JP2974088B2 - Carbon dioxide detection sensor - Google Patents

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 more particularly to improvement of durability.

[0002]

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

As a carbon dioxide gas sensor based on such a principle, for example, 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 platinum alone or sodium carbonate or the like is coated as the reference electrode, which is then placed in air or carbon dioxide gas. Sealed to standard. Accordingly, the carbon dioxide gas as the gas to be measured can be brought into contact with the above-mentioned detection electrode but cannot come into contact with the reference electrode on the opposite side.

[0004] This sensor is usually 400-600 during operation.
Heated to a constant temperature of about ℃, the electromotive force of sodium ions is generated at the detection electrode in accordance with the partial pressure of carbon dioxide in the test gas that comes into contact with the detection electrode. Since the proportional sodium ions are conducted in the ion conductor, the concentration of carbon dioxide can be detected by measuring the electromotive force.

However, in the case of a conventional carbon dioxide gas sensor in which the sensing electrode is coated with sodium carbonate as described above and NASICON is used as the ion conductor, the electromotive force characteristics are greatly affected by the element temperature. Yes,
Since stable characteristics are exhibited only when heated to 550 ° C. or higher, the element is heated to a high temperature and used even though the durability is reduced.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention exhibits stable electromotive force characteristics even when the operating temperature is lowered, so that the carbon dioxide gas concentration can be detected with high accuracy at a lower operating temperature and the durability is improved. Another object of the present invention is to provide an improved and highly reliable carbon dioxide gas detection sensor.

[0007]

In order to achieve the above object, the present invention provides a carbon dioxide gas sensor comprising a detection electrode and a reference electrode sandwiching an ion conductor, wherein the detection material for the detection electrode is: A composition using a mixture of sodium carbonate, calcium, barium and at least one alkaline earth metal carbonate selected from strontium, and at least one compound selected from magnesium carbonate and barium peroxide. Adopted.

The ion conductor in the carbon dioxide gas detection sensor of the present invention is, for example, β alumina or NASICO.
A sodium ion conductor such as a sintered body of N 2 can be used, but is not limited thereto. As the reference electrode, for example, one formed of a platinum net or a platinum vapor-deposited film to which platinum black is adhered is used, and in some cases, may be coated with the same material as the detection electrode. Such a reference electrode is covered with a gas-impermeable cover so as not to be affected by the concentration of carbon dioxide in the test gas.

The detection material in the carbon dioxide gas detection sensor according to 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, a mixture containing at least one compound selected from magnesium carbonate and barium peroxide as the third component is fused onto the detection electrode. The mixing ratio at this time varies slightly depending on the combination of materials, but it is preferable to increase the mixing ratio of the second component to the first component in order to improve the moisture resistance.

[0010]

In the carbon dioxide gas detection sensor of the present invention, when the gas to be measured is brought into contact with the heater while the heater is energized and heated, an electromotive force corresponding to the concentration of carbon dioxide in the gas is output between the two electrodes. The carbon dioxide gas detection sensor of the present invention has good detection output characteristics even at a low temperature because it uses an ion conductor containing a specific component.

[0011]

FIG. 1 shows the structure of a carbon dioxide sensor according to the present invention. In the figure, 1 is a carbon dioxide gas detection sensor, and 2 is a detection electrode. The detection electrode 2 is obtained by, for example, coating a detection material layer 3 on a platinum net 2a to which platinum black is adhered and fusing it. Reference numeral 4 denotes an ion conductor. Reference numeral 5 denotes a reference electrode, which is formed of, for example, a platinum net having platinum black adhered thereto.
A cover 6 made of glass or the like for shielding from a test gas
And sealed. Reference numeral 7 denotes a ceramic substrate, and reference numeral 8 denotes a heater made of a platinum film provided on the back surface of the substrate.

The carbon dioxide gas detection sensor 1 configured as described above is installed in the chamber 10 of the measuring apparatus shown in FIG.
Heating is performed by the heater 8. Air, oxygen and carbon dioxide gas are mixed to a predetermined concentration through flow meters 11, 12 and 13 and supplied to a chamber 10, and an electromotive force between the detection electrode 2 and the reference electrode 5 is measured by a voltmeter 9. . Note that 14
Reference numeral denotes a water tank for adding moisture to the test gas, reference numeral 16 denotes a trap for preventing backflow, and reference numeral 15 denotes an exhaust port.

[First Embodiment] Sodium carbonate, barium carbonate and barium peroxide are mixed at a molar ratio of 1: 2: 1, heated and melted, and then crushed to obtain an ion conductor pellet (NASICON) 4. Platinum net 2a with platinum black provided on the surface of
This was fused to form a detection material layer 3. On the other hand, a heating resistance wire is formed by sputtering platinum on the
A reference electrode 5 was prepared by further sputtering platinum on the upper surface of the alumina-based ceramic substrate 7 prepared as described above. Attached and fixed, and further, an alumina-based inorganic heat-resistant paint is applied around the pellet portion provided with the reference electrode 5 to seal against an atmospheric gas, and the carbon dioxide gas detection sensor A of the present invention configured as shown in FIG. Obtained.

[First Comparative Example] A carbon dioxide gas detection of a comparative example was performed 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 to provide a detection material. Sensor a was obtained.

With respect to the carbon dioxide detection sensor A of the first embodiment, the detection output characteristic was measured by changing the carbon dioxide concentration while setting the element temperature to 450 ° C., and the results are shown in FIG. The detection output characteristics of the carbon dioxide gas detection sensor a of the first comparative example were measured in exactly the same manner except that the element temperatures were set to 550 ° C. and 450 ° C., and the results are also shown in FIG. From these results, it is understood that the detection output of the carbon dioxide gas detection sensor of the comparative example decreases when the element temperature decreases, whereas the detection output of the carbon dioxide gas detection sensor of the present invention is high even when the element temperature is low.

[Second Embodiment] The procedure of the first embodiment is the same as that of the first embodiment except that sodium carbonate, barium carbonate and magnesium carbonate are mixed at a molar ratio of 1: 2: 1 to form a detection material. The carbon dioxide detection sensor B of the invention was obtained.

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

Third Embodiment A molar ratio of sodium carbonate, strontium carbonate and magnesium carbonate of 1: 2:
A carbon dioxide gas detection sensor C of the present invention was obtained in the same manner as in the first example, except that the mixture was changed to 1 to obtain a detection material.

SECOND COMPARATIVE EXAMPLE The same procedure as in the first example was carried out except that sodium carbonate and strontium carbonate were mixed at a molar ratio of 1: 2 to provide a detection material. Sensor b was obtained.

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

Fourth Embodiment A detection material is prepared by mixing sodium carbonate, calcium carbonate, and barium peroxide at a molar ratio of 1: 2: 1 to obtain a detection material. The carbon dioxide detection sensor D of the invention was obtained.

[Third Comparative Example] A carbon dioxide gas detection of a comparative example was performed in the same manner as in the first example except that sodium carbonate and calcium carbonate were mixed at a molar ratio of 1: 2 to obtain a detection material. Sensor c was obtained.

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

[0024]

As described above, the carbon dioxide gas detection sensor of the present invention can perform accurate detection at a relatively low temperature, and can efficiently heat the element, thus requiring less power consumption. Therefore, it has the advantages of a long service life, a simple structure, and easy manufacture.

[Brief description of the drawings]

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

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

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

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

FIG. 5 is a graph showing detection output characteristics 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 graph showing detection output characteristics with respect to a carbon dioxide gas concentration of a carbon dioxide gas detection sensor D of a fourth embodiment of the present invention and a carbon dioxide gas detection sensor c of a third comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detecting element 2 Detecting electrode 2a Platinum net 3 Detecting material layer 4 Ion conductor pellet 5 Reference electrode 6 Cover 7 Ceramic substrate 8 Heater 9 Voltmeter 10 Chamber 11,12,13 Flowmeter 14 Water tank 15 Exhaust port 16 Trap

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/416 G01N 27/406

Claims (1)

(57) [Claims] In a carbon dioxide gas sensor having a detection electrode and a reference electrode opposed to each other with an ion conductor interposed therebetween, at least one selected from sodium carbonate, calcium, barium and strontium as a detection material for the detection electrode. A carbon dioxide gas sensor comprising a mixture of a carbonate of an alkaline earth metal and at least one compound selected from magnesium carbonate and barium peroxide.