Patent US2735909A successfully refreshed from Google Patents.
Patent US4619905A successfully refreshed from Google Patents.
US4619905A
Expired / Lapsed
US
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Process for the synthesis of silicon nitride
Assignee: Verizon Laboratories Inc
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Filing: 1984-12-24
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Granted: 1986-10-28
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Expires: 2004-12-24
Abstract
Abstract A process for the preparation of silicon nitride powders, which are suitable for the manufacture of high quality structural ceramics is described. The synthesis process is based on the reduction of silicon dioxide by carbon in a nitrogen stream at elevated temperatures to form alpha silicon nitride. Silicon nitride powders of various morphologies are obtained by this technique by varying either the type of reactants used or the process conditions. Structural ceramics with densities exceeding 99% of theoretical and having satisfactory mechanical strength and oxidation resistance were sintered from powders synthesized by the method of this invention.
Inventors
- 👤 Samuel Natansohn
- 👤 Gary Czupryna
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 02:59
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/515; C04B35/58; C04B35/584; C01; C01B; C01B21/00; C01B21/06; C01B21/068; C01B21/0685; C01P; C01P2002/00; C01P2002/02; C01P2004/00; C01P2004/01; C01P2004/03; C01P2004/60; C01P2004/61
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
116 words
A method for making silicon nitride powder comprising the steps: Step 1 mixing carbon and silicon dioxide having a weight ratio from about 1 to about 4 to form a homogeneous powder mixture; Step 2 heating the powder mixture from step 1 from about 1400° C. to about 1550° C. in a nitrogen stream for a time sufficient to form silicon nitride, the nitrogen stream having a velocity from about one to about 3 cm/sec, said carbon having an oil absorption value less than 100 ml/100 g; and Step 3 heat treating the product from step 2 in air at about 600° C. to about 700° C. for a time sufficient to completely oxidize residual carbon.
Claim 2
Independent Claim
116 words
A method for making silicon nitride powder comprising the steps: Step 1 mixing carbon and silicon dioxide having a weight ratio from about 1 to about 4 to form a homogeneous powder mixture; Step 2 heating the powder mixture from step 1 from about 1400° C. to about 1550° C. in a nitrogen stream for a time sufficient to form silicon nitride, the nitrogen stream having a velocity from about one to about 3 cm/sec, said carbon having an oil absorption value less than 100 ml/100 g; and Step 3 heat treating the product from step 2 in air at about 600° C. to about 700° C. for a time sufficient to completely oxidize residual carbon.
Claim 3
Dependent Claim
28 words
A method for making silicon nitride powder in accordance with claim 1 wherein the carbon and silicon dioxide have a weight ratio from about 1.5 to about 2.0.
Claim 4
Dependent Claim
26 words
A method for making silicon nitride powder in accordance with claim 1 wherein the velocity of the nitrogen is from about 1.2 to about 2.5 cm/sec.
Claim 5
Dependent Claim
79 words
A method for making silicon nitride powder in accordance with claim 1 wherein step 2 comprises heating the powder mixture from step 1 in a tray from about 1400° C. to about 1550° C. in a nitrogen stream for about 2 to about 10 hours to form silicon nitride, the nitrogen stream having a velocity from about one to about 3 cm/sec, the powder mixture from step 1 being in the tray at a depth greater than 5 mm.
Claim 6
Dependent Claim
29 words
A method for making silicon nitride powder in accordance with claim 4 wherein the depth of the powder mixture from step 1 in the tray is about 35 mm.
Claim 7
Dependent Claim
170 words
A ceramic article comprising silicon nitride and a densification aid, the ceramic article having a modulus of rupture at 1400° C. equal to or greater than 70 ksi and an oxidation rate at 1350° C. equal to or less than 4.4×10 -12 Kg 2 m -4 sec -1 , the silicon nitride in the ceramic article being made by the method comprising the steps: Step 1 mixing carbon and silicon dioxide having a weight ratio from about 1 to about 4 to form a homogeneous powder mixture; Step 2 heating the powder mixture from step 1 from about 1400° C. to about 1550° C. in a nitrogen stream for a time sufficient to form silicon nitride, the nitrogen stream having a velocity from about one to about 3 cm/sec, said carbon having an oil absorption value less than 100 ml/100 g; and Step 3 heat treating the product from step 2 in air at about 600° C. to about 700° C. for a time sufficient to completely oxidize residual carbon.
Claim 8
Dependent Claim
170 words
A ceramic article comprising silicon nitride and a densification aid, the ceramic article having a modulus of rupture at 1400° C. equal to or greater than 70 ksi and an oxidation rate at 1350° C. equal to or less than 4.4×10 -12 Kg 2 m -4 sec -1 , the silicon nitride in the ceramic article being made by the method comprising the steps: Step 1 mixing carbon and silicon dioxide having a weight ratio from about 1 to about 4 to form a homogeneous powder mixture; Step 2 heating the powder mixture from step 1 from about 1400° C. to about 1550° C. in a nitrogen stream for a time sufficient to form silicon nitride, the nitrogen stream having a velocity from about one to about 3 cm/sec, said carbon having an oil absorption value less than 100 ml/100 g; and Step 3 heat treating the product from step 2 in air at about 600° C. to about 700° C. for a time sufficient to completely oxidize residual carbon.
Claim 9
Dependent Claim
17 words
A ceramic article in accordance with claim 6 wherein said densification aid is about 6 w/o yttria.
Claim 10
Dependent Claim
191 words
A ceramic article comprising silicon nitride and a densification aid, the ceramic article having a modulus of rupture at 1400° C. equal to or greater than 70 ksi and an oxidation rate at 1350° C. equal to or less than 4.4×10 -12 Kg 2 m -4 sec -1 , the ceramic article being made by the method comprising the steps: Step 1 mixing carbon and silicon dioxide having a weight ratio from about 1 to about 4 to form a homogeneous powder mixture. Step 2 heating the powder mixture from step 1 from about 1400° C. to about 1550° C. in a nitrogen stream for a time sufficient to form silicon nitride, the nitrogen stream having a velocity from about one to about 3 cm/sec, said carbon having an oil absorption value less than 100 ml/100 g; Step 3 heat treating the product from step 2 in air at about 600° C. to about 700° C. for a time sufficient to completely oxidize residual carbon; Step 4 mixing the produce from step 3 with a densification aid; and Step 5 densifying the product from step 4 to form a ceramic article.
Claim 11
Dependent Claim
191 words
A ceramic article comprising silicon nitride and a densification aid, the ceramic article having a modulus of rupture at 1400° C. equal to or greater than 70 ksi and an oxidation rate at 1350° C. equal to or less than 4.4×10 -12 Kg 2 m -4 sec -1 , the ceramic article being made by the method comprising the steps: Step 1 mixing carbon and silicon dioxide having a weight ratio from about 1 to about 4 to form a homogeneous powder mixture. Step 2 heating the powder mixture from step 1 from about 1400° C. to about 1550° C. in a nitrogen stream for a time sufficient to form silicon nitride, the nitrogen stream having a velocity from about one to about 3 cm/sec, said carbon having an oil absorption value less than 100 ml/100 g; Step 3 heat treating the product from step 2 in air at about 600° C. to about 700° C. for a time sufficient to completely oxidize residual carbon; Step 4 mixing the produce from step 3 with a densification aid; and Step 5 densifying the product from step 4 to form a ceramic article.
Claim 12
Dependent Claim
34 words
A ceramic article in accordance with claim 8 wherein step 5 is isostatic pressing and sintering the product from step 4 to form a ceramic article having a density greater than 99% of theoretical.
Claim 13
Dependent Claim
32 words
A ceramic article in accordance with claim 8 wherein step 5 is hot pressing the product from step 4 to form a ceramic article having a density greater than 99% of theoretical.
Claim 14
Dependent Claim
87 words
A ceramic article in accordance with claim 6 wherein step 2 comprises heating the powder mixture from step 1 in a tray from about 1400° C. to about 1550° C. in a nitrogen stream for about 2 to about 10 hours to form silicon nitride, the nitrogen stream having a velocity from about one to about 3 cm/sec, the powder mixture from step 1 being in the tray at a depth greater than 5 mm, said carbon having an oil absorption value less than 100 ml/100 g.
Claim 15
Dependent Claim
25 words
A ceramic article in accordance with claim 11 wherein the depth of the powder mixture from step 1 in the tray is about 35 mm.
Claim 16
Dependent Claim
87 words
A ceramic article in accordance with claim 8 wherein step 2 comprises heating the powder mixture from step 1 in a tray from about 1400° C. to about 1550° C. in a nitrogen stream for about 2 to about 10 hours to form silicon nitride, the nitrogen stream having a velocity from about one to about 3 cm/sec, the powder mixture from step 1 being in the tray at a depth greater than 5 mm, said carbon having an oil absorption value less than 100 ml/100 g.
Claim 17
Dependent Claim
25 words
A ceramic article in accordance with claim 13 wherein the depth of the powder mixture from step 1 in the tray is about 35 mm.
Claim 18
Dependent Claim
17 words
A ceramic article in accordance with claim 8 wherein said densification aid is about 6 w/o yttria.
Claim 19
Dependent Claim
41 words
A method for making silicon nitride powder in accordance with claim 1 wherein said velocity of said nitrogen stream of step 2 being sufficient to form a silicon nitride powder morphology characterized by the morphology depicted in FIGS. 1 and 2.
Claim 20
Dependent Claim
39 words
A method for making silicon nitride powder in accordance with claim 1 wherein said velocity of said nitrogen stream of step 2 being sufficient to form a silicon nitride powder morphology characterized by the morphology depicted in FIG. 3.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1989-10-27 | 1990-04-28 | 1990-10-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-10-27 | 1994-04-28 | 1994-10-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-10-27 | 1998-04-28 | 1998-10-28 | $7700.00 | Window Closed / Lapsed |