JPH087182B2 - Carbon dioxide sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ion used in a place for measuring a carbon dioxide concentration such as for horticulture, environmental hygiene, disaster prevention, and industrial use or for controlling a device by using the measured value. The present invention relates to a solid electrolyte type carbon dioxide gas sensor having a structure using a conductor.

2. Description of the Related Art In recent years, the needs for carbon dioxide gas sensors have been increasing mainly in the fields of air conditioning and agriculture and livestock, and various gas sensors have been developed and put into practical use, but many problems remain in their reliability and stability. . Especially, water vapor, salt particles, cigarette smoke,
Durability against polluted environments such as oily smoke is a concern.

Hereinafter, an example of the conventional carbon dioxide gas sensor described above will be described with reference to FIGS. 6 and 7.

FIG. 6 and FIG. 7 show the structure of a conventional solid electrolyte type carbon dioxide gas sensor. In Fig. 6, thin plate NASICON as an ion conductor made of solid electrolyte
The (sodium ion conductor ceramics) plate 11 is fixedly provided with a pair of porous electrode layers 12a and 12b made of a material such as Au for extracting an electric signal at both ends thereof. A coating layer 13 made of a metal carbonate is formed on a part or all of either one of 12 and 12b,
The electrode layer on the side where the coating layer 13 is formed is referred to as a cathode layer 12a, and the other is referred to as an anode layer 12b, which constitutes the gas sensing portion 1. NAS
The composition of ICON is Na _{1 + X} Zr ₂ Si _X P _3-X O ₁₂ , (0 ≦ X ≦ 3).

Further, the gas sensing portion 1 of FIG. 7 is provided with a heating heater 2 on the lower surface of one side, and a pair of lead wires 3a and 3b drawn from the anode and anode layers 12a and 12b and a lead wire drawn from the heating heater 2. It is connected to the pin 7 via 5a and 5b, and the pin 7 is fixed by penetrating the lower pedestal 6. The lead wires 3a, 3b and the lead wires 5a, 5b are connected for signal output and voltage application, respectively, and the pin 7 is connected to the outside at the portion penetrating the pedestal 6. The protector 4 is made of stainless steel wire mesh to protect the gas sensing unit 1, the heater 2, the lead wires 3a, 3b, 5a, 5b contained therein from mechanical damage and to improve the contact with the measurement atmosphere. It is fixed to.

In the above configuration, first, the gas sensing unit 1 is heated to the measurement temperature by the heater 2 and brought into contact with the outside atmosphere.

The carbon dioxide gas in the atmosphere reaches the gas sensing portion 1 by diffusion or convection through the opening of the protector 4, and the two electrode layers, that is, the cathode layer 12 depending on the carbon dioxide concentration at that time.
a, electromotive force is generated in the anode layer 12b. This electromotive force is applied to the cathode layer 1
2a, the anode layer 12b was taken out through the lead wires 3a and 3b and the pin 7, and the carbon dioxide concentration in the atmosphere was electrically detected.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, the above configuration has the following problems. That is, when the measurement atmosphere is in a high humidity environment or in a state where dew condensation is likely to occur, and when the carbon dioxide sensor is in an unheated state, the metal carbonate that constitutes the gas sensing part is , When forming a hydrate or hydride, respectively, and then heating it again, the absorbed water evaporates, causing expansion and contraction, gradually peeling from the cathode layer, or dissolving in dew condensation water and eluting. As a result, there is a problem that elements from the coating layer 13 to the cathode layer 12a are deteriorated and reproduction becomes impossible.

The present invention solves the above problems, and provides a carbon dioxide gas sensor having high reliability even if the gas sensing unit is repeatedly placed in a heated or unheated state in a high humidity environment without impairing responsiveness. It is intended for.

Means for Solving the Problem A carbon dioxide gas sensor of the first means for achieving this object is to have a pair of porous electrode layers at both ends, and to be electrically conductive to metal ions that can form a metal carbonate. An ion conductive ceramics plate, a metal carbonate that forms a dissociation equilibrium with carbon dioxide in a shape that covers a part or all of one electrode layer of the ion conductive ceramics plate, and the ion conductive ceramics plate And a gas sensing part formed by joining a pair of lead wires to the pair of electrode layers, and a heating part for heating the gas sensing part to an operating temperature. It is equipped with and.

The second means for achieving this object is a carbon dioxide gas sensor, in the above means, an ion conductive ceramics having the same composition as the ion conductive ceramics plate in the coating layer in which one electrode layer carries a metal carbonate, A coating layer is formed by adding a substance having the same composition as the electrode layer.

The carbon dioxide gas sensor of the third means for achieving this object is an ion conductive ceramics having the same composition as the ion conductive ceramics plate on the electrode layer on the side where the coating layer is formed in the first means or the second means. The electrode layer is formed by adding fine powder.

The carbon dioxide gas sensor of the fourth means for achieving this object is constituted by a gas permeable film which covers a part or all of the coating layer in the first, second and third means.

The carbon dioxide gas sensor of the fifth means for achieving this object is constituted by a hygroscopic gas permeable membrane to which a hygroscopic substance is added to cover a part or the whole of the coating layer in the first, second or third means. It is a thing.

By the first means of this constitution, the coating layer made of metal carbonate contains the water-insoluble ion conductive ceramics as an aggregate, so that the coating layer is formed by changing the humidity of the atmosphere or heating during measurement. The metal carbonate that is used is prevented from expanding and contracting due to moisture absorption and drying, and prevents the coating layer from peeling off from the electrode layer.

By the second means of this configuration, the following electrode reaction that controls the response of the sensor because the three-phase interface of the electrode layer material-metal carbonate-ion conductive ceramics is uniformly distributed in the coating layer, that is, Is promoted and responsiveness is improved.

By the third means of this configuration, diffusion of the metal ions generated in the electrode reaction (1), which is involved in the responsiveness of the sensor because the ion conductive ceramics are added in the electrode layer, is promoted in the electrode layer. Responsiveness is improved.

By the fourth means of this configuration, since the coating layer is coated with the gas permeable film, it is possible to suppress the migration of water vapor in the atmosphere to the coating layer, and to strengthen the adhesion with the electrode layer, The coating layer peels off from the electrode layer.
It is suppressed from falling off.

Since the coating layer is coated with the hygroscopic gas-permeable film by the fifth means of this configuration, the moisture in the atmosphere is fixed in the gas-permeable film before the transfer to the coating layer, and the transfer to the coating layer is prevented. It is further suppressed.

Example Hereinafter, a first example of the present invention will be described with reference to FIG.

FIG. 1 shows the structure of a gas sensing portion of a carbon dioxide gas sensor according to a first embodiment of the present invention. The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, the coating layer 13 covering the cathode layer 12a of the two electrode layers is an ion conductive ceramic plate (hereinafter abbreviated as NASICON plate) in a saturated aqueous solution of sodium carbonate 131 which is one kind of metal carbonate. Ion conductive ceramic fine powder of the same composition as 11 (hereinafter abbreviated as NASICON fine powder) 132, sodium carbonate 131 at 50 wt% and NASICON fine powder 132 at 50 wt% are uniformly mixed to form a slurry. It is formed by uniformly coating the surface of the layer 12a and then drying it at about 200 ° C.

The operation of the carbon dioxide sensor configured as described above will be described below.

The carbon dioxide gas sensor having the above-mentioned configuration is similar to the conventional one in the carbon dioxide gas detection operation, and therefore its details are omitted.

Therefore, the behavior of the coating layer 13 in which fine particles of NASICON are mixed with sodium carbonate 131, which is a constituent element for improving the humidity resistance of the present sensor, in a high temperature and high humidity environment will be described below.

In the above configuration, first, the case where the gas sensing unit 1 is placed in a non-heated state in a high temperature and high humidity atmosphere will be described.

In this case, the sodium carbonate 131 contained in the coating layer 13 absorbs moisture in the atmosphere and swells due to its hygroscopicity. However, NASICON fine powder 1 contained in the coating layer 13
32 serves as an aggregate of the coating layer 13, and sodium carbonate 131
It acts to suppress the flow and elution due to the absorption of moisture. Therefore, even if placed in high temperature and high humidity in the non-heated state, it is difficult for the cathode layer 12a to elute and fall off, and deterioration and damage of the gas sensing part 1 can be prevented.

Next, a case will be described in which the coating layer 13 in the hygroscopic state is changed from the non-heated state to the heated state.

In this case, the sodium carbonate 131 in the coating layer 13 releases the absorbed water in the non-heated state, changes its form, and tries to move in the coating layer 13, but in the coating layer 13 The water-insoluble NASICON fine powder 132, which plays a role, hinders the flow and prevents the coating layer 13 adhered to the cathode layer 12a from peeling and falling off.

Further, since the mixed NASICON fine powder 132 has the same composition as the NASICON plate 11 which is a constituent member of the gas sensing unit 1, even when the temperature reaches about 500 ° C. during operation, it does not react with other constituent elements. .

As described above, by adding the NASICON fine powder to the coating layer 13, it is possible to prevent the sodium carbonate from peeling and falling off from the cathode layer 12a due to repeated moisture absorption and drying. Therefore, the coating layer 13 becomes fine powder from the cathode layer 12a, and it is possible to prevent deterioration and breakage of one element of the gas sensing unit due to the progressive peeling and dropping.

The second embodiment of the present invention will be described below with reference to FIG.

FIG. 2 shows the configuration of the gas sensing portion 1 of the solid electrolyte type carbon dioxide gas sensor according to the second embodiment of the present invention. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 2, the coating layer 13 fixed to the cathode layer 12a
NASICON board 11 in a saturated aqueous solution of sodium carbonate 131
The same composition as NASICON fine powder 132 and the same composition as cathode layer 12a
u Paste 133 and 10 wt% each were added and kneaded evenly to form a paste, which was screen-printed on the surface of the cathode layer 12a, dried at 150 ° C for 10 minutes, and then baked at 800 ° C for 10 minutes to form. It was done.

The operation of the carbon dioxide sensor configured as described above will be described below. However, the carbon dioxide detection operation and the behavior of the coating layer under high temperature and high humidity are substantially the same as those in the first embodiment, so that there is a difference. Only the points will be mentioned.

By the way, the carbon dioxide sensor of the present embodiment has the cathode layer 12a and N
The following electrode reactions occur at the three-phase interface between the ASICON plate 11 and the coating layer 13.

That is, Therefore, in the case of the first embodiment, the three-phase interface is the coating layer.
Although present only on the joint surface between the cathode 13 and the cathode layer 12a, in the case of the present embodiment, the particles of the Au paste 133 and the NASICON fine powder 132 are uniformly dispersed throughout the sodium carbonate 131 constituting the coating layer 13. Therefore, since the three-phase interface is distributed throughout the coating layer 13, the above equation (1) is applied to the coating layer 13
Since it occurs in the whole, the reaction of the formula (1) is promoted, and the responsiveness of the gas sensing unit 1 element is improved as compared with the first embodiment.

Further, since the Au particles 133 also play the role of an aggregate like the NASICON fine powder 132, the moisture resistance of the coating layer 13 is improved.

As described above, by simultaneously adding NASICON fine powder and Au particles to the coating layer 13, moisture absorption and drying of sodium carbonate are repeated, so that the powder is separated from the surface of the cathode layer 12a into fine powder, and gas detection due to falling off It is possible to prevent deterioration of the element of the first part and at the same time improve the response of the element.

The third embodiment of the present invention will be described below with reference to FIG.

FIG. 3 shows the structure of a gas sensing portion of a solid electrolyte type carbon dioxide gas sensor according to a third embodiment of the present invention. The same parts as those in the second embodiment are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 3, the cathode layer 12a fixed to the NASICON plate 11
Is a NASIC of the same composition as NASICON board 11 in Au paste 121a.
10 wt% of ON fine powder 122a was added, and uniformly kneaded into a paste, which was screen-printed on NASICON plate 11 at 150 ° C.
It was dried for 10 minutes and then baked at 800 ° C for 10 minutes.

The operation of the carbon dioxide gas sensor configured as described above will be described below. However, the carbon dioxide gas sensing operation and the behavior of the coating layer 13 under high temperature and high humidity are the same as those in the second embodiment. Only described below.

Incidentally, the carbon dioxide sensor of the present embodiment because it contains NASICON fines 122a is Na ⁺ ion conductor in the cathode layer 12a, in the coating layer 13 (1) Na ⁺ ions produced by expression via a NASICON fines Since the cathode layer 12a can be diffused in the cathode layer 12a, the reaction of the formula (1) can be further smoothly proceeded as compared with the case of the second embodiment, and the responsiveness of one element of the gas sensing unit is improved. Can be expected, the porosity of the cathode layer 12a can be improved, and diffusion of CO ₂ and O ₂ gas, which is involved in the reaction of the formula (1), can be promoted.

As described above, by adding the NASICON fine powder in the cathode layer, it is possible to promote the diffusion of Na ⁺ ions, CO ₂ gas, and O ₂ gas, and thus improve the responsiveness of the device. .

The fourth embodiment of the present invention will be described below with reference to FIG.

FIG. 4 shows the structure of a gas sensing portion of a solid electrolyte type carbon dioxide gas sensor according to a fourth embodiment of the present invention. The same parts as those in the third embodiment are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 4, the gas permeable film 14 covering only the cathode layer 12a and the coating layer 13 or only the coating layer 13 has 10 wt% of NASICON fine powder 142 which imparts permeability to the amorphous glass sealing material 141.
The added material is uniformly kneaded, and a paste-like material is coated on the coating layer 13 and part or all of the portion exposed to the atmosphere of the cathode layer 12a, and then dried at 150 ° C. for 15 minutes, and further, It is a gas permeable film that is formed by baking at 800 ℃ for 10 minutes and that can be manufactured by adjusting the aperture ratio according to the amount of NASICON fine powder added.

The operation of the carbon dioxide sensor configured as described above will be described below. However, since there are many similar parts in the carbon dioxide detection operation and the like, only the differences will be described below.

By the way, in the carbon dioxide sensor of the present embodiment, since the gas permeable film 14 is coated on the surface of the coating layer 13,
Even if the gas sensing unit 1 is left unheated under high temperature and high humidity, the moisture in the atmosphere is suppressed from being transferred to the coating layer 13. In addition to being suppressed, the flow of the absorbed sodium carbonate 131 is blocked. Therefore, the moisture resistance of the coating layer is improved, and the deterioration and damage of the gas sensing unit 1 element itself under high temperature and high humidity and dew condensation atmosphere can be prevented more reliably than in the third embodiment.

Hereinafter, the fifth embodiment of the present invention will be described with reference to FIG.

FIG. 5 shows the structure of a gas sensing portion of a solid electrolyte type carbon dioxide gas sensor according to a fifth embodiment of the present invention. The same parts as those in the fourth embodiment are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 5, the hygroscopic gas permeable film 14a that covers only the cathode layer 12a and the coating layer 13 or only the coating layer 13 is formed on the amorphous glass sealing material 141 with 10wt% of silica gel fine powder 143 that imparts hygroscopicity and gas permeability. % Evenly mix the added one,
After coating a part or all of the paste layer that is in contact with the atmosphere of the coating layer 13 and the cathode layer 12a, it is dried at 150 ° C for 15 minutes, and further baked at 800 ° C for 10 minutes. Also in this case, as in the fourth embodiment, the gas permeable membrane can be manufactured by adjusting the aperture ratio according to the addition amount of the silica gel fine powder 143.

The operation of the carbon dioxide gas sensor configured as described above will be described below. However, since there are many similar parts in the carbon dioxide gas detection operation and the like, only the differences will be described.

By the way, in the carbon dioxide sensor of the present embodiment, since the gas permeable film 14 having a hygroscopic property is coated on the surface of the coating layer 13, when the gas sensing unit 1 is left unheated under high temperature and high humidity. Moreover, the moisture in the atmosphere is absorbed when moving in the hygroscopic gas permeable film 14a, and the coating film 13 is left in an atmosphere having a lower humidity than it actually is. It can be expected that the moisture resistance of No. 1 will be further improved as compared with the fourth example.

Effects of the Invention As described above, according to the present invention, since the ion-conducting molamix having the same composition as that of the ion-conducting ceramics plate, which is a component of the gas sensing part, is added in the coating layer, The element of the gas sensing part that prevents the reaction deterioration of the electrode layer on the coating layer side at the time of heating, suppresses the flow due to repeated moisture absorption and drying of the metal carbonate, and separates or drops the coating layer from the cathode layer. Deterioration can be prevented.

Further, according to the second aspect in addition to the above-mentioned structure, since the substance having the same composition as that of the cathode layer is added to the coating layer, an electrode reaction occurring in the cathode layer also occurs in the coating layer and is promoted. The response of the element can be improved.

According to the third aspect in addition to the above structure, since the ion conductive ceramics is added in the cathode layer,
The diffusion of metal ions generated by the electrode reaction in the cathode layer is promoted, and the response of the gas sensing element is further improved.

Further, in addition to the above structure, according to the fourth aspect, since the coating layer having a hygroscopic property is coated with the gas permeable film, it is possible to suppress migration of water vapor in the atmosphere to the coating layer. Therefore, the humidity resistance under high temperature and high humidity is improved, and the deterioration of the gas sensing element can be prevented.

Further, in addition to the above configuration, according to the fifth claim,
Since the coating layer is coated with a hygroscopic gas permeable film to which a hygroscopic substance is added, the water vapor in the atmosphere fixes the water immediately before it shifts to the coating layer. Can be suppressed from moving to the coating layer, and deterioration of the gas sensing element due to repeated moisture absorption and drying can be prevented.

 As described above, each has a great effect in practical use.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the configuration of a gas sensing portion of a carbon dioxide gas sensor according to a first embodiment of the present invention, and FIG. 2 is a configuration of a gas sensing portion of a carbon dioxide gas sensor according to a second embodiment of the present invention. FIG. 3 is a vertical cross-sectional view showing the structure of the gas sensing portion of the carbon dioxide sensor according to the third embodiment of the present invention, and FIG. 4 is a carbon dioxide sensor according to the fourth embodiment of the present invention. FIG. 5 is a vertical cross-sectional view showing the configuration of the gas sensing unit of FIG. 5, FIG. 5 is a vertical cross-sectional view showing the configuration of the gas sensing unit of the carbon dioxide sensor according to the fifth embodiment of the present invention, and FIG. 6 is a gas of the conventional carbon dioxide sensor. FIG. 7 is a vertical cross-sectional view showing the structure of the sensing unit, and FIG. 7 is a vertical cross-sectional view showing the assembly structure of the carbon dioxide gas sensor of the related art and the present invention. 1 ... Gas sensing part, 2 ... Heater, 3a, 3b ... Lead wire, 4 ... Protector, 5a, 5b ... Lead wire, 6 ... Pedestal, 11 ... NASICON plate, 12a, 12b ... Electrode Layer (cathode layer, anode layer), 13 ... Covering layer, 14 ... Gas permeable membrane, 14a ...
Hygroscopic gas permeable membrane, 131 …… Sodium carbonate, 132 ……
NASICON fine powder, 133 …… Au paste, 121a …… Au paste, 122a …… NASICON fine powder, 141 …… Amorphous glass seal, 142 …… NASICON fine powder, 143 …… Silica gel fine powder.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location G01N 27/46 ZAB

Claims (5)

[Claims] 1. An ion conductive ceramics plate having a pair of porous electrode layers at both ends and having conductivity with respect to metal ions capable of forming a metal carbonate, and the ion conductive ceramics plate. A coating layer is formed of a metal carbonate formed to cover a part or all of one electrode layer and an ion conductive ceramic having the same composition as the ion conductive ceramic plate, and a pair of leads is formed on the electrode layer. A carbon dioxide gas sensor comprising: a gas sensing unit configured by joining wires; and a heating unit heating the gas sensing unit to an operating temperature. 2. The carbon dioxide gas sensor according to claim 1, wherein a substance having the same composition as that of the electrode layer is added to the coating layer. 3. The carbon dioxide sensor according to claim 1 or 2, wherein an ion conductive ceramic having the same composition as that of the ion conductive ceramic plate is added to the electrode layer on the side where the coating layer is formed. 4. The carbon dioxide gas sensor according to claim 1, 2, or 3, wherein a part or all of the coating layer is covered with a gas permeable film. 5. The method according to claim 1, wherein a part or all of the coating layer is covered with a hygroscopic gas permeable film containing a hygroscopic substance.
2. The carbon dioxide gas sensor according to item 2, item 2, item 3, or item 4.