Preparation of β‐Silicon Nitride Seeds for Self‐Reinforced Silicon Nitride Ceramics

Abstract

This paper describes a method for the preparation of silicon nitride (Si3N4) seeds that have an average aspect ratio of ∼4. The seeds are prepared via heat treatment of a powder mixture that contains alpha‐phase‐rich Si3N4 and 0.5 wt% Y2O3 at a temperature of 1800°C and a nitrogen pressure 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 grain‐boundary phase in hot phosphoric acid, followed by an ultrasonic treatment (for 30 min). The method can be used to produce large quantities of seeds.