Processing and characterization of polymer derived SiOC foam with hierarchical porosity by HF etching

A simple process for synthesizing SiOC foams with low density (45 – 115 kg/m3) and high porosity (95–98%) is reported here. The process involves the impregnation of a flexible polyurethane foam with a preceramic polymer solution and pyrolysis in inert atmosphere. SEM analysis showed that the resultant SiOC foam had a fully open interconnected porous structure with dense struts. N2 adsorption test performed on the as–pyrolyzed SiOC foams showed very low surface area, which can be increased by leaching out the SiO2–rich network by HF, leaving behind a mesoporous C–rich SiOC foam. Remarkably high surface area up to 147 m2/g (7350 m2/liter) has been reached after 24 h etching. HF etching leads to decrease of the compressive strength. However, a good combination of compressive strength (80 kPa), porosity (95%) and surface area (7315 m2/liter) of the foam has been obtained and it makes the SiOC foam a potential candidate for specific applications.