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
  • G01N27/4073—Composition or fabrication of the solid electrolyte
  • G01N27/4074—Composition or fabrication of the solid electrolyte for detection of gases other than oxygen
• • 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

Definitions

• the invention is based on a sensor for determining the concentration of oxidizable constituents in a gas mixture, in particular for determining one or more of the gases NOx, CO, H2 and preferably unsaturated hydrocarbons according to the type of the main claim.
• a sensor for determining the concentration of oxidizable constituents in a gas mixture in particular for determining one or more of the gases NOx, CO, H2 and preferably unsaturated hydrocarbons according to the type of the main claim.
• increased concentrations of oxidizable constituents, in particular NOx, CO, H2 and hydrocarbons can occur, for example, as a result of a component malfunction, such as an injection valve, or as a result of incomplete combustion.
• a component malfunction such as an injection valve
• JP-OS 60-61654 describes a method for determining oxidizable gases, according to which a stoichiometric reaction with oxygen takes place on a first measuring electrode made of platinum metals and on one or more further metallic measuring electrodes with reduced catalytic activity for the oxygen equilibrium reaction quasi-equilibrium states can be set.
• the Nernst voltages E1 and E2 are measured between the measuring electrodes and a reference electrode which is exposed to a reference gas with a constant oxygen partial pressure, and from it Difference calculated on the basis of calibration curves, the concentration of the gas components.
• the sensor according to the invention with the features of the main claim, on the other hand, enables increased miniaturization, design simplification and more cost-effective production.
• the molecules of the measuring gas can therefore diffuse through the pores of the solid electrolyte to the reference electrode, where the thermodynamic equilibrium is established.
• the reference electrode is therefore exposed to an oxygen partial pressure which corresponds to the thermodynamic equilibrium. It is therefore possible to dispense with the supply of a reference gas, which considerably simplifies the construction of the probe.
• Solid electrolyte material A particular advantage is that the gases that disturb the reference signal can be oxidized in a targeted manner, which simplifies signal evaluation or even makes it possible in the first place.
• the measuring electrodes can expediently also be porous, which further improves the diffusion of the molecules of the measuring gas to the reference electrode.
• the electrode adhesion and thus the life of the sensor is improved. It is also particularly advantageous to build up the measuring electrodes from semiconductors, as a result of which the selectivity towards individual gas components to be detected can be significantly increased.
• Figure 1 shows a section through a sensor according to the invention.
• An insulating planar ceramic substrate 6 carries a reference electrode 3 made of preferably platinum, a porous solid electrolyte 5, measuring electrodes 1 and 2 and a gas-permeable protective layer 4 on one large surface in layers one above the other, and a heater device 7 with cover 8 is applied to the opposite large surface of the substrate .
• the heater device 7 For determining the concentration of oxidizable constituents in exhaust gases of the sensor by means of the heater device 7 is heated to a temperature between 300 and 1000 C ⁇ , ⁇ advantageously heated to 600 C.
• the measuring gas diffuses through the porous solid electrolyte to the reference electrode 3, which catalyzes the setting of the oxygen equilibrium potential.
• the measuring electrodes 1, 2, on the other hand, are constructed so that they have a reduced catalytic activity for the oxygen equilibrium reaction.
• the sensor generates a cell voltage across the oxygen ion-conducting solid electrolyte by means of a first half-cell reaction set with the aid of the reference electrode and a second half-cell reaction on at least one measuring electrode influenced by the oxidizable gas components to be determined.
• the concentrations of the gas components are determined from the voltage values using calibration curves.
• the senor according to the invention can therefore be used with a reference electrode which catalyzes the equilibrium setting of the gas mixture and a measuring electrode which is not or only slightly able to catalyze the equilibrium setting of the gas mixture.
• measuring electrodes as shown in FIG. 1, or also several measuring electrodes, each with different catalytic activity, for establishing oxygen equilibrium states.
• the measuring electrodes then react with different voltages depending on the type of gas, based on the reference electrode.
• Arrangements with at least two measuring electrodes also make it possible to determine the cross sensitivity of one to completely or at least partially compensate for the first measuring electrode by the signal of a further measuring electrode, by adjusting the sensitivity of this further measuring electrode to the interfering gas components accordingly.
• the solid electrolyte is formed, e.g. by adding 0.01 to 10% by volume of platinum powder so that the solid electrolyte converts the gases to be measured catalytically, so that only the gases corresponding to the thermodynamic equilibrium arrive at the reference electrode or that the solid electrolyte only converts the gases which disturb the reference signal .
• one or more measuring electrodes are made porous in addition to the Fe electrolyte, which facilitates gas diffusion to the reference electrode.
• metallic electrode materials such as those e.g. are described in JP-OS 60-61654, or semiconductors which have a high specific sensitivity for certain oxidizable gases.
• Semiconducting oxides or mixed oxides which can be doped with acceptor and / or donor, are particularly suitable.
• the high sensitivity of e.g. Acceptor- and donor-doped n-type titanium dioxide for unsaturated hydrocarbons in particular is caused by the adsorptive interaction of the orbitals of the Pi bonds of the unsaturated hydrocarbons with the acceptor sites on the semiconductor surface.
• niobium and 3% of one of the transition metals nickel, copper or iron-doped rutile is printed as a 30 ⁇ m thick screen printing layer on a substrate which carries a reference electrode made of platinum, for example, and a solid electrolyte layer above it.
• a heater device is applied to the opposite side of the substrate.
• the sensor is sintered at 1200 ⁇ C for 90 minutes with a heating / cooling ramp of 300 ° C / hour. After sintering, the solid electrolyte has pores in the size range from 10 nm to 100 ⁇ m.
• the voltage across the ⁇ o cell is measured at a resistance of 1 MOhm between the reference and rutile electrodes.
• the sensor is heated to 600 ⁇ C with its heater.
• Simulated exhaust gas with 10% oxygen, 5% water and 5% carbon dioxide and 30 ppm sulfur dioxide is used as the measurement gas.
• Oxidizable gases are mixed in the amounts given in the table.
• Rutile electrode comparison electrode with 7% Nb and 3% Ni Cu Fe 20% Au and 80% Pt oxidizable gases (ppm)
• the table shows that a rutile semiconductor electrode with 7% niobium as donor and 3% nickel as acceptor shows the greatest selectivity for propene as the leading substance.
• the gold-platinum system known according to the prior art shows a particularly high cross-sensitivity to water.

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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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Publications (1)

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Cited By (3)

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Citations (5)

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• 1996
  • 1996-06-11 DE DE19623212A patent/DE19623212A1/de not_active Withdrawn
• 1997
  • 1997-03-03 WO PCT/DE1997/000380 patent/WO1997047962A1/de not_active Ceased
  • 1997-03-03 KR KR1019980710088A patent/KR20000016502A/ko not_active Ceased
  • 1997-03-03 EP EP97914159A patent/EP0904533B1/de not_active Expired - Lifetime
  • 1997-03-03 JP JP50103298A patent/JP3933697B2/ja not_active Expired - Fee Related
  • 1997-03-03 DE DE59710230T patent/DE59710230D1/de not_active Expired - Lifetime
  • 1997-03-03 CN CN97195441A patent/CN1221490A/zh active Pending
  • 1997-03-03 US US09/202,313 patent/US6174421B1/en not_active Expired - Fee Related

Patent Citations (5)

Non-Patent Citations (1)

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