US4892848A
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Silicon nitride sintered body and process for preparation thereof
Assignee: Kyocera Corp
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Filing: 1986-07-29
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Granted: 1990-01-09
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Expires: 2006-07-29
Abstract
Abstract Disclosed is a process for the preparation of a silicon nitride sintered body, which comprises steps of (i) molding a composition comprising (a) 87 to 98% by weight of silicon nitride and (b) 2 to 13% by weight of a sintering aid comprising an oxide or nitride of aluminum or an element of the group IIIa of the Periodic Table and an inorganic oxide capable of forming a liquid phase component having a melting point lower than that of silicon nitride, the inorganic oxide being present in an amount of 1 to 7% by weight based on the composition, (ii) sintering the molded body in a nitrogen atmosphere at a temperature forming a liquid phase containing said liquid phase component having a low melting point, and (iii) heat-treating the resulting sintered body in a nitrogen atmosphere at a temperature higher than the sintering temperature to volatilize the liquid phase component having a low melting point from the liquid phase. In the obtained sintered body, the oxygen content in the surface layer is controlled below 3% by weight, and the flexural strength at 1300 DEG C. of the surface layer is higher than that of the inner portion.
Inventors
- 👤 Makoto Yoshida
- 👤 Kiyoshi Yokoyama
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 20:18
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/515; C04B35/58; C04B35/584; C04B35/593; C04B35/5935
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
206 words
A process for preparation of a silicon nitride sintered body, which process comprises (i) molding a composition comprising (a) 87 to 98% by weight of silicon nitride and (b) 2 to 13% by weight of a sintering aid, said sintering aid comprising an oxide or nitride of aluminum or other element of group IIIa of the Periodic Table and an inorganic oxide capable of forming a liquid phase component having a melting point lower than that of silicon nitride, the inorganic oxide being present in an amount of 1 to 7% by weight based on the composition, thereby forming a molded body; (ii) sintering the molded body in a nitrogen atmosphere at a first temperature within the range of 1650° and 1800° C. and sufficient to form a liquid phase comprising said liquid phase component, thereby forming a sintered body; and (iii) heat-treating the sintered body in a nitrogen atmosphere at a second temperature within the range of 1900° and 2000° C. and sufficient to volatilize the liquid phase component, thereby forming a final product having a surface layer and an inner phase, said heat-treating being carried out so that oxygen content of the surface layer of the final product is lower than 3% by weight.
Claim 2
Dependent Claim
206 words
A process for preparation of a silicon nitride sintered body, which process comprises (i) molding a composition comprising (a) 87 to 98% by weight of silicon nitride and (b) 2 to 13% by weight of a sintering aid, said sintering aid comprising an oxide or nitride of aluminum or other element of group IIIa of the Periodic Table and an inorganic oxide capable of forming a liquid phase component having a melting point lower than that of silicon nitride, the inorganic oxide being present in an amount of 1 to 7% by weight based on the composition, thereby forming a molded body; (ii) sintering the molded body in a nitrogen atmosphere at a first temperature within the range of 1650° and 1800° C. and sufficient to form a liquid phase comprising said liquid phase component, thereby forming a sintered body; and (iii) heat-treating the sintered body in a nitrogen atmosphere at a second temperature within the range of 1900° and 2000° C. and sufficient to volatilize the liquid phase component, thereby forming a final product having a surface layer and an inner phase, said heat-treating being carried out so that oxygen content of the surface layer of the final product is lower than 3% by weight.
Claim 3
Dependent Claim
30 words
A process according to claim 1, wherein the sintering aid comprises said inorganic oxide and an oxide or nitride of an element of the group IIIa of the Periodic Table.
Claim 4
Dependent Claim
35 words
A process according to claim 1, wherein the inorganic oxide is SiO 2 , MgO, WO 3 , MoO 3 , B 2 O 3 , SrO, TiO 2 , CaO or Li 2 O.
Claim 5
Dependent Claim
20 words
A process according to claim 1, wherein the inorganic oxide is SiO 2 contained in silicon nitride as an impurity.
Claim 6
Dependent Claim
22 words
A process according to claim 2, wherein the oxide of the element of the group IIIa of the Periodic Table is yttria.
Claim 7
Dependent Claim
23 words
A process according to claim 1, wherein said sintering is carried out under a pressure higher than thermodynamic equilibrium pressure of silicon nitride.
Claim 8
Dependent Claim
22 words
A process according to claim 1, wherein said heat-treating is carried out subsequently to said sintering by elevating the temperature in situ.
Claim 9
Dependent Claim
200 words
A process for preparation of a silicon nitride sintered body, which process comprises (i) molding a composition comprising (a) 87 to 98% by weight of silicon nitride and (b) 2 to 13% by weight of a sintering aid, said sintering aid comprising an oxide or nitride of aluminum or other element of group IIIa of the Periodic Table and an inorganic oxide capable of forming a liquid phase component having a melting point lower than that of silicon nitride, the inorganic oxide being present in an amount of 1 to 7% by weight based on the composition, thereby forming a molded body; (ii) sintering the molded body in a nitrogen atmosphere at a first temperature within the range of 1650° and 1800° C. and sufficient to form a liquid phase comprising said liquid phase component, thereby forming a sintered body; and (iii) heat-treating the sintered body in a nitrogen atmosphere at a second temperature within the range of 1900° and 2000° C. while forcibly substituting nitrogen gas in the atmosphere to maintain vapor pressure of the liquid phase component in the atmosphere at a low level to form a final product, whereby volatilization of the liquid phase component is promoted.
Claim 10
Dependent Claim
200 words
A process for preparation of a silicon nitride sintered body, which process comprises (i) molding a composition comprising (a) 87 to 98% by weight of silicon nitride and (b) 2 to 13% by weight of a sintering aid, said sintering aid comprising an oxide or nitride of aluminum or other element of group IIIa of the Periodic Table and an inorganic oxide capable of forming a liquid phase component having a melting point lower than that of silicon nitride, the inorganic oxide being present in an amount of 1 to 7% by weight based on the composition, thereby forming a molded body; (ii) sintering the molded body in a nitrogen atmosphere at a first temperature within the range of 1650° and 1800° C. and sufficient to form a liquid phase comprising said liquid phase component, thereby forming a sintered body; and (iii) heat-treating the sintered body in a nitrogen atmosphere at a second temperature within the range of 1900° and 2000° C. while forcibly substituting nitrogen gas in the atmosphere to maintain vapor pressure of the liquid phase component in the atmosphere at a low level to form a final product, whereby volatilization of the liquid phase component is promoted.
Claim 11
Dependent Claim
35 words
A process according to claim 8, wherein the inorganic oxide is SiO 2 , MgO, WO 3 , MoO 3 , B 2 O 3 , SrO, TiO 2 , CaO or Li 2 O.
Claim 12
Dependent Claim
20 words
A process according to claim 8, wherein the inorganic oxide is SiO 2 contained in silicon nitride as an impurity.
Claim 13
Dependent Claim
24 words
A process according to claim 1, wherein the oxygen content of the surface layer of the final product is 2.5% by weight or less.
Claim 14
Dependent Claim
18 words
A process according to claim 1, wherein said composition comprises 90 to 95% by weight of silicon nitride.
Claim 15
Dependent Claim
18 words
A process according to claim 8, wherein said composition comprises 90 to 95% by weight of silicon nitride.
Claim 16
Dependent Claim
19 words
A process according to claim 1, wherein said inorganic oxide comprises 2 to 5% by weight of said composition.
Claim 17
Dependent Claim
19 words
A process according to claim 8, wherein said inorganic oxide comprises 2 to 5% by weight of said composition.
Claim 18
Dependent Claim
218 words
A process for preparation of a silicon nitride sintered body, which process comprises (i) molding a composition comprising (a) silicon nitride and (b) 2 to 13% by weight of a sintering aid, said sintering aid comprising an oxide or nitride of an element of group IIIa of the Periodic Table and an inorganic oxide capable of forming a liquid phase component having a melting point lower than that of silicon nitride, the inorganic oxide being present in an amount of up to 7% by weight base on the composition, thereby forming a molded body; (ii) sintering the molded body in a non-oxidizing atmosphere at a first temperature within the range of 1650° and 1800° C. and sufficient to form a liquid phase comprising said liquid phase component, thereby forming a sintered body; and (iii) heat-treating the sintered body in a non-oxidizing atmosphere at a second temperature within the range of 1900° and 2000° C., whereby volatilization of the liquid phase component is promoted, said heat-treating being carried out (1) while forcibly substituting non-oxidizing gas in the atmosphere to maintain vapor pressure of the liquid phase component in the atmosphere at a low level to form a final product or (2) so that oxygen content of the surface layer of the final product is lower than 3% by weight.
Claim 19
Dependent Claim
218 words
A process for preparation of a silicon nitride sintered body, which process comprises (i) molding a composition comprising (a) silicon nitride and (b) 2 to 13% by weight of a sintering aid, said sintering aid comprising an oxide or nitride of an element of group IIIa of the Periodic Table and an inorganic oxide capable of forming a liquid phase component having a melting point lower than that of silicon nitride, the inorganic oxide being present in an amount of up to 7% by weight base on the composition, thereby forming a molded body; (ii) sintering the molded body in a non-oxidizing atmosphere at a first temperature within the range of 1650° and 1800° C. and sufficient to form a liquid phase comprising said liquid phase component, thereby forming a sintered body; and (iii) heat-treating the sintered body in a non-oxidizing atmosphere at a second temperature within the range of 1900° and 2000° C., whereby volatilization of the liquid phase component is promoted, said heat-treating being carried out (1) while forcibly substituting non-oxidizing gas in the atmosphere to maintain vapor pressure of the liquid phase component in the atmosphere at a low level to form a final product or (2) so that oxygen content of the surface layer of the final product is lower than 3% by weight.
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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) | 1993-01-08 | 1993-07-10 | 1994-01-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-01-08 | 1997-07-10 | 1998-01-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-01-08 | 2001-07-10 | 2002-01-09 | $7700.00 | Window Closed / Lapsed |