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Preparation of Highly Efficient Nd-Fe-B Magnetic Powders by Reduction/Diffusion Process

환원/확산 공정에 의한 고성능 Nd-Fe-B 자성분말의 제조

  • Kim, Dongsoo (Powder/Ceramics Division, Korea Institute of Materials Science) ;
  • Chen, Chunqiang (University of Science and Technology) ;
  • Baek, Younkyoung (Powder/Ceramics Division, Korea Institute of Materials Science) ;
  • Choi, Chuljin (Powder/Ceramics Division, Korea Institute of Materials Science)
  • 김동수 (한국기계연구원 부설 재료연구소, 분말/세라믹연구본부) ;
  • 진춘강 (과학기술연합대학원대학교) ;
  • 백연경 (한국기계연구원 부설 재료연구소, 분말/세라믹연구본부) ;
  • 최철진 (한국기계연구원 부설 재료연구소, 분말/세라믹연구본부)
  • Received : 2013.04.09
  • Accepted : 2013.06.17
  • Published : 2013.06.28

Abstract

A novel route to prepare Nd-Fe-B magnetic particles by utilizing both spray drying and reduction/diffusion processes was investigated in this study. Precursors were prepared by spray drying method using the aqueous solutions containing Nd salt, Fe salt and boric acid with stoichiometric ratios. Precursor particles could be obtained with various sizes from 2 to $10{\mu}m$ by controlling concentrations of the solutions and the average size of $2{\mu}m$ of precursors were selected for further steps. After heat treatment of precursors in air, Nd and Fe oxides were formed through desalting procedure, followed by reduction processes in Hydrogen ($H_2$) atmosphere and with Calcium (Ca) granules in Argon (Ar) successively. Moreover, diffusion between Nd and Fe occurred during Ca reduction and $Nd_2Fe_{14}B$ particles were formed. With Ca amount added to particles after $H_2$ reduction, intrinsic coercivity was changed from 1 to 10 kOe. In order to remove and leach CaO and residual Ca, de-ionized water and dilute acid were used. Acidic solutions were more effective to eliminate impurities, but Fe and Nd were dissolved out from the particles. Finally, $Nd_2Fe_{14}B$ magnetic particles were synthesized after washing in de-ionized water with a mean size of $2{\mu}m$ and their maximum energy product showed 9.23 MGOe.

Acknowledgement

Supported by : 산업기술연구회

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