US5445776A
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US
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Method for producing high density sintered silicon nitride (Si3 N.sub.4
Assignee: Kobe Steel Ltd
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Filing: 1991-12-31
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Granted: 1995-08-29
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Expires: 2011-12-31
Abstract
Abstract The specification describes a method for producing high density sintered silicon nitride(Si 3 N 4 ) having a relative density of at least 98%. In a first step, silicon nitride powder is compacted into a desired shape. It is then presintered in a second step, generally, under normal pressure to obtain a presintered body having a relative density of at least 92%. In a third step, the presintered body is subjected to a hot isostatic pressing(HIP) in an inert gas atmosphere of 1500-2100° C. and of nitrogen gas partial pressure of at least 500 atm. Since the presintering does not require any capsule, it is possible to produce high density sintered Si 3 N 4 of complex configurations. As a sintering aid, Y 2 O 3 --Al 2 O 3 --MgO system sintering aid is particularly effective. To improve the strength of sintered Si 3 N 4 , it is effective to add a heat treatment step after the HIP and maintain the temperature of the sintered Si 3 N 4 , above 500° C. for a while. Between the second and third steps, the temperature of the presintered body is preferably maintained above 500° C. These temperature controls are effective not only to improve the strength of sintered Si 3 N 4 but also to save the thermal energy and to shorten the production cycle.
Inventors
- 👤 Katuhiko Honma
- 👤 Tsuneo Tatsuno
- 👤 Hiroshi Okada
- 👤 Masato Moritoki
- 👤 Takao Fujikawa
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 12:44
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/515; C04B35/58; C04B35/584; C04B35/593; C04B35/5935
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
193 words
A method for producing high density sintered silicon nitride (Si 3 N 4 ) having a relative density of at least 98%, said method comprising: forming silicon nitride powder into a desired shape to obtain a silicon nitride green compact; presintering said green compact under a nitrogen gas atmosphere ranging in pressure from 1 to 30 atmospheres at an elevated temperature into a presintered body having a relative density of at least 92%; removing the presintered body at a temperature of at least 500° C. from the presintering furnace; cooling the heated presintered body to room temperature; charging the cooled presintered body into a hot isostatic pressing furnace which has been preheated to 500° C. or higher; subjecting said presintered body to hot isostatic pressing without being confined by a capsule in an inert gas atmosphere of a temperature in the range of 1500°-2100° C. and of a nitrogen gas partial pressure of at least 500 atm until the relative density of at least 98% is reached; and upon completion of the hot isostatic pressing, discharging the sintered body from the hot isostatic pressing furnace at a temperature of at least 500° C.
Claim 2
Independent Claim
193 words
A method for producing high density sintered silicon nitride (Si 3 N 4 ) having a relative density of at least 98%, said method comprising: forming silicon nitride powder into a desired shape to obtain a silicon nitride green compact; presintering said green compact under a nitrogen gas atmosphere ranging in pressure from 1 to 30 atmospheres at an elevated temperature into a presintered body having a relative density of at least 92%; removing the presintered body at a temperature of at least 500° C. from the presintering furnace; cooling the heated presintered body to room temperature; charging the cooled presintered body into a hot isostatic pressing furnace which has been preheated to 500° C. or higher; subjecting said presintered body to hot isostatic pressing without being confined by a capsule in an inert gas atmosphere of a temperature in the range of 1500°-2100° C. and of a nitrogen gas partial pressure of at least 500 atm until the relative density of at least 98% is reached; and upon completion of the hot isostatic pressing, discharging the sintered body from the hot isostatic pressing furnace at a temperature of at least 500° C.
Claim 3
Dependent Claim
24 words
The method as claimed in claim 1, wherein said silicon nitride powder contains at least 80% by weight of α-Si 3 N 4 .
Claim 4
Dependent Claim
17 words
The method as claimed in claim 1, wherein said silicon nitride powder further contains a sintering aid.
Claim 5
Dependent Claim
65 words
The method as claimed in claim 3, wherein said sintering aid is one or more compounds selected from the group consisting of Y 2 O 3 , Al 2 O 3 , MgO, ZrO 2 , TiO 2 , BeO, La 2 O 3 , CeO 2 , TiN, and AlN and is contained in a total amount of not more than 30% by weight.
Claim 6
Dependent Claim
27 words
The method as claimed in claim 3 or 4, wherein said sintering aid is a Y 2 O 3 --Al 2 O 3 --MgO system powder mixture.
Claim 7
Dependent Claim
33 words
The method as claimed in claim 5, wherein said silicon nitride powder contains 3-13% of Y 2 O 3 , 0.5-4% of Al 2 O 3 and 0.5-6% of MgO, all by weight.
Claim 8
Dependent Claim
48 words
The method as claimed in claim 1, wherein said presintered body contains 20-80% by weight of β-Si 3 N 4 and the content of β-Si 3 N 4 in the sintered silicon nitride(Si 3 N 4 ) is increased to 80% or higher through the hot isostatic pressing.
Claim 9
Dependent Claim
35 words
The method as claimed in claim 7, wherein the content of β-Si 3 N 4 in the sintered silicon nitride(Si 3 N 4 ) is increased to 90% or higher through the hot isostatic pressing.
Claim 10
Dependent Claim
14 words
The method as claimed in claim 1, wherein the presintering temperature is 1400°-1800° C.
Claim 11
Dependent Claim
45 words
The method as claimed in claim 1, wherein said presintered body is buried in powder consisting principally of at least one nitride ceramics selected from the group consisting of silicon nitride, aluminum nitride and boron nitride and is then subjected to the hot isostatic pressing.
Claim 12
Dependent Claim
21 words
The method as claimed in claim 1, wherein the hot isostatic pressing is carried out at a temperature of 1700°-2000° C.
Claim 13
Dependent Claim
25 words
The method as claimed in claim 1, wherein the hot isostatic pressing is carried out for a period of from 1 minute to 3 hours.
Claim 14
Dependent Claim
24 words
The method as claimed in claim 1, wherein the nitrogen partial pressure during the hot isostatic pressing is maintained at 700 atm or higher.
Claim 15
Dependent Claim
24 words
The method as claimed in claim 1, wherein the nitrogen partial pressure during the hot isostatic pressing is maintained at 2500 atm or lower.
Claim 16
Dependent Claim
23 words
The method as claimed in claim 1, wherein the hot isostatic pressing is carried out at a temperature higher than the presintering temperature.
Claim 17
Dependent Claim
27 words
The method as claimed in claim 1, wherein grain boundaries of the sintered silicon nitride(Si 3 N 4 ) are crystallized in the final heat treatment step.
Claim 18
Dependent Claim
28 words
The method as claimed in claim 1, wherein grain boundaries of the sintered silicon nitride (Si 3 N 4 ) are crystallized in the hot isostatic pressing step.
Claim 19
Dependent Claim
27 words
The method as claimed in claim 1, wherein said silicon nitride powder has been obtained in accordance with a gas phase reaction method or thermal decomposition method.
Claim 20
Dependent Claim
43 words
The method as claimed in claim 1, wherein the hot isostatic pressing is carried out at a temperature lower by at least 100° C. than the decomposition temperature of Si 3 N 4 at the pressure employed in the hot isostatic pressing step.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1998-08-28 | 1999-02-27 | 1999-08-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2002-08-28 | 2003-02-27 | 2003-08-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2006-08-28 | 2007-02-27 | 2007-08-29 | $7700.00 | Window Closed / Lapsed |