Humidity effects in Fe16N2 fine powder preparation by low-temperature nitridation
✍ Scribed by Kohetsu Yamanaka; Yuki Onuma; Shohei Yamashita; Yuji Masubuchi; Takashi Takeda; Shinichi Kikkawa
- Publisher
- Elsevier Science
- Year
- 2010
- Tongue
- English
- Weight
- 808 KB
- Volume
- 183
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
Low-temperature nitridation has been reported to produce ferromagnetic a 00 -Fe 16 N 2 by ammonia nitridation of a-Fe fine powder, which was obtained from the reduction of vapor-grown g-Fe 2 O 3 . The effects of humidity during this preparation were investigated in the present study. a 00 -Fe 16 N 2 was inconsistently obtained, and at low yield, from Fe 3 O 4 fine powder (MT-40) prepared from aqueous solution. Reducing the adsorbed water content in the iron oxide starting powder resulted in improved reproducibility of the a 00 -Fe 16 N 2 yield of the nitridation. The use of a smaller-diameter reaction tube, less than 25 mm in diameter, enabled more reproducible preparation from vapor-grown g-Fe 2 O 3 powder (CI-30). The reaction yield was further improved by using high-quality ammonia with a water content of r 0.05 ppm. Minimizing the humidity made it possible to obtain a fine powder with a high a 00 -Fe 16 N 2 content. Enhancement of the magnetization to 210 emu g À 1 at room temperature was observed from a nitrided mixture of a 00 -Fe 16 N 2 with residual a-Fe, compared to 199 emu g À 1 for an a-Fe fine powder reduced from g-Fe 2 O 3 . However, excess nitrogen and residual oxygen in the nitrided products reduced the magnetization below the value of a-Fe powder after nitridation. The magnetization was enhanced in nitrided products with a nitrogen content slightly below the stoichiometric amount for a 00 -Fe 16 N 2 .