Claims
- 1. A process for the preparation of substantially polycrystalline silicon carbide fibers comprising the steps of:
- a) forming fibers from a preceramic polymeric precursor comprising methylpolydisilylazane resins;
- b) infusibilizing said fibers; and
- c) pyrolyzing said fibers at a temperature in excess of 1600.degree. C. in a nonoxidizing atmosphere to form substantially polycrystalline silicon carbide fibers;
- said polymeric precursor or said fibers containing or having incorporated therein at least about 0.2% by weight boron either prior to step a), or during at least one of steps a), b), and c).
- 2. The process of claim 1 in which said substantially polycrystalline silicon carbide fibers have at least 75% crystallinity.
- 3. The process of claim 1 in which said substantially polycrystalline silicon carbide fibers have a density of at least about 2.9 gm/cc.
- 4. The process of claim 1 in which said fibers formed in step a) are formed by spinning.
- 5. The process of claim 4 in which said fibers formed in step a) are formed by melt spinning.
- 6. The process of claim 4 in which said fibers formed in step a) are formed by wet spinning.
- 7. The process of claim 4 in which said fibers formed in step a) are formed by dry spinning.
- 8. The process of claim 1 in which said fibers are infusibilized by curing said fibers in air.
- 9. The process of claim 1 in which said fibers are infusibilized by curing said fibers in an atmosphere containing a mixture of boron trichloride and ammonia or amine.
- 10. The process of claim 1 in which said fibers are infusibilized by curing said fibers in an atmosphere containing diborane.
- 11. The process of claim 1 in which said fibers are infusibilized by curing said fibers with gamma irradiation.
- 12. The process of claim 1 in which said fibers are infusibilized by curing said fibers with ultraviolet light.
- 13. The process of claim 1 in which said fibers are infusibilized by curing said fibers first in an atmosphere containing nitric oxide followed by curing said fibers in an atmosphere containing boron trichloride or diborane.
- 14. The process of claim 1 in which boron is incorporated into said polymeric precursor during said pyrolyzing step by exposing said polymeric precursor to a boron-containing gas.
- 15. The process of claim 1 in which said nonoxidizing atmosphere comprises a gas selected from the group consisting of argon, helium, and mixtures thereof.
- 16. The process of claim 1 in which said pyrolysis step includes heating said fibers to about 1800.degree. C. and maintaining that temperature for about one hour.
- 17. The process of claim 1 in which boron is incorporated directly into said polymeric precursor by reacting said precursor with a boron-containing compound.
- 18. The process of claim 1 in which boron is incorporated into said polymeric precursor during said infusibilization step by exposing said polymeric precursor to a boron-containing gas.
- 19. Substantially polycrystalline silicon carbide fibers containing at least about 0.2% by weight boron, a density of at least about 2.9 gm/cm.sup.3, and an average grain size of less than about 0.5 micrometers.
- 20. The fibers of claim 19 in which said fibers have a diameter of less than about 50 micrometers.
Government Interests
The U.S. Government has rights in this invention pursuant to Contract No. F33615-83-C-5006 awarded by the U.S. Air Force.
US Referenced Citations (19)
Non-Patent Literature Citations (1)
Entry |
"Composition and Structure of Ceramic Fibers Prepared from Polymer Precursors" Lipowitz et al. Advanced Ceram. Mat'ls 2[2] 121-128 1987. |