Structural evolution of polymer precursor of silicon carbide ceramics during pyrolysis

Takeyama, Akinori; Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito

In order to prepare crack-free silicon carbide hydrogen separation membrane, how volume shrinkage or expansion of polymer precursor, polycarbosilne (PCS) take places when it is converted into silicon carbide ceramics during pysolysis was investigated. PCS powder cured by electron beam irradiation with several dose of 12,16,18,24 MGy in helium atmosphere was pysolysed at 923 K to convert them into SiC ceramic powder. As the dose was increased, ceramic yield was gradually increased, indicating amount of decomposed gas evolved during pyrolysis was decreased. Density of obtained SiC ceramic powders was decreased with increasing dose. By electron beam irradiation, network structure of PCS was developed and decomposition gas seemed to be easily accumulated in the network structure. It follows that PCS powder swelled as decomposition gas was accumulated and swelling was lowered density of SiC ceramic powders. Furthermore, surface area of SiC ceramic powder was increased from 0 m/g for 12 MGy to 0.6 m/g for 24 MGy by swelling. Consequently, swelling suppressed volume shrinkage of PCS powder during pyrolysis.