Humidity effects in Fe₁₆N₂ fine powder preparation by low-temperature nitridation

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• 作者：Kohetsu Yamanaka ; Yuki Onuma ; Shohei Yamashita ; Yuji Masubuchi ; Takashi Takeda ; Shinichi Kikkawa
• 关键词：Fe₁₆N₂ ; Iron nitride ; Ferromagnetic ; Fine powder ; Low temperature nitridation ; Preparation
• 刊名：Journal of Solid State Chemistry
• 出版年：2010
• 出版时间：September 2010
• 年：2010
• 卷：183
• 期：9
• 页码：2236-2241
• 全文大小：807 K

文摘

Low-temperature nitridation has been reported to produce ferromagnetic α″-Fe₁₆N₂ by ammonia nitridation of α-Fe fine powder, which was obtained from the reduction of vapor-grown γ-Fe₂O₃. The effects of humidity during this preparation were investigated in the present study. α″-Fe₁₆N₂ was inconsistently obtained, and at low yield, from Fe₃O₄ 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 α″-Fe₁₆N₂ 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 γ-Fe₂O₃ powder (CI-30). The reaction yield was further improved by using high-quality ammonia with a water content of ≤0.05 ppm. Minimizing the humidity made it possible to obtain a fine powder with a high α″-Fe₁₆N₂ content. Enhancement of the magnetization to 210 emu g⁻¹ at room temperature was observed from a nitrided mixture of α″-Fe₁₆N₂ with residual α-Fe, compared to 199 emu g⁻¹ for an α-Fe fine powder reduced from γ-Fe₂O₃. However, excess nitrogen and residual oxygen in the nitrided products reduced the magnetization below the value of α-Fe powder after nitridation. The magnetization was enhanced in nitrided products with a nitrogen content slightly below the stoichiometric amount for α″-Fe₁₆N₂.