JP3109020B2 - Carbon dioxide detection element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon dioxide detection element.

[0002]

2. Description of the Related Art Conventionally, as this type of carbon dioxide gas detecting element, for example, a carbon dioxide gas detecting element in which an alkali metal ion conductive ceramic and an oxygen ion conductive ceramic are bonded together has been used.

[0003]

A carbon dioxide gas detecting element formed by bonding an alkali metal ion conductive ceramic and an oxygen ion conductive ceramic has been said to have excellent durability against water vapor. However, when the alkali metal ion conductive ceramics and the oxygen ion conductive ceramics are bonded together, there is a problem as described below. Bonding strength between ceramics is low. Since the bonding between the ceramics is performed at a high temperature (about 1300 ° C.), an intermediate layer without ion conduction is generated. When an intermediate layer made of a conductive paste is provided between the joining of ceramics, the adhesive strength is still weak and the response speed is reduced. When the ceramics are joined by mechanical pressure welding, there is no mechanical strength because they are not joined.

[0004] Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a carbon dioxide detection element having excellent steam resistance and mechanical strength. It is another object of the present invention to provide a carbon dioxide gas detecting element having good high-speed response and excellent repetition reproducibility.

[0005]

Means for Solving the Problems] carbon dioxide detector according to this invention to achieve the above object, an alkali metal ion conductive glass or layer and the oxygen ion conductive ceramic alkaline earth metal ion conductive glass And the sensing electrode is connected to the surface opposite to the bonding surface of the alkali metal ion conductive glass or alkaline earth metal ion conductive glass, and the side opposite to the bonding surface of the oxygen ion conductive ceramics. Is connected to the reference electrode, and a metal carbonate is provided on the detection electrode.

[0006]

In the present invention, the alkali metal ion conductive glass or the alkaline earth metal ion conductive glass and the oxygen ion conductive ceramic have good ion conductivity, are joined with high mechanical strength, and are used as a solid electrolyte. Since glass is used, the density is improved as compared with ceramics.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view of a detecting unit for explaining a configuration of a carbon dioxide gas detecting element according to an embodiment of the present invention. In FIG. 1, 1 is a disk-shaped alkali metal ion conductive glass, 2 is a disk-shaped oxygen ion conductive ceramic, and the oxygen ion conductive ceramic 2 is an alkali metal ion conductive glass. It is bonded to the glass 1 in close contact. Reference numeral 3 denotes a metal carbonate, 4a denotes a porous detection electrode side electrode formed on the surface opposite to the bonding surface of the alkali metal ion conductive glass 1, and the metal carbonate 3 is applied to the alkali metal ion conductive glass 1. The structure is provided so as to cover the formed detection electrode side electrode 4a.

Reference numeral 4b denotes a reference electrode side electrode formed on the surface opposite to the bonding surface of the oxygen ion conductive ceramics 2, 5a denotes a lead wire connected to the detection electrode side electrode 4a, 5a
b is a lead wire connected to the reference electrode 4b. Reference numeral 6 denotes an alumina tube, which is bonded and sealed to the oxygen ion conductive ceramics 2 and welded to the glass tube 7.

The above-described alkali metal ion conductive glass 1 is made of, for example, glass that conducts alkali metal ions such as Li ⁺ , Na ⁺ , and K ⁺ . The alkali metal ion conductive glass 1 does not have to be perfect glass (amorphous), and may be partially devitrified (crystals are precipitated from a glassy state). Further, as the oxygen ion conductive ceramics 2, for example, YSZ (yttria stabilized zirconia), CSZ (calcia stabilized zirconia), MSZ (magnesia stabilized zirconia), or the like can be used.

The metal carbonate 3 is composed of Li ₂ CO ₃ , Na
₂ CO ₃ , K ₂ CO ₃ , CaCO ₃ , BaCO ₃ , MgC
Carbonates such as O ₃ and SrCO ₃ can be used, and it is not necessary that the metal ions conducted in the alkali metal ion conductive glass 1 and the metal element of the carbonate 3 match. The detection electrode 4a is desirably porous. The detection electrode 4a and the reference electrode 4b are made of gold, platinum or an electron conductive ceramic.

Next, a description will be given of a method of manufacturing the carbon dioxide gas detecting element thus constituted. Na as an alkali metal ion conductive glass _{1 2 CO 3 · Al 2 O} 3 · 4SiO 2
Was used. The _{Na 2 CO 3 · Al 2 O} 3 · 4SiO 2 is
It was prepared by mixing reagent-grade Na ₂ CO ₃ , Al ₂ O ₃ , and SiO ₂ , pressing and molding to obtain pellets having a diameter of about 10 mm and a thickness of 1 mm, and sintering them at about 1350 ° C.

As the oxygen ion conductive ceramics 2, 8
About 10 mm in diameter and about 1 mm in thickness containing mol% of Y ₂ O ₃
Zirconia pellets were used. The zirconia pellets were individually sintered at about 1600 ° C. and cooled, and then Na ₂ CO ₃ .Al ₂ O ₃ .4S was placed on the zirconia pellets.
The iO ₂ pellets are overlapped, baked at about 1100 ° C. and joined, and zirconia pellets / Na ₂ CO ₃ .Al ₂ O _3.
A 4SiO ₂ pellet laminate was formed. In this case, Na
_{Since 2} CO ₃ .Al ₂ O ₃ .4SiO ₂ and zirconia pellets are bonded to glass and ceramics, they are firmly bonded.

Next, the zirconia pellets / Na ₂ CO ₃
Platinum paste was applied to the non-bonded end faces of the Al ₂ O ₃ .4SiO ₂ pellet laminate in a range of 4 mm × 4 mm to form a detection electrode 4a and a reference electrode 4b.
At the same time, a platinum wire having a diameter of about 0.08 mm coated with a platinum paste is placed on each of the detection electrode side electrode 4a and the reference electrode side electrode 4b, and baked in a furnace at about 800 ° C. for 20 minutes, and the detection electrode side lead wire 5a And the reference electrode side lead wire 5b. In addition, even if a platinum wire coated with a platinum paste is placed on the detection electrode 4a and the reference electrode 4b and put in a furnace and fired, the platinum paste does not come off because the platinum paste has a high viscosity. Next, an aqueous solution of Na ₂ CO ₃ was applied on the detection electrode side electrode 4a, and dried at about 80 ° C. to produce a carbon dioxide gas detection element.

The carbon dioxide gas detecting element thus formed has an outer diameter of about 1 c on the oxygen ion conductive ceramics 2.
An alumina tube 6 having an inner diameter of 0.6 cm, an inner diameter of 0.6 cm, and a length of 10 cm is fixed by using an inorganic adhesive (not shown).
Is welded and fixed to a glass tube 7 having an outer diameter of about 1 cm, an inner diameter of 0.6 cm, and a length of 15 cm.

[0015] Figure 2 is a SEM photograph showing the surface structure of _{Na 2 CO 3 · Al 2 O} 3 · 4SiO 2 as an alkali metal ion conductive glass 1. As apparent from FIG Na ₂
CO ₃ .Al ₂ O ₃ .4SiO ₂ is extremely dense,
Although it is vitreous as a whole, crystalline substances (granular parts that look like small white dots) are also seen.

FIG. 3 shows Na ₂ CO ₃ .Al ₂ O ₃ .4SiO
₂ shows the results of analysis using XRD (X-ray diffraction) in order to obtain more detailed knowledge of ₂ . In addition, XRD
Used Cuka radiation. As is clear from FIG. 3, a broad pattern based on vitreousness was observed, but a plurality of sharp peaks were also observed, confirming that a crystalline substance was present. Therefore, from the results of FIGS. 2 and 3,
It is glassy as a whole, but is considered to contain about 10 wt% or less of a crystalline substance.

FIG. 4 shows a characteristic measuring apparatus for measuring the characteristics of the actually manufactured carbon dioxide gas detecting element. Measurement of carbon dioxide by this characteristic measuring device
The electromotive force of the carbon dioxide detection element 20 shown in FIG. 4 was measured by an electrometer 31 and the ambient temperature was measured by a multimeter 33 using a thermocouple 32, and the measured value was taken into a computer. The ambient temperature was measured using an infrared furnace 35 and a thermocouple 36.
By the temperature controller 37.

In this case, the carbon dioxide detecting element 20 is inserted into the infrared furnace 35, and the synthetic AIR (79% H ₂ , 21% O ₂ , C
O ₁ ppm or less, CO _{2 2} ppm or less, HCl 1 pp
m, H ₂ O 10 ppm or less) or this synthetic AI
A gas having a carbon dioxide concentration of 1000 ppm diluted with R is flown, and the synthetic AIR or the carbon dioxide concentration diluted with the synthetic AIR of 10 ppm, 1
The measurement was performed by flowing a gas of 00 ppm, 1000 ppm, and 10000 ppm. The flow rate was about 50 ml / 1 minute on the detection electrode side electrode 4a side and the reference electrode side electrode 4b side, respectively, and the ambient temperature was about 470 ° C.

FIG. 5 is a diagram showing the results of measuring the electromotive force values for various carbon dioxide concentrations at about 470 ° C. using the above-described characteristic measuring device. In this case, a synthetic AIR or a gas having a carbon dioxide concentration of 1000 ppm flows on the reference electrode side electrode 4b side of the carbon dioxide gas detection element 20, and a synthetic AIR or carbon dioxide gas concentration of 10 pp flows on the detection electrode side electrode 4a side.
m, 100ppm, 1000ppm, 10000ppm
DRY gas and synthetic AIR or carbon dioxide concentration of 10
ppm, 100ppm, 1000ppm, 10000p
The results obtained by flowing pm WET gas (humidified gas that has passed through water in a glass tube) are shown.

As is apparent from FIG.
An electromotive force value having good linearity with respect to the carbon dioxide gas concentration was obtained in the range of 0000 ppm. Further, in the case of WET gas, compared to the case of using DRY gas, 100%
At 00 ppm, the electromotive force values are the same,
2 mV at ppm, 5 mV at 10 ppm, 10 pp
The output of m was 7 mV, and that of synthetic AIR was 9 mV. Further, even when the gas on the side of the reference electrode 4b was changed to synthetic AIR and carbon dioxide concentration of 1000 ppm, the electromotive force value hardly changed.

FIG. 6 is a diagram showing the electromotive force characteristics with respect to the carbon dioxide concentration of a carbon dioxide detection element made of a conventional crystalline sodium ion conductive ceramic alone. As is clear from FIG. 6, in the conventional configuration, the sensitivity to the change in the concentration of carbon dioxide gas is lower in the case of the WET gas than in the case of using the DRY gas. Also, once
The humidified element was measured again with DRY gas, and showed no original electromotive force. Therefore, it is clear that the configuration according to the present embodiment has better reproducibility than the conventional configuration.

FIG. 7 is a graph showing the results of measuring the response speed characteristics of the carbon dioxide detection element 20. In FIG. In this case, at an ambient temperature of 470 ° C., synthetic AIR or carbon dioxide gas having a concentration of 1000 ppm is supplied to the reference electrode 4b, and DRY of carbon dioxide having a concentration of 100 ppm and carbon dioxide having a concentration of 1000 ppm is supplied to the detection electrode 4a. This is a result of switching between a gas or a WET gas of a carbon dioxide gas having a concentration of 100 ppm and a carbon dioxide gas having a concentration of 1000 ppm (humidified gas that has passed through water in a glass tube) at intervals of 15 minutes. As is clear from FIG. 7, in the case of DRY gas, the 90% response speed is about 1 minute, and in the case of WET gas, the response speed is about 3 minutes, which is extremely high. Also, the reference electrode 4b
There was no difference in response speed due to the difference in carbon dioxide on the side.

The gas on the side of the reference electrode 4b is synthesized A
Even when switching to IR and carbon dioxide gas with a concentration of 1000 ppm, there was no change in the electromotive force, so that the reference electrode 4 b side in the glass tube 7 and the detection electrode side in the infrared furnace 35 as shown in FIG. Even if the same gas flows through the electrode 4a, the concentration of carbon dioxide can be measured.

FIG. 9 is a perspective view showing a configuration of another embodiment of the carbon dioxide gas detecting element according to the present invention, and the same components as those in FIG. 1 are denoted by the same reference numerals. 9 differs from FIG. 1 in that a vent 8 penetrating the alumina tube 6 is provided.

In such a configuration, since the same gas as the detection electrode 4a flows through the vent 8 to the reference electrode 4b, the concentration of carbon dioxide can be measured in the same manner as described above.

FIG. 10 is a plan view showing the structure of a carbon dioxide gas detecting element according to still another embodiment of the present invention, and FIG. 11 is a sectional view of the detecting element portion. Is attached. In these figures, the difference from FIG. 1 is that the side surfaces of an alkali metal ion conductive glass 1 formed in a columnar shape and an oxygen ion conductive ceramics 2 formed in a columnar shape in the same manner as in FIG. It has a juxtaposed structure in which the sensing electrode side electrode 4a and the reference electrode side electrode 4b are respectively taken out from the side surfaces facing each other.
It is structured to be adhered on A.

In FIG. 10, reference numerals 101, 102 denote electrode pads, 10a, and 10a of the ceramic heater 10.
b is a heater lead wire connected to the electrode pads 101 and 102, respectively. The ceramic heater 1
As shown in FIG. 12, the heater main body 103 is formed by folding back a plurality of times in the heating section 10A as shown in FIG. 12, and the carbon dioxide element disposed on the heating section 10A is continuously heated at about 470 ° C. for a long time. It has a heating structure.

In such a configuration, the detection electrode 4
Since the same gas flows on the side a and the side of the reference electrode 4b, the concentration of carbon dioxide can be measured as described above. Also,
According to such a configuration, the alkali metal ion conductive glass 1 and the oxygen ion conductive ceramics 2 have a structure in which the side surfaces are joined to each other, so that the element structure can be downsized.
Further, the use of the ceramic heater 10 makes it possible to reduce power consumption. That is, the infrared furnace 35 described above is used.
Has a length of 25 cm, an outer diameter of 5 cm, an inner diameter of 3 cm, and consumes about several hundred watts. On the other hand, the ceramic heater 10 has a length of 3 cm, a width of 5 mm and a power consumption of about 2 W. A carbon dioxide element formed on the ceramic heater 10 is about 3 mm square and 1 mm thick. Low power consumption can be achieved by bonding a carbon dioxide element on top and heating directly.

FIG. 13 is a plan view showing the configuration of another embodiment of the carbon dioxide gas detecting element according to the present invention, and FIG. 14 is a sectional view of the detecting element portion. I have. In these figures, the difference from FIG. 1 is that the alkali metal ion conductive glass 1 and the oxygen ion conductive ceramics 2 are joined to each other, and the sensing electrode side electrode 4a and the reference electrode side It is configured to have a laminated structure from which the electrode 4b is taken out, and is adhered and arranged on the heating portion 10A of the ceramic heater 10 in which the vent 8 is formed by the inorganic adhesive 9.

Even in such a configuration, the same gas flows on the sensing electrode side electrode 4a side and the reference electrode side electrode 4b side, and is not affected by the oxygen concentration in the surrounding atmosphere. Concentration measurement is possible. Further, the element structure can be reduced in size and power consumption can be reduced.

FIG. 15 is a plan view showing a configuration of another embodiment of the carbon dioxide gas detecting element according to the present invention, and FIG. 16 is a sectional view of the detecting element portion. I have. In these figures, the difference from FIG. 11 is that the side-bonded laminate of the alkali metal ion conductive glass 1 and the oxygen ion conductive ceramics 2 exposes the sensing electrode side electrode 4a side of the alkali metal ion conductive glass 1. In this structure, these peripheral surfaces including the reference electrode side electrode 4b are sealed with a non-permeable sealing material 11 so as to surround them, and are adhered and arranged on the ceramic heater 10 with an inorganic adhesive 9.

Even in such a configuration, the concentration of carbon dioxide can be measured without the need for a special reference gas on the side of the reference electrode 4b. Further, according to such a configuration, a non-permeable seal is formed so as to surround these peripheral surfaces including the reference electrode side electrode 4b side of the laminate of the alkali metal ion conductive glass 1 and the oxygen ion conductive ceramics 2. By being sealed with the stopper 11, the influence of an interference gas such as water vapor on the joint between the alkali metal ion conductive glass 1 and the oxygen ion conductive ceramics 2 can be cut off, and the reference electrode 4 b By supplying oxygen to the side from the sealing material 11, the influence of the oxygen concentration in the surrounding atmosphere is eliminated. Further, the element structure can be reduced in size and power consumption can be reduced.

FIG. 17 is a sectional view showing a configuration of another embodiment of the carbon dioxide gas detecting element according to the present invention, and the same components as those in FIG. 14 are denoted by the same reference numerals. 17 differs from FIG. 14 in that the laminate of the alkali metal ion conductive glass 1 and the oxygen ion conductive ceramics 2 is a detection electrode 4a of the alkali metal ion conductive glass 1.
The side is exposed and is sealed with a non-permeable sealing material 11 so as to surround these peripheral surfaces including the reference electrode 4 b side, and is fixedly arranged on the ceramic heater 10.

Also in such a configuration, the concentration of carbon dioxide can be measured without the need for a special reference gas on the side of the reference electrode 4b. Further, according to such a configuration, it is possible to cut off the influence of an interference gas such as water vapor on the joint between the alkali metal ion conductive glass 1 and the oxygen ion conductive ceramics 2 and to reduce the influence of the reference electrode 4b. By supplying oxygen from the sealing material 11, the influence of the oxygen concentration in the surrounding atmosphere is eliminated. Further, the element structure can be reduced in size and power consumption can be reduced. Further, there is no need to provide an opening in the ceramic heater 10,
The package is simplified.

In the above-described embodiment, the case where the alkali metal ion conductive glass is used as the solid electrolyte has been described. However, the present invention is not limited to this case. The same effect as described above can be obtained by using an alkaline earth metal ion conductive glass that conducts alkaline earth metal ions.

In the above-described embodiment, the crystalline material contained in the alkali metal ion conductive glass is about 1%.
Although the case of 0 wt% or less has been described, the present invention is not limited to this, and the same effect as described above can be obtained even if an alkali metal ion conductive glass containing a crystalline substance of about 40 wt% or less is used. Can be

[0037]

As described above, according to the present invention,
A glass / ceramic laminate in which alkali metal ion-conducting glass or alkaline earth metal ion-conducting glass and oxygen ion-conducting ceramics are firmly bonded, so that carbon dioxide gas has excellent water vapor pressure resistance and mechanical strength An extremely excellent effect that the detection element can be realized with good reproducibility is obtained.

Further, according to the present invention, the alkali metal ion conductive glass or the alkaline earth metal ion conductive glass and the oxygen ion conductive ceramic are firmly joined to form a glass / ceramic laminate, Therefore, an extremely excellent effect of realizing a carbon dioxide gas detecting element excellent in high-speed response and reproducibility can be obtained.

According to the present invention, the carbon dioxide gas concentration can be measured even when the same gas is supplied to the reference electrode and the detection electrode, so that a special reference gas is supplied to the reference electrode. An extremely excellent effect that an unnecessary carbon dioxide detection element can be realized is obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view of an element portion showing a configuration of an embodiment of a carbon dioxide detection element according to the present invention.

FIG. 2 is a photograph showing a particle structure of an alkali metal ion conductive glass according to the present invention.

FIG. 3 is a view showing an analysis result of an alkali metal ion conductive glass according to the present invention by X-ray diffraction.

FIG. 4 is a block diagram showing a measuring device for measuring characteristics of a carbon dioxide gas detecting element according to the present invention.

FIG. 5 is a graph showing the relationship between carbon dioxide and carbon dioxide in a carbon dioxide gas detecting element according to the present invention.
It is a figure showing an electromotive force characteristic.

FIG. 6 shows carbon dioxide gas in a conventional carbon dioxide gas detection element.
It is a figure showing an electromotive force characteristic.

FIG. 7 is a diagram showing the response characteristics of the carbon dioxide detection element according to the present invention.

FIG. 8 is a block diagram showing a characteristic evaluation device for evaluating characteristics of a carbon dioxide gas detecting element according to the present invention.

FIG. 9 is a perspective view of an element portion showing a configuration of another embodiment of the carbon dioxide gas detecting element according to the present invention.

FIG. 10 is a plan view showing a configuration of still another embodiment of the carbon dioxide detection element according to the present invention.

FIG. 11 is a cross-sectional view of the detection element unit of FIG.

12 is a plan view showing a configuration of the ceramic heater of FIG.

FIG. 13 is a plan view showing a configuration of another embodiment of the carbon dioxide detection element according to the present invention.

FIG. 14 is a cross-sectional view of the detection element unit of FIG.

FIG. 15 is a plan view showing a configuration of another embodiment of the carbon dioxide gas detecting element according to the present invention.

FIG. 16 is a cross-sectional view of the detection element unit of FIG.

FIG. 17 is a cross-sectional view of a detecting element section showing a configuration of another embodiment of the carbon dioxide detecting element according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Alkali metal ion conductive glass, 2 ... Oxygen ion conductive ceramics, 3 ... Metal carbonate, 4a ... Porous detection electrode side electrode, 4b ... Reference electrode side electrode, 5a ... Detection electrode side lead wire, 5b ... Reference electrode side lead wire, 6 ... Alumina tube, 7
... glass tube, 8 ... vent, 9 ... inorganic adhesive, 10 ... ceramic heater, 11 ... sealing material.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-107219 (JP, A) JP-A-5-119015 (JP, A) JP-A-6-160347 (JP, A) JP-A-6-160347 229978 (JP, A) JP-A-6-160348 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/416 G01N 27/406 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A a layer of the layer and the oxygen ion-conducting ceramic of the alkali metal ion conductive glass or alkaline earth metal ion conductive glass is bonded, wherein the alkali metal ion conductive glass or alkaline earth metal ion conductivity A detection electrode is connected to a surface opposite to the bonding surface of the glass, and a reference electrode is connected to a surface opposite to the bonding surface of the oxygen ion conductive ceramic, and a metal is provided on the detection electrode. A carbon dioxide detection element provided with a carbonate.