Porosity and strength of silicon carbide foams prepared using preceramic polymers

Two types of polymeric precursors for silicon carbide (SiC) were dissolved in dichloromethane. Subsequently, between 10-80 wt% of silicon nitride (Si3N4) and titanium carbide (TiC) powder were added separately into the solutions to make SiC-Si3N4 and SiC-TiC suspensions. Cubes of polyurethane (PU) foams were soaked in precursor solution and suspensions and pyrolyzed in flowing nitrogen to produce SiC, SiC-Si3N4 and SiC-TiC composite foams. Some foams were heated further in nitrogen to 1600 degreesC. Shrinkage observed after pyrolysis and further heating the foams was measured and can be reduced by varying the concentration of polymeric precursor, Si3N4 and TiC content. The foams produced have porosities in the range 85-96%. The average compressive strength of the foams is in the range of 1.1-1.6 MPa.