Claims
- 1. A process for liquid phase sintering of silicon carbide comprising:
- forming a mixture consisting essentially of silicon carbide particles having a size of from about 2 to about 5 microns and from about 0.5 percent to about 19.5 percent by weight of a rare earth oxide and from about 0.5 percent to about 19.5 percent by weight alumina;
- forming a shape with said mixture; and
- sintering said mixture at a temperature of from about 1700.degree. to about 2200.degree. centrigrade for about 1 minute to about 30 minutes to form a liuqid phase and a resultant sintered ceramic body having a hardness exceeding about 22 GPa comprising 2% to 20% by weight of a compound wherein the molar ratio of rare earth oxide to alumina in said compound is at least three to five and from about 80% to about 98% by weight silicon carbide.
- 2. The process of claim 1 wherein said silicon carbide particles are alpha phase silicon carbide particles.
- 3. The process of claim 1 wherein said silicon carbide particles are beta phase silicon carbide particles.
- 4. The process of claim 1 wherein said silicon carbide particles comprise a mixture of alpha phase and beta phase silicon carbide particles.
- 5. The process of claim 1 wherein said sintering temperature is between about 1900.degree. and 2100.degree. centigrade.
- 6. The process according to claim 1 wherein said mixture of silicon carbide particles, rare earth oxide and alumina is sintered for for about 1 minute to less than 15 minutes.
- 7. The process according to claim 1 including hot isostatically pressing said densified mixture at a pressure and for a period of time to increase the density of said sintered body.
- 8. The process of claim 1 including hot isostatically pressing said densified mixture at a pressure and for a period of time to increase the density of said sintered silicon carbide body to greater than about 99% of theoretical.
- 9. The process of claim 8 wherein said sintering and hot isostatic steps are combined so that a green ceramic body is first sintered to a state of closed porosity in a pressure of less than about 15 MPa and said resultant ceramic body is then pressurized at pressures of at least 35 MPa to reduce the porosity.
- 10. A sintered ceramic body comprising a uniform mixture of:
- from about 80% to about 98% by weight silicon carbide, and from about 2% to about 23% by weight of a compound, said compound comprising:
- alumina, and a rare earth oxide, wherein the molar ratio of rare earth oxide to alumina in said compound is at least three to five, and wherein said sintered ceramic body has a density greater than 95% of theoretical, and a hardness greater than 20 GPa.
- 11. The sintered ceramic body of claim 10 wherein said molar ratio of rare earth oxide to alumina is at least 1:1.
- 12. The sintered ceramic body of claim 11 wherein said molar ratio of rare earth oxide to alumina is 2:1.
- 13. The sintered ceramic body of claim 10 wherein said rare earth oxide is Y.sub.2 O.sub.3.
- 14. The sintered ceramic body of claim 13 wherein the silicon carbide has average grain sizes of less than ten micrometers.
- 15. The sintered ceramic body of claim 10 wherein said compound of rare earth oxide and alumina comprises less than 10 percent by weight of the sintered ceramic body.
- 16. The sintered ceramic body of claim 10 wherein said ceramic body has a hardness which exceeds 23 GPa.
- 17. The sintered ceramic body of claim 10 wherein said sintered ceramic body has a hardness which exceeds 26 GPa.
Parent Case Info
This application is a continuation of application Ser. No. 002,146 filed Jan. 12, 1987, now abandoned.
GOVERNMENT CONTRACT IDENTIFICATION STATEMENT
This invention was made with government support under Contract No. DE-AC03-84ER80191, awarded by the Department of Energy. The Government has cetain rights in this invention.
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Continuations (1)
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Number |
Date |
Country |
Parent |
2146 |
Jan 1987 |
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