Liquid-Phase-Assisted Catalytic Nitridation of Silicon and In Situ Growth of α-Si3N4

Abstract

Si3N4 powders were synthesized with Fe, Co, or Ni as catalysts using Si powder at 1250 °C in a nitrogen atmosphere by liquid-phase-assisted catalytic nitridation synthesis (LPA–CNS). The catalytic effects of the metals on the nitridation of silicon powder were investigated by mixing the powder with 2 wt% by mass of Fe, Co, or Ni in a high-temperature liquid phase in flowing nitrogen. The α-Si3N4 micro-morphology could be effectively changed by adjusting the type of catalyst in the initial reaction mixtures. Fe, Co, and Ni promoted the formation of α-Si3N4 at 1250 °C and controlled the morphology of the α-Si3N4 particles. The hexagonal flakes of α-Si3N4 with a better defined morphology were obtained using Ni as the catalyst, compared to that obtained from the other two catalysts.

Utilization of Silicon Dust to Prepare Si3N4 Used for Steelmaking Additives: Thermodynamics and Kinetics

“…Figure 12a depicts the process controlled by the VLS mechanism during the nitriding of Si dust, As the temperature increases, the liquid phase of the Si-Fe alloy is generated and starts to adsorb N 2 molecules, and when the dissolved N 2 exceeds its solubility, it will precipitate on the surface and react with Si in the liquid phase to generate Si 3 N 4 nuclei. These nuclei keep absorbing Si and N in the gas phase and generate Si 3 N 4 along a certain direction and continue to grow against Si-Fe [33]. At the same time, the change in the morphology of the Si particles is due to the exothermic nitriding reaction.…”

Preparation of high‐purity α‐Si3N4 powder via multifunctional synergistic catalysis and pretreatment method

“…The former exhibits higher sintering activity and is the preferred choice for Si 3 N 4 -based materials. [9][10][11][12] Currently, the primary approaches for preparing α-Si 3 N 4 powder encompass direct nitridation of silicon powder, [13][14][15][16] carbothermal reduction nitridation, [17][18][19] self-propagating high temperature synthesis, [20][21][22] thermal decomposition, [23][24][25] sol-gel method, [26][27][28] and high temperature gas phase reaction. [29][30][31] Nevertheless, these preparation methods all have their disadvantages.…”

“…Flaky α-Si 3 N 4 and Si 3 N 4 whiskers were prepared in the molten salt environment of NaCl-NaF. 11,[39][40][41][42] Na 2 SiF 6 is used to prepare equiaxed Si 3 N 4 . 21 SiC nanowires were obtained in a molten salt mixture composed of KCl and KF.…”

“…It primarily exists in two forms, α‐Si 3 N 4 and β‐Si 3 N 4 . The former exhibits higher sintering activity and is the preferred choice for Si 3 N 4 ‐based materials 9–12 . Currently, the primary approaches for preparing α‐Si 3 N 4 powder encompass direct nitridation of silicon powder, 13–16 carbothermal reduction nitridation, 17–19 self‐propagating high temperature synthesis, 20–22 thermal decomposition, 23–25 sol–gel method, 26–28 and high temperature gas phase reaction 29–31 .…”

“…Notably, molten salt assisted method exhibits favorable results, especially in the field of ceramics. Flaky α‐Si 3 N 4 and Si 3 N 4 whiskers were prepared in the molten salt environment of NaCl–NaF 11,39–42 . Na 2 SiF 6 is used to prepare equiaxed Si 3 N 4 21 .…”