Strength and microstructure of silicon nitride fabricated by post-sintering process using low-purity silicon powder as raw materials

Influence of sintering temperature on the strength and micro-structure were investigated on silicon nitride specimens fabricated by pressureless post-sintering process using low-purity silicon powder as raw materials. Densification of reaction-bonded silicon nitride with sintering aid did not proceed further upon setting the post-sintering temperature at 1600 or 1650degreesC due to the volatilization of species and poor sinterbility. Sintering at 1850degreesC provided almost fully densified silicon nitride having an average strength of 521 MPa, the grains of this materials were relatively fine but did not develop into a rod-like shape.