JP2021043022A - Solid electrolyte sensor - Google Patents

Abstract

To provide a solid electrolyte sensor that has a long durable period when the sensor can normally measure an electromotive force generated in a solid electrolyte in association with ion conductivity even when a measurement atmosphere is at high temperatures.SOLUTION: In a solid electrolyte sensor 1, a first space S1 and a second space S2 are divided since a sensor element 10, which is made of a solid electrolyte, is bottomed and cylindrical. The sensor includes: a first electrode 21 located in the outer surface in a closed end part of the sensor element; an electric conduction path 25 continuous to the first electrode, the path being a coating film made of the same metal as that of the first electrode and extending in the axial direction to the outer surface of the cylindrical part of the sensor element; and a second electrode 22 in the inner surface of the sensor element.SELECTED DRAWING: Figure 1

Description

The present invention relates to a solid electrolyte sensor.

Various solid electrolyte sensors have been proposed that detect the concentration of gases such as hydrogen gas, oxygen gas, carbon dioxide gas, and water vapor by using a solid electrolyte (ionic conductive ceramics) as a sensor element. I am making a proposal. These solid electrolyte sensors use the principle of a concentration cell in which a potential difference occurs in the solid electrolyte due to the difference in the concentration of the same ion, and when the concentration of the gas to be detected differs between the two spaces sandwiching the sensor element, Measure the electromotive force generated in the sensor element. If the concentration of the gas to be detected in the first space is known among the two spaces, the gas concentration in the second space can be known from the measured electromotive force and the temperature of the sensor element by the Nernst equation. it can. Alternatively, when the gas concentration is unknown by measuring the electromotive force by changing the gas concentration in the second space and creating a calibration curve in advance while the gas concentration in the first space is constant. The gas concentration in the second space can be known from the measured value of the electromotive force of.

Therefore, in such a solid electrolyte sensor, it is necessary that two spaces are partitioned by the sensor element. In the conventional solid electrolyte sensor proposed by the applicant, the sensor element is formed into a bottomed tubular shape, or the sensor element is fixed to one end or the middle of the tubular holder via a sealing material to form a holder. Two spaces are partitioned by forming a bottomed tubular shape in combination with the sensor element (see, for example, Patent Document 1).

When measuring the electromotive force generated by ion conduction, an electrode is provided on the surface of the sensor element that is in contact with one of the two spaces, and an electrode is also provided on the surface that is in contact with the other space. Is connected to the electrometer with a lead wire. Generally, a platinum electrode is used as an electrode, and a platinum wire is used as a lead wire.

However, if the measurement atmosphere is a high temperature atmosphere such as in an industrial furnace, the platinum wire used as the lead wire may be broken. If the lead wire is broken, the electromotive force cannot be measured, so it is necessary to remove the solid electrolyte sensor from the industrial furnace and repair it. Therefore, even if the other parts of the solid electrolyte sensor are normal, the useful life in which the electromotive force can be normally measured is shortened only by the disconnection of the lead wire, which has been a problem.

Japanese Unexamined Patent Publication No. 2016-027317

Therefore, in view of the above circumstances, it is an object of the present invention to provide a solid electrolyte sensor having a long service life, which can normally measure the electromotive force generated in the solid electrolyte due to ion conduction even when the measurement atmosphere is high temperature. It is a thing.

In order to solve the above problems, the solid electrolyte according to the present invention is used.
"The shape of the sensor element formed of the solid electrolyte is a bottomed cylinder, which separates the first space and the second space.
In the first space, the first electrode provided on the outer surface at the closed end of the sensor element and
A metal coating made of the same metal as the first electrode and formed on the outer surface of the tubular portion of the sensor element so as to extend in the axial direction, and an electric conduction path continuous with the first electrode.
In the second space, a second electrode provided on the inner surface of the sensor element is provided. "

The "metal film" provided on the outer surface of the sensor element is formed of the same metal as the first electrode, and can be formed by applying and baking a metal paste for an electrode. Examples of the metal paste for electrodes include platinum paste for electrodes, palladium paste for electrodes, and silver paste for electrodes.

The inventor of the present invention explains that the platinum wire used as a lead wire in a conventional solid electrolyte sensor may be broken when the measurement atmosphere is high temperature because the member constituting the sensor thermally expands. It was considered that a large tension acts on the platinum wire.

On the other hand, in this configuration, an electrical conduction path, which is a metal coating, is formed on the outer surface of the tubular portion of the sensor element as a configuration for conducting electrical conduction instead of the lead wire. The electric conduction path formed by the metal film has a “face” structure, and unlike a wire rod, there is no risk of breakage. Therefore, even if the measurement atmosphere is high temperature, the electromotive force generated in the solid electrolyte due to ionic conduction can be normally measured for a long period of time.

Since the metal film as the electric conduction path is formed of the same metal as the first electrode, the temperature of the part of the sensor element where the first electrode is provided and the part where the electric conduction path is formed are different. Even if they are different, no thermoelectromotive force is generated, so that the electromotive force associated with ion conduction can be accurately measured.

The solid electrolyte sensor according to the present invention has the above configuration instead of the above configuration.
"The sensor element formed of solid electrolyte is fixed to one end or the middle of the holder formed in a tubular shape with an electrically insulating material, and the overall shape is a bottomed tubular shape, so that the first space and the first space The two spaces are separated,
In the first space, the first electrode provided on the surface of the sensor element and
An electrical conduction path, which is the same metal as the first electrode and is a metal coating formed on the outer surface of the holder so as to extend in the axial direction.
A wire rod made of the same metal as the first electrode and connecting the first electrode and the electric conduction path, and
In the second space, a second electrode provided on the surface of the sensor element is provided. "

The above-mentioned solid electrolyte sensor has a configuration in which two spaces are partitioned only by the sensor element, but the solid electrolyte sensor having this configuration has two spaces by holding the sensor element in a tubular holder. Is a partitioned configuration. In this configuration, the electrical conduction path by the metal coating is formed on the outer surface of the holder made of an electrically insulating material. The electrical conduction path in the holder and the first electrode are connected by a metal wire.

Since this wire has a very short length, even if the solid electrolyte sensor is used in a high temperature atmosphere, the tension acting due to thermal expansion is not as large as that of the conventional lead wire, and the possibility of disconnection is small. That is, an electric conduction path having a "surface" structure and not likely to break like a wire is connected to the first electrode by a short wire having a small risk of disconnection. Therefore, even if the measurement atmosphere is high temperature, the electromotive force generated in the solid electrolyte due to ionic conduction can be normally measured for a long period of time.

Here, a solid electrolyte sensor in which the holder itself is made of metal and the end portion of the holder is pressed against an electrode to make the entire holder an electrical conduction path is commercially available. In the case of such a configuration, it is difficult to form the holder with a noble metal like the electrode, so that the type of metal differs between the holder and the electrode. Then, when the temperature differs between the sensor element and the holder, a thermoelectromotive force is generated, and the electromotive force generated in the solid electrolyte due to ionic conduction cannot be accurately measured. On the other hand, in this configuration, since the electric conduction path formed by the metal film and the wire rod for connecting the electric conduction path to the first electrode are made of the same metal, even if there is a connecting portion having a different temperature somewhere. , There is no risk of thermoelectromotive force.

Further, in a field where a solid electrolyte sensor is actually used such as an industrial furnace, a plurality of solid electrolyte sensors such as an oxygen sensor and a hydrogen sensor are often installed in one furnace. In such a case, if the holder itself is made of metal, the holders of the plurality of solid electrolyte sensors are energized through the electrically conductive furnace wall, and thus cannot be used. On the other hand, in this configuration, since an electric conduction path is partially formed on the surface of the holder made of an electrically insulating material, a plurality of solid electrolytes are formed even if the furnace wall is electrically conductive. The holders of each sensor will not be energized. Therefore, the solid electrolyte sensor having this configuration has an advantage that a plurality of solid electrolyte sensors can be installed in one furnace without any problem.

As described above, according to the present invention, it is possible to provide a solid electrolyte sensor having a long service life, which can normally measure the electromotive force generated in the solid electrolyte due to ion conduction even when the measurement atmosphere is high temperature.

FIG. 1A is a side view of the solid electrolyte sensor according to the first embodiment of the present invention, and FIG. 1B is a vertical sectional view of the solid electrolyte sensor according to the first embodiment. FIG. 2A is a vertical cross-sectional view of the solid electrolyte sensor according to the second embodiment, and FIG. 2B is a vertical cross-sectional view of the solid electrolyte sensor of the modified example.

Hereinafter, the solid electrolyte sensor, which is a specific embodiment of the present invention, will be described with reference to the drawings. In the solid electrolyte sensor of the present embodiment, the first space S1 and the second space S2 are partitioned by the sensor element 10 formed of the solid electrolyte. The two spaces are partitioned only by the sensor element 10, and in the solid electrolyte sensor 2 of the second embodiment, the two spaces are partitioned by holding the sensor element 10 in the holder 30. is there.

As shown in FIG. 1, the solid electrolyte sensor 1 has a bottomed tubular shape of the sensor element 10, so that two spaces are partitioned only by the sensor element 10. The bottomed tubular internal space is the second space S2, and the external space is the first space S1.

In the sensor element 10, the first electrode 21 is provided on the outer surface at the closed end portion, that is, the surface on the first space S1 side, and the second electrode 22 is provided on the surface on the second space S2 side. The first electrode 21 and the second electrode 22 are porous metal coatings formed by applying and baking a metal paste for electrodes. For example, both the first electrode 21 and the second electrode 22 are platinum electrodes. The first electrode 21 of the present embodiment is provided so as to orbit the closed end portion of the sensor element 10.

In the sensor element 10, a metal film is formed on the outer surface of the tubular portion so as to extend in the axial direction of the tubular portion, which constitutes the electric conduction path 25. The electrical conduction path 25 is formed by applying and baking the same electrode metal paste used to form the first electrode 21. The electrical conduction path 25 extends long in a strip shape in the axial direction of the tubular portion of the sensor element 10, and one end thereof is continuous with the first electrode 21. The other end of the electric conduction path 25 is formed to be wide so as to go around the tubular portion, and the first lead wire (not shown) is connected to the wide portion 25e. As the first lead wire, a wire rod 40 made of the same metal as the metal forming the first electrode 21 and the electric conduction path 25 is used.

A second lead wire 42 is connected to the second electrode 22. By connecting the first lead wire and the second lead wire 42 to an electrometer (not shown), the electromotive force generated between the first electrode 21 and the second electrode 22 is detected.

A thermocouple 51 for detecting the temperature of the sensor element 10 is inserted in the second space S2, and each wire of the thermocouple 51 and the second lead wire 42 are an electrically insulating rod 50. It is inserted into one of a plurality of holes pierced in the axial direction. Further, an introduction pipe 60 for introducing the reference gas is inserted in the second space S2. The reference gas is a gas having a known concentration of the detection target gas, but the atmosphere may be used as the reference gas. In that case, the second space S2 may be opened to the atmosphere without inserting the introduction pipe.

The solid electrolyte sensor 1 having the above configuration is used for inserting the closed end portion side of the sensor element 10 into a hole provided in a furnace wall of an industrial furnace or the like and detecting the gas concentration in the furnace. Therefore, the atmosphere of the first space S1 is the measurement atmosphere.

In the solid electrolyte sensor 1 of the first embodiment, a lead wire is used to measure the electromotive force generated between the first electrode 21 and the second electrode 22 in the portion placed in the high temperature measurement atmosphere. Absent. Since the portion of the sensor element 10 on the open end side can be placed outside the measurement atmosphere (outside the furnace), the first lead wire does not become hot and there is no risk of disconnection.

The electric conduction path 25, which is a metal film formed on the outer surface of the sensor element 10, has a “surface” structure and is unlikely to break like the wire rod 40. Therefore, even if the measurement atmosphere is high temperature, ions are formed. The electromotive force generated in the solid electrolyte due to conduction can be measured normally over a long period of time.

Since the metal coating as the electric conduction path 25 and the first lead wire are made of the same metal as the first electrode 21, the temperature of the connection portion between the first electrode 21 and the electric conduction path 25 and the electric conduction Even if the temperature of the connection portion between the path 25 and the first lead wire is different, no thermoelectromotive force is generated, and the electromotive force associated with ionic conduction can be accurately measured.

Next, the solid electrolyte sensor 2 of the second embodiment will be described. As shown in FIG. 2A, the solid electrolyte sensor 2 has a sensor element 10 formed of a solid electrolyte fixed to one end of a holder 30 formed of an electrically insulating material in a tubular shape. The first space S1 and the second space S2 are partitioned by the shape of the bottomed cylinder. The bottomed tubular internal space is the second space S2, and the external space is the first space S1.

The holder 30 is made of a material having electrical insulation and heat resistance, such as alumina ceramics and mullite ceramics. The sensor element 10 is fixed to one end of the holder 30 via a sealing material 39.

In the sensor element 10, the first electrode 21 is provided on the surface of the first space S1 side. Similar to the first embodiment, the first electrode 21 is a porous metal film formed by applying and baking a metal paste for an electrode.

A metal film is formed on the outer surface of the holder 30 in a strip shape extending in the axial direction, which constitutes the electric conduction path 25. The electric conduction path 25 is formed by applying and baking the same metal paste for electrodes used for forming the first electrode 21. On the end side of the holder 30 closer to the sensor element 10, the electric conduction path 25 is formed wide so as to orbit the holder 30, and a metal wire rod 40 connects this portion and the first electrode. There is. The wire rod 40 is the same metal wire rod 40 as the first electrode 21 and the electric conduction path 25. Although the wire rod 40 is very short, it is connected between the end of the electric conduction path 25 and the first electrode 21 so as to be slightly bent.

On the other end side of the holder 30, the electric conduction path 25 is formed wide so as to go around the holder 30, and a first lead wire (not shown) is connected to this portion. As the first lead wire, a wire rod 40 made of the same metal as the metal forming the first electrode 21, the wire rod 40, and the electric conduction path 25 is used.

The configuration of the solid electrolyte sensor 2 in the second space S2 is the same as the configuration of the solid electrolyte sensor 1 in the second space S2 (second electrode 22, second lead wire 42, thermocouple 51, introduction pipe 60).

Although FIG. 2A illustrates a case where the bottomed tubular sensor element 10 is opened inside the holder 30, the sensor element 10 is opened so as to be opened outside the holder 30. It may be fixed to the holder 30. Further, the shape of the sensor element 10 fixed to one end of the holder 30 is not limited to the bottomed tubular shape, but may be a columnar shape or a flat plate shape.

In the solid electrolyte sensor 2, the electric conduction path 25 made of a metal coating is formed on the outer surface of the holder made of an electrically insulating material, and the electric conduction path 25 and the first electrode 21 are connected by a metal wire 40. Has been done. Since the wire rod 40 has a very short length, even if the solid electrolyte sensor 2 is used in a high temperature atmosphere, the tension acting due to thermal expansion is not large and the possibility of disconnection is small. That is, the electric conduction path 25, which has a “surface” structure and is not likely to break like the wire rod 40, is connected to the first electrode by the short wire rod 40 having a small risk of disconnection. Therefore, even if the measurement atmosphere is high temperature, the electromotive force generated in the solid electrolyte due to ionic conduction can be normally measured for a long period of time.

Further, since the metal coating as the electric conduction path 25, the first lead wire, and the wire rod 40 are made of the same metal as the first electrode 21, the temperature of the connection portion between the first electrode 21 and the wire rod 40 , Even if the temperature of the connection part between the wire rod 40 and the electric conduction path 25 and the temperature of the connection part between the electric conduction path 25 and the first lead wire are different somewhere, no thermoelectromotive force is generated and ions are generated. The electromotive force associated with conduction can be measured accurately.

As a modification of the second embodiment, as shown in FIG. 2B, the sensor element 10 is fixed in the middle of the tubular holder 30 via the sealing material 39, so that there are two. It can be a solid electrolyte sensor 2b in which the space is partitioned. In this case, since the holder 30 and the sensor element 10 have a combined shape and have two bottomed tubular portions, the concept of distinguishing between the internal space and the external space does not occur, but one of them is the first space. Let S1 be, and let the other be the second space S2.

The solid electrolyte sensor 2b is different from the solid electrolyte sensor 2 in the fixed position of the sensor element 10 with respect to the holder 30, and the other configurations are the same as those of the solid electrolyte sensor 2. Even with such a configuration, the above-mentioned effects are exhibited.

Although FIG. 2B illustrates the case where the shape of the sensor element 10 is columnar, the shape of the sensor element 10 fixed in the middle of the holder 30 is not limited to the columnar shape, and is a bottomed cylinder. It can be in the shape of a flat plate or in the shape of a flat plate.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to the above embodiments, and as shown below, various improvements are made without departing from the gist of the present invention. And the design can be changed.

For example, in the above embodiment, the first electrode 21, the wire rod 40, the electric conduction path 25, and the first lead wire, which are configured to carry out electric conduction on the first space S1 side, are formed of the same metal. As illustrated, in addition to these, the second lead wire 42 can also be made of the same metal. By doing so, even if the temperature of the sensor element 10 is slightly different between the first electrode 21 side and the second electrode 22 side, the measured electromotive force may include the thermoelectromotive force. Can be eliminated.

1,2,2b Solid electrolyte sensor 10 Sensor element 21 First electrode 22 Second electrode 25 Electrical conduction path 30 Holder 40 Wire rod S1 First space S2 Second space

Claims (2)

The shape of the sensor element formed of the solid electrolyte is a bottomed cylinder, so that the first space and the second space are separated.
In the first space, the first electrode provided on the outer surface at the closed end of the sensor element and
A metal coating made of the same metal as the first electrode and formed on the outer surface of the tubular portion of the sensor element so as to extend in the axial direction, and an electric conduction path continuous with the first electrode.
A solid electrolyte sensor comprising: in the second space, a second electrode provided on the inner surface of the sensor element. The sensor element formed of the solid electrolyte is fixed to one end or the middle of the holder formed in the shape of a cylinder made of an electrically insulating material, and the overall shape is a bottomed cylinder, so that the first space and the second space and the second space are formed. The space is partitioned,
In the first space, the first electrode provided on the surface of the sensor element and
An electrical conduction path, which is the same metal as the first electrode and is a metal coating formed on the outer surface of the holder so as to extend in the axial direction.
A wire rod made of the same metal as the first electrode and connecting the first electrode and the electric conduction path, and
A solid electrolyte sensor comprising: in the second space, a second electrode provided on the surface of the sensor element.

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