US4623498A
Expired / Lapsed
US
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Method of improving quality of hot pressed Si3 N4 bodies
Assignee: Ceradyne Inc
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Filing: 1984-07-12
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Granted: 1986-11-18
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Expires: 2004-07-12
Abstract
Abstract A method of improving the quality of hot pressed Si 3 N 4 bodies is disclosed. Unpurified silicon powder and admixed oxygen carrying agents are compacted to form a preform. The preform is nitrided, facilitated by the presence of certain impurities, to agglomerate the mixture to an increased density no greater than 2.7 gm/cm 3 . The nitrided preform is immersed in one or more stages in one or more leaching solutions of effective concentration to remove the selected impurities. The treated preform is then hot pressed to full density accompanied by a substantial reduction or absence of undesirable impurities such as iron silicide, which can conventionally form during hot pressing.
Inventors
- 👤 Elaine C. Beckwith
- 👤 Andre Ezis
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 13:33
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/515; C04B35/58; C04B35/584; C04B35/593
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
165 words
A method of making a silicon nitride comprising object, comprising: (a) forming a preform by compacting a mixture of unpurified silicon powder and oxygen carrying agents in an amount effective to form intergranular second phase crystallites with Si 3 N 4 upon heating in a nitrogen bearing atmosphere; (b) heating the preform in a nitrogen atmosphere to react the ingredients thereof and agglomerate the mixture to an increased density no greater than 2.7 gm/cm 3 , said agglomerated preform being constituted of silicon nitride, silicon oxynitride crystallites, silicate, and impurities from the group consiting of Si, Fe, silicides, Fe 2 O 3 , and other oxygen carrying agents other than SiO 2 ; (c) immersing said heat treated preform in one or more stages in one or more leaching solutions of effective concentration to substantially remove at least one of said group of impurities; and (d) heating said treated preform to heat fusing condition to form a unitary, substantially fully dense silicon nitride comprising object.
Claim 2
Independent Claim
165 words
A method of making a silicon nitride comprising object, comprising: (a) forming a preform by compacting a mixture of unpurified silicon powder and oxygen carrying agents in an amount effective to form intergranular second phase crystallites with Si 3 N 4 upon heating in a nitrogen bearing atmosphere; (b) heating the preform in a nitrogen atmosphere to react the ingredients thereof and agglomerate the mixture to an increased density no greater than 2.7 gm/cm 3 , said agglomerated preform being constituted of silicon nitride, silicon oxynitride crystallites, silicate, and impurities from the group consiting of Si, Fe, silicides, Fe 2 O 3 , and other oxygen carrying agents other than SiO 2 ; (c) immersing said heat treated preform in one or more stages in one or more leaching solutions of effective concentration to substantially remove at least one of said group of impurities; and (d) heating said treated preform to heat fusing condition to form a unitary, substantially fully dense silicon nitride comprising object.
Claim 3
Dependent Claim
18 words
The method as in claim 1 in which said silicon powder has relative purity of at least 97%.
Claim 4
Dependent Claim
58 words
The method as in claim 1 in which said oxygen carrying agents comprise Y 2 O 3 , Al 2 O 3 (each having a relative purity of at least 99.99%), and SiO 2 , the latter being present substantially as an oxide coating on said silicon powder, and said intergranular second phases comprise essentially yttrium silicon oxynitrides.
Claim 5
Dependent Claim
50 words
The method as in claim 3, in which in one stage of step (c) an aqueous solution of one of hydrochloric acid, sulfuric acid, acetic acid, oxalic acid or nitric acid is used to leach out the impurities of iron, silicides, iron oxide, and unreacted Y 2 O 3 .
Claim 6
Dependent Claim
34 words
The method as in claim 4, in which in a second stage of step (c) an aqueous solution of sodium hydroxide, potassium hydroxide, or their equivalent, is used to substantially leach out free silicon.
Claim 7
Dependent Claim
22 words
The method as in claim 1 in which said density of said preform is in the range of 50-72% of full theoretical.
Claim 8
Dependent Claim
46 words
The method as in claim 1, in which said oxygen carrying agents are selected from the group consisting of Y 2 O 3 , Al 2 O 3 , SiO 2 , MgO, CeO 2 , ZrO 2 , HfO 2 , and other rare earths.
Claim 9
Dependent Claim
22 words
The method as in claim 1, in which at least one of said leaching solutions is an aqueous solution of hydrochloric acid.
Claim 10
Dependent Claim
24 words
The method as in claim 8, in wich the concentration of hydrochloric acid in said solution is in the range of 3-10 molar percent.
Claim 11
Dependent Claim
32 words
The method as in claim 1, in which said leaching solutions are selected from the group consisting of aqueous solutions of hydrochloric acid, sulfuric acid, acetic acid, oxalic acid, and nitric acid.
Claim 12
Dependent Claim
27 words
The method as in claim 10, in which a second solution is additionally and separately employed containing sodium hydroxide in a concentration of about 5 molar percent.
Claim 13
Dependent Claim
20 words
The method as in claim 8, in which the period of immersion in said leaching solution is for 6-48 hours.
Claim 14
Dependent Claim
29 words
The method as in claim 8, in which the immersion period in said leaching solution is determined by the attainment of a predetermined degree of color in said solution.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1989-11-17 | 1990-05-19 | 1990-11-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-11-17 | 1994-05-19 | 1994-11-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-11-17 | 1998-05-19 | 1998-11-18 | $7700.00 | Window Closed / Lapsed |