Synthesis of nanoporous silicon carbide via the preceramic polymer route

Nanoporous silicon carbide materials were prepared by the pyrolysis of the preceramic polymer, polycarbosilane (PCS), with and without the addition of an inert filler (nano- and micron-sized silicon carbide powders). Hydrosilylation crosslinking of PCS with divinylbenzene prior to pyrolysis appeared to have little influence on the development of micro- and mesoporosity. Maximum micropore volumes were 0.28 cm3 g−1 for non-crosslinked PCS and 0.25, 0.33 and 0.32 cm3 g−1 for PCS crosslinked with 2, 6 and 10 wt.% DVB respectively. Micropore volumes decreased under hydrothermal conditions to 0.03 cm3 g−1 for non-crosslinked and 0 cm3 g−1 for crosslinked PCS. Porosity was also lost at temperatures above 700 °C. The addition of nano-sized SiC powders to PCS prior to pyrolysis maintained mesoporosity to temperatures of 1200 °C, however, micron-sized SiC powders did not maintain porosity above 800 °C. The modal pore size in pellets formed by compressing micron-sized powders with the preceramic polymer was 5 μm compared to 30 nm when nano-sized powders were used.