US3899560A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of preparing transparent alumina
Assignee: Avco Corp
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Filing: 1972-02-14
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Granted: 1975-08-12
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Expires: 1992-02-14
Abstract
Abstract The invention is directed to a transparent alumina material and a method of preparing this material. The material is characterized as a dense primary recrystallized polycrystalline structure having a degree of preferred crystal orientation. The material is transparent to visible and infrared light and quantitative values are given. The transparent alumina covered by this invention is made by means of hot forging and an annealing process for powders or dense compacts of high-purity alumina.
Inventors
- 👤 David J Sellers
- 👤 William H Rhodes
- 👤 Thomas Vasilos
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 20:30
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/01; C04B35/10; C04B35/111; B; B01; B01J; B01J3/00; B01J3/06; B01J3/065
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
117 words
A PROCESS FOR PRODUCING TRANSPARENT POLYCRYSTALLINE ALUMINA HAVING A PRIMARY RECRYSTALLIZED GRAIN STRUCTURE WITH C AXIS ORIENTATION OF GRAINS PARALLEL TO THE DIRECTION OF PLASTIC DEFORMATION OF THE ALUMINA CRYSTALS COMPRISING: FORMING A COMPACT XONSISTING ESSENTIALLY OF SUBMICRON PARTICLES OF HIGH PURITY POLYCRYSTALLINE ALUMINA HAVING A PURITY IN EXCESS OF 99.90%: STABLIIZING THE COMPACT AT A TEMPERATURE IN THE REGION OF 1800*C TO 1900*C WITHOUT SUBSTANTIAL GRAIN GROWTH, HOT FORGING SAID COMPACT BY COMPRESSING WITHOUT LATERAL CONSTRAINTS AT A PRESSURE OF AT LEAST 3000 P. S. I. TO INTRODUCE INTO SAID COMPACT MATERIAL A STRAIN IN EXCESS OF THE CRITICAL STRAIN, AND ANNEALING SAID COMPACT UNDER PRESSURE FOR 70 MINUTES TO 6 HOURS TO INDUCE PRIMARY RECRYSTALLIZATION.
Claim 2
Dependent Claim
117 words
A PROCESS FOR PRODUCING TRANSPARENT POLYCRYSTALLINE ALUMINA HAVING A PRIMARY RECRYSTALLIZED GRAIN STRUCTURE WITH C AXIS ORIENTATION OF GRAINS PARALLEL TO THE DIRECTION OF PLASTIC DEFORMATION OF THE ALUMINA CRYSTALS COMPRISING: FORMING A COMPACT XONSISTING ESSENTIALLY OF SUBMICRON PARTICLES OF HIGH PURITY POLYCRYSTALLINE ALUMINA HAVING A PURITY IN EXCESS OF 99.90%: STABLIIZING THE COMPACT AT A TEMPERATURE IN THE REGION OF 1800*C TO 1900*C WITHOUT SUBSTANTIAL GRAIN GROWTH, HOT FORGING SAID COMPACT BY COMPRESSING WITHOUT LATERAL CONSTRAINTS AT A PRESSURE OF AT LEAST 3000 P. S. I. TO INTRODUCE INTO SAID COMPACT MATERIAL A STRAIN IN EXCESS OF THE CRITICAL STRAIN, AND ANNEALING SAID COMPACT UNDER PRESSURE FOR 70 MINUTES TO 6 HOURS TO INDUCE PRIMARY RECRYSTALLIZATION.
Claim 3
Dependent Claim
21 words
A method as described in claim 1 in which the aspect ratio of the dense compact is in excess of 0.03.
Claim 4
Dependent Claim
109 words
A process for producing transparent polycrystalline alumina having a primary recrystallized grain structure with C axis orientation of grains parallel to the direction of plastic deformation of the alumina crystals comprising: forming a compact consisting essentially of submicron particles of high purity polycrystalline alumina having a purity in excess of 99.90%; stabilizing the compact at a temperature in the region of 1800*C to 1900*C; hot forging said compact by compressing without lateral constraints in said temperature range to introduce into said compact material a strain in excess of the critical strain; and annealing said compact under pressure within said temperature range for inducing primary recrystallization of the compact material.
Claim 5
Dependent Claim
109 words
A process for producing transparent polycrystalline alumina having a primary recrystallized grain structure with C axis orientation of grains parallel to the direction of plastic deformation of the alumina crystals comprising: forming a compact consisting essentially of submicron particles of high purity polycrystalline alumina having a purity in excess of 99.90%; stabilizing the compact at a temperature in the region of 1800*C to 1900*C; hot forging said compact by compressing without lateral constraints in said temperature range to introduce into said compact material a strain in excess of the critical strain; and annealing said compact under pressure within said temperature range for inducing primary recrystallization of the compact material.
Claim 6
Dependent Claim
15 words
A method as described in claim 3 in which said compressive pressure exceeds 3000 p.s.i.
Claim 7
Dependent Claim
20 words
A method as described in claim 3 wherein the aspect ratio of the dense compact is in excess of 0.03.
Claim 8
Dependent Claim
21 words
A method as described in claim 3 in which said annealing is maintained for a minimum of 70 to 120 minutes.
Claim 9
Dependent Claim
28 words
A method as described in claim 3 in which the compact dimensions are altered by at least 5% to induce a strain in excess of the critical strain.
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) | 1978-08-11 | 1979-02-10 | 1979-08-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-08-11 | 1983-02-10 | 1983-08-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-08-11 | 1987-02-10 | 1987-08-12 | $7700.00 | Window Closed / Lapsed |