Preparation of beta-silicon nitride seeds for self-reinforced silicon nitride ceramics

This paper describes a method for the preparation of silicon nitride (Si3N4 ) seeds that have an average aspect ratio of similar to 4, The seeds are pr epared via heat treatment of a powder mixture that contains oc-phase-rich S i3N4 and 0.5 wt% Y2O3 at a temperature of 1800 degrees C and a nitrogen pre ssure of 35 kPa. A Y-Si-O-N liquid forms during heat treatment; this liquid acts as a flux for seed precipitation. During cooling, the Y-Si-O-N liquid transforms to a thin intergranular grain-boundary phase and causes strong agglomeration of the seeds. The seeds can be isolated by dissolving the gra in-boundary phase in hot phosphoric acid, followed by an ultrasonic treatme nt (for 30 min). The method can be used to produce large quantities of seed s.