Processing of Ceramic Foams from Polymeric Precursor-Alumina Suspensions

A polysilane was used as the precursor for silicon carbide (SiC) and different amounts of it was dissolved in dichloromethane. Subsequently, between 10 to 80 %wt of alumina (Al ₂ O ₃ ) powder was added into the solutions to make SiC-Al ₂ O ₃ suspensions. Cubes of polyurethane (PU) foams with open cells in the size range 500-1200μm were soaked in these suspensions and pyrolysed in flowing nitrogen to produce SiC-Al ₂ O ₃ composite foams. Some foams were heated further in nitrogen to 1300°C. The foams produced consist of an open cell structure and hole-free solid struts which were also cracks free in the polysilane-Al ₂ O ₃ 80:2Owt% formulation. The retention of shape during processing was excellent. Shrinkage observed after pyrolysis and further heating the foams was measured and can be controlled by varying the Al ₂ O ₃ content. The foams produced have porosities in the range 87 to 95%. The maximum compressive strength of the pyrolysed foams prepared using the polysilane-Al ₂ O ₃ 80:20 wt% formulation was 2.3MPa.