JPH10104197A - Sox gas sensor and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an SOX gas sensor short in the response time to the fluctuations of the concn. of SOX gas and enabled in continuous measurement. SOLUTION: In an SOX gas sensor measuring the concn. of SOX gas by measuring the potential difference between the auxiliary electrode 12 formed on the SOX gas contact side surface of a ceramic substrate 10 composed of yttria stabilized zirconia ceramic and the standard electrode 16 formed on the air contact side surface of the ceramic substrate 10, silver and silver sulfate are mixed in the auxiliary electrode 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to SO _X a gas sensor and a manufacturing method thereof, is more particularly formed on one surface side of the ceramic substrate made of oxide ion conducting ceramic, containing a substance that reacts with SO _X Gas and a sub electrode, the potential difference is measured between the reference electrode formed on the other surface of the ceramic substrate, to SO _X gas sensor and a fabrication method thereof for measuring the SO _X gas concentration.

[0002]

2. Description of the Related Art A conventional SO _X gas sensor uses a ceramic substrate made of an oxide ion conductive ceramic, typically a ceramic substrate made of a yttria-stabilized zirconia ceramic (hereinafter sometimes referred to as a YSZ ceramic substrate). A sub-electrode (detection electrode) mainly composed of a mixture of silver sulfate and barium sulfate and containing a substance that reacts with SO _X gas is formed on one side thereof, and YSZ
A standard electrode (reference electrode) is formed on the other surface of the ceramic substrate. In such a SO _X gas sensor,
On one side of the YSZ ceramic substrate on which the sub-electrode is formed, S
While introducing O _X gas, the other side of the YSZ ceramic board in contact with the air, to measure the potential difference between the standard electrode formed on the other surface of the auxiliary electrode and the YSZ ceramic board.
The potential difference between the electrodes is generated based on an electromotive force mainly caused by a chemical reaction occurring in the sub-electrode, and has a predetermined relationship with the SO _X gas concentration (partial pressure). Therefore, by measuring the potential difference between the electrodes, the SO _X gas concentration (partial pressure) is measured.
You can know.

[0003]

According to such an SO _X gas sensor, the SO _X gas concentration can be continuously measured.
It is promising as a sensor that continuously measures the concentration of SO _X gas in flue gas of a boiler or the like, and continuously monitors the amount of SO _X gas discharged. However, the conventional SO _X gas sensor has a response time of about 20 to a change in SO _X gas concentration.
３０30 minutes, so the amount of sulfur contained in flue gas
The response time is slow for monitoring _OX gas and cannot be put to practical use. Therefore, the SO has a short response time and can be continuously measured.
_{There is a} need for an _X gas sensor. Further, a conventional SO _X gas sensor is configured such that a predetermined amount of a sulfate such as powdery silver sulfate or barium sulfate is placed on a YSZ ceramic substrate and then pressed by a hydrostatic pressure into a predetermined shape. Melting at a temperature close to ℃, or forming a powdery sulfate into a sheet, cutting it into a predetermined shape, placing the cut piece at a predetermined position on a YSZ ceramic substrate, and placing it in an electric furnace for 800 It is formed by a method of melting at a temperature around ℃. However, such a conventional method of manufacturing a SO _X gas sensor requires complicated techniques such as a sulfate treatment step and requires a skilled technique. Therefore, there is a demand for a method of manufacturing an SO _X gas sensor that has simple steps and is easy to operate.
An object of the present invention, SO response time to changes in _X gas concentration while providing a short and continuous measurable SO _X gas sensor, SO _X obtained by and easy work such SO _X gas sensor in a simple process An object of the present invention is to provide a method for manufacturing a gas sensor.

[0004]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors have found that a silver layer with a platinum electrode obtained by firing a silver paste applied on one side of a YSZ ceramic substrate is obtained. After contacting with SO _X gas for aging for a predetermined time, a platinum electrode was formed on the other surface of the YSZ ceramic substrate and used as a SO _X gas sensor.
The response time to fluctuations in SO _X gas concentration is lower
It was found that the time was significantly shorter than that of the _X gas sensor,
The present invention has been reached. That is, the present invention relates to a sub-electrode formed on one surface of a ceramic substrate made of oxide ion conductive ceramic and containing a substance that reacts with SO _X gas, and a standard electrode formed on the other surface of the ceramic substrate. measuring the potential difference between the measures SO _X gas concentration S
In O _X gas sensor, in SO _X gas sensor, characterized in that the silver and the silver sulfate is mixed in the sub electrode. Further, the present invention is an oxide formed on one surface of the ceramic substrate made of an ion conductive ceramic, and the secondary electrode containing a material which reacts with SO _X gas, standard electrode formed on the other surface of the ceramic substrate When manufacturing a SO _X gas sensor for measuring the potential difference between the ceramic substrate and the SO _X gas concentration, a silver paste applied to a predetermined portion of one side of the ceramic substrate is fired to form a silver layer made of silver. Then, an SO ₃ gas is brought into contact with the silver layer to form a sub-electrode in which silver and silver sulfate are mixed, thereby producing a SO _X gas sensor.

In the present invention, the SO _X gas concentration can be accurately measured by forming the sub-electrode on the SO _X gas contact side surface of the ceramic substrate and forming the standard electrode on the air contact side surface of the ceramic substrate. Further, by using yttria-stabilized zirconia ceramic as the oxide ion conductive ceramic, the heat resistance of the SO _X gas sensor can be improved. Further, by connecting a platinum wire to a platinum mesh embedded in the sub-electrode, SO ₂ gas can be converted to SO ₃ gas, and accurate measurement of SO _X gas concentration can be performed.

[0006] SO _X gas sensor according to the present invention, SO _X
The detailed reason why the response time to the change in gas concentration can be significantly shorter than that of the conventional SO _X gas sensor is not clear, but is presumed as follows. That is, SO _X
In the gas sensor, the following reaction (Chemical Formula 1) occurs as a whole, but the reaction of Chemical Formula 2 in the silver phase of the sub-electrode, the chemical formula 3 in the silver sulfate phase, and the reaction of oxide ion conductive ceramics. In the resulting ceramic substrate, the reaction of Chemical Formula 4 has occurred.

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Embedded image On the other hand, in the SO _X gas sensor of the present invention, since silver and silver sulfate are mixed in the sub-electrode, the diffusion distance of ions such as Ag ⁺ and O ²⁻ in the sub-electrode is smaller than that of the conventional SO _X gas sensor. As compared with the sub-electrode mainly composed of silver sulfate and barium sulfate, the reaction of [Chemical Formula 3] is easily caused, and the response time to the fluctuation of the SO _X gas concentration can be shortened as compared with the conventional SO _X gas sensor. It is thought that it was.

[0007]

FIG. 1 shows an example of an SO _X gas sensor according to the present invention. The SO _X gas sensor shown in FIG. 1 is a ceramic substrate (YSZ ceramic) made of yttria-stabilized zirconia ceramic (YSZ ceramic) used as a ceramic substrate made of an oxide ion conductive ceramic.
On the ceramic substrate 10, an electrode 14 is provided on a sub-electrode 12 formed on the SO _X gas contact side surface, and a standard electrode 16 is formed on the air contact side surface. Further, the electrode 14 and the standard electrode 16 are connected to a voltmeter 22 via platinum wires 18 and 20, and the electrode 14 and the standard electrode 16 are connected.
Can be measured. In this SO _X gas sensor, the sub-electrode 12 is formed in a convex portion 22 that projects annularly from the SO _X gas contact side surface of the YSZ ceramic substrate 10, and silver and silver sulfate are mixed.

The electrode 14 is formed by welding one end of a platinum wire 18 to a platinum mesh embedded in the sub-electrode 12, and the standard electrode 16 is formed on the air contact side surface of the YSZ ceramic substrate 10 by sputtering or the like. A platinum net obtained by welding one end of a platinum wire 20 is joined to the platinum layer thus formed. In this manner, by welding the platinum wire 18 to the electrode 14 made of a platinum network, the platinum forming the platinum wire 18 can serve as a catalyst to sufficiently convert SO ₂ gas or the like to SO ₃ gas. _X gas concentration can be measured accurately.
Further, the platinum layer forming the standard electrode 16 can promote the above-mentioned reaction of Chemical Formula 4.

The SO _X gas sensor shown in FIG. 1 has an annular convex portion 2 on the SO _X gas contact side surface of a YSZ ceramic substrate 10.
After a silver paste layer is formed by applying a silver paste inside 2, the silver paste layer is baked at a temperature equal to or lower than the melting point of silver, specifically, at a temperature equal to or lower than 750 ° C., and contained in the silver paste. The binder is removed to form a silver layer composed of silver. At this time, a silver layer in which the electrode 14 is embedded integrally can be formed by firing the silver paste layer in which the electrode 14 made of a platinum mesh body with one end of the platinum wire 18 welded is embedded near the surface. Further, the sub-electrode 12 (detection electrode) in which silver and silver sulfate are mixed can be formed by performing aging for about several tens of hours while maintaining the temperature at about 600 ° C. while bringing the SO ₃ gas into contact with the silver layer. This sub electrode 12
The electrode 14 is formed by welding a platinum wire to a platinum mesh embedded in the sub-electrode 12. Such electrodes 14, platinum net member platinum wire was welded was calcined by placing the surface of the silver paste, after integrating the silver layer and the platinum net member, by aging at SO ₃ gas, secondary It can be integrated with the electrode 12. As described above, since the SO _X gas sensor according to the present invention can be obtained by bringing the silver layer obtained by firing the silver paste layer into contact with the SO ₃ gas, it can be manufactured by an extremely simple process. .

In the present invention, since the sub-electrode 12 (detection electrode) is formed by bringing the SO ₃ gas into contact with the silver layer, silver and silver sulfate are mixed. This means that when the cross section and the surface of the sub-electrode 12 are observed with a microscope, a pink layer is observed, and the EPMA (Electron p.
According to analysis using a robe microanalyzer, it is considered that silver and silver sulfate are mixed and silver sulfide is also formed. Further, a standard electrode 16 (reference electrode) can be formed by welding a platinum net having one end of a platinum wire 20 welded to a platinum layer formed on the air contact side surface of the YSZ ceramic substrate 10 by sputtering or the like.

As shown in FIG. 1, one end surface of a cylindrical body 24 made of YSZ ceramic is brought into contact with the SO _X gas contact side surface of the YSZ ceramic substrate 10 and glass-sealed with the obtained SO _X gas sensor. I have. A platinum net 26 is provided in the middle of the cylinder 26, and the SO ₂ gas or the like in the SO _X gas introduced into the cylinder 24 from the direction of the arrow in FIG.
Convert to O ₃ gas. The platinum net 26 may be a platinum wire. The SO _X gas sensor shown in FIG.
When the SO _X gas is introduced into the cylindrical body 24 mounted on the YSZ ceramic substrate 10 from the direction of the arrow while holding the platinum net 26, the platinum wire 18 and the platinum net forming the electrode 14, the SO _X gas in the SO _X gas is maintained. SO ₂ gas or the like is converted into SO ₃ gas, and the SO ₃ gas diffuses in the sub-electrode 12. At the same time, on the air contact side of the YSZ ceramic substrate 10 forming the SO _X gas sensor, O ²⁻ generated by the above-described reaction of Chemical Formula 4 also diffuses in the sub-electrode 12. In addition, Ag ⁺ is present in the sub-electrode 12 due to the above-described reaction of [Chemical Formula 2], and the above-described reaction of [Chemical Formula 3] occurs in the sub-electrode 12 to generate electromotive force. Since a certain relationship exists between the electromotive force and the SO ₃ gas concentration, the electrode 1
The SO ₃ gas concentration can be measured by measuring the potential difference between 4 and 16.

In the SO _X gas sensor shown in FIG.
The response curves for the variation of the O _X gas concentration shown in FIG. The response curve shown in FIG. 2 shows a change in the potential difference from when the gas containing 100 ppm of SO ₂ gas was introduced into the cylinder 24 in the direction of the arrow in FIG. 1 until the gas was cut off after 2 hours. . Furthermore, showing the SO _X gas sensor and conventional SO _X gas sensor shown in FIG. 1, the response curves for the variation of the SO _X gas concentration under the same conditions as that for determining the response curve shown in Figure 2 in FIG. 3 is a response curve of the SO _X gas sensor shown in FIG. 1, and a response curve B is a response curve of the conventional SO _X gas sensor. Here, in the conventional SO _X gas sensor, a predetermined amount of a mixture of powdered silver sulfate and barium sulfate is placed on a YSZ ceramic substrate, and then subjected to isostatic pressing to form into a predetermined shape.
It is fired at a temperature of 99 ° C. to form a sub-electrode.
Also in such a conventional SO _X gas sensor, one end surface of a cylindrical body made of YSZ ceramic comes into contact with the surface of the YSZ ceramic substrate on which the sub-electrode is formed, and glass sealing is performed. Have been.

The response time is obtained from the response curve.
The response time is, as shown in FIG. _XAfter the introduction of gas
The potential difference between the electrodes 14 and 16 is the equilibrium potential difference (see FIG. 3).
Until it reaches 90% of 100%)
Means between. The response curve A shown in FIG._XMoth
The response time obtained from the response curve of the sensor is about 2-3 minutes.
It was around. On the other hand, the response curve B (conventional SO
_XResponse time determined from the response curve of the gas sensor) is about 20
３０30 minutes and the SO shown in FIG._XGas sensor response
It can be seen that the time has been significantly reduced.

[0014] above, SO _X gas sensor shown in FIG. 1 has been described, although the standard electrode 16 of the YSZ ceramic board is placed in contact with the air, as shown in FIG. 4, S
During flue 28 O _X gas content of the flue gas passes through, SO
_{An X} gas sensor may be provided. Even in such a case, the SO _X gas concentration can be measured using oxygen ions in the gas. However, in this case, when the oxygen partial pressure in the flue gas fluctuates, the reference voltage fluctuates, and the measured value of the SO _X gas concentration may fluctuate. Further, in the SO _X gas sensor according to the present invention, the sub-electrode 12 is formed by contacting the silver layer with the SO ₃ gas and performing aging. However, the sub-electrode 12 is formed by mixing silver sulfate in the silver paste. In this case, aging for bringing the baked silver layer into contact with SO ₃ gas may not be performed. Further, in addition to silver sulfate, a sulfate such as barium sulfate may be mixed in the silver paste as needed. Further, a ceramic substrate made of calcia-stabilized zirconia may be used instead of the YSZ ceramic substrate.

[0015]

The SO according to the present invention_XThe gas sensor is SO
_XResponse time to gas concentration fluctuations_Xgas
Shorter time than sensor
Can be determined. Further, the manufacturing process is the same as the conventional S
O_XIt can be shortened compared to the gas sensor manufacturing process.
And can be easily manufactured. Therefore, the present invention
Such SO_XThe gas sensor detects S in flue gas such as a boiler.
O _XThe gas concentration can be suitably used for monitoring.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an SO _X gas sensor according to the present invention and a usage mode thereof.

FIG. 2 is a graph illustrating a response time of the SO _X gas sensor according to the present invention.

FIG. 3 is an explanatory diagram illustrating another usage mode of the SO _X gas sensor according to the present invention.

FIG. 4 is a graph showing the response time of a conventional SO _X gas sensor.

[Explanation of symbols]

Reference Signs List 10 YSZ ceramic substrate 12 Sub-electrode 14, 16 Electrode 18, 20 Platinum wire A Response curve of SO _X gas sensor according to the present invention B Response curve of conventional SO _X gas sensor

[Procedure amendment]

[Submission date] October 2, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an SO _X gas sensor according to the present invention and a usage mode thereof.

FIG. 2 is a graph illustrating a response time of the SO _X gas sensor according to the present invention.

[3] according to the present invention SO _X gas sensor and a conventional SO _X
It is the graph which compared the response curve with a gas sensor.

FIG. 4 shows another usage of the SO _X gas sensor according to the present invention .
FIG.

Claims (7)

[Claims] 1. A sub-electrode formed on one surface of a ceramic substrate made of an oxide ion conductive ceramic and containing a substance that reacts with SO _X gas, and a standard electrode formed on the other surface of the ceramic substrate. And measure the potential difference between
In SO _X gas sensor for measuring O _X gas concentration, SO _X gas sensor, characterized in that the silver and the silver sulfate is mixed in the sub electrode. 2. The SO _X gas sensor according to claim 1, wherein the oxide ion conductive ceramic is a yttria-stabilized zirconia ceramic. 3. The SO _X gas sensor according to claim 1, wherein a platinum wire is connected to a platinum mesh body embedded in the sub-electrode. 4. The SO _X gas sensor according to claim 1, wherein the sub-electrode is formed on an SO _X gas contact side surface of the ceramic substrate, and the standard electrode is formed on an air contact side surface of the ceramic substrate. 5. A sub-electrode formed on one surface of a ceramic substrate made of an oxide ion conductive ceramic and containing a substance that reacts with SO _X gas, and a standard electrode formed on the other surface of the ceramic substrate. And measure the potential difference between
When manufacturing a SO _X gas sensor for measuring the O _X gas concentration, a silver paste applied to a predetermined portion of one surface of the ceramic substrate is fired to form a silver layer made of silver. _{3. A} method for manufacturing an SO _X gas sensor, comprising forming a sub-electrode in which silver and silver sulfate are mixed by contacting _three gases. 6. As an oxide ion conductive ceramic,
The method for manufacturing an SO _X gas sensor according to claim 5, wherein a yttria-stabilized zirconia ceramic is used. 7. The SO _X gas sensor according to claim 5, wherein a silver layer is formed by firing a silver paste layer in which an electrode made of a platinum mesh connected to one end of a platinum wire is embedded near a surface layer. Production method.