EP0004184A1
Expired / Lapsed
EP
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Gas sensing element and method for its production
Assignee: British Gas Corp
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Filing: 1979-03-07
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Granted: —
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Expires: 1999-03-07
Abstract
Abstract Catalytic gas sensors comprise a noble metal filament onto which is applied alumina having a particle size of not greater than 100A° and a catalyst material is impregnated into the dried alumina. The alumina may be dried by passage of an electric current through the filament and, prior to coating the filament may be stabilised by coating with a thermally decomposable aluminium salt and decomposed by passing a pulsed electric current.
Inventors
- 👤 John Michael Sonley
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 15:57
CPC Classifications
G; G01; G01N; G01N27/00; G01N27/02; G01N27/04; G01N27/14; G01N27/16
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
90 words
A catalytic gas sensing element comprising a noble metal filament having a pourous coating of alumina which coating is impregnated with a material which catalyses the oxidation of hydrocarbons wherein said element is formed by applying a slurry of alumina onto the filament, drying the applied slurry, applying a solution of the catalytic material to be dried alumina drying the thus impregnated alumina and activating the catalytic material and wherein the particle size of the alumina, in at least the outer regions of the coating, is not more than 100Å.
Claim 2
Dependent Claim
90 words
A catalytic gas sensing element comprising a noble metal filament having a pourous coating of alumina which coating is impregnated with a material which catalyses the oxidation of hydrocarbons wherein said element is formed by applying a slurry of alumina onto the filament, drying the applied slurry, applying a solution of the catalytic material to be dried alumina drying the thus impregnated alumina and activating the catalytic material and wherein the particle size of the alumina, in at least the outer regions of the coating, is not more than 100Å.
Claim 3
Dependent Claim
29 words
An element as claimed on Claim 1 wherein the alumina particles are conglomerates formed from smaller particles, the average size of said conglomerate being not greater than 100 i.
Claim 4
Dependent Claim
17 words
An element as claimed in Claim 1 wherein the particle size is from 50 - 70 I.
Claim 5
Dependent Claim
28 words
An element as claimed in Claim 1 wherein the alumina contains up to 0.6% by weight of sulphur present in at least the outer regions of the coating.
Claim 6
Dependent Claim
20 words
An element as claimed in Claim 1 wherein there is a further coating of alumina on the catalyst impregnated coating.
Claim 7
Dependent Claim
27 words
An element as claimed in Claim 1 wherein the filament is a stabilised filament produced by coating the noble metal with aluminium nitrate and decomposing the nitrate.
Claim 8
Dependent Claim
17 words
An element as claimed in Claim 1 wherein the catalyst material is selected from platinum and palladium.
Claim 9
Dependent Claim
12 words
An element is claimed in Claim 1 wherein the alumina is gamma-alumina.
Claim 10
Independent Claim
110 words
A method for the production of catalytic gas sensing element which process comprises stabilising a filament of a noble metal by applying thereto a coating of a thermally decomposable salt of aluminium, decomposing the aluminium salt to alumina by the application of a pulsed electrical energy source to the filament, applying a slurry of alumina wherein the particle size of the alumina is not greater than 100 i. to the stabilised filament, drying the slurry, applying a solution of a material which catalyses the oxidation of hydrocarbons on to the dried alumina slurry and exposing the thus formed bead to conditioning atmosphere comprising a mixture of natural gas and air.
Claim 11
Independent Claim
110 words
A method for the production of catalytic gas sensing element which process comprises stabilising a filament of a noble metal by applying thereto a coating of a thermally decomposable salt of aluminium, decomposing the aluminium salt to alumina by the application of a pulsed electrical energy source to the filament, applying a slurry of alumina wherein the particle size of the alumina is not greater than 100 i. to the stabilised filament, drying the slurry, applying a solution of a material which catalyses the oxidation of hydrocarbons on to the dried alumina slurry and exposing the thus formed bead to conditioning atmosphere comprising a mixture of natural gas and air.
Claim 12
Dependent Claim
35 words
A method as claimed in Claim 9 wherein the alumina is gamma alumina and the slurry contains an aqueous binder in buld volume ratio of from 1 to 3 parts alumina per 1 part binder.
Claim 13
Dependent Claim
30 words
A method is claimed in Claim 10 wherein the aqueous binder is a solution of aluminium nitrate and wherein the concentration of aluminium nitrate is less than 2% by weight.
Claim 14
Dependent Claim
52 words
A method as claimed in Claim 9 wherein the decomposible aluminium salt is decomposed by passing a current of between 0.1 to 0.5 amps for a period of 1 to 10 seconds and pulsing with an electric current through the coating with a 1 - 10 volt, 5,000 - 2000p F discharge.
Claim 15
Dependent Claim
60 words
A method as claimed in Claim 9 wherein the alumina slurry is dried by passing an electric current through the filament at a rate of 20 - 30 mA for a period of 0.5 to 2.0 hours and thereafter increasing the current at a rate of 3 - 5 mA/minute until a current of 300 - 500 mA is achieved.
Claim 16
Dependent Claim
19 words
A method is claimed in Claim 9 wherein a further coating of alumina is applied immediately prior to conditioning.
References Cited (Backward Citations)
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