JP2019138764A - Gas sensor - Google Patents

Abstract

To provide a gas sensor that can detect the concentration of a specific gas in a detected gas without being affected by the concentration of the oxygen gas in the detected gas.SOLUTION: A gas sensor 1 includes: a sensor element 2 having a solid electrolyte 21 and a pair of electrodes 22 and 23; and a heater 3. The solid electrolyte 21 is made of an orientation apatite solid electrolyte. The control temperature of the heater 3 is set so that the temperature of the electrode 22 of the pair of electrodes 22 and 23, which is exposed to a detection gas g, is in the range of 300°C to 550°C. The gas sensor 1 detects the concentration of the specific gas containing oxygen atoms other than oxygen molecules in the detected gas g on the basis of the electromotive force E, without being affected by the concentration of the oxygen in the detected gas g.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gas sensor that detects the concentration of a specific gas contained in a detection gas.

  The gas sensor is used, for example, to detect the concentration of oxygen gas or the concentration of a specific gas in the detection gas using exhaust gas exhausted from an internal combustion engine such as a vehicle as the detection gas. In a gas sensor that detects the concentration of a specific gas such as NOx in the exhaust gas, the pump electrode for pumping out oxygen gas in the exhaust gas, and the concentration of the specific gas in the exhaust gas after the oxygen gas concentration is adjusted by the pump electrode A sensor electrode to be detected is provided on the solid electrolyte body. Further, the solid electrolyte body and each electrode are heated to a temperature showing activity with respect to oxygen gas and a specific gas by a heater. As such a gas sensor for detecting a specific gas in the exhaust gas, there is one disclosed in Patent Document 1, for example.

JP 2000-275215 A

  A sensor electrode used in a conventional gas sensor that detects the concentration of a specific gas in exhaust gas has catalytic activity for oxygen gas and the specific gas. Therefore, unless the concentration of oxygen gas in the exhaust gas is reduced as much as possible using the pump electrode, the concentration of the specific gas cannot be detected with high accuracy.

  Further, when the oxygen gas is pumped out by the pump electrode, the concentration of the oxygen gas remaining in the exhaust gas after the oxygen gas concentration is adjusted also varies. In this case, the accuracy of detecting the concentration of the specific gas may deteriorate. That is, in the conventional gas sensor, the accuracy of detecting the concentration of the specific gas in the exhaust gas is affected by the performance of the pump electrode.

  Therefore, in the gas sensor, there is room for further improvement in order to accurately detect the concentration of the specific gas in the exhaust gas without being affected by the concentration of the oxygen gas in the exhaust gas (detection gas).

  The present invention has been made in view of such problems, and is obtained by providing a gas sensor capable of accurately detecting the concentration of a specific gas in a detection gas without being affected by the concentration of the oxygen gas in the detection gas. It is a thing.

One aspect of the present invention includes a solid electrolyte body (21) having oxygen ion conductivity, and a pair of electrodes (22, 23) provided on both surfaces (211 and 212) through the solid electrolyte body. A sensor element (2);
A heater (3) for heating the sensor element to an activation temperature,
In the gas sensor (1) configured to detect an electromotive force or current generated between the pair of electrodes via the solid electrolyte body,
The solid electrolyte _{body, A 9.33 + x [T 6.00} -y M y] O 26.0 + z ( However, A: La, Ce, Pr , Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca At least one element selected from the group consisting of Sr and Ba, at least one element selected from T: Si and Ge, at least one element selected from the group consisting of M: B, Ge, Zn, Sn, W and Mo; x: -1.00 to 1.00, y: 1.00 to 3.00, z: -2.00 to 2.00, and the ratio of the number of moles of A to the number of moles of M (A / M) is 3.00 to 10.0.) Is formed of an oriented apatite solid electrolyte having a chemical formula of
The control temperature of the heater is set so that the surface temperature of the center position (C) of the detection electrode (22) exposed to the detection gas (g) of the pair of electrodes is within a range of 300 to 550 ° C. And
Based on the electromotive force or the current, it is configured not to be affected by the oxygen concentration in the detection gas, and is configured to detect the concentration of a specific gas containing oxygen atoms, excluding oxygen molecules, contained in the detection gas. In the gas sensor.

In the gas sensor of one embodiment, an oriented apatite solid electrolyte having a chemical formula of A _{9.33 + x} [T _{6.00- y My} ] O _{26.0 + z} is used as the solid electrolyte body. This solid electrolyte body is activated even in a low temperature range of 300 to 550 ° C. and has a property of conducting oxygen ions (oxide ions, O ²⁻ ). Further, the control temperature of the heater in the gas sensor is set so that the surface temperature at the center position of the detection electrode provided in the solid electrolyte body is within a range of 300 to 550 ° C.

  When the surface temperature of the center position of the detection electrode is heated within the range of 300 to 550 ° C., the temperature at the position facing the detection electrode in the solid electrolyte body is also in the temperature range close to the range of 300 to 550 ° C. Heated inside. And in the low temperature range of 300-550 degreeC, oxygen gas (oxygen molecule) contained in the detection gas which contacts a detection electrode is hardly decomposed | disassembled. Further, in this low temperature region, it is possible to form a state in which most of the gas components in the detection gas decomposed at the detection electrode become the specific gas. Thereby, in the gas sensor, it is not necessary to adjust the concentration of the oxygen gas in order to detect the concentration of the specific gas in the detection gas.

  Therefore, the concentration of the specific gas in the detection gas can be detected without using an electrode for pumping oxygen gas from the detection gas. Even when the concentration of oxygen gas in the detection gas varies, the concentration of the specific gas in the detection gas can be detected without being affected by this.

  Therefore, according to the gas sensor of the above aspect, the concentration of the specific gas in the detection gas can be accurately detected without being affected by the concentration of the oxygen gas in the detection gas.

  When the surface temperature at the center position of the detection electrode under the control of the heater is less than 300 ° C., the temperature of the detection electrode and the solid electrolyte body may be too low and they may not be activated. On the other hand, when the surface temperature at the center position of the detection electrode under the control of the heater exceeds 550 ° C., the temperature of the detection electrode and the solid electrolyte body is high, and the detection of the concentration of the specific gas has an influence by the concentration of oxygen gas. There is a risk of receiving.

  A part of the detection electrode heated by the control of the heater may be less than 300 ° C. or more than 550 ° C. Further, the entire detection electrode can be within a range of 300 to 550 ° C. by controlling the heater.

  The solid electrolyte body may have a property of conducting oxygen ions even at a temperature exceeding 550 ° C.

  In addition, the reference numerals in parentheses of the constituent elements shown in one embodiment of the present invention indicate the correspondence with the reference numerals in the drawings in the embodiments, but the constituent elements are not limited only to the contents of the embodiments.

(Oriented apatite solid electrolyte)
A specific configuration of the oriented apatite solid electrolyte will be described.
“Orientation” in an oriented apatite solid electrolyte means that the solid electrolyte body has an orientation axis (crystal axis), and the orientation axis may be uniaxial or biaxial. . In particular, the oriented apatite solid electrolyte preferably has c-axis orientation.

  La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba mentioned as the “A” element in the chemical formula are ions having a positive charge, and are apatite. It is an element that is a lanthanoid or an alkaline earth metal that can constitute a type hexagonal crystal structure. Among these, it is preferable to use at least one of the group consisting of La, Nd, Ba, Sr, Ca, and Ce from the viewpoint of further improving the conductivity of oxygen ions. More preferably, either La or Nd, or a combination of La and at least one of the group consisting of Nd, Ba, Sr, Ca and Ce is used.

As the “T” element in the chemical formula, Si, Ge, or a combination of Si and Ge can be used.
The “M” element of the chemical formula is introduced in the gas phase by reaction with a metastable precursor (A _{2.00 + x} TO _{5.00 + z} described later). Thereby, while changing this precursor to an apatite structure, the crystal | crystallization in a solid electrolyte can be orientated to one direction.

_{A 9.33 + x [T 6.00-} y M y] O 26.0 + orientation apatitic solid electrolyte having the formula of _z is a precursor having the chemical formula of _{A 2.00 + x TO 5.00 + z} , feel containing M element It can be obtained by heating in the phase and reacting the precursor with the M element. “A” in this chemical formula represents at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba. “T” in the chemical formula represents an element containing at least one of Si and Ge. “X” in the chemical formula represents a numerical value in the range of −1.00 to 1.00, and “z” in the chemical formula represents a numerical value in the range of −2.00 to 2.00. “M element” refers to at least one element selected from the group consisting of B, Ge, Zn, Sn, W, and Mo.

  As the “M” element, any element can be used as long as the precursor can be in a gas phase at a temperature of 1000 ° C. or higher at which the precursor has an apatite structure and a necessary vapor pressure can be obtained. “Necessary vapor pressure” refers to a vapor pressure that can move in an atmosphere in a gas phase, and can diffuse within the grain from the surface of the precursor to the inside to advance the reaction. From this viewpoint, examples of the “M” element include at least one element selected from the group consisting of B, Ge, Zn, W, Sn, and Mo. Among these, it is preferable to use at least one of B, Ge, and Zn in terms of a high degree of orientation and high productivity (orientation speed).

"X" in the chemical formula of the _{"A 9.33 + x [T 6.00-} y M y] O 26.0 + z ", from the viewpoint of can increase the conductivity of the orientation degree and the oxygen ions, -1.00～1.00 It is preferable that it is 0.00-0.70, and it is further more preferable that it is 0.45-0.65. “Y” in the chemical formula is preferably from 1.00 to 3.00, more preferably from 1 to 2, more preferably from the viewpoint of filling the position of the “T” element in the apatite-type crystal lattice. More preferably, it is 00 to 1.62. “Z” in the chemical formula is preferably −2.00 to 2.00, and preferably −1.50 to 1.50 from the viewpoint of maintaining electrical neutrality in the apatite crystal lattice. More preferably, it is more preferably -1.00 to 1.00.

  Further, in the chemical formula, the ratio (A / M) of the number of moles of the “A” element to the number of moles of the “M” element, in other words, the ratio of (9.33 + x) / y in the chemical formula is the apatite crystal lattice. From the viewpoint of maintaining the spatial occupancy ratio in the case, it is preferably 3.00 to 10.0, more preferably 6.20 to 9.20, and 7.00 to 9.00. Further preferred.

_{"A 9.33 + x [T 6.00-} y M y] O 26.0 + z " Specific examples of the formula _{of, La 9.33 + x (Si 4.70} B 1.30) O 26.0 + z, La 9.33 + x (Si 4.70 Ge 1.30 ) O _{26.0 + z} , La _{9.33 + x} (Si _4.70 Zn _1.30 ) O _{26.0 + z} , La _{9.33 + x} (Si _4.70 W _1.30 ) O _{26.0 + z} , La _{9.33 + x} (Si _4.70 Sn _1.30 ) O _{26.0 + z} La _{9.33 + x} (Ge _4.70 B _1.30 ) O _{26.0 + z} . However, the oriented apatite solid electrolyte is not limited to these.

The Lotgering orientation degree, which is the orientation degree measured by the Lotgering method of the oriented apatite solid electrolyte, is preferably 0.6 or more, more preferably 0.8 or more, and 0.9 or more. More preferably. In order to set the Lotgering orientation degree of the oriented apatite solid electrolyte to 0.6 or more, the precursor represented by A _{2.00 + x} TO _{5.00 + z} has a single phase and a high density (relative density of 80% or more). It is preferable to prepare. However, the manufacturing method of the oriented apatite solid electrolyte is not limited to this manufacturing method.

The oxygen ion conductivity of the oriented apatite solid electrolyte at 500 ° C. is preferably 10 ⁻⁴ S / cm or more, more preferably 10 ⁻³ S / cm or more, and 10 ⁻² S / cm. More preferably, the above is used. In order to set the oxygen ion conductivity to 10 ⁻⁴ S / cm or more, the Lotgering orientation degree is preferably set to 0.6 or more.

The transport number of the oriented apatite solid electrolyte is preferably 0.80 or more, more preferably 0.90 or more, and further preferably 0.95 or more. In order to set this transport number to 0.80 or more, it is preferable to set the purity of “A _{9.33 + x} [T _{6.00- y My} ] O _{26.0 + z} ” to 90% or more.

(Method for producing oriented apatite solid electrolyte)
The content described in International Publication WO2016 / 111110 can be used for the manufacturing method of an oriented apatite type solid electrolyte.

(electrode)
The pair of electrodes is preferably composed of an electrode material having electron conductivity even in a low temperature range of 300 to 550 ° C. The detection electrode of the pair of electrodes is preferably composed of an electrode material having catalytic activity for a specific gas containing oxygen atoms, excluding oxygen molecules, even in a low temperature range of 300 to 550 ° C.

The detection electrode is preferably composed of an electrode material having catalytic activity for NO, NO ₂ , N ₂ O, CO, H ₂ O or CO ₂ as a specific gas in the detection gas in a low temperature range of 300 to 550 ° C. . In particular, an oxide of W (tungsten) can be used for the detection electrode as an electrode material having selectivity of catalytic activity with respect to NO ₂ .

  In order to improve the heat resistance of the electrode material, it is preferable to use a compound of W and another element for the detection electrode. The detection electrode can contain Zn (zinc) in order to suppress sublimation of the electrode material and increase the basicity of the surface of the electrode material. In addition, by increasing the basicity, the detection electrode can easily adsorb the acidic gas. Further, the detection electrode can contain Re (rhenium) in order to form a donor that improves the electron conductivity in the electrode material.

Sensing _{electrodes, A x Zn 1-x B} y W 1-y O 4 + x / 2 + y / 2 ( provided that, A: In, B: Re , x: 0~0.1, y: 0~0 .1)) can be used. In this case, the detection electrode has heat resistance at 300 to 550 ° C., and a detection electrode having selectivity of catalytic activity with respect to NO ₂ can be formed.

Incidentally, "A" and "B" in the formula _{A x Zn 1-x B y} W 1-y O 4 + x / 2 + y / 2 , if you have a selectivity of the catalyst activity for NO _2, respectively An element different from n or Re may be used.

  The reference electrode of the pair of electrodes can be configured using Pt, a Pt alloy (an alloy of Pt and another noble metal), an electrically conductive oxide such as a perovskite oxide, or the like. The reference electrode refers to an electrode facing the detection electrode through the solid electrolyte body. The reference electrode can be an atmospheric electrode that is exposed to the atmosphere.

  When the electrode material provided on the surface of the solid electrolyte body is sintered together with the solid electrolyte body, the detection electrode and the reference electrode may contain the same components as the solid electrolyte body in the electrode material. . On the other hand, when the detection electrode and the reference electrode are formed on the surface of the solid electrolyte body by performing plating or the like, the electrode material may not contain the same components as the solid electrolyte body.

1 is a cross-sectional view showing a gas sensor according to a first embodiment. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the state by which the gas sensor concerning the 1st Embodiment was arrange | positioned to piping of the internal combustion engine. Sectional drawing which shows the other gas sensor concerning Embodiment 1. FIG. Sectional drawing which shows the gas sensor concerning Embodiment 2. FIG. FIG. 5 is a VV sectional view of FIG. 4 according to the second embodiment. FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 4 according to the second embodiment. Sectional drawing which shows the gas sensor concerning Embodiment 3. FIG. VIII-VIII sectional drawing of FIG. 7 concerning Embodiment 3. FIG. IX-IX sectional drawing of FIG. 7 concerning Embodiment 3. FIG. Confirmation test according to 1, the detection of the concentration of NO _2, the graph showing the results of confirming whether affected by changes in the concentration of O _2. According to the verification test 2, a graph showing the results of confirmation of whether it is possible to quantitatively detect the concentration of NO _2.

A preferred embodiment of the gas sensor described above will be described with reference to the drawings.
<Embodiment 1>
As shown in FIG. 1, the gas sensor 1 of this embodiment includes a sensor element 2 and a heater 3. The sensor element 2 includes a solid electrolyte body 21 having oxygen ion (oxide ion, O ²⁻ ) conductivity, and a pair of electrodes 22 and 23 provided on both sides of the surface through the solid electrolyte body 21. The heater 3 is configured to heat the sensor element 2 to an activation temperature. The gas sensor 1 is configured to detect an electromotive force E generated between the pair of electrodes 22 and 23 via the solid electrolyte body 21. The figure schematically shows the main part of the gas sensor 1.

The solid electrolyte body 21 is composed of an oriented apatite solid electrolyte having a chemical formula of A _{9.33 + x} [T _{6.00- y My} ] O _{26.0 + z} . Here, “A” in the chemical formula represents at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba. “T” in the chemical formula represents at least one element of Si and Ge. “M” in the chemical formula represents at least one element selected from the group consisting of B, Ge, Zn, Sn, W, and Mo. “X” in the chemical formula represents a numerical value in the range of −1.00 to 1.00, “y” in the chemical formula represents a numerical value in the range of 1.00 to 3.00, and “z” in the chemical formula Indicates a numerical value within the range of -2.00 to 2.00. The ratio of the number of moles of “A” to the number of moles of “M” (A / M) is 3.00 to 10.0.

The control temperature of the heater 3 is set so that the surface temperature of the center position C of the detection electrode 22 exposed to the detection gas g of the pair of electrodes 22 and 23 is 300 to 550 ° C. Based on the electromotive force E, the gas sensor 1 is not affected by the oxygen concentration in the detection gas g, and the concentration of the specific gas containing oxygen atoms (O), excluding oxygen molecules (O ₂ ), contained in the detection gas g. Configured to detect.

Below, the gas sensor 1 of this form is demonstrated.
(Internal combustion engine 5)
As shown in FIG. 2, the gas sensor 1 according to the present embodiment is disposed in a pipe 51 of an exhaust system of an internal combustion engine (engine) 5 of a vehicle, and an exhaust gas flowing in the pipe 51 is used as a detection gas g. The specific gas is detected. The gas sensor 1 can be provided upstream of the location where the catalyst 52 is disposed in the pipe 51, and can also be provided downstream of the location where the catalyst 52 is disposed in the pipe 51. Moreover, the piping which arrange | positions the gas sensor 1 can also be used as the piping of the suction side of the supercharger which raises the density of the air which the internal combustion engine 5 suck | inhales using waste gas. Further, the pipe in which the gas sensor 1 is arranged may be a pipe in an exhaust gas recirculation mechanism that recirculates a part of the exhaust gas exhausted from the internal combustion engine 5 to the exhaust passage to the intake passage of the internal combustion engine 5.

  Further, the gas sensor 1 can be arranged in piping of a hybrid vehicle in addition to piping of a general vehicle that travels using fuel. The gas sensor 1 of the present embodiment is used for detecting the concentration of a specific gas containing oxygen atoms in the exhaust gas exhausted from the internal combustion engine 5 excluding oxygen molecules.

(Gas sensor 1)
The gas sensor 1 of this embodiment detects NO ₂ as a specific gas containing oxygen atoms excluding oxygen molecules. NO ₂ has the property of being decomposed into NO at a high temperature exceeding 550 ° C. Therefore, the control temperature for heating the solid electrolyte body 21 and the pair of electrodes 22 and 23 by the heater 3 is set within a range of 300 to 550 ° C., and NO ₂ contained in the detection gas g is decomposed into NO. prevent.

  As shown in FIG. 1, the gas sensor 1 of the present embodiment has a difference between the potential of the atmospheric electrode 23 determined from the oxygen concentration in the atmosphere a and the potential of the detection electrode 22 determined from the concentration of the specific gas in the detection gas g. The electromotive force E generated between the atmospheric electrode 23 and the detection electrode 22 is detected via the solid electrolyte body 21. The gas sensor 1 includes an electromotive force detection circuit 41 that detects an electromotive force E generated between the pair of electrodes 22 and 23, and an energization circuit 42 that energizes the heater 3. The electromotive force detection circuit 41 and the energization circuit 42 are formed in a sensor control unit (SCU, electronic control unit) 4.

  The gas sensor 1 can also be configured to detect a current generated between the pair of electrodes 22 and 23 via the solid electrolyte body 21. In this case, a voltage can be applied between the pair of electrodes 22 and 23 via the solid electrolyte body 21.

(Sensor element 2)
The solid electrolyte body 21 of this embodiment is composed of a lanthanum silicate oriented apatite solid electrolyte having a chemical formula of La _{9.33 + x} [Si _{6.00- y My} ] O _{26.0 + z} . Examples of the lanthanum silicate oriented apatite type solid electrolyte include La _{9.33 + x} (Si _4.70 B _1.30 ) O _{26.0 + z} , La _{9.33 + x} (Si _4.70 Ge _1.30 ) O _{26.0 + z} , La _{9.33 + x} (Si _4.70 Zn _1.30 ) O _{26.0 + z} , La _{9.33 + x} (Si _4.70 W _1.30 ) O _{26.0 + z} , La _{9.33 + x} (Si _4.70 Sn _1.30 ) O _{26.0 + z} , La _{9.33 + x} (Ge _4.70 B _1.30 ) O _{26.0 + z} or the like can be used. The lanthanum silicate-based solid electrolyte has anisotropy in the conductivity of oxygen ions. Therefore, by conducting crystal grain orientation, the conductivity of oxygen ions in the lanthanum silicate solid electrolyte can be increased.

  As shown in FIG. 1, the solid electrolyte body 21 is formed in a plate shape. The pair of electrodes 22 and 23 are provided on the first plate surface 211 of the solid electrolyte body 21, provided on the detection plate 22 exposed to the detection gas g, and the second plate surface 212 of the solid electrolyte body 21, and the reference It consists of an atmospheric electrode 23 (reference electrode) exposed to the atmosphere a as gas. The second plate surface 212 is located on the opposite side of the first plate surface 211. The atmospheric electrode 23 is provided at a position facing the detection electrode 22 through a solid electrolyte. The solid electrolyte body 21 is provided with an insulating member 24 for separating a path through which the detection gas g is guided to the detection electrode 22 and a path through which the atmosphere a is guided to the atmosphere electrode 23.

  The solid electrolyte body 21 of this embodiment is formed in a disc shape. The member 24 is formed in a cylindrical shape, and the solid electrolyte body 21 is disposed on the inner peripheral side of the member 24.

  Moreover, as shown in FIG. 3, the solid electrolyte body 21 can also be formed in a bottomed cylindrical shape (cup shape). In this case, the detection electrode 22 can be provided on the outer peripheral surface of the bottomed cylindrical solid electrolyte body 21, and the atmospheric electrode 23 can be provided on the inner peripheral surface of the bottomed cylindrical solid electrolyte body 21. Further, a protective layer made of a porous ceramic material can be provided on the surface of the detection electrode 22. The figure schematically shows the main part of the gas sensor 1.

  Although not shown, the gas sensor 1 includes a housing for attaching the sensor element 2 to the pipe 51 and the like, a first cover attached to the housing and covering the gas detection part of the sensor element 2, a pair of electrodes 22 and 23, and the heater 3. Is provided with a wiring part for wiring the sensor control unit 4 to the sensor control unit 4, a second cover attached to the housing and covering the wiring part.

  The crystal grains of the solid electrolyte body 21 of this embodiment are oriented in the c axis as the crystal axis. In the solid electrolyte body 21, the c-axis of crystal grains of the solid electrolyte is directed in a direction parallel to or inclined with respect to the plate thickness direction in which the pair of electrodes 22 and 23 are opposed to each other. Oxygen ions can easily move along the c-axis direction.

Detection electrode _{22, In x Zn 1-x Re} y W 1-y O 4 + x / 2 + y / 2 ( provided that, x: 0~0.1, y:. To 0-0.1 to) the An electrode material having a chemical formula is used. This detection electrode 22 has heat resistance at 300 to 550 ° C., and has selectivity of catalytic activity with respect to NO ₂ (nitrogen dioxide gas). That is, the detection electrode 22 has catalytic activity with respect to NO ₂ as the specific gas in the detection gas g. Further, the detection electrode 22 is excellent in the performance of adsorbing NO ₂ and the performance of decomposing NO ₂ .

  The atmospheric electrode 23 is configured using Pt. The atmospheric electrode 23 can be composed of various electrode materials having electron conductivity.

  As shown in FIG. 1, when the detection electrode 22 is formed in a flat plate shape, the center position C of the detection electrode 22 means the position of the center of gravity within the plane of the detection electrode 22. As shown in FIG. 3, when the detection electrode 22 is formed in a cylindrical shape, the center position C of the detection electrode 22 refers to a circumferential center position in the axial direction of the detection electrode 22.

(Heater 3)
As shown in FIG. 1, the heater 3 is configured to heat the solid electrolyte body 21 and the pair of electrodes 22 and 23 by energization heating. The heater 3 is formed using a heating element that generates Joule heat when energized. The heater 3 of this embodiment is disposed around the solid electrolyte body 21 in the cylindrical member 24. The heating element constituting the heater 3 can be formed in a nearly linear shape in order to increase its resistance value, and can be arranged in a meandering state as appropriate. In addition, the heater 3 can be laminated with a predetermined distance from the solid electrolyte body 21.

  The control temperature of the heater 3 by the energization circuit 42 can be set as the target temperature of the detection electrode 22 when the gas sensor 1 detects the concentration of the specific gas. The detection electrode 22 is controlled to a specific temperature within a range of 300 to 550 ° C. by the heater 3. Accordingly, the portion of the atmospheric electrode 23 and the solid electrolyte body 21 sandwiched between the detection electrode 22 and the atmospheric electrode 23 is also controlled to a temperature close to a specific temperature.

  The heat generation center of the heater 3 can be arranged near the position facing the center position C of the detection electrode 22 or near the position facing the center position C of the detection electrode 22. The heat generation center of the heater 3 refers to the center position of the heat generator that constitutes the heater 3.

  The heater 3 of the gas sensor 1 in FIG. 3 can be configured by a heating element provided around the central shaft portion 30 of insulating ceramics. In this case, the heat generation center of the heater 3 refers to a circumferential center position in the axial direction of the heater 3.

  The control temperature of the heater 3, in other words, the target temperature of the detection electrode 22 can be adjusted by appropriately changing the voltage applied to the heating element of the heater 3, the energization time, and the like. The energization circuit 42 can apply an AC voltage subjected to PWM (pulse width modulation) or the like to the heater 3.

  The temperature of the detection electrode 22 can be obtained according to the magnitude of this impedance by measuring the impedance between the pair of electrodes 22 and 23 or the impedance of both ends of the heater 3. The temperature of the detection electrode 22 can also be measured by a temperature detection element or the like. The energization circuit 42 receives the feedback of the temperature of the detection electrode 22 and can adjust the energization amount to the heater 3 so that the temperature of the detection electrode 22 becomes the target temperature.

(Function and effect)
In the gas sensor 1 of this embodiment, an oriented apatite solid electrolyte having a chemical formula of A _{9.33 + x} [T _{6.00- y My} ] O _{26.0 + z} is used as the solid electrolyte body 21. The solid electrolyte body 21 is activated even in a low temperature range of 300 to 550 ° C. and has a property of conducting oxygen ions. The control temperature of the heater 3 in the gas sensor 1 is set so that the temperature of the detection electrode 22 provided in the solid electrolyte body 21 is 300 to 550 ° C.

  When the surface temperature of the center position C of the detection electrode 22 is heated within a range of 300 to 550 ° C., the temperature at the position facing the detection electrode 22 in the solid electrolyte body 21 is also within a range of 300 to 550 ° C. Heated within a near temperature range. And in the low temperature range of 300-550 degreeC, oxygen gas (oxygen molecule) contained in the detection gas g which contacts the detection electrode 22 is hardly decomposed | disassembled. In the low temperature range, most of the gas components in the detection gas g that are decomposed at the detection electrode 22 are specific gases. Thereby, in the gas sensor 1, in order to detect the density | concentration of the specific gas in the detection gas g, it becomes unnecessary to adjust the density | concentration of oxygen gas.

Therefore, the concentration of NO ₂ in the detection gas g can be detected without using an electrode for pumping oxygen gas from the detection gas g. Even when the concentration of the oxygen gas in the detection gas g varies, the concentration of NO ₂ in the detection gas g can be detected without being affected by this.

Therefore, according to the gas sensor 1 of the present embodiment, the concentration of NO ₂ as the specific gas in the detection gas g can be accurately detected without being affected by the concentration of the oxygen gas in the detection gas g.

  A solid electrolyte body of a conventional gas sensor is composed of zirconia to which yttria is added. And in order to activate the conductivity of oxygen ion by this solid electrolyte body, it is necessary to heat a solid electrolyte body to 600-650 degreeC or more. And the detection electrode provided in the solid electrolyte body decomposes | disassembles specific gas, such as NOx containing oxygen gas and oxygen atom in the detection gas g. Therefore, in order to detect the concentration of the specific gas, it is necessary to make the concentration of the oxygen gas in the detection gas g as low as possible.

  On the other hand, the solid electrolyte body 21 of the gas sensor 1 of the present embodiment has oxygen ion conductivity in a low temperature range where the oxygen gas is not decomposed. For this reason, the gas sensor 1 of the present embodiment detects the concentration of the specific gas in the detection gas g in this low temperature range, thereby reducing the concentration of the specific gas without being influenced by the concentration of oxygen gas (oxygen partial pressure). Can be detected.

<Embodiment 2>
As shown in FIGS. 4, 5, and 6, the gas sensor 1 according to the present embodiment generates a gas generated between the detection electrode 22 and the atmospheric electrode 23 via the solid electrolyte body 21 in accordance with the change in the concentration of the specific gas. It is configured to detect power E or current I.

  The sensor element 2 of this embodiment is of a laminated type in which the heater 3 is formed on the insulator 240 laminated on the plate-shaped solid electrolyte body 21. The detection electrode 22 is disposed on the first plate surface 211 of the solid electrolyte body 21 that is exposed to the detection gas g.

  The heater 3 of this embodiment is constituted by a heating element embedded in an insulator 240 laminated on the second plate surface 212 of the solid electrolyte body 21. The insulator 240 is made of an insulating ceramic such as alumina (aluminum oxide). A protective layer that covers the detection electrode 22 may be formed on the first plate surface 211 of the solid electrolyte body 21. The protective layer can be formed of a ceramic porous body.

  As shown in FIGS. 4 and 6, the insulator 240 is formed with an air duct 26 into which the air a is introduced. The atmospheric duct 26 is formed between the recess 242 formed in the insulator 240 and the second plate surface 212 of the solid electrolyte body 21 provided with the atmospheric electrode 23.

  The sensor control unit 4 of this embodiment includes a detection circuit 43 that detects an electromotive force E or current I generated between the detection electrode 22 and the atmospheric electrode 23 via the solid electrolyte body 21 in addition to the energization circuit 42.

  The sensor element 2 and the heater 3 of this embodiment are formed by laminating and sintering a green sheet of an insulator 240 provided with the heater 3 on the solid electrolyte body 21 provided with a pair of electrodes 22 and 23. The Before this sintering, the pair of electrodes 22 and 23 can be formed by printing a paste of an electrode material on the plate-like solid electrolyte body 21. Further, before the sintering, the heating element constituting the heater 3 prints a paste of the heating element material on one green sheet of the insulator 240, and this paste is used with the other green sheet of the insulator 240. It can be formed by being sandwiched between them. The recess 242 in the insulator 240 can be formed using a paste of a ceramic material.

  In the gas sensor 1 of the present embodiment, other configurations such as the solid electrolyte body 21 and the pair of electrodes 22 and 23 are the same as the configurations described in the first embodiment. Also in this embodiment, the same effect as in the case of Embodiment 1 can be obtained. Furthermore, also in this embodiment, the constituent elements indicated by the same reference numerals as those shown in the first embodiment are the same as the constituent elements shown in the first embodiment.

<Embodiment 3>
As shown in FIGS. 7 to 9, the gas sensor 1 of the present embodiment detects a current I generated between the detection electrode 22 and the atmospheric electrode 23 via the solid electrolyte body 21 in accordance with a change in the concentration of the specific gas. It is configured to Further, the gas sensor 1 of the present embodiment limits the flow rate of the detection gas g supplied to the detection electrode 22 and applies a voltage F that generates a limiting current characteristic between the atmospheric electrode 23 and the detection electrode 22. The current I that changes depending on the concentration of the specific gas is detected.

  The sensor element 2 of this embodiment is of a stacked type in which the detection gas chamber 25 and the heater 3 are formed on insulators 24A and 24B stacked on a plate-like solid electrolyte body 21. The detection electrode 22 is disposed in a detection gas chamber 25 formed by the first insulator 24 </ b> A laminated on the solid electrolyte body 21. The detection gas chamber 25 is formed between the recess 241 formed in the first insulator 24A and the first plate surface 211 of the solid electrolyte body 21 where the detection electrode 22 is provided.

  As shown in FIGS. 7 and 8, the first insulator 24A is provided with a diffusion resistance part 251 for introducing the detection gas g into the detection gas chamber 25 under a predetermined diffusion resistance. The diffused resistor portion 251 can be configured by a through hole such as a pinhole formed in the first insulator 24A. Further, the diffusion resistance portion 251 can also be configured by a ceramic porous body disposed inside or on the surface of the through hole formed in the first insulator 24A. Moreover, the ceramic porous body can be filled in all or part of the through holes.

  The heater 3 of this embodiment is configured by a heating element embedded in the second insulator 24 </ b> B laminated on the second plate surface 212 of the solid electrolyte body 21. The second plate surface 212 is located on the opposite side of the solid electrolyte body 21 from the first plate surface 211 on which the first insulator 24A is laminated. The first insulator 24A and the second insulator 24B are made of insulating ceramics such as alumina (aluminum oxide).

  As shown in FIGS. 7 and 9, the second insulator 24B is formed with an air duct 26 into which the air a is introduced. The atmospheric duct 26 is formed between the recess 242 formed in the second insulator 24B and the second plate surface 212 of the solid electrolyte body 21 provided with the atmospheric electrode 23.

  The sensor control unit 4 of this embodiment includes a voltage application circuit 44 that applies a voltage F between the atmospheric electrode 23 and the detection electrode 22, and the detection electrode 22 and the atmospheric air via the solid electrolyte body 21 in addition to the energization circuit 42. A current detection circuit 45 that detects a current I generated between the electrode 23 and the electrode 23;

  In the sensor element 2 and the heater 3 of this embodiment, the green sheet of the first insulator 24A and the second insulator 24B provided with the heater 3 is laminated on the solid electrolyte body 21 provided with the pair of electrodes 22 and 23. And formed by sintering. Before this sintering, the pair of electrodes 22 and 23 can be formed by printing a paste of an electrode material on the plate-like solid electrolyte body 21. Further, before sintering, the heating element constituting the heater 3 prints a paste of the heating element material on one green sheet of the insulator 24B, and this paste is used with the other green sheet of the insulator 24B. It can be formed by being sandwiched between them. Further, the recess 241 in the first insulator 24A and the recess 242 in the second insulator 24B can be formed using a paste of a ceramic material.

  In the gas sensor 1 of this embodiment, the detection accuracy can be increased by detecting the concentration of the specific gas using the limiting current characteristic. In the gas sensor 1 of the present embodiment, other configurations such as the solid electrolyte body 21 and the pair of electrodes 22 and 23 are the same as the configurations described in the first embodiment. Also in this embodiment, the same effect as in the case of Embodiment 1 can be obtained. Furthermore, also in this embodiment, the constituent elements indicated by the same reference numerals as those shown in the first embodiment are the same as the constituent elements shown in the first embodiment.

<Other embodiments>
In the first to third embodiments, in addition to detecting the concentration of NO ₂ , the gas sensor 1 uses any one of NO, N ₂ O, CO, H ₂ O, and CO ₂ as a specific gas. It can be configured to detect the concentration. In this case, the detection electrode 22 can be made of an electrode material having selectivity of catalytic activity with respect to the specific gas to be detected.

The detection electrode 22 can also have catalytic activity for NOx containing NO, NO ₂ , and N ₂ O. In this case, the gas sensor 1 functions as a NOx sensor that detects NOx as the specific gas in the detection gas g. This NOx sensor operates in a low temperature range, and can detect NOx with almost no influence of the concentration of oxygen gas.

<Confirmation test 1>
In this confirmation test, when the concentration of NO ₂ in the detection gas g is detected using the gas sensor 1 shown in the first embodiment, the concentration of O ₂ in the detection gas g is changed to detect the concentration of NO _2. , Whether it was affected by the change in O ₂ concentration was confirmed.

A voltage of 0.45 V was applied between the atmospheric electrode 23 and the detection electrode 22, and the concentration of NO ₂ in the detection gas g was 200 ppm. The control temperature (target temperature) for heating the detection electrode 22 by the heater 3 was set to 400 ° C. Further, the concentration of O ₂ in the detection gas g was varied between 5 and 15% by volume. The balance in the detection gas g was N ₂ .

FIG. 10 shows the result of detecting the concentration of NO ₂ in the detection gas g in this confirmation test. In the figure, the current density [nA / cm ² ] indicating the concentration of NO ₂ in the detection gas g when the concentration of O ₂ in the detection gas g is varied between 5 and 15% by volume is 681 to 710 nA / Although it changed slightly between cm ² , it hardly changed. From this result, according to the gas sensor 1 shown in Embodiment 1, it was confirmed that the detection of the concentration of NO ₂ was hardly affected by the change in the concentration of O ₂ .

<Confirmation test 2>
In this confirmation test, it was confirmed whether or not the concentration of NO ₂ in the detection gas g can be quantitatively detected using the gas sensor 1 shown in the third embodiment.

A voltage of 0.45 V was applied between the atmospheric electrode 23 and the detection electrode 22, and the control temperature (target temperature) at which the detection electrode 22 was heated by the heater 3 was 400 ° C. In addition, the concentration of NO ₂ in the detection gas g was varied between 100 and 400 ppm. The concentration of O ₂ in the detection gas g was 10% by volume, and the balance in the detection gas g was N ₂ .

FIG. 11 shows the result of detecting the concentration of NO ₂ in the detection gas g in this confirmation test. In the figure, the current density [nA / cm ² ] indicating the concentration of NO ₂ detected when the concentration of NO ₂ in the detection gas g is changed between 100 and 400 ppm is high in the concentration of NO _2. It was detected so high. From this result, it was confirmed that according to the gas sensor 1 shown in Embodiment 3, the concentration of NO ₂ in the detection gas g can be quantitatively detected.

  The present invention is not limited only to each embodiment, and further different embodiments can be configured without departing from the scope of the invention. Further, the present invention includes various modifications, modifications within an equivalent range, and the like.

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Sensor element 21 Solid electrolyte body 22 Detection electrode 23 Atmospheric electrode 3 Heater

Claims (6)

A sensor element (2) having a solid electrolyte body (21) having oxygen ion conductivity, and a pair of electrodes (22, 23) provided on both surfaces (211 and 212) through the solid electrolyte body;
A heater (3) for heating the sensor element to an activation temperature,
In the gas sensor (1) configured to detect an electromotive force or current generated between the pair of electrodes via the solid electrolyte body,
The solid electrolyte _{body, A 9.33 + x [T 6.00} -y M y] O 26.0 + z ( However, A: La, Ce, Pr , Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca At least one element selected from the group consisting of Sr and Ba, at least one element selected from T: Si and Ge, at least one element selected from the group consisting of M: B, Ge, Zn, Sn, W and Mo; x: -1.00 to 1.00, y: 1.00 to 3.00, z: -2.00 to 2.00, and the ratio of the number of moles of A to the number of moles of M (A / M) is 3.00 to 10.0.) Is formed of an oriented apatite solid electrolyte having a chemical formula of
The control temperature of the heater is set so that the surface temperature of the center position (C) of the detection electrode (22) exposed to the detection gas (g) of the pair of electrodes is within a range of 300 to 550 ° C. And
Based on the electromotive force or the current, it is configured not to be affected by the oxygen concentration in the detection gas, and is configured to detect the concentration of a specific gas containing oxygen atoms, excluding oxygen molecules, contained in the detection gas. Gas sensor. The gas sensor according to claim 1, wherein the specific gas is any one of NO, NO ₂ , N ₂ O, CO, H ₂ O, and CO ₂ . The detection _{electrode, A x Zn 1-x B} y W 1-y O 4 + x / 2 + y / 2 ( provided that, A: In, B: Re , x: 0~0.1, y: 0~ The gas sensor according to claim 1, wherein the gas sensor is configured using an electrode material having a chemical formula of 0.1. Of the pair of electrodes, an electrode provided on the opposite side of the detection electrode via the solid electrolyte body is exposed to the atmosphere as an atmospheric electrode (23),
Due to the difference between the potential of the atmospheric electrode determined from the oxygen concentration in the atmosphere and the potential of the detection electrode determined from the concentration of the specific gas, an occurrence occurs between the atmospheric electrode and the detection electrode via the solid electrolyte body. The gas sensor according to claim 1, wherein the gas sensor is configured to detect electric power (E). Of the pair of electrodes, an electrode provided on the opposite side of the detection electrode via the solid electrolyte body is exposed to the atmosphere as an atmospheric electrode (23),
The sensor element is configured such that the detection gas contacts the detection electrode under a predetermined diffusion resistance,
In a state where a voltage (F) is applied between the atmospheric electrode and the detection electrode, according to a change in the concentration of the specific gas, between the detection electrode and the atmospheric electrode via the solid electrolyte body. The gas sensor of any one of Claims 1-3 comprised so that the electric current (I) which arises in this may be detected. The detection electrode is disposed in a detection gas chamber (25) formed by a first insulator (24A) laminated on the solid electrolyte body,
The first insulator is provided with a diffusion resistance portion (251) for introducing the detection gas into the detection gas chamber under a predetermined diffusion resistance,
The said heater is comprised with the heat generating body embed | buried under the 2nd insulator (24B) laminated | stacked on the opposite side to the side on which the said 1st insulator was laminated | stacked in the said solid electrolyte body. The gas sensor described in 1.

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