US4457958A
Expired / Lapsed
US
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Method of strengthening silicon nitride ceramics
Assignee: Boeing North American Inc
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Filing: 1981-05-22
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Granted: 1984-07-03
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Expires: 2001-05-22
Abstract
Abstract Si 3 N 4 ceramics having a glassy phase densification aid are heated while their surface is in contact with SiO 2 . The SiO 2 forms one side of a diffusion couple and draws the glassy phase out of the ceramic. The SiO 2 can be provided by heating the ceramic in air to form an SiO 2 scale by the oxidation of Si 3 N 4 , or by imbedding the ceramic in SiO 2 powder. Surface pits, if any, formed during oxidation, are removed by grinding.
Inventors
- 👤 Frederick F. Lange
- 👤 David R. Clarke
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 02:30
CPC Classifications
C; C04; C04B; C04B41/00; C04B41/009; C04B35/00; C04B35/515; C04B35/58; C04B35/584; C04B41/45; C04B41/50; C04B41/5025; C04B41/5035; C04B41/80; C04B41/81; C04B41/85; C04B41/87
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
95 words
A post-fabrication method of increasing the high temperature strength of a dense, polyphase silicon nitride (Si 3 N 4 ), structural ceramic, comprising the steps of: providing a densified Si 3 N 4 ceramic having a glassy phase; providing silicon dioxide (SiO 2 ) on the surface of said Si 3 N 4 ceramic; heating said Si 3 N 4 ceramic and said SiO 2 at a temperature sufficient to cause diffusion of impurity and additive cations from said glassy phase into said SiO 2 ; and removing surface pits formed during said heating step.
Claim 2
Dependent Claim
95 words
A post-fabrication method of increasing the high temperature strength of a dense, polyphase silicon nitride (Si 3 N 4 ), structural ceramic, comprising the steps of: providing a densified Si 3 N 4 ceramic having a glassy phase; providing silicon dioxide (SiO 2 ) on the surface of said Si 3 N 4 ceramic; heating said Si 3 N 4 ceramic and said SiO 2 at a temperature sufficient to cause diffusion of impurity and additive cations from said glassy phase into said SiO 2 ; and removing surface pits formed during said heating step.
Claim 3
Dependent Claim
49 words
The method as claimed in claim 1, wherein said step of providing SiO 2 comprises heating said Si 3 N 4 ceramic in an oxidizing atmosphere, whereby an SiO 2 scale is formed on said Si 3 N 4 ceramic by oxidation of said Si 3 N 4 ceramic.
Claim 4
Dependent Claim
26 words
The method as claimed in claim 1, wherein said step of providing SiO 2 comprises packing said Si 3 N 4 ceramic in SiO 2 powder.
Claim 5
Dependent Claim
40 words
The method as claimed in claim 1, wherein said Si 3 N 4 ceramic comprises an Si-Mg-O-N ceramic and said cations comprise Mg and cations from impurities selected from the group consisting of Ca, Fe, Al, Mn, Na, and K.
Claim 6
Dependent Claim
45 words
The method as claimed in claim 1, wherein said Si 3 N 4 ceramic having a glassy phase comprises an Si-Ce-O-N ceramic and said cations comprise Ce and cations from impurities selected from the group consisting of Mg, Ca, Fe, Al, Mn, Na and K.
Claim 7
Dependent Claim
46 words
The method as claimed in claim 1, wherein said Si 3 N 4 ceramic having a glassy phase comprises an Si-Y-O-N ceramic and said cation comprise Y and cations from impurities selected from the group consisting of Mg, Ca, Fe, Al, Mn, Na and K impurities.
Claim 8
Dependent Claim
45 words
The method as claimed in claim 1, wherein said Si 3 N 4 ceramic having a glassy phase comprises an Si-Al-O-N ceramic and said cation comprises Al and cations from impurities selected from the group consisting of Mg, Ca, Fe, Mn, Na, and K impurities.
Claim 9
Independent Claim
134 words
A method of fabricating an improved silicon nitride (Si 3 N 4 ), structural ceramic, comprising the steps of: providing a mixture of Si 3 N 4 powder and a sufficient quantity of a densification aid to cause rapid densification due to the formation of a liquid glassy phase during sintering; sintering said mixture to form a dense Si 3 N 4 ceramic; providing silicon dioxide (SiO 2 ) on the surface of said Si 3 N 4 ceramic; heating said Si 3 N 4 ceramic and said SiO 2 at a temperature sufficient to cause diffusion of impurities and additive cations from silicates in said glassy phase into said SiO 2 ; and grinding said Si 3 N 4 ceramic to a depth sufficient to remove surface pits formed during said heating step.
Claim 10
Independent Claim
134 words
A method of fabricating an improved silicon nitride (Si 3 N 4 ), structural ceramic, comprising the steps of: providing a mixture of Si 3 N 4 powder and a sufficient quantity of a densification aid to cause rapid densification due to the formation of a liquid glassy phase during sintering; sintering said mixture to form a dense Si 3 N 4 ceramic; providing silicon dioxide (SiO 2 ) on the surface of said Si 3 N 4 ceramic; heating said Si 3 N 4 ceramic and said SiO 2 at a temperature sufficient to cause diffusion of impurities and additive cations from silicates in said glassy phase into said SiO 2 ; and grinding said Si 3 N 4 ceramic to a depth sufficient to remove surface pits formed during said heating step.
Claim 11
Dependent Claim
36 words
The method as claimed in claim 8, wherein said densification aid comprises a glassy, phase-forming material containing SiO 2 and an element selected from the group consisting of Mg, Ce, Y, Nd, Be, Al, and La.
Claim 12
Independent Claim
72 words
A method of increasing the high temperature strength of a densified, polyphase Si-Mg-O-N, structural ceramic, comprising the steps of: providing said Si-Mg-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature sufficient to cause diffusion of Mg out of said ceramic and into said SiO 2 ; and grinding said Si-Mg-O-N ceramic to a depth sufficient to remove surface pits formed during said heating step.
Claim 13
Independent Claim
72 words
A method of increasing the high temperature strength of a densified, polyphase Si-Mg-O-N, structural ceramic, comprising the steps of: providing said Si-Mg-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature sufficient to cause diffusion of Mg out of said ceramic and into said SiO 2 ; and grinding said Si-Mg-O-N ceramic to a depth sufficient to remove surface pits formed during said heating step.
Claim 14
Independent Claim
63 words
A method of increasing the high temperature strength of a densified, polyphase Si-Ce-O-N, structural ceramic, comprising the steps of: providing said Si-Ce-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature sufficient to cause diffusion of Ce out of said ceramic and into said SiO 2 ; and removing surface pits formed during said heating step.
Claim 15
Independent Claim
63 words
A method of increasing the high temperature strength of a densified, polyphase Si-Ce-O-N, structural ceramic, comprising the steps of: providing said Si-Ce-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature sufficient to cause diffusion of Ce out of said ceramic and into said SiO 2 ; and removing surface pits formed during said heating step.
Claim 16
Independent Claim
63 words
A method of increasing the high temperature strength of a densified, polyphase Si-Y-O-N, structural ceramic, comprising the steps of: providing said Si-Y-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature sufficient to cause diffusion of Y out of said ceramic and into said SiO 2 ; and removing surface pits formed during said heating step.
Claim 17
Independent Claim
63 words
A method of increasing the high temperature strength of a densified, polyphase Si-Y-O-N, structural ceramic, comprising the steps of: providing said Si-Y-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature sufficient to cause diffusion of Y out of said ceramic and into said SiO 2 ; and removing surface pits formed during said heating step.
Claim 18
Independent Claim
57 words
A method of increasing the high temperature strength of a densified, polyphase Si-Mg-O-N, structural ceramic, comprising the steps of: providing said Si-Mg-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature of at least 1400° C. for at least 24 hours; and removing surface pits formed during said heating step.
Claim 19
Independent Claim
57 words
A method of increasing the high temperature strength of a densified, polyphase Si-Mg-O-N, structural ceramic, comprising the steps of: providing said Si-Mg-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature of at least 1400° C. for at least 24 hours; and removing surface pits formed during said heating step.
Claim 20
Independent Claim
57 words
A method of increasing the high temperature strength of a densified, polyphase Si-Y-O-N, structural ceramic, comprising the steps of: providing said Si-Y-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature of at least 1600° C. for at least 24 hours; and removing surface pits formed during said heating step.
Claim 21
Independent Claim
57 words
A method of increasing the high temperature strength of a densified, polyphase Si-Y-O-N, structural ceramic, comprising the steps of: providing said Si-Y-O-N ceramic; providing SiO 2 on the surface of said ceramic; heating said ceramic at a temperature of at least 1600° C. for at least 24 hours; and removing surface pits formed during said heating 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) | 1987-07-03 | 1988-01-02 | 1988-07-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-07-03 | 1992-01-02 | 1992-07-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-07-03 | 1996-01-02 | 1996-07-03 | $7700.00 | Window Closed / Lapsed |