe, 그리고 $(BH)_{max}$ = 14.61 MGOe였고, Nb를 첨가함으로서 보자력이 증가하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.93.1-93.1
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• 2012

세라믹 고온초전도체는 에너지 저장장치의 핵심소재로 사용된다. 초전도 플라이휠 에너지 저장장치(Superconductor flywheel energy storage system)는 전기 에너지를 운동 에너지로 변환하여 저장하는 친환경, 고효율 에너지 저장장치이다. 에너지를 최소화하는데 사용되는 초전도 베어링은 고온초전도체와 영구자석으로 구성된다. 베어링에는 희토류계 초전도 물질(RE-Ba-Cu-O, RE:Rare-earth elements)가 사용된다. 베어링의 효율은 영구자석의 자력크기, 초전도체의 자기부상력과 포획자력에 비례한다. 에너지 저장효율을 높이려면 고온 초전도체의 임계전류밀도(초전도체 내부에 흘릴 수 있는 전기량)를 높이고, 초전도 결정립의 크기를 키워야 한다. 결정크기를 키우는 공정으로 종자결정성장법(Seed growth process)이 사용된다. 초전도체 제조공정은 분말의 성형, incongruent melting을 포함하는 부분 용융, 액상에서의 입성장, 포정반응을 통한 초전도 결정의 성장과정을 포함한다. 본 발표에서는 초전도 에너지 저장장치의 기본 원리, 초전도 베어링의 구성, 베어링용 초전도체의 제조방법과 특성(자기부상력과 포획자력) 평가기술, 차세대 에너지 저장장치로서의 초전도 플라이휠 에너지 저장장치의 전망에 대해 요약하였다.

• Polymer(Korea)
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• v.25 no.2
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• pp.240-245
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• 2001

The effect of additives on the orientation of magnetic Sr-ferrite powders has been studied during powder injection molding under applied magnetic field for fabricating multi-pole anisotropic sintered Sr-ferrite magnets. The orientation of the Sr-ferrite powders depends sensitively on the fluidity of powder-binder mixture, related to the binder additives and the injection molding temperature, and the magnetic field intensity. The orientation of Sr-ferrite powders is good for the compacts with stearic acid added in the binder system of paraffin wax/carnauba wax/HDPE, but it is poor for the compacts with silane coupling agent added. The orientation of Sr-ferrites higher than 80% is achieved at the following useful conditions; apparent viscosity lower than 2500 poise in 1000 sec$^{-1}$ shear rate and applied magnetic field higher than 4 kOe.

• Journal of Powder Materials
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• v.26 no.2
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• pp.146-155
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• 2019

Rare earth magnets are the strongest type of permanent magnets and are integral to the high tech industry, particularly in clean energies, such as electric vehicle motors and wind turbine generators. However, the cost of rare earth materials and the imbalance in supply and demand still remain big problems to solve for permanent magnet related industries. Thus, a magnet with abundant elements and moderate magnetic performance is required to replace rare-earth magnets. Recently, $a^{{\prime}{\prime}}-Fe_{16}N_2$ has attracted considerable attention as a promising candidate for next-generation non-rare-earth permanent magnets due to its gigantic magnetization (3.23 T). Also, metastable $a^{{\prime}{\prime}}-Fe_{16}N_2$ exhibits high tetragonality (c/a = 1.1) by interstitial introduction of N atoms, leading to a high magnetocrystalline anisotropy constant ($K_1=1.0MJ/m^3$). In addition, Fe has a large amount of reserves on the Earth compared to other magnetic materials, leading to low cost of raw materials and manufacturing for industrial production. In this paper, we review the synthetic methods of metastable $a^{{\prime}{\prime}}-Fe_{16}N_2$ with film, powder and bulk form and discuss the approaches to enhance magnetocrystalline anisotropy of $a^{{\prime}{\prime}}-Fe_{16}N_2$. Future research prospects are also offered with patent trends observed thus far.

• Journal of the Korean Magnetics Society
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• v.8 no.5
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• pp.275-281
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• 1998

Effects of coupling agents on the rheological and magnetic properties of plastic ferrite magnets were investigated. Magnetic powder used was Sr-ferrite, and binder used was polypropylene (PP), and coupling agents used were ${\gamma}$-methacryloxypropyl trimethoxy silane (A174) and isopropyl triisostearoyl titanate (TTS). It was found that the addition of coupling agents to the PP/ferrite system reduced the melt viscosity and increased the magnetic properties considerably, and the treatment with TTS showed greater effect than A174 did. By comparison with that of the untreated one, the apparent viscosities of the mixtures treated with A174 and TTS decreased 23 % and 50%, respectively, at the shear rate of $1280\; sec^{-1}$ . Untreated plastic magnets showed remanent flux density $(B_r)$ of 1.89 kG and maximum energy energy product $(BH_{max})$ of 0.84 MGOe, and A174 treated magnets showed of Br 2.25 Kg and $BH_{max}$ of 1.23 MGOe. TTS treated magnets showed $B_r$ of 2.35 kG and $BH_{max}$ of 1.33 MGOe.