The effect of silicon particle size on the characteristics of porous sintered reaction bonded silicon nitride

Abstract The effect of silicon particle size on the β-phase ratio, microstructure and the flexural strength of porous sintered reaction-bonded silicon nitride(SRBSN) was systematically investigated. Six kinds of raw powders containing Yb2O3 addtive (5, 10 wt%), prepared with different particle size distribution, were prepared by planetary ball-milling duration of 0, 3, 24 h. The behavior of α-to-β phase transformation of Si3N4 sintered at 1650 °C and 1750 °C, was found to be in good relation with SiO2 molar ratio over all the oxide additives. High flexural strength of SRBSN over 400 MPa was obtained when the amount of SiO2 was less than 0.7 owing to having the rod-like β-particles. Otherwise, the flexural strength of SRBSN became lower due to major occurrence of the equiaxed β-particles. This significant difference was considered to be caused from the seeding effect of β-ratio of RBSN samples as well as the different solubility of nitrogen element in the eutectic liquid phase.