JPH07103937A - Gas sensor - Google Patents

Abstract

PURPOSE:To provide a gas sensor which can detect SOX (sulfur oxide) gases effectively, whose electrode or the like is not corroded by the SOX gases, which is operated stably and whose reliability is high and to lower the operating temperature of the gas sensor. CONSTITUTION:In a gas sensor for detection of SOX gases, a sub-electrode 20 by a sulfate is installed on a base material 10 formed of a solid electrolyte material. In the gas sensor, a mixed substance of a sulfate which contains silver sulfate is used as the sulfate used for the subelectrode 20, a metal electrode 30 which contains silver is installed on the surface of the subelectrode 20, and the surface of the metal electrode 30 is covered with a platinum film 40.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an gas sensor, particularly to a gas sensor used for the detection of SO _X (sulfur oxide) gas.

[0002]

2. Description of the Related Art A solid electrolyte material has a characteristic of having high ionic conductivity, and therefore, it is utilized for a gas sensor by taking advantage of the characteristic. For example, since zirconia ceramics have oxygen ion conductivity, they are suitable as an oxygen gas sensor, and are used as oxygen concentration detection sensors. In addition, the solid electrolyte material is provided with a sulfate or a carbonate as an auxiliary electrode, so
_A gas sensor that detects _X gas or CO _X gas can be used.

SO _x using the above solid electrolyte material as a base material
When configuring a gas sensor for detecting gas or CO _X gas, a sulfate or carbonate is provided as a sub-electrode on the base material, and a detection electrode made of platinum or the like is provided on the sub-electrode and the back surface side of the base material. The gas is detected by providing an electromotive force generated between the electrodes.

[0004]

By the way, when the gas sensor using the above solid electrolyte material is used, the base material is used while being heated to a high temperature in order to improve the ionic conductivity of the solid electrolyte material. For example, when yttria-stabilized zirconia ceramics is used as the solid electrolyte material, it must be heated to 650 ° C. or higher before use.

As a solid electrolyte material, there is a material that operates at a lower temperature than zirconia ceramics, etc.
O For _X gas gas sensor for sensing must use corrosion resistance excellent material such as zirconia ceramics as a solid electrolyte material because of its very high corrosive SO _X gas, such corrosion When using a material with excellent properties, the operating temperature must be high. Also,
The detection electrode provided on the base material is also corroded by the SO _X gas, which causes a problem that the reliability of the sensor is reduced.

Therefore, the present invention has been made to solve these problems, and an object thereof is SO
Has sufficient reliability as a gas sensor for _X gas detection,
Another object of the present invention is to provide a gas sensor whose operating temperature can be lowered and which can be easily handled.

[0007]

The present invention has the following constitution in order to achieve the above object. That is, it is a gas sensor for SO _X gas detection, in which a sub-electrode made of sulfate is provided on a base material made of a solid electrolyte material, and a mixture of sulfates containing silver sulfate is used as the sulfate used for the sub-electrode. Then, a metal electrode containing silver is provided on the surface of the sub-electrode, and the surface of the metal electrode is covered with a platinum film. Also, yttria-stabilized zirconia ceramics is used as the solid electrolyte material of the base material. Further, as the sulfate used for the sub-electrode, a sulfate having a good ion conductivity such as lithium sulfate, barium sulfate, calcium sulfate, and sodium sulfate is used in addition to silver sulfate. Further, as the sulfate used for the sub-electrode, a substance having low hygroscopicity such as lithium sulfate and barium sulfate is mixed and used. Further, a silver-palladium electrode is used as the metal electrode.

[0008]

SUMMARY OF THE INVENTION The gas sensor according to the present invention is used for detecting SO _X gas. A solid electrolyte material is used as a base material, and a sub-electrode made of sulfate is formed on the base material. It is characterized in that a metal electrode is formed on and a detection electrode is further provided. As a solid electrolyte material used as a substrate, yttria-stabilized zirconia ceramics is effective from the viewpoint of corrosion resistance and stability. Further, as the sulfate used as the sub-electrode, it is preferable to use a mixture of sulfates containing silver sulfate.

Further, metallic silver is used as the metallic electrode. When a metal electrode is formed by metallizing a metal paste, it is preferable to add palladium to silver to form the electrode. This is because the adhesion between the sub electrode and the metal electrode can be improved by adding palladium. Further, the surface of the metal electrode is covered with a platinum film to form a detection electrode. The platinum film is provided to prevent the metal electrode from being sulfided by SO _X gas and to have heat resistance when the gas sensor is heated to a high temperature. The other detection electrode provided on the back surface of the base material is also preferably formed of platinum.

The reason why the sulfate provided on the sub-electrode is made to contain silver sulfate is to detect SO _X gas by the following reaction. This reaction occurs at the silver-palladium electrode part. In the sub-electrode part In the base material part It depends on the reaction of each. Thus, silver sulfate is an essential substance as a constituent of the sub-electrode, and silver is also an essential constituent as a metal electrode.

When forming the sub-electrode, it is possible to form the sub-electrode using only silver sulfate, but since silver sulfate is expensive and has a low melting point of 654 ° C., it is used as a mixture with another sulfate. Is good. As the sulfate forming the auxiliary electrode, for example, lithium sulfate, barium sulfate, calcium sulfate, sodium sulfate and the like can be used. The amount of silver sulfate added to the mixture of these sulfates as a sub-electrode can be about 0.5 mol% to 15 mol%,
It is preferably about 5 mol%.

The use of sulfates other than silver sulfate such as lithium sulfate and barium sulfate as described above increases the ionic conductivity in the sub-electrode by adding these sulfates, thereby detecting gas. It also has the purpose of increasing the sensitivity. For example, when silver sulfate is added to a mixture of lithium sulfate and sodium sulfate, sodium sulfate has a high ionic conductivity, but has a hygroscopic property, so that the mixing ratio is limited to about 80 mol%. As described above, when forming the sub-electrode, it is preferable to set the mixing ratio in consideration of the hygroscopicity and function of the sulfate.

In the present invention, the metal electrode is coated with a platinum film so that the metal electrode is not exposed to SO _X gas. this is,
This is because the metallic silver of the metal electrode is easily sulfided by SO _X gas, and this is prevented by the platinum film. In fact, by coating the electrodes with a platinum film, SO _x
It is possible to prevent the electrodes from corroding due to the gas, and it is possible to effectively improve the reliability of the SO _X gas sensor. Silver or silver-palladium used for the metal electrode is S
Since it is excellent in reactivity with O _X gas and silver ions are easily generated by SO _X gas, it becomes possible to operate the gas sensor without raising the temperature to the conventional temperature.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a gas sensor according to the present invention. In the figure, 10 is a base material formed of yttria-stabilized zirconia ceramics, and 10 a is a frame body formed on the base material 10. The base material 10 is formed by a firing method similar to a general ceramic substrate manufacturing method.

Reference numeral 20 is a sub-electrode formed of a sulfate on the inner portion of the frame portion 10a. In the examples, the composition was 5 mol% silver sulfate, 57 mol% lithium sulfate, and 38% barium sulfate. 30 is silver formed on the surface of the sub-electrode 20
It is a palladium electrode. 40 is a silver-palladium electrode 30
Is a platinum film provided to cover the surface of the. Platinum film 4
At 0, a platinum wire 42 is provided as a lead wire. Platinum film 40
Is one of the detection electrodes of the gas sensor. Also, the base material 10
The other detection electrode 50 is formed of platinum on the lower surface of the. 52 is a platinum wire as a lead wire.

When the sub-electrode 20 is formed, it is formed by laminating a mixture of sulfates such as silver sulfate and lithium sulfate in the frame portion 10a, pressurizing, melting and solidifying at a temperature of 800 ° C. or higher. . Sub-electrode 20 has a thickness of 1 m
It was about m. Further, the silver-palladium electrode 30 is formed by forming a mixed paste of silver and palladium, applying the paste on the sub-electrode 20 and baking it, and the platinum film 40 is applied to the silver-palladium electrode 30 using the platinum paste. And then fired.

The gas sensor of the embodiment has the above configuration,
It could be used for detecting SO _X gas even at a low temperature of about 450 ° C. The sub electrode 20 and a silver - palladium electrode 30 is able to detect a suitably SO _X gas is prevented from being corroded by SO _X gas. In this way, the operating temperature can be lowered as compared with the conventional ones, because the silver-palladium electrode 30 is likely to generate silver ions by SO _X gas, and silver sulfate is mixed with other sulfates. This is because the sub-electrode 20 can be formed stably by increasing the gas detection sensitivity. The preferred operating temperature of the gas sensor of the embodiment is 500
C to 600C.

FIG. 2 shows another embodiment of the gas sensor. This gas sensor is an example in which a detection electrode is provided on the same surface side of the base material 10. The configurations of the sub-electrode 20, the silver-palladium electrode 30, and the platinum film 40 are the same as those in the above example, and the other detection electrode 50 is arranged on the upper surface of the base material 10.

[0019]

The gas sensor according to the present invention, as described above, it is possible to detect the SO _X gas effectively, without the electrode or the like is attacked by SO _X gas, operates stably, and reliable It can be provided as a highly effective sensor. Further, the operating temperature of the gas sensor can be lowered as compared with that of the conventional one, and the gas sensor can be easily handled, and so on.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an embodiment of a gas sensor.

FIG. 2 is a sectional view showing the configuration of another embodiment of the gas sensor.

[Explanation of symbols]

 10 Base Material 10a Frame Part 20 Sub-electrode 30 Silver-palladium Electrode 40 Platinum Film 42 Platinum Wire 50 Detecting Electrode 52 Platinum Wire

Claims (5)

[Claims] 1. A gas sensor for detecting SO _X gas, wherein a sub-electrode made of a sulfate is provided on a base material made of a solid electrolyte material, wherein a sulfate containing silver sulfate as a sulfate used for the sub-electrode is mixed. A gas sensor characterized in that a body is used, a metal electrode containing silver is provided on the surface of the sub-electrode, and the surface of the metal electrode is covered with a platinum film. 2. The gas sensor according to claim 1, wherein yttria-stabilized zirconia ceramics is used as the solid electrolyte material of the base material. 3. The sulfate used for the sub-electrode, in addition to silver sulfate, lithium sulfate, barium sulfate, calcium sulfate,
The gas sensor according to claim 1, wherein a sulfate having a good ion conductivity such as sodium sulfate is used. 4. The gas sensor according to claim 1, wherein a substance having a low hygroscopic property such as lithium sulfate or barium sulfate is mixed and used as a sulfate salt used for the sub-electrode. 5. The gas sensor according to claim 1, wherein a silver-palladium electrode is used as the metal electrode.