Claims
- 1. A crosslinkable preceramic composition comprising about 40-70% by weight of a low molecular weight polysilazane having a relative viscosity of 1.12-1.16, measured as a solution of 5% by weight of the polymer in tetrahydrofuran, about 15-35% by weight of a medium molecular weight polysilazane having a relative viscosity of 1.3-1.4, measured as a solution of 5% by weight of the polymer in tetrahydrofuran, and about 5-30% by weight of an unsaturated organic or organosilicon compound containing at least two alkenyl groups.
- 2. The composition of claim 1 wherein the polysilazanes are polymers which have been prepared by reacting an organodihalosilane with ammonia and polymerizing the ammonolysis product with a basic deprotonation catalyst.
- 3. The composition of claim 2 wherein the organodihalosilane is methyldichlorosilane and the basic catalyst is potassium hydride.
- 4. The composition of claim 1 wherein the unsaturated compound is an organosilicon compound.
- 5. The composition of claim 4 wherein the organosilicon compound is a compound corresponding to one of the formulas:
- SiE.sub.4,
- [R.sub.m (E).sub.3-m Si].sub.2 Z.sub.n, and
- cyclo[R.sub.p (E).sub.2-p SiT].sub.q
- wherein E is a substituted or unsubstituted vinyl or allyl group; Z is O, S, NH, NR', methylene, ethylene, phenylene, or other organic bridge; T is O, S, NH, NR', methylene, CH.dbd.CH, or C.tbd.C; R and R' are independently selected from substituted and unsubstituted alkyl groups containing 1-6 carbons and substituted and unsubstituted aryl groups containing 6-10 carbons; m is 0, 1, or 2; n and p represent 0 or 1; and q is at least 3 when T is O and is otherwise at least 2.
- 6. The composition of claim 5 wherein the organosilicon compound is one or more compounds corresponding to the formula cyclo[R(CH.sub.2 .dbd.CH)SiNH].sub.q.
- 7. The composition of claim 6 wherein R is methyl and q is at least 3.
- 8. The composition of claim 1 containing a free radical initiator as a catalyst to promote crosslinking.
- 9. A composition suitable for use in injection molding and comprising about 15-30% by weight of the composition of claim 1 and about 85-70% by weight of a ceramic powder selected from silicon carbide, silicon nitride, and mixtures thereof.
- 10. The composition of claim 9 comprising about 75% by weight of silicon carbide, about 15% by weight of the low molecular weight polysilazane, about 5% by weight of the medium molecular weight polysilazane, about 5% by weight of one or more compounds corresponding to the formula cyclo[CH.sub.3 (CH.sub.2 .dbd.CH)SiNH].sub.q wherein q is at least 3, and a catalytic amount of azobisisobutyronitrile; the polysilazanes being polymers which have been prepared by reacting methyldichlorosilane with ammonia and polymerizing the ammonolysis product with potassium hydride.
- 11. A process which comprises (A) injecting into a mold a crosslinkable injection molding composition comprising (1) about 70-85% by weight of a ceramic powder selected from silicon carbide, silicon nitride, and mixtures thereof and (2) about 30-15% by weight of a preceramic composition comprising about 40-70% by weight of a low molecular weight polysilazane having a relative viscosity of 1.12-1.16, measured as a solution of 5% by weight of the polymer in tetrahydrofuran, about 15-35% by weight of a medium molecular weight polysilazane having a relative viscosity of 1.3-1.4, measured as a solution of 5% by weight of the polymer in tetrahydrofuran, and about 5-30% by weight of an unsaturated organic or organosilicon compound containing at least two alkenyl groups and (B) heating the molding composition at a temperature sufficient to effect crosslinking.
- 12. A composition suitable for use in forming the matrix of a fiber/matrix composite and comprising about 30-60% by weight of the composition of claim 1 and about 70-40% by weight of (A) carbide, silicon nitride, and mixtures thereof and (B) 0-30% by weight of one or more polysilazanes.
- 13. The composition of claim 12 comprising about 60% by weight of a 75/25 silicon carbide/polysilazane mixture, about 25% by weight of the low molecular weight polysilazane, about 10% by weight of the medium molecular weight polysilazane, about 5% by weight of one or more compounds corresponding to the formula cyclo[CH.sub.3 (CH.sub.2 .dbd.CH)SiNH].sub.q wherein q is at least 3, and a catalytic amount of azobisisobutyronitrile; the polysilazanes being polymers which have been prepared by reacting methyldichlorosilane with ammonia and polymerizing the ammonolysis product with potassium hydride and which have respective relative viscosities of 1.12-1.16 and 1.3-1.4, measured as solutions of 5% by weight of the polymers in tetrahydrofuran.
- 14. A prepreg comprising oxidation-resistant carbon fibers bonded in the composition of claim 12 as a matrix.
- 15. A fiber-reinforced ceramic composite comprising oxidation-resistant carbon fibers bonded in a silicon carbide/silicon nitride ceramic matrix and prepared by laminating layers of the prepreg of claim 14 and heating the resultant laminate at a temperature of at least 850.degree. C. to pyrolyze the matrix.
- 16. A prepreg comprising oxidation-resistant carbon fibers bonded in the composition of claim 1 as a matrix.
- 17. A fiber-reinforced ceramic composite comprising oxidation-resistant carbon fibers bonded in a ceramic matrix and prepared by laminating layers of the prepreg of claim 16 and heating the resultant laminate at a temperature of at least 850.degree. C. to pyrolyze the matrix.
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a continuation-in-part of copending application Ser. No. 552,872, filed Jul. 16, 1990, now abandoned, which in turn is a continuation-in-part of Ser. No. 464,229, filed Jan. 12, 1990, now abandoned.
US Referenced Citations (8)
Foreign Referenced Citations (1)
Number |
Date |
Country |
0341923 |
May 1989 |
EPX |
Continuation in Parts (2)
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Number |
Date |
Country |
Parent |
552872 |
Jul 1990 |
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Parent |
464229 |
Jan 1990 |
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