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
  • G01N27/403—Cells and electrode assemblies
  • G01N27/406—Cells and probes with solid electrolytes
  • G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
• • 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
  • G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
  • G01N27/4071—Cells and probes with solid electrolytes for investigating or analysing gases using sensor elements of laminated structure
  • G01N27/4072—Cells and probes with solid electrolytes for investigating or analysing gases using sensor elements of laminated structure characterized by the diffusion barrier
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0011—Sample conditioning
  • G01N33/0013—Sample conditioning by a chemical reaction

Definitions

• the invention relates to a sensor element of a gas sensor with a means for pre-catalysis for determining gas components in gas mixtures according to the preamble of claim 1.
• Amperometric gas sensors for determining the concentration of gas components in the exhaust gases of internal combustion engines are usually operated according to the so-called limit current principle.
• a limit current situation is only reached if the electrochemical pump cells in the gas sensor are able to pump out the entire content of the gas to be determined (for example oxygen) present in the measuring gas from the measuring gas space of the gas sensor.
• the gas to be determined for example oxygen
• oxygen-evacuating gas sensor this must also be ensured with an atmospheric oxygen content of approximately 20% by volume.
• a diffusion barrier is integrated between the gas outlet opening of the sensor element and the measuring gas space which contains the electrochemical pump cell.
• a gas sensor is described in the patent specification DE 37 28 289 Cl, which contains a diffusion barrier with a platinum content of up to 90% by weight.
• the main disadvantage of this is the large amount of platinum required for this, which has a negative effect on the production costs of the gas sensor.
• the gas sensor according to the invention with the characterizing features of claim 1 has the advantage; that gas constituents of a gas mixture can be determined very precisely even with combustion mixtures set to be rich, despite the associated lack of oxygen.
• a coarse-pored, catalytically active area upstream of the diffusion barrier is created in that a protective layer formed over the electrodes arranged on the large area of the sensor element additionally also covers the gas outlet opening.
• FIG. 1 shows a cross section through the large area of the sensor element according to the invention in accordance with a first exemplary embodiment
• FIG. 2 shows a cross section through the large area of the sensor element in accordance with a second exemplary embodiment
• FIG. 3 shows a cross section through the large area of the sensor element in accordance with a further exemplary embodiment.
• FIG. 1 shows the basic structure of a first embodiment of the present invention.
• 10 designates a planar sensor element of an electrochemical gas sensor, which has, for example, a plurality of oxygen ion-conducting solid electrolyte layers 11a, 11b, 11c, lld, lle and llf.
• the solid electrolyte layers 11a-11f are designed as ceramic foils and form a planar ceramic body.
• the integrated shape of the planar ceramic body of the sensor element 10 is produced by laminating together the ceramic films printed with functional layers and then sintering the laminated structure in a manner known per se.
• Each of the solid electrolyte layers 11a-11f is made of solid ion material which conducts oxygen ions, such as, for example, Y 2 O 3 partially or fully stabilized ZrO 2 .
• the sensor element 10 contains a measurement gas space 13 and, for example, in a further layer plane 11 an air reference channel 15, which at one end leads out of the planar body of the sensor element 10 and is connected to the air atmosphere.
• an outer pump electrode 20 is arranged on the solid electrolyte layer 11a, which can be covered with a porous protective layer (not shown) and which is arranged in a ring shape around a gas inlet opening 17.
• the associated inner pump electrode 22 On the side of the solid electrolyte layer 11a facing the measuring gas space 13 there is the associated inner pump electrode 22, which is also designed in a circular shape adapted to the circular geometry of the measuring gas space 13. Both pump electrodes 20, 22 together form a pump cell.
• a measuring electrode 21 is located in the measuring gas space 13 opposite the inner pump electrode 22. This is also designed, for example, in the form of a ring.
• An associated reference electrode 23 is arranged in the reference gas channel 15. Measuring and reference electrodes 21, 23 together form a Nernst or concentration cell.
• all electrodes used contain a catalytically active material, such as platinum, the electrode material being used as a cermet for all electrodes in a manner known per se in order to interact with the ceramic Sintering foils.
• a resistance heater 39 is also embedded in the ceramic base body of the sensor element 10 between two electrical insulation layers. The resistance heater is used to heat the sensor element 10 to the necessary operating temperature.
• a porous diffusion barrier 12 is arranged upstream of the measuring gas chamber 13 in the diffusion direction of the measuring gas of the inner pump electrode 22 and the measuring electrode 21.
• the porous diffusion barrier 12 forms a diffusion resistance with respect to the gas diffusing to the electrodes 21, 22.
• a basic prerequisite for the functional humidity of an amperometric gas sensor is that the electrochemical pump cell of the sensor element is always able to remove the entire oxygen content from the measuring gas space 13 even at high oxygen concentrations.
• the maximally occurring oxygen content is the atmospheric with approx. 20 vol. %.
• a diffusion barrier 12 is connected upstream of the measuring gas space 13 and thus also the inner pump electrode 22, which leads to a reduction in the oxygen content in the measuring gas space 13 by gas phase diffusion.
• the other gas components occurring in the exhaust gas are also subject to diffusion and the composition of the gas atmosphere present in the measuring gas space 13 is dependent on the diffusion rate of the individual gas components. Especially with a rich exhaust gas, this leads to a strong accumulation of hydrogen in the measurement gas space 13 and thus to a falsified measurement value of the gas sensor.
• the hydrogen content in the exhaust gas can be reduced if it is on a catalytically active one
• the diffusion barrier 12 has a coarsely porous, catalytically active area 14. This is in front of the diffusion barrier 12 in the direction of flow of the gas mixture.
• the porosity is selected so that only an insignificant diffusion resistance is opposed to the penetrating gas mixture; however, the layer thickness should not be less than a certain minimum in order to allow the gas mixture to come into intensive contact with the catalytically active surface of the coarse-pored area.
• the coarse porous catalytically active region 14 contains metals such as Pt, Ru, Rh, Pd, Ir or a mixture thereof as catalytically active components.
• the catalytically active components can either be added as a powder to a printing paste, from which the coarse porous catalytically active area 14 is produced by means of a printing process, or the catalytic activation takes place by impregnating the already sintered coarse porous catalytically active area with a metal salt solution and a subsequent heat treatment in a manner known per se.
• FIG. 2 shows a second embodiment of the sensor element according to the invention, FIG. 2 showing a section of the sensor element shown in FIG. 1.
• the coarse-porous, catalytically active region 14a at least partially encompasses the space upstream of the diffusion barrier 12, but, as shown in FIG. 2, it can also occupy the entire region between the diffusion barrier 12 and the gas inlet opening 17.
• the lengthened path of the penetrating gases within the coarse porous catalytically active region 14a ensures a catalytic equilibrium between the gas components. This is particularly important because, for example, the equilibrium of the water gas equilibrium is slow under the conditions prevailing in the exhaust gas.
• FIG. 3 shows a further embodiment of the sensor element according to the invention, FIG. 3 likewise showing a section of the sensor element shown in FIG. 1.
• the outer pump electrode 20 arranged on the large surface of the sensor element has a coarse-pored protective layer
• the protective layer 16 covered, which the electrode before the entry of solid contaminants conditions, such as soot particles, protects. If the protective layer 16 is provided with catalytically active components and additionally applied over the gas inlet opening 17, the area of the protective layer 16 covering the gas inlet opening 17 serves as a coarse porous area of the diffusion barrier 12. This arrangement is characterized by simple manufacture, since no additional process step is necessary is.
• one or more substances are added to the coarse porous catalytically active region 14, 14a, 16, which remove sulfur oxides from the penetrating exhaust gas.
• This can be barium nitrate, for example.
• a catalytically active and coarse porous area of a diffusion barrier for pre-catalysis in exhaust gas sensors is not limited to the exemplary embodiments listed, but also in multi-chamber sensors, in sensors with several pump and concentration cells or sensors with gas inlet openings arranged on the end face can be used.
• a coarse-porous catalytically active layer 14, 14a, 16 can also be subordinated to the fine-porous region of the diffusion barrier 12.

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• 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)

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• 2000
  • 2000-03-21 DE DE10013882A patent/DE10013882A1/de not_active Ceased
• 2001
  • 2001-03-15 EP EP01921199A patent/EP1277047A1/de not_active Withdrawn
  • 2001-03-15 WO PCT/DE2001/000985 patent/WO2001071333A1/de not_active Application Discontinuation
  • 2001-03-15 KR KR1020027011669A patent/KR20020086611A/ko not_active Application Discontinuation
  • 2001-03-15 JP JP2001569269A patent/JP2003528314A/ja active Pending
  • 2001-03-15 US US10/239,121 patent/US20030154764A1/en not_active Abandoned

Non-Patent Citations (1)

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