JP2002350388A - Carbon dioxide sensing element of solid electrolyte type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon dioxide sensing element of solid electrolyte type having such properties that the electromotive force does not vary even in the case the sensing element with a non-heated state is left for a long time in a highly moist atmosphere with a condition such as high humidity, dew formation or the like, the variation of the electromotive force is little even in the case of being used for a long time, and the period, during which the electromotive force varies and becomes stable in the case that the concentration of the carbon dioxide largely fluctuates, is reduced. SOLUTION: The carbon dioxide sensing element of solid electrolyte type is formed by joining a working electrode and a reference electrode to the surface of a solid electrolyte layer. The solid electrolyte layer is composed of a solid electrolyte material containing either NaNd9 (SiO4 )6 O2 or LiNd9 (SiO4 )O2 , and if necessary at least one kind of compound selected from materials of titanium oxide, zirconium oxide and silicic acid zirconium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide carbon dioxide sensor element for measuring the concentration of carbon dioxide contained in an atmosphere. More specifically, the present invention relates to a solid electrolyte type carbon dioxide sensor element which can be suitably used for environmental measurement in which the concentration of a gas to be detected changes greatly.

[0002]

2. Description of the Related Art In recent years, interest in a living environment, particularly an indoor environment, has been increasing. For example, a carbon dioxide gas sensor element which monitors indoor carbon dioxide gas concentration and automatically ventilates when the carbon dioxide gas concentration becomes high. An air purifier equipped with is developed. Also, from the viewpoint of pollution prevention or countermeasures, the importance of so-called environmental measurement for constantly measuring changes in the concentration of carbon dioxide in the environment is increasing. As a carbon dioxide sensor element incorporated in a control device or an alarm device such as an air purifying device, or an environment measuring device, it has features of high gas selectivity, easy downsizing, wide operating conditions, and excellent maintainability. A solid electrolyte type carbon dioxide sensor element is suitable.

[0003] A solid electrolyte type carbon dioxide sensor element generally causes (a) an equilibrium reaction between (b) an electron conductive substance and carbon dioxide as a gas to be measured in a "solid electrolyte layer" as an ion conductor. It has a basic structure in which a “working electrode” containing an auxiliary electrode material and a “reference electrode” containing (c) an electron conducting material are joined. In such a carbon dioxide gas sensor element, 10 mm is supplied by an attached heater.
When left in an atmosphere containing the gas to be measured while being heated to a constant temperature of 0 ° C. to 600 ° C., the dissociation equilibrium reaction between the auxiliary electrode material contained in the working electrode layer and the gas to be measured equilibrates. The mobile ion concentration of the solid electrolyte layer changes in the vicinity of the working electrode layer until it reaches the working electrode layer, and as a result, there is a certain constant depending on the gas concentration to be measured between the working electrode layer and the reference electrode layer via the solid electrolyte layer. Since the electromotive force is generated, the concentration of the gas to be measured can be known by measuring the electromotive force.

In a conventionally known solid electrolyte type carbon dioxide sensor element, NASICON (Na _{1 + A} Zr ₂ S) is used as a solid electrolyte for forming a solid electrolyte layer.
_{i A P 3-A O 12} , where 0 ≦ A ≦ 3), Li -β-A
A sodium ion conductive material such as l ₂ O ₃ and a lithium ion conductive material are examples of electron conductive materials contained in the working electrode and the reference electrode (the materials are necessary for detecting electromotive force). In general, a noble metal material such as gold or platinum having excellent heat resistance and oxidation resistance is used, and an alkali metal carbonate or an alkaline earth metal carbonate is generally used as an auxiliary electrode substance contained in the working electrode.

[0005]

However, such a conventional solid electrolyte type carbon dioxide sensor element, when left unheated in a high-humidity atmosphere or a dew-condensation atmosphere, causes a rise in a predetermined carbon dioxide gas concentration. The problem is that the power is significantly reduced as compared to before leaving the device unattended (hereinafter, the phenomenon that such a phenomenon is likely to occur is referred to as poor moisture resistance stability, and the fact that such a phenomenon is unlikely to occur is also referred to as high moisture resistance stability). There is. In a conventional solid electrolyte type carbon dioxide sensor element generally used, the time required for the electromotive force to change and stabilize according to the fluctuation of the carbon dioxide gas concentration (hereinafter referred to as response time) is as long as 10 minutes or more. Therefore, there is a problem in use for environmental measurement in which the concentration of the gas to be detected changes greatly and the response time (response speed) to the change is an important factor.

It is known that the problem of the moisture resistance stability can be solved by using a solid electrolyte layer containing lithium titanium silicate (Li ₂ TiSiO ₅ ) (Japanese Patent Application Laid-Open No. 2001-33426). )But,
Since this element has been developed as a sensor element for on-off control or an alarm device in the above-described air purifying apparatus, a response time (response speed) that does not cause much problem in performance evaluation has been studied. . In addition, the solid electrolyte type carbon dioxide sensor element using the solid electrolyte layer containing Li ₂ TiSiO ₅ does not change the value of the electromotive force even if it is left in a high humidity atmosphere without heating for a long time. It is an excellent thing that has the feature that the time until the electromotive force is stabilized after the start is started, but if the state where heating is continued is continued for a long time, the electromotive force value at a predetermined carbon dioxide gas concentration is compared with the initial value. There is a problem of change (so-called drift occurs). For example, when a long-term stability test shown in Examples described later is performed using an element whose solid electrolyte layer is made only of Li ₂ TiSiO ₅ ,
After 350 days of continuous use, the electromotive force at 350 ppm and 2000 ppm is about 10% lower. Such a drift problem can be solved by forming a feedback control system or the like, but the circuit becomes complicated, and from the viewpoint of miniaturization of the sensor element and reduction of power consumption, such a control system is difficult. Addition is undesirable.

Accordingly, an object of the present invention is to provide a solid electrolyte type carbon dioxide sensor element having high moisture resistance stability, a short response time, and hardly causing drift even when used continuously for a long time.

[0008]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors have found that NaNd ₉ (SiO ₄ ) ₆ is used as a solid electrolyte for forming a solid electrolyte layer of a solid electrolyte type carbon dioxide sensor element. O ₂ or LiNd ₉ (SiO
₄ ) When a solid electrolyte containing ₆ O ₂ is used, it has been found that the moisture resistance stability is improved, drift is less likely to occur, and the response time is drastically shortened. Was.

That is, the present invention relates to a solid electrolyte type carbon dioxide sensor element in which a working electrode and a reference electrode are joined to the surface of a solid electrolyte layer, wherein the solid electrolyte layer is made of NaNd ₉
(SiO ₄ ) ₆ O ₂ or LiNd ₉ (SiO ₄ ) ₆ O ₂
And a solid electrolyte type carbon dioxide sensor element comprising a solid electrolyte containing:

In the solid electrolyte type carbon dioxide sensor element of the present invention, the solid electrolyte constituting the solid electrolyte layer is
Those further containing at least one compound selected from the group consisting of titanium oxide, zirconium oxide, and zirconium silicate are characterized by higher moisture resistance stability.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The solid electrolyte type carbon dioxide sensor element of the present invention has a solid electrolyte layer of NaNd ₉ (Si
The greatest feature is to use a solid electrolyte layer made of a solid electrolyte containing O ₄ ) ₆ O ₂ or LiNd ₉ (SiO ₄ ) ₆ O ₂ . These solid electrolytes generate a certain electromotive force according to the concentration of carbon dioxide, so they can be used not only as carbon dioxide sensors, but also by using these solid electrolytes, improve the moisture resistance stability and generate drift. , And the response time can be suppressed to, for example, 2 minutes or less. Note that the solid electrolyte means a conductive solid in which ions are conductive carriers, and may contain a substance having no ionic conductivity as long as it has ionic conductivity as a whole.

The solid electrolyte type carbon dioxide sensor element of the present invention.
NaNd used in₉(SiO₄) ₆O₂And LiN
d₉(SiO₄)₆O₂Means that an X-ray diffraction measurement was performed
Sometimes JCPDS card number (file number) 3
2-1133 NaNd₉(SiO₄)₆O₂}and
JCPDS card number (file number) 32-576
｛LiNd₉(SiO₄)₆O₂Diffraction pattern shown in｝
Mean the same compound from the X-ray diffraction pattern
Chemical composition of each compound if it can be recognized as a substance
(Composition ratio of each constituent element) is as shown in the above composition formula
May slightly deviate from the
You may go out. These NaNd₉(SiO ₄)₆O₂
And LiNd₉(SiO₄)₆O₂Is Na₂C
O₃, Li₂CO ₃, SiO₂, Nd₂(CO₃)₃What
Which powder is used for various metals or metalloids
Element) to a ratio that matches the above composition formula.
After mixing, bake at a temperature in the range of 400 ° C to 1300 ° C.
Can be obtained. Also, NaOC
₂H₅, LiOCH₃, Si (OC₂H₅)₄, Nd
(OC₃H₇)₃And other metal alkoxides
Is the ratio of semi-metallic elements (elements that can be cations)
Mix in a ratio that matches the composition formula and hydrolyze it
・ Polycondensation to obtain sol or gel,
After crushing, bake in the temperature range of 400 ° C to 1300 ° C.
Can also be obtained. In addition, metal Alco
When using an oxide, each metal alkoxide is hydrolyzed.
Sol and gel are obtained by dissolving and polycondensing,
Of course, it does not matter if they are mixed so that

The solid electrolyte type carbon dioxide sensor element of the present invention.
The solid electrolyte layer used in NaNd ₉(SiO₄)₆O
₂Or LiNd₉(SiO₄)₆O₂Only one of
It may consist of, but further improves the moisture resistance stability
For titanium oxide, zirconium oxide, and zirconium silicate
At least one compound selected from the group consisting of conium
Preferably, a substance is added. The content of these additives is
Although not particularly limited, the solid electrolyte layer can be easily formed,
It is also necessary to improve the stability of electromotive force during continuous use.
NaNd₉(SiO₄)₆O₂or
Is LiNd₉(SiO₄)₆O₂To 1 mole per mole.
It is preferably from 0.5 to 5 mol, particularly preferably from 0.1 to 2 mol.
No. In addition, from the viewpoint of the effect, the ion contained in the solid electrolyte layer
Preferably, the conductive material is one kind.
Different types of known ions as long as the effect of
A conductive compound may be included.

In the present invention, NaNd₉(SiO₄)
₆O₂Or LiNd₉(SiO₄) ₆O₂And as needed
Titanium oxide, zirconium oxide, and zirconium silicate depending on
At least one compound selected from the group consisting of
The method for forming the solid electrolyte layer containing is not particularly limited.
However, in advance, NaNd₉(SiO₄)₆O₂Powder or L
iNd₉(SiO₄)₆O₂Prepare the powder, and
Titanium oxide, silica, zirconia
A, from the group consisting of lithium silicate and zirconium silicate
Powder of at least one selected compound (hereinafter, optional)
Also called component powder. ) Is added and mixed after
Shaping and then sintering, or NaNd₉(SiO
₄)₆O₂Or LiNd₉(SiO₄)₆O₂Raw materials and
A predetermined amount of the powder mixture of various substances
After adding and mixing the desired component powder, molding and sintering
And so on. In addition, the above
The raw materials used in the method include carbonates as described above,
Metal alkoxides, various metal alkoxides
Is a sol or gel obtained by mixing and hydrolysis and polycondensation.
Can be used. Also, sintering of optional component powders
Sometimes, it may be added in the form of a raw material that is converted into each compound.

The mixed powder is formed by the above method and the above method.
The method of sintering is not particularly limited. A method of sintering after forming by pressing such as a uniaxial press or an isotropic isostatic press; kneading a powder with a binder and a solvent to form a paste; A method of forming into a sheet and sintering; a method of forming the paste into a thick film on a substrate by a screen printing method or the like, followed by baking and baking the paste on the substrate. At this time, the sintering is performed at 400 ° C to 1500 ° C, preferably 1000 to 1500 ° C.
It can be performed by heating in a temperature range of 1300 ° C. In the above method, at this time, NaNd
₉ (SiO ₄ ) ₆ O ₂ or LiNd ₉ (SiO ₄ ) ₆ O
₂ are formed. Although the thickness of the solid electrolyte layer is not particularly limited, it is generally 0.02 mm to 2.0 mm.
mm.

In addition to these production methods, Li ₂ O, Si
A solid electrolyte layer can also be obtained using a mixture of synthetic raw material powders such as O ₂ and Nd ₂ O ₃ as a target and using a thin film forming technique such as sputtering or vapor deposition.

[0017] The carbon dioxide sensor element of the present invention comprises NaNd.
₉(SiO₄)₆O₂Or LiNd ₉(SiO₄)₆O
₂, And if necessary, titanium oxide, zirconium oxide,
And at least one selected from the group consisting of zirconium silicate
Is a solid electrolyte composed of a solid electrolyte containing one type of compound.
Except for using the decomposition layer, the conventional solid electrolyte gas
There is no particular difference from the sensor element. That is, FIG.
1 shows the structure of a body electrolyte type carbon dioxide sensor element according to the present invention.
Similarly, the carbon dioxide sensor element of the solid electrolyte layer
Has a basic structure with a working electrode and a reference electrode joined to the surface
I do. The solid electrolyte type carbon dioxide sensor element shown in FIG.
The heater 6 connected to the heating power supply 7 has a back surface
Alumina, crystallized glass, aluminum nitride bonded to aluminum
Layered reference electrode on a ceramic substrate 4
3, the solid electrolyte layer 2, and the laminar working electrode 1 are arranged in this order.
When the laminated body is stacked, the reference electrode 3 of the laminated body is ceramic.
With an adhesive 5 so as to be in contact with the substrate.
And a potential difference between the reference electrode 3 and the working electrode 1 is measured.
Voltmeter 8 is electrically connected to both electrodes.
The carbon dioxide sensor element of the present invention is exactly the same as that shown in FIG.
Although the same structure can be adopted, this structure is merely an example.
It is not limited to this. Eg working electrode and reference
The electrode arrangement is in contact with the working and reference electrode layers.
If it is, there is no particular limitation. Also, regarding the connection mode of the heater,
However, the present invention is not limited to the above-described embodiment.
Is not particularly limited as long as it is not inhibited. In addition, some
The temperature of the device is set to 100 by heating the device from outside.
If it is possible to maintain a constant temperature of
It is not necessary to use a heater.

The structure, material, shape, size, etc. of the working electrode, the reference electrode, and the members constituting these electrodes used in the carbon dioxide gas sensor element of the present invention are also employed in the conventional solid electrolyte type gas sensor element. Can be applied without any restrictions. These members will be described below using the carbon dioxide sensor element of the present invention having the structure shown in FIG. 1 as an example.

First, a working electrode made of a layered material having a total thickness of 0.001 to 0.03 mm including an electron conductive material and an auxiliary electrode material capable of causing an equilibrium reaction with a gas to be measured is used. it can. Here, the electron conductive material is a material for outputting an electromotive force of the sensor element, similarly to the electron conductive material included in the reference electrode layer described later, and includes a noble metal element such as platinum, gold, palladium, and silver. Alloy or a mixture of two or more of these noble metal elements is generally employed, but platinum, gold, or a mixture or alloy thereof is particularly preferably employed because of its excellent corrosion resistance. . The auxiliary electrode material is not particularly limited as long as it can cause an equilibrium reaction with carbon dioxide in an atmosphere containing carbon dioxide, and alkali metal carbonates such as sodium carbonate and lithium carbonate or these are usable. Or an alkaline earth metal carbonate such as calcium carbonate or magnesium carbonate or a mixture thereof is used. However, since an equilibrium reaction with carbon dioxide gas easily occurs, sodium carbonate or lithium carbonate is preferably used. . Although the content ratio of both substances (electron conductive substance and auxiliary electrode substance) contained in the working electrode is not particularly limited, since the fluctuation of the electromotive force of the sensor element during continuous use is small, the total weight of the working electrode (both substances) Is preferably 20 to 95% by weight, particularly preferably 40 to 90% by weight based on the total weight of the electron conductive material. The structure of the working electrode is not particularly limited, (i) a structure in which the electron conductive material and the auxiliary electrode material are stacked in a layer on the surface of the solid electrolyte layer, and (ii) an auxiliary electrode material formed on the surface of the solid electrolyte layer. A known structure such as a structure in which a part or all of the layer is covered with an electron conductive material, (iii) a structure in which an auxiliary electrode material is dispersed in the electron conductive material, etc. The structure of (iii) is preferred. Further, the working electrode having these structures is prepared by kneading an electron conductive material and an auxiliary electrode material alone or after mixing with a solvent and a binder to form a paste, and baking the paste on the surface of the solid electrolyte layer by a screen printing method or the like; It can be formed by a method such as a method of forming the electron conductive material and the auxiliary electrode material by a thin film forming technique such as sputtering or vapor deposition.

As the reference electrode, a layered material having a thickness of 0.001 to 0.03 mm made of the above-mentioned electron conductive material, preferably platinum, gold, or a mixture or alloy thereof is preferably employed. You. The reference electrode can also be formed by the same method as the above working electrode.

The carbon dioxide sensor element of the present invention can be used in the same manner as the conventional solid electrolyte type carbon dioxide sensor element.
It is used by leaving it in an atmosphere that may contain carbon dioxide as a gas to be detected under the condition maintained at a constant temperature of 0 ° C., and the carbon dioxide in the atmosphere is measured based on the electromotive force measured by the voltmeter. Although it can measure concentration, it is not only high in moisture resistance stability but also hard to drift even if used continuously for a long time, so it is possible to reduce the size because no feedback control system is required . For this reason,
When using the gas sensor element mounted on various devices, when using the carbon dioxide sensor element of the present invention,
The device itself can be made compact without taking up space, and the degree of freedom in design can be increased. In addition, since the carbon dioxide sensor element of the present invention has a short response time when the concentration of carbon dioxide in the atmosphere changes, a sensor for an environment measuring device that requires a quick response to investigate the correspondence to the cause of disturbance or the like. It can be particularly suitably used as an element.

[0022]

EXAMPLES The present invention will be described specifically with reference to the following examples, but the present invention is not limited to these examples.

Example 1 FIG. 1 shows a solid electrolyte type carbon dioxide sensor element.
An element having a cross-sectional structure such as
Was. That is, first, NaOCH₃, Nd (OC₃H ₇)₃,
And Si (OC₂H₅)₄Becomes 1: 9: 6 in molar ratio
And hydrolyzed the metal alkoxide compound
After drying at 100 ° C, firing at 900 ° C for 3 hours
NaNd₉(SiO₄)₆O
₂Was obtained. NaNd₉(SiO₄)₆O₂Is synthesized
This was confirmed by X-ray diffraction. Then get
NaNd₉(SiO₄)₆O₂After uniaxially molding the powder,
Sinter for 6 hours at 1030 ° C in air
To form a solid electrolyte layer. The resulting pellet
Is obtained from the metal alkoxide as described above.
NaNd₉(SiO₄)₆O₂As a standard sample,
When pellets were identified by the Rietveld method,
100% NaNd₉(SiO₄)₆O₂Consists of
It was confirmed that.

Next, terpineol in which 5% by weight of ethylcellulose is dissolved is kneaded with gold powder as an electron conductive material and 25% by weight of lithium carbonate in a proportion of 100% by weight of the total weight of the working electrode to form a paste. On one side of the solid electrolyte layer by screen printing, drying, 650
The working electrode having a thickness of 0.015 mm was obtained by sintering for 30 minutes in the air at ℃. Further, gold powder as an electron conductive material is kneaded with terpineol in which 5% by weight of ethyl cellulose is dissolved to form a paste, and this is screen-printed on the surface of the solid electrolyte layer opposite to the surface on which the working electrode is formed,
Drying and baking for 30 minutes in air at 650 ° C.
A 015 mm reference electrode was obtained. Then, an alumina substrate equipped with a platinum heater formed by a screen printing method using a commercially available platinum paste is bonded to the reference electrode with an adhesive made of glass such that a surface on which the heater is not formed is a bonding surface. Then, a solid electrolyte type carbon dioxide sensor element was manufactured.

The solid electrolyte type carbon dioxide sensor element manufactured as described above was subjected to a moisture resistance test, a long-term stability test, and a response time measurement as shown in the following (1) to (3).

(1) Moisture resistance test Immediately after producing a solid electrolyte type carbon dioxide sensor element, the sensor element was placed in a chamber in which the concentration of carbon dioxide gas could be freely controlled, and a DC voltage was applied to a heater from a power supply to bring the sensor element to 450 °
Heated. Then, 24 hours later, the concentration of carbon dioxide in the chamber was set to 350 ppm and 2000 ppm, and the electromotive force at each concentration was measured and used as the initial electromotive force. The electromotive force at 350 ppm and 20
The difference from the electromotive force value at the time of 00 ppm was obtained, and this was used as the initial sensitivity. After measuring the initial electromotive force in this manner, the sensor element is taken out of the chamber and placed in a constant temperature / humidity chamber maintained at a temperature of 60 ° C. and a relative humidity of 90%, and the heater of the sensor element is turned off. After being left in a heated state for 7 days, it was taken out of the thermo-hygrostat, and the electromotive force at each concentration was measured in the same manner as when the initial electromotive force and sensitivity were measured. The difference between the initial electromotive force and sensitivity and the electromotive force and sensitivity after standing in a thermo-hygrostat was determined, respectively, and the resistance of the sensor element in a high-temperature and high-humidity atmosphere in a non-heated heater state was examined.

(2) Long-term stability test Immediately after the production of the sensor element, a DC voltage was applied to the heater from a power supply, and the sensor element was placed in the chamber at 450 ° C. for 24 hours.
Heated for hours. Twenty-four hours later, the concentrations of carbon dioxide in the chamber were set to 350 ppm and 2000 ppm, and the electromotive force at each concentration was measured and used as the initial electromotive force. In addition, the electromotive force at 350 ppm and 2000 p
The difference from the electromotive force value at pm was determined, and this was used as the initial sensitivity. Thereafter, the sensor element was taken out of the chamber, and the heating state at 450 ° C. in the atmosphere was maintained. 60
One day later, the sensor element was put into the chamber again, the carbon dioxide gas concentration was set to 350 ppm and 2000 ppm, and the electromotive force at each concentration was measured. In addition, the electromotive force at 350 ppm and 2000 p
The difference from the electromotive force at the time of pm was determined, and this was defined as the sensitivity on the 60th day. Differences between the initial electromotive force and sensitivity and the electromotive force and sensitivity after heating at 450 ° C. for 60 days were determined, respectively, and the long-term stability of the sensor element when heating was continued was evaluated.

(3) Measurement of Response Time After the sensor element was placed in a chamber maintained at a carbon dioxide concentration of 350 ppm, a DC voltage was applied from a power source to a heater to heat the sensor element to 450 ° C. After measuring the electromotive force at this time and confirming that the electromotive force became constant, the sensor element was immediately held in a separate chamber in which the carbon dioxide gas concentration was maintained at 2000 ppm while the temperature of the sensor element was maintained at 450 ° C. And the electromotive force was measured, and the time from the transfer to the chamber until the electromotive force became constant was defined as the response time.

When a moisture resistance test was performed by the above method, the initial electromotive forces at 350 ppm and 2000 ppm were 211 mV and 163 mV, respectively.
The sensitivity was 48 mV. 350 ppm and 20 ppm
The electromotive force after the high humidity exposure treatment at 00 ppm was 208 mV and 162 mV, respectively, and the sensitivity was 46 mV. Thus, it was confirmed that the electromotive force hardly decreased even when the high humidity exposure treatment was performed. The results of the long-term stability test show that the initial electromotive force and sensitivity are 350 ppm: 2.
10 mV, 2000 ppm: 164 mV, and sensitivity 46
mV, and the electromotive force and sensitivity after 60 days are 350 pp
m: 209 mV, 2000 ppm: 163 mV, and sensitivity: 46 mV, and the performance hardly changed even after long-term use. The response time was as short as 2 minutes.

Example 2 A solid electrolyte type carbon dioxide sensor element was prepared and evaluated in the same manner as in Example 1 except that LiNd ₉ (SiO ₄ ) ₆ O ₂ powder was used as a raw material powder for the solid electrolyte layer. . Note that LiNd ₉ (SiO ₄ ) ₆ O ₂ powder is NaOCH
₃ was obtained in the same manner as in Example 1 except that LiOCH ₃ was used instead of ₃ . Table 1 shows the composition of the solid electrolyte layer determined by the Rietveld method using LiNd ₉ (SiO ₄ ) ₆ O ₂ as a standard sample for the pellets used as the solid electrolyte layer.
Table 2 shows the results of the moisture resistance stability test, the results of the long-term stability test, and the response time.

[0031]

[Table 1]

[0032]

[Table 2]

Examples 3 to 6 NaNd ₉ (SiO ₄ ) ₆ O ₂ powder or LiNd ₉ (S
TiO ₂ , ZrO ₂ , and ZrS are added to iO ₄ ) ₆ O ₂ powder.
A solid electrolyte type carbon dioxide sensor element was produced in the same manner as in Example 1 except that a solid electrolyte layer was formed by mixing at least one kind of powder selected from the group consisting of iO _{4 so as} to have a composition ratio shown in Table 1. did. Note that NaNd ₉ (SiO
_{4) 6} O ₂ powder and _{LiLa 9 (SiO 4) 6 O} 2 powder was used which was obtained in the same manner as in Example 1 and 2. Further, commercially available powders of TiO ₂ , ZrO ₂ , and ZrSiO ₄ were used as they were. The obtained fixed electrolyte layer and sensor element were evaluated in the same manner as in Example 1. Table 1 shows the composition of the solid electrolyte layer obtained by the Rietveld method, and Table 2 shows the results of the moisture resistance stability test, the results of the long-term stability test, and the response time. As shown in Table 2, both the moisture resistance stability and the long-term stability were good, and the stabilization times were all within 2 minutes.

Comparative Example 1 A solid electrolyte type carbon dioxide sensor element was manufactured in the same manner as in Example 1 except that a solid electrolyte layer made of NASICON was used for the solid electrolyte layer. The solid electrolyte layer is made of zirconium silicate and sodium phosphate by Na ₃ Zr ₂ Si ₂ PO
After the powder was uniaxially molded by mixing so as to have a composition of ₁₂ and sintering in an air atmosphere at 1100 ° C. for 6 hours,
It was obtained by sintering in an air atmosphere at 1200 ° C. for 10 hours to obtain a disc-shaped pellet. The obtained fixed electrolyte layer and sensor element were evaluated in the same manner as in Example 1. Table 1 shows the composition of the solid electrolyte layer obtained by the Rietveld method, and Table 2 shows the results of the moisture resistance stability test, the results of the long-term stability test, and the response time. As shown in Table 2, the electromotive force after the high humidity exposure treatment decreased by 200 mV or more, and also after the long-term stability test, the electromotive force decreased by 20 mV or more. Furthermore, the stabilization time was 12 minutes.

[0035]

The solid electrolyte type carbon dioxide sensor element of the present invention does not change its electromotive force even when it is left in a high humidity atmosphere in a non-heated state for a long time. It is excellent in that the time until the electric power is stabilized is short, and the drift hardly occurs even when used continuously for a long time. The feature that the drift is unlikely to occur means that a device or a circuit for correcting the drift is not required, which not only enhances the reliability of the device, but also reduces the size of the device itself or a device mounted with the device. There is also a secondary effect of increasing the degree of freedom in device design and equipment design.
In addition, the response time when the carbon dioxide concentration fluctuates is short. For example, even if the carbon dioxide concentration instantaneously changes about six times, the electromotive force is stabilized within two minutes. Therefore, the solid electrolyte type carbon dioxide sensor element of the present invention can be particularly suitably used as a carbon dioxide sensor element for environmental measurement which requires a high response speed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a conventional typical solid electrolyte type carbon dioxide sensor element.

[Explanation of symbols]

 1. Working electrode 2. Solid electrolyte layer 3. Reference electrode 4. Ceramic plate 5. Adhesive 6. Heater 7. Power supply 8. voltmeter

Claims (2)

[Claims] 1. A solid electrolyte type carbon dioxide sensor element comprising a working electrode and a reference electrode joined to the surface of a solid electrolyte layer, wherein the solid electrolyte layer is made of NaNd ₉ (SiO ₄ ) _6.
A solid electrolyte type carbon dioxide sensor element comprising a solid electrolyte containing O ₂ or LiNd ₉ (SiO ₄ ) ₆ O ₂ . 2. A solid electrolyte constituting a solid electrolyte layer,
The solid oxide carbon dioxide sensor element according to claim 1, comprising at least one compound selected from the group consisting of titanium oxide, zirconium oxide, and zirconium silicate.