JP2022140082A - gas detector - Google Patents

Abstract

To provide a gas detector that can detect both a carbon monoxide gas and an oxygen gas with high sensitivity.SOLUTION: A gas detector includes a carbon monoxide and oxygen gas sensor 10 in a casing 11. The carbon monoxide and oxygen gas sensor 10 includes a solid electrolyte substrate 1 that forms a tubular structure with one end closed, a carbon monoxide sensing action electrode 2 and a carbon monoxide sensing counter electrode 3 that are connected with ion conductivity on an outer surface of the solid electrolyte substrate through the solid electrolyte substrate, an oxygen sensing action electrode 4 provided on the outer surface of the solid electrolyte substrate, an oxygen sensing counter electrode 5 provided on an inner surface of the solid electrolyte substrate, and a heater 7 inserted into the tubular structure formed by the solid electrolyte substrate.SELECTED DRAWING: Figure 1

Description

The present invention relates to gas detectors. In particular, it relates to a gas detector equipped with a gas sensor capable of detecting both carbon monoxide and oxygen with high sensitivity.

For the detection and determination of the concentration of carbon monoxide gas constituents in the gas mixture to be measured, it is conventionally known to use sensors constructed on the basis of solid electrolytes and operated according to the mixed-potential principle (e.g. , see Patent Document 1).

Patent document 1 discloses a gas sensor by the applicant. The gas sensor forms a pair of electrodes on a solid electrolyte substrate and measures the electromotive force generated between the electrodes to selectively emit carbon monoxide gas at a high output in a high temperature environment exceeding 500 ° C. As well as being able to detect, oxygen gas can also be detected.

JP 2020-095014 A

The carbon monoxide gas sensor disclosed in Patent Document 1 may not be able to obtain sufficient electromotive force depending on the structure around the solid electrolyte substrate on which the pair of electrodes is formed, and it may be difficult to detect carbon monoxide gas. rice field. In particular, a gas sensor in which a pair of electrodes are formed on a solid electrolyte substrate is housed in a casing with one end being open so that the gas to be detected can flow in from the open end, and the surroundings of the solid electrolyte substrate are placed. In some cases, sufficient electromotive force cannot be obtained when the heater is heated by an annular heater provided on the inner wall of the casing.

As a result of intensive studies, the inventors have found that the flow velocity of the gas to be measured over the electrode for detecting carbon monoxide gas affects the electromotive force (gas sensitivity). Then, the present inventors came up with the flow velocity of the gas to be measured necessary to obtain a predetermined gas sensitivity and the structure for realizing this, and completed the present invention. More specifically, the problem was solved by adjusting the temperature of the electrode on the solid electrolyte substrate housed in the casing to within a predetermined temperature range, and creating a structure that allows convection of the gas to be measured inside the casing. rice field.

The present invention, according to one embodiment, is a gas detector comprising a carbon monoxide and oxygen gas sensor within a casing, comprising:
The carbon monoxide and oxygen gas sensors are
a solid electrolyte substrate forming a tubular structure with one closed end;
a carbon monoxide sensing working electrode and a carbon monoxide sensing counter electrode which are ionically conductively connected to the outer surface of the solid electrolyte substrate via the solid electrolyte substrate;
an oxygen detecting working electrode provided on the outer surface of the solid electrolyte substrate; an oxygen detecting counter electrode provided on the inner surface of the solid electrolyte substrate;
and a heater inserted into a tubular structure formed by the solid electrolyte substrate.

In the gas detector, it is preferable that the inner wall surface of the casing is provided with a heat insulating material.

In the gas detector, it is preferable that there is a clearance of 1.0 to 6.0 mm between the inner wall surface of the casing or a heat insulating material provided on the inner wall surface of the casing and the outer surface of the solid electrolyte substrate.

In the gas detector, the carbon monoxide detecting working electrode is a sintered body containing metal particles made of platinum-gold alloy particles and solid electrolyte particles,
The carbon monoxide detection counter electrode, the oxygen detection working electrode, and the oxygen detection counter electrode are preferably sintered bodies containing platinum particles and solid electrolyte particles.

According to another embodiment, the present invention is a method for detecting carbon monoxide gas and oxygen gas using the gas detector according to any one of the above, comprising:
a step of driving the heater, wherein the flow velocity of the gas to be measured on the carbon monoxide detection working electrode and the carbon monoxide detection counter electrode is set to 6.35 mm/s or more;
obtaining an electromotive force between the carbon monoxide sensing working electrode and the carbon monoxide sensing counter electrode;
obtaining an electromotive force between said oxygen sensing working electrode and said oxygen sensing counter electrode.

In the method for detecting carbon monoxide gas and oxygen gas, the temperatures of the carbon monoxide sensing working electrode and the carbon monoxide sensing counter electrode are set to about 600° C. to 750° C., and the temperatures of the oxygen sensing working electrode and the oxygen sensing counter electrode are set to about It is preferable to further include a step of setting the temperature to 700°C to 800°C.

The gas detector according to the present invention can detect both carbon monoxide and oxygen with high sensitivity.

FIG. 1 is a conceptual diagram showing the partial structure of the gas detector according to the first embodiment of the present invention. FIG. 2 is a conceptual diagram showing a partial cross-sectional structure of the gas detector according to the first embodiment of the present invention. FIG. 3 is a conceptual diagram showing a partial cross-sectional structure in the mode of use of the gas detector according to the first embodiment of the present invention. FIG. 4 is a conceptual diagram showing a partial structure of a gas detector according to a second embodiment of the invention. FIG. 5 is a conceptual diagram showing a partial cross-sectional structure of a gas detector according to a second embodiment of the present invention. FIG. 6 is a graph showing the relationship between the flow rate of 2000 ppm CO gas on the carbon monoxide detecting working electrode and the counter electrode and the electromotive force −Ewc (mV) between the carbon monoxide detecting working electrode and the counter electrode. 7 is a graph showing the relationship between the CO gas concentration and the electromotive force −Ewc (mV) between the carbon monoxide detection electrode and the counter electrode in the gas sensor of Example 1. FIG. 8 is a graph showing the relationship between the CO gas concentration and the electromotive force −Ewc (mV) between the carbon monoxide detection electrode and the counter electrode in the gas sensor of Example 2. FIG. FIG. 9 is a conceptual diagram showing a partial cross-sectional structure of a gas detector according to a comparative example.

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]
The present invention, according to a first embodiment, relates to a gas detection meter. In this embodiment, the gas detector comprises carbon monoxide and oxygen gas sensors. The carbon monoxide and oxygen gas sensor contains carbon monoxide (CO) gas and oxygen (O ₂ ) gas, which are detection target gases, and detects a temperature of approximately 500 ° C. or higher, for example, 600 to 500 ° C. This gas sensor is capable of separately detecting two detection target gases in an atmosphere of 800°C. Hereinafter, in this specification, carbon monoxide gas may be referred to as CO gas, and oxygen gas as O ₂ gas. Also, the carbon monoxide and oxygen gas sensors are sometimes abbreviated simply as gas sensors.

FIG. 1 is a partial schematic view of the gas detector according to the first embodiment, and FIG. 2 is a partial schematic sectional view. Further, FIG. 3 is a conceptual diagram in the case of using the gas detector by inserting it through a wall into a region in which the gas to be measured flows. A gas detector according to the first embodiment will be described below with reference to FIGS. In this specification, the drawings may not accurately show the relative dimensions between each member for the purpose of describing each embodiment. 1-3, the gas detector 20 comprises a tubular casing 11 having an open end 11a and a gas sensor 10 housed inside the casing.

The gas sensor 10 comprises a solid electrolyte substrate 1 forming a tubular structure with one closed end, and a carbon monoxide sensing working electrode connected to the outer surface of the solid electrolyte substrate in an ion-conducting manner through the solid electrolyte substrate. 2 and carbon monoxide detection counter electrode 3, an oxygen detection working electrode 4 provided on the outer surface of the solid electrolyte substrate 1, an oxygen detection counter electrode 5 provided on the inner surface of the solid electrolyte substrate 1, and the solid electrolyte substrate 1. a heater 7 inserted into the tubular structure to be formed, and a carbon monoxide detector and an oxygen detector. The gas sensor 10 according to this embodiment can be said to have a carbon monoxide gas sensor section and an oxygen gas sensor section provided on a common solid electrolyte substrate 1 . Each gas sensor unit will be described below.

The carbon monoxide gas sensor section according to this embodiment includes a solid electrolyte substrate 1, a carbon monoxide sensing working electrode 2, a carbon monoxide sensing counter electrode 3, and a carbon monoxide sensing section connected to these electrodes.

The solid electrolyte substrate 1, as shown in FIGS. 1 and 2, is a tubular structure with one end closed. More specifically, the solid electrolyte substrate 1 is formed in an elongated cylindrical body having a constant diameter and extending for a predetermined length. It has a test tube shape with a closed tip, which is the other end in the direction. The tip has a rounded curved shape. In the present specification, the cylindrical portion of the solid electrolyte substrate 1 having a constant diameter is referred to as the side wall portion of the solid electrolyte substrate 1, and the rounded curved portion is referred to as the tip portion. Further, the outer surface of the tubular structure is referred to as the outer surface of the solid electrolyte substrate 1 and the inner surface thereof as the inner surface of the solid electrolyte substrate 1 . The solid electrolyte substrate 1 is preferably made of stabilized zirconia, and examples thereof include zirconia stabilized by rare earth metal oxides 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.

A carbon monoxide detection working electrode 2 and a carbon monoxide detection counter electrode 3 are formed on the outer surface of the side wall portion of the solid electrolyte substrate 1 . In FIG. 1, the carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 are respectively formed in contact with the solid electrolyte substrate 1, and the carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 are spaced apart. The length Le from the tip of the solid electrolyte substrate 1 to the carbon monoxide sensing working electrode 2 may be approximately the same as the length from the _tip of the solid electrolyte substrate 1 to the carbon monoxide sensing counter electrode 3 . The length Le from each of the carbon monoxide detection working electrode 2 and the carbon _monoxide detection counter electrode 3 to the tip of the solid electrolyte substrate 1 is not particularly limited, but it depends on the installation position of the heater heating element 7a described later. , the length _Le is preferably such that the temperatures of the carbon monoxide detection working electrode 2 and the carbon monoxide detection counter electrode 3 are approximately the same. More specifically, when placed in the atmosphere to be measured and the heater is driven, the temperatures of both the carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 are set to 600 to 750°C. L _e can be determined as follows. The carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 are also configured to be in contact with the same gaseous atmosphere. Therefore, the carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 are arranged in such a manner that the atmosphere of the carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 is not blocked by the solid electrolyte substrate 1 or other members. do.

The carbon monoxide detection working electrode 2 and the carbon monoxide detection counter electrode 3 may be connected to each other through the solid electrolyte substrate 1 in an ion-conducting manner. Another ion-conductive member may be interposed between the counter electrode 3 and the counter electrode 3 . In addition to the carbon monoxide detection working electrode 2 and the carbon monoxide detection counter electrode 3, a reference electrode (not shown) may be further provided. Alternatively, two or more pairs of carbon monoxide sensing working electrodes and carbon monoxide sensing counter electrodes can be provided at different positions on the solid electrolyte substrate.

The carbon monoxide sensing working electrode 2 is a sintered body containing metal particles made of an alloy of platinum (Pt), a noble metal such as Pt, and gold (Au) or rhodium (Rh), and solid electrolyte particles. you can More specifically, the alloy is preferably an alloy of Pt and Au. Hereinafter, an alloy of Pt and Au may be referred to as a Pt—Au alloy. Such a sintered body is obtained by dissolving a mixture containing metal particles made of a Pt—Au alloy and solid electrolyte particles in an organic solvent such as ethyl cellulose dissolved in 2,2,4 trimethyl-3-hydroxypentyisobutyrate. The paste obtained by dispersing in an appropriate solvent is coated and molded, for example, in a thin layer shape on the solid electrolyte substrate 1, and fired at 1200 to 1400 ° C. in the atmosphere. .

The mass ratio of Pt and Au in the Pt—Au alloy used as the metal particles 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, more preferably 96:4 to 92:8. The metal particles made of the Pt—Au alloy preferably have an average particle size of about 0.5 to 2.5 μm, more preferably about 1 to 2 μm. As used herein, the average particle size refers to the average particle size measured by observation using a scanning electron microscope (SEM).

The solid electrolyte particles may be stabilized zirconia particles, and may be one or more selected from any stabilized zirconia exemplified as the material of the solid electrolyte substrate 1 . In addition, the stabilized zirconia may have the same composition as the stabilized zirconia that is the main component of the solid electrolyte substrate 1, or the stabilized zirconia may have a different composition. The solid electrolyte particles are particularly preferably yttria-stabilized zirconia particles. The solid electrolyte particles preferably have an average particle size of about 0.1 to 1 μm, more preferably about 0.2 to 0.5 μm. In addition, the relationship between the average particle sizes of the metal particles made of the Pt—Au alloy and the yttria-stabilized zirconia particles may be the same or different. is preferably larger than the particle size of the yttria-stabilized zirconia particles.

In the carbon monoxide sensing working electrode 2, the mass ratio of the metal particles made of the Pt—Au alloy and the solid electrolyte particles may be arbitrary and is not particularly limited, but is preferably 99:1 to 1:99. , 85:15 to 15:85. The film thickness of the carbon monoxide sensing working electrode 2 containing metal particles made of a Pt—Au alloy may be, for example, 1 to 15 μm, preferably 5 to 10 μm. The film thickness here refers to the film thickness of the sintered body after firing.

The carbon monoxide detection counter electrode 3 may be a sintered body containing Pt particles and solid electrolyte particles. 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—Au alloy. Also, 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 constituting the carbon monoxide sensing working electrode 2, preferably yttria-stabilized zirconia particles. In the carbon monoxide detection counter electrode 3, the mass ratio of the Pt particles and the solid electrolyte particles may be arbitrary, and is not particularly limited, but is preferably 99:1 to 1:99, and 85:15 to 15: About 85 is preferable. The method for producing the sintered body containing these particles may be the same as the method for producing the sintered body constituting the carbon monoxide sensing working electrode 2 . The film thickness of the carbon monoxide detection counter electrode 3 is not particularly limited. For example, it may be about 8 to 60 μm, and within this range there is no change in carbon monoxide detection characteristics. The film thickness here refers to the film thickness of the sintered body after firing.

The carbon monoxide detector includes detection circuitry and wiring. The wiring includes a wiring having one end connected to the carbon monoxide detection counter electrode 3 and the other end connected to the detection circuit. The detection circuit may be a general electrometer capable of measuring the electromotive force (potential difference) between the carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 . Also, 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.

Next, the oxygen gas sensor section according to this embodiment includes a solid electrolyte substrate 1, an oxygen detecting working electrode 4, an oxygen detecting counter electrode 5, and an oxygen detecting section (not shown) connected to these electrodes.

The oxygen sensing working electrode 4 is provided on the outer surface of the solid electrolyte substrate 1 , preferably on the outer surface of the tip portion of the solid electrolyte substrate 1 . That is, the oxygen sensing working electrode 4 is formed in the same atmosphere as the carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 . On the other hand, the oxygen detection counter electrode 5 is provided on the inner surface of the solid electrolyte substrate 1 , preferably on the inner surface of the tip portion of the solid electrolyte substrate 1 . In the illustrated embodiment, the oxygen sensing counter electrode 5 is ionically connected to the oxygen sensing working electrode 4 through the solid electrolyte substrate 1, and is positioned substantially facing the oxygen sensing working electrode 4 to detect oxygen. functions as an electrode in contact with the calibration gas for Therefore, the oxygen detecting counter electrode 5 is configured to be shielded by the solid electrolyte substrate 1 from the atmosphere with which the oxygen detecting working electrode 4 is in contact, that is, from the gas atmosphere to be measured.

The materials and manufacturing methods of the oxygen-sensing working electrode 4 and the oxygen-sensing counter electrode 5 can be selected from options similar to those exemplified for the carbon monoxide sensing counter electrode 3. Preferably, the material of the carbon monoxide sensing counter electrode 3 And the manufacturing method is the same. The film thicknesses of the oxygen detecting working electrode 4 and the oxygen detecting counter electrode 5 may be 10 to 60 μm, and the film thicknesses of the oxygen detecting working electrode 4 and the oxygen detecting counter electrode 5 may be the same or different.

An oxygen detector is connected between the oxygen detecting working electrode 4 and the oxygen detecting counter electrode 5 . The oxygen detection unit includes an oxygen detection circuit (not shown), wiring connecting between the oxygen detecting working electrode 4 and the oxygen detecting circuit, and wiring connecting between the oxygen detecting counter electrode 5 and the oxygen detecting circuit. including. The configuration of the oxygen detection circuit and wiring may be similar to the configuration of the carbon monoxide detection circuit and wiring. The oxygen detection unit can detect oxygen by measuring the electromotive force caused by the difference between the oxygen concentration of the atmosphere with which the oxygen detecting working electrode 4 is in contact and the oxygen concentration of the atmosphere with which the oxygen detecting counter electrode is in contact. can.

The heater 7 is inserted into a space formed inside the tubular structure of the solid electrolyte substrate 1, preferably fixed, and heats the solid electrolyte substrate 1 and the at least four electrodes from the inside of the solid electrolyte substrate 1. The heater 7 is mainly composed of a heating portion 7a and a wiring portion (supporting portion) 7b, and may have any shape as long as the heating portion 7a can be inserted into the internal space of the solid electrolyte substrate 1. FIG. An example of the heater 7 is a rod heater having a cylindrical heat-generating portion 7a, but is not limited to a specific shape. The heater 7 may have any specifications as long as it can heat the solid electrolyte substrate 1 and at least four electrodes provided in contact therewith to a predetermined temperature and can ensure insulation. More specifically, the carbon monoxide sensing working electrode 2 and carbon monoxide sensing counter electrode 3 are heated to 600 to 750°C, and the oxygen sensing working electrode 4 and oxygen sensing counter electrode 5 are heated to 700 to 800°C. I wish I could.

The insertion position of the heater 7 for heating to such a temperature is such that the heat generating portion 7a is in the vicinity of the oxygen detecting counter electrode 5 and the heat generating portion 7a does not come into contact with the oxygen detecting counter electrode 5 and the inner surface of the solid electrolyte substrate 1. is preferred. Therefore, the heater 7 can be fixed on the base end (not shown) side of the wiring portion 7b. The distance _Lh of the tip of the heat generating portion 7a from the tip of the solid electrolyte substrate 1 is not particularly limited, but can be, for example, 4.0 to 6.0 mm. Also, the distance between the side surface of the heat generating portion 7a and the inner surface of the side wall portion of the solid electrolyte substrate 1 is not particularly limited, but can be set to 0.5 to 1.0, for example. Further, the axial length of the tubular structure of the solid electrolyte substrate 1 of the heating portion 7a can be set to 1.0 to 10 mm.

The casing 11 is a cylindrical body having an open end 11a and extending for a predetermined length with a constant diameter. A filter (not shown) is attached to the open end 11 a so that the gas to be measured can enter the casing 11 . The casing 11 encloses the entire gas sensor 10 , and the gas sensor 10 is arranged such that a space serving as a flow path for the gas to be measured is formed between the casing 11 and the solid electrolyte substrate 1 . In this embodiment, the distance between the inner wall surface of the casing 11 and the outer surface of the solid electrolyte substrate ₁ is called a clearance L1. By increasing the clearance L1, the convection of the gas to be measured can be promoted, and the velocity of the gas to be measured above the carbon monoxide detecting working electrode ₂ and the counter electrode 3 can be increased. The clearance L ₁ is preferably constant over the entire length of the solid electrolyte substrate 1, and may be 1.5 to 6.0 mm, preferably 3.0 to 6.0 mm.

The casing 11 can detachably fix the gas sensor 10 at the proximal end, which is the end opposite to the open end 11a. Thereby, in the gas detector, only the gas sensor 10 portion can be replaced. When the gas sensor 10 is fixed to the casing 11 , the tubular casing 11 and the tubular solid electrolyte substrate 1 have substantially the same central axis, and the solid electrolyte substrate 1 is located near the free end 11 a of the casing 11 . is located at the tip of Thereby, the clearance L1 can be made constant over the entire length of the solid electrolyte substrate ₁ . Although the distance from the open end 11a to the tip of the solid electrolyte substrate 1 is not particularly limited, it is preferably 5 to 15 mm.

FIG. 3 is a conceptual diagram when the gas detector is used by inserting it into the wall of equipment where the gas to be measured flows. Gas detector 20 includes gas sensor 10 , casing 11 , mounting flange 13 , calibration gas inlet 14 , and terminal portion 15 . Then, it is directly inserted into a wall 30 such as a facility through which the gas to be measured flows. Gas detector 20 is secured to wall 30 at mounting flange 13 . In FIG. 3, the side where the casing 11 containing the gas sensor 10 protrudes with the wall 30 as the boundary is the atmosphere of the gas to be measured, such as a flue, and the side where the terminal portion 15 is arranged is the atmospheric atmosphere. A guide tube 12 is attached to the casing 11 in the flow path of the gas to be measured so that the gas to be measured is guided to the gas sensor 11 .

Next, a method for manufacturing a gas detector having such a configuration will be described. The manufacturing method of the gas detector according to this embodiment includes the following steps.
(1) a step of forming a carbon monoxide sensing working electrode 2, a carbon monoxide sensing counter electrode 3, an oxygen sensing working electrode 4, and an oxygen sensing counter electrode 5 on the solid electrolyte substrate 1; Inserting 7 and fixing to casing 11

First Step: Electrode and Wiring Forming Step In the electrode forming step, a carbon monoxide sensing working electrode 2 , a carbon monoxide sensing counter electrode 3 , an oxygen sensing working electrode 4 and an oxygen sensing counter electrode 5 are formed on the solid electrolyte substrate 1 . The material and method for forming each electrode are as described above. A paste made of the material of the carbon monoxide sensing working electrode 2 and a paste made of the materials of the carbon monoxide sensing counter electrode 3, the oxygen sensing working electrode 4, and the oxygen sensing counter electrode 5 were prepared, and these were placed on the solid electrolyte substrate 1 on a predetermined basis. Form in position and bake. The carbon monoxide detection working electrode 2 and the carbon monoxide detection counter electrode 3 are preferably formed so that the printed pattern of the electrodes reaches the vicinity of the open end of the solid electrolyte substrate 1 . Next, the wiring of the Pt wire is attached. Pt paste is preferably used for attaching wires to the oxygen-detecting working electrode 4 and the oxygen-detecting counter electrode 5, and is preferably fired at 950 to 1300.degree. Attachment of wires to the carbon oxide detecting working electrode 2 and carbon monoxide detecting counter electrode 3 is preferably performed by connecting the aforementioned printed pattern with a Pt wire and Pt paste in the vicinity of the open end and firing at 950 to 1300°C. The solid electrolyte substrate 1 may be a commercially available product, or may be manufactured by molding a solid electrolyte material into a desired shape prior to the first step. Through the first step, a gas sensor including a solid electrolyte substrate 1, a carbon monoxide sensing working electrode 2, a carbon monoxide sensing counter electrode 3, an oxygen sensing working electrode 4, an oxygen sensing counter electrode 5, and wiring can be obtained.

Second step: assembly step Next, the heater 7 is inserted into the solid electrolyte substrate 1 formed with the electrodes 2, 3, 4, and 5 obtained in the first step so that the heat generating portion 7a is at a predetermined position. , place and fix. Next, solid electrolyte substrate 1 is fixed to casing 11 at its proximal end. Further, the mounting flange 13, the calibration gas inlet 14, and the terminal portion 15 can be assembled to form a gas detector.

Next, a gas detection method using the gas detector according to this embodiment will be described. As shown in FIG. 3, the gas detector 20 can be directly inserted into a flue or the like through which the high-temperature gas to be measured flows to measure carbon monoxide and oxygen concentrations. In this case, generally, the tip of the solid electrolyte substrate 1 closest to the high-temperature gas to be measured, that is, the position where the oxygen detecting working electrode 4 is provided becomes the hottest. Then, the closer to the proximal end, the lower the temperature, and the temperature distribution generally depends on the distance from the distal end. A gas to be measured is introduced into the guide tube 12 and then into the outer periphery of the solid electrolyte substrate 1 inside the casing 11 . By driving the heater 7, the temperatures of the oxygen detecting working electrode 4 and the oxygen detecting counter electrode 5 are set to 700 to 800°C, and the temperatures of the carbon monoxide detecting working electrode 2 and the carbon monoxide detecting counter electrode 3 are set to 600 to 750°C. and Since the heater 7 is inside the tubular structure of the solid electrolyte substrate ₁ , a sufficient clearance L1 should be provided without forming a soaking zone in the flow path of the gas to be measured on the outer periphery of the solid electrolyte substrate 1. can provide a flow velocity of at least 6.35 mm/s to the gas to be measured. An electromotive force based on the mixed potential is generated between the carbon monoxide detecting working electrode 2 and the carbon monoxide detecting counter electrode 3, and the carbon monoxide concentration in the gas to be measured can be obtained.

On the other hand, a calibration gas such as air is introduced into the inner periphery of the solid electrolyte substrate 1 . These introduction paths are airtightly blocked so that the atmospheres of the gas to be measured and the gas for calibration are not mixed. By heating the solid electrolyte substrate 1 to 500° C. or higher, the difference in oxygen partial pressure between the measurement target gas in contact with the oxygen detecting working electrode 4 and the calibration gas in contact with the oxygen detecting counter electrode 5 causes the solid electrolyte substrate 1 to An electromotive force is generated in the (stabilized zirconia member), and the oxygen concentration in the gas to be measured can be obtained by measuring this electromotive force.

According to the first embodiment of the present invention, it is possible to give a flow velocity to the gas to be measured in the casing, detect carbon monoxide gas with sufficient sensitivity, and detect the concentration of oxygen gas. A detector can be obtained.

[Second embodiment]
The invention, according to a second embodiment, relates to a gas detection meter. The gas detector according to the second embodiment is characterized in that, in the gas detector according to the first embodiment, a heat insulating material is further provided on the inner wall of the casing. FIG. 4 is a partial schematic view of the gas detector according to the second embodiment, and FIG. 5 is a partial schematic sectional view. 4 and 5, the same members as in FIGS. 1 to 3 are given the same reference numerals. In the gas detector according to the second embodiment, the configuration of the gas sensor 10 and their relative positional relationship may be the same as in the first embodiment.

The heat insulating material 9 provided on the inner wall surface of the casing 11 may be a heat insulating material commonly used in electrical equipment that has the property of being heat resistant enough to be used at the operating temperature of the sensor. The heat insulating material 9 is preferably provided at least at a position facing the solid electrolyte substrate 1 on the inner wall surface of the casing 11 so as to surround the solid electrolyte substrate 1 . In one aspect, it can be provided continuously with the same thickness over almost the entire area from the free end 11a to the base end. However, the inner wall of the casing 11 may have a region where the heat insulating material is not provided, a discontinuous portion, or a portion with a different thickness. In this embodiment in which the heat insulating material 9 is provided, the distance between the heat insulating material 9 and the outer surface of the solid electrolyte substrate ₁ is defined as the clearance L2. The clearance L2 is preferably 1.0 to _2.5 mm, more preferably 1.5 to 2.5 mm.

According to the gas detector according to the second embodiment, by providing the heat insulating material 9 on the inner wall surface of the casing 11, while maintaining all the advantages of the first embodiment, power saving is achieved and heating of the casing 11 is reduced. can be prevented, and corrosion and damage to the casing 11 can be reduced.

(Example 1)
A CO and _O2 gas sensor according to the first embodiment of the present invention was manufactured. As the solid electrolyte substrate 1, a test tube-shaped yttria-stabilized zirconia substrate (manufactured by Nippon Kagaku Togyo Co., Ltd., product number ZR-8Y) having an inner diameter of 4 mm, an outer diameter of 6 mm, and a length of 97 mm was coated with a carbon monoxide detection working electrode on the outer surface. 2. A carbon monoxide detection counter electrode 3, an oxygen detection working electrode 4, and an oxygen detection counter electrode 5 were formed on the inner surface as shown in FIG. The carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 were formed at positions 21 mm from the tip of the solid electrolyte substrate 1, and the oxygen sensing working electrode 5 was formed on the curved surface of the tip. The oxygen detection counter electrode 5 was formed on the inner surface of the tip portion of the solid electrolyte substrate 1 facing the oxygen detection electrode 4 with the solid electrolyte substrate 1 interposed therebetween. The carbon monoxide detection working electrode 2 is a mixture (mixture mass ratio 80:19) in an organic solvent (ethyl cellulose dissolved in 2,2,4-trimethyl-3-hydroxypentyisobutyrate). The carbon monoxide detection counter electrode 3, the oxygen detection working electrode 4, and the oxygen detection counter electrode 5 are mixtures 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) was molded using a paste dispersed in the same organic solvent as above. In addition, Pt wires were used as wiring, and fixed on the electrodes with respective electrode materials. Then, by firing them at 1300° C. in the atmosphere, a sensor structure including each electrode and wiring was produced. After baking, the thickness of the carbon monoxide sensing working electrode was 9.6 μm, the thickness of the carbon monoxide sensing counter electrode was 8.8 μm, the thickness of the oxygen sensing working electrode was 25 μm, and the thickness of the oxygen sensing counter electrode was 30 μm. After that, a detection circuit for carbon monoxide and oxygen was connected to each electrode, and a heater 7 was fixed to the solid electrolyte substrate 1 . The heater 7 is a rod heater having a cylindrical heat generating portion with a diameter of 3 mm and an axial length of 100 mm. The gas sensor 10 thus obtained was fixed to a stainless steel casing 11 having an inner diameter of 18 mm to manufacture a gas detector. The clearance L1 was set to ₆ mm.

(Example 2)
A gas detector shown in FIGS. 4 and 5 was manufactured in the same manner as in Example 1 except that the inner wall surface of the casing 11 was covered with a heat insulating material having a thickness of 3.5 mm. The clearance L2 was set to _2.5 mm.

(Comparative example)
The structure of Example 2 was the same as that of Example 2, except that an annular heater was provided inside the heat insulating material of the inner wall surface of the casing, and was used as a comparative example. FIG. 9 is a conceptual partial cross-sectional view of a gas detector of a comparative example. In the comparative example, a heat insulating material 59, a heater 57, and a heat insulating material 59 are arranged in a coaxial tubular shape from the inner wall of the casing 511 toward the inside in the radial direction of the casing 511, and the adjacent members are in contact with each other. Further, the annular heater 57 is provided from the open end 511a of the casing 511 to a position that completely covers the tip of the solid electrolyte substrate 51, and faces the carbon monoxide detection working electrode 52 and the carbon monoxide detection counter electrode 53. could not be established. No heater was provided in the space inside the solid electrolyte substrate 51 . In the gas detector of the comparative example, the clearance L3 _, which is the distance between the heat insulating material 59 and the outer surface of the solid electrolyte substrate 51, was 0.65 mm.

(Evaluation of sensitivity by CO gas flow rate)
On a solid electrolyte substrate made of yttria-stabilized zirconia, a carbon monoxide detection working electrode, a carbon monoxide detection counter electrode, and wiring were prepared in the same manner as in Example 1, and a carbon monoxide detection circuit was connected to obtain CO gas. A carbon monoxide gas sensor for sensitivity evaluation by flow velocity was manufactured. CO gas was brought into contact with the working electrode and the counter electrode of the manufactured gas sensor for sensitivity evaluation while changing the flow rate, and the electromotive force -Ewc (mV) between the working electrode and the counter electrode was measured. The CO gas concentration was 2000 ppm and the electrode temperature was 620°C. In addition, the flow velocity here is the flow velocity of CO gas on the carbon oxide detection working electrode and the carbon monoxide detection counter electrode. It was measured by a method of obtaining the flow velocity from the gas flow rate in the quartz tube after heating. FIG. 6 is a graph showing the relationship between the CO gas flow rate and the electromotive force −Ewc (mV) between the carbon monoxide detecting working electrode and the counter electrode. From FIG. 6, in order to obtain an electromotive force of 50 mV, which is the sensitivity required for carbon monoxide detection, the flow velocity of CO gas on the carbon monoxide detection electrode and the carbon monoxide detection counter electrode should be set to about 6.35 mm / s. I found that I needed to do more.

(Evaluation of Examples 1 and 2 and Comparative Example)
Using the gas detectors of Example 1, Example 2, and Comparative Example, the oxygen concentration was set to 3%, and the CO concentration was increased from 0 ppm to 2000 ppm to detect the occurrence between the carbon monoxide detection working electrode and the carbon monoxide detection counter electrode. Power - Ewc was measured. The temperatures of the carbon monoxide detection working electrode 2 and the carbon monoxide detection counter electrode 3 in Examples 1 and 2 were 620°C, the temperature of the oxygen detection working electrode 4 was 750°C, and the temperature of the oxygen detection counter electrode 5 was 750°C. . In the detector of the comparative example, the temperatures of the carbon monoxide sensing working electrode 2 and the carbon monoxide sensing counter electrode 3 were 620°C, the temperature of the oxygen sensing working electrode 4 was 750°C, and the temperature of the oxygen sensing counter electrode 5 was 750°C.

FIG. 7 shows the relationship between the CO gas concentration and the electromotive force −Ewc between the carbon monoxide sensing working electrode and the carbon monoxide sensing counter electrode in the gas detectors of Example 1 and Comparative Example. FIG. 8 shows the relationship between the CO gas concentration and the electromotive force −Ewc between the carbon monoxide sensing working electrode and the carbon monoxide sensing counter electrode in the gas sensors of Example 2 and Comparative Example. In both Examples 1 and 2, sufficient CO sensitivity was obtained within the CO concentration range to be detected, whereas CO sensitivity was not obtained in the gas sensor of the comparative example. In addition, although not shown, the electromotive force between the oxygen sensing working electrode and the oxygen sensing counter electrode -Ewc was 40 mV or more in both Examples 1 and 2 and the comparative example, and the atmospheric oxygen concentration ( 21%) and the oxygen concentration (3%) of the atmosphere to be measured.

比較例のガス検出計では、測定対象ガスの速度が小さいため、一酸化炭素検知作用極５２及び対極５３表面に供給されるＣＯ量が少なく、ＣＯ供給と、気相ＣＯ酸化反応とが競争し、ＣＯが供給されても気相ＣＯ酸化反応で消費されてしまい、３相界面へ到達するＣＯ量が低下する。ゆえに、３相界面での酸化・還元反応が生じにくくなり、十分な起電力が得られなかったと考えられる。 Although not intending to be bound by theory, it is considered that the electromotive force could not be obtained in the gas detector of the comparative example due to the following mechanism. In the gas detector of the comparative example shown in FIG. 9, the flow path of the gas to be measured facing the annular heater 57 becomes a soak zone, and the flow velocity of the gas to be measured due to convection becomes zero. Therefore, the velocity of the gas to be measured on the carbon monoxide detecting working electrode 52 and the counter electrode 53 farther from the inflow port 511a of the gas to be measured also becomes close to zero. In a mixed-potential type carbon monoxide gas sensor configured based on a solid electrolyte, a gas phase CO oxidation reaction occurring in an electrode represented by the following formula (1) and a three-phase (gas phase) represented by the following formula (2) , electrode, solid electrolyte substrate) interface progresses. Then, on the solid electrolyte substrate under a heating atmosphere of about 500° C. or higher, an electromotive force resulting from the reaction of formula (2) is obtained due to conduction of oxygen ions.

In the gas detector of the comparative example, since the velocity of the gas to be measured is small, the amount of CO supplied to the surfaces of the carbon monoxide detection working electrode 52 and the counter electrode 53 is small, and the CO supply competes with the vapor-phase CO oxidation reaction. , even if CO is supplied, it is consumed in the vapor-phase CO oxidation reaction, and the amount of CO reaching the three-phase interface is reduced. Therefore, it is considered that the oxidation/reduction reaction at the three-phase interface is less likely to occur, and a sufficient electromotive force cannot be obtained.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and various modifications can be made within the scope of the gist of the invention described in the claims.・Changes are possible.

The gas detector according to the present invention can be inserted into the flue of a boiler or the like to simultaneously monitor the concentration of carbon monoxide and oxygen in combustion exhaust with sufficient sensitivity. Therefore, it becomes possible to construct a combustion control system such as a boiler, which contributes to energy saving.

Reference Signs List 1 Solid electrolyte substrate 2 Carbon monoxide detection working electrode 3 Carbon monoxide detection counter electrode 4 Oxygen detection working electrode 5 Oxygen detection counter electrode 7 Heater 7a Exothermic part 7b Wiring part 9 Heat insulating material 10 Gas sensor 11 Casing 11a Casing open end 12 guide tube 13 mounting flange 14 calibration gas inlet 15 terminal section 20 gas detector 30 wall g gas to be measured

Claims (6)

A gas detector comprising a carbon monoxide and oxygen gas sensor within a casing,
The carbon monoxide and oxygen gas sensors are
a solid electrolyte substrate forming a tubular structure with one closed end;
a carbon monoxide sensing working electrode and a carbon monoxide sensing counter electrode which are ionically conductively connected to the outer surface of the solid electrolyte substrate via the solid electrolyte substrate;
an oxygen detecting working electrode provided on the outer surface of the solid electrolyte substrate; an oxygen detecting counter electrode provided on the inner surface of the solid electrolyte substrate;
and a heater inserted into a tubular structure formed by the solid electrolyte substrate. 2. The gas detector according to claim 1, wherein said casing inner wall surface is provided with heat insulating material. 3. The gas according to claim 1, wherein there is a clearance of 1.0 to 6.0 mm between the inner wall surface of the casing or a heat insulating material provided on the inner wall surface of the casing and the outer surface of the solid electrolyte substrate. detector. The carbon monoxide sensing working electrode is a sintered body containing metal particles made of platinum and gold alloy particles and solid electrolyte particles,
The gas detector according to any one of claims 1 to 3, wherein the carbon monoxide sensing counter electrode, the oxygen sensing working electrode, and the oxygen sensing counter electrode are sintered bodies containing platinum particles and solid electrolyte particles. . A method for detecting carbon monoxide gas and oxygen gas using the gas detector according to any one of claims 1 to 4,
a step of driving the heater, wherein the flow velocity of the gas to be measured on the carbon monoxide detection working electrode and the carbon monoxide detection counter electrode is set to 6.35 mm/s or more;
obtaining an electromotive force between the carbon monoxide sensing working electrode and the carbon monoxide sensing counter electrode;
and obtaining an electromotive force between the oxygen sensing working electrode and the oxygen sensing counter electrode. The carbon monoxide sensing working electrode and the carbon monoxide sensing counter electrode are set at temperatures of about 600°C to 750°C, and the temperature of the oxygen sensing working electrode and the oxygen sensing counter electrode is set at about 700°C to 800°C. 6. The method according to item 5.

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