Polycrystalline SiC fibers from organosilicon polymers
Various organosilicon polymers have been converted into small diameter, fine-grained silicon carbide fibers by melt spinning, crosslinking, and pyrolyzing to greater than 1600 C. 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 fibres with up to 2.6 GPa (380 ksi) tensile strength, greater than 420 GPa (greater than 60 Msi) elastic modulus, and 3.1-3.2 mg/cu m density have been prepared via this process. Their microstructure consists of greater than 95 wt pct B-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/1800 C with minimal change in properties.