• Title/Summary/Keyword: sintered magnet

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Synthesis of DyF3 paste and Magnetic Properties of GBDPed Nd-Fe-B Magnets (DyF3 paste 제조 및 이를 이용한 Nd-Fe-B 입계확산 자석의 특성 연구)

  • Jeon, Kwang-Won;Cha, Hee-Ryoung;Lee, Jung-Goo
    • Journal of Powder Materials
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    • v.23 no.6
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    • pp.437-441
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    • 2016
  • Recently, the grain boundary diffusion process (GBDP), involving heavy rare-earth elements such as Dy and Tb, has been widely used to enhance the coercivity of Nd-Fe-B permanent magnets. For example, a Dy compound is coated onto the surface of Nd-Fe-B sintered magnets, and then the magnets are heat treated. Subsequently, Dy diffuses into the grain boundaries of Nd-Fe-B magnets, forming Dy-Fe-B or Nd-Dy-Fe-B. The dip-coating process is also used widely instead of the GBDP. However, it is quite hard to control the thickness uniformity using dip coating. In this study, first, a $DyF_3$ paste is fabricated using $DyF_3$ powder. Subsequently, the fabricated $DyF_3$ paste is homogeneously coated onto the surface of a Nd-Fe-B sintered magnet. The magnet is then subjected to GBDP to enhance its coercivity. The weight ratio of binder and $DyF_3$ powder is controlled, and we find that the coercivity enhances with decreasing binder content. In addition, the maximum coercivity is obtained with the paste containing 70 wt% of $DyF_3$ powder.

Recycling of Sintered Nd-Fe-B Magnets Doped with PrNd Nanoparticles

  • Zhang, Xuefeng;Liu, Fei;Liu, Yanli;Ma, Qiang;Li, Yongfeng;Zhao, Qian;Wang, Gaofeng;Li, Zhubai
    • Journal of Magnetics
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    • v.20 no.2
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    • pp.97-102
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    • 2015
  • The waste of sintered Nd-Fe-B magnets was recycled using the method of dopingPrNd nanoparticles. The effect of PrNd nanoparticle doping on the magnetic properties of the regenerated magnets has been studied. As the content of the PrNd nanoparticles increases, the coercivity increases monotonically, whereas both the remanence and the maximum energy products reach the maximum values for 4 wt% PrNd doping. Microstructural observation reveals that the appropriate addition of PrNd nanoparticles improves the magnetic properties and refines the grain. Domain investigation shows that the self-pinning effect of the rare earth (Re)-rich phase is enhanced by PrNd nano-particle doping. Compared to the magnet with 4 wt% PrNd alloy prepared using the dual-alloy method, the regenerated magnet doped with the same number of PrNd nanoparticles exhibits better magnetic properties and a more homogeneous microstructure. Therefore, it is concluded that PrNd nanoparticle doping is an efficient method for recycling the leftover scraps of Nd-Fe-B magnets.

Magnetic Properties and Thermomagnetic Analysis of Cast and Hot-Pressed Pr, Nd-Fe-B Magnets (주조 및 열간압축된 Pr, Nd-Fe-B계 영구자석의 열자기 분석과 자기적 특성)

  • 김동엽;이동구;정원용
    • 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.

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The fabrication of bulk magnet stacked with HTS tapes for the magnetic levitation

  • Park, Insung;Kim, Gwantae;Kim, Kyeongdeok;Sim, Kideok;Ha, Hongsoo
    • Progress in Superconductivity and Cryogenics
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    • v.24 no.3
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    • pp.47-51
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    • 2022
  • With the innovative development of bio, pharmaceutical, and semiconductor technologies, it is essential to demand a next-generation transfer system that minimizes dust and vibrations generated during the manufacturing process. In order to develop dust-free and non-contact transfer systems, the high temperature superconductor (HTS) bulks have been applied as a magnet for levitation. However, sintered HTS bulk magnets are limited in their applications due to their relatively low critical current density (Jc) of several kA/cm2 and low mechanical properties as a ceramic material. In addition, during cooling to cryogenic temperatures repeatedly, cracks and damage may occur by thermal shock. On the other hand, the bulk magnets made by stacked HTS tapes have various advantages, such as relatively high mechanical properties by alternate stacking of the metal and ceramic layer, high magnetic levitation performance by using coated conductors with high Jc of several MA/cm2, consistent superconducting properties, miniaturization, light-weight, etc. In this study, we tried to fabricate HTS tapes stacked bulk magnets with 60 mm × 60 mm area and various numbers of HTS tape stacked layers for magnetic levitation. In order to examine the levitation forces of bulk magnets stacked with HTS tapes from 1 to 16 layers, specialized force measurement apparatus was made and adapted to measure the levitation force. By increasing the number of HTS tapes stacked layers, the levitation force of bulk magnet become larger. 16 HTS tapes stacked bulk magnets show promising levitation force of about 23.5 N, 6.538 kPa at 10 mm of levitated distance from NdFeB permanent magnet.

Effects of Injection Conditions on the Mechanical Properties of Nd-Fe-B Dielectromagnets

  • B.Slusarek;D.Bialo;J.Gromek;T.Kulesza
    • Journal of Magnetics
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    • v.4 no.2
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    • pp.52-54
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    • 1999
  • Injection molding is one of the methods to prepare dielectromagnets-permanent magnets made from hard magnetic powder (or from mixture of powders) bonded by dielectric materials. Magnetic properties of dielectromagnets are worse than those of sintered magnets made from the same hard magnetic powders, but this type of the permanent magnet has many advantages. One of them is simpler technology-easier in comparison to the technology of sintered magnets. The injection molded dielectromagnets do not need any final treatment. This technology permits to control magnetic, thermal and mechanical properties of dielectromagnets. The main chracteristics of dielectormagnets are magnetic properties, however mechanical properties have serious influence onto a range of their applications. The main factors shaping mechanical properties have serious influence onto a range of their applications. The main factors shaping mechanical properties of dielectromagnets are the kind and quantity of resin and the technology. The purpose of this investigateion was to find the correlation between infection conditions and the mechanical properties of dielectromagnets. Influence of two parameters of injection, temperature and pressure on mechanical and magnetic properties of dielectromagnets were not significantly changed. Increasing of pressure of injection also does not influence on mechanical properties of analysed samples, however increasing of temperature of injection significantly improved both compression and bending strength.

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Study on the Rigidity of the Solid-HDDR Treated Nd-Fe-B-type Materials

  • Kang, S.J.;Kwon, H.W.
    • Journal of Magnetics
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    • v.3 no.1
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    • pp.9-14
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    • 1998
  • A non-coercive cast Nd-Fe-B-type material can be easily converted into a coercive one by employing HDDR process. Applying the conventional HDDR process to the Nd-Fe-B-type material generally leads to a powder-like material. HDDR treated material in a solid form can, however, be realised if the process is properly modified (solid-HDDR). In the present study, the change of rigidity (compressive strength) of the Nd-Fe-B-type material during the solid-HDDR has been investigated using a homogeneous sintered magnet with composition $Nd_{13.8}Dy_{0.7}Fe_{78.25}Si_{0.15}Mn_{0.6}B_{6.5}.$ It has been found that the low strength of the hydrided material was improved by the subsequent disproportionation. The restoration of the strength was explained by the eutectoid-like disproportionation structure containing fine neodymium hydride rod embedded in tough iron matrix. The high strength of disproportionated material was reduced radically in earlier stage of recombination, and this wes explained by the reduction of the disproportionated phase. The reduced strength was, however, recovered by further recombination, and this was explained by the fact that as the recombination continues the recombined grains adhere together. The optimally HDDR processed material has a comparable or even higher strength with respect to the initial sintered material prior to the solid-HDDR. The present study suggested that the rigidity of Nd-Fe-B-type material could be retained even after the solid-HDDR.

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Coercivity Enhancement of Nd23Dy10Fe64TM2B1 Sintered Magnet by Convergent Heat Treatment (Convergent 열처리를 통한Nd23Dy10Fe64TM2B1 소결자석의 보자력 향상)

  • Kim, Hoon-Sup;Kim, Se-Hoon;Kim, Jin-Woo;Kim, Young-Do
    • Journal of Powder Materials
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    • v.17 no.1
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    • pp.1-6
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    • 2010
  • In this study, a convergent heat treatment was performed in certain temperature regions in order to control the microstructures of Nd-rich phases and to reduce thermal stress on grain boundaries which could be caused during expansion and shrinkage of Nd-rich and $Nd_2Fe_{14}B$ phases. The difference of thermal expansion coefficient between $Nd_2Fe_{14}B$ and Nd-rich phases is the mechanism for convergent heat treatment. The Nd-rich phases which were located in junctions could penetrate into the grain boundaries between $Nd_2Fe_{14}B$ phases due to the difference of thermal expansion coefficient. Through the convergent heat treatment, the microcracks that were observed in cyclic heat treatment were not observed and coercivity was increased to 34.05 kOe at 8 cycles.

Effect of Strip-cast Conditions on the Formation of Microstructures in Nd-Fe-B alloys (Strip-cast 조건이 Nd-Fe-B 합금의 미세조직 형성에 미치는 영향)

  • Lee, D.H.;Jang, T.S.;Kim, D.H.;Kim, Andrew S.
    • 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.

Separation of Neodymium from NdEeB Permanent Magnetic Scrap (NdFeB계 영구자석 스크랩으로부터 네오디뮴의 분리회수)

  • Yoon Ho-Sung;Kim Chul-Joo;Lee Jin-Yeung;Kim Sung-Don;Kim Joon-Soo;Lee Jae-Chun
    • Resources Recycling
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    • v.12 no.6
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    • pp.57-63
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    • 2003
  • In this study, the separation of neodymium was investigated from NdFeB permanent magnet scrap. Decomposition and leach-ing process of NdFeB permanent magnet scrap by oxidation roasting and sulfuric arid leaching were examined. Neodymium could be separated from iron by double salt precipitation using sodium sulfate. The optimum conditions established for decom-position and leaching are as follows: oxidation roasting temperature is $500^{\circ}C$ for sintered scrap and $700^{\circ}C$ for bonded scrap, concentration of sulfuric acid in leaching solution is 2.0 M, leaching temperature and time is $50^{\circ}C$ and 2 hrs, and pulp density is 15%. The leaching yield of neodymium and iron was 99.4% and 95.7% respectively. The optimum condition for separation of neodymium by double-salt precipitation was 2 equivalents of sodium sulfate and $50^{\circ}C$ The yield of neodymium was above 99.9%.