JPH04344456A - Sensor for detecting carbon dioxide - Google Patents

Abstract

PURPOSE:To enable highly accurate detection of carbon dioxide concentration by using as a detecting material of a detecting electrode a mixture of sodium carbonate, a carbonate of an alkaline earth metal and at least one compound selected from magnesium carbonate and barium peroxide. CONSTITUTION:A detecting electrode 2 and a reference electrode 5 are provided opposite to each other with an ion conductor 4 therebetween. A sodium ion conductor can be used as the conductor 4 or any other conductor may be used. A detecting material is formed when a mixture wherein sodium carbonate serving as a first component, at least one carbonate selected as a second component from calcium carbonate, barium carbonate and strontium carbonate, and at least one compound selected as a third component from magnesium carbonate and barium peroxide are blended together is fused on the electrode 2. When electricity is transmitted to a heater 8 and a gas to be measured is brought into contact with the heater 8, an electromotive force equivalent to the concentration of carbon dioxide in the gas is output between both of the electrodes 2, 5 and measured by a voltmeter 9.

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, and particularly to improved durability.

0002

2. Description of the Related Art Solid electrolyte sensors currently being developed are generally constructed by providing a sensing electrode and a reference electrode on both sides of a solid electrolyte which is an ion conductor. To detect gas components present in the 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 ions and the target gas component is used as a solid electrolyte. It is used as a detection material for electrodes such as platinum.

[0003] As a carbon dioxide gas sensor based on such a principle, for example, β alumina (general formula Na2O ・n
Al2O3, n=5-11) and NASICON (
General formula Na1-x Zr2 P 3-x Six O
There are examples using sodium ion conductors such as 12). In this case, the detection electrode is a platinum mesh coated with sodium carbonate, and the reference electrode is platinum alone or coated with sodium carbonate, etc., and then placed in air or carbon dioxide. The standard one is sealed. Therefore, carbon dioxide gas as the gas to be measured can come into contact with the above-mentioned detection electrode, but cannot come into contact with the reference electrode on the opposite side.

[0004] When this sensor is activated, it normally has a
It is heated to a constant temperature of about 600 degrees Celsius, and an electromotive force of sodium ions is generated at the detection electrode in response to the partial pressure of carbon dioxide in the sample gas that comes into contact with the detection electrode, resulting in the difference in electromotive force between the two electrodes. Because sodium ions proportional to

However, as mentioned above, the sensing electrode is coated with sodium carbonate, and NASICON is used as an ion conductor.
In the case of conventional carbon dioxide gas sensors that use Despite this, the device was heated to a high temperature for use.

[0006]

[Problems to be Solved by the Invention] Therefore, the present invention exhibits stable electromotive force characteristics even at lower operating temperatures. Therefore, carbon dioxide concentration can be detected with high accuracy even at lower operating temperatures, and durability is achieved. The purpose of the present invention is to provide an improved and highly reliable carbon dioxide detection sensor.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a carbon dioxide gas sensor in which a sensing electrode and a reference electrode are disposed opposite to each other with an ion conductor interposed therebetween. A composition using a mixture of sodium carbonate, at least one carbonate of an alkaline earth metal selected from calcium, barium, and strontium, and at least one compound selected from magnesium carbonate and barium peroxide. Adopted.

The ion conductor in the carbon dioxide detection sensor of the present invention is, for example, β alumina or NAS.
A sodium ion conductor such as a sintered body of ICON can be used, but is not limited thereto. Further, the reference electrode is made of, for example, a platinum mesh coated with platinum black or a platinum vapor-deposited film, and may be coated with the same material as the detection electrode depending on the case. Such a reference electrode is covered with a gas-impermeable cover so that it is not affected by the concentration of carbon dioxide gas in the test gas.

The detection material in the carbon dioxide detection sensor of the present invention comprises a mixture of sodium carbonate as a first component and at least one carbonate selected from calcium carbonate, barium carbonate and strontium carbonate as a second component; Further, as a third component, a mixture containing at least one compound selected from magnesium carbonate and barium peroxide is fused onto the sensing electrode. The blending ratio at this time varies somewhat depending on the combination of materials, but in order to obtain good moisture resistance, it is preferable to increase the blending ratio of the second component to the first component.

0010

[Operation] In the carbon dioxide detection sensor of the present invention, when a gas to be measured is brought into contact with the heater in a heated state, an electromotive force corresponding to the concentration of carbon dioxide in the gas is output between both electrodes. Since the carbon dioxide gas detection sensor of the present invention uses an ion conductor containing specific components, it has good detection output characteristics even at low temperatures.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of a carbon dioxide gas detection sensor according to the present invention. In the figure, 1 is a carbon dioxide gas detection sensor, and 2 is a detection electrode. This sensing electrode 2 is made by covering and fusing a sensing material layer 3 onto a platinum mesh 2a coated with, for example, platinum black. Further, 4 is an ion conductor. 5 is a reference electrode, which is formed of, for example, a platinum mesh coated with platinum black;
A cover 6 made of glass or the like to shield from the test gas
It is covered and sealed. Note that 7 is a ceramic substrate, and 8 is a heater made of a platinum film provided on the back surface of the substrate.

The carbon dioxide detection sensor 1 configured as described above is installed in the chamber 10 of the measuring device shown in FIG.
It is heated by the heater 8. Air, oxygen, and carbon dioxide gas are mixed to a predetermined concentration through flowmeters 11, 12, and 13 and supplied to chamber 10, and the electromotive force between detection electrode 2 and reference electrode 5 is measured with voltmeter 9. . In addition, 14
1 is a water tank for adding moisture to the gas to be detected, 16 is a trap for preventing backflow, and 15 is an exhaust port.

[First Example] Sodium carbonate, barium carbonate, and barium peroxide were mixed in a molar ratio of 1:2:1, heated and melted, and then crushed to form ion conductor pellets (NASICON) 4. A detection material layer 3 was prepared by fusion bonding onto a platinum black-coated platinum wire mesh 2a provided on the surface of the detection material layer 3. On the other hand, a reference electrode 5 is provided by sputtering platinum on the top surface of the alumina ceramic substrate 7, which is used as a heater 8 by forming a heating resistance wire by sputtering platinum on the back surface. After placing the ion conductor pellet 4, the heater 8 is energized to fuse and fix the pellet 4, and an alumina-based inorganic heat-resistant paint is applied around the part of the pellet where the reference electrode 5 is provided to seal it against atmospheric gas. hand,
Carbon dioxide gas detection sensor A of the present invention configured as shown in FIG.
I got it.

[First Comparative Example] Carbon dioxide gas detection in a comparative example was carried out in the same manner as in the first example except that sodium carbonate and barium carbonate were mixed at a molar ratio of 1:2 and used as the detection material. I got sensor a.

Regarding the carbon dioxide detection sensor A of the first embodiment, the detection output characteristics were measured with the element temperature at 450° C. and the carbon dioxide concentration varied, and the results are shown in FIG. The detection output characteristics of the carbon dioxide detection sensor a of the first comparative example were also measured in the same manner except that the element temperatures were 550° C. and 450° C., and the results are also shown in FIG. From this result, it can be seen that the carbon dioxide detection sensor of the comparative example has a detection output that decreases as the element temperature decreases, whereas the carbon dioxide detection sensor of the present invention has a high detection output even when the element temperature is low.

[Second Example] The present invention was carried out in the same manner as in the first example, except that sodium carbonate, barium carbonate, and magnesium carbonate were mixed at a molar ratio of 1:2:1 and used as the detection material. A carbon dioxide detection sensor B of the invention was obtained.

The detection output characteristics of the carbon dioxide detection sensor B of the second embodiment were measured in exactly the same manner as above except that the element temperature was 500° C., and the results are shown in FIG. The detection output characteristics of the carbon dioxide detection sensor a of the first comparative example were also measured in the same manner except that the element temperatures were 550° C. and 500° C., and the results are also shown in FIG. 4. Looking at these results, it can be seen that the carbon dioxide detection sensor of the present invention has a high detection output even when the element temperature is low.

[Third Example] Sodium carbonate, strontium carbonate, and magnesium carbonate were mixed in a molar ratio of 1:2:
A carbon dioxide gas detection sensor C of the present invention was obtained in the same manner as in the first embodiment except that the detection material was prepared by mixing the components to become 1.

[Second Comparative Example] Carbon dioxide gas detection in a comparative example was carried out in the same manner as in the first embodiment except that sodium carbonate and strontium carbonate were mixed at a molar ratio of 1:2 and used as the detection material. Sensor b was obtained.

The detection output characteristics of the carbon dioxide detection sensor C of the third embodiment were measured in exactly the same manner as described above except that the element temperature was 500° C., and the results are shown in FIG. The detection output characteristics of the carbon dioxide detection sensor b of the second comparative example were also measured in the same manner except that the element temperatures were 550° C. and 500° C., and the results are also shown in FIG. Looking at these results, it can be seen that the carbon dioxide detection sensor of the present invention has a high detection output even when the element temperature is low.

[Fourth Example] The present invention was carried out in the same manner as in the first example, except that sodium carbonate, calcium carbonate, and barium peroxide were mixed in a molar ratio of 1:2:1 as the detection material. A carbon dioxide detection sensor D of the invention was obtained.

[Third Comparative Example] Carbon dioxide gas detection in a comparative example was carried out in the same manner as in the first embodiment except that sodium carbonate and calcium carbonate were mixed at a molar ratio of 1:2 and used as the detection material. Sensor c was obtained.

The detection output characteristics of the carbon dioxide gas detection sensor D of the fourth embodiment were measured in the same manner as above except that the element temperature was 500° C., and the results are shown in FIG. The detection output characteristics of the carbon dioxide gas detection sensor c of the second comparative example were also measured in the same manner except that the element temperatures were 550° C. and 500° C., and the results are also shown in FIG. Looking at these results, it can be seen that the carbon dioxide detection sensor of the present invention has a high detection output even when the element temperature is low.

[0024]

[Effects of the Invention] As described above, the carbon dioxide detection sensor of the present invention can perform accurate detection at relatively low temperatures, and furthermore, it can heat the element efficiently, so it consumes less power. Therefore, it has the advantage of long life, simple structure, and easy manufacture.

[Brief explanation of the drawing]

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

FIG. 2 is a configuration diagram of a detection output characteristic measuring device of a carbon dioxide detection sensor.

FIG. 3 is a detection output characteristic diagram with respect to the carbon dioxide concentration of the carbon dioxide detection sensor A of the first embodiment of the present invention and the carbon dioxide detection sensor a of the first comparative example.

FIG. 4 is a detection output characteristic diagram with respect to carbon dioxide concentration of a carbon dioxide gas detection sensor B according to a second embodiment of the present invention and a carbon dioxide gas detection sensor a according to a first comparative example.

FIG. 5 is a detection output characteristic diagram with respect to carbon dioxide concentration of a carbon dioxide gas detection sensor C according to a third embodiment of the present invention and a carbon dioxide gas detection sensor b according to a second comparative example.

FIG. 6 is a detection output characteristic diagram with respect to carbon dioxide concentration of a carbon dioxide gas detection sensor D according to a fourth embodiment of the present invention and a carbon dioxide gas detection sensor C according to a third comparative example.

[Explanation of symbols]

1 Detection element 2
Detection electrode 2a
Platinum mesh 3 Detection material layer 4
Ion conductor pellet 5
Reference electrode 6
Cover 7 Ceramic substrate 8 Heater 9
Voltmeter 10
Chamber 11, 12, 13 Flowmeter

Claims (1)

[Claims] Claim 1: A carbon dioxide gas sensor comprising a sensing electrode and a reference electrode disposed opposite to each other with an ion conductor interposed therebetween, wherein the sensing materials for the sensing electrode include sodium carbonate, calcium,
Carbon dioxide gas detection characterized by using a mixture of at least one alkaline earth metal carbonate selected from barium and strontium and at least one compound selected from magnesium carbonate and barium peroxide. sensor.