EP0222783A1 - Self heated sensor package - Google Patents

Self heated sensor package

Info

Publication number
EP0222783A1
EP0222783A1 EP86902248A EP86902248A EP0222783A1 EP 0222783 A1 EP0222783 A1 EP 0222783A1 EP 86902248 A EP86902248 A EP 86902248A EP 86902248 A EP86902248 A EP 86902248A EP 0222783 A1 EP0222783 A1 EP 0222783A1
Authority
EP
European Patent Office
Prior art keywords
heating element
sensor
solid electrolyte
oxygen
ceramic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP86902248A
Other languages
German (de)
French (fr)
Other versions
EP0222783A4 (en
Inventor
Anil K. Agarwal
Joseph N. Panzarino
Malcolm E. Washburn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Saint Gobain Abrasives Inc
Original Assignee
Norton Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Norton Co filed Critical Norton Co
Publication of EP0222783A1 publication Critical patent/EP0222783A1/en
Publication of EP0222783A4 publication Critical patent/EP0222783A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • 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
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/406—Cells and probes with solid electrolytes
    • G01N27/4067—Means for heating or controlling the temperature of the solid electrolyte

Definitions

  • Zirconia stabilized with Y 2 O 3 , CaO, MgO, etc. is widely used for oxygen sensors in a variety of industrial and automotive applications.
  • Stabilized zirconia being a solid state oxygen ion conductor preferentially transports oxygen ions from a gas stream having a higher oxygen partial pressure to a gas stream having a lower oxygen partial pressure, if the two gas streams are isolated, of course.
  • the transport rate (response time) is governed by the operating temperature.
  • the E.M.F. of this oxygen cell is given by the following Nernst Equation:
  • An in situ oxygen sensing apparatus accomplishing the objective of the invention is provided by the use of a ceramic (preferably silicon carbide) resistance heating element surrounding the solid electrolyte and heating the electrolyte sensor by radiation and convection.
  • a ceramic preferably silicon carbide
  • FIG. 1 is a perspective view of a sensor of the invention.
  • Figure 2 is a cross sectional view of the sensor element.
  • Figure 3 is a top view of one of the heating elements.
  • Figure 4 is a side view of a heating element.
  • Silicon carbide igniters have been commercially used for igniting gases and operate successfully in the typical atmospheres as mentioned above. These igniters have survived the most stringent requirement of thermal and gas cycling for extended periods of time. So much so that they have been a accepted by the home appliance market. Needless to say these markets are very conservative in product selection because of reliability and cost consciousness. Typical igniters are described in U.S. Patent 3,875,477.
  • FIG. 1 A working unit which uses two planoconcave SiC heating elements, 11, 12, surrounding ZrO 2 13 sensor tube is shown in Figure 1. This whole assembly is mounted on an insulating ceramic disk 14 which butts against a furnace port and seals the furnace atmosphere completely.
  • the electronics is controlled from a separate unit which processes the E.M.F. from connectors 15, 16, and correlates that to the oxygen partial pressure in the furnace.
  • the heaters are powered through connectors 17, 18, 19, cind 20.
  • Figure 3 shows in more detail a longitudinal cross section through the sensor element 13 and associated annular electrodes 21 and 22, with leads 23 and 24 to the connections in the base 14.
  • the leads may be protected by a flame sprayed coating
  • porous electrodes 21 and 22 may be protected by a plasma or flame sprayed coating 21', 22', of a material of the same composition as the solid electrolyte, or a porous coating of a refractory material such as cordierite or spinel.
  • the connectors from the electrodes may be connected to a high impedance voltmeter or the other measuring and control devices, not part of the present invention, but well known in the art.
  • Figure 3 shows a top view of one of the heating elements 11 or 12, and Figure 4 shows a left side view of the heating element of Figure 3.
  • the element is provided with slots 31, 32, and 33, so arranged that the element effectively has outer legs 35 and 36 which function as opposite electrical ends of a conductor, whereby a voltage drop applied across the ends 35 and 36 produces a heating current in the silicon carbide body.
  • the surface directed toward the sensor 13 is shown as parabolic at 50 in Figure 3 to direct the heat on to the sensor with maximum efficiency. Other concave shapes such as circular may be used.
  • the preferred sensor solid electrolyte is doped zirconia
  • the particular chemistry of the sensor is not part of this invention and the sensor may be made of any suitable material which can conduct oxygen ions and produce a voltage across its electrodes in respo ⁇ se to an oxygen partial pressure differential.
  • the geometry of the heating elements of the heater is such that the most resistant (smallest conductive cross section) of the heater is interior of the sides and ends of the elements. Thus the highest temperature is directed at the sensor.
  • Such control of the heating location by adjusting the geometry of the unit, is possible because of the use of conductive ceramic material in the heater having a relatively high resistivity as compared to metallic conductor resistance heating elements. In cases where battery power is used or the power supply is limited, the increased efficiency of the heater produced by the illustrated geometry is an added benefit.
  • a chamber is formed around the sensor which acts as a buffer to prevent immediate direct access of the ambient gas outside the heater.
  • excess oxygen will tend to react with any uncombusted products, thereby insuring an aquilibrium oxygen partial pressure condition for the sensed gas.
  • the buffer chamber formed by the heater protects the sensor against fouling by solid combustion products.
  • SiC heating elements have been found to be inoperative in that false readings of oxygen content are obtained after 3 to 6 months of use. This is apparently caused by slow oxidation of free silicon or free carbon in the elements. While simple heating of the elements in an oxidizing atmosphere at 1200 °C. for 10 to 15 hours avoids this problem, added protection of the elements can be achieved by filling the surface pores of the SiC heaters with fine ceramic powder such as Si 3 N 4 , and heating to oxidize any materials which would interfere with the accuracy.
  • the Si 3 N 4 is preferably applied in the form of a slurry.
  • the pores may be filled with a mixture of fine silicon carbide and sodium silicate, fired to a glassy dry state.
  • Other pore filling material such as fine silicon nitride may also be used as taught in U.S. Patent 4,187,344.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Measuring Oxygen Concentration In Cells (AREA)

Abstract

Un ensemble détecteur d'oxygène comporte un détecteur à électrolyte solide (13) et un élément (11, 12) de chauffage au carbure de silicium disposé de façon à entourer l'électrolyte solide et à irradier vers lui de la chaleur à partir des surfaces convexes (50).An oxygen sensor assembly includes a solid electrolyte detector (13) and a silicon carbide heating element (11, 12) arranged to surround the solid electrolyte and to radiate heat therefrom from surfaces convex (50).

Description

SELF HEATED SENSOR PACKAGE
Zirconia stabilized with Y2O3, CaO, MgO, etc. is widely used for oxygen sensors in a variety of industrial and automotive applications. Stabilized zirconia, being a solid state oxygen ion conductor preferentially transports oxygen ions from a gas stream having a higher oxygen partial pressure to a gas stream having a lower oxygen partial pressure, if the two gas streams are isolated, of course. The transport rate (response time) is governed by the operating temperature. The E.M.F. of this oxygen cell is given by the following Nernst Equation:
, where R is gas constant, T is temperature in °K, N is charge, F is the Faraday constant, PO2(I) and PO2(II) are oxygen partial pressure in the two sides respectively. Several models are commercially available today. They all can be classified in two following categories: 1) In situ type
2) Sampling Type In the in situ type the sensor is placed into the furnace and senses the atmospheric oxygen. The sensor is heated by the furnace heat or, if insufficient, by external platinum or nichrome heators wrapped around it to provide the temperature for adequate operation. The heating elements have to be protected from the furnace atmosphere which addes complexity and weight. The complexity of the in situ sensors is avoided by a sampling type of device wherein a probe is inserted into the furnace or other atmosphere to be measured and a sample is drawn out which is then passed through an external sensor maintained in at desired temperature. This type of device is also useful as a portable unit. However, the problem of condensation of the gases through the line from the furnace to be measured to the sensor unit comes into play. One has to heat the line to prevent condensation and also worry about the calibration of the sensor to the operating temperature of the furnace rather than of the sensor to obtain the correct PO2. Looking at the above situation, there exists a need for an efficient in situ device with an inert heating element which is stable against atmosphere and temperature and also is inexpensive for real time atmosphere monitoring. Some of the applications for such a device are in diffusion furnaces, gas analysis, sintering and brazing furnaces, glass melting, combustion and heat treatment furnaces, nitriding furnaces, etc. BRIEF SUMMARY OF THE INVENTION
An in situ oxygen sensing apparatus accomplishing the objective of the invention is provided by the use of a ceramic (preferably silicon carbide) resistance heating element surrounding the solid electrolyte and heating the electrolyte sensor by radiation and convection. IN THE DRAWINGS Figure 1 is a perspective view of a sensor of the invention.
Figure 2 is a cross sectional view of the sensor element.
Figure 3 is a top view of one of the heating elements.
Figure 4 is a side view of a heating element. DETAILED DESCRIPTION OF THE INVENTION
Silicon carbide igniters have been commercially used for igniting gases and operate successfully in the typical atmospheres as mentioned above. These igniters have survived the most stringent requirement of thermal and gas cycling for extended periods of time. So much so that they have been a accepted by the home appliance market. Needless to say these markets are very conservative in product selection because of reliability and cost consciousness. Typical igniters are described in U.S. Patent 3,875,477.
A working unit which uses two planoconcave SiC heating elements, 11, 12, surrounding ZrO2 13 sensor tube is shown in Figure 1. This whole assembly is mounted on an insulating ceramic disk 14 which butts against a furnace port and seals the furnace atmosphere completely. The electronics is controlled from a separate unit which processes the E.M.F. from connectors 15, 16, and correlates that to the oxygen partial pressure in the furnace. The heaters are powered through connectors 17, 18, 19, cind 20.
Figure 3 shows in more detail a longitudinal cross section through the sensor element 13 and associated annular electrodes 21 and 22, with leads 23 and 24 to the connections in the base 14. The leads may be protected by a flame sprayed coating
23' and 24'. Similarly, porous electrodes 21 and 22 may be protected by a plasma or flame sprayed coating 21', 22', of a material of the same composition as the solid electrolyte, or a porous coating of a refractory material such as cordierite or spinel..
The connectors from the electrodes may be connected to a high impedance voltmeter or the other measuring and control devices, not part of the present invention, but well known in the art.
Figure 3 shows a top view of one of the heating elements 11 or 12, and Figure 4 shows a left side view of the heating element of Figure 3. The element is provided with slots 31, 32, and 33, so arranged that the element effectively has outer legs 35 and 36 which function as opposite electrical ends of a conductor, whereby a voltage drop applied across the ends 35 and 36 produces a heating current in the silicon carbide body. The surface directed toward the sensor 13 is shown as parabolic at 50 in Figure 3 to direct the heat on to the sensor with maximum efficiency. Other concave shapes such as circular may be used.
While the preferred sensor solid electrolyte is doped zirconia, the particular chemistry of the sensor is not part of this invention and the sensor may be made of any suitable material which can conduct oxygen ions and produce a voltage across its electrodes in respoηse to an oxygen partial pressure differential. Referring to the drawing, it should be noted that the geometry of the heating elements of the heater is such that the most resistant (smallest conductive cross section) of the heater is interior of the sides and ends of the elements. Thus the highest temperature is directed at the sensor. Such control of the heating location, by adjusting the geometry of the unit, is possible because of the use of conductive ceramic material in the heater having a relatively high resistivity as compared to metallic conductor resistance heating elements. In cases where battery power is used or the power supply is limited, the increased efficiency of the heater produced by the illustrated geometry is an added benefit.
When the heater surrounds the outside of the sensor, as in Figures 2 and 3 of the drawing, a chamber is formed around the sensor which acts as a buffer to prevent immediate direct access of the ambient gas outside the heater. In addition, since gas accessing the space between the heater and the sensor must flow close to the hot surfaces of the heating element, excess oxygen will tend to react with any uncombusted products, thereby insuring an aquilibrium oxygen partial pressure condition for the sensed gas. In addition the buffer chamber formed by the heater protects the sensor against fouling by solid combustion products.
Conventionally prepared SiC heating elements have been found to be inoperative in that false readings of oxygen content are obtained after 3 to 6 months of use. This is apparently caused by slow oxidation of free silicon or free carbon in the elements. While simple heating of the elements in an oxidizing atmosphere at 1200 °C. for 10 to 15 hours avoids this problem, added protection of the elements can be achieved by filling the surface pores of the SiC heaters with fine ceramic powder such as Si3N4, and heating to oxidize any materials which would interfere with the accuracy. The Si3N4 is preferably applied in the form of a slurry. In a comparison test of an atmosphere at a pressure of one atmosphere containing an oxygen partial pressure of about 10-4 atmospheres of oxygen, an untreated SiC heater and a ceramic coated but unvented heater both gave erroneous readings of the oxygen partial pressure as 10-16 atmosphere. When an SiC element .which had been treated at 1200°C. for
10 to 15 hours was employed, the correct pressure of 10 -4 atmosphere was obtained, as was the case when the sensor was employed in a temperature controlled atmosphere with no SiC element. Thus, treatment of the SiC to remove all materials oxidizable at the temperature range involved (around 700°C.) and/or treatment to prevent access of the oxidizeable material to the atmosphere being tested is required.
For added protection of the heating element against oxidation, the pores may be filled with a mixture of fine silicon carbide and sodium silicate, fired to a glassy dry state. Other pore filling material such as fine silicon nitride may also be used as taught in U.S. Patent 4,187,344.
Another type of ceramic heating element would be that described in copending U.S. Patent application S.N. 669,399 filed November 11, 1984, in which structures with controlled electrical characteristics are created with mixtures of aluminum nitride, molybdenum disilicide, and silicon carbide. In accordance with the teachings of that patent specification, silicon nitride or boron nitride may be used as the nitride phase. U.S. Patents 3,890,250; 3,649,310; and 3,875,476 also disclose ceramic heating elements.

Claims

C L A I M S
1. A device for measuring the oxygen partial pressure in gases comprising a solid electrolyte element having an inside and an outside and having one end closed, one side of which is exposed to a reference pressure of oxygen, the other side of which is exposed to the oxygen partial pressure to be measured, a heating element spaced from and surrounding one side of said solid electrolyte so as to form a chamber, said heating element being ceramic, heated by electrical resistance, and including heat radiating surfaces spaced from and concentric with said solid electrolyte element, said heating element being free of oxidizable material.
2. A device as in claim 1, in which the heating element is composed of at least two parts having concave inner radiating surfaces, and having a central concentrated heat zone.
3. A device as in claim 1, in which the heating element is mounted in one end in a non-conducting ceramic base.
4. A device as in claim 1, in which the said ceramic heating element is composed of a material selected from the group consisting of silicon carbide, silicon nitride, molybdenum disilicide and mixtures thereof.
EP19860902248 1985-03-28 1986-03-24 Self heated sensor package. Withdrawn EP0222783A4 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US71705485A 1985-03-28 1985-03-28
US717054 1985-03-28

Publications (2)

Publication Number Publication Date
EP0222783A1 true EP0222783A1 (en) 1987-05-27
EP0222783A4 EP0222783A4 (en) 1988-05-10

Family

ID=24880531

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19860902248 Withdrawn EP0222783A4 (en) 1985-03-28 1986-03-24 Self heated sensor package.

Country Status (5)

Country Link
EP (1) EP0222783A4 (en)
JP (1) JPS62502774A (en)
KR (1) KR880700264A (en)
CA (1) CA1243351A (en)
WO (1) WO1986005882A1 (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3121589B1 (en) 2015-07-22 2018-03-07 Institute of Solid State Physics, University of Latvia Oxygen gas sensor
DE102020101219A1 (en) 2020-01-20 2021-07-22 UMS - Umwelt-, Membran- und Sensortechnik GmbH & Co. KG Improved luminescence based oxygen sensor

Family Cites Families (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3598711A (en) * 1967-11-15 1971-08-10 Bailey Meter Co Electrochemical oxygen analyzer
US3576730A (en) * 1968-04-19 1971-04-27 Gen Electric Nickel/nickel oxide reference electrodes for oxygen partial preddure measurements
US3616413A (en) * 1968-10-08 1971-10-26 Westinghouse Electric Corp Solid electrolyte oxygen sensor
US3597345A (en) * 1968-11-18 1971-08-03 Westinghouse Electric Corp Oxygen detection apparatus
US3767469A (en) * 1971-09-01 1973-10-23 Bailey Meter Co In-situ oxygen detector
US4005001A (en) * 1973-03-27 1977-01-25 Westinghouse Electric Corporation Combustibles sensor
DE2351815C3 (en) * 1973-10-16 1981-11-19 Robert Bosch Gmbh, 7000 Stuttgart Electrochemical measuring sensor for the determination of the oxygen content in exhaust gases, especially in exhaust gases from internal combustion engines
US3875476A (en) * 1974-01-10 1975-04-01 Honeywell Inc Igniter element
US3875477A (en) * 1974-04-23 1975-04-01 Norton Co Silicon carbide resistance igniter
US4098650A (en) * 1976-11-08 1978-07-04 Thermo-Lab Instruments, Inc. Method and analyzer for determining moisture in a mixture of gases containing oxygen
US4327122A (en) * 1980-08-13 1982-04-27 General Motors Corporation Evaporated electrodes for zirconia exhaust gas oxygen sensors
DE3211533A1 (en) * 1981-04-13 1982-12-02 Process Electronic Analyse Und Oxygen-measuring probe
DE3242959C2 (en) * 1981-11-20 1986-02-20 Kabushiki Kaisha Kobe Seiko Sho, Kobe Isostatic hot press device

Also Published As

Publication number Publication date
KR880700264A (en) 1988-02-22
EP0222783A4 (en) 1988-05-10
WO1986005882A1 (en) 1986-10-09
CA1243351A (en) 1988-10-18
JPS62502774A (en) 1987-10-22

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Inventor name: PANZARINO, JOSEPH, N.

Inventor name: WASHBURN, MALCOLM, E.

Inventor name: AGARWAL, ANIL, K.