Claims
- 1. A process for increasing the density of a reaction bonded silicon nitride article, which comprises the step of sintering the reaction bonded silicon nitride article of a density of at least 2.2 g/cm.sup.3 in an atmosphere consisting essentially of nitrogen at substantially atmospheric pressure at a temperature of 1600.degree. to 2000.degree. C., while the article is embedded in a protective powder comprising silicon nitride, boron nitride, or a mixture of silicon nitride and boron nitride, and one or more sintering additives for silicon nitride, said sintering additives being present in the protective powder in an amount of from 3 to 20% by weight, wherein said sintering additives are selected from the group consisting of MgO, Y.sub.2 O.sub.3, Mg.sub.3 N.sub.2, CeO.sub.2 and mixtures thereof with Fe.
- 2. The process of claim 1, wherein the reaction bonded silicon nitride article to be sintered also comprises one or more sintering additives uniformly dispersed therein in an amount not exceeding 20% by weight, said reaction bonded silicon nitride article to be sintered being formed by forming silicon powder into a compact containing said sintering additives and then nitriding the same to yield said reaction bonded silicon nitride article.
- 3. The process of claim 1, wherein the protective powder comprises MgO.
- 4. The process of claim 1, wherein the protective powder comprises from 5 to 15% by weight of sintering additives.
- 5. The process of claim 1, wherein said compact contains from 1 to 12% by weight of sintering additives.
- 6. The process of claim 5, wherein the compact contains MgO and Y.sub.2 O.sub.3 sintering additives.
- 7. The process of claim 1, wherein the sintering is carried out at temperature from 1600.degree. to 1900.degree. C.
- 8. The process of claim 1, wherein the protective powder is degassed before the sintering treatment.
- 9. The process of claim 2, wherein said silicon powder has a density of at least 1.3 g/cm.sup.3.
- 10. The process of claim 2, wherein said silicon powder compact is nitrided at 1350.degree. to 1450.degree. C.
- 11. The process of claim 10, wherein said nitriding of said silicon powder compact increases the density thereof without substantial dimensional change, thereby providing said reaction bonded silicon nitride compact of a density of at least 2.2 g/cm.sup.3.
- 12. The process of claim 11, wherein the final density of the sintered silicon nitride article is close to the theoretical density of 3.18 g/cm.sup.3.
- 13. The process of claim 12, wherein said silicon powder has a particle size of from 0.1 to 44.mu..
- 14. The process of claim 13, wherein said reaction bonded silicon nitride article has a density on the order of 1.5-2.6 g/cm.sup.3.
- 15. The process of claim 1, wherein said protective powder consists essentially of said silicon nitride, boron nitride, or a mixture of silicon nitride and boron nitride, and said one or more sintering additives.
- 16. The process for increasing the density of a reaction bonded silicon nitride article, which comprises the step of sintering the reaction bonded silicon nitride article of a density of at least 2.2 g/cm.sup.3 in an atmosphere consisting essentially of nitrogen at substantially atmospheric pressure at a temperature of 1600.degree. to 2000.degree. C., while the compact is embedded in a protective powder consisting silicon nitride, boron nitride or a mixture of silicon nitride and boron nitride, and one or more sintering additives for silicon nitride, said sintering additives being present in the protective powder in an amount of from 3 to 20% by weight, wherein said reaction bonded silicon nitride compact to be sintered also comprises one or more sintering additives selected from the group consisting of MgO, Y.sub.2 O.sub.3, Mg.sub.3 N.sub.2, CeO.sub.2 and mixtures thereof with Fe uniformly dispersed therein in an amount not exceeding 20% by weight, said reaction bonded silicon nitride compact to be sintered being formed by forming a silicon powder into a compact containing said sintering aids and then nitriding the same to yield said reaction bonded silicon nitride article.
- 17. The process of claim 1, wherein the reaction bonded silicon nitride article product is structurally and chemically homogeneous.
- 18. The process of claim 1, wherein the article is embedded in the protective powder by the steps which consist of placing the article on a layer of the protective powder and then embedding the article in the protective powder.
- 19. The process of claim 1, wherein the protective powder consists of silicon nitride and the one or more sintering additives.
- 20. The process of claim 1, wherein the protective powder consists of boron nitride and one or more sintering additives.
- 21. The process of claim 1, wherein the protective powder consists of silicon nitride, boron nitride and the one or more sintering additives.
- 22. A process for increasing the density of a reaction bonded silicon nitride article which comprises the steps of:
- forming silicon powder into a compact and nitriding the same to yield the reaction bonded silicon nitride article;
- sintering the reaction bonded silicon nitride article of a density of at least 2.2 g/cm.sup.3 in an atmosphere consisting essentially of nitrogen at substantially atmospheric pressure at a temperature of 1600.degree. to 2000.degree. C., while the article is embedded in a protective powder comprising silicon nitride, boron nitride, or a mixture of silicon nitride and boron nitride, and one or more sintering additives for silicon nitride, said sintering additives being present in the protective powder in an amount of from 3 to 20% by weight, wherein said sintering additives are selected from the group consisting of MgO, Y.sub.2 O.sub.3, Mg.sub.3 N.sub.2, CeO.sub.2 and mixtures thereof with Fe.
- 23. The process of claim 16, wherein the reaction bonded silicon nitride article product is structurally and chemically homogeneous.
- 24. The process of claim 16, wherein the article is embedded in the protective powder by the steps which consist of placing the article on a layer of the protective powder and then embedding the article in the protective powder.
- 25. The process of claim 16, wherein the protective powder consists of silicon nitride and the one or more sintering additives.
- 26. The process of claim 16, wherein the protective powder consists of boron nitride and the one or more sintering additives.
- 27. The process of claim 16, wherein the protective powder consists of silicon nitride, boron nitride and the one or more sintering additives.
- 28. The process of claim 22, wherein the reaction bonded silicon nitride article product is structurally and chemically homogeneous.
- 29. The process of claim 22, wherein the article is embedded in the protective powder by the steps which consist of placing the article on a layer of the protective powder and then embedding the article in the protective powder.
- 30. The process of claim 22, wherein the protective powder consists of silicon nitride and the one or more sintering additives.
- 31. The process of claim 22, wherein the protective powder consists of boron nitride and the one or more sintering additives.
- 32. The process of claim 22, wherein the protective powder consists of silicon nitirde, boron nitride and the one or more sintering additives.
Priority Claims (3)
Number |
Date |
Country |
Kind |
69899 A/77 |
Dec 1977 |
ITX |
|
69900 A/77 |
Dec 1977 |
ITX |
|
69777 A/78 |
Dec 1978 |
ITX |
|
Parent Case Info
This is a continuation of application Ser. No. 970,592, filed Dec. 18, 1978, now abandoned.
Foreign Referenced Citations (1)
Number |
Date |
Country |
1448732 |
Sep 1976 |
GBX |
Continuations (1)
|
Number |
Date |
Country |
Parent |
970592 |
Dec 1978 |
|