Preparation of silicon carbide-silicon nitride composite foams from pre-ceramic polymers

Silicon carbide-silicon nitride composite foams were prepared by immersing a polyurethane foam in a polysilane precursor solution mixed with Si3N4 powder to form a pre-foam followed by heating in nitrogen at over 900 C. XRD patterns indicated that a SiC-Si3N4 composite was formed after sintering the ceramic foam at over 1500 C. Micrographs showed that most of these foams had well-defined open-cell structures and macro-defect free struts. The shrinkage was reduced considerably due to the addition of Si3N4 particles. 40 refs.