Claims
- 1. The process of forming a shaped body of silicon nitride having a transverse rupture strength in excess of 40,000 psi, which comprises the steps of compressing fine silicon powder to a green density of at least 1.45 grams/cc., the starting silicon powder having a generally uniform particle size and being essentially free of particles having a diameter greater than about 10 microns, sintering the compressed powder in an inert atmosphere essentially free of nitrogen, carbon, and oxygen, to form an interlocking silicon structure having silicon to silicon bonds between the fine particles, the maximum cross-sectional dimensions in the interlocking silicon structure being on the order of a few microns, and thereafter firing the silicon structure in a nitrogen containing atmosphere to convert the structure into a continuous silicon nitride body having essentially no pores greater than 15 microns a portion of the nitriding step being above the sintering temperature.
- 2. The process of claim 1 wherein the starting powder contains at least 1% total impurities selected from the group consisting of iron, aluminum and calcium.
- 3. The process of forming a shaped body of silicon nitride having a transverse rupture strength in excess of 40,000 psi. which comprises the steps of compressing fine silicon powder to a green density of at least 1.45 grams/cc., the starting silicon powder being essentially free of particles having a diameter greater than about 10 microns and having an average diameter on the order of 2 microns, sintering the compressed powder to a temperature on the order of 1100.degree. C. in an inert atmosphere essentially free of nitrogen, carbon, and oxygen, to form an interlocking silicon structure having silicon to silicon bonds between the fine particles, the maximum cross-sectional dimensions in the interlocking silicon structure being on the order of a few microns, and thereafter firing the silicon structure in a nitrogen containing atmosphere to convert the structure into a continuous silicon nitride body having essentially no pores greater than 15 microns a portion of the nitriding step being above the sintering temperature.
- 4. The process of claim 3 including the step of machining the sintered product to final shape prior to firing in nitrogen.
- 5. The process of claim 1 wherein the sintering is continued until the sintered product has a transverse rupture strength in excess of 1000 psi.
- 6. The process of claim 1 wherein the sintering step is combined with the compressing step.
- 7. The process of forming a shaped body of silicon nitride having a transverse rupture strength in excess of 40,000 psi., which comprises the steps of compressing fine silicon powder to a green density of at least 1.45 grams/cc., the starting silicon powder having a generally uniform particle size and being essentially free of particles having a diameter greater than about 10 microns, sintering the compressed powder in an inert atmosphere essentially free of nitrogen, carbon and oxygen, to form an interlocking silicon structure having silicon to silicon bonds between the fine particles, the silicon structure strength depending on silicon to silicon bonds rather than glassy bonds, the maximum cross-sectional dimensions in the interlocking silicon structure being on the order of a few microns, and thereafter firing the silicon structure in a nitrogen containing atmosphere to convert the structure into a continuous silicon nitride body having essentially no pores greater than 15 microns a portion of the nitriding step being above the sintering step, the individual silicon nitride particles of the body being bonded by silicon nitride recrystallization rather than by containing interstitial impurities.
RELATED APPLICATIONS
This application is a continuation in part of my co-pending application Ser. No. 370,745 filed June 18, 1973 which was a continuation in part of my application Ser. No. 263,578 filed June 16, 1972 and both now abandoned.
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
2618565 |
Nicholsen |
Nov 1952 |
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3778231 |
Taylor |
Dec 1973 |
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Non-Patent Literature Citations (4)
Entry |
High Temperature Properties of Reaction Bonded Silicon Nitride, M.E. Washburn et al., 6 pp. Nov. 1973. |
Parr et al., Preparation, Micro-Structure, and Mechanical Properties of Silicon Nitride, Special Ceramics, pp. 102-135. |
Fulrath et al., Ceramic Microstructure, pp. 852 and 264-265, 853 (1966). |
Evans, A. G. et al., "The Strength and Oxidation of Reaction Sintered Silicon Nitride", Jour. of Materials Sci. 5 (1970) pp. 314-325. |
Continuation in Parts (2)
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Number |
Date |
Country |
Parent |
370745 |
Jun 1973 |
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Parent |
263578 |
Jun 1972 |
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