Preparation of porous SiC by freeze drying of polycarbosilane emulsion

Porous SiC beads were prepared by freeze-drying a polycarbosilane (PCS) emulsion. The water-in-oil (w/o) emulsion, which was composed of water, PCS dissolved p-xylene, and sodium xylenesulfonate (SXS) as an emulsifier, was frozen by dropping it onto a liquid N₂ bath; this process resulted in 1~2 mm sized beads. Beads were cured at 200 °C for 1 h in air and heat-treated at 800 °C and 1400 °C for 1 h in an Ar gas flow. Two types of pores, lamella-shaped and spherical pores, were observed. Lamellar-shaped pores were found to develop during the freezing of the xylene solvent. Water droplets in the w/o emulsion were changed into spherical pores under freeze-drying. At 1400 °C of heat-treatment, porous SiC was synthesized with a low level of impurities.