# US 5,707,568 A · Preparation of substantially polycrystalline silicon carbide fibers from methylpolysilanes > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,707,568 A - Document ID: US5707568A - Status: Granted - Kind: A - Application number: 07/456,832 - Filed: 1989-12-18 - Granted: 1998-01-13 - Earliest claimed: 1989-12-18 - Assignees: Dow Corning Corporation - Inventors: David Charles Deleeuw; Jonathan Lipowitz; Paul Pu-yuan Lu; James Alan Rabe - Web page: https://patentgrep.com/patent/US5707568A ## CPC - C04B 35/571: obtained from {Si-containing} polymer precursors {or organosilicon monomers} - C03C 13/06: Mineral fibres, e.g. slag wool, mineral wool, rock wool - D01F 9/10: by decomposition of organic substances (D01F9/12 takes precedence) - C04B: LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE {(roofing granules E04D7/005)}; CERAMICS (devitrified glass-ceramics C03C10/00); REFRACTORIES; TREATMENT OF NATURAL STONE - C03C: CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS - D01F: CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS ## Abstract 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 methylpolysilane 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.degree. 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/cm.sup.3. 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. ## Claims ### Claim 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 methylpolysilane 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). ### Claim 2 (depends on 1) The process of claim 1 in which said substantially polycrystalline silicon carbide fibers have at least 75% crystallinity. ### Claim 3 (depends on 1) The process of claim 1 in which said substantially polycrystalline silicon carbide fibers have a density of at least about 2.9 gm/cm.sup.3. ### Claim 4 (depends on 1) The process of claim 1 in which said fibers formed in step a) are formed by spinning. ### Claim 5 (depends on 4) The process of claim 4 in which said fibers formed in step a) are formed by melt spinning. ### Claim 6 (depends on 4) The process of claim 4 in which said fibers formed in step a) are formed by wet spinning. ### Claim 7 (depends on 4) The process of claim 4 in which said fibers formed in step a) are formed by dry spinning. ### Claim 8 (depends on 1) The process of claim 1 in which said fibers are infusibilized by curing said fibers in air. ### Claim 9 (depends on 1) The process of claim 1 in which said fibers are infusibilized by curing said fibers first in an atmosphere containing boron trichloride followed an atmosphere containing ammonia or amine. ### Claim 10 (depends on 1) The process of claim 1 in which said fibers are infusibilized by curing said fibers in an atmosphere containing diborane. ### Claim 11 (depends on 1) The process of claim 1 in which said fibers are infusibilized by curing said fibers with gamma irradiation. ### Claim 12 (depends on 1) The process of claim 1 in which said fibers are infusibilized by curing said fibers with ultraviolet light. ### Claim 13 (depends on 1) The process of claim 1 in which said fibers are infusibilized by exposing said fibers first in an atmosphere containing nitric oxide followed by exposing said fibers in an atmosphere containing boron trichloride or diborane. ### Claim 14 (depends on 1) The process of claim 1 in which said fibers are infusibilized by curing said fibers by heating said fibers in an atmosphere containing ammonia or an amine. ### Claim 15 (depends on 1) 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. ### Claim 16 (depends on 1) The process of claim 1 in which said nonoxidizing atmosphere comprises a gas selected from the group consisting of argon, helium, and mixtures thereof. ### Claim 17 (depends on 1) 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. ### Claim 18 (depends on 1) The process of claim 1 in which boron is incorporated directly into said polymeric precursor by reacting said precursor with a boron-containing compound. ### Claim 19 (depends on 1) 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.