Effect of the particle size of raw silicon powder on the dielectric properties of porous reaction-bonded silicon nitride ceramics

Low density silicon nitride with about 55% porosity and globed macropores was prepared by reaction-bonded raw silicon powder and adding 30% in mass pore-forming agent of benzoic acid ball-like particles. Effects of the particle size of raw silicon powder on the dielectric properties of reaction-bonded porous silicon nitride were investigated. The results clearly indicate that the specimens prepared with fine powders have lower dielectric constant ε′ and dielectric loss tanδ than that prepared using coarse powders. The ε′ of the specimen prepared by the silicon powder with a minimum average particle size of 7 μm is the lowest, about 2.5.The change of the particle size of silicon powder will affect the rate of the reaction in the course of reaction sintering and the micro-structure and phase composition of specimen. More Si₃N₄ phase, less Si₂ON₂ phase and residual Si, smaller size of micropores will result after the decrease of average particle size of raw silicon powder.