JP2020095014A - Gas sensor - Google Patents

Abstract

To provide a gas sensor capable of detecting carbon monoxide gas or both carbon monoxide gas and oxygen gas in a high-temperature environment.SOLUTION: A carbon monoxide gas sensor includes: a solid electrolyte substrate 11; and at least a pair of electrodes 12, 13 connected to each other in an ionically conductive manner through the solid electrolyte substrate. The pair of electrodes includes: a first electrode 12 composed of a sintered body containing metal particles selected from alloy particles of platinum and rhodium or alloy particles of platinum and gold, and solid electrolyte particles; and a second electrode 13 composed of the sintered body containing platinum particles and solid electrolyte particles.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gas sensor. In particular, the present invention relates to a gas sensor capable of detecting carbon monoxide in a high temperature environment, and a gas sensor capable of detecting both carbon monoxide and oxygen in a high temperature environment.

It is known in the prior art to use a sensor which is constructed on the basis of a solid electrolyte and which operates according to the mixed potential principle for the detection of gas constituents or the determination of the gas concentration in a measurement gas mixture (see, for example, US Pat. 1 and 2).

Patent Document 1 discloses a mixed potential type gas sensor capable of detecting nitrogen oxides under the condition where a voltage is applied. Patent Document 2 discloses a mixed potential type gas sensor that detects NH ₃ , nitrogen oxides, and hydrocarbon compounds. In this sensor, utilizing the fact that due to the difference in reactivity between the electrode based on the Pt-Au paste and the gold-plated platinum electrode, a mixed potential is generated between the two electrodes bonded by the solid electrolyte, The concentration of the target compound in the measurement gas is measured.

JP 2002-162383 A Japanese Patent No. 4914447

In the mixed potential type gas sensor, a mixed potential corresponding to the gas concentration at the three-phase interface between the solid electrolyte, the electrode and the gas phase is generated due to the difference in reactivity of the pair of electrodes with respect to the detected gas, and The mixed potential difference between the electrodes can be measured as the electromotive force of the sensor. As a means for producing a difference in reactivity between a pair of electrodes, the chemical composition of the electrodes is changed, or one of the electrodes is covered with a catalyst having a reactivity different from that of the electrode material. It was

For the purpose of measuring gas components in a boiler flue, it is necessary to operate the gas sensor in a high temperature environment exceeding 500°C, for example, a high temperature environment of 700°C to 800°C. However, at such a temperature, there are problems such as heat resistance of the electrode material and stability of the catalyst. On the other hand, when the electrode pair is composed of an electrode material whose main component is platinum (Pt), the heat resistance of which has been confirmed, a difference in reactivity to the detection gas between the electrodes may be obtained due to the high temperature environment. This is difficult, and the sensor output is generally small.

The present inventors have found that by forming an electrode having a specific composition on a solid electrolyte substrate, carbon monoxide gas can be selectively detected at high output in a high temperature environment exceeding 500°C. The present invention has been completed.

[1] According to one embodiment, the present invention provides a carbon monoxide gas sensor, which includes a solid electrolyte substrate and at least a pair of electrodes ionically conductive via the solid electrolyte substrate, The first electrode is a sintered body containing metal particles selected from alloy particles of platinum and rhodium or alloy particles of platinum and gold, and solid electrolyte particles, platinum particles, and solid electrolyte particles. And a second electrode made of a sintered body containing.
[2] In the gas sensor of [1], it is preferable that the solid electrolyte substrate and the solid electrolyte particles contain stabilized zirconia.
[3] According to another embodiment of the present invention, there is provided a method for manufacturing the carbon monoxide gas sensor according to [1] or [2], wherein the first and second electrodes are provided on the solid electrolyte substrate. The step of forming and the solid electrolyte substrate on which the first and second electrodes are formed are contacted with a mixed gas containing carbon monoxide, oxygen and nitrogen gas for 4 hours or more under a temperature condition of 800° C. or higher. And a step of causing the method.
[4] According to another embodiment, the present invention provides a method for detecting carbon monoxide gas using the carbon monoxide gas sensor according to [1] or [2], wherein the temperature of the solid electrolyte substrate is Relates to a method including a step of measuring a potential difference between the first and second electrodes in an atmosphere having a temperature of 500° C. or higher.
[5] According to another embodiment of the present invention, there is provided a carbon monoxide and oxygen gas sensor, comprising a solid electrolyte substrate, a first electrode provided on the solid electrolyte substrate, and a solid electrolyte substrate. A second electrode that is ionically connected through the first electrode and the solid electrolyte substrate; and an ion that is provided on the solid electrolyte substrate and that includes the second electrode and the solid electrolyte substrate. And a third electrode electrically conductively connected, the first electrode comprising: metal particles selected from alloy particles of platinum and rhodium or alloy particles of platinum and gold; and solid electrolyte particles. The second and third electrodes are sintered bodies containing platinum particles and solid electrolyte particles, the atmosphere being in contact with the first and second electrodes, and the third electrode being in contact with each other. The present invention relates to a gas sensor that is shielded from the atmosphere.
[6] The gas sensor according to [5], further including a carbon monoxide detection unit connected to the first and second electrodes and an oxygen detection unit connected to the second and third electrodes. Is preferred.
[7] In the gas sensor of [5], a fourth electrode provided on the solid electrolyte substrate and electrically connected to the first electrode via the solid electrolyte substrate, and the first and the fourth electrodes. Further comprising a carbon monoxide detection circuit connected to the fourth electrode and an oxygen detection unit connected to the second and third electrodes, wherein the fourth electrode is in the same atmosphere as the first electrode. It is preferable that the fourth electrode be a sintered body containing platinum particles and solid electrolyte particles.
[8] In the gas sensor according to any one of [5] to [7], the solid electrolyte substrate is a tubular structure whose one end is a closed end, and the first and second electrodes are the tubular structure. It is preferable that the third electrode is provided on an outer wall portion and the third electrode is provided on an inner wall portion of the tubular structure.
[9] In the gas sensor according to [7], it is preferable that the fourth electrode is provided on an outer wall portion of the tubular structure.
[10] According to another embodiment of the present invention, there is provided a carbon monoxide and oxygen gas sensor, which comprises a first solid electrolyte substrate and a first electrode provided on the first solid electrolyte substrate. A carbon monoxide gas sensor unit provided on the first solid electrolyte substrate, comprising the first electrode and a second electrode connected in an ion conductive manner via the first solid electrolyte substrate; Solid electrolyte substrate, a third electrode provided on the second solid electrolyte substrate, and a second solid electrolyte substrate provided on the second solid electrolyte substrate via the third electrode and the second solid electrolyte substrate. An oxygen gas sensor section including a fourth electrode connected in an ion conductive manner is provided in a casing, and the first electrode is a metal particle selected from alloy particles of platinum and rhodium or alloy particles of platinum and gold. And a solid electrolyte particle, wherein the second, third and fourth electrodes are platinum particles and a solid electrolyte particle, and the first, second, And a gas sensor in which the atmosphere in contact with the third electrode and the atmosphere in contact with the fourth electrode are blocked.
[11] According to yet another embodiment, the present invention is a method for manufacturing a gas sensor according to the above [5], wherein the solid electrolyte substrate includes at least the first, second, and third electrodes. The step of forming an electrode and the solid electrolyte substrate on which the electrode including the first, second and third electrodes is formed include carbon monoxide, oxygen and nitrogen gas under a temperature condition of 800° C. or higher. The present invention relates to a method including a step of contacting with a mixed gas for 4 hours or more.
[12] In the gas sensor according to any one of [1], [2], and [5] to [10], the metal particles contained in the first electrode are alloy particles of platinum and rhodium, It is preferable that the mass ratio of platinum to rhodium is 3:7 to 5:5, the film thickness of the first electrode is 10 to 20 μm, and the film thickness of the second electrode is 10 to 32 μm.
[13] In the gas sensor according to any one of [1], [2], and [5] to [10], the metal particles contained in the first electrode are alloy particles of platinum and gold, It is preferable that the mass ratio of platinum to gold is 98:2 to 90:10, the film thickness of the first electrode is 1 to 15 μm, and the film thickness of the second electrode is 10 to 32 μm.

According to the present invention, it is possible to provide a mixed potential type gas sensor that can operate even in a high temperature environment of 500° C. or higher and that can selectively detect carbon monoxide gas.

FIG. 1 is a conceptual diagram showing a sectional structure of a gas sensor according to a first embodiment of the present invention. FIG. 2 is a conceptual diagram showing a planar structure of the gas sensor according to the first aspect of the second embodiment of the present invention. FIG. 3 is a conceptual diagram showing a cross-sectional structure of the gas sensor according to the first aspect of the second embodiment of the present invention. FIG. 4 is a conceptual diagram showing a planar structure of a gas sensor according to a second aspect of the second embodiment of the present invention. FIG. 5 is a conceptual diagram showing a cross-sectional structure of a gas sensor according to a second aspect of the second embodiment of the present invention. FIG. 6 is a conceptual diagram showing a planar structure of a gas sensor according to a third aspect of the second embodiment of the present invention. FIG. 7 shows the mass ratio of Rh in the Pt—Rh alloy particles constituting the first electrode and the electromotive force ΔEwc (mV) between the first electrode and the second electrode in the gas sensor of Example 4. It is a graph which shows a relationship. FIG. 8 is a graph showing the relationship between the CO gas concentration and the electromotive force ΔEwc (mV) between the first electrode and the second electrode in the gas sensor of Example 4. FIG. 9 shows the mass ratio of Au in the Pt—Au alloy particles forming the first electrode and the electromotive force ΔEwc (mV) between the first electrode and the second electrode in the gas sensor of Example 5. It is a graph which shows the relationship with. FIG. 10 is a graph showing the relationship between the CO gas concentration and the electromotive force ΔEwc (mV) between the first electrode and the second electrode in the gas sensor of Example 5.

Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the embodiments described below.

[First Embodiment: Carbon Monoxide Gas Sensor]
The gas sensor according to the first embodiment of the present invention is a carbon monoxide gas sensor, including a solid electrolyte substrate and at least a pair of electrodes ionically conductively connected via the solid electrolyte substrate, The electrodes include a first electrode and a second electrode. The gas sensor according to the present embodiment includes a carbon monoxide (CO) gas that is a detection target gas, a gas that includes a non-detection target gas as a measurement target, and can detect carbon monoxide at approximately 500° C. or higher. It is a gas sensor. The gas sensor according to this embodiment will be described with reference to FIG. FIG. 1 is a schematic sectional view of a carbon monoxide gas sensor according to the first embodiment.

As shown in FIG. 1, the gas sensor includes a solid electrolyte substrate 11 and at least one pair of electrodes. The pair of electrodes includes a first electrode 12 and a second electrode 13 provided on the solid electrolyte substrate 11.

The solid electrolyte substrate 11 is a member that forms a three-phase interface between the solid electrolyte, the first or second electrode 12 or 13 and the gas phase containing the gas to be detected, and enables ion conduction. The shape of the solid electrolyte substrate 11 is not particularly limited as long as the first and second electrodes 12 and 13 can be coupled so as to be ion-conductive. Therefore, for example, in addition to the flat plate-shaped substrate shown in FIG. 1, a cylindrical substrate or a cylindrical substrate whose one end is closed as shown in FIG. 2 described later may be used.

The solid electrolyte substrate 11 is preferably stabilized zirconia, and examples thereof include zirconia stabilized with a rare earth metal oxide such as yttria and ceria, calcia-stabilized zirconia, and magnesia-stabilized zirconia, but are not limited thereto. From the viewpoint of ion conductivity, it is particularly preferable to use yttria-stabilized zirconia.

The pair of electrodes includes at least a first electrode 12 that functions as a working electrode and a second electrode 13 that functions as a counter electrode. In FIG. 1, each of the first electrode 12 and the second electrode 13 is formed in contact with the solid electrolyte substrate 11, and the first electrode 12 and the second electrode 13 are provided apart from each other. .. However, it is sufficient that the first electrode 12 and the second electrode 13 are ionically conductively coupled via the solid electrolyte substrate 11, and for example, between the first electrode 12 and the solid electrolyte substrate 11. Alternatively, another member having ion conductivity may be interposed. Further, in FIG. 1, the first electrode 12 and the second electrode 13 are provided apart from each other on one surface of the flat plate-shaped solid electrolyte substrate 11, but the flat plate-shaped solid electrolyte substrate 11 is provided. It is also possible to arrange the first electrode on one surface and the second electrode on the other surface. However, it is necessary that the first electrode and the second electrode are in contact with the same vapor phase atmosphere, and the atmosphere between the first electrode and the second electrode is blocked by the solid electrolyte substrate. The first electrode and the second electrode are arranged in a manner not to be performed. Further, a reference electrode may be provided in addition to the first and second electrodes serving as a working electrode and a counter electrode, or two or more pairs of electrodes may be provided at different positions on the solid electrolyte substrate.

The first electrode 12 may be, in one aspect, a sintered body containing metal particles made of an alloy of platinum (Pt) and rhodium (Rh) and solid electrolyte particles. Hereinafter, in the present specification, an alloy of Pt and Rh may be referred to as a Pt-Rh alloy. Such a sintered body is obtained by dissolving a mixture containing metal particles made of Pt-Rh alloy and solid electrolyte particles in a suitable solvent such as an organic solvent in which ethyl cellulose is dissolved in 224 trimethyl 3 hydroxypentyisobutyrate. It can be obtained by applying the paste obtained by dispersion to the solid electrolyte substrate 11 in a thin layer shape, for example, and firing it at 1200 to 1400° C. in the atmosphere.

At this time, the mass ratio of Pt and Rh in the Pt-Rh alloy may be arbitrary and is not particularly limited. The mass ratio of Pt and Rh may be, for example, 99:1 to 1:99, preferably 3:7 to 5:5, and more preferably 35:65 to 45:55. The average particle diameter of the metal particles made of Pt-Rh alloy is preferably about 0.5 to 2.5 μm, more preferably about 1 to 2 μm. In the present specification, the average particle diameter means the average particle diameter measured by observation with a scanning electron microscope (SEM).

The solid electrolyte particles may be stabilized zirconia particles, and may be one or more kinds selected from any of the stabilized zirconia mentioned as the material of the solid electrolyte substrate 11. The stabilized zirconia having the same composition as the stabilized zirconia that is the main component of the solid electrolyte substrate 11 may be used, or the stabilized zirconia having a different composition may be used. The solid electrolyte particles are particularly preferably yttria-stabilized zirconia particles. The average particle size of the solid electrolyte particles is preferably about 0.1 to 1 μm, more preferably about 0.2 to 0.5 μm. The relationship between the average particle diameters of the metal particles made of an alloy of Pt and Rh and the yttria-stabilized zirconia particles may be the same or different, and in one embodiment, the particles of the Pt-Rh alloy are included. The diameter is preferably larger than the particle diameter of the yttria-stabilized zirconia particles.

In the first electrode 12, the mass ratio of the metal particles made of Pt-Rh alloy and the solid electrolyte particles may be arbitrary and is not particularly limited, but is preferably 99:1 to 1:99, and 85 It is preferably about 15 to 15:85. The film thickness of the first electrode 12 containing metal particles made of a Pt-Rh alloy may be, for example, 10 to 20 μm, and preferably 12 to 18 μm. The film thickness here means the film thickness of the sintered body after firing.

In another aspect, the first electrode 12 may be a sintered body containing metal particles made of an alloy of platinum (Pt) and gold (Au) and solid electrolyte particles. Hereinafter, an alloy of Pt and Au may be referred to as a Pt-Au alloy. The mass ratio of Pt and Au in the Pt-Au alloy may be arbitrary and is not particularly limited. The mass ratio of Pt and Au may be, for example, 99:1 to 1:99, preferably 98:2 to 90:10, and more preferably 96:4 to 92:8. The average particle size of Pt-Au alloy particles, the type and average particle size of solid electrolyte particles, the mass ratio between Pt-Au alloy particles and solid electrolyte particles, and the size relationship of particle sizes, and the method for producing a sintered body are described in Pt. It may be the same as the method for producing the sintered body containing the metal particles made of the —Rh alloy and the solid electrolyte particles. The film thickness of the first electrode 12 containing metal particles made of a Pt-Au alloy may be, for example, 1 to 15 μm, and is preferably 5 to 10 μm. The film thickness here means the film thickness of the sintered body after firing.

The second electrode 13 may be a sintered body containing Pt particles and solid electrolyte particles, even when the working electrode according to any of the above-described embodiments is used. The average particle size of the Pt particles at this time may be the same as the average particle size of the metal particles made of the Pt-Rh alloy. Further, the type and average particle size of the solid electrolyte particles may be the same as the type and average particle size of the solid electrolyte particles forming the first electrode 12. In the second electrode 13, the mass ratio of Pt particles and solid electrolyte particles may be arbitrary and is not particularly limited, but is preferably 99:1 to 1:99, and 85:15 to 15:85. It is preferably about the same. The solid electrolyte particles forming the second electrode 13 may be the same composition as the solid electrolyte particles forming the first electrode 12 and/or the stabilized zirconia forming the solid electrolyte substrate 11. Well, it may be a stabilized zirconia of different composition. The solid electrolyte particles forming the second electrode 13 may preferably be yttria-stabilized zirconia particles. The method for manufacturing the sintered body containing these particles may be the same as the method for manufacturing the sintered body forming the first electrode 12. The film thickness of the second electrode 13 is not particularly limited, but it may be thicker than that of the first electrode 12, and may be, for example, 10 to 32 μm, and preferably 15 to 30 μm. The film thickness here means the film thickness of the sintered body after firing. The thickness of the second electrode 13 is the same regardless of whether the first electrode 12 has a composition containing metal particles made of a Pt-Rh alloy or a composition containing metal particles made of a Pt-Au alloy. You can

The gas sensor according to the present embodiment includes a carbon monoxide detection unit (not shown) connected to each of the first electrode 12 and the second electrode 13. The carbon monoxide detection unit includes a detection circuit and wiring. The wiring has one end connected to the first electrode 12 and the other end connected to the detection circuit, and one end connected to the second electrode 13 and the other end connected to the detection circuit. including. The detection circuit may be a general electrometer capable of measuring the electromotive force (potential difference) between the first electrode 12 and the second electrode 13. The wiring may be a wiring made of a conductive member, and may be a Pt wire or a wiring made of a sintered body having the same composition as the electrode material to which the wiring is connected.

The gas sensor according to the present embodiment may include a heater (not shown) as a further optional element. The heater may be a device capable of raising the temperature of the solid electrolyte substrate 11 to a predetermined temperature as necessary, and may be a thin layer type heater made of a tungsten (W) thin film or a platinum (Pt) thin film, It may be a ceramic heater or any other heater. When the gas sensor shown in FIG. 1 further includes a heater, the heater is, for example, on one surface of the solid electrolyte substrate 11 and on the side opposite to where the first electrode 12 and the second electrode 13 are provided. An insulating film may be provided on the surface of the first electrode 12 and the second electrode 13 so that the heater faces the solid electrolyte substrate 11 and the insulating film. Alternatively, the heater can be provided in the vicinity of the solid electrolyte substrate without making contact with the solid electrolyte substrate, but is not limited to a particular mode.

Next, a method of manufacturing the gas sensor having such a configuration will be described. The method of manufacturing the gas sensor according to the present embodiment includes the following steps.
(1) a step of forming the first and second electrodes on the solid electrolyte substrate, and (2) the solid electrolyte substrate on which the first and second electrodes are formed, at a temperature condition of 800° C. or higher, Step of contacting with a mixed gas containing carbon monoxide, oxygen, and nitrogen gas for 4 hours or more

First Step: Electrode Forming Step In the electrode forming step, the first and second electrodes 12 and 13 are formed on the solid electrolyte substrate 11. The method of forming each electrode is as described above. Both the paste made of the first electrode 12 material and the paste made of the second electrode 13 material are formed on the solid electrolyte substrate 11, and the first and second electrodes 12 and 13 are respectively connected to the detection circuit. It is preferable that these wirings are baked after the wirings for connecting the wirings are arranged on the solid electrolyte substrate 11. The solid electrolyte substrate 11 may be a commercially available product, or may be manufactured by molding the solid electrolyte material into a desired shape prior to the first step. Further, in a gas sensor having a heater, which is an optional component, on a solid electrolyte substrate, a heater electrode pattern made of Pt paste or the like is formed by a printing method or the like on which an electrically insulating layer such as alumina is laminated in advance. By firing, a heater can be formed on the solid electrolyte substrate 11. By the first step, the gas sensor structure including the solid electrolyte substrate 11, the first and second electrodes 12, 13 and the wiring can be obtained.

Second step: mixed gas contact step In the mixed gas contact step, the mixed gas containing carbon monoxide, oxygen, and nitrogen gas at 800° C. or higher, preferably about 800 to 900° C., is used as the gas sensor structure obtained in the first step. Contact the body. The composition of the mixed gas is preferably 1000 to 3000 ppm of carbon monoxide, 2 to 5 volume% of oxygen, and the balance of nitrogen. The mixed gas may contain a trace amount of other unavoidable components. The contact time may be 4 hours or longer, preferably 5 hours or longer, more preferably 7 hours or longer, and the upper limit is not particularly limited, but may be up to about 20 hours.

(Gas detection method)
According to another embodiment, the present invention relates to a carbon monoxide gas detection method using the gas sensor according to the above embodiment. Such a gas detection method can also be called an operation method of a gas sensor. The gas detection method according to the present embodiment includes a step of measuring a potential difference between the first and second electrodes in an atmosphere in which the temperature of the solid electrolyte substrate is 500° C. or higher, for example, 600 to 800° C.

In the method according to the present embodiment, the measurement target gas is generally a gas that may contain carbon monoxide gas. Typically, a gas having a temperature of 500° C. or higher, such as a refuse incinerator or a sludge incinerator, may be, for example, 600 to 800° C. or 700 to 800° C., but is not limited thereto. When detecting gas, the sensor according to the first embodiment can be installed in a flue or the like through which the gas to be measured flows. In this case, the gas sensor is installed such that both the first and second electrodes 12 and 13 are in contact with the gas to be measured.

When carbon monoxide as the detection target gas is present in the measurement target gas, an electromotive force is generated between the first and second electrodes, and the electromotive force can be detected as a potential difference by the detection circuit. Then, the carbon monoxide gas concentration can be obtained based on this potential difference.

According to the first embodiment of the present invention, it is possible to obtain a carbon monoxide gas sensor that can operate in a high temperature atmosphere of 500° C. or higher, for example, 600 to 800° C. and can detect carbon monoxide gas. .

[Second Embodiment: Carbon Monoxide and Oxygen Gas Sensor]
The gas sensor according to the second embodiment of the present invention is a carbon monoxide and oxygen gas sensor. The gas sensor according to the present embodiment includes a carbon monoxide (CO) gas and an oxygen (O ₂ ) gas, which are detection target gases, and a non-detection target gas, and an atmosphere of approximately 500° C. or higher, for example, 600 to 800° C. In the above, it is a gas sensor capable of separately detecting two kinds of detection target gases.

A gas sensor according to a first aspect of the second embodiment is a solid electrolyte substrate, a first electrode provided on the solid electrolyte substrate, and a solid electrolyte substrate provided with the first electrode and the solid electrolyte substrate. A second electrode electrically connected via the solid electrolyte substrate and a third electrode provided on the solid electrolyte substrate and electrically connected via the second electrode and the solid electrolyte substrate. Including. A gas sensor according to a first aspect (hereinafter, simply referred to as the first aspect) of the second embodiment will be described with reference to FIGS. FIG. 2 is a schematic plan view of the gas sensor according to the first aspect, and FIG. 3 is a schematic cross-sectional view of the gas sensor according to the first aspect.

The gas sensor shown in FIGS. 2 and 3 includes a solid electrolyte substrate 21, a first electrode 22, a second electrode 23, and a third electrode 24 in a casing 27. Further, it further includes a carbon monoxide detection unit connected to the first and second electrodes 22 and 23, and an oxygen detection unit connected to the second and third electrodes 23 and 24.

In the embodiment shown in FIGS. 2 and 3, the solid electrolyte substrate 21 is a tubular structure whose one end is closed. More specifically, the solid electrolyte substrate 21 is formed in an elongated cylindrical shape having a constant diameter and extending for a predetermined length, and the base end portion in the longitudinal direction is opened and the tip end portion in the longitudinal direction is closed. , Has a test tube shape. The tip has a rounded curved surface. The material of the solid electrolyte substrate 21 can be selected from the same options as illustrated in the first embodiment.

In this aspect, the first electrode 22 is provided on the outer wall portion of the solid electrolyte substrate 21. The material and manufacturing method of the first electrode 22 can be selected from the same options as those exemplified for the first electrode (working electrode) of the first embodiment. The first electrode 22 can function as a working electrode for carbon monoxide detection.

The second electrode 23 is provided on the outer wall of the solid electrolyte substrate 21, which corresponds to the tip of the test tube, and is separated from the first electrode 22. The first electrode 22 and the second electrode 23 are ionic conductively connected via the solid electrolyte substrate 21. The material and manufacturing method of the second electrode 23 can be selected from the same options as those exemplified for the second electrode (counter electrode) of the first embodiment. The second electrode 23 functions as a counter electrode for detecting carbon monoxide and also as an electrode in contact with a measurement target gas for detecting oxygen.

A carbon monoxide detector is connected to the first electrode 22 and the second electrode 23. The carbon monoxide detection unit includes a detection circuit 25, a wiring connecting the first electrode 22 and the detection circuit 25, and a wiring connecting the second electrode 23 and the detection circuit 25. .. The detection circuit 25 and the wiring can be selected from the same options as described in the first embodiment. The carbon monoxide detection unit can obtain an electromotive force between the first electrode 22 and the second electrode 23, and can detect carbon monoxide.

The third electrode 24 is provided on the inner wall portion of the solid electrolyte substrate 21, which corresponds to the tip portion of the test tube shape. In the illustrated embodiment, the third electrode 24 is connected to the second electrode 23 via the solid electrolyte substrate 21 so as to be ionically conductive, and has a positional relationship in which the third electrode 24 substantially opposes the second electrode 23. Functions as an electrode in contact with the calibration gas. The material and manufacturing method of the third electrode 24 can be selected from the same options as those exemplified for the second electrode 13 (counter electrode) of the first embodiment, and preferably the second electrode in the present embodiment. The material and manufacturing method of the electrode 23 are the same. Further, in the present embodiment, the third electrode 24 is configured to be shielded by the solid electrolyte substrate 21 from the atmosphere in contact with the second electrode 23, that is, the measurement target gas atmosphere.

An oxygen detector is connected between the second electrode 23 and the third electrode 24. The oxygen detection unit includes a detection circuit 26, a wiring that connects the second electrode 23 and the detection circuit 26, and a wiring that connects the third electrode 24 and the detection circuit 26. The detection circuit 26 and the wiring may be the same as those described in the first embodiment. The oxygen detector can detect oxygen by measuring the electromotive force due to the difference between the oxygen concentration of the atmosphere in contact with the second electrode 23 and the oxygen concentration in contact with the third electrode 24 via the wiring. ..

In the gas sensor according to this aspect, a solid electrolyte substrate 21 having first to third electrodes 22, 23, 24 formed therein is housed in a casing 27. The inner wall of the casing 27 may optionally be provided with a heater (not shown). The heater can be provided around the solid electrolyte substrate 21 in a manner capable of heating the solid electrolyte substrate 21, and can be connected to an external power source. The configuration of the heater can be selected from the modes described in the first embodiment.

A gas detection method by the gas sensor according to this aspect will be described. The gas sensor according to this aspect can be directly inserted into a flue or the like through which a high-temperature measurement target gas flows, and can measure carbon monoxide and oxygen concentrations. In this case, generally, the tip of the solid electrolyte substrate 21, that is, the position where the second electrode 23 is provided, has the highest temperature, and the temperature becomes lower as it approaches the base, and the temperature distribution is generally from the tip. Depends on the distance. The measurement target gas is introduced into the outer periphery of the solid electrolyte substrate 21 in the casing 27, and the calibration gas, for example, air is introduced into the inner periphery of the solid electrolyte substrate 21. These introduction paths are hermetically closed so that the two atmospheres are not mixed. Then, the solid electrolyte substrate 21 is heated to 500° C. or higher by the heat of the measurement target gas itself or by the heater, so that the measurement target gas contacting the electrode 23 of the second electrode contacts the third electrode 24. Due to the difference in oxygen partial pressure from the calibration gas, an electromotive force is generated in the solid electrolyte substrate 21 (stabilized zirconia member), and by measuring this electromotive force, the oxygen concentration in the measurement target gas can be obtained. it can. Similarly, when carbon monoxide is present in the measurement target gas, an electromotive force based on the mixed potential is generated between the first electrode 22 and the second electrode 23, and the carbon monoxide in the measurement target gas is generated. The concentration can be obtained. According to the gas sensor of the first aspect, since the oxygen detection electrode is commonly used as the counter electrode for carbon monoxide detection, it is not necessary to separately provide a counter electrode for carbon monoxide detection, and the cost for forming the electrode can be reduced. There is.

The sensor according to the second embodiment is not limited to the illustrated first mode, and various modifications are possible. As another aspect, a carbon monoxide and oxygen gas sensor according to the second aspect of the second embodiment will be described with reference to FIGS. 4 and 5. FIG. 4 is a schematic plan view of the gas sensor according to the second aspect, and FIG. 5 is a schematic sectional view of the gas sensor according to the second aspect. The sensor 3 according to the second aspect includes a fourth electrode 38 in addition to the solid electrolyte substrate 31, the first electrode 32, the second electrode 33, and the third electrode 34. Then, in place of the carbon monoxide detection unit connected to the first and second electrodes in the first aspect, carbon monoxide including the detection circuit 35 connected to the first electrode 32 and the fourth electrode 38. A detection unit is provided. The oxygen detection unit including the detection circuit 36 is connected to the second electrode 33 and the third electrode 34.

The fourth electrode 38 can be provided on the outer wall surface of the test tube-shaped solid electrolyte substrate 31 described in the first embodiment. The installation location of the fourth electrode 38 is, for example, a position where the distance from the tip of the test tube-shaped solid electrolyte substrate 31 is substantially the same as that of the first electrode 32, that is, the first electrode 32 and the fourth electrode 38. It is preferable that the temperatures of the electrodes 38 are substantially the same. Then, it suffices that the fourth electrode 38 is connected to the first electrode 32 via the solid electrolyte substrate 31 so as to be ionic conductive. The sintered body forming the fourth electrode 38 and the method of manufacturing the same may be the same as those of the second electrode 23 in the first aspect. The fourth electrode 38 functions as a counter electrode for carbon monoxide detection. With such a configuration, as compared with the first embodiment, the fourth electrode 38 serving as a counter electrode for carbon monoxide detection is arranged on the low temperature side, combustion of carbon monoxide is prevented, and highly accurate detection is performed. It can be performed.

In the second aspect, on a single solid electrolyte substrate 31, a first electrode 32 that functions as a working electrode for carbon monoxide detection, a fourth electrode 38 that functions as a counter electrode for carbon monoxide detection, and oxygen. It includes a second electrode 33 that functions as an electrode that contacts the measurement target gas for detection, and a third electrode 34 that functions as an electrode that contacts the calibration gas for oxygen detection. And the 3rd electrode 34 is comprised so that it may be in the atmosphere shielded from the measuring object gas. With such a configuration, the oxygen concentration and the carbon monoxide concentration in the measurement target gas can be detected as in the first aspect of the second embodiment. In the carbon monoxide and oxygen gas sensor according to the second aspect of the second embodiment, in particular, it becomes possible to dispose the first electrode 32 and the fourth electrode 38 at the same temperature position, thereby making CO more sensitive. It is advantageous in that it can be detected.

As another example, a carbon monoxide and oxygen gas sensor according to the third aspect of the second embodiment will be described with reference to FIG. FIG. 6 is a schematic plan view of the gas sensor according to the third aspect. The sensor 4 according to the third aspect includes a carbon monoxide gas sensor unit 41 and an oxygen gas sensor unit 42 separately in a single casing 43. That is, a first solid electrolyte substrate 411, a first electrode 412 provided on the first solid electrolyte substrate, a first solid electrolyte substrate provided on the first solid electrolyte substrate, and the first electrode and the first solid electrolyte substrate are provided. A carbon monoxide gas sensor unit 41 including a second electrode 413 that is ionically connected via a solid electrolyte substrate, a second solid electrolyte substrate 421, and a second solid electrolyte substrate provided on the second solid electrolyte substrate. A third electrode 423, and a fourth electrode (not shown) provided on the second solid electrolyte substrate and connected to the third electrode and the second solid electrolyte substrate in an ion conductive manner. An oxygen gas sensor section including

The carbon monoxide gas sensor unit 41 in the third aspect can be configured similarly to the carbon monoxide gas sensor in the first embodiment. That is, the first solid electrolyte substrate 411 is provided with a first electrode 412 functioning as a working electrode and a second electrode 413 functioning as a counter electrode in a manner capable of ion conduction, and these electrodes are provided with a detection circuit. It is also possible to adopt a configuration in which a detection unit (not shown) including is connected. The compositions and manufacturing methods of the first electrode 412 and the second electrode 413 may be the same as those of the working electrode and the counter electrode in the first embodiment. The shape of the illustrated first solid electrolyte substrate is a flat plate shape like the first embodiment, but may be the test tube shape shown in FIGS. 2 to 5, and the first electrode and the second electrode However, it may be any mode as long as it can contact the measurement target gas.

On the other hand, the oxygen gas sensor unit includes, on the second solid electrolyte substrate 421, a third electrode 423 that functions as an electrode that contacts the measurement target gas for oxygen detection, and an electrode that contacts the calibration gas for oxygen detection. And a fourth electrode that functions as an ion conductive member, and a detection unit (not shown) including a detection circuit may be connected to these electrodes. The shape of the second solid electrolyte substrate may be the test tube shape shown in FIGS. 2 to 5 or may be the flat plate shape, but the third electrode 423 comes into contact with the gas to be measured, The electrode is cut off from the measurement target gas atmosphere and comes into contact with the calibration gas. When the third electrode and the fourth electrode are formed on the flat plate-shaped solid electrolyte substrate (not shown), for example, the third electrode is formed on one surface of the flat plate-shaped solid electrolyte substrate, A structure in which the fourth electrode is formed on the other surface, and the flow path of the gas to be measured and the flow path of the calibration gas are blocked in the casing by another member that is hermetically bonded to the solid electrolyte substrate. Can be The composition and manufacturing method of the third electrode 423 and the fourth electrode can be the same as those of the counter electrode of the carbon monoxide gas sensor described in detail in the first embodiment, and the sintering including Pt particles and solid electrolyte particles. It is preferably the body.

In the third aspect, the carbon monoxide gas sensor portion 41 and the oxygen gas sensor portion 42 can be combined in any manner in the same casing 43. For example, the carbon monoxide gas sensor unit 41 and the oxygen gas sensor unit 42 according to the third aspect can be installed while changing their positional relationships while maintaining their respective structures. Specifically, the placement positions of the first electrode 412 and the second electrode 413 can be controlled in a more suitable mode for detecting carbon monoxide, and the placement positions can be set at optimal positions according to the temperature distribution in the casing. Alternatively, a heater for heating the carbon monoxide gas sensor portion may be optionally provided. The mode of the heater in this case may be the mode described in the first embodiment. Further, also in the third aspect, as in the first aspect, it is possible to optionally provide a heater. In this case, a heater can be provided around the oxygen gas sensor portion 42 in a manner capable of heating the portion of the second solid electrolyte substrate 421 where the electrode is provided.

The principle of carbon monoxide gas detection and oxygen gas detection in this embodiment is the same as that described in the first embodiment. In particular, the carbon monoxide and oxygen gas sensor according to the present aspect can be provided at a location showing an optimum temperature for carbon monoxide detection because the carbon monoxide detection electrode pair is independent of the oxygen detection electrode pair. Become.

(Example 1)
The CO gas sensor according to the first embodiment of the present invention was manufactured. As a solid electrolyte substrate, a pair of electrodes composed of a first electrode and a second electrode was formed on a yttria-stabilized zirconia substrate (manufactured by Nippon Kagaku Sangyo, product number ZR-8Y). The first electrode (working electrode) was a mixture (mixture) of alloy particles (average particle size 1.5 μm) having a composition ratio of Rh and Pt of 65:35 and yttria-stabilized zirconia particles (average particle size 0.5 μm). A mass ratio 80:19) was molded using a paste in which an organic solvent (ethyl cellulose was dissolved in 224 trimethyl 3-hydroxypentyisobutyrate) was dispersed. The second electrode (counter electrode) was a mixture of Pt particles (average particle size 1.5 μm) and yttria-stabilized zirconia particles (average particle size 0.5 μm) (mixing mass ratio 80:19) in the same organic solvent as above. It was molded using the paste dispersed in. In addition, Pt wire was used as the wiring, and it was fixed on the electrode with each electrode material. Then, these were fired at 1350° C. in the atmosphere to prepare a sensor structure including the first and second electrodes and wiring. Then, a gas contact process was implemented. Specifically, a mixed gas having a composition ratio (volume ratio) CO:O ₂ :N ₂ =0.2:3.0:96.8 is heated to 800° C., and the sensor structure is mixed for a predetermined time. Contacted with gas. The contact step was carried out with the holding time set to 2.5 hours, 5 hours, and 7.5 hours, and the detection circuit was connected to produce three types of gas sensors.

(Example 2)
A gas sensor structure was manufactured in the same manner as in Example 1 except that the composition of the first electrode (working electrode) was changed as follows. The composition of the first electrode (working electrode) was a mixture of alloy particles of Au and Pt with a composition ratio of 1:99 (average particle diameter 1.5 μm) and yttria-stabilized zirconia particles (average particle diameter 0.5 μm). (Mixed mass ratio 80:19). The gas contact step was performed in the same manner as in Example 1 to produce three types of gas sensors.

(Evaluation of Examples 1 and 2)
When the gas sensors of Example 1 and Example 2 were changed from an atmosphere of oxygen 3.0 vol%, CO 50 ppm, nitrogen balance atmosphere to an atmosphere of oxygen 3.0 vol%, CO 2000 ppm, nitrogen balance at an ambient temperature of 700° C. Table 1 shows the relative comparison results of the output changes. In the table, the sensor output means the first output of each gas sensor when the potential difference between the first electrode and the second electrode of the gas sensor manufactured with the holding time in the mixed gas being 2.5 hours is 1. It can be defined by the ratio of the potential difference between the electrode and the second electrode.

Table 1 shows that the sensor output increases depending on the contact time with the mixed gas (holding time in the mixed gas) regardless of the electrode composition.

(Example 3)
A carbon monoxide and oxygen gas sensor according to the second embodiment of the present invention was manufactured. A gas sensor having the configuration of FIGS. 2 and 3 was produced in line with the first aspect of the second embodiment. The composition of the solid electrolyte substrate was the same as in Example 1. The composition of the first electrode was the same as that of the working electrode of Example 1, and the compositions of the second and third electrodes were the same as those of the counter electrode of Example 1. As a result, although the data are not specified, the results of the range in which both the output of the carbon monoxide sensor and the output of the oxygen sensor function as a sensor were obtained.

(Example 4)
A sensor was manufactured in the same manner as in Example 1 except that the composition ratio of the Pt-Rh alloy was changed in the first electrode, which is the working electrode for detecting CO. That is, three types of Pt—Rh alloy particles having a mass ratio of Rh and Pt of 40:60, 50;50, and 60:40, respectively, were mixed with the stabilized zirconia particles in the same manner as in Example 1. Next, a paste prepared by dispersing the mixture in an organic solvent was formed by screen printing so that the printed film thickness became a predetermined thickness, and the paste was baked at 1300° C. in the atmosphere. In order to measure the electromotive force of the electrode, a Pt wire was baked and fixed at 1000° C. in the atmosphere using a paste having an electrode composition.

(Example 5)
A sensor was manufactured in the same manner as in Example 2 except that the composition ratio of the Pt—Au alloy was changed in the first electrode, which is the working electrode for detecting CO. That is, two types of Pt—Au alloy particles having a mass ratio of Au and Pt of 1:99 and 5:95, respectively, were mixed with the stabilized zirconia particles in the same manner as in Example 2. Next, a paste prepared by dispersing the mixture in an organic solvent was formed by screen printing so that the printed film thickness became a predetermined thickness, and the paste was baked at 1300° C. in the atmosphere. In order to measure the electromotive force of the electrode, a Pt wire was baked and fixed at 1000° C. in the atmosphere using a paste having an electrode composition.

(Evaluation of Examples 4 and 5)
Using the gas sensors of Example 4 and Example 5, the oxygen concentration was set to 3%, the CO concentration was increased stepwise from 0 ppm to 2000 ppm, and the electromotive force ΔEwc between the first electrode and the second electrode was measured. The temperature was measured in the order of the preset temperature of the electric furnace: 600°C, 650°C, 700°C, 750°C, 800°C. As the sensor temperature, a measured value of a thermocouple placed in the vicinity of the sensor (about +15°C with respect to the set value of the electric furnace) was used.

FIG. 7 is a graph showing the relationship between the CO sensitivity and the composition ratio of Pt and Rh forming the first electrode at a sensor temperature of 615° C. of the gas sensor of Example 4. The horizontal axis represents the mass ratio of Rh in the metal particles made of Pt-Rh alloy constituting the electrode (the mass ratio of Rh to the total mass of Pt and Rh), and the vertical axis represents the first electrode (W) which is the working electrode. Shows the electromotive force ΔEwc (mV) between the second electrode (C) which is the opposite electrode. The graph shows the characteristics when the CO concentration is 200 ppm. The characteristic lines (5 μm, 14 μm, 23 μm) in the graph represent the film thickness of the first electrode (after firing). The film thickness of the second electrode (after firing) was 10 μm in each case. Although not shown, the characteristics shown in FIG. 7 showed a similar tendency even at CO concentrations up to 2000 pm.

FIG. 8 shows the CO gas concentration, the first electrode and the first electrode in the gas sensor of Example 4 in which the mass ratio of Rh in the metal particles made of Pt—Rh alloy is 0.6 and the thickness of the first electrode is 14 μm. The relationship with the electromotive force ΔEwc (mV) between the two electrodes is shown. Sufficient CO sensitivity was obtained in the range of 600 to 800° C. and in the range of CO concentration to be detected.

FIG. 9 is a graph showing the relationship between the CO sensitivity and the composition ratio of Au and Pt forming the first electrode at a sensor temperature of 615° C. in the gas sensor of Example 5. The horizontal axis represents the mass ratio of Au in the metal particles made of AuPt alloy that composes the electrode (the mass ratio of Au to the total mass of Au and Rh), and the vertical axis represents the counter electrode with the first electrode (W) that is the detection electrode. Shows the electromotive force ΔEwc (mV) between the second electrodes (C). The graph shows the characteristics when the CO concentration is 200 ppm. The characteristic lines (5 μm, 14 μm, 23 μm) in the graph represent the film thickness of the first electrode (after firing). The film thickness of the second electrode (after firing) was 10 μm in each case.

FIG. 10 shows the CO gas concentration, the first electrode and the first electrode in the gas sensor of Example 5 in which the mass ratio of Au in the metal particles made of Pt-Au alloy is 0.05 and the thickness of the first electrode is 5 μm. The relationship with the electromotive force ΔEwc (mV) between the two electrodes is shown. Sufficient CO sensitivity was obtained in the range of 600 to 800° C. and in the range of CO concentration to be detected.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the specific embodiments, and various modifications are possible within the scope of the gist of the present invention described in the claims. -Can be changed.

The gas sensor according to the present invention can detect CO in a high temperature environment, and can be inserted into a flue such as a boiler to monitor the CO concentration in combustion exhaust gas. Combining with an existing oxygen concentration sensor makes it possible to construct a combustion control system such as a boiler, thus contributing to energy saving.

1 Carbon monoxide gas sensor 2, 3, 4 Carbon monoxide and oxygen gas sensor 41 Carbon monoxide gas sensor part, 42 Oxygen gas sensor part 11, 21, 31, 411, 421 Solid electrolyte substrate 12 1st electrode, 13 2nd electrode 22 first electrode, 23 second electrode, 24 third electrode 32 first electrode, 33 second electrode, 34 third electrode, 38 fourth electrode 412 first electrode, 413 second Electrode, 423 Third electrode 25, 26, 35, 36 Detection circuit 27, 37, 43 Casing

Claims (13)

A solid electrolyte substrate,
Includes at least a pair of electrodes that are ionically connected through the solid electrolyte substrate,
The pair of electrodes,
A first electrode composed of a sintered body containing metal particles selected from alloy particles of platinum and rhodium or alloy particles of platinum and gold; and solid electrolyte particles;
A carbon monoxide gas sensor including a second electrode formed of a sintered body containing platinum particles and solid electrolyte particles. The gas sensor according to claim 1, wherein the solid electrolyte substrate and the solid electrolyte particles include stabilized zirconia. A method for manufacturing a carbon monoxide gas sensor according to claim 1 or 2, wherein
Forming the first and second electrodes on the solid electrolyte substrate;
A step of bringing the solid electrolyte substrate having the first and second electrodes formed thereon into contact with a mixed gas containing carbon monoxide, oxygen, and nitrogen gas under a temperature condition of 800° C. or higher for 4 hours or longer. Method. A method for detecting carbon monoxide gas using the gas sensor according to claim 1 or 2,
A method comprising: measuring a potential difference between the first and second electrodes in an atmosphere in which the temperature of the solid electrolyte substrate is 500° C. or higher. A solid electrolyte substrate,
A first electrode provided on the solid electrolyte substrate;
A second electrode provided on the solid electrolyte substrate and connected to the first electrode via the solid electrolyte substrate so as to be ionically conductive;
A third electrode provided on the solid electrolyte substrate and electrically connected to the second electrode via the solid electrolyte substrate;
A carbon monoxide and oxygen gas sensor comprising:
The first electrode is a sintered body containing metal particles selected from alloy particles of platinum and rhodium or alloy particles of platinum and gold, and solid electrolyte particles,
The second and third electrodes are sintered bodies containing platinum particles and solid electrolyte particles,
A gas sensor in which an atmosphere in contact with the first and second electrodes and an atmosphere in contact with the third electrode are blocked. The gas sensor according to claim 5, further comprising a carbon monoxide detection unit connected to the first and second electrodes and an oxygen detection unit connected to the second and third electrodes. A fourth electrode provided on the solid electrolyte substrate and electrically connected to the first electrode via the solid electrolyte substrate;
A carbon monoxide detection circuit connected to the first and fourth electrodes,
Further comprising an oxygen detector connected to the second and third electrodes,
The fourth electrode is in the same atmosphere as the first electrode,
The gas sensor according to claim 5, wherein the fourth electrode is a sintered body containing platinum particles and solid electrolyte particles. The solid electrolyte substrate is a tubular structure whose one end is a closed end, the first and second electrodes are provided on an outer wall portion of the tubular structure, and the third electrode is an inner wall of the tubular structure. The gas sensor according to any one of claims 5 to 7, which is provided in the portion. The gas sensor according to claim 7, wherein the fourth electrode is provided on an outer wall portion of the tubular structure. A first solid electrolyte substrate;
A first electrode provided on the first solid electrolyte substrate;
A carbon monoxide gas sensor unit provided on the first solid electrolyte substrate, comprising the first electrode and a second electrode connected in an ion conductive manner via the first solid electrolyte substrate;
A second solid electrolyte substrate,
A third electrode provided on the second solid electrolyte substrate,
An oxygen gas sensor unit provided on the second solid electrolyte substrate and provided with the third electrode and a fourth electrode connected in an ion conductive manner via the second solid electrolyte substrate is provided in a casing. A carbon monoxide and oxygen gas sensor, comprising:
The first electrode is a sintered body containing metal particles selected from alloy particles of platinum and rhodium or alloy particles of platinum and gold, and solid electrolyte particles,
The second, third and fourth electrodes are sintered bodies containing platinum particles and solid electrolyte particles,
A gas sensor in which an atmosphere in contact with the first, second, and third electrodes and an atmosphere in contact with the fourth electrode are blocked. A method of manufacturing a gas sensor according to claim 5, wherein
Forming an electrode including at least the first, second and third electrodes on the solid electrolyte substrate;
The solid electrolyte substrate on which the electrodes including the first, second and third electrodes are formed is mixed with a mixed gas containing carbon monoxide, oxygen and nitrogen gas at a temperature of 800° C. or higher for 4 hours or longer. Contacting. The metal particles contained in the first electrode are alloy particles of platinum and rhodium, and the mass ratio of platinum and rhodium is 3:7 to 5:5,
The gas sensor according to claim 1, wherein the film thickness of the first electrode is 10 to 20 μm, and the film thickness of the second electrode is 10 to 32 μm. The metal particles contained in the first electrode are alloy particles of platinum and gold, and the mass ratio of platinum and gold is 98:2 to 90:10,
The gas sensor according to claim 1, wherein the film thickness of the first electrode is 1 to 15 μm, and the film thickness of the second electrode is 10 to 32 μm.