• Journal of the Korean Magnetics Society
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• v.12 no.2
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• pp.57-63
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• 2002

In order to increase the magnetic properties of a Nd-Fe-B sintered magnet, the general factors including particle size and its distribution, volume fraction of Nd$_2$Fe$_{14}$B phase, degree of alignment of Nd$_2$Fe$_{14}$B grain, oxygen content and grain size etc. should be optimized by controlling the composition of Nd-Fe-B alloy as well as the manufacturing process. In this study, fabrication of the Nd-Fe-B sintered magnet was carried out in a laboratory scale by controlling the composition of Nd-Fe-B alloy and the manufacturing process. The optimum milling condition was found by investigating the milling media, milling time and ball size. The addition of FeGa was effective to increase the coercivity of the Nd-Fe-B sintered magnet. A remanence of 14.4 kG, a coercivity of 9.4 kOe and a maximum energy product of 47 MGOe were obtained from the sintered magnet.

• Journal of the Korean Magnetics Society
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• v.2 no.1
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• pp.37-43
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• 1992

Minor phases in cast and hot-pressed R(R=Pr, Nd)-Fe-B magnet were investigated through thermomagnetic analysis. The relationship between minor phases and coercivities of R-Fe-B magnets was studied. ${\alpha}-Fe$ and $Nd_{2}Fe_{17}$ were precipitated in as-cast Pr-Fe-B and Nd-Fe-B alloys respectively. These phases were considered to deteriorate the magnetic properties of R-Fe-B magnets. During the heat treatment, ${\alpha}-Fe$ and $Nd_{2}Fe_{17}$ were annihilated and the magnetic properties of cast R-Fe-B magnet were improved. Hot-pressed Nd-Fe-B magnet showed better thermal stability than sintered magnet.

• Journal of the Korean Magnetics Society
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• v.12 no.3
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• pp.88-93
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• 2002

Rapidly solidified NdFeB powders were mixed with fine powders of pure metal elements before CA-press employed to obtain a fully dense isotropic precursor. Subsequently, the precursor was deformed by CA-deformation to obtain an anisotropic magnet. The CA-deformed anisotropic NdFeB magnets with 0.3 wt.% Zn or Sn exhibited the coercivities about 80% higher (11.4. and 11.2 kOe, respectively) than that (6.4 kOe) of the additive-free magnet.

• Journal of the Korean Magnetics Society
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• v.22 no.6
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• pp.221-227
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• 2012

High performance permanent magnets have become the subject of considerable attention because of the potential applications in the traction motors of hybrid and electric vehicles and wind generators. Nd-Fe-B magnets have attracted considerable interest due to a large maximum energy product. However, Nd-Fe-B magnet cannot be used in high temperature (${\sim}200^{\circ}C$) applications due to the thermal degradation of coercivity. Therefore, the development of high coercivity Nd-Fe-B permanent magnet is a challenging issue. In case of high coercivity Nd-Fe-B permanent magnet, an increment in the intrinsic coercivity can be easily achieved by substituting Nd atoms with Dy or Tb atoms. However, these heavy rare-earth elements are known to cause a decrease in remanence due to the antiferromagnetic coupling between Dy and Fe atoms. In addition, Dy is relatively expensive and being limited in quantity. Hence, a new technology that can increase the coercivity of Nd-Fe-B sintered magnet using only a small amount, or even, no amount of heavy rare-earth elements is being investigated. This article describes the research trend in reducing the heavy rare-earth elements in Nd-Fe-B magnets.

• Journal of the Korean Magnetics Society
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• v.11 no.6
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• pp.250-255
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• 2001

Magnetic properties of the isotropic and anisotropic NdFeB magnets obtained by the Current-Applied Pressure-Assisted (CAPA) process from a melt-spun NdFeB powder were investigated using B-H loop analyser. The coercivity of the isotropic magnets is sensitive to the applied pressure in the CA-pressing and increases with increasing the pressure. The remanence of the anisotropic magnet increases with increasing the degree of deformation, and it results in the increase of a maximum energy Product. The best magnetic Properies of the isotropic and anistropic magnet are B$\sub$r/= 8.7 kG, $\sub$i/H$\sub$c/= 16.9 kOe, (BH)$\sub$max/= 16.5 and B$\sub$r/= 13.6 kG, $\sub$i/H$\sub$c/= 10.9 kOe, (BH)$\sub$max/= 44.2 MGOe, respectively.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.236-237
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• 2002

최근에 고도의 전자산업이 발전함에 따라 고성능의 회토류계 영구자석재료의 산업적 요구가 크게 증가함을 보여 왔다. 이는 자동차, 항공 산업뿐만 아니라 정보산업 및 전자산업에 이르기까지 폭넓게 적용되기 때문이다. Nd-Fe-B 영구자석이 1983년 최초로 발견되어진 이후로 Nd-Fe-B 자석의 연구와 개발에 많은 노력을 기울이고 있다. Nd$_2$Fe$_{14}$B 종류의 자석은 기존에는 일반적으로 분말야금 방법과 급냉방법으로 제작되었다. 그러나 두 방법 모두 소모적이고, 불필요한 에너지를 필요로 하며 원재료로써 고순도의 금속을 사용함으로써 생산단가가 증가되는 단점이 있다. (중략)

• Polymer(Korea)
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• v.26 no.1
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• pp.98-104
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• 2002

This study was investigated to fabricate the isotropic $Nd_2Fe_{14}B$/epoxy bonded magnets with high characteristics paroduced by compression molding. The magnetic characteristics of the bonded magnets were directly proportional to the density of the magnets and were enhanced by using raw $Nd_2Fe_{14}B$ magnetic powders, having the mean particle size of $200{\mu} m$.without additional milling process. The high characteristics of the bonded magnets were achieved at the following conditions: epoxy resin of 2.0 wt%, silane coupling agent of 0.8 wt%, curing agent of 0.7 wt% on the base of magnetic powders, and curing condition of $150^{\circ}C$/3 hrs. The bonded magnets at the optimum conditions indicated the high characteristics such as the density of 6.1 g/㎤, the remanent flux density of 7.1 kG, the maximum energy product of 9.7 MGOe, and the compressive strength of 17 kg/$mm^2$.

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.34-40
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• 2002

In order to improve the microstructure of the strip cast Nd-Fe-B alloys that are frequently used for production of high energy sintered magnets, influence of various strip casting conditions on the microstructure and phase formation and distribution were investigated. Nd-Fe-B strips consisting of microstructures suitable for preparation of high energy sintered magnets could be obtained when the wheel speed was below 5 m/s. The compositional limit that can avoid the crystallization of free iron in the as-cast state was estimated to be Nd$\_$14/Fe$\_$79/B$\_$7/. Regardless of the compositional variation, <001> preferred orientation of Nd$_2$Fe$\_$14/B normal to the strip surface was always occurred below 5 m/s, which would eventually enhance the grain alignment during pressing the powder under a magnetic field. While the coercivity of the strip cast alloys increased with the increase of the wheel speed, mainly due to the refinement of Nd$_2$Fe$\_$14/B grains, it decreased with the reduction of Nd content in the alloy composition as the formation of free iron increased.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.10a
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• pp.63-67
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• 1997

환원확산법은 저렴한 Nd 산화물을 환원제를 이용하여 환원시키고 환원된 Nd가 Fe, FeB와 확산하여 주상인 Nd$_2$Fe14B가 만들어지는 공정으로 환원제로 사용된 CaO나 미반응 Ca 및 잔존 산소함량을 조절하는데 어려움이 있어 아직까지는 상업되지 못하고 있는 실정이다. 본 연구에서는 환원확산법을 이용하여 Nd-Fe-B계 영구자석에 사용될 미세분말을 제조하고 그 자기적 특성을 관찰하였다.

• Resources Recycling
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• v.27 no.1
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• pp.38-44
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• 2018

A large amount of Nd-Fe-B magnet scraps are generated during magnet manufacture process. In this study, selective chlorination of the rare earth elements by hydrogen chloride gas which obtained from the pyrolysis of polyvinyl chloride (PVC) was investigated. In thermogravimetric analysis, drastic weight loss was occurred at about 500 K and 710 K. At the isothermal experiments, the weight loss reaches about 30% above 673 K. XRD patterns characterized that after each experiments, ${\alpha}$-Fe, Nd oxychloride, Nd chloride, and Fe chlorides were formed, and the leaching residues remain only ${\alpha}$-Fe. The yields of Nd, Dy, and Fe for the isothermal experiment were increased with temperature and peaked at 873 K. As PVC ratio increased, the yields of Nd, Dy and Fe were also increased.