Sintered reaction-bonded silicon nitride foams with a high level of interconnected porosity

Sintered reaction-bonded silicon nitride (SRBSN) foams with very high porosity levels of up to 85 vol% and pore interconnectivity have been fabricated in this study. SRBSN foams were fabricated based on gel-casting of Si-PMMA suspensions followed by nitriding and sintering. The addition of MgO and Y2O3–Al2O3 as sintering additives resulted in significant changes in the foam microstructure. Small amounts of MgO completely prevented the whisker-forming reactions during nitridation while the addition of Y2O3–Al2O3 could not prevent whisker formation during nitridation. It was observed that regardless of the sintering aid system, SRBSN foams were whisker-free and revealed high pore interconnectivity after sintering. The SRBSN foam struts were only composed of β-Si3N4 grains embedded in an intergranular amorphous phase.