US5013696A
Expired / Lapsed
US
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Preparation of high uniformity polycrystalline ceramics by presintering, hot isostatic pressing and sintering and the resulting ceramic
Assignee: General Electric Co
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Filing: 1989-09-25
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Granted: 1991-05-07
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Expires: 2009-09-25
Abstract
Abstract Polycrystalline ceramic bodies having uniform transparent optical characteristics are produced by providing a green compact, presintering that compact at a temperature in the range from about 1,350° C. to about 1,650° C. until the closed porosity stage is reached, hot isostatic pressing the presintered compact to collapse substantially all pores disposed at grain boundaries and resintering the hot isostatically pressed compact at a temperature in the range from 1,700° C.-1,950° C. to cause grain growth under conditions in which pores, within those grains which are consumed by the growth of other grains, collapse as the grain boundary of the growing grain passes through the location of the pore in the smaller grain being consumed.
Inventors
- 👤 Charles D. Greskovich
- 👤 William P. Minnear
- 👤 Milivoj K. Brun
- 👤 Robert J. Riedner
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 09:02
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/50; C04B35/505; C04B35/01; C04B35/10; C04B35/111; C04B35/115; C04B35/622; C04B35/64; C04B35/645; C04B35/6455
Claims Analysis
Total Claims: 46
Claim 1
Independent Claim
82 words
A method of producing a ceramic body comprising: providing a green compact of appropriate configuration and composition; presintering said compact at a temperature sufficient to promote grain growth to a substantially closed pore stage; hot isostatic pressing said presintered compact at a temperature and pressure sufficient to eliminate most pores which are located at grain boundaries; and resintering said body to induce further grain growth and further densification by reducing the number density of pores by a factor of at least 125.
Claim 2
Independent Claim
82 words
A method of producing a ceramic body comprising: providing a green compact of appropriate configuration and composition; presintering said compact at a temperature sufficient to promote grain growth to a substantially closed pore stage; hot isostatic pressing said presintered compact at a temperature and pressure sufficient to eliminate most pores which are located at grain boundaries; and resintering said body to induce further grain growth and further densification by reducing the number density of pores by a factor of at least 125.
Claim 3
Dependent Claim
23 words
The method recited in claim 1 wherein: said resintering step is carried out at a higher temperature than said hot isostatic pressing step.
Claim 4
Dependent Claim
23 words
The method recited in claim 1 wherein: after said presintering step said body has an average grain size of less than 10 microns.
Claim 5
Dependent Claim
25 words
The method recited in claim 3 wherein: after said presintering step said body has an average grain size of between 10 microns and 200 microns.
Claim 6
Dependent Claim
25 words
The method recited in claim 3 wherein: after said resintering step, said body has an average grain size of between 10 microns and 50 microns.
Claim 7
Independent Claim
109 words
A method of making a high density ceramic with low residual porosity comprising: providing a green ceramic body; pre-sintering said green ceramic body until the body reaches the closed pore stage, under conditions in which a fine grain structure is produced; hot isostatic pressing said pre-sintered body for a period of time and at a temperature sufficient to eliminate substantially all pores disposed at grain boundaries; and sintering said hot isostatically pressed body at a temperature at which further densification and grain growth take place under conditions in which grain boundary migration is slow enough to permit pore disappearance for substantially all pores past which a grain boundary migrates.
Claim 8
Independent Claim
109 words
A method of making a high density ceramic with low residual porosity comprising: providing a green ceramic body; pre-sintering said green ceramic body until the body reaches the closed pore stage, under conditions in which a fine grain structure is produced; hot isostatic pressing said pre-sintered body for a period of time and at a temperature sufficient to eliminate substantially all pores disposed at grain boundaries; and sintering said hot isostatically pressed body at a temperature at which further densification and grain growth take place under conditions in which grain boundary migration is slow enough to permit pore disappearance for substantially all pores past which a grain boundary migrates.
Claim 9
Dependent Claim
14 words
The method recited in claim 6 wherein said ceramic has a cubic crystal structure.
Claim 10
Dependent Claim
12 words
The method recited in claim 7 wherein said ceramic comprises yttrium oxide.
Claim 11
Dependent Claim
12 words
The method recited in claim 8 wherein said ceramic comprises gadolinium oxide.
Claim 12
Dependent Claim
57 words
The method recited in claim 8 wherein: said pre-sintering step is carried out in the temperature range between about 1,350° C. and about 1,600° C.; said hot isostatic pressing step is carried out at substantially the same temperature as said pre-sintering step; and said resintering step is carried out at a temperature in excess of 1,650° C.
Claim 13
Dependent Claim
24 words
The method recited in claim 6 wherein: said pre-sintering step is performed at a temperature in the range from 1,600° C. to 1,650° C.
Claim 14
Dependent Claim
34 words
The method recited in claim 11 wherein: said hot isostatic pressing step is performed at a temperature in the range between 1,500° C. and 1,550° C. at a pressure in excess of 5,000 psi.
Claim 15
Dependent Claim
22 words
The method recited in claim 12 wherein said resintering step is performed at a temperature between about 1,700° C. and 1,950° C.
Claim 16
Dependent Claim
79 words
The method recited in claim 6 wherein said pre-sintering step is carried out at a temperature of substantially 1,625° C. for about 4 hours in dry hydrogen followed by about 1 hour in wet hydrogen; said hot isostatic pressing is carried out at a temperature of about 1,650° C. at a pressure of about 25,000 psi or more; and said resintering step is carried out at a temperature of at least 1,850° C. for a period of about 2
Claim 17
Dependent Claim
20 words
The method recited in claim 14 wherein: said resintering step is carried out at a temperature of about 1,925° C.
Claim 18
Dependent Claim
14 words
The method recited in claim 6 wherein: said ceramic has a hexagonal crystal structure.
Claim 19
Dependent Claim
12 words
The method recited in claim 16 wherein: said ceramic comprises aluminum oxide.
Claim 20
Dependent Claim
54 words
A polycrystalline ceramic body: having a volume of at least 1 mm 3 ; having an optical attenuation coefficient of less than 10 cm -1 , at a measurement frequency in the visible region of the electromagnetic spectrum whereby said body is transparent; and being free of pore clusters larger than 10 microns across.
Claim 21
Dependent Claim
54 words
A polycrystalline ceramic body: having a volume of at least 1 mm 3 ; having an optical attenuation coefficient of less than 10 cm -1 , at a measurement frequency in the visible region of the electromagnetic spectrum whereby said body is transparent; and being free of pore clusters larger than 10 microns across.
Claim 22
Dependent Claim
18 words
The ceramic body recited in claim 18 wherein: said body consists of material having a cubic crystal structure.
Claim 23
Dependent Claim
13 words
The ceramic body recited in claim 19 wherein: said body comprises yttrium oxide.
Claim 24
Dependent Claim
13 words
The ceramic body recited in claim 20 wherein: said body comprises gadolinium oxide.
Claim 25
Dependent Claim
13 words
The ceramic body recited in claim 18 wherein: said body comprises gadolinium oxide.
Claim 26
Dependent Claim
34 words
The ceramic body recited in claim 18 exhibiting an optical attenuation coefficient which, at a fixed measurement frequency in the visible region of the electromagnetic spectrum, is uniform throughout said body to within 10%.
Claim 27
Dependent Claim
19 words
The ceramic body recited in claim 18 wherein: said optical attenuation coefficient is less than 3 cm -1 .
Claim 28
Dependent Claim
43 words
The ceramic body recited in claim 18 wherein: said ceramic is substantially 67 mole percent Y 2 O 3 , 30 mole percent Gd 2 O 3 , 3 mole percent Eu 2 O 3 and 150 ppm Pr 2 O 3 .
Claim 29
Dependent Claim
20 words
The ceramic body recited in claim 25 wherein: said body has less than one pore cluster per cm 3 .
Claim 30
Dependent Claim
34 words
The ceramic body recited in claim 18 exhibiting an optical attenuation coefficient which, at a fixed measurement frequency in the visible region of the electromagnetic spectrum, is uniform throughout said body to within 1%.
Claim 31
Dependent Claim
38 words
A polycrystalline ceramic body: exhibiting an optical attenuation coefficient which, at a fixed measurement frequency in the visible region of the electromagnetic spectrum, is uniform throughout said body to within 3% and less than 10 cm -1 .
Claim 32
Dependent Claim
38 words
A polycrystalline ceramic body: exhibiting an optical attenuation coefficient which, at a fixed measurement frequency in the visible region of the electromagnetic spectrum, is uniform throughout said body to within 3% and less than 10 cm -1 .
Claim 33
Dependent Claim
17 words
The ceramic body recited in claim 28 having: an average grain size of less than 10 microns.
Claim 34
Dependent Claim
18 words
The ceramic body recited in claim 28 having: an average grain size between 10 microns and 200 microns.
Claim 35
Dependent Claim
19 words
The ceramic body recited in claim 28 having: an average grain size of between 10 microns and 50 microns.
Claim 36
Dependent Claim
54 words
A polycrystalline ceramic body: having a non-cubic crystal structure; having a volume of at least 1 mm 3 ; having an optical attenuation coefficient of less than 15 cm -1 , at a measurement frequency in the visible region of the electromagnetic spectrum; and being free of pore clusters larger than 12 microns across.
Claim 37
Dependent Claim
54 words
A polycrystalline ceramic body: having a non-cubic crystal structure; having a volume of at least 1 mm 3 ; having an optical attenuation coefficient of less than 15 cm -1 , at a measurement frequency in the visible region of the electromagnetic spectrum; and being free of pore clusters larger than 12 microns across.
Claim 38
Dependent Claim
12 words
The ceramic body recited in claim 32 wherein said body comprises alumina.
Claim 39
Dependent Claim
21 words
The method recited in claim 1 wherein: said composition is single phased throughout the presintering, hot isostatic pressing and resintering steps.
Claim 40
Dependent Claim
27 words
The method recited in claim 1 wherein: the presintering, hot isostatic pressing and resintering steps are all carried out at temperatures at which no liquid eutectic forms.
Claim 41
Dependent Claim
21 words
The method recited in claim 6 wherein: said composition is single phased throughout the pre-sintering, hot isostatic pressing and resintering steps.
Claim 42
Dependent Claim
27 words
The method recited in claim 6 wherein: the presintering, hot isostatic pressing and resintering steps are all carried out at temperatures at which no liquid eutectic forms.
Claim 43
Independent Claim
88 words
A method of producing a transparent ceramic body comprising: providing a green compact of appropriate configuration and composition; presintering said compact at a temperature sufficient to promote grain growth to a substantially closed pore stage; hot isostatic pressing said presintered compact at a temperature and pressure sufficient to eliminate most pores which are located at grain boundaries; and resintering said body to induce further grain growth and densification by reducing the number density of pores by a factor of at least 125 and to render said body transparent.
Claim 44
Independent Claim
88 words
A method of producing a transparent ceramic body comprising: providing a green compact of appropriate configuration and composition; presintering said compact at a temperature sufficient to promote grain growth to a substantially closed pore stage; hot isostatic pressing said presintered compact at a temperature and pressure sufficient to eliminate most pores which are located at grain boundaries; and resintering said body to induce further grain growth and densification by reducing the number density of pores by a factor of at least 125 and to render said body transparent.
Claim 45
Independent Claim
116 words
A method of making a transparent high density ceramic with low residual porosity comprising: providing a green ceramic body; pre-sintering said green ceramic body until the body reaches the closed pore stage, under conditions in which a fine grain structure is produced; hot isostatic pressing said pre-sintered body for a period of time and at a temperature sufficient to eliminate substantially all pores disposed at grain boundaries; and resintering said hot isostatically pressed body at a temperature at which further densification and grain growth take place under conditions in which grain boundary migration is slow enough to permit pore disappearance for substantially all pores past which a grain boundary migrates to thereby render said body transparent.
Claim 46
Independent Claim
116 words
A method of making a transparent high density ceramic with low residual porosity comprising: providing a green ceramic body; pre-sintering said green ceramic body until the body reaches the closed pore stage, under conditions in which a fine grain structure is produced; hot isostatic pressing said pre-sintered body for a period of time and at a temperature sufficient to eliminate substantially all pores disposed at grain boundaries; and resintering said hot isostatically pressed body at a temperature at which further densification and grain growth take place under conditions in which grain boundary migration is slow enough to permit pore disappearance for substantially all pores past which a grain boundary migrates to thereby render said body transparent.
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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) | 1994-05-06 | 1994-11-05 | 1995-05-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-05-06 | 1998-11-05 | 1999-05-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-05-06 | 2002-11-05 | 2003-05-07 | $7700.00 | Window Closed / Lapsed |