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
  • G01N27/417—Systems using cells, i.e. more than one cell and probes with solid electrolytes
• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
• • 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

Definitions

• the invention is based on a sensor element for limit current sensors according to the preamble of the main claim.
• the diffusion limit current is measured at a constant voltage applied to the two electrodes of the sensor element. This current is linearly dependent on the oxygen concentration in an exhaust gas produced during combustion processes, as long as the diffusion of the gas to the pump electrode determines the speed of the overall reaction taking place.
• the known limit current sensors are usually used for
• planar polarographic probes can be started from platelet-shaped or foil-shaped oxygen-conducting solid electrolytes, for example. made of stabilized zirconium dioxide, which are coated on both sides with an inner and outer pump electrode with associated conductor tracks.
• the inner pump electrode is advantageously located at the end of a diffusion gap
• sensor elements and detectors which have in common that they each have a pump cell and a sensor cell which consist of platelet-shaped or foil-shaped oxygen-conducting solid electrolytes and two electrodes arranged thereon and have a common diffusion gap or diffusion channel.
• a certain disadvantage of known polarographic probes and sensor elements is that the front part of the inner pump electrode facing the supplied measuring gas is subjected to greater stress than the rear part of the pump electrode facing away from the supplied measuring gas. This leads to a high electrode polarization, which requires a high pump voltage. The latter in turn harbors the risk of electrolyte decomposition in the area of the inner pump electrode.
• Diffusion channel for the measuring gas is arranged, as well as with conductor tracks for the pump electrodes, in the diffusion channel on the side opposite the inner pump electrode to arrange at least one second inner pump electrode which is short-circuited with the first inner pump electrode.
• Laminating films based on stabilized ZrO 2 is that their manufacturing process is relatively complicated and their internal resistance is still relatively.
• the sensor element according to the invention with the characterizing features of the main claim has significant advantages over the known planar sensor elements. So it is with less
• the sensor element according to the invention can be used in place of known sensor elements with a planar structure in limit current sensors of conventional design. Broadband sensors come into question (for ⁇ 1) Lean sensors (for ⁇ > 1).
• the sensor element according to the invention can thus be designed solely as a pump cell, optionally with a heating element, for. B. as a lean sensor for diesel engines, and as such in a conventional sensor housing, for. B.
• the sensor element according to the invention can also have a sensor cell (Nernst cell), which is provided with an additional air reference channel and one of them
• Electrode is arranged in the area of the pump electrode in the diffusion channel of the pump cell and the other electrode is located in the
• Air reference channel is located.
• Figure 1 is a schematic cross section through the electrode part of a first embodiment of a sensor element according to the Invention with rectangular electrodes.
• FIG. 2 shows the layout of a sensor element with that in FIG. 1
• FIG. 3 shows a schematic cross section through the electrode part of a second embodiment of a sensor element according to the invention, in which the electrodes are arranged in a ring around the central measurement gas inlet opening;
• Fig. 4 shows the layout of a sensor element with the electrode part shown in Fig. 3.
• the first embodiment of a sensor element according to the invention shown schematically in FIGS. 1 and 2, consists of the carrier or substrate 1, the diffusion gap 2, the inner pump electrode (cathode) 3 with the associated conductor track 3 '
• Solid electrolyte layer 4 the outer pump electrode (anode) 6 with associated conductor track 6 ', the insulation layer 5, the engobe 8 and the cover 9.
• the sample gas entry occurs at 7.
• the second embodiment of a sensor element according to the invention consists of the carrier or substrate 1, the diffusion gap 2, the inner pump electrode (cathode) 3 arranged in a ring around the central measuring gas inlet opening 7 with the associated conductor track 3 ', the solid electrolyte layer 4, the outer pump electrode (anode) 6 arranged in a ring around the central measurement gas inlet opening 7 with the associated conductor track 6 ', the insulation layer 5, the engobe 8 and the cover 9.
• the carrier or substrate 1 of the sensor elements according to the invention consists of a ceramic material, as is usually used for the production of sensor elements, for example based on ZrO 2 or Al 2 O 3 . It has proven to be advantageous to use films made of unsintered ceramic material with a layer thickness of 0.3 to 2.0 mm, in particular of approximately 1.0 mm, to produce the sensor elements.
• the diffusion gap 2 advantageously has a filling of coarsely porous sintered ceramic
• the porosity of the filling can be created by adding pore formers which burn, decompose or evaporate during the sintering process.
• Typical pore formers that can be used are e.g. B. thermal carbon black, plastics, e.g. B.
• salts e.g. B. ammonium carbonate and organic substances, such as. B. theobromine and indanthrene blue.
• Such pore formers are added to the porous sintering starting material in such an amount that a material with a porosity of z. B. 10 to 50%.
• the middle one is added to the porous sintering starting material in such an amount that a material with a porosity of z. B. 10 to 50%.
• Pore diameter which can be determined by the particle size of the pore former used, is preferably included
• the diffusion gap 2 has a filling that both a Knudsen and a gas phase diffusion take place. This means that in front of the inner pump electrode 3 acts as a diffusion barrier for the sample gas channel system for a
• the pump electrodes 5 and 6 preferably consist of a
• Platinum group metal especially platinum, or alloys of platinum group metals or alloys of platinum group metals with other metals. They may contain a ceramic scaffold material, e.g. B. in the form of a YSZ powder, with a volume fraction of preferably about 40 vol%. They are porous and as thin as possible. They preferably have a thickness of 8 to 15 ⁇ m.
• the conductor tracks belonging to the pump electrodes preferably also consist of platinum or a platinum alloy of the type described. They can also be produced from a paste based on a precious metal cermet. Pastes suitable for printing on the electrodes and conductor tracks can be made in a known manner using organic ones
• Binders and / or adhesion promoters, plasticizers and organic solvents are produced. If at the same time insulating intermediate layers are to be produced, then smaller amounts of compounds with a 5-valent or higher-valent cation can be added to the pastes, e.g. B.
• Nb 2 O 5 Nb 2 O 5 .
• adhesion-improving additives are z. B. Al 2 O 3 or ZrO 2 .
• An advantageous precious metal cermet paste for producing a conductor track can thus consist, for example, of: 85 parts by weight of Pt powder (3 m 2 / g)
• the solid electrolyte layer 4 consists of one of the known oxides of tetravalent metals used for the production of O 2- ion conductive solid electrolyte foils, such as in particular ZrO 2 , CeO 2 , HfO 2 and ThO 2 with a content of divalent alkaline earth oxides and / or preferably trivalent oxides Rare Earth.
• the layer can contain about 50 to 97 mol% of ZrO 2 , CeO 2 , HfO 2 or ThO 2 and 50 to 3 mol% of CaO, MgO or SrO and / or rare earth oxides and especially Y. 2 O 3 exist.
• ZrO 2 , CeO 2 , HfO 2 or ThO 2 with a content of divalent alkaline earth oxides and / or preferably trivalent oxides Rare Earth.
• the layer can contain about 50 to 97 mol% of ZrO 2 , CeO 2 , HfO 2 or ThO 2 and 50 to 3 mol% of Ca
• the thickness of the layer can advantageously be 10-200 ⁇ m, in particular 15 to 50 ⁇ m.
• the pastes used to produce the solid electrolyte layer can also be produced using binders and / or adhesion promoters, plasticizers and organic solvents.
• An advantageous paste for producing the solid electrolyte layer has, for. B. The following composition: 40 g zirconium dioxide and
• the insulation layer 5, which insulates the conductor 6 'of the outer pump electrode 6 from the solid electrolyte layer 4, consists of an insulating layer, for. B. based on Al 2 O 3 , as they are usually produced in the manufacture of planar sensor elements, to isolate conductor tracks from a solid electrolyte.
• the insulation layer 5 can be 15-20 ⁇ m thick, for example.
• Carrier is a carrier based on solid electrolytes, for example a ZrO 2 carrier.
• the arrangement of such insulation layers is not absolutely necessary, ie they can
• the engobe or protective layer 8 is porous and consists, for example, of a layer based on Al 2 O 3 or Mg spinel, as is usually used in planar sensor elements for covering electrodes.
• the porous engobe consists of an Al 2 O 3 and / or Mg spinel matrix with ZrO 2 particles of the type known from DE-OS 37 37 215 embedded therein.
• the cover 9 can be constructed from the same material as the engobe. As a rule, however, a somewhat fine-grained material is used to produce the cover. example
• a film made of zirconium dioxide stabilized with yttrium and having a layer thickness of 0.5 mm was used as the carrier.
• the diffusion gap was introduced in thick-film technology through a screen printing layer made from a mixture of theobromine and coarse-grained ZrO 2 with a grain size of 10 ⁇ m, the theobromine during the later sintering process in the temperature range around 300 ° C., leaving about
• the ZrO 2 solid electrolyte layer was produced by printing on a paste of ZrO 2 stabilized with Y 2 O 3 and having a particle size of ⁇ 1-2 ⁇ m.
• the printed layer had a thickness of 80 vm.
• the pump electrodes, which consist of platinum, were also applied using known screen printing technology, with the outer electrodes being applied to them
• the conductor tracks were produced from a conventional Pt cermet paste from 85 parts by weight of Pt powder and 15 parts by weight of YSZ powder.
• a paste was applied to create the ring-shaped engobe
• the engobe had a thickness of approx.
• the cover was also based on a paste
• the central sample gas inlet opening had a diameter of 0.25 mm.
• the coated carrier was subjected to a sintering process in which it lasted for about 3 hours was heated to a temperature in the range of 1380 ° C.
• the sensor element produced was inserted into a housing of the type known from DF-OS 32 06 903 and used to determine the ⁇ value of gas mixtures. Excellent reproducible results have been obtained.
• the manufacture of a sensor element according to the invention is carried out mechanically in multiple use.
• the width of the probe is advantageously approximately 4 to 6 mm.
• Electrode diameter is advantageously 3 to 4 mm, z. B. 3.6 mm.

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• Chemical & Material Sciences (AREA)
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• Engineering & Computer Science (AREA)
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• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• Measuring Oxygen Concentration In Cells (AREA)

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• 1988
  • 1988-10-14 DE DE3834987A patent/DE3834987A1/de active Granted
• 1989
  • 1989-10-03 AU AU43284/89A patent/AU4328489A/en not_active Abandoned
  • 1989-10-03 KR KR1019900701256A patent/KR900702364A/ko not_active Application Discontinuation
  • 1989-10-03 WO PCT/DE1989/000625 patent/WO1990004171A1/de unknown
  • 1989-10-13 ES ES8903458A patent/ES2016207A6/es not_active Expired - Lifetime

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