Polycrystalline SiC Fibers from Organosilicon Polymers

Various organosilicon polymers have been converted into small diameter, finegrained silicon carbide fibers by melt spinning, crosslinking, and pyrolyzing to >1600ď. The high pyrolysis temperature densifies the fiber and causes CO evolution which removes nearly all oxygen. An additive prevents the loss of strength normally associated with such treatments. Silicon carbide fibers with up to 2.6 GPa (380 ksi) tensile strength, >420 GPa (>60 Msi) elastic modulus, and 3.1--3.2 mglm3 density have been prepared via this process. Their microstructure consists of >9S wt% β-SiC crystallites averaging 30-40 nm diameter, with varying amounts of graphitic carbon between the SiC grains. Under inert conditions, the fibers can be thermally aged at least 12 h/1800ď with minimal change in properties.