Herstellung von polykristallinen Siliciumcarbidfasern aus Methylpolydisilazanen, enthaltend Bor, sowie derartige Siliciumcarbidfasern

摘要

A process for the preparation of substantially polycrystalline silicon carbide fibers is provided. The fibers may be fabricated to have a small diameter and are thermally stable at high temperatures. The process is carried out by initially forming fibers from a preceramic polymeric precursor comprising methylpolydisilylazane resins. The fibers are then infusibilized to render them nonmelting followed by a pyrolysis step in which the fibers are heated to a temperature in excess of 1600 DEG C. in a nonoxidizing atmosphere to form substantially polycrystalline silicon carbide fibers. The substantially polycrystalline silicon carbide fibers which are formed by the process of the present invention have at least 75% crystallinity and have a density of at least about 2.9 gm/cc. The polymeric precursor or the fibers contain, or have incorporated therein, at least about 0.2% by weight boron. This incorporation of boron may be accomplished either prior to or during formation of the fibers or during at least one of the infusibilizing or pyrolyzing steps of the process.