JP7033945B2 - Gas sensor - Google Patents

Description

The present invention relates to a gas sensor that detects the concentration of a specific gas contained in the 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 by using the exhaust gas exhausted from an internal combustion engine such as a vehicle as a detection gas. In the gas sensor that detects the concentration of a specific gas such as NOx in the exhaust gas, the pump electrode for pumping out the oxygen gas in the exhaust gas and the concentration of the specific gas in the exhaust gas after the concentration of the oxygen gas is adjusted by the pump electrode are determined. A sensor electrode for detection is provided on the solid electrolyte body. In addition, the solid electrolyte and each electrode are heated by a heater to a temperature showing activity against oxygen gas and a specific gas. As a gas sensor that detects a specific gas in such an exhaust gas, for example, there is one shown in Patent Document 1.

Japanese Patent Application Laid-Open No. 2000-275215

The sensor electrode used in the conventional gas sensor for detecting the concentration of the specific gas in the exhaust gas has catalytic activity for oxygen gas and the specific gas. Therefore, unless the concentration of oxygen gas in the exhaust gas is lowered as much as possible by using the pump electrode, the concentration of the specific gas cannot be detected accurately.

Further, when the pumping of oxygen gas by the pump electrode fluctuates, the concentration of oxygen gas remaining in the exhaust gas after the concentration of oxygen gas is adjusted also fluctuates. 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, there is room for further improvement in order for the gas sensor 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 the above problems, and has been obtained in an attempt to provide a gas sensor capable of accurately detecting the concentration of a specific gas in a detection gas without being affected by the concentration of oxygen gas in the detection gas. It is a thing.

One aspect of the present invention has a solid electrolyte body (21) having conductivity of oxygen ions, and a pair of electrodes (22, 23) provided on both surfaces (121,212) via the solid electrolyte body. Sensor element (2) and
A heater (3) for heating the sensor element to an active temperature is provided.
In the gas sensor (1) configured to detect the electromotive force or current generated between the pair of electrodes via the solid electrolyte.
The solid electrolyte is A _{9.33 + x} [T _{6.00- y} My] O _{26.0 + z} (however, A: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca. , At least one element in the group consisting of Sr and Ba, at least one element in T: Si and Ge, at least one element in 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 It is composed of an oriented apatite type solid electrolyte having a chemical formula of 3.00 to 10.0).
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 the electrodes is in the range of 300 to 550 ° C. Ori,
The detection electrodes are A _x Zn _1-x By W _1-y O ₄ + _{x / 2 + y / 2} (however, A: In, B: Re, x: 0 to 0.1, y: 0 to It is composed of an electrode material having the chemical formula of (0.1).
Based on the electromotive force or the current, the detection gas is configured to detect the concentration of NO ₂ as a specific gas containing an oxygen atom, excluding oxygen molecules, which is not affected by the oxygen concentration in the detection gas. It is in the gas sensor.

In the gas sensor of the above aspect, an oriented apatite type 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. 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 ion, ^O2- ). 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 on the solid electrolyte body is in the range of 300 to 550 ° C.

By heating the surface temperature of the center position of the detection electrode within the range of 300 to 550 ° C, the temperature of 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. It is heated inside. In the low temperature range of 300 to 550 ° C., the oxygen gas (oxygen molecule) contained in the detection gas in contact with the detection electrode is hardly decomposed. Further, in this low temperature region, it is possible to form a state in which most of the gas components decomposed in the detection electrode among the gas components in the detection gas become the specific gas. This eliminates the need for the gas sensor to adjust the concentration of oxygen gas in order to detect the concentration of the specific gas in the detection gas.

Therefore, it is possible to detect the concentration of the specific gas in the detection gas without using an electrode for pumping oxygen gas from the detection gas. Then, even when the concentration of oxygen gas in the detection gas fluctuates, 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.

If the surface temperature of the center position of the detection electrode under the control of the heater is less than 300 ° C., the temperatures of the detection electrode and the solid electrolyte may be too low to activate them. 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 is high, and the detection of the concentration of the specific gas is affected by the concentration of the oxygen gas. There is a risk of receiving it.

Some of the detection electrodes heated by the control of the heater may be below 300 ° C or above 550 ° C. Further, by controlling the heater, the entire detection electrode can be set to be in the range of 300 to 550 ° C.

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

Further, although the reference numerals in parentheses of each component shown in one aspect of the present invention indicate the correspondence with the reference numerals in the figure in the embodiment, each component is not limited to the content of the embodiment.

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

La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr and Ba, which are mentioned as the "A" element of the chemical formula, become positively charged ions and become apatite. An element that is a lanthanoid or alkaline earth metal that can constitute a type hexagonal structure. Among these, from the viewpoint of being able to further increase the conductivity of oxygen ions, it is preferable to use at least one of the group consisting of La, Nd, Ba, Sr, Ca and Ce. Further, it is more preferable to use an element of either La or Nd, or a combination of La and at least one of the group consisting of Nd, Ba, Sr, Ca and Ce.

As the "T" element of the chemical formula, an element of 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). This allows the precursor to be transformed into an apatite structure and the crystals in the solid electrolyte to be oriented in one direction.

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

The "M" element may be any element that can form a vapor phase at a temperature of 1000 ° C. or higher at which the precursor has an apatite structure and can obtain the required vapor pressure. The "required vapor pressure" refers to a vapor pressure that can move in the atmosphere in a vapor phase state and can diffuse in the grain from the surface of the precursor toward the inside to proceed with the reaction. From this point of view, examples of the "M" element include at least one element in 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 high degree of orientation and high productivity (alignment rate).

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

Further, in the chemical formula, the ratio of the number of moles of the "A" element to the number of moles of the "M" element (A / M), in other words, the ratio of (9.33 + x) / y in the chemical formula is an apatite type crystal lattice. From the viewpoint of maintaining the spatial occupancy rate in the above, 3.00 to 10.0 is preferable, 6.20 to 9.20 is more preferable, and 7.00 to 9.00 is preferable. More preferred.

Specific examples of the chemical formula of "A _{9.33 + x} [T _{6.00- y} My] O _{26.0 + z} " are 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} and the like. However, the oriented apatite type solid electrolyte is not limited to these.

The degree of orientation of the oriented apatite type solid electrolyte, which is the degree of orientation measured by the lotgering method, is preferably 0.6 or more, more preferably 0.8 or more, and 0.9 or more. It is more preferable to do so. Orientation In order to make the lotgering orientation of the apatite-type solid electrolyte 0.6 or more, the precursor indicated by A _{2.00 + x} TO _{5.00 + z} should be single-phase and high-density (relative density 80% or more). It is preferable to prepare. However, the method for producing an oriented apatite-type solid electrolyte is not limited to this production method.

The conductivity of oxygen ions in the oriented apatite-type 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. The above is more preferable. In order to make the conductivity of oxygen ions 10 ^-4 S / cm or more, it is preferable that the degree of orientation of lotgering is 0.6 or more.

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

(Manufacturing method of oriented apatite type solid electrolyte)
As a method for producing an oriented apatite-type solid electrolyte, the contents described in International Publication WO2016 / 111110 can be incorporated.

(electrode)
The pair of electrodes is preferably made of an electrode material having electron conductivity even in a low temperature range of 300 to 550 ° C. Of the pair of the electrodes, the detection electrode is preferably composed of an electrode material having catalytic activity for a specific gas containing an oxygen atom, 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, for the detection electrode, an oxide of W (tungsten) can be used as an electrode material having selectivity of catalytic activity for NO ₂ .

Further, 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. Further, the detection electrode may contain Zn (zinc) in order to suppress sublimation of the electrode material and increase the basicity of the surface of the electrode material. By increasing the basicity, the detection electrode can easily adsorb acid gas. Further, the detection electrode can contain Re (rhenium) in order to form a donor that improves the electron conductivity in the electrode material.

The detection electrodes are A _x Zn _1-x By W _{1-y O 4 + x / 2 + y / 2} (however, A: In, B: Re, x: 0 to 0.1, y: 0 to 0). It can be constructed by using an electrode material having the chemical formula of (1). In this case, it is possible to form a detection electrode in which the detection electrode has heat resistance at 300 to 550 ° C. and has selectivity of catalytic activity for NO ₂ .

The chemical formulas "A" and "B" of A _x Zn _1-x By W _{1-y O 4 + x / 2 + y / 2} have the selectivity of catalytic activity for NO ₂ , respectively. It can also be an element different from n or Re.

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

When the electrode material provided on the surface of the solid electrolyte is sintered together with the solid electrolyte, the detection electrode and the reference electrode may contain the same components as the solid electrolyte 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 by plating or the like, the electrode material may not contain the same components as the solid electrolyte.

The cross-sectional view which shows the gas sensor which concerns on Embodiment 1. FIG. An explanatory diagram showing a state in which a gas sensor is arranged in a pipe of an internal combustion engine according to the first embodiment. FIG. 6 is a cross-sectional view showing another gas sensor according to the first embodiment. The cross-sectional view which shows the gas sensor which concerns on Embodiment 2. FIG. 4 is a sectional view taken along line VV according to the second embodiment. FIG. 4 is a sectional view taken along line VI-VI according to the second embodiment. FIG. 3 is a cross-sectional view showing a gas sensor according to the third embodiment. FIG. 7 is a cross-sectional view taken along the line VIII-VIII of FIG. 7 according to the third embodiment. FIG. 7 is a sectional view taken along line IX-IX of FIG. 7 according to the third embodiment. The graph which shows the result of having confirmed whether the detection of the concentration of NO ₂ by the confirmation test 1 is influenced by the change of the concentration of O ₂ . The graph which shows the result of having confirmed whether the concentration of NO ₂ which concerns on a confirmation test 2 can be detected quantitatively.

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 has a solid electrolyte 21 having conductivity of oxygen ions (oxide ions, O ^2- ), and electrodes 22 and 23 provided on both surfaces of the solid electrolyte 21 via the solid electrolyte 21. The heater 3 is configured to heat the sensor element 2 to an active temperature. The gas sensor 1 is configured to detect the electromotive force E generated between the pair of electrodes 22 and 23 via the solid electrolyte 21. The figure schematically shows the main part of the gas sensor 1.

The solid electrolyte 21 is composed of an oriented apatite-type 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 in the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr and Ba. The chemical formula "T" represents at least one element of Si and Ge. "M" in the chemical formula represents at least one element in the group consisting of B, Ge, Zn, Sn, W and Mo. "X" in the chemical formula indicates a numerical value in the range of -1.00 to 1.00, "y" in the chemical formula indicates a numerical value in the range of 1.00 to 3.00, and "z" in the chemical formula. Indicates a numerical value in the range of −2.00 to 2.00. The ratio (A / M) of the number of moles of "A" to the number of moles of "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 detected gas g, and determines the concentration of the specific gas contained in the detected gas g, excluding the oxygen molecule (O ₂ ), and containing the oxygen atom (O). It is configured to detect.

The gas sensor 1 of this embodiment will be described below.
(Internal combustion engine 5)
As shown in FIG. 2, the gas sensor 1 of the present embodiment is arranged in the pipe 51 of the exhaust system of the internal combustion engine (engine) 5 of the vehicle, and the exhaust gas flowing in the pipe 51 is used as the detection gas g in the detection gas g. It detects a specific gas of. The gas sensor 1 can be provided on the upstream side of the location where the catalyst 52 is arranged in the pipe 51, and can also be provided on the downstream side of the location where the catalyst 52 is arranged in the pipe 51. Further, the pipe in which the gas sensor 1 is arranged may be a pipe on the suction side of the supercharger that increases the density of the air sucked by the internal combustion engine 5 by using the exhaust 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 the piping of a hybrid vehicle or the like in addition to the piping of a general vehicle traveling by using fuel. Further, the gas sensor 1 of the present embodiment is used for detecting the concentration of a specific gas containing an oxygen atom excluding oxygen molecules in the exhaust gas exhausted from the internal combustion engine 5.

(Gas sensor 1)
The gas sensor 1 of this embodiment detects NO ₂ as a specific gas containing an oxygen atom 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 21 and the pair of electrodes 22 and 23 by the heater 3 is set in the 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 is based on the difference between the potential of the atmospheric electrode 23 determined by the oxygen concentration in the atmosphere a and the potential of the detection electrode 22 determined by the concentration of the specific gas in the detected gas g. It is configured to detect the electromotive force E generated between the atmospheric electrode 23 and the detection electrode 22 via the solid electrolyte body 21. The gas sensor 1 has 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 the sensor control unit (SCU, electronic control device) 4.

The gas sensor 1 can also be configured to detect the current generated between the pair of electrodes 22 and 23 via the solid electrolyte 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 21 of this embodiment is composed of a lanthanum silicate-based oriented apatite-type solid electrolyte having a chemical formula of La _{9.33 + x} [Si _{6.00- y} My] O _{26.0 + z} . Examples of this lanthanum silicate-based 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} etc. can be used. Lanthanum silicate-based solid electrolytes have anisotropy in the conductivity of oxygen ions. Therefore, by orienting the crystal grains, the conductivity of oxygen ions in the lanthanum silicate-based solid electrolyte can be enhanced.

As shown in FIG. 1, the solid electrolyte 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 and are provided on the detection electrode 22 exposed to the detection gas g and the second plate surface 212 of the solid electrolyte body 21 as a reference. It consists of an atmospheric electrode 23 (reference electrode) exposed to the atmosphere a as a 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 via a solid electrolyte. The solid electrolyte 21 is provided with an insulating member 24 for separating a path in which the detection gas g is guided to the detection electrode 22 and a path in which the atmosphere a is guided to the atmosphere electrode 23.

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

Further, as shown in FIG. 3, the solid electrolyte body 21 can also be formed into 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 is attached to a housing for attaching the sensor element 2 to a pipe 51 or the like, a first cover that covers the gas detection portion of the sensor element 2, a pair of electrodes 22, 23, and a heater 3. The sensor control unit 4 is provided with a wiring portion for wiring the sensor, a second cover attached to the housing and covering the wiring portion, and the like.

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

The detection electrode 22 is of In _x Zn _1-x Re _y W _1-y O _{4 + x / 2 + y / 2} (where x: 0 to 0.1 and y: 0 to 0.1). It is constructed using an electrode material having a chemical formula. The detection electrode 22 has heat resistance at 300 to 550 ° C. and has selectivity for catalytic activity for NO ₂ (nitrogen dioxide gas). That is, the detection electrode 22 has catalytic activity for NO ₂ as a specific gas in the detection gas g. Further, the detection electrode 22 is excellent in the ability to adsorb NO ₂ and the ability to decompose NO ₂ .

The atmospheric electrode 23 is configured by using Pt. The atmospheric electrode 23 can be made 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 in the plane of the detection electrode 22. Further, 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 means 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 21 and the pair of electrodes 22 and 23 by energizing and heating. The heater 3 is formed by using a heating element that generates Joule heat when energized. The heater 3 of the present embodiment is arranged around the solid electrolyte 21 in the cylindrical member 24. The heating element constituting the heater 3 can be formed in a state close to a linear shape in order to increase its resistance value, and can be arranged in a state of meandering as appropriate. Further, the heater 3 can be laminated on the solid electrolyte 21 at a predetermined interval.

The control temperature of the heater 3 by the energization circuit 42 can be set as a target temperature of the detection electrode 22 when the concentration of the specific gas is detected by the gas sensor 1. The detection electrode 22 is controlled by the heater 3 to a specific temperature within the range of 300 to 550 ° C. Accordingly, the portion of the atmospheric electrode 23 and the solid electrolyte 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 the position facing the center position C of the detection electrode 22. The heat generating center of the heater 3 means the center position of the heating element constituting 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 the insulating ceramics. In this case, the heat generating center of the heater 3 means 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 determined according to the magnitude of the impedance measured by measuring the impedance between the pair of electrodes 22 and 23 or the impedance at both ends of the heater 3. Further, the temperature of the detection electrode 22 can be measured by a temperature detection element or the like. The energization circuit 42 receives feedback of the temperature of the detection electrode 22, and can adjust the amount of energization to the heater 3 so that the temperature of the detection electrode 22 reaches the target temperature.

(Action effect)
In the gas sensor 1 of this embodiment, an oriented apatite type 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 21. The solid electrolyte 21 is activated even in a low temperature range of 300 to 550 ° C. and has a property of conducting oxygen ions. Further, the control temperature of the heater 3 in the gas sensor 1 is set so that the temperature of the detection electrode 22 provided on the solid electrolyte body 21 is 300 to 550 ° C.

By heating the surface temperature of the center position C of the detection electrode 22 within the range of 300 to 550 ° C, the temperature of the position of the solid electrolyte 21 facing the detection electrode 22 also falls within the range of 300 to 550 ° C. It is heated within a near temperature range. In the low temperature range of 300 to 550 ° C., the oxygen gas (oxygen molecule) contained in the detection gas g in contact with the detection electrode 22 is hardly decomposed. Further, in this low temperature region, most of the gas components decomposed in the detection electrode 22 among the gas components in the detection gas g are specific gases. This eliminates the need for the gas sensor 1 to adjust the concentration of oxygen gas in order to detect the concentration of the specific gas in the detection gas g.

Therefore, it is possible to detect the concentration of NO ₂ in the detected gas g without using an electrode for pumping oxygen gas from the detected gas g. Then, even when the concentration of oxygen gas in the detection gas g fluctuates, 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, it is possible to accurately detect the concentration of NO ₂ as a specific gas in the detection gas g without being affected by the concentration of the oxygen gas in the detection gas g.

The solid electrolyte of a conventional gas sensor is composed of zirconia or the like to which yttria is added. Then, in order to activate the conductivity of oxygen ions by this solid electrolyte, it is necessary to heat the solid electrolyte to 600 to 650 ° C. or higher. Then, the detection electrode provided on the solid electrolyte decomposes oxygen gas and a specific gas such as NOx containing an oxygen atom in the detection gas g. Therefore, in order to detect the concentration of the specific gas, it is necessary to reduce the concentration of oxygen gas in the detected gas g as much as possible.

On the other hand, the solid electrolyte 21 of the gas sensor 1 of the present embodiment has the conductivity of oxygen ions in a low temperature region where oxygen gas is not decomposed. Therefore, the gas sensor 1 of the present embodiment detects the concentration of the specific gas in the detected gas g in this low temperature region, so that the concentration of the specific gas can be measured without being affected by the concentration of the oxygen gas (oxygen partial pressure). Can be detected.

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

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

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

Further, as shown in FIGS. 4 and 6, the insulator 240 is formed with an atmospheric duct 26 into which the atmosphere 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.

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

The sensor element 2 and the heater 3 of this embodiment are formed by laminating a green sheet of an insulator 240 provided with a heater 3 on a solid electrolyte body 21 provided with a pair of electrodes 22 and 23 and sintering the mixture. To. Prior to this sintering, the pair of electrodes 22 and 23 can be formed by printing a paste of the electrode material on the plate-shaped solid electrolyte 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 240, and this paste is applied to the other green sheet of the insulator 240. It can be formed by sandwiching it between them. Further, the recess 242 in the insulator 240 can be formed by using a paste of a ceramic material.

Other configurations of the solid electrolyte 21, the pair of electrodes 22, 23, etc. in the gas sensor 1 of the present embodiment are the same as those shown in the first embodiment. Further, also in this embodiment, the same action and effect as in the case of the first embodiment can be obtained. Further, also in this embodiment, the components indicated by the same reference numerals as those shown in the first embodiment are the same as those shown in the first embodiment.

<Embodiment 3>
As shown in FIGS. 7 to 9, the gas sensor 1 of the present embodiment detects the current I generated between the detection electrode 22 and the atmospheric electrode 23 via the solid electrolyte body 21 in response to a change in the concentration of the specific gas. It is configured to do. 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 in a state where a voltage F that causes a limit current characteristic is applied between the atmosphere electrode 23 and the detection electrode 22. It has a configuration for detecting a current I that changes depending on the concentration of a specific gas.

The sensor element 2 of this embodiment is a laminated type in which a detection gas chamber 25 and a heater 3 are formed on insulators 24A and 24B laminated on a plate-shaped solid electrolyte 21. The detection electrode 22 is arranged in the detection gas chamber 25 formed by the first insulator 24A 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 provided with the detection electrode 22.

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

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

Further, as shown in FIGS. 7 and 9, an atmospheric duct 26 into which the atmosphere a is introduced is formed in the second insulator 24B. 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.

In the sensor control unit 4 of the present embodiment, in addition to the energization circuit 42, the voltage application circuit 44 for applying a voltage F between the atmospheric electrode 23 and the detection electrode 22, and the detection electrode 22 and the atmosphere via the solid electrolyte 21 are provided. It has 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 the present embodiment, the green sheet of the first insulator 24A and the second insulator 24B provided with the heater 3 are laminated on the solid electrolyte body 21 provided with the pair of electrodes 22 and 23. It is formed by sintering. Prior to this sintering, the pair of electrodes 22 and 23 can be formed by printing a paste of the electrode material on the plate-shaped solid electrolyte 21. Further, before sintering, the heating element constituting the heater 3 is printed with a paste of the heating element material on one green sheet of the insulator 24B, and this paste is applied to the other green sheet of the insulator 24B. It can be formed by sandwiching it between them. Further, the recess 241 in the first insulator 24A and the recess 242 in the second insulator 24B can be formed by using a paste of a ceramic material.

In the gas sensor 1 of this embodiment, the detection accuracy can be improved by detecting the concentration of the specific gas by utilizing the limit current characteristic. Other configurations of the solid electrolyte 21, the pair of electrodes 22, 23, etc. in the gas sensor 1 of the present embodiment are the same as those shown in the first embodiment. Further, also in this embodiment, the same action and effect as in the case of the first embodiment can be obtained. Further, also in this embodiment, the components indicated by the same reference numerals as those shown in the first embodiment are the same as those shown in the first embodiment.

<Other embodiments>
In the first to third embodiments, the gas sensor 1 uses any one of NO, N ₂ O, CO, H ₂ O, and CO ₂ as a specific gas in addition to detecting the concentration of NO ₂ , and the specific gas of the 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 for the specific gas to be detected.

Further, the detection electrode 22 may 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 a specific gas in the detected gas g. This NOx sensor operates in a low temperature range and can detect NOx almost without being affected by the concentration of oxygen gas.

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

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 set to 200 ppm. The control temperature (target temperature) for heating the detection electrode 22 by the heater 3 was set to 400 ° C. In addition, the concentration of O ₂ in the detected gas g was varied between 5 and 15% by volume. The balance of the detected gas g was N ₂ .

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

<Confirmation test 2>
In this confirmation test, it was confirmed whether the concentration of NO ₂ in the detected gas g can be quantitatively (linya) detected by 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) for heating the detection electrode 22 by the heater 3 was set to 400 ° C. In addition, the concentration of NO ₂ in the detected gas g was varied between 100 and 400 ppm. The concentration of O ₂ in the detected gas g was 10% by volume, and the balance of the detected gas g was N ₂ .

FIG. 11 shows the results of detecting the concentration of NO ₂ in the detected gas g in this confirmation test. In the figure, the current density [nA / cm ² ] indicating the detected concentration of NO ₂ when the concentration of NO ₂ in the detected gas g is changed between 100 and 400 ppm has a high concentration of NO ₂ . It was detected high. From this result, it was confirmed that the gas sensor 1 shown in the third embodiment can quantitatively detect the concentration of NO ₂ in the detected gas g.

The present invention is not limited to each embodiment, and further different embodiments can be configured without departing from the gist thereof. In addition, the present invention includes various modifications, modifications within a uniform range, and the like.

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

Claims (4)

A solid electrolyte body (21) having conductivity of oxygen ions, and a sensor element (2) having a pair of electrodes (22, 23) provided on both surfaces (121,212) via the solid electrolyte body.
A heater (3) for heating the sensor element to an active temperature is provided.
In the gas sensor (1) configured to detect the electromotive force or current generated between the pair of electrodes via the solid electrolyte.
The solid electrolyte is A _{9.33 + x} [T _{6.00- y} My] O _{26.0 + z} (however, A: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca. , At least one element in the group consisting of Sr and Ba, at least one element in T: Si and Ge, at least one element in 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 It is composed of an oriented apatite type solid electrolyte having a chemical formula of 3.00 to 10.0).
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 the electrodes is in the range of 300 to 550 ° C. Ori,
The detection electrodes are A _x Zn _1-x By W _1-y O ₄ + _{x / 2 + y / 2} (however, A: In, B: Re, x: 0 to 0.1, y: 0 to It is composed of an electrode material having the chemical formula of (0.1).
Based on the electromotive force or the current, the detection gas is configured to detect the concentration of NO ₂ as a specific gas containing an oxygen atom, excluding oxygen molecules, which is not affected by the oxygen concentration in the detection gas. Being a gas sensor. Of the pair of the electrodes, the electrode provided on the side opposite to the detection electrode via the solid electrolyte body is exposed to the atmosphere as an atmospheric electrode (23).
The electromotive force generated between the atmospheric electrode and the detection electrode via the solid electrolyte is caused by the difference between the potential of the atmospheric electrode determined by the oxygen concentration in the atmosphere and the potential of the detection electrode determined by the concentration of the specific gas. The gas sensor according to claim 1 , which is configured to detect the electric power (E). Of the pair of the electrodes, the electrode provided on the side opposite to the detection electrode via the solid electrolyte body is exposed to the atmosphere as an atmospheric electrode (23).
The sensor element is configured so that the detection gas comes into contact with the detection electrode under a predetermined diffusion resistance.
With the voltage (F) applied between the atmospheric electrode and the detection electrode, between the detection electrode and the atmospheric electrode via the solid electrolyte in response to a change in the concentration of the specific gas. The gas sensor according to claim 1 , which is configured to detect the current (I) generated in. The detection electrode is arranged 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.
3. The heater is composed of a heating element embedded in a second insulator (24B) laminated on the side opposite to the side on which the first insulator is laminated in the solid electrolyte body. The gas sensor described in.

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