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

Definitions

• the invention relates to an electrochemical gas sensor for determining the concentration of oxidizable gas components in gas mixtures according to the preamble of claim 1.
• An electrochemical gas sensor is known from DE-OS 23 04 464, in which an electrode made of gold or silver which does not catalyze the equilibrium of the gas mixture is provided and which interacts with an electrode made of platinum which catalyzes the equilibrium of the measurement gas.
• the catalytically inactive electrode material alien cause a competitive reaction to take place at the electrode between the oxygen and the oxidizable or reducible gas components.
• the free oxygen entrained in the measuring gas for example C3H6 or CO
• such a gas sensor has a considerable cross-sensitivity to the oxygen also present in the gas mixture.
• the gas sensor according to the invention with the characterizing features of claim 1 has the advantage that the cross sensitivity to oxygen can be reduced by pumping in oxygen. Another advantage is that a basic sensor element that is sophisticated in terms of production technology can be used, which only has to be changed by modifying the electrodes.
• a so-called broadband sensor for determining the oxygen concentration which consists of a pump cell and a concentration cell (measuring cell), serves as the base sensor element, a mixed potential sensor with an upstream oxygen pump cell being formed.
• the use of the basic sensor element which is technically mature, offers considerable cost advantages compared to a sensor element structure that is specialized for each application.
• FIG. 1 An embodiment of the invention is shown in the drawing and explained in more detail in the following description.
• the figure shows a cross section through a sensor element of a gas sensor according to the invention.
• the figure shows a planar sensor element 10 of an electrochemical gas sensor, which for example has a plurality of oxygen ion conductors
• Solid electrolyte carrier layers 11a, 11b, 11c and lld are designed as ceramic foils and form a planar ceramic body after sintering.
• the integrated form of the planar ceramic body 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 carrier layers 11a to 11d is made of solid electrolyte material which conducts oxygen ions, such as ZrO 2 stabilized with Y 2 O 3 .
• the sensor element 10 has an electrochemical pump cell
• the resistance heater 14 is between the
• Solid electrolyte carrier layers 11c and 11d are arranged and embedded in an electrical insulation 15 made, for example, of A1 2 0 3 .
• the resistance element 14 heats the sensor element 10 to the corresponding operating temperature of 500 ° C., for example.
• the pump cell 12 has an outer pump electrode 16 and an inner pump electrode 17.
• the measuring cell 13 is designed with a measuring electrode 18 and a reference electrode 19.
• the outer pump electrode 16 is covered with a porous protective layer 21 and exposed to the measurement gas.
• the inner pump electrode 17 of the pump cell 12 and the measuring electrode 18 of the measuring cell 13 are located opposite one another in a measuring gas chamber 22 which is connected to a Gas access hole 23 communicates with the sample gas.
• the reference electrode 19 is located in a reference gas channel which is connected to a reference gas, for example air.
• a porous diffusion barrier 25 is arranged in front of the inner pump electrode 17 and the measuring electrode 18 within the measuring gas space 22.
• the porous diffusion barrier 25 forms a diffusion resistance with respect to the gas diffusing to the electrodes 17, 18.
• the described construction of the sensor element 10 corresponds to a so-called broadband sensor for determining the lambda value in gas mixtures from ⁇ ⁇ 1 to ⁇ > 1.
• all electrodes are made of a material that catalyzes the equilibrium adjustment of the gas mixture, for example platinum or a platinum cermet - Material executed.
• At least the measuring electrode 18 arranged in the measuring gas space 22 is made of a material that the oxidizable gases, such as HC, H 2 , CO and NH 3 , in contrast to the said broadband sensor, at least the measuring electrode 18 arranged in the measuring gas space 22 is made of a material that the oxidizable gases, such as HC, H 2 , CO and NH 3 , in contrast to the said broadband sensor, at least the measuring electrode 18 arranged in the measuring gas space 22 is made of a material that the
• Equilibrium adjustment of the gas mixture is not or not fully catalyzed.
• a material is, for example, gold or a gold-platinum alloy, the gold content in the platinum / gold alloy being 0.5 to 20% by weight, preferably 10% by weight.
• These materials ensure that the measuring electrodes 18 arranged in the measuring gas chamber 22 are selective with respect to the oxidizable gas components contained in the gas mixture.
• the further inner pump electrode 17 arranged in the measuring gas chamber 22 also from a material which is unable or not completely able to catalyze the equilibrium setting of the gas mixture.
• the inner pump electrode 17 contains a platinum / gold alloy with a gold content of 0.1 to 3% by weight, preferably 0.3 to 0.8% by weight.
• the materials are co-sinterable, i.e. that they are the one for sintering the
• Solid electrolyte carrier layers 11a to 11d withstand the required sintering temperatures of, for example, 1400 ° C.
• these are made of a cermet material, like the electrodes 16, 19.
• cermet electrodes contain a ceramic component which advantageously corresponds to the material of the adjacent solid electrolyte carrier layers 11a to 11d.
• a pump voltage is applied to the pump electrodes 16, 17, which, depending on the oxygen partial pressure in the sample gas, is polarized such that oxygen is pumped out of the sample gas chamber 22 at high oxygen partial pressure in the exhaust gas and oxygen is pumped into the sample gas chamber 22 at low oxygen partial pressure in the sample gas becomes.
• a corresponding circuit arrangement is provided, which also ensures that an essentially constant oxygen partial pressure is maintained in the measuring gas chamber 22.
• the measuring electrode 18 is a so-called mixed potential electrode, which catalyzes no or at least no complete equilibrium adjustment of the gas mixture.
• the measuring electrode 18 forms a so-called mixed potential sensor, which is used in particular for determining hydrocarbons.
• the material of the measuring electrode 18 which does not catalyze or does not completely catalyze the equilibrium of the gas mixture has the effect that on the measuring electrode 18 between the oxygen contained in the gas mixture and the reduced oxygen
• the reference air 19 has a constant high level with the reference air
• the adsorbed hydrocarbons react at the measuring electrode 18 and a potential difference is formed between the measuring electrode 18 and the Reference electrode 19, which can be tapped as an EMF from a measuring instrument, not shown.
• the EMF is therefore dependent on the concentration of the hydrocarbons contained in the gas mixture. With a high concentration of hydrocarbons there is a high one

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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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• 1999
  • 1999-03-18 DE DE19912100A patent/DE19912100B4/de not_active Expired - Fee Related
• 2000
  • 2000-03-10 DE DE50005079T patent/DE50005079D1/de not_active Expired - Lifetime
  • 2000-03-10 WO PCT/DE2000/000754 patent/WO2000057168A1/de not_active Ceased
  • 2000-03-10 JP JP2000606993A patent/JP2002540399A/ja not_active Ceased
  • 2000-03-10 US US09/936,847 patent/US6890422B1/en not_active Expired - Lifetime
  • 2000-03-10 EP EP00916810A patent/EP1163511B1/de not_active Expired - Lifetime

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