JPH06317558A - Carbon dioxide sensor and its manufacture - Google Patents

Abstract

PURPOSE:To easily manufacture a solid electrolyte-type carbon dioxide sensor, to increase the productivity of the sensor and to make the sensor remarkably thin and small. CONSTITUTION:A laminated structure is formed in such a way that a solid electrolyte layer 3 is formed on the surface of a gas-nonpermeable ceramic substrate 2, that a detection electrode layer 4 and a counter electrode layer 5 are formed on it in a mutually separated state and that a metal carbonate layer 6 is formed on the detection electrode layer 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an air conditioner and a disaster prevention facility,
The present invention relates to an electrolytic carbon dioxide sensor used for measuring the concentration of carbon dioxide generated in a gardening facility and the like, and to a method for manufacturing the same, and more particularly to a carbon dioxide sensor using a solid electrolyte and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional carbon dioxide gas sensor generally uses a carbon dioxide gas absorbing solution such as an ammonium chloride solution as an electrolyte that causes a potential change according to the carbon dioxide concentration. However, since it has drawbacks such as an increase in the size of the entire sensor and an increase in manufacturing cost, the use of solid electrolytes such as sodium ion conductive ceramics (Na ₃ Zr ₂ Si ₂ PO ₁₂ ) in recent years has made We are aiming for miniaturization.

As an example thereof, a solid electrolyte type carbon dioxide sensor described on page 92 of "Nikkei New Materials" (published on November 20, 1989) has a heater 51 inside as shown in FIG. On the surface of the gas impermeable ceramics substrate 50 in which is embedded a solid electrolyte 52 in the form of pellets, which is made of sodium ion conductive ceramics granulated into a prism shape, is fixed in a horizontally long state, and the solid electrolyte On both left and right end surfaces of 52, a chip-shaped detection electrode 53 in which Na ₂ CO ₃ is bonded to a gold electrode and La _0.5 Sr _0.5 CoO are bonded to the gold electrode.
_The chip-shaped counter electrodes 54 joined to each other are fixed to each other,
Further, the exposed portion of the detection electrode 53 is covered with a gas permeable film 55 that selectively permeates carbon dioxide gas, and the exposed portion of the solid electrolyte 52 and the counter electrode 54 is covered with a gas blocking film 56. Has become.

When the sample gas containing carbon dioxide gas comes into contact with the surface of the detection electrode 53 while the heater 51 is energized and heated, carbon dioxide gas is generated between the counter electrode 54 and the counter electrode 54 due to the redox reaction of the detection electrode 53. Electromotive force according to the concentration of
That is, an output voltage is generated, and the gas concentration is measured by detecting the output voltage with a voltmeter.

[0005]

However, since the carbon dioxide sensor shown in FIG. 5 is assembled by assembling pellet-shaped parts and chip-shaped parts together, there is a limit to miniaturization and at the same time, miniaturization is required. As a result, each part becomes finer, which makes assembly work more difficult, which deteriorates workability and lowers productivity. Therefore, the present invention has a technical object to miniaturize the solid electrolyte type carbon dioxide gas sensor as much as possible without lowering the productivity.

[0006]

In order to solve this problem, a carbon dioxide sensor according to the present invention has a solid electrolyte layer formed on the surface of a gas impermeable ceramic substrate, and the surface of the solid electrolyte layer is formed on the surface thereof. A sensing electrode layer and a counter electrode layer are formed with a certain distance in the direction, and a metal carbonate layer is formed on the surface of the sensing electrode layer to form a laminated structure. Further, the method for manufacturing a carbon dioxide sensor according to the present invention,
The solid electrolyte layer, the detection electrode layer, the counter electrode layer, and the metal carbonate layer are formed by screen-printing a paste that is a material for each of these layers.

[0007]

According to the present invention, the solid electrolyte constituting each part of the carbon dioxide sensor, the detection electrode and the counter electrode are formed in layers, respectively, and these are sequentially laminated on the surface of the gas impermeable ceramics substrate. Since the same layered metal carbonate is laminated on the surface of,
Compared to a conventional sensor in which pellet-shaped components and chip-shaped components are assembled together and bonded to each other, manufacturing is easy and productivity is high, and at the same time, the entire sensor is significantly thin and small.

Further, in the production of the sensor, if each layer such as the solid electrolyte and the electrode is formed by screen printing with a paste-like material, for example, when it is formed by another printing means such as physical vapor deposition method such as sputtering. In comparison, the time required to form each layer is extremely short, and at the same time, the masking process and etching process using expensive equipment are not required, so the productivity of the sensor is further increased and its manufacturing cost is also greatly reduced. To be done.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a sectional view of a carbon dioxide sensor showing a first embodiment of the present invention, FIGS. 2 and 3 are plan and bottom views of the sensor, and FIG. 4 is a sectional view of a carbon dioxide sensor showing a second embodiment of the present invention. It is a figure.

In the carbon dioxide gas sensor 1 of the first embodiment shown in FIGS. 1 to 3, a solid electrolyte layer 3 is formed on the surface of a gas impermeable ceramics substrate 2 half-cut to a predetermined size. A sensing electrode layer 4 and a counter electrode layer 5 are formed on the surface of 3 with a certain distance in the surface direction,
In addition, a metal carbonate layer 6 is formed on the surface of the detection electrode layer 4, and a heater layer 7 forming a resistance circuit is further formed on the back surface of the ceramic substrate 2 to form a laminated structure.

A method of manufacturing the sensor 1 will be described. For example, a paste-like high resistance metal is formed on the back surface of the gas impermeable ceramics substrate 2 made of an alumina sintered plate having a length of 2.5 mm, a width of 3.0 mm and a thickness of 0.3 mm. Screen printing of the resistance circuit consisting of 1) and baking for 20 minutes at 200 ° C. form a very thin heater layer 7 with low power consumption. next,
On the surface of the ceramic substrate 2, a strip-shaped blank portion 8 occupying an area of about one-third of the surface is left, and a paste-like electrolyte is screen-printed on the other portions.
And baking for 20 minutes to form the solid electrolyte layer 3. The electrolyte paste was 100 g of sodium ion conductive ceramics (Na ₃ Zr ₂ Si ₂ PO ₁₂ ), 70 g of terpineol as an organic vehicle, and 12 parts of ethyl cellulose.
g, surfactant 12g, castor oil 10cc, linseed oil 10
The one prepared by adding cc to a paste was used.

On the surface of the solid electrolyte layer 3, a commercially available precious metal paste prepared by mixing gold dissolved in aqua regia with oil and forming a paste is used. Screen printing is performed in parallel at two locations so as to extend in a strip shape across the surface of the portion 8, and after drying, it is baked at 1025 ° C. for 6 hours, part of which is baked onto the surface of the ceramic substrate 2. Forming a sensing electrode layer 4 and a counter electrode layer 5 fused to the surface of the solid electrolyte layer 3.

Next, the sensing electrode layer 4 was screen-printed with a paste-like metal carbonate on a part of the surface in a size of 0.6 mm square, dried, and then heated at 700 ° C. for 10 minutes. Thus, the metal carbonate layer 6 fused to the surface of the detection electrode layer 4 is formed. The metal carbonate paste is, for example,
A mixture of alkali metal carbonate and alkaline earth metal carbonate in which Li ₂ CO ₃ and CaCO ₃ were mixed at a molar ratio of 9: 5 was used at 750 ° C.
To 100 g of mixed carbonate obtained by heating and melting with, and crushing after cooling, add 70 g of terpineol as an organic vehicle, 12 g of polymethylmethacrylate, 12 g of surfactant, 10 cc of castor oil, 10 cc of linseed oil and paste. What was prepared in the shape of was used.

The sensing electrode layer 4 and the counter electrode layer 5 are composed of
Lead wires 9a and 9b such as gold wires are connected to the surface of the portion directly baked on the surface of the ceramic substrate 2 by thermocompression bonding. Further, the entire sensor 1 is covered with a film of a ceramic adhesive which is the gas impermeable material 10 except for the surface of the metal carbonate layer 6 which causes a redox reaction.

The carbon dioxide sensor 1 manufactured by the above method is
The detection electrode layer 4 is installed in the gas chamber into which two kinds of sample gases with CO ₂ concentration of 300 ppm and 3000 ppm are introduced.
According to the experimental results of measuring the output voltage generated between the counter electrode layer 5 and the counter electrode layer 5, the voltage values are 350 mV and 270 m, respectively.
Since the output voltage becomes V and the output voltage drops by 80 mV when the CO ₂ concentration of the sample gas increases 10 times, it can be said that the sensor 1 has extremely good detection sensitivity.

The output voltages when the same two kinds of sample gas as described above are introduced into the gas chamber in a state where they are humidified to a saturated state by passing through a humidifying bottle are 355 mV and 27, respectively.
It was 5 mV, and it was found that the detection sensitivity of the sensor 1 was not affected by changes in humidity. This is because the metal carbonate layer 6 formed on the surface of the detection electrode layer 4 is made of a mixture of alkali metal carbonate and alkaline earth metal carbonate. Further, if the entire surface of the sensor 1 is covered with the film of the gas impermeable material 10 except the surface of the metal carbonate layer 6, the influence of volatile components contained in the gas is completely eliminated. And extremely stable detection sensitivity can be obtained. If the surface of the counter electrode layer 5 is covered with a metal oxide and the film of the gas impermeable material 10 is formed on the surface, the stability in long-term use is further improved.

Next, the carbon dioxide gas sensor 11 of the second embodiment shown in FIG. 4 is subjected to screen printing using the same paste material as in the first embodiment by the gas impermeable ceramics substrate 2
, The counter electrode layer 5 is formed on the surface of the ceramic substrate 2, and the solid electrolyte layer 3 is formed on the surface of the counter electrode layer 5 so as to cover the entire surface thereof. A detection electrode layer 4 is formed on the surface of the solid electrolyte layer 3, and a metal carbonate layer 6 is further formed on the surface of the detection electrode layer 4 so as to cover the entire surface. Although not shown, as in the case of the first embodiment, the entire surface of the sensor 11 except the surface of the metal carbonate layer 6 may be covered with a film of a gas impermeable ceramic material.

In this sensor 11, the result of the output voltage characteristic experiment is comparable to that of the sensor 1 of the first embodiment.
Further, there is an advantage that the whole structure can be made thin and small, the manufacturing is easy, the productivity is high, and the cost can be reduced. However, since the detection electrode layer 4 and the counter electrode layer 5 are close to each other, if there is a slight deviation in the screen printing machine that forms each layer, an interlayer short circuit between the layers 4 and 5 may occur, especially Solid electrolyte layer 3 interposed between layers 4 and 5
If pinholes etc. occur during screen printing of
An interlayer short circuit easily occurs from the pinhole portion. Therefore, the manufacturing yield of the sensor is not good.

On the other hand, the sensor 1 of the first embodiment is
Both the sensing electrode layer 4 and the counter electrode layer 5 are solid electrolyte layers 3
Since they are formed on the same surface with a certain distance, there is no possibility of causing an interlayer short circuit even if the screen printing machine for forming both layers has some deviation. Further, even if a pinhole or the like is generated in the solid electrolyte layer 3, there is no possibility of causing an interlayer short circuit, so that there is an advantage that the manufacturing yield is very good. The gas impermeable ceramics substrate 2 according to the present invention is not limited to alumina, but has a small coefficient of thermal expansion such as zirconia and a non-sodium ion conductive ceramics substrate close to the coefficient of thermal expansion of the solid electrolyte layer 3. Can also be used.

[0020]

According to the present invention, the carbon dioxide gas sensor can be made extremely thin and small as compared with the conventional one, and at the same time, the productivity can be greatly improved and the manufacturing cost can be reduced, which is a very excellent effect. There is.

[Brief description of drawings]

FIG. 1 is a sectional view of a carbon dioxide sensor showing a first embodiment of the present invention.

FIG. 2 is a plan view of the carbon dioxide sensor shown in FIG.

FIG. 3 is a bottom view of the carbon dioxide sensor shown in FIG.

FIG. 4 is a sectional view of a carbon dioxide sensor showing a second embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conventional carbon dioxide sensor.

[Explanation of symbols]

 1 ... Carbon dioxide sensor 2 ... Gas impermeable ceramic substrate 3 ... Solid electrolyte layer 4 ... Detection electrode layer 5 ... Counter electrode layer 6 ... Metal carbonate layer 7 ... Heater Layer 10 ... Gas impermeable material 11 ... Carbon dioxide sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Yoko Matsutoku 1-9-9, Hachiman-cho, Higashi-Kurume, Tokyo Metropolitan Co., Ltd. (72) Inventor Mitsuyuki Imai, Tokyo 1-29, Yawatacho, Higashi-Kurume City In the Optec Diddy Melco Laboratory Co., Ltd. (72) Nobumasa Egashira 2-14-40 Ofuna, Kamakura City, Kanagawa Prefecture Living Systems Research Center (72) ) Inventor Kenji Nomura 2-14-40 Ofuna, Kamakura City, Kanagawa Prefecture Living Systems Research Center, Mitsubishi Electric Corporation

Claims (8)

[Claims] 1. A solid electrolyte layer (3) is formed on the surface of a gas impermeable ceramics substrate (2) heated by a heater, and the surface of the solid electrolyte layer (3) has a constant distance in the surface direction. The detection electrode layer (4) and the counter electrode layer (5) separated from each other.
And a metal carbonate layer (6) is formed on the surface of the detection electrode layer (4) to provide a carbon dioxide sensor (1). 2. A counter electrode layer (5) is formed on the surface of a gas impermeable ceramics substrate (2) heated by a heater, and a solid electrolyte layer (3) is formed on the surface of the counter electrode layer (5).
Is formed, a sensing electrode layer (4) is formed on the surface of the solid electrolyte layer (3), and a metal carbonate layer (6) is further formed on the surface of the sensing electrode layer (4) to form a laminated structure. Carbon dioxide sensor (11) characterized by being characterized by: 3. A heater layer (7) forming a resistance circuit is formed on the back surface of the ceramic substrate (2).
Alternatively, the carbon dioxide sensor according to item 2. 4. The carbon dioxide sensor according to claim 1, wherein the metal carbonate layer (6) is made of a mixture of an alkali metal carbonate and an alkaline earth metal carbonate. 5. The carbon dioxide sensor according to claim 1, wherein the entire surface of the metal carbonate layer (6) except the surface thereof is covered with a film of a gas impermeable material (10). 6. A solid electrolyte layer (3) is formed by screen-printing a pasty electrolyte on the surface of a gas impermeable ceramics substrate (2), and then the solid electrolyte layer (2).
A noble metal in paste form is screen-printed on each of the two surfaces at a predetermined distance in the surface direction to form a sensing electrode layer (4) and a counter electrode layer (5), and the sensing electrode layer is further provided. A method for producing a carbon dioxide sensor (1), characterized in that a paste-like metal carbonate is screen-printed on the surface of (4) to form a metal carbonate layer (6). 7. A counter electrode layer (5) is formed by screen-printing a pasty noble metal on the surface of the gas impermeable ceramics substrate (2), and then the paste electrode is formed on the surface of the counter electrode layer (5). Of the solid electrolyte is screen-printed to form a solid electrolyte layer (3), and a paste-like noble metal is screen-printed on the surface of the solid electrolyte layer (3) to form a detection electrode layer (4). A carbon dioxide sensor (1) characterized by forming a metal carbonate layer (6) by screen-printing a paste metal carbonate on the surface of the electrode layer (4).
Manufacturing method of 1). 8. The carbon dioxide gas sensor according to claim 6, wherein the heater layer (7) is formed by screen-printing a resistance circuit with a paste-like high resistance metal on the back surface of the gas impermeable ceramics substrate (2). Production method.