High temperature pyrolysis of preceramic polymers to microporous amorphous ceramics

Pyrolysis of preceramic polymer precursor (PCP's) as a route to nonoxide ceramics has bean studied for over thirty years. Typically, however, the emphasis has been on structural applications as ceramic fibers, coatings or as infiltration media for monolithic or ceramic-fiber reinforced ceramics. This paper presents data on five methods recently discovered for the synthesis of microporous nonoxide ceramics, with surface area up to 780m(2)/gm and micropore volume up to 0.28cm(3)/gm, by PCP pyrolysis. Pyrolysis of pure PCP's in ammonia produces microporous materials stable over a pyrolysis temperature range of 500-1000 degrees C, whereas pyrolysis of pure PCP's in inert gas yields microporous materials only over a limited range of pyrolysis temperatures from about 425-625 degrees C. Micropore neck closure is postulated as the mechanism limiting temperature stability.