US4167550A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Methods of manufacture of beta-alumina
Assignee: Chloride Silent Power Ltd
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Filing: 1978-01-18
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Granted: 1979-09-11
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Expires: 1998-01-18
Abstract
Abstract In the manufacture of beta-alumina, particularly for use as a solid electrolyte in an electro-chemical cell or other energy conversion device, a compact of beta-alumina particles or of particles which react together on heating to form beta-alumina is sintered in a succession of cycles of heating and cooling such that not less than 5% and not more than 95% of the overall linear shrinkage takes place in any one cycle.
Inventors
- 👤 James H. Duncan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 04:20
CPC Classifications
H; H01; H01M; H01M10/00; H01M10/36; H01M10/39; H01M10/3909; H01M10/3918; C; C01; C01F; C01F7/00; C01F7/02; C01F7/028; C01P; C01P2006/00; C01P2006/10; Y; Y02; Y02E; Y02E60/00; Y02E60/10
Claims Analysis
Total Claims: 35
Claim 1
Independent Claim
149 words
A method of manufacturing an impervious polycrystalline cationically conductive beta-alumina article, said method comprising sintering a compact of beta-alumina particles or a compact of particles that react together before or during sintering to form beta-alumina; said sintering being conducted in successive cycles, each cycle comprising heating to a temperature above the sintering temperature followed by cooling of at least 25° C., wherein there is partial sintering in each cycle and completion of sintering in a last cycle; and wherein said heating and said cooling are carried out at temperatures and for times sufficient to densify said article; and wherein grain growth is reduced or eliminated while permitting phase conversion from β to β" phase to continue by cooling between periods of partial sintering; and further wherein not more than 95% of overall linear shrinkage occurring during said sintering takes place during any one cycle of heating followed by cooling.
Claim 2
Independent Claim
149 words
A method of manufacturing an impervious polycrystalline cationically conductive beta-alumina article, said method comprising sintering a compact of beta-alumina particles or a compact of particles that react together before or during sintering to form beta-alumina; said sintering being conducted in successive cycles, each cycle comprising heating to a temperature above the sintering temperature followed by cooling of at least 25° C., wherein there is partial sintering in each cycle and completion of sintering in a last cycle; and wherein said heating and said cooling are carried out at temperatures and for times sufficient to densify said article; and wherein grain growth is reduced or eliminated while permitting phase conversion from β to β" phase to continue by cooling between periods of partial sintering; and further wherein not more than 95% of overall linear shrinkage occurring during said sintering takes place during any one cycle of heating followed by cooling.
Claim 3
Dependent Claim
28 words
A method as claimed in claim 1 wherein at least 5% of the overall linear shrinkage occurs in each cycle of heating and cooling for densifying the compact.
Claim 4
Dependent Claim
92 words
A method as claimed in claim 1 comprising the steps of forming a compact of beta-alumina particles or of particles that react together before or during sintering to form beta-alumina and sintering the compact to densify it by a succession of at least two cycles of heating to a temperature above the sintering temperature followed by cooling by at least 25° C., each cycle being such that not less than 5% and not more than 95% of the overall shrinkage during the whole of the sintering operation occurs in any one cycle.
Claim 5
Dependent Claim
99 words
A method as claimed in claim 1 comprising the steps of forming a compact of particles that react together before or during sintering to form beta-alumina and sintering the compact by a plurality of cycles of heating to a temperature above the sintering temperature followed by cooling by at least 25° C., in the first of which cycles the heating and cooling is such as to produce a linear shrinkage of at least 0.6% but not greater than 11.4%, further linear shrinkage of at least 0.6% and not greater than 11.4% being produced in the subsequent cycle or cycles.
Claim 6
Dependent Claim
70 words
A method as claimed in claim 1 comprising the steps of densifying a compact of beta-alumina particles by sintering using at least two cycles of heating to above the sintering temperature and cooling by at least 25° C. to produce a linear shrinkage of between 10% and 30%, the cycles being such that not more than 95% nor less than 5% of the overall shrinkage occurs in any one cycle.
Claim 7
Dependent Claim
25 words
A method as claimed in claim 1 wherein the cooling after a temperature maximum in each cycle before the last is at least 50° C.
Claim 8
Dependent Claim
30 words
A method as claimed in claim 1 wherein the shrinkage during a first heating and cooling cycle of the sintering is between 30 and 90% of the overall linear shrinkage.
Claim 9
Dependent Claim
30 words
A method as claimed in claim 1 wherein the shrinkage during a first heating and cooling cycle of the sintering is between 35% and 65% of the overall linear shrinkage.
Claim 10
Dependent Claim
109 words
A method as claimed in claim 1 and in which the beta-alumina is sintered in a closed crucible wherein a firing schedule is used, which comprises a temperature rise to a first peak temperature between 1450° C. and 1600° C., then cooling by at least 25° C., then a reheat to a second peak temperature, which is at least 10° C. higher than the first peak temperature, but which does not exceed 1900° C. to complete sintering, then cooling, the rate of heating to the first peak temperature and of the subsequent cooling being such that between 5% and 95% of the overall linear shrinkage occurs in this cycle.
Claim 11
Dependent Claim
35 words
A method as claimed in claim 9 and for manufacturing a beta-alumina containing about 2% by weight of magnesia with or without lithia, wherein the first peak temperature is between 1490° C. and 1530° C.
Claim 12
Dependent Claim
30 words
A method as claimed in claim 9 and for manufacturing a lithia-containing beta-alumina with up to 0.5% magnesia wherein the first peak temperature is between 1525° C. and 1555° C.
Claim 13
Dependent Claim
19 words
A method as claimed in claim 9 wherein the second peak temperature is between 1500° C. and 1650° C.
Claim 14
Dependent Claim
38 words
A method as claimed in claim 9 wherein at least one of the firing stages is effected as fast firing in a pass-through furnace and at least one other firing stage is effected by a batch type process.
Claim 15
Dependent Claim
40 words
A method as claimed in claim 9 wherein, in the temperature rise up to the first peak temperature, the temperature rise between about 1400° C. and the first peak temperature is at a rate of about 70° C. per hour.
Claim 16
Dependent Claim
26 words
A method as claimed in claim 9 wherein said cooling following the first peak temperature is at a rate of at least 60° C. per hour.
Claim 17
Dependent Claim
22 words
A method as claimed in claim 15 wherein said reheat is at a temperature rise of at least 40° C. per hour.
Claim 18
Dependent Claim
21 words
A method as claimed in claim 15 wherein said reheat is at a temperature rise of about 120° C. per hour.
Claim 19
Dependent Claim
70 words
A method as claimed in claim 1 comprising sintering beta-alumina, wherein a firing schedule is used which comprises a temperature rise to a first peak temperature at which between 40% and 70% of sintering has been achieved, then cooling by at least 25° C., then a reheat to a second peak temperature at least 10° C. higher than the first peak temperature in order to complete sintering, and then cooling.
Claim 20
Dependent Claim
22 words
A method as claimed in claim 18, wherein the first peak temperature is such that about 50% of sintering has been achieved.
Claim 21
Dependent Claim
83 words
A method as claimed in claim 1 wherein sintering of a compressed powder shape is effected by passing through a fast-firing furnace to sinter the material, allowing it to cool to a temperature below the sintering temperature and then passing it through a fast-firing furnace at least once again to complete the sintering, the successive cycles of heating and cooling being such that not more than 95% of the overall linear shrinkage takes place during any one cycle of heating followed by cooling.
Claim 22
Dependent Claim
146 words
A method as claimed in claim 1 wherein sintering of a compressed powdered shape is effected by passing the compressed shape through a fast-firing furnace to sinter the material, allowing it to cool to a temperature below the sintering temperature and then passing it again through a fast-firing furnace to raise the temperature of the shape to a sintering temperature and to complete sintering, the temperature of the article in the sintering zone in the first pass being between 1450° C. and 1725° C. and the temperature in the sintering zone in the second pass being between 1550° C. and 1800° C., the second pass having a temperature between 25° C. and 250° C. higher than the first stage, the rate of movement through the furnace being such that between 5% and 95% of the overall linear shrinkage occurs in the first pass through the furnace.
Claim 23
Dependent Claim
34 words
A method as claimed in claim 21 wherein the article is cooled between the stages to a temperature below 1500° C. and at least 25° C. below the firing temperature of the preceding stage.
Claim 24
Dependent Claim
23 words
A method as claimed in claim 21 wherein the sintering is effected in a single pass-through furnace with a double peaked hot zone.
Claim 25
Dependent Claim
39 words
A method as claimed in claim 21 wherein the rate of movement through the furnace is such that the heating of the article, as it moves into the furnace, is at a rate greater than 200° C. per minute.
Claim 26
Dependent Claim
31 words
A method as claimed in claim 21 wherein the dimensions of the furnace are such that, in each sintering stage, the duration at the sintering temperature is less than 3 minutes.
Claim 27
Dependent Claim
23 words
A method as claimed in claim 21 wherein a maximum temperature of 1500° C. to 1625° C. is employed for the first firing.
Claim 28
Dependent Claim
38 words
A method as claimed in claim 21 wherein a temperature of 1650° C. to 1775° C. is employed for the second firing, the second firing being at a temperature of 100° to 200° greater than the first firing.
Claim 29
Dependent Claim
22 words
A method as claimed in claim 1 wherein, before sintering, the green shape is pre-fired at a temperature below the sintering temperature.
Claim 30
Dependent Claim
29 words
A method as claimed in claim 28 wherein the pre-firing is at a temperature of 700° C. to 900° C. and for a period of 4 to 5 hours.
Claim 31
Dependent Claim
73 words
A method as claimed in claim 1 comprising the steps of firing to give partial densification, such that the linear shrinkage is between 5% and 95% of the total shrinkage, subjecting the material to a heat treatment of between 1 and 24 hours at a temperature to increase the proportion of β to β" with minimum effect on the grain growth and, after this heat treatment, firing the article to complete the densification.
Claim 32
Dependent Claim
25 words
A method as claimed in claim 30 wherein said heat treatment is at a temperature below the firing temperature employed to give said partial densification.
Claim 33
Dependent Claim
21 words
A method as claimed in claim 30 wherein said heat treatment is at a temperature between 1200° C. and 1650° C.
Claim 34
Dependent Claim
21 words
A method as claimed in claim 30 wherein said heat treatment is at a temperature between 1400° C. and 1600° C.
Claim 35
Dependent Claim
46 words
A method as claimed in claim 1 wherein after sintering, the article is annealed by heating for at least 1 hour to a temperature between 1200° C. and 1600° C., this temperature being at least 50° C. below the minimum sintering temperature for the composition employed.
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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) | 1982-09-10 | 1983-03-12 | 1983-09-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1986-09-10 | 1987-03-12 | 1987-09-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1990-09-10 | 1991-03-12 | 1991-09-11 | $7700.00 | Window Closed / Lapsed |