JPH05157724A - Carbon dioxide gas sensor - Google Patents

Abstract

PURPOSE:To enable interference gas dependency of output and durability of a solid electrolyte type carbon dioxide gas sensor to be improved. CONSTITUTION:An interference gas dependency is improved according to the catalyst operation by adding a catalyst substance 1 to a detection pole layer 103. Also, by coating the detection pole layer 103 with a gas-transmission film where the catalyst substance 1 is added, the detection pole layer 103 and a measurement atmosphere are shielded by catalyst operation and influence of interference gas is eliminated for preventing interference gas dependency of output, thus preventing deterioration due to corrosion gas, etc., of the detection pole layer 103. Therefore, a stable output can be obtained over a long period of time, thus obtaining a highly reliable carbon dioxide gas sensor.

Description

Detailed Description of the Invention

[0001]

The present invention relates to facility horticulture, environmental hygiene,
The present invention relates to a solid electrolyte type carbon dioxide gas sensor used in a place for measuring and controlling carbon dioxide concentration for disaster prevention, industrial use and the like.

[0002]

2. Description of the Related Art In recent years, there has been a growing need for carbon dioxide sensors mainly in the fields of air conditioning and agriculture and livestock, and various types of sensors have been developed and put into practical use. However, in practice, many problems remain in its reliability.

An example of a conventional carbon dioxide gas sensor will be described below with reference to FIG. As shown in the figure, a thin plate-shaped NAXS (sodium ion conductor) plate 101, which is a solid electrolyte, is provided with a pair of electrode layers 102, a detection electrode layer 103 and a reference electrode layer 104, at both ends thereof. 10
3 is formed by dispersing and adding a metal carbonate 105 (for example, sodium carbonate or a mixture of sodium carbonate and barium carbonate) in the electrode layer using Au in a mixture of one kind or two kinds or more. The electrode layer 104 was formed of an electrode layer using Au and constituted the gas sensing unit 106. A heating unit 107 is fixed to the lower part of one surface of the gas sensing unit 106 with an adhesive 108 to heat the gas sensing unit 106 to a measurement temperature. The sensor output is the detection electrode layer 10
3. Lead wire 1 taken out from each of the reference electrode layers 104
It is taken out through 09a and 109b.

In the above structure, the gas sensing section 106 constitutes the following battery. Ie

[0005]

[Chemical 1]

[0006] The gas sensing unit 10 which constitutes such a battery
When 6 is heated to the measurement temperature by the heating unit 107, the following battery reaction occurs in the detection electrode layer 103 and the reference electrode layer 104.

[0007]

[Chemical 2]

An electromotive force represented by the following equation is generated between both electrodes.

[0009]

[Equation 1]

Here, E ⁰ is a constant, R is a gas constant, T is an absolute temperature, F is a Faraday constant, αNa ₂ O and αNa ₂ CO ₃ are the activities of Na ₂ O and Na ₂ CO ₃ , respectively, and PCO ₂ Indicates the partial pressure of CO ₂ in the air. α Na ₂ CO ₃ can be set to 1 in a normal stable state, and α Na ₂ O can be regarded as a constant because it is determined by the composition of NAXS. Therefore, if T, which is the operating temperature of the sensor, is constant, the electromotive force E (output) is a function of PCO ₂ . Therefore, the detection electrode layer 103 and the reference electrode layer 1
The CO ₂ concentration can be obtained by taking out this electromotive force E (output) from No. 04 via the lead wires 109a and 109b.

[0011]

However, the above-mentioned structure has the following problems. That is, when a gas other than carbon dioxide gas (hereinafter referred to as an interference gas) in the measurement atmosphere was present, the interference gas was involved in the electrode reaction shown in Chemical formula 2 of the detection electrode layer 103. Therefore, when the interference gas concentration in the measurement atmosphere changes, the electromotive force, that is, the sensor output changes in accordance with the change, which has an output dependency on the interference gas, and the carbon dioxide concentration cannot be accurately measured.

Further, if a corrosive gas such as hydrogen sulfide is present in the atmosphere, the detection electrode layer 103 is contaminated and causes deterioration.

An object of the present invention is to solve the above-mentioned problems, and an object thereof is to provide a carbon dioxide gas sensor having a high reliability by reducing the dependency of the output on the interference gas and preventing the deterioration of the detection electrode layer 103.

[0014]

The first means for achieving the object of the present invention is to provide a pair of electrode layers on both ends of an ion conductive ceramics plate made of a solid electrolyte, and to provide the pair of electrode layers. To one of the electrode layers, a sensing electrode layer is formed by adding a mixture of one kind or two or more kinds of metal carbonates that form dissociation equilibrium with carbon dioxide gas, and a catalyst substance is added to the detecting electrode layer. And a heating unit for heating the gas sensing unit to a measurement temperature.

The second means is to provide a pair of electrode layers on both ends of an ion conductive ceramic plate made of a solid electrolyte, and dissociate carbon dioxide gas from carbon dioxide gas in any one electrode layer of the pair of electrode layers. A sensing layer is formed by adding a mixture of one or more kinds of metal carbonates that form an equilibrium, and the sensing electrode layer or a part of the surface of the ion conductive ceramics plate including the sensing electrode layer or The whole is covered with a gas permeable membrane to which a catalyst substance is added.

[0016]

According to the present invention, by adding the catalyst substance to the detection electrode layer by the constitution of the above-mentioned first means, the catalyst substance in the detection electrode layer interferes during the electrode reaction shown in (Chemical Formula 2) due to the catalyst action. By decomposing the gas, the influence of the interference gas in the atmosphere on the detection electrode layer can be reduced, and the dependency of the output on the interference gas can be reduced.

Further, according to the structure of the second means, by covering the sensing electrode layer with the gas permeable film to which the catalytic substance is added, the interfering gas is decomposed by the catalytic substance when passing through the gas permeable film. By blocking the sensing electrode layer from the interfering gas in the measurement atmosphere, it is possible to prevent the dependency of the sensing electrode layer due to the influence of the interfering gas in the atmosphere and the deterioration of the sensing electrode layer due to corrosive gas, and it is stable for a long time The output is obtained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS.

The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted. As shown in FIG. 1, a pair of electrode layers 102, a reference electrode layer 104 and a detection electrode layer 103, are formed on both ends of a NAXS plate 101 made of sodium ion conductive ceramics. For the detection electrode layer 103, a mixture of sodium carbonate and barium carbonate, that is, a metal carbonate 105 is added to an Au paste which is an electrode material, and a hydrocarbon isomerization catalyst or a dehydrating catalyst (for example, Al ₂ O ₃ ) powder,
That is, 5 to 30% by weight of the catalyst substance 1 was added and mixed to form a paste, which was screen-printed or applied, dried and then baked.

The operation of the carbon dioxide sensor having the above structure will be described below. In the above configuration, the effect of the interference gas in the atmosphere exerted on (Formula 2) shown in the conventional example is mitigated by the catalytic action of the catalytic substance 1 added to the detection electrode layer 103. As a result, the dependency of the output on the ambient interference gas is reduced.

As described above, according to the carbon dioxide gas sensor of the first embodiment of the present invention, the influence of the interference gas on the detection electrode layer 103 can be reduced and the dependence of the output on the interference gas can be reduced. ..

In this embodiment, the catalyst substance 1 is Al₂O₃When
But B₂O₃ー Al₂O₃, H₂B₂O_Four, SiO₂, SiO₂ー Al₂O₃, SiO₂-M
gO, CaO, MgO, Cu, Cu-Ni alloy, Ag, ZnO, Gd₂O₃, Pr
₂O₃, Y₂O ₃, Nd₂O₃, Dy₂O₃, Sm₂O₃, ZnZrO₃, V₂O₃, Cr₂O
₃(CrO₃), Mo, W, MoO₃, WO₃, UO₂Re (-Pt) Fe₂O₃, Co etc
Of hydrocarbon isomerization catalyst or dehydration catalyst (Chemical formula 2)
Any substance that does not interfere with the reaction in the sensing electrode layer 103 shown in
Any substance may be used.

Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

As shown, the sensing electrode layers 103 and N
A part of the AXS plate 101 is covered with a powder of a hydrocarbon isomerization catalyst or a dehydrating catalyst (for example, Al ₂ O ₃ ), that is, a gas permeable membrane 2 to which a catalyst substance 1 is added. There is. The gas-permeable film 2 is an amorphous glass film formed by applying a paste-like amorphous glass sealing material, and then drying and firing it.

In the above structure, the sensing electrode layer 103 is completely shielded from the interfering gas in the atmosphere because the interfering gas in the atmosphere is decomposed by the catalytic substance 1 when passing through the gas permeable membrane 2. Therefore, the detection electrode layer 103 is not affected by the interference gas of the measurement atmosphere, the dependence of the output on the atmosphere interference gas can be prevented, and at the same time, the corrosive gas and the like are decomposed by the catalytic substance 1 before reaching the detection electrode layer 103. Therefore, deterioration of the detection electrode layer 103 is prevented, and stable output can be obtained for a long period of time.

As described above, according to the carbon dioxide sensor of the second embodiment of the present invention, the dependence of the output on the interference gas can be prevented and the deterioration of the detection electrode layer 103 can be prevented, so that the stable output can be obtained for a long period of time. Can be obtained.

In this embodiment, the catalyst substance 1 is Al₂O₃When
But B₂O₃ー Al₂O₃, H₂B₂O_Four, SiO₂, SiO₂ー Al₂O₃, SiO₂-M
gO, CaO, MgO, Cu, Cu-Ni alloy, Ag, ZnO, Gd₂O₃, Pr
₂O₃, Y₂O ₃, Nd₂O₃, Dy₂O₃, Sm₂O₃, ZnZrO₃, V₂O₃, Cr₂O
₃(CrO₃), Mo, W, MoO₃, WO₃, UO₂Re (-Pt) Fe₂O₃, Co etc
Of hydrocarbon isomerization catalyst or dehydration catalyst (Chemical formula 2)
Any substance that does not interfere with the reaction in the sensing electrode layer 103 shown in
Any substance may be used.

[0028]

As described above, according to the present invention, by adding the catalytic substance to the detection electrode layer, it is possible to prevent the malfunction of the sensor due to the atmospheric interference gas and improve the responsiveness.

Further, by adding a catalytic substance to the gas permeable film covering a part or all of the surface of the sensing electrode layer or the surface of the ion conductive ceramics plate including the sensing electrode layer, gas permeation to the conventional gas sensing part is achieved. Since the detection electrode layer can be easily shielded from the interference gas in the atmosphere simply by adding a protective film, malfunctions due to the interference gas can be prevented, and substances that deteriorate the detection electrode layer such as corrosive gas in the atmosphere can also be blocked. It is possible to prevent deterioration of the detection electrode layer and obtain stable output over a long period of time.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the configuration of a carbon dioxide gas sensor according to a first embodiment of the present invention.

FIG. 2 is a vertical sectional view showing the configuration of a carbon dioxide sensor according to a second embodiment of the present invention.

FIG. 3 is a vertical sectional view showing the configuration of a conventional carbon dioxide sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 catalyst substance 2 gas permeable membrane 101 ion conductive ceramics plate (NAXS plate) 102 pair of electrode layers 103 sensing electrode layer 105 metal carbonate 106 gas sensing unit 107 heating unit

Claims (2)

[Claims] 1. A pair of electrode layers are provided at both ends of an ion conductive ceramics plate made of a solid electrolyte, and one or two or more kinds of metal carbonates are provided in either one of the pair of electrode layers. A carbon dioxide gas sensor, comprising a gas sensing unit configured by adding a mixture to form a sensing electrode layer, and adding a catalytic substance to the sensing electrode layer, and a heating unit heating the gas sensing unit to a measurement temperature. 2. A pair of electrodes is provided at both ends of an ion conductive ceramic plate made of a solid electrolyte, and one of the pair of electrode layers has a mixture of one kind or two or more kinds of metal carbonates. Is added to form a detection electrode layer, and a part or all of the surface of the detection electrode layer or the ion conductive ceramics plate including the detection electrode layer is covered with a gas permeable film to form a gas permeable film. The carbon dioxide gas sensor according to claim 1, which is configured by adding a catalytic substance.