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 the 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. The remarkably high surface area up to 147 m2/g (7350 m2/liter) has been reached after 24 h etching. HF etching leads to a 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.