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Patent US4919689A successfully refreshed from Google Patents.
US4919689A
Expired / Lapsed
US
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Self-reinforced silicon nitride ceramic of high fracture toughness
Assignee: Dow Chemical Co
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Filing: 1989-02-28
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Granted: 1990-04-24
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Expires: 2009-02-28
Abstract
Abstract A process for preparing a self-reinforced silicon nitride ceramic body of high fracture toughness comprising hot-pressing a powder mixture containing silicon nitride, magnesium oxide, yttrium oxide and calcium oxide under conditions such that densification and the in situ formation of β-silicon nitride whiskers having a high aspect ratio occur. A novel silicon nitride ceramic of high fracture toughness is disclosed comprising a β-silicon nitride crystalline phase wherein at least about 20 volume percent of the phase is in the form of whiskers having an average aspect ratio of at least about 2.5; a glassy second phase containing magnesium oxide, yttrium oxide, calcium oxide, and silica in a total amount not greater than about 35 weight percent; and not greater than about 10 weight percent of the total weight as other phases.
Inventors
- 👤 Aleksander J. Pyzik
- 👤 Douglas B. Schwarz
- 👤 William J. Dubensky
- 👤 Donald R. Beaman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 07:00
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/515; C04B35/58; C04B35/584; C04B35/593; C04B35/622; C04B35/64; C04B35/645; C04B35/71; C04B35/78; C04B35/80
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
145 words
A silicon nitride ceramic body having a fracture toughness greater than about 6 MPa (m) 1/2 , as measured by the Chevron notch technique at about 23° C., consisting essentially of (a) a crystalline phase of β-silicon nitride of which at least about 20 volume percent, as measured in a plane by scanning electron microscopy, is in the form of whiskers having an average aspect ratio of at least about 2.5; and (b) a glassy phase in an amount not greater than about 35 weight percent of the total weight comprising magnesium oxide in a range from about 15 percent to about 51 percent, yttrium oxide in a range from about 36 percent to about 63 percent, calcium oxide in a range from about 0.1 percent to about 15 percent, and silica in a range from about 3 percent to about 30 percent by weight.
Claim 2
Dependent Claim
145 words
A silicon nitride ceramic body having a fracture toughness greater than about 6 MPa (m) 1/2 , as measured by the Chevron notch technique at about 23° C., consisting essentially of (a) a crystalline phase of β-silicon nitride of which at least about 20 volume percent, as measured in a plane by scanning electron microscopy, is in the form of whiskers having an average aspect ratio of at least about 2.5; and (b) a glassy phase in an amount not greater than about 35 weight percent of the total weight comprising magnesium oxide in a range from about 15 percent to about 51 percent, yttrium oxide in a range from about 36 percent to about 63 percent, calcium oxide in a range from about 0.1 percent to about 15 percent, and silica in a range from about 3 percent to about 30 percent by weight.
Claim 3
Dependent Claim
43 words
The composition of claim 1 wherein the weight ratio of yttrium oxide to magnesium oxide is in a range from about 0.7 to about 4.2.; and wherein not greater than about 10 weight percent of the total weight is present as other phases.
Claim 4
Dependent Claim
19 words
The composition of claim 1 wherein the percentage of silicon nitride whiskers is at least about 35 volume percent.
Claim 5
Dependent Claim
18 words
The composition of claim 1 wherein the whiskers have an average aspect ratio of at least about 5.5.
Claim 6
Dependent Claim
18 words
The composition of claim 1 wherein the fracture toughness is greater than about 7 MPa (m) 1/2 .
Claim 7
Dependent Claim
23 words
The composition of claim 5 wherein the fracture toughness ranges from about 9 MPa (m) 1/2 to about 14 MPa (m) 1/2 .
Claim 8
Dependent Claim
33 words
The composition of claim 1 wherein the fracture toughness as measured by the Chevron notch technique at 1000° C. ranges from about 7 MPa (m) 1/2 to about 12 MPa (m) 1/2 .
Claim 9
Dependent Claim
23 words
The composition of claim 1 wherein the Palmqvist toughness measured at about 23° C. ranges from about 37 kg/mm to about 52 kg/mm.
Claim 10
Dependent Claim
23 words
The composition of claim 8 wherein the Palmqvist toughness measured at about 23° C. ranges from about 45 kg/mm to about 52 kg/mm.
Claim 11
Dependent Claim
25 words
The composition of claim 1 wherein the fracture strength measured at room temperature is in the range from about 685 MPa to about 925 MPa.
Claim 12
Dependent Claim
25 words
The composition of claim 1 wherein the fracture strength measured at 1000° C. is in the range from about 580 MPa to about 650 MPa.
Claim 13
Dependent Claim
10 words
A cutting tool fabricated from the composition of claim 1.
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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) | 1993-04-23 | 1993-10-23 | 1994-04-24 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-04-23 | 1997-10-23 | 1998-04-24 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-04-23 | 2001-10-23 | 2002-04-24 | $7700.00 | Window Closed / Lapsed |