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US3999947A
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US
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Reducing gas sensor and a method of producing the same
Assignee: Panasonic Holdings Corp
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Filing: 1975-10-01
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Granted: 1976-12-28
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Expires: 1995-10-01
Abstract
Abstract This invention provides a reducing gas sensor which has a gas sensitive element of γ-ferric oxide (γ-Fe 2 O 3 ), a pair of electrodes and a heater element. The γ-ferric oxide is in the form of a thin film, a plate or a thin surface layer on a sintered plate of α-ferric oxide. This invention also provides a method of producing the reducing gas sensor, which includes the steps of firing γ-Fe 2 O 3 , γ-FeOOH or Fe 3 O 4 powder on a substrate and applying thereto a pair of electrodes and a heater element; or sintering alpha-ferric oxide (α-Fe 2 O 3 ) and reducing it to magnetite and oxidizing it at the surface thereof to γ-ferric oxide as a gas sensitive element. The sensitivity (R A /R G ) of the gas sensitive element of γ-ferric oxide is 10 to 130° at 270° C in an atmosphere containing 0.1 to 1 percent by volume propane gas, and the reducing gas sensor has high sensitivity and stability.
Inventors
- 👤 Toshihiro Mihara
- 👤 Masatake Ayusawa
- 👤 Keiji Matsumoto
- 👤 Kunio Sato
- 👤 Yoshio Iida
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 12:27
CPC Classifications
G; G01; G01N; G01N27/00; G01N27/02; G01N27/04; G01N27/12
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
65 words
A reducing gas sensor comprising a gas sensitive element composed mainly of γ-ferric oxide (γ-Fe 2 O 3 ), a pair of electrodes on said sensitive element, and a heater element adjacent said elements, whereby when said gas sensitive element is heated to an elevated temperature it undergoes a rapid decrease in electrical resistance upon coming in contact with an atmosphere containing a reducing gas.
Claim 2
Dependent Claim
65 words
A reducing gas sensor comprising a gas sensitive element composed mainly of γ-ferric oxide (γ-Fe 2 O 3 ), a pair of electrodes on said sensitive element, and a heater element adjacent said elements, whereby when said gas sensitive element is heated to an elevated temperature it undergoes a rapid decrease in electrical resistance upon coming in contact with an atmosphere containing a reducing gas.
Claim 3
Dependent Claim
22 words
A reducing gas sensor according to claim 1, wherein said gas sensitive element is composed of a sintered body of γ-ferric oxide.
Claim 4
Dependent Claim
24 words
A reducing gas sensor according to claim 2, wherein said gas sensitive element is in the form of a sintered plate of γ-ferric oxide.
Claim 5
Dependent Claim
28 words
A reducing gas sensor according to claim 2, wherein said gas sensitive element is in the form of a sintered film of γ-ferric oxide on an insulator substrate.
Claim 6
Dependent Claim
32 words
A reducing gas sensor according to claim 2, wherein said gas sensitive element is in the of a thin surface layer of γ-ferric oxide formed on a sintered plate of α-ferric oxide.
Claim 7
Independent Claim
68 words
A method of producing a reducing gas sensor, comprising firing an iron oxide at a temperature between 100° C and 600° C for 30 minutes to 5 hours in an oxidizing atmosphere to obtain a sintered γ-ferric oxide (γ-Fe 2 O 3 ) as a gas sensitive element, applying a pair of electrodes to said gas sensitive element and placing a heater element near said gas sensitive element.
Claim 8
Independent Claim
68 words
A method of producing a reducing gas sensor, comprising firing an iron oxide at a temperature between 100° C and 600° C for 30 minutes to 5 hours in an oxidizing atmosphere to obtain a sintered γ-ferric oxide (γ-Fe 2 O 3 ) as a gas sensitive element, applying a pair of electrodes to said gas sensitive element and placing a heater element near said gas sensitive element.
Claim 9
Dependent Claim
71 words
A method of producing a reducing gas sensor according to claim 6, wherein said sintered γ-ferric oxide is obtained by mixing γ-ferric oxide powder and water to prepare a homogeneous mixture, applying said mixture to an insulator substrate to form thereon a thin film of said mixture, and firing said thin film at a temperature between 350° C and 600° C for 30 minutes to 5 hours in an oxidizing atmosphere.
Claim 10
Dependent Claim
71 words
A method of producing a reducing gas sensor according to claim 6, wherein said sintered γ-ferric oxide is obtained by mixing powdered lepidocrocite (γ-FeOOH) and water to prepare a homogeneous mixture, applying said mixture to an insulator substrate to form thereon a thin film of said mixture, and firing said thin film at a temperature between 150° C and 600° C for 30 minutes to 5 hours in an oxidizing atmosphere.
Claim 11
Dependent Claim
75 words
A method of producing a reducing gas sensor according to claim 6, wherein said sintered γ-ferric oxide is obtained by mixing powdered magnetite (γ-Fe 3 O 4 ) and water to prepare a homogeneous mixture, applying said mixture to an insulator substrate to form thereon a thin film of said mixture, and firing said thin film at a temperature between 100° C and 600° C for 30 minutes to 5 hours in an oxidizing atmosphere.
Claim 12
Dependent Claim
76 words
A method of producing a reducing gas sensor according to claim 6, wherein said sintered γ-ferric oxide is obtained by pressing magnetite powder to prepare a plate of said magnetite, prefiring said plate at a temperature between 600° and 1100° C for 30 minutes to 10 hours in a non-oxidizing atmosphere, and firing said prefired plate of magnetite at a temperature between 100° and 600° C for 30 minutes to 5 hours in an oxidizing atmosphere.
Claim 13
Dependent Claim
120 words
A method of producing a reducing gas sensor according to claim 6, wherein said sintered γ-ferric oxide is obtained by mixing α-ferric oxide powder and polyvinyl alcohol solution to prepare a homogeneous mixture, appyling said mixture to an insulator substrate to form thereon a thin film of said mixture, prefiring said thin film at a temperature between 700° and 1300° C for 1 to 10 hours in an oxidizing atmosphere, firing said prefired film at a temperature between 200° and 450° C for 15 minutes to 3 hours in hydrogen gas saturated with water vapor, and further firing the thus fired film at a temperature between 100° C and 600° C for 1 to 5 hours in an oxidizing atmosphere.
Claim 14
Dependent Claim
118 words
A method of producing a reducing gas sensor according to claim 6, wherein said sintered γ-ferric oxide is obtained by pressing α-ferric oxide powder to prepare a plate of said α-ferric oxide, prefiring said plate at a temperature between 800° and 1000° C for 1 to 3 hours in an oxidizing atmosphere, firing said prefired plate at a temperature between 200° and 450° C for 10 minutes to 2 hours in hydrogen gas saturated with water vapor, and further firing the thus fired plate at a temperature between 100° and 600° C for 30 minutes to 3 hours in an oxidizing atmosphere so as to transform the thin surface layer of said further fired plate to γ-ferric oxide.
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) | 1979-12-28 | 1980-06-28 | 1980-12-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-12-28 | 1984-06-28 | 1984-12-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-12-28 | 1988-06-28 | 1988-12-28 | $7700.00 | Window Closed / Lapsed |