EP0843813A1 - Sensor for determining the concentration of oxidisable elements in a gas compound - Google Patents

Sensor for determining the concentration of oxidisable elements in a gas compound

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Publication number
EP0843813A1
EP0843813A1 EP97923831A EP97923831A EP0843813A1 EP 0843813 A1 EP0843813 A1 EP 0843813A1 EP 97923831 A EP97923831 A EP 97923831A EP 97923831 A EP97923831 A EP 97923831A EP 0843813 A1 EP0843813 A1 EP 0843813A1
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Prior art keywords
sensor according
semiconductor
measuring
acceptor
donor
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EP97923831A
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German (de)
French (fr)
Inventor
Bernd Schumann
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Robert Bosch GmbH
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Robert Bosch GmbH
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    • 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
    • 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

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.
  • Exhaust gases from gasoline and diesel engines, internal combustion engines and combustion systems can cause increased concentrations of oxidizable constituents, in particular NOx, CO, H2 and hydrocarbons, for example as a result of a component malfunction, such as an injection valve, or as a result of incomplete combustion. To optimize the combustion reactions, it is therefore necessary to know the concentration of these exhaust gas components.
  • JP-OS 60-61654 describes a method for determining oxidizable gases, according to which an ⁇ tochiometric 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. There are the Nernst voltages El and E2 between the measuring electrodes and a reference electrode measured, which is exposed to a reference gas with constant oxygen partial pressure, and from their difference based on calibration curves, the concentration of the gas components is calculated.
  • the senor according to the invention with the features of the main claim has improved analytical performance features, in particular a higher sensitivity and selectivity with respect to individual sample gas components to be determined.
  • Sensitivity and selectivity of the measuring electrodes are improved by doping the in particular oxidic or mixed-oxide semiconductors with acceptors and / or donors.
  • the conductivity of the measuring electrodes is improved by adding donors, especially in higher concentrations compared to the acceptors.
  • Particularly powerful electrodes are obtained if the acceptor is selected from the range of transition metals and / or rare earths and / or the donor is one or both of the elements tantalum and niobium.
  • An increased miniaturization, a simplification of construction and a less expensive production are achieved by sintering the solid electrolyte porous.
  • the thermodynamic equilibrium can advantageously also be set in the solid electrolyte by selecting a catalytically active 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 also be porous, which further improves the diffusion of the molecules of the measuring gas to the reference electrode. By adding additives to the solid electrolyte in the areas adjacent to the electrodes which correspond to the electrode materials, the electrode adhesion and thus the life of the sensor is improved.
  • Figure 1 shows a section through a sensor according to the invention.
  • a sensor according to the invention is shown in section in FIG.
  • An electrically insulating planar ceramic substrate 6 carries a reference electrode 3 made of, for example, platinum, a solid electrolyte 5, on one large surface in layers one above the other.
  • a heater device 7 with a cover ⁇ is applied to the opposite large surface of the substrate.
  • the solid electrolyte can be sintered porously, but the person skilled in the art can also choose other solutions known to him, such as via a reference channel or a reference gas atmosphere.
  • the sensor generates a cell voltage above 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 calibration values are used to determine the concentrations of the gas components from the voltage values.
  • the sensor according to the invention is thus in the simplest case with a reference electrode which
  • measuring electrodes as shown in FIG. 1, or also several measuring electrodes, each with different catalytic activity, for setting oxygen Equilibrium states.
  • the measuring electrodes then react with different voltages depending on the type of gas, based on the reference electrode.
  • the solid electrolyte is formed, e.g. by adding 0.01 to 10% by volume of platinum 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 solid electrolyte, thereby facilitating gas diffusion to the reference electrode.
  • Semiconductors which have a high specific sensitivity for certain oxidizable gases are used as measuring electrode materials.
  • Oxides or mixed oxides, in particular based on rutile or dirutile or mixtures thereof, which can be doped with acceptor and / or donor are particularly suitable. Titanium and / or zirconium dioxide are advantageously used.
  • Suitable donors are in particular tantalum and niobium, preferably elements with higher valence than the metals forming the semiconductor; suitable acceptors are transition metals, in particular nickel, copper, cobalt and / or chromium, preferably nickel, copper and / or cobalt, and rare earths.
  • the acceptor can be contained in the semiconductor as a solid solution or as a segregated component.
  • the concentrations of the acceptors and donors are each in the range from 0.01 to 25%; at lower proportions, there is no improvement in the properties of the measuring electrodes, and at higher proportions grid defects occur.
  • the high sensitivity of e.g. Acceptor and donor-doped 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 electrophilic acceptor sites on the semiconductor surface.
  • the following example describes a production method for a sensor according to the invention: Rutile doped with 7% niobium and 3% of one of the transition metals nickel, copper or iron is printed as a 30 ⁇ m thick screen printing layer on a substrate which has a reference electrode, for example made of platinum, and above it Solid electrolyte layer carries. 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.
  • the solid electrolyte After sintering, the solid electrolyte has pores in the size range from 10 nm to 100 ⁇ m. With the aid of a platinum conductor track insulated from the solid electrolyte and which only contacts the measuring electrode, the voltage across the cell thus constructed is measured at a resistance of 1 MOhm between the reference and the rutile electrode. 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.
  • the last line of the table below shows the voltage values for a mixed potential electrode made of 20% gold and 80% platinum, which represents a measuring electrode according to the prior art.

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  • Chemical Kinetics & Catalysis (AREA)
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Abstract

The invention concerns a sensor for determining the concentration of oxidisable elements in a gas compound, in particular for determining one or more of the gases, NOx, CO, H2 and especially unsaturated hydrocarbons, by measuring the tension between a measuring electrode (1, 2) and a reference electrode (3) or by measuring the tension between two measuring electrodes [(1) and (2)]. Selectivity of response for individual components of the measured gases can be improved by using specific material for the measuring electrodes, in particular semiconductors. By using porous fixed electrolytes, a reference gas atmosphere can be avoided and, therefore, increased miniaturisation and constructive simplification can be achieved.

Description

Sensor zur Bestimmung der Konzentration oxidierbarer Bestandteile in einem GasgemischSensor for determining the concentration of oxidizable components in a gas mixture
Stand der TechnikState of the art
Die Erfindung geht aus von einem Sensor zur Bestimmung der Konzentration oxidierbarer Bestandteile in einem Gasgemisch, insbesondere zur Bestimmung eines oder mehrerer der Gase NOx, CO, H2 und vorzugsweise ungesättigte Kohlenwasserstoffe nach der Gattung des Hauptanspruches. In Abgasen von Otto- und Dieselmotoren, von Verbrennungsmaschinen und Verbrennungsanlagen können erhöhte Konzentrationen oxidierbarer Bestandteile, insbesondere von NOx, CO, H2 und Kohlenwasserstoffe auftreten z.B. als Folge einer Komponentenfehlfunktion, wie eines Einspntzventils, oder als Folge einer unvollständigen Verbrennung. Zur Optimierung der Verbrennungsreaktionen ist es daher notwendig, die Konzentration dieser Abgasbestandteile zu kennen. In der JP-OS 60-61654 ist eine Methode zur Bestimmung oxidierbarer Gase beschrieben, wonach an einer ersten Meßelektrode aus Platinmetallen eine εtochiometrische Umsetzung mit Sauerstoff erfolgt und an einer oder mehreren weiteren metallischen Meßelektroden mit reduzierter katalytischer Aktivität für die Sauerstoff- Gleichgewichtsreaktion Quasi- Gleichgewichtszustände eingestellt werden. Es werden die Nernst- Spannungen El und E2 zwischen den Meßelektroden und einer Referenzelektrode gemessen, die einem Referenzgas mit konstantem Sauerstoffpartialdruck ausgesetzt ist, und aus ihrer Differenz aufgrund von Kalibrierungskurven die Konzentration der Gaskomponenten berechnet.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. Exhaust gases from gasoline and diesel engines, internal combustion engines and combustion systems can cause increased concentrations of oxidizable constituents, in particular NOx, CO, H2 and hydrocarbons, for example as a result of a component malfunction, such as an injection valve, or as a result of incomplete combustion. To optimize the combustion reactions, it is therefore necessary to know the concentration of these exhaust gas components. JP-OS 60-61654 describes a method for determining oxidizable gases, according to which an εtochiometric 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. There are the Nernst voltages El and E2 between the measuring electrodes and a reference electrode measured, which is exposed to a reference gas with constant oxygen partial pressure, and from their difference based on calibration curves, the concentration of the gas components is calculated.
Vorteile der ErfindungAdvantages of the invention
Der erfmdungsgemaße Sensor mit den Merkmalen des Hauptanspruches hat demgegenüber verbesserte analytische Leistungsmerkmale, insbesondere eine höhere Empfindlichkeit und Selektivität gegenüber einzelnen zu bestimmenden Meßgaskomponenten.In contrast, the sensor according to the invention with the features of the main claim has improved analytical performance features, in particular a higher sensitivity and selectivity with respect to individual sample gas components to be determined.
Durch die in den Unteranspruchen aufgeführten Maßnahmen sind vorteilhafte Weiterbildungen und Verbesserungen des im Hauptanspruch angegebenen Sensors möglich. Empfindlichkeit und Selektivität der Meßelektroden werden durch Dotieren der insbesondere oxidischen oder mischoxidischen Halbleiter mit Akzeptoren und/oder Donatoren verbessert.Advantageous further developments and improvements of the sensor specified in the main claim are possible through the measures listed in the subclaims. Sensitivity and selectivity of the measuring electrodes are improved by doping the in particular oxidic or mixed-oxide semiconductors with acceptors and / or donors.
Durch Zugabe von Donatoren, insbesondere in höheren Konzentrationen gegenüber den Akzeptoren, wird die Leitfähigkeit der Meßelektroden verbessert. Besonders leistungsfähige Elektroden werden erhalten, wenn der Akzeptor aus der Reihe der Übergangsmetalle und/oder Seltenen Erden ausgewählt wird und/oder der Donator eines oder beide der Elemente Tantal und Niob ist. Eine erhöhte Miniaturisierung, eine konstruktive Vereinfachung und eine kostengünstigere Herstellung werden erreicht, indem der Festelektrolyt porös gesintert wird. Dadurch kann auf die Zuführung eines Referenzgases verzichtet werden, was den Sondenaufbau erheblich vereinfacht. Die Einstellung des thermodynamischen Gleichgewichtes kann in vorteilhafter Weise auch bereits im Feεtelektrolyten durch die Auswahl eines katalytisch wirksamen Festelektrolytmaterials erfolgen. Als besonderer Vorteil ist dabei anzusehen, daß dadurch gezielt die das Referenzsignal störenden Gase oxidiert werden können, was die Signalauswertung vereinfacht oder überhaupt erst ermöglicht.The conductivity of the measuring electrodes is improved by adding donors, especially in higher concentrations compared to the acceptors. Particularly powerful electrodes are obtained if the acceptor is selected from the range of transition metals and / or rare earths and / or the donor is one or both of the elements tantalum and niobium. An increased miniaturization, a simplification of construction and a less expensive production are achieved by sintering the solid electrolyte porous. As a result, the supply of a reference gas can be dispensed with, which considerably simplifies the construction of the probe. The thermodynamic equilibrium can advantageously also be set in the solid electrolyte by selecting a catalytically active 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.
In zweckmäßiger Weise können zusätzlich zumAdvantageously, in addition to
Festelektrolyten auch die Meßelektroden porös sein, wodurch die Diffusion der Moleküle des Meßgases zur Referenzelektrode weiter verbessert wird. Indem dem Festelektrolyten in den den Elektroden angrenzenden Bereichen Zusätze beigemischt werden, die den Elektrodenstoffen entsprechen, wird die Elektrodenhaftung und somit die Lebensdauer des Sensors verbessert.Solid electrolytes, the measuring electrodes can also be porous, which further improves the diffusion of the molecules of the measuring gas to the reference electrode. By adding additives to the solid electrolyte in the areas adjacent to the electrodes which correspond to the electrode materials, the electrode adhesion and thus the life of the sensor is improved.
Zeichnungdrawing
Die Erfindung wird im folgenden anhand einer Zeichnung und einem Ausfuhrungsbeispiel näher beschrieben. Figur 1 zeigt einen Schnitt durch einen erfindungsgemäßen Sensor.The invention is described below with reference to a drawing and an exemplary embodiment. Figure 1 shows a section through a sensor according to the invention.
Beschreibung der AusführungsbeispieleDescription of the embodiments
In Figur 1 ist ein erfindungsgemäßer Sensor im Schnitt dargestellt. Ein elektrisch isolierendes planares keramisches Substrat 6 trägt auf der einen Großfläche in übereinanderliegenden Schichten eine Referenzelektrode 3 aus beispielsweise Platin, einen Festelektrolyten 5, Meßelektroden 1 und 2 sowie eine gasdurchlässige Schutzschicht 4. Auf der gegenüberliegenden Großfläche des Substrats ist eine Heizervorrichtung 7 mit Abdeckung δ aufgebracht.A sensor according to the invention is shown in section in FIG. An electrically insulating planar ceramic substrate 6 carries a reference electrode 3 made of, for example, platinum, a solid electrolyte 5, on one large surface in layers one above the other. Measuring electrodes 1 and 2 and a gas-permeable protective layer 4. A heater device 7 with a cover δ is applied to the opposite large surface of the substrate.
Zur Bestimmung der Konzentration oxidierbarer Bestandteile in Abgasen wird der Sensor mittels der Heizervorrichtung 7 auf eine Temperatur zwischen 300 und 1000 "C, vorteilhafterweise auf 600 βC erhitzt.For determining the concentration of oxidizable constituents in exhaust gases of the sensor by means of the heater device 7 to a temperature between 300 and 1000 "C is advantageously heated to 600 C β.
Um die Diffusion des Meßgases zur Referenzelektrode und die Einstellung des Sauerstoff- Gleichgewichtpotentials zu ermöglichen, kann der Festelektrolyt porös gesintert sein, der Fachmann kann aber auch andere, ihm bekannte Lösungen wählen, wie z.B. über einen Referenzkanal oder eine Referenzgasatmoεphäre.In order to allow the measurement gas to diffuse to the reference electrode and to set the oxygen equilibrium potential, the solid electrolyte can be sintered porously, but the person skilled in the art can also choose other solutions known to him, such as via a reference channel or a reference gas atmosphere.
Der Sensor erzeugt über dem Sauerstoffionenleitenden Festelektrolyten eine Zellspannung durch eine erste mit Hilfe der Referenzelektrode eingestellte Halbzellenreaktion und eine zweite durch die zu bestimmenden oxidierbaren Gaskomponenten beeinflußte Halbzellenreaktion an mindestens einer Meßelektrode, über Kalibrierungskurven werden aus den Spannungswerten die Konzentrationen der Gaskomponenten ermittelt.The sensor generates a cell voltage above 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 calibration values are used to determine the concentrations of the gas components from the voltage values.
Der erfindungsgemäße Sensor ist somit im einfachsten Fall mit einer Referenzelektrode, die dieThe sensor according to the invention is thus in the simplest case with a reference electrode which
Gleichgewichtseinstellung des Gasgemisches katalysiert und einer Meßelektrode, die die Gleichgewichtseinstellung des Gasgemisches nicht oder nur wenig zu katalysieren vermag, einsatzfähig.Equilibrium adjustment of the gas mixture catalyzed and a measuring electrode, which is unable to catalyze the equilibrium adjustment of the gas mixture or can catalyze only a little.
Es ist jedoch auch möglich, zwei Meßelektroden aufzubringen, wie in Figur 1 dargestellt, oder auch mehrere Meßelektroden mit jeweils unterschiedlicher katalytischer Aktivität zur Einstellung von Sauerstoff- Gleichgewichtszuständen. Die Meßelektroden reagieren dann mit unterschiedlicher, von der Gasart abhängiger Spannung, bezogen auf die Referenzelektrode.However, it is also possible to apply two measuring electrodes, as shown in FIG. 1, or also several measuring electrodes, each with different catalytic activity, for setting oxygen Equilibrium states. The measuring electrodes then react with different voltages depending on the type of gas, based on the reference electrode.
Bei Anordnungen mit zwei oder mehreren Meßelektroden mit unterschiedlicher katalytischer Aktivität besteht auch die Möglichkeit, Spannungen zwischen den Meßelektroden zur Bestimmung oxidierbarer Gase auszuwerten. Bei Spannungsmessungen zwischen Elektroden, die in der gleichen Ebene und im gleichen Abstand zur Heizervorrichtung angeordnet sind, wie z.B. die Elektroden 1 und 2 in Figur 1 , wird zudem der Seebeck- Effekt ausgeschaltet. Durch Anordnungen mit mindestens zwei Meßelektroden besteht des weiteren die Möglichkeit, die Querempfindlichkeit einer ersten Meßelektrode vollständig oder zumindest teilweise durch das Signal einer weiteren Meßelektrode zu kompensieren, indem die Empfindlichkeit dieser weiteren Meßelektrode auf die störenden Gaskomponenten entsprechend eingestellt wird.In the case of arrangements with two or more measuring electrodes with different catalytic activity, there is also the possibility of evaluating voltages between the measuring electrodes in order to determine oxidizable gases. For voltage measurements between electrodes that are arranged in the same plane and at the same distance from the heater device, e.g. electrodes 1 and 2 in FIG. 1, the Seebeck effect is also switched off. Arrangements with at least two measuring electrodes also make it possible to completely or at least partially compensate for the cross sensitivity of a first measuring electrode by the signal from a further measuring electrode, by adjusting the sensitivity of this further measuring electrode to the interfering gas components.
Nach einer weiteren Ausführungsform ist der Festelektrolyt so ausgebildet, z.B. durch Zusatz von 0,01 bis 10 Vol.-% Platin, daß der Festelektrolyt die zu messenden Gase katalytisch umsetzt, so daß nur die dem thermodynamischen Gleichgewicht entsprechenden Gase an der Referenzelektrode ankommen oder daß der Festelektrolyt nur die das Referenzsignal störenden Gase umsetzt.According to a further embodiment, the solid electrolyte is formed, e.g. by adding 0.01 to 10% by volume of platinum 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.
Nach einer weiteren Alternative werden zusätzlich zum Festelektrolyten eine oder mehrere Meßelektroden porös ausgebildet, wodurch die Gasdiffusion zur Referenzelektrode erleichtert wird. Als Meßelektrodenstoffe werden Halbleiter eingesetzt, die eine hohe spezifische Empfindlichkeit für bestimmte oxidierbare Gase haben. Besonders geeignet sind Oxide oder Miεchoxide, insbesondere auf Rutil- oder Dirutilbasis oder Mischungen daraus, die Akzeptor- und/oder Donator- dotiert sein können. In vorteilhafter Weise werden Titan- und/oder Zirkoniumdioxid verwendet.According to a further alternative, one or more measuring electrodes are made porous in addition to the solid electrolyte, thereby facilitating gas diffusion to the reference electrode. Semiconductors which have a high specific sensitivity for certain oxidizable gases are used as measuring electrode materials. Oxides or mixed oxides, in particular based on rutile or dirutile or mixtures thereof, which can be doped with acceptor and / or donor are particularly suitable. Titanium and / or zirconium dioxide are advantageously used.
Geeignete Donatoren sind insbesondere Tantal und Niob, vorzugsweise Elemente mit höherer Valenz als die den Halbleiter bildenden Metalle; geeignete Akzeptoren sind Ubergangsmetalle, insbesondere Nickel, Kupfer, Kobalt und/oder Chrom, vorzugsweise Nickel, Kupfer und/oder Kobalt, sowie Seltene Erden. Dabei kann der Akzeptor als feste Losung oder als seggregierter Bestandteil im Halbleiter enthalten sein.Suitable donors are in particular tantalum and niobium, preferably elements with higher valence than the metals forming the semiconductor; suitable acceptors are transition metals, in particular nickel, copper, cobalt and / or chromium, preferably nickel, copper and / or cobalt, and rare earths. The acceptor can be contained in the semiconductor as a solid solution or as a segregated component.
Die Konzentrationen der Akzeptoren und Donatoren liegen jeweils im Bereich von 0,01 bis 25%; bei niedrigeren Anteilen werden keine Eigenschaftsverbesserungen der Meßelektroden erreicht und bei höheren Anteilen treten Gitterstorungen auf.The concentrations of the acceptors and donors are each in the range from 0.01 to 25%; at lower proportions, there is no improvement in the properties of the measuring electrodes, and at higher proportions grid defects occur.
Die hohe Empfindlichkeit von z.B. Akzeptor- und Donator¬ dotiertem Titandioxid für insbesondere ungesättigte Kohlenwasserstoffe ist durch die adsorptive Wechselwirkung der Orbitale der Pi-Bmdungen der ungesättigten Kohlenwasserstoffe mit den elektrophilen Akzeptorplatzen auf der Halbleiteroberflache bedingt.The high sensitivity of e.g. Acceptor and donor-doped 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 electrophilic acceptor sites on the semiconductor surface.
Damit der die Leitfähigkeit verringernde Akzeptoranteil nicht in vollem Umfang elektronisch wirksam werden kann, ist es vorteilhaft, der Elektrode einen die Leitfähigkeit erhöhenden Donator zuzusetzen, insbesondere in höherer Konzentration als den Akzeptor. Ein Herstellungsverfahren für einen erfindungsgemäßen Sensor beschreibt das nachfolgende Beispiel: Mit 7% Niob und 3% eines der übergangεmetalle Nickel, Kupfer oder Eisen dotiertes Rutil wird als 30 μm dicke Siebdruckschicht auf ein Substrat aufgedruckt, das eine Referenzelektrode, beispielsweise aus Platin, und darüber eine Festelektrolytεchicht trägt. Auf der gegenüberliegenden Seite des Substrats ist eine Heizervorrichtung aufgebracht. Der Sensor wird bei 1200 °C 90 Minuten lang mit einer Aufheiz-/Abkühlrampe von 300 °C/Stunde gesintert. Der Festelektrolyt hat nach dem Sintern Poren im Größenbereich von 10 nm bis lOOμm. Mit Hilfe einer isoliert zum Festelektrolyten angebrachten Platinleiterbahn, die nur die Meßlelektrode kontaktiert, wird die Spannung an der so aufgebauten Zelle an einem Widerstand von 1 MOhm zwischen der Referenz- und der Rutilelektrode gemessen. Der Sensor wird dabei mit seiner Heizervorrichtung auf 600 °C erhitzt.So that the acceptor portion that reduces the conductivity cannot be fully electronically effective, it is advantageous to add a donor that increases the conductivity to the electrode, in particular in a higher concentration than the acceptor. The following example describes a production method for a sensor according to the invention: Rutile doped with 7% niobium and 3% of one of the transition metals nickel, copper or iron is printed as a 30 μm thick screen printing layer on a substrate which has a reference electrode, for example made of platinum, and above it Solid electrolyte layer carries. 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 μm. With the aid of a platinum conductor track insulated from the solid electrolyte and which only contacts the measuring electrode, the voltage across the cell thus constructed is measured at a resistance of 1 MOhm between the reference and the rutile electrode. The sensor is heated to 600 ° C with its heater.
Als Meßgas wird simuliertes Abgas mit 10 % Sauerstoff, 5 % Wasser und 5 % Kohlendioxid sowie 30 ppm Schwefeldioxid eingesetzt. Oxidierbare Gase werden in den in der Tabelle angegebenen Mengen zugemischt.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.
Zum Vergleich sind in der letzten Zeile der nachfolgenden Tabelle die Spannungswerte für eine Mischpotentialelektrode aus 20 % Gold und 80 % Platin angegeben, die eine Meßelektrode nach dem Stand der Technik darstellt. For comparison, the last line of the table below shows the voltage values for a mixed potential electrode made of 20% gold and 80% platinum, which represents a measuring electrode according to the prior art.
Tabelle: Spannungswerte (in mV) in Abhängigkeit von der Konzentration an oxidierbaren Gasen und der Zusammensetzung der MeßelektrodeTable: Voltage values (in mV) depending on the concentration of oxidizable gases and the composition of the measuring electrode
Spannungen in mVVoltages in mV
RutilelektrodeRutile electrode
Vergleichselektrode mit 7%Nb und 3% Ni Cu Fe 20%Au und 80%Pt oxidierbare Gase (ppm)Comparative electrode with 7% Nb and 3% Ni Cu Fe 20% Au and 80% Pt oxidizable gases (ppm)
Propen 460 150 45 60 320Propene 460 150 45 60 320
180 120 36 47 280180 120 36 47 280
90 90 27 35 18090 90 27 35 180
H2 460 30 12 20 500H2 460 30 12 20 500
180 17 6 10 450180 17 6 10 450
90 5 3 4 38090 5 3 4 380
CO 460 40 3 16 70CO 460 40 3 16 70
180 15 - 7 35180 15 - 7 35
90 7 - 6 2390 7 - 6 23
Aus der Tabelle ist ersichtlich, daß eine Rutil- Halbleiterelektrode mit 7 % Niob als Donator und 3 % Nickel als Akzeptor die größte Selektivität für Propen als Leitsubstanz zeigt. Das nach dem Stand der Technik bekannte Gold- Platin- System zeigt demgegenüber eine besonders große Wasserstoffquerempfmdlichkeit. From the table it can be seen that a rutile semiconductor electrode with 7% niobium as donor and 3% nickel as acceptor shows the greatest selectivity for propene as the lead substance. In contrast, the gold-platinum system known according to the prior art shows a particularly high hydrogen cross sensitivity.

Claims

Ansprüche Expectations
1. Sensor zur Bestimmung der Konzentration oxidierbarer Bestandteile in einem Gasgemisch, insbesondere zur Bestimmung eines oder mehrerer der Gase NOx , CO, H2 und vorzugsweise ungesättigte Kohlenwasεerstoffe, bei dem in übereinanderliegenden Schichten auf der einen Großfläche eineε planaren elektriεch iεolierenden Subεtrats(6) eine die Gleichgewichtseinstellung des Gasgemisches katalysierende Referenzelektrode (3), ein ionenleitender Festelektrolyt (5), und mindestens eine dem Meßgaε ausgesetzte Meßelektrode (1,2), die die Gleichgewichtseinstellung des Gasgemisches nicht oder nur wenig zu katalysieren vermag, angeordnet sind, dadurch gekennzeichnet, daß die Meßelektrode (1,2) als Hauptkomponente einen oder mehrere Halbleiter enthält.1. 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, in which a planar, electrically isolating substrate (6) is provided in layers lying on top of one another on a large area Equilibrium adjustment of the gas mixture catalyzing reference electrode (3), an ion-conducting solid electrolyte (5), and at least one measuring electrode (1,2) exposed to the measuring gas, which cannot or only slightly catalyze the equilibrium adjustment of the gas mixture, characterized in that the Measuring electrode (1, 2) contains one or more semiconductors as the main component.
2. Sensor nach Anspruch 1, dadurch gekennzeichnet, daß auf dem Festelektrolyten (5) zwei Meßelektroden (1,2) beabstandet nebeneinander angeordnet sind.2. Sensor according to claim 1, characterized in that on the solid electrolyte (5) two measuring electrodes (1,2) are arranged spaced apart.
3. Sensor nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß der Halbleiter Akzeptor- und/oder Donator- dotiert ist.3. Sensor according to claim 1 or 2, characterized in that the semiconductor acceptor and / or donor is doped.
4. Sensor nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß der Halbleiter ein Oxid oder ein ein- oder mehrphasiges Mischoxid ist, insbesondere ein Rutil oder Dirutil oder eine Mischung daraus. 4. Sensor according to one of claims 1 to 3, characterized in that the semiconductor is an oxide or a single or multi-phase mixed oxide, in particular a rutile or dirutile or a mixture thereof.
5. Sensor nach Anspruch 4, dadurch gekennzeichnet, daß der Halbleiter aus Titanoxid besteht.5. Sensor according to claim 4, characterized in that the semiconductor consists of titanium oxide.
6. Sensor nach einem der Ansprüche 3 bis 5, dadurch gekennzeichnet, daß der Donator in größerer Konzentration als der Akzeptor vorliegt.6. Sensor according to one of claims 3 to 5, characterized in that the donor is present in greater concentration than the acceptor.
7. Sensor nach einem der Ansprüche 3 bis 6, dadurch gekennzeichnet, daß der Donator em Element mit höherer Valenz als das oder die den Halbleiter bildenden Metalle7. Sensor according to any one of claims 3 to 6, characterized in that the donor element having a higher valence than the one or more metals forming the semiconductor
8. Sensor nach Anspruch 7, dadurch gekennzeichnet, daß der Donator Tantal und/oder Niob ist.8. Sensor according to claim 7, characterized in that the donor is tantalum and / or niobium.
9. Sensor nach einem der Ansprüche 3 DIS 8, dadurch gekennzeichnet, daß der Halbleiter als Akzeptor em oder mehrere Übergangselemente, insbesondere Nickel, Kupfer, Kobalt und/oder Chrom, vorzugsweise Nickel, Kupfer und/oder Kobalt und/oder Seltene Erden enthalt9. Sensor according to one of claims 3 DIS 8, characterized in that the semiconductor contains as an acceptor em or more transition elements, in particular nickel, copper, cobalt and / or chromium, preferably nickel, copper and / or cobalt and / or rare earths
10. Sensor nach Anspruch 9, dadurch gekennzeichnet, daß der Akzeptor als feste Losung oder als seggregierter Bestandteil im Halbleiter enthalten ist.10. Sensor according to claim 9, characterized in that the acceptor is contained as a solid solution or as a segregated component in the semiconductor.
11. Sensor nach einem der Ansprüche 3 bis 10, dadurch gekennzeichnet, daß der Halbleiter Donator und/oder Akzeptor in einer Konzentration von jeweils 0,01 bis 25 % enthalt.11. Sensor according to one of claims 3 to 10, characterized in that the semiconductor contains donor and / or acceptor in a concentration of 0.01 to 25%.
12. Sensor nach Anspruch 11, dadurch gekennzeichnet, daß der Halbleiter 0,5 bis 15 % Niob und 0,25 bis 7 % Nickel, vorzugsweise 7 % Niob und 3 % Nickel enthalt 12. Sensor according to claim 11, characterized in that the semiconductor contains 0.5 to 15% niobium and 0.25 to 7% nickel, preferably 7% niobium and 3% nickel
EP97923831A 1996-06-12 1997-05-16 Sensor for determining the concentration of oxidisable elements in a gas compound Withdrawn EP0843813A1 (en)

Applications Claiming Priority (3)

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DE19623434 1996-06-12
DE19623434A DE19623434A1 (en) 1996-06-12 1996-06-12 Sensor for determining the concentration of oxidizable components in a gas mixture
PCT/DE1997/000996 WO1997047963A1 (en) 1996-06-12 1997-05-16 Sensor for determining the concentration of oxidisable elements in a gas compound

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US6022464A (en) 2000-02-08
KR19990036337A (en) 1999-05-25
CN1195403A (en) 1998-10-07

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