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

A new method of forming silicon carbide-silicon nitride composite foams is presented. These are prepared by immersing a polyurethane foam in a polysil ane precursor solution mixed with Si3N4 powder to form a pre-foam followed by heating it in nitrogen at > 900 degrees C. X-ray diffraction patterns in dicate that a SiC-Si3N4 composite was formed after sintering the ceramic fo am at > 1500 degrees C. Micrographs show that most of these foams have well -defined open-cell structures and macro-defect free struts. The shrinkage i s reduced considerably due to the addition of Si3N4 particles. (C) 2000 Els evier Science Ltd. All rights reserved.