Preparation and Performance of Si₃N₄ Hollow Microspheres by the Template Method and Carbothermal Reduction...

Silicon nitride (Si₃N₄) hollow microspheres with smaller particle size and narrower distribution can be used to prepare closed-cell ceramics as the pore-forming agent to improve heat insulation performance and wave-transparent performance of porous Si₃N₄ ceramics. In this work, Si₃N₄ hollow microspheres with a diameter of about 1 μm and a wall thickness of approximately 150 nm were prepared by using the template method combined with the carbothermal reduction nitridation method. The optimum preparation temperature of the Si₃N₄ hollow microspheres is 1450 °C. The morphology, microstructure, and phase composition of the prepared Si₃N₄ hollow microspheres were characterized. The formation mechanism of the Si₃N₄ hollow microspheres was discussed. The dielectric properties of Si₃N₄ hollow microspheres were measured using the waveguide method at 8.2-12.4 GHz. The results show that the wave-transparent performance of the Si₃N₄ hollow microspheres is similar to those of α-Si₃N₄ particles. It can be used as the pore-forming agent or matrix for preparing lightweight, heat-insulating, wave-transparent, and high-strength porous Si₃N₄ ceramics.