Patent US4510112A successfully refreshed from Google Patents.
US4510112A
Expired / Lapsed
US
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Process for fabricating ZnO-based varistors
Assignee: United States, ENERGY THE, Department of
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Filing: 1983-01-21
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Granted: 1985-04-09
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Expires: 2003-01-21
Abstract
Abstract The invention is a process for producing ZnO-based varistors incorporating a metal oxide dopant. In one form, the invention comprises providing a varistor powder mix of colloidal particles of ZnO and metal-oxide dopants including Bi2O3. The mix is hot-pressed to form a compact at temperatures below 850 DEG C. and under conditions effecting reduction of the ZnO to sub-stoichiometric oxide. This promotes densification while restricting liquid formation and grain growth. The compact then is heated under conditions restoring the zinc oxide to stoichiometric composition, thus improving the varistor properties of the compact. The process produces fine-grain varistors characterized by a high actual breakdown voltage and a high average breakdown voltage per individual grain boundary.
Inventors
- 👤 Robert J. Lauf
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 17:38
CPC Classifications
H; H01; H01C; H01C7/00; H01C7/10; H01C7/105; H01C7/108; H01C7/112; H01C17/00; H01C17/30
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
79 words
A process for producing a metal-oxide varistor, comprising: providing a varistor sol-gel powder mix including ZnO and at least one metal-oxide dopant, forming a densified compact of said mix by hot-pressing the same until the density of said compact exceeds about 50% of theoretical in a reducing atmosphere so as to reduce said ZnO to sub-stoichiometric zinc oxide, and heating the resulting compact in an oxidizing atmosphere so as to effect restoration of said sub-stoichiometric oxide to stoichiometric ZnO.
Claim 2
Dependent Claim
79 words
A process for producing a metal-oxide varistor, comprising: providing a varistor sol-gel powder mix including ZnO and at least one metal-oxide dopant, forming a densified compact of said mix by hot-pressing the same until the density of said compact exceeds about 50% of theoretical in a reducing atmosphere so as to reduce said ZnO to sub-stoichiometric zinc oxide, and heating the resulting compact in an oxidizing atmosphere so as to effect restoration of said sub-stoichiometric oxide to stoichiometric ZnO.
Claim 3
Dependent Claim
17 words
The process of claim 1 wherein said hot-pressing is conducted at a temperature below about 1,100° C.
Claim 4
Dependent Claim
18 words
The process of claim 1 wherein said hot-pressing is conducted in vacuum and in the presence of carbon.
Claim 5
Dependent Claim
17 words
The process of claim 3 wherein said hot-pressing is conducted at a temperature below about 850° C.
Claim 6
Dependent Claim
74 words
A process for producing a metal-oxide varistor, comprising: providing a varistor sol-gel powder mix of colloidal particles of ZnO and at least one metal-oxide dopant; forming a compact of said mix by hot-pressing the same at a temperature below about 1100° C. in a reducing atmosphere so as to reduce said ZnO to sub-stoichiometric zinc oxide, and heating said compact in an oxidizing atmosphere so as to restore said sub-stoichiometric oxide to stoichiometric ZnO.
Claim 7
Dependent Claim
74 words
A process for producing a metal-oxide varistor, comprising: providing a varistor sol-gel powder mix of colloidal particles of ZnO and at least one metal-oxide dopant; forming a compact of said mix by hot-pressing the same at a temperature below about 1100° C. in a reducing atmosphere so as to reduce said ZnO to sub-stoichiometric zinc oxide, and heating said compact in an oxidizing atmosphere so as to restore said sub-stoichiometric oxide to stoichiometric ZnO.
Claim 8
Dependent Claim
17 words
The process of claim 5 wherein said hot-pressing is conducted at a temperature below about 850° C.
Claim 9
Dependent Claim
91 words
A process for producing a metal-oxide varistor, comprising: providing a varistor powder mix by calcining a gel comprising zinc-oxide and metal-oxide dopants including bismuth oxide, hot-pressing said mix at a temperature below about 1100° C. in a reducing atmosphere so as to reduce the zinc oxide to sub-stoichiometric oxide and formation of a powder compact having a density exceeding about 50% of the theoretical value, heating said compact in an oxidizing atmosphere to restore the sub-stoichiometric zinc oxide to stoichiometric zinc oxide, and providing the resulting compact with space ohmic electrodes.
Claim 10
Dependent Claim
91 words
A process for producing a metal-oxide varistor, comprising: providing a varistor powder mix by calcining a gel comprising zinc-oxide and metal-oxide dopants including bismuth oxide, hot-pressing said mix at a temperature below about 1100° C. in a reducing atmosphere so as to reduce the zinc oxide to sub-stoichiometric oxide and formation of a powder compact having a density exceeding about 50% of the theoretical value, heating said compact in an oxidizing atmosphere to restore the sub-stoichiometric zinc oxide to stoichiometric zinc oxide, and providing the resulting compact with space ohmic electrodes.
Claim 11
Dependent Claim
17 words
The process of claim 7 wherein said hot-pressing is conducted at a temperature below about 850° C.
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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) | 1988-04-08 | 1988-10-08 | 1989-04-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-04-08 | 1992-10-08 | 1993-04-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-04-08 | 1996-10-08 | 1997-04-09 | $7700.00 | Window Closed / Lapsed |