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<p>High-purity (≥ 90 wt%, up to ~ 95 wt%) and high-coercivity (up to 1.86 kOe) α′′-Fe<sub>16</sub>N<sub>2</sub> microparticles were synthesized by modifying the initial microstructure of α-Fe<sub>2</sub>O<sub>3</sub> precursors using aerosol processing. Three distinct α-Fe<sub>2</sub>O<sub>3</sub> powders were prepared through spray pyrolysis of Fe(NO<sub>3</sub>)<sub>3</sub> (SP-nitrate) and spray drying, followed by calcination of Fe(NO<sub>3</sub>)<sub>3</sub> (SD-nitrate) or Fe<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub> (SD-oxalate). Following identical H<sub>2</sub> reduction and NH<sub>3</sub> nitridation, the resulting powders exhibited high α′′-Fe<sub>16</sub>N<sub>2</sub> phase fractions (90 to 95 wt%). Despite diverse oxide origins, the final nitride crystallite size converged to ~ 17–18&#xa0;nm for all samples, while coercivity varied systematically: 1.14 kOe for SP-nitrate, 1.46 kOe for SD-nitrate, and 1.86 kOe for SD-oxalate. These differences align with the precursor-derived microstructure rather than modest variations in phase purity or crystallite size effects. The SD-oxalate route yielded the most intricate and porous particle morphology. Subsequent reduction and nitridation increased this porosity, generating numerous pore walls, edges, and rough surfaces that could serve as domain-wall pinning sites, consistent with the highest coercivity. These findings suggest that adjusting the aerosol route and precursor chemistry to regulate the precursor microstructure offers a practical and scalable approach to enhance the coercivity of rare-earth-free α′′-Fe<sub>16</sub>N<sub>2</sub>.</p>

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Scalable aerosol routes to enhance coercivity in α′′-Fe16N2 powders through α-Fe2O3 microstructure control

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年10月29日

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  • Jihyeong Jeong,
  • Hye Jin Park,
  • Hye Young Koo,
  • Dohoon Kim,
  • Jung-Goo Lee,
  • Youn-Kyoung Baek

摘要

High-purity (≥ 90 wt%, up to ~ 95 wt%) and high-coercivity (up to 1.86 kOe) α′′-Fe16N2 microparticles were synthesized by modifying the initial microstructure of α-Fe2O3 precursors using aerosol processing. Three distinct α-Fe2O3 powders were prepared through spray pyrolysis of Fe(NO3)3 (SP-nitrate) and spray drying, followed by calcination of Fe(NO3)3 (SD-nitrate) or Fe2(C2O4)3 (SD-oxalate). Following identical H2 reduction and NH3 nitridation, the resulting powders exhibited high α′′-Fe16N2 phase fractions (90 to 95 wt%). Despite diverse oxide origins, the final nitride crystallite size converged to ~ 17–18 nm for all samples, while coercivity varied systematically: 1.14 kOe for SP-nitrate, 1.46 kOe for SD-nitrate, and 1.86 kOe for SD-oxalate. These differences align with the precursor-derived microstructure rather than modest variations in phase purity or crystallite size effects. The SD-oxalate route yielded the most intricate and porous particle morphology. Subsequent reduction and nitridation increased this porosity, generating numerous pore walls, edges, and rough surfaces that could serve as domain-wall pinning sites, consistent with the highest coercivity. These findings suggest that adjusting the aerosol route and precursor chemistry to regulate the precursor microstructure offers a practical and scalable approach to enhance the coercivity of rare-earth-free α′′-Fe16N2.