US4508671A
Expired / Lapsed
US
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Method of making an anisotropic silicon nitride comprising object by use of higher density and fully reacted preforms
Assignee: Ceradyne Inc
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Filing: 1983-07-19
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Granted: 1985-04-02
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Expires: 2003-07-19
Abstract
Abstract A method is disclosed of densifying a silicon nitride comprising compact having 5-17% by weight yttrium silicon oxynitride and having a density of 2.0-2.6 gm/cm 3 . The method comprises (a) partially sintering the compact at a temperature of 3000°-3200° F. for a period of 0.5-72 hours to form a semidense body with a density of 2.9-3.15 gm/cm 3 , and (b) hot pressing a stacked assembly of said bodies in the hot zone of a hot pressing cavity to form fully dense anisotropic products, each body being separated from the other within the assembly by a distance no greater than 0.03 inch, and the stacked assembly occupying substantially the entire length of the hot zone of the hot pressing cavity.
Inventors
- 👤 Andre Ezis
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 22:18
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/622; C04B35/64; C04B35/645; C04B35/515; C04B35/58; C04B35/584; C04B35/593
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
136 words
A method of densifying a silicon nitride comprising compact having 5-17% by weight yttrium silicon oxynitride and having a density of 2.0-2.6 gm/cm 3 , comprising the steps of: (a) partially sintering said compact at a temperature of 3000°-3200° F. for a period of 0.5-72 hours to form a semidense body with a density of 2.9-3.15 gm/cm 3 ; and (b) sequentially hot pressing a stacked assembly of said bodies by sliding said bodies through the hot zone of a hot pressing cavity during hot pressing cycle at a temperature and pressure to form fully dense anistropic products, each body being separated from the other within the assembly during such sliding by a distance no greater than 0.030 inch, said stacked assembly occupying substantially the entire length of the hot zone of said hot pressing cavity.
Claim 2
Independent Claim
136 words
A method of densifying a silicon nitride comprising compact having 5-17% by weight yttrium silicon oxynitride and having a density of 2.0-2.6 gm/cm 3 , comprising the steps of: (a) partially sintering said compact at a temperature of 3000°-3200° F. for a period of 0.5-72 hours to form a semidense body with a density of 2.9-3.15 gm/cm 3 ; and (b) sequentially hot pressing a stacked assembly of said bodies by sliding said bodies through the hot zone of a hot pressing cavity during hot pressing cycle at a temperature and pressure to form fully dense anistropic products, each body being separated from the other within the assembly during such sliding by a distance no greater than 0.030 inch, said stacked assembly occupying substantially the entire length of the hot zone of said hot pressing cavity.
Claim 3
Dependent Claim
43 words
The method as in claim 1, in which said hot pressing is carried out to hot press a train of said stacked assembly of bodies in said hot pressing cavity to approach continuous hot pressing, said sliding being along the axis of stacking.
Claim 4
Dependent Claim
40 words
The method as in claim 2, in which the width to height ratio of said bodies is 1:3 to 1:40 and the number of bodies within each stacked assembly is at least five and each are aligned in single file.
Claim 5
Dependent Claim
27 words
The method as in claim 1, in which said hot pressing is carried out with an applied pressure of 1000-2000 psi and a temperature of 1600°-1760° C.
Claim 6
Dependent Claim
29 words
The method as in claim 1, in which said time dwell of each body in said assembly in said hot zone of the hot pressing cavity is 0.25-2.0 hours.
Claim 7
Dependent Claim
22 words
The method as in claim 1, in which the compaction ratio of hot pressing is in the range of 1.05:1 to 1.2:1.
Claim 8
Dependent Claim
21 words
The method as in claim 1, in which the hot pressed bodies each have a density of 3.2-3.45 gm/cm 3 .
Claim 9
Dependent Claim
98 words
The method as in claim 2, in which said hot pressing is carried out in an elongated tubular hot pressing cavity, the central zone being directly heated to form a hot zone and zones on either side of said hot zone experiencing a temperature gradient to permit, respectively, preheating or progressive cooling down, each stacked assembly of bodies being contained within an inert sleeve effective to slide within said cavity during the hot pressing cycle, said assemblies of said train being indexed along said cavity providing for a predetermined time dwell within each station along said tubular cavity.
Claim 10
Dependent Claim
37 words
The method as in claim 8, in which the assemblies are indexed along at least five stations in consecutive order, including an entrance zone, a preheat zone, a hot zone, a cooling zone, and an exit zone.
Claim 11
Dependent Claim
17 words
The method as in claim 9 in which the time dwell within each zone is 0.25-2 hours.
Claim 12
Independent Claim
256 words
A method of making a silicon nitride comprising product, by the steps of: (a) forming a plurality of compacts from a mixture of powdered silicon and reactive oxygen carrying agents, the latter being effective to form upon heating at least one second phase crystallite dispersed throughout the compact, said reactive oxygen carrying agents being present in an amount to substantially fully react said silicon upon heating in nitrogen, whereby said compact will consist essentially of Si 3 N 4 and 5-17% by weight second phase crystallites; (b) heating said compacts in a nitriding atmosphere to a temperature level for a period of time to effectively form a silicon nitride comprising body with a density of 2.0-2.6 gm/cm 3 and consisting essentially of Si 3 N 4 and 5-17% by weight second phase crystallites; (c) partially sintering said bodies at a temperature of 3000°-3200° F. for a period of 0.5-72 hours to form a semidense body having a density of 2.9-3.15 gm/cm 3 and consisting essentially of the chemistry resulting from said heating in step (b); and (d) sequentially hot pressing an assembly of said partially sintered bodies, stacked in single file order, by sliding said bodies through the hot zone of a hot pressing cavity during the hot pressing cycle at a temperature and pressure to form fully dense anisotropic products, each body being separated from the other within said assembly by a distance no greater than 0.03 inch, said stacked assembly occupying substantially the entire length of said hot zone of said hot pressing cavity.
Claim 13
Independent Claim
256 words
A method of making a silicon nitride comprising product, by the steps of: (a) forming a plurality of compacts from a mixture of powdered silicon and reactive oxygen carrying agents, the latter being effective to form upon heating at least one second phase crystallite dispersed throughout the compact, said reactive oxygen carrying agents being present in an amount to substantially fully react said silicon upon heating in nitrogen, whereby said compact will consist essentially of Si 3 N 4 and 5-17% by weight second phase crystallites; (b) heating said compacts in a nitriding atmosphere to a temperature level for a period of time to effectively form a silicon nitride comprising body with a density of 2.0-2.6 gm/cm 3 and consisting essentially of Si 3 N 4 and 5-17% by weight second phase crystallites; (c) partially sintering said bodies at a temperature of 3000°-3200° F. for a period of 0.5-72 hours to form a semidense body having a density of 2.9-3.15 gm/cm 3 and consisting essentially of the chemistry resulting from said heating in step (b); and (d) sequentially hot pressing an assembly of said partially sintered bodies, stacked in single file order, by sliding said bodies through the hot zone of a hot pressing cavity during the hot pressing cycle at a temperature and pressure to form fully dense anisotropic products, each body being separated from the other within said assembly by a distance no greater than 0.03 inch, said stacked assembly occupying substantially the entire length of said hot zone of said hot pressing cavity.
Claim 14
Dependent Claim
42 words
The method as in claim 4, in which said reactive oxygen carrying powder agents consist essentially of Y 2 O 3 in an amount of 3-19% by weight of said silicon and said second phase crystallites are comprised of yttrium silicon oxynitrides.
Claim 15
Dependent Claim
44 words
The method as in claim 12, in which said oxygen carrying agents additionally include an oxide of aluminum effective to form a protective amorphous coating on the oxynitrides, said oxide of aluminum being present in an amount of 0.4-5% by weight of the mixture.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1988-04-01 | 1988-10-01 | 1989-04-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-04-01 | 1992-10-01 | 1993-04-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-04-01 | 1996-10-01 | 1997-04-02 | $7700.00 | Window Closed / Lapsed |