JPH06288966A - Carbon dioxide sensor - Google Patents

Abstract

PURPOSE:To provide a carbon dioxide sensor which is not affected by the moisture content in a gas to be inspected and improved in response characteris tic against the concentration variation of carbon dioxide. CONSTITUTION:In the objective sensor in which a detecting electrode 2 and reference electrode 4 are counterposed to each other on both sides of an ionic conductive material 3, a mixture prepared by mixing an alkaline earth metal carbonate with an alkaline metal carbonate at a mixing rate of 1 to 1 is used as the detecting material of the detecting electrode 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte type carbon dioxide sensor.

[0002]

2. Description of the Related Art A solid electrolyte sensor currently being developed is usually constructed by providing a detection electrode and a reference electrode on both sides of a solid electrolyte which is an ionic conductor. In order to detect a gas component existing in the atmosphere using such a sensor, an ionic conductor in which specific ions move is used as a solid electrolyte, and a compound containing the specific ion and a target gas component is used, for example. It is used as a coating material for electrodes such as platinum.

An example of a carbon dioxide gas sensor based on such a principle is β-alumina (general formula: Na ₂ O.nAl ₂ O).
₃ , n = 5-11) and NASICON (general formula Na _1-x Zr ₂ P _3-x
There is an example using a sodium ion conductor such as Si _x O ₁₂ ). In this case, a platinum mesh or the like coated with sodium carbonate is used as the detection electrode, and only platinum or this is coated with sodium carbonate or the like as the reference electrode, and then this is placed in air or carbon dioxide gas. The one sealed in is standard. Therefore, the carbon dioxide gas as the gas to be measured can be brought into contact with the above-mentioned detection electrode, but cannot be brought into contact with the reference electrode on the opposite side.

This sensor normally operates in the range of 400-600 during operation.
The sodium ion electromotive force is generated in the detection electrode in response to the partial pressure of carbon dioxide gas in the test gas that is heated to a constant temperature of about ℃, and the difference in the electromotive force between the two electrodes Since proportional sodium ions are conducted in the ionic conductor, the carbon dioxide concentration can be detected by measuring this electromotive force.

However, in the case of the conventional carbon dioxide gas sensor in which the detection electrode is coated with sodium carbonate and NASICON is used as the ionic conductor as described above, the electromotive force characteristic is greatly influenced by the water content in the test gas. There is a problem in that the response characteristics to the change in the carbon dioxide concentration are not good, in addition to the above-mentioned problems.

On the other hand, an improved method has been proposed in which the sensing electrode portion is covered with a gas permeable film that allows carbon dioxide gas to permeate but does not allow water to permeate, but the method of forming the permeable film is very troublesome. In addition to the above, it is difficult to solve the above problems by this method.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and an object of the present invention is to provide a carbon dioxide detection sensor having improved humidity characteristics and response characteristics.

[0008]

In order to achieve the above object, a carbon dioxide gas detection sensor of the present invention is a carbon dioxide gas sensor in which a detection electrode and a reference electrode are opposed to each other with an ion conductor interposed therebetween. As the coating material of (3), a material formed from a mixture of more than 1 mol of alkaline earth metal carbonate with respect to 1 mol of alkali metal carbonate was used.

That is, in the carbon dioxide gas detecting sensor of the present invention, the detecting electrode is, for example, 1 mol of alkali metal carbonate and 1 mol of alkali earth metal carbonate on the electrode portion formed of platinum net or the like to which platinum black is attached. Is coated with a mixture of more than 1 mol. The alkali metal carbonate used in such a mixture is preferably one or more carbonates selected from lithium carbonate, sodium carbonate and potassium carbonate, and the alkaline earth metal carbonates are calcium carbonate, strontium carbonate and carbonate. It is preferably one or more carbonates selected from barium.

As the solid electrolyte, for example, β-alumina or a sodium ion conductor such as NASICON sintered body can be used, but the solid electrolyte is not limited thereto. The reference electrode used is, for example, a platinum net to which platinum black is attached or a platinum vapor-deposited film.In some cases, it may be a mixture of an alkali metal carbonate and an alkaline earth metal carbonate like the detection electrode. It may be coated. Such a reference electrode is covered with a gas impermeable cover so that it is not affected by the concentration of carbon dioxide in the test gas.

[0011]

The carbon dioxide detection sensor configured as described above corresponds to the partial pressure of carbon dioxide in the test gas when the test gas comes into contact with the detection electrode while being heated to about 400 to 600 ° C. Since an electromotive force is generated in the detection electrode, by measuring the electromotive force between the detection electrode and the reference electrode, the concentration of carbon dioxide gas in the test gas can be quickly detected without being affected by humidity. it can.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows the structure of the carbon dioxide detection sensor of the present invention. In the figure, 1 is a carbon dioxide gas detection sensor, and 2 is a detection electrode. This detection electrode 2 is obtained by coating a detection material layer 2b of a mixture of an alkali metal carbonate and an alkaline earth metal carbonate on an electrode portion 2a made of a platinum net to which platinum black is attached, for example.

3 is an ionic conductor, and 4 is a reference electrode, which is formed of, for example, a platinum net with platinum black attached,
Cover 5 made of glass or the like for shielding from the test gas
It is covered and sealed with. Reference numeral 6 is a ceramic substrate, and 7 is a heater made of a platinum film provided on the back surface of the substrate.

The carbon dioxide detection sensor 1 is installed in the chamber 9 of the measuring device shown in FIG. 2 and heated by the heater 7. Flowmeters 10, 11 and 1 for air, O ₂ and carbon dioxide
The mixture is supplied to the chamber 9 through 2 to have a predetermined concentration, and the voltmeter 8 measures the electromotive force between the detection electrode 2 and the reference electrode 5. In addition, 13 is a water tank for adding moisture to the test gas, 14 is a trap for preventing backflow, and 15 is an exhaust port.

(Example 1) NASICO as the ionic conductor 3
As shown in FIG. 1, N 2 is used, and the sensing material layer 2b covering the platinum mesh electrode portion 2a is a mixture of sodium carbonate and barium carbonate in a molar ratio of 1: 1.1. Carbon dioxide detecting sensor A of the present invention having a structure
Got

The carbon dioxide detection sensor A is heated by the heater 7 by the measuring device shown in FIG. 2 so that the element temperature is 550 ° C., and the electromotive force characteristic for carbon dioxide having a concentration of 100 to 2000 ppm is 50% in relative humidity. The results measured in the medium and dry air are shown in FIG. Also, set the concentration of carbon dioxide to 300p.
FIG. 4 shows the results of measuring the response characteristics with respect to the change in concentration by changing between pm and 1000 ppm.

Comparative Example 1 Instead of using sodium carbonate and barium carbonate in a molar ratio of 1: 1.1, a ratio of 1: 0.8 is used.
Example 1 except that the sensing electrode was coated with the above mixture.
A carbon dioxide sensor a having the same structure as above was obtained.

Further, the electromotive force characteristics with respect to carbon dioxide gas were measured in humid air and dry air in the same manner as in Example 1, and FIG. 5 shows the response characteristics to changes in carbon dioxide concentration as in Example 1. The measurement result is shown in FIG.

From these results, it can be seen that Example 1 is significantly less affected by humidity than Comparative Example 1,
It can also be seen that the response speed has also been improved.

(Example 2) The same as Example 1 except that a mixture of lithium carbonate and calcium carbonate in a molar ratio of 1: 1.1 was used in place of the mixture of sodium carbonate and barium carbonate. A carbon dioxide sensor B having a different structure was obtained. The carbon dioxide detection sensor B showed the same humidity resistance characteristics and response speed as the carbon dioxide detection sensor A.

Example 3 Exactly the same as Example 1 except that a mixture of potassium carbonate and strontium carbonate in a molar ratio of 1: 1.1 was used in place of the mixture of sodium carbonate and barium carbonate. A carbon dioxide detection sensor C having a different structure was obtained. This carbon dioxide detection sensor C also showed the same humidity resistance characteristics and response speed as the carbon dioxide detection sensor A.

[0022]

As described above, in the carbon dioxide gas detection sensor of the present invention, the detection electrode is coated with a mixture of more than 1 mol of alkaline earth metal carbonate with respect to 1 mol of alkali metal carbonate. Not only is the electromotive force characteristic of the gas less affected by the water content of the test gas, but the response characteristic to changes in the carbon dioxide concentration is also excellent.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a carbon dioxide detection sensor of the present invention.

FIG. 2 is a configuration diagram of an apparatus for measuring an electromotive force characteristic of a carbon dioxide detection sensor with respect to carbon dioxide.

FIG. 3 is a detection characteristic diagram of carbon dioxide gas in humid air and dry air of the carbon dioxide gas detection sensor A according to the embodiment of the present invention.

FIG. 4 is a response characteristic diagram of the carbon dioxide detection sensor A with respect to a change in carbon dioxide concentration.

FIG. 5 is a detection characteristic diagram of carbon dioxide gas in wet air and dry air of a carbon dioxide gas detection sensor a of a comparative example.

FIG. 6 is a response characteristic diagram of the carbon dioxide detection sensor a with respect to a change in carbon dioxide concentration.

[Explanation of symbols]

 1 Carbon Dioxide Gas Detection Sensor 2 Detection Electrode 2a Electrode Part 2b Detection Material Layer 3 Ion Conductor 4 Reference Electrode 5 Cover 6 Ceramic Substrate 7 Heater 8 Voltmeter 9 Chambers 10, 11, 12 Flowmeter 13 Water Tank 14 Trap 15 Exhaust Port

[Procedure amendment]

[Submission date] July 19, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

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[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

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[0002]

2. Description of the Related Art A solid electrolyte sensor currently being developed is usually constructed by providing a detection electrode and a reference electrode on both sides of a solid electrolyte which is an ionic conductor. In order to detect a gas component existing in an atmosphere using such a sensor, an ion conductor in which specific ions move is used as a solid electrolyte, and a compound containing the specific ion and a target gas component is detected. As a material, for example, an electrode such as platinum is coated and used.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

However, as described above, sodium carbonate is used as the sensing material of the sensing electrode, and N is used as the ion conductor.
In the case of the conventional carbon dioxide gas sensor using ASIC, not only the electromotive force characteristics are greatly affected by the water content in the test gas, but also the response characteristics to the carbon dioxide concentration change are not good. It was

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

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[0008]

In order to achieve the above object, a carbon dioxide gas detection sensor of the present invention is a carbon dioxide gas sensor in which a detection electrode and a reference electrode are opposed to each other with an ion conductor interposed therebetween. As the detection material of 1., a material formed from a mixture of more than 1 mol of alkaline earth metal carbonate with respect to 1 mol of alkali metal carbonate was used.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

Comparative Example 1 Instead of using sodium carbonate and barium carbonate in a molar ratio of 1: 1.1, a ratio of 1: 0.8 is used.
A carbon dioxide gas detection sensor a having the same structure as in Example 1 except that the above mixture was used as the detection material was obtained.

[Procedure correction 6]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

[0022]

As described above, in the carbon dioxide detection sensor of the present invention, the detection electrode uses a mixture of more than 1 mol of alkaline earth metal carbonate to 1 mol of alkali metal carbonate as a detection material. In addition to the fact that the electromotive force characteristics for carbon dioxide gas are not easily affected by the water content in the test gas, the response characteristics for changes in carbon dioxide concentration are excellent.

Claims (3)

[Claims] 1. A carbon dioxide gas sensor comprising a detection electrode and a reference electrode that are placed opposite to each other with an ionic conductor sandwiched therebetween. As a coating material for the detection electrode, 1 mol of alkaline earth metal carbonate is used per 1 mol of alkali metal carbonate. A sensor for detecting carbon dioxide, characterized by using a material formed from a mixture exceeding a mole. 2. The alkaline earth metal carbonate is calcium,
The carbon dioxide detection sensor according to claim 1, wherein the carbon dioxide detection sensor is one of strontium and barium carbonate. 3. The carbon dioxide gas detection sensor according to claim 1, wherein the alkali metal carbonate is one or more carbonates of lithium, sodium and potassium.