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<p>Technology for in situ synthesis of superfine Si<sub>3</sub>N<sub>4</sub>–NbN composite powders without the need for subsequent milling via solid-state interaction in the Si<sub>3</sub>N<sub>4</sub>–Nb reaction mixture was developed for the production of nitride ceramics by spark plasma sintering and hot pressing. The regularities of solid-state interaction during vacuum heat treatment of the β-Si<sub>3</sub>N<sub>4</sub>–27.4 wt.% Nb reaction powder mixture, calculated for the synthesis of higher niobium nitride by the 4Nb + Si<sub>3</sub>N<sub>4</sub> = 4NbN + 3Si reaction, were analyzed. The interaction of the mixture components was studied under isothermal holding for 1 h at 1000, 1100, 1200, 1300, and 1400°C. Solid-state interaction with Si<sub>3</sub>N<sub>4</sub> was found to occur at 1000°C, resulting in the formation of a nitrogen solid solution in niobium (α-Nb). At 1100°C, the formation of lower nitride Nb<sub>2</sub>N and lower silicide Nb<sub>5</sub>Si<sub>3</sub> was observed. An increase in the temperature to 1200 and 1300°C led to a greater amount of Nb<sub>5</sub>Si<sub>3</sub>, whereas the amount of Nb<sub>2</sub>N hardly changed. At 1400°C, the product contained a mixture of γ-Nb<sub>5</sub>Si<sub>3</sub> and NbSi<sub>2</sub> silicides, while the lower nitride was absent. Thermodynamic calculations confirmed that the formation of higher niobium nitrides under these vacuum heat treatment conditions was thermodynamically unfavorable. Based on the established structural and phase regularities of solid-state interaction in the Si<sub>3</sub>N<sub>4</sub>–Nb mixture, a two-stage synthesis process was developed. This process was implemented in a single cycle consisting of vacuum heat treatment at 1000°C, followed by nitriding at 1200 and 1300°C. Nitriding at 1300°C yielded a powder composed of Si3N4 and a mixture likely containing three higher niobium nitrides of different polymorphic modifications. Using the developed synthesis process, experimental batches of Si<sub>3</sub>N<sub>4</sub>–20 vol.% NbN and Si<sub>3</sub>N<sub>4</sub>–10 vol.% NbN composite powders were produced. Analysis of the experimental batches showed that all synthesized powders possessed the required phase composition and were superfine. The particle size of the Si<sub>3</sub>N<sub>4</sub>–20 vol.% NbN powder ranged from 400 nm to 9 μm and that of the Si<sub>3</sub>N<sub>4</sub>–10 vol.% NbN powder ranged from 1.5 to 5 μm.</p>

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Synthesis of Si3N4–NbN Composite Powders

  • 期刊论文

  • 发表日期：

    2025年3月1日

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  • O. M. Myslyvchenko,
  • R. V. Lytvyn,
  • I. A. Polyakov,
  • I. V. Kud,
  • R. M. Mediukh,
  • L. A. Krushynska,
  • O. B. Zgalat-Lozynskyy

摘要

Technology for in situ synthesis of superfine Si3N4–NbN composite powders without the need for subsequent milling via solid-state interaction in the Si3N4–Nb reaction mixture was developed for the production of nitride ceramics by spark plasma sintering and hot pressing. The regularities of solid-state interaction during vacuum heat treatment of the β-Si3N4–27.4 wt.% Nb reaction powder mixture, calculated for the synthesis of higher niobium nitride by the 4Nb + Si3N4 = 4NbN + 3Si reaction, were analyzed. The interaction of the mixture components was studied under isothermal holding for 1 h at 1000, 1100, 1200, 1300, and 1400°C. Solid-state interaction with Si3N4 was found to occur at 1000°C, resulting in the formation of a nitrogen solid solution in niobium (α-Nb). At 1100°C, the formation of lower nitride Nb2N and lower silicide Nb5Si3 was observed. An increase in the temperature to 1200 and 1300°C led to a greater amount of Nb5Si3, whereas the amount of Nb2N hardly changed. At 1400°C, the product contained a mixture of γ-Nb5Si3 and NbSi2 silicides, while the lower nitride was absent. Thermodynamic calculations confirmed that the formation of higher niobium nitrides under these vacuum heat treatment conditions was thermodynamically unfavorable. Based on the established structural and phase regularities of solid-state interaction in the Si3N4–Nb mixture, a two-stage synthesis process was developed. This process was implemented in a single cycle consisting of vacuum heat treatment at 1000°C, followed by nitriding at 1200 and 1300°C. Nitriding at 1300°C yielded a powder composed of Si3N4 and a mixture likely containing three higher niobium nitrides of different polymorphic modifications. Using the developed synthesis process, experimental batches of Si3N4–20 vol.% NbN and Si3N4–10 vol.% NbN composite powders were produced. Analysis of the experimental batches showed that all synthesized powders possessed the required phase composition and were superfine. The particle size of the Si3N4–20 vol.% NbN powder ranged from 400 nm to 9 μm and that of the Si3N4–10 vol.% NbN powder ranged from 1.5 to 5 μm.