Preparation of Highly Heat–Resistant Sm–Fe–N Magnetic Powder by Reduction–Diffusion Process
Materials Transactions 2020 Volume 61 Issue 11 Pages 2201-2207
Ruka Matsuda, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto, Takashi Ishikawa and Yukinobu Yoneyama
Abstract
We previously described the preparation of Mn- or Cr-containing core–shell Sm–Fe–N powders exhibiting high thermal stability by a reduction–diffusion process, in which powder mixtures of Sm2Fe17, Sm2O3, Mn3O4 or Cr2O3, and Ca were annealed and nitrided followed by the removal of residual CaO by washing with ethylene glycol in a glove box. We also found that Sm–Fe–N powder prepared by this process showed high heat resistance even without Mn or Cr addition. In the present work, we investigated the effects of the washing solvent and atmosphere on the coercivity, heat resistance, and microstructure of Sm–Fe–N powders. The heat resistance of the Sm–Fe–N powders was strongly dependent on their O content. Washing with ethylene glycol rather than water effectively suppressed oxidation during washing. Furthermore, the washing atmosphere also affected the increase in O content of the powders. The Sm–Fe–N powder washed with ethylene glycol in a glove box showed high heat resistance and the same microstructure before and after the heat resistance test. In contrast, the powder washed with water in air exhibited low heat resistance owing to the occurrence of α-Fe precipitation during the heat resistance test.
その他特記事項
This work was (in part) supported by the Elements Strategy Initiative Center for Magnetic Materials (ESICMM),Grant Number JPMXP0112101004, through the Ministry of Education, Culture, Sports, Science and Technology (MEXT).
