US3200011A - Electrically heatable filaments - Google Patents

Electrically heatable filaments Download PDF

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Publication number
US3200011A
US3200011A US211802A US21180262A US3200011A US 3200011 A US3200011 A US 3200011A US 211802 A US211802 A US 211802A US 21180262 A US21180262 A US 21180262A US 3200011 A US3200011 A US 3200011A
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filament
catalyst
coating
refractory material
filaments
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US211802A
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Baker Alan Richard
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National Research Development Corp UK
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National Research Development Corp UK
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Priority claimed from US790935A external-priority patent/US3092799A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
    • G01N27/16—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature caused by burning or catalytic oxidation of surrounding material to be tested, e.g. of gas
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S264/00—Plastic and nonmetallic article shaping or treating: processes
    • Y10S264/19—Inorganic fiber

Definitions

  • This known arrangement could be such that oxidation of the combustible gas, for example by the oxygen contained in a sample of air under test, would take place at the surface of one of these filaments thus to alter its resistance, but such oxidation and change of resistance at the other filament would be inhibited.
  • the detector filament in such an arrangement is therefore capable of not only producing sufficient heat to promote the said oxidation but of varying its own resistance with change of heat resuiting from oxidation of combustible gas.
  • the detecting filaments are often heated to a temperature of 900 C. or more, depending upon the particular metal of which the filaments are made. At these relatively high temperatures, metal evaporates from the surface of the filament, in consequence of which, the resistance of the filament is continually increasing, especially during the oxidation of combustible gases. This continuous increase in resistance, which is greater in the detecting filament than in the compensating filament, causes an increase in the zero reading of the bridge circuit which latter must therefore be reset at frequent intervals.
  • the object of the present invention is to provide a method of manufacturing a heatable device such as described in the specification forming part of United States patent application Serial No. 790,935.
  • the method of making the said electrically heatable device for the detection of combustible gas in a combustion supporting atmosphere by the utilisation of the change of temperature of an electric heating filament includes the steps of coating the surface of the filament with a refractory material and adding to this refractory material a catalyst.
  • This catalyst when heated to a suitable temperature by the filament will promote oxidation of the gas on the surface of the catalyst so that inward conduction of heat from this oxidation will take place through the said refractory coating to raise the temperature of the filament.
  • the further step is included of adding to the exterior of the coated filament a further coating of refractory material, and the device may be heated to cause some of the catalyst to diffuse through said further coating to the outer surface thereof.
  • This further coating will be hereinafter explained.
  • a filament 57 which may be of metal of the platinum group and in the form of a helically coiled wire, is embedded within or com- "ice pietely surrounded by an oxide or other refractory material, which may for example be alumina or silica, so as to form a coating or pellet 58.
  • the alumina or silica is applied to the filament by causing evaporation and decomposition by the application of heat to a paste or solution of a compound such as a nitrate, hydroxide or alkali silicate.
  • the alumina pellet may be formed by the application to the coiled filament 57 of successive layers or portions of a saturated solution of aluminum nitrate in water, and after the application of each layer or portion, heating the layers or portions by passing an electric current through the filament.
  • a catalyst such as palladium or a mixture of platinum and palladium may be added which, by impregnation tends to form an outer coating 59 surrounding the oxide pellet 58 of the filament constitutting the detecting element.
  • This catalyst may be applied as a solution or dispersion of a compound or compounds of one or more metals of the platinum group.
  • catalyst solution which may be used, is obtained by mixing:
  • the liquid is removed and the catalyst made active by heating in air, or if necessary, in another gas.
  • the catalyst may be condensed on the pellet 53 by heating either the internal filament 57, or an external filament in close proximity to the pellet, to a temperature above 1000 C.
  • the compensating filament may comprise a similarly embedded filament to the refractory material surrounding which no catalyst has been added.
  • the apparatus has to be used with the filaments operating at high temperature, there is tendency for small quantities of the filament material to diffuse into the refractory surrounding these filaments, which diffused material may, give rise to catalytic action, so that, in the case of the compensating filament, it is desirable to add to the refractory coating of this, a suitable metallic oxide such as chromium oxide or some other catalyst poison.
  • the pellet 58 is provided with an additional coating of alumina or other refractory material applied on the top of the external coating of catalyst 59. After heating to approximately 1000 C. for a few minutes, prefreably in a combustible gas, enough of the catalyst 59 diffuses through the additional coating to the external surface of the latter. The effect of this coating is to reduce the loss in catalytic activity which occurs when the detecting element is heated for several hours in air or in low concentrations of methane.
  • filaments When the filaments are to be used in apparatus for the detection of one non-combustible gas in the presence of another or others, or high concentrations of a combustible gas in air such as described, for example, in co-pending United States patent application Serial No. 790,870, two similar filaments may be used, to both of which a catalyst poison has been added.
  • the amount of oxidation of the combustible gas at the filament wire is very considerably reduced and the filament can be operated at a lower temperature than would be the case should an exposed filament be used, as a result of which the rate of evaporation of metal from the wire filament is negligible.
  • the operational life of the embedded filament is considerably longer than is the case with exposed filaments.
  • the refractory coating in effect, also adds considerable strength to the filament.
  • the method of making an electrically heatable device for the detection of combustible gas in air by the utilisation of the change of electrical resistance of an electric heating filament including firstly the step of coating the filament with a refractory material, secondly the step of adding to the refractory material a catalyst, thirdly the step of addingto the exterior of the filament a further coating of refractory material, and finally the step of heating the device to cause some of the catalyst to dilfuse through said further coating to the outer surface thereof.
  • step of heating to remove the liquid and to render the catalyst active, fo-urthly the step of adding to the exterior of the coated filament a further coating of refractory material, and finally the step of heating the device to cause some of the catalyst to diffuse through 'said further coating to the outer surface thereof.

Description

Aug. 10, 1965 A. R. BAKER ELEGTRICALLY HEATABLE FILAMENTS Original Filed Feb. 5, 1959 Z In 01%: mff w United States Patent 3,200,011 ELECTRICALLY HEATABLE FILAMENTS :Alan Richard Baker, Shefiield, England, assignor to Na- This invention relates to electrically heatable filaments for use in connection with the detection of combustible gas in a combustion supporting atmosphere, for which purpose it is usual to employ a pair of filaments constituting detecting and compensating elements, respectively, arranged in a Wheatstone bridge circuit. This known arrangement could be such that oxidation of the combustible gas, for example by the oxygen contained in a sample of air under test, would take place at the surface of one of these filaments thus to alter its resistance, but such oxidation and change of resistance at the other filament would be inhibited. The detector filament in such an arrangement is therefore capable of not only producing sufficient heat to promote the said oxidation but of varying its own resistance with change of heat resuiting from oxidation of combustible gas.
In apparatus of the above type, the detecting filaments are often heated to a temperature of 900 C. or more, depending upon the particular metal of which the filaments are made. At these relatively high temperatures, metal evaporates from the surface of the filament, in consequence of which, the resistance of the filament is continually increasing, especially during the oxidation of combustible gases. This continuous increase in resistance, which is greater in the detecting filament than in the compensating filament, causes an increase in the zero reading of the bridge circuit which latter must therefore be reset at frequent intervals.
The present application is a divisional application in respect of certain features originally included in United States patent application Serial No. 790,935, and now Patent No. 3,092,799, which last mentioned application relates to an electrically heatable device for use in the detection of combustible gases in air.
The object of the present invention is to provide a method of manufacturing a heatable device such as described in the specification forming part of United States patent application Serial No. 790,935.
According to the present invention, the method of making the said electrically heatable device for the detection of combustible gas in a combustion supporting atmosphere by the utilisation of the change of temperature of an electric heating filament, includes the steps of coating the surface of the filament with a refractory material and adding to this refractory material a catalyst. This catalyst, when heated to a suitable temperature by the filament will promote oxidation of the gas on the surface of the catalyst so that inward conduction of heat from this oxidation will take place through the said refractory coating to raise the temperature of the filament. Preferably, although not necessarily, the further step is included of adding to the exterior of the coated filament a further coating of refractory material, and the device may be heated to cause some of the catalyst to diffuse through said further coating to the outer surface thereof. The purpose of this further coating will be hereinafter explained.
The invention will now be described, by way of example, with reference to the accompanying drawing.
Referring now to the said drawing, a filament 57 which may be of metal of the platinum group and in the form of a helically coiled wire, is embedded within or com- "ice pietely surrounded by an oxide or other refractory material, which may for example be alumina or silica, so as to form a coating or pellet 58. The alumina or silica is applied to the filament by causing evaporation and decomposition by the application of heat to a paste or solution of a compound such as a nitrate, hydroxide or alkali silicate. More particularly, the alumina pellet may be formed by the application to the coiled filament 57 of successive layers or portions of a saturated solution of aluminum nitrate in water, and after the application of each layer or portion, heating the layers or portions by passing an electric current through the filament.
When the detector device is to be used in apparatus for the detection of combustible gas in air, such as described, for example, in my co-pending United States patent application Serial No. 790,870, and now Patent No. 3,117,843, a catalyst such as palladium or a mixture of platinum and palladium may be added which, by impregnation tends to form an outer coating 59 surrounding the oxide pellet 58 of the filament constitutting the detecting element. This catalyst may be applied as a solution or dispersion of a compound or compounds of one or more metals of the platinum group. One example of catalyst solution which may be used, is obtained by mixing:
1.2 ml. of 8 percent (by weight) palladous chloride (PdCl in 6 N hydrochloric acid,
0.8 m1. of 5 percent (by weight) of chloroplatinic acid (H PtCl l-I O) in water 0.2 ml. of 10 percent (by weight) of aluminum nitrate (Al(NO .6H O) in water.
The liquid is removed and the catalyst made active by heating in air, or if necessary, in another gas.
Alternatively the catalyst may be condensed on the pellet 53 by heating either the internal filament 57, or an external filament in close proximity to the pellet, to a temperature above 1000 C. In so far as the compensating filament is concerned this may comprise a similarly embedded filament to the refractory material surrounding which no catalyst has been added. When the apparatus has to be used with the filaments operating at high temperature, there is tendency for small quantities of the filament material to diffuse into the refractory surrounding these filaments, which diffused material may, give rise to catalytic action, so that, in the case of the compensating filament, it is desirable to add to the refractory coating of this, a suitable metallic oxide such as chromium oxide or some other catalyst poison.
According to a modification adapted more particularly for use as a detecting element, and having its filament embedded with an oxide or other refractory material such as alumina or silica coated externally with a catalyst in the manner already described, the pellet 58 is provided with an additional coating of alumina or other refractory material applied on the top of the external coating of catalyst 59. After heating to approximately 1000 C. for a few minutes, prefreably in a combustible gas, enough of the catalyst 59 diffuses through the additional coating to the external surface of the latter. The effect of this coating is to reduce the loss in catalytic activity which occurs when the detecting element is heated for several hours in air or in low concentrations of methane.
When the filaments are to be used in apparatus for the detection of one non-combustible gas in the presence of another or others, or high concentrations of a combustible gas in air such as described, for example, in co-pending United States patent application Serial No. 790,870, two similar filaments may be used, to both of which a catalyst poison has been added.
Where a detecting device according to the invention is used, the amount of oxidation of the combustible gas at the filament wire is very considerably reduced and the filament can be operated at a lower temperature than would be the case should an exposed filament be used, as a result of which the rate of evaporation of metal from the wire filament is negligible. The necessity, therefore, to make frequent zero adjustments to the electrical bridge as required by the use of an exposed filament in gas detection apparatus as hitherto employed, no longer arises.
In addition, the operational life of the embedded filament is considerably longer than is the case with exposed filaments. The refractory coating, in effect, also adds considerable strength to the filament.
I claim:
1. The method of making an electrically heatable device for the detection of combustible gas in air by the utilisation of the change of electrical resistance of an electric heating filament, including firstly the step of coating the filament with a refractory material, secondly the step of adding to the refractory material a catalyst, thirdly the step of addingto the exterior of the filament a further coating of refractory material, and finally the step of heating the device to cause some of the catalyst to dilfuse through said further coating to the outer surface thereof.
2. In the method of making an electrically heatable detecting device as claimed in claim 1, the final heating step being performed at approximately 1000 C. in an environment of combustible gas.
3. The method of making an electrically heatable device for detection of combustible gas in air by the utilisation of the change of electrical resistance of an electric heating filament, including firstly the step of coating the filament with a refractory material and secondly the step of adding to the refractory material a catalyst solution obtained by mixing:
1.2 ml. of 8 percent (by Weight) of palladous chloride (PdCl in 6, N hydrochloric acid,
0.8 ml, of 5 percent (by Weight) of chloroplatinic acid (H Pt Cl .6H O) in Water,
0.2 ml. of 10 percent (by weight) of aluminum nitrate (A-l(NO .6H O) in water;
thirdly the step of heating to remove the liquid and to render the catalyst active, fo-urthly the step of adding to the exterior of the coated filament a further coating of refractory material, and finally the step of heating the device to cause some of the catalyst to diffuse through 'said further coating to the outer surface thereof.
References Cited by the Examiner UNITED STATES PATENTS RICHARD D. NEVIUS, Primary Examiner.

Claims (1)

1. THE METHOD OF MAKING AN ELECTRICALLY HEATABLE DEVICE FOR THE DETECTION OF COMBUSTIBLE GAS IN AIR BY THE UTILISATION OF THE CHANGE OF ELECTRICAL RESISTANCE OF AN ELECTRIC HEATING FILAMENT, INCLUDING FIRSTLY THE STEP OF COATING THE FILAMENT WITH A REFRACTORY MATERIAL, SECONDLY THE STEP OF ADDING TO THE REFRACTORY MATERIAL A CATALYST, THRIDLY THE STEP OF ADDING TO THE EXTERIOR OF THE FILAMENT A FURTHER COATING OF REFRACTORY MATERIAL, AND FINALLY THE STEP OF HEATING THE DEVICE TO CAUSE SOME OF THE CATALYST TO DIFFUSE THROUGH SAID FURTHER COATING TO THE OUTER SURFACE THEREOF.
US211802A 1959-02-03 1962-07-23 Electrically heatable filaments Expired - Lifetime US3200011A (en)

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Application Number Priority Date Filing Date Title
US790935A US3092799A (en) 1958-02-18 1959-02-03 Apparatus for detecting combustible gases having an electrically conductive member enveloped in a refractory material
US211802A US3200011A (en) 1959-02-03 1962-07-23 Electrically heatable filaments

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Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3340013A (en) * 1963-09-09 1967-09-05 Foxboro Co Flame detector
US3625756A (en) * 1969-01-21 1971-12-07 Naoyoshi Taguchi Method for making a gas-sensing element
US3955268A (en) * 1974-09-13 1976-05-11 Chou Chen Yen Method of fabricating an electrolytic cell gas sensor
US4033169A (en) * 1974-08-09 1977-07-05 Nissan Motor Co., Ltd. Hydrocarbon concentration sensor for use in engine exhaust gas
US4045177A (en) * 1976-08-16 1977-08-30 Cse Corporation Apparatus for detecting combustible gases
FR2401419A1 (en) * 1977-08-25 1979-03-23 English Electric Valve Co Ltd COMBUSTIBLE GAS DETECTOR
US4200608A (en) * 1978-06-15 1980-04-29 The United States Of America As Represented By The Secretary Of The Army Detector for fumes of hydrazine and its derivatives
US4228128A (en) * 1979-03-19 1980-10-14 Ford Motor Company Exhaust gas sensor having porous, metal-impregnated ceramic element
US4303612A (en) * 1978-03-08 1981-12-01 Diffracto Ltd. Gas sensitive devices
FR2484689A1 (en) * 1980-06-11 1981-12-18 Mine Safety Appliances Co ELECTRICALLY HEATABLE ELEMENT FOR GAS DETECTION INSTRUMENTS, AND MANUFACTURING METHOD THEREOF
US4313907A (en) * 1980-04-21 1982-02-02 National Mine Corporation Apparatus for the detection of a combustible gas
US4325912A (en) * 1980-07-01 1982-04-20 Beckman Instruments, Inc. Carbon monoxide detection apparatus
EP0062466A1 (en) * 1981-04-04 1982-10-13 English Electric Valve Company Limited Combustible-gas detectors
DE3446982A1 (en) * 1983-12-23 1985-07-11 Rexnord Inc., Milwaukee, Wis. ACTIVE ELEMENT RESISTANT TO POISONING A COMBUSTIBLE GAS SENSOR AND METHOD FOR PRODUCING THE ELEMENT
US4818348A (en) * 1987-05-26 1989-04-04 Transducer Research, Inc. Method and apparatus for identifying and quantifying simple and complex chemicals
US5055266A (en) * 1984-03-02 1991-10-08 Arch Development Corporation Method for detecting toxic gases
US5217692A (en) * 1989-10-17 1993-06-08 E.T.R. Elektronik Technologie Rump Gmbh Gas sensor arrangement
US5234837A (en) * 1989-04-06 1993-08-10 Charbonnages De France Pseudo-continuous process for interrogating a combustible gas detector
US5549871A (en) * 1993-01-21 1996-08-27 Servomex Plc Sensor for combustible gases
US20080156076A1 (en) * 2006-12-29 2008-07-03 Ravosh Samari Low Power Combustible Gas Sensor

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2363478A (en) * 1939-12-23 1944-11-28 Boeke Jan Method and device for detecting traces of foreign gases, vapors, or mists in the atmosphere
DE898089C (en) * 1948-10-02 1953-11-26 Physikalisches Untersuchungsla Measuring device for qualitative or quantitative analysis of media capable of flow
FR1061692A (en) * 1950-11-18 1954-04-14 Baker & Co Inc Device for the catalytic ignition of finely divided fuels
US2757104A (en) * 1953-04-15 1956-07-31 Metalholm Engineering Corp Process of forming precision resistor
US2782103A (en) * 1951-10-12 1957-02-19 Phillips Petroleum Co Analyzer for gaseous mixtures

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2363478A (en) * 1939-12-23 1944-11-28 Boeke Jan Method and device for detecting traces of foreign gases, vapors, or mists in the atmosphere
DE898089C (en) * 1948-10-02 1953-11-26 Physikalisches Untersuchungsla Measuring device for qualitative or quantitative analysis of media capable of flow
FR1061692A (en) * 1950-11-18 1954-04-14 Baker & Co Inc Device for the catalytic ignition of finely divided fuels
US2782103A (en) * 1951-10-12 1957-02-19 Phillips Petroleum Co Analyzer for gaseous mixtures
US2757104A (en) * 1953-04-15 1956-07-31 Metalholm Engineering Corp Process of forming precision resistor

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3340013A (en) * 1963-09-09 1967-09-05 Foxboro Co Flame detector
US3625756A (en) * 1969-01-21 1971-12-07 Naoyoshi Taguchi Method for making a gas-sensing element
US4033169A (en) * 1974-08-09 1977-07-05 Nissan Motor Co., Ltd. Hydrocarbon concentration sensor for use in engine exhaust gas
US3955268A (en) * 1974-09-13 1976-05-11 Chou Chen Yen Method of fabricating an electrolytic cell gas sensor
US4045177A (en) * 1976-08-16 1977-08-30 Cse Corporation Apparatus for detecting combustible gases
FR2401419A1 (en) * 1977-08-25 1979-03-23 English Electric Valve Co Ltd COMBUSTIBLE GAS DETECTOR
US4303612A (en) * 1978-03-08 1981-12-01 Diffracto Ltd. Gas sensitive devices
US4200608A (en) * 1978-06-15 1980-04-29 The United States Of America As Represented By The Secretary Of The Army Detector for fumes of hydrazine and its derivatives
US4228128A (en) * 1979-03-19 1980-10-14 Ford Motor Company Exhaust gas sensor having porous, metal-impregnated ceramic element
US4313907A (en) * 1980-04-21 1982-02-02 National Mine Corporation Apparatus for the detection of a combustible gas
FR2484689A1 (en) * 1980-06-11 1981-12-18 Mine Safety Appliances Co ELECTRICALLY HEATABLE ELEMENT FOR GAS DETECTION INSTRUMENTS, AND MANUFACTURING METHOD THEREOF
US4325912A (en) * 1980-07-01 1982-04-20 Beckman Instruments, Inc. Carbon monoxide detection apparatus
EP0062466A1 (en) * 1981-04-04 1982-10-13 English Electric Valve Company Limited Combustible-gas detectors
DE3446982A1 (en) * 1983-12-23 1985-07-11 Rexnord Inc., Milwaukee, Wis. ACTIVE ELEMENT RESISTANT TO POISONING A COMBUSTIBLE GAS SENSOR AND METHOD FOR PRODUCING THE ELEMENT
US5055266A (en) * 1984-03-02 1991-10-08 Arch Development Corporation Method for detecting toxic gases
US4818348A (en) * 1987-05-26 1989-04-04 Transducer Research, Inc. Method and apparatus for identifying and quantifying simple and complex chemicals
US5234837A (en) * 1989-04-06 1993-08-10 Charbonnages De France Pseudo-continuous process for interrogating a combustible gas detector
US5217692A (en) * 1989-10-17 1993-06-08 E.T.R. Elektronik Technologie Rump Gmbh Gas sensor arrangement
US5549871A (en) * 1993-01-21 1996-08-27 Servomex Plc Sensor for combustible gases
US20080156076A1 (en) * 2006-12-29 2008-07-03 Ravosh Samari Low Power Combustible Gas Sensor
US7833482B2 (en) 2006-12-29 2010-11-16 Honeywell International Inc. Low power combustible gas sensor

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