US4981633A
Expired / Lapsed
US
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Process for preparing a PTC thermistor
Assignee: Alfred University
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Filing: 1988-04-29
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Granted: 1991-01-01
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Expires: 2008-04-29
Abstract
Abstract A process for preparing a positive temperature coefficient thermistor is disclosed. This thermistor is comprised of at least about 60 weight percent of undoped, crystalline, ferroelectric material, and it has a room-temperature resistivity of less than 5,000 ohm-centimeters, an undegraded resistivity of at least about 1,000,000 ohm-centimeters, a degraded resistivity of at least about 900,000 ohm-centimeters, a ratio between its undegraded resistivity and its room-temperature resistivity of at least about 1,000, and a ratio between its undegraded resistivity and its degraded resistivity not exceeding 2.0. The process of this invention is comprised of the steps of sequentially: (1) providing a powder composition comprised of at least about 60 weight percent of undoped, crystalline, ferroelectric material; (2) fabricating the powder composition into a shaped powder compact; (3) sintering said powder compact by subjecting it to a temperature of from about 1150 to about 1450 degrees centigrade for at least about 1 hour, thereby forming a consolidated, sintered body; (4) reducing said sintered body by subjecting it to a temperature of from about 700 to about 1,400 degrees centigrade for at least about 30 minutes while maintaining said sintered body under a reducing atmosphere comprised of hydrogen; and (5) halogenating said reduced, sintered body by subjecting it to a source of halogen while maintaining it in a closed container at a temperature of from about 700 to about 1200 degrees centigrade for at least about 5 minutes.
Inventors
- 👤 Aldo B. Alles
- 👤 Vasantha R. W. Amarakoon
- 👤 Vernon L. Burdick
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 20:28
CPC Classifications
H; H01; H01C; H01C17/00; H01C17/30; C; C04; C04B; C04B35/00; C04B35/01; C04B35/46; C04B35/462; C04B35/465; C04B35/468; C04B35/4682; C04B35/495
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
224 words
A process for preparing a positive temperature coefficient thermistor comprised of at least about 50 weight percent of undoped, crystalline, ferroelectric material, wherein said thermistor has a room-temperature resistivity of less than 5,000 ohm-centimeters, an undegraded resistivity of at least about 1,000,000 ohm-centimeters, a degraded resistivity of at least about 900,000 ohm-centimeters, a ratio between its undegraded resistivity and its room-temperature resistivity of at least about 1,000, and a ratio between its undegraded resistivity and its degraded resistivity not exceeding 2.0, comprising the steps of sequentially: (a) providing a powder composition comprised of at least about 60 weight percent of undoped, crystalline, ferroelectric material; (b) fabricating the powder composition into a shaped powder compact; (c) sintering said powder compact by subjecting it to a temperature of from about 1150 to about 1450 degrees centigrade for at least about 1 hour, thereby forming a consolidated, sintered body; (d) reducing said sintered body by subjecting it to a temperature of from about 700 to about 1,400 degrees centigrade for at least about 30 minutes while maintaining said sintered body under a reducing atmosphere comprised of hydrogen; and (e) halogenating said reduced, sintered body by subjecting it to a source of halogen while maintaining it in a closed container at a temperature of from about 700 to about 1200 degrees centigrade for at least about 5 minutes.
Claim 2
Dependent Claim
224 words
A process for preparing a positive temperature coefficient thermistor comprised of at least about 50 weight percent of undoped, crystalline, ferroelectric material, wherein said thermistor has a room-temperature resistivity of less than 5,000 ohm-centimeters, an undegraded resistivity of at least about 1,000,000 ohm-centimeters, a degraded resistivity of at least about 900,000 ohm-centimeters, a ratio between its undegraded resistivity and its room-temperature resistivity of at least about 1,000, and a ratio between its undegraded resistivity and its degraded resistivity not exceeding 2.0, comprising the steps of sequentially: (a) providing a powder composition comprised of at least about 60 weight percent of undoped, crystalline, ferroelectric material; (b) fabricating the powder composition into a shaped powder compact; (c) sintering said powder compact by subjecting it to a temperature of from about 1150 to about 1450 degrees centigrade for at least about 1 hour, thereby forming a consolidated, sintered body; (d) reducing said sintered body by subjecting it to a temperature of from about 700 to about 1,400 degrees centigrade for at least about 30 minutes while maintaining said sintered body under a reducing atmosphere comprised of hydrogen; and (e) halogenating said reduced, sintered body by subjecting it to a source of halogen while maintaining it in a closed container at a temperature of from about 700 to about 1200 degrees centigrade for at least about 5 minutes.
Claim 3
Dependent Claim
15 words
The process as recited in claim 1, wherein said ferroelectric material has the perovskite structure.
Claim 4
Dependent Claim
24 words
The process as recited in claim 2, wherein said powder composition is comprised of at least about 80 weight percent of said ferroelectric material.
Claim 5
Dependent Claim
33 words
The process as recited in claim 3, wherein said ferroelectric material is selected from the group consisting of barium titanate, strontium titanate, potassiuim niobate, lead titanate, lithium tantalate, lithium niobate, and mixtures theroef.
Claim 6
Dependent Claim
14 words
The process as recited in claim 4, wherein said ferroelectric material is barium titanate.
Claim 7
Dependent Claim
22 words
The process as recited in claim 4, wherein said powder composition is comprised of at least 95 weight percent of barium titanate.
Claim 8
Dependent Claim
20 words
The process as recited in claim 6, wherein said thermistor has a room-temperature resistivity of less than about 1,000 ohm-centimeters.
Claim 9
Dependent Claim
26 words
The process as recited in claim 7, wherein the ratio between the undegraded resistivity and the room-temperature resistivity of said thermistor is at least about 10,000.
Claim 10
Dependent Claim
27 words
The process as recited in claim 8, wherein the ratio between the undegraded resistivity and the degraded resistivity of said thermistor is no greater than about 1.5.
Claim 11
Dependent Claim
27 words
The process as recited in claim 9, wherein the ratio between the undegraded resistivity and the degraded resistivity of said thermistor is no greater than about 1.2.
Claim 12
Dependent Claim
21 words
The process as recited in claim 10, wherein said powder composition is fabricated into a reticulated cylindrical body prior to sintering.
Claim 13
Dependent Claim
20 words
The process as recited in claim 10, wherein said powder composition is fabricated into a disc shape prior to sintering.
Claim 14
Dependent Claim
34 words
The process as recited in claim 10, wherein said powder compact is sintered by subjecting it to a temperature of from about 1280 to about 1375 degrees centigrade for at least about 2 hours.
Claim 15
Dependent Claim
23 words
The process as recited in claim 13, wherein said reducing atmosphere is comprised of at least about 10 percent, by volume, of hydrogen.
Claim 16
Dependent Claim
17 words
The process as recited in claim 14, wherein said reducing atmosphere consists of hydorgen and inert gas.
Claim 17
Dependent Claim
64 words
The process as recited in claim 13, wherein said sintered body is reduced by subjecting it to a temperature of from about 100 to about 1250 degrees centigrade for from about 45 to about 75 minutes under a reducing atmosphere comprised of from about 70 to about 90 volume percent of hydrogen and from about 30 to about 10 percent, by volume, of nitrogen.
Claim 18
Dependent Claim
47 words
The process as recited in claim 15, wherein said reduced, sintered body is halogenated by subjecting it to a source of halogen while maintaining it in a closed container at a temperature of from about 800 to about 1100 degrees centigrade for at least about 30 minutes.
References Cited (Backward Citations)
No citation records indexed.
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| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1993-12-31 | 1994-07-02 | 1995-01-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-12-31 | 1998-07-02 | 1999-01-01 | $3760.00 | Window Closed / Lapsed |
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