JPS6029651A - Gas sensor for detecting many kinds of gases - Google Patents

Abstract

PURPOSE:To improve mass productivity and a reliability by using the same one as a base body sensor, and forming a metallic oxide catalyst layer selected by a gas component, on this base body sensor. CONSTITUTION:10wt% PbO-TiO2-SiO2 glass powder is weighed confront with 90wt% WO3 powder, and this glass frit material and the WO3 powder are mixed. Subsequently, a vehicle consisting of nitrocellulose-alpha-terpineol is added to said mixture and kneading is executed, by which a paste for a thick film is made. By using this paste, a lower electrode of a sensor use substrate prepared separately is printed, formed and dried. Upper electrodes 8, 9, 10 and 11 are printed on gas detecting material layers (base body sensors) 3, 4, 6 and 7 by using platinum paste and dried. They are calcined on a belt furnace for thick film, and a base body sensor of a WO3 sandwich type for four element which has formed the electrodes on the upper and lower faces of the gas detecting material layers 3, 4, 6 and 7 is made. A metallic oxide catalyst layer is covered formed on the upper electrode of the WO3 base body sensor, and a gas detecting gas sensor which has integrated sensor elements is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an improvement of a gas sensor for detecting various types of waste having a selective detection function for various types of gases.

[Background of the invention]

As gas detection materials, 8n02, Fe2O3, ZnO
Oxide semiconductors such as oxide semiconductors are generally known.

Due to the presence of valleys, these oxide semiconductors
Its resistance value changes greatly, and this property is used to detect gas leaks.However, this type of waste detection material has poor selectivity for similar gases. Therefore, gas leak alarms using this gas detection material have the problem of many false alarms and low reliability as a gas leak alarm.

For example, in a home kitchen, alcohol used during cooking or alcohol gas generated when drinking alcohol may cause an alarm to be issued as if LPG or city gas were leaking.

When such false alarms occur frequently, the common experience is to turn off the alarm and proceed.

If you forget to turn on the alarm even after turning it off, it will not function as an alarm, and you may not realize that there is actually a gas leak due to the sense of relief that there is an alarm. This could lead to serious accidents such as gas explosions and gas poisoning.

Therefore, the sense of relief that comes with the presence of alarms can instead lead to disaster, and the manufacturers of alarms can't help but be responsible for the huge social problem.

In response to this, Japanese Patent Laid-Open No. 53-3629 proposes a gas sensing material whose surface is coated with cupric oxide.

However, even if a gas detection material is coated with only cupric oxide, it is insufficient to provide a gas identification function, and the result is only 7.

Currently, as an improved version of this, a multi-gas selective integrated gas sensor has been proposed that integrates multiple sensors in order to provide selectivity for many types of waste, and is able to detect gas leaks according to gas components. Some are designed to prevent false alarms. .

For example, in the case of a sensor that can select from four types of waste, four different detection materials are used as the base sensor.

This base sensor is coated with an oxide catalyst layer that is sensitive to the presence of debris, and the combination of this oxide catalyst layer and the type of base sensor provides gas selectivity.

However, in order to form different base sensors, for example, four types of base sensors, the base sensors are made into pastes using four different manufacturing processes, and each paste is baked on an insulating substrate at a different firing temperature. Manufacturing processes will become more diverse. Depending on the type of parent body sensor, variations may occur in the sensor resistor, and temperatures ranging from a high resistance value (1084Ω) to a low resistance value (100Q) may rise at t.

This diversification of manufacturing processes results in poor m:i characteristics, the 1lIij rating of the broadcaster becomes expensive, which prevents it from being widely used in general households, and is impractical.Furthermore, due to variations in sensor resistance values, [Object of the Invention] The present invention solves the above-mentioned conventional drawbacks, and provides a practical and highly reliable song that can be used for specific carp alarms. It is an object of the present invention to provide a gas sensor for detecting a variety of gases, which has a dregs identification function that is selectively sensitive to gases.

[Summary of the invention]

That is, the present invention simplifies the manufacturing process and improves practicality by making it possible to use one type of matrix sensor instead of using multiple types of matrix sensors selected according to the type of waste as in the past. This system has improved reliability by forming a plurality of base sensors made of the same material on an insulating substrate, and on top of these base sensors, a monohagiide catalyst coating having a catalytic activity depending on the type of waste is applied. It was formed.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below. The inventors used the same material as the base sensor and conducted numerous experiments in order to discover the unique sensitivity to gas components in relation to the oxide catalyst coating layer formed on the base sensor.

As a result, a base sensor was selected from a large number of metal oxides, and metal oxides with different activation energies were mixed and coated with an oxide catalyst on the base sensor made of the selected metal oxide. By forming a layer, even if the base sensor is made of the same material, the selectivity can be increased depending on the waste component.
We found that this difference occurs.

This will be explained in more detail below. FIG. 1 shows an embodiment of a sensor according to the present invention.

First, an example of a method for manufacturing a sensor element according to the present invention will be described as follows.

To explain the manufacturing of the sensor substrate, first, a heater pattern 5 is formed on the back side of an alumina substrate 1 with a purity of 96% using a platinum paste (TR760A manufactured by Nichi-Chinese Matsusei Co., Ltd.) by a screen printing method. Next, platinum paste (T R
760A) Print the pattern of the lower electrode 2 using f and dry it. Next, put this alumina substrate 1 into an electric furnace 12
Bake at 00°C for 2 hours. As a result, a sensor substrate having the lower electrode 2 formed on the front surface and the heater 5 formed on the back surface was prepared.

Next, manufacturing of the mother body sensor will be explained.

WOs powder (for example, commercially available 99.9% manufactured by Kojundo Kagaku Co., Ltd.).

Weigh an appropriate amount of 99.9% (manufactured by Rare Metallic). The raw material powder particle size of this powder is granulated in advance.

P for 90% by weight (hereinafter abbreviated as wt%) of this raw material powder
Weigh out 10 wt% of bO-TiO2-8i (Jz-based glass powder) and mix this glass frit system with the WO3 powder.

For 10 g of this mixed powder, nitrocellulose-α
- Mixing is carried out by adding 3rr'Ll of a vehicle consisting of terpineol to produce a paste for thick films.

This paste was printed to a thickness of 40 μm on the lower electrode of the sensor substrate prepared earlier and dried. After drying, gas sensing material layers (base sensor) 3, 4, 6
．． Upper electrodes 8, 9, 10, and 11 are printed on 7 using platinum paste (Tl is also 760A) and dried. After drying, it was baked in a thick film belt furnace at a maximum temperature of 900°C for 10 minutes to produce a 4-element WO3 Sanderuch-type matrix sensor with electrodes formed on the upper and lower surfaces of the gas detection material layers 3.4 and 6.7. Next, on the base sensor made of the same material of this WO3, different oxide catalyst layers are formed depending on the gas components, and methane gas, which is a city gas component, carbon oxide scum, hydrogen gas, and interference gas are representative. Using alcohol as an example, we will explain a catalyst material that selectively detects four complementary residue components using four elements.

Table 1 shows the results of investigating the sensitivity of various oxide catalysts to methane gas.

In Table 1, the test numbered No. 1 is a test in which the gas detection sensitivity of the WO3 matrix sensor was investigated without forming a catalyst layer. Tests Nn2 to Nn6 used WO3 as the base sensor and varied the catalyst layer material. As a result, it was found that the catalyst layer material was a mixture of ZnO and Sn02, which exhibited a unique sensitivity to methane gas. found.

Tests Nn7 and 8 were conducted using the above catalyst layer materials (ZnO and 5n0
This study investigated the scum detection sensitivity when the base sensor was changed using the mixed material of 2), and this S combination shows that although the catalyst layer material is the same, the sensitivity to methane scum is unique to methane scum. showed no sensitivity.

From this test result, we found that the specific sensitivity Kf for methane gas
It has become clear that what is shown can be obtained by using WOa as a base sensor and forming a catalyst layer containing a mixture of ZnO and Sn02 on the base sensor, and it is possible to selectively detect only methane gas among other gases. It was confirmed that it can be done.

The mixing ratio of the catalyst layer material at this time is 30 parts Zn0 and 5 nO
z 70 copies.

Table 2 shows the results of investigating the sensitivity of various oxide catalysts to carbon monoxide.

Table 2 In Table 2, the NcLl test investigated the gas detection sensitivity of the WOs parent sensor without forming a tentacle layer.

Regarding the sensitivity to each gas, the same results as in Table 1 were obtained. Tests 2 to 6 used WO3 as the base sensor and varied the catalyst layer material, and as a result, a mixture of Cr2O3 and CO2O3 as the catalyst layer material showed a unique sensitivity to carbon monoxide. There was found.

Test positives 7 and 8 were obtained using the above catalyst layer materials (Cr2O3 and CO2
03 mixture material) was used to investigate the scum detection sensitivity when the base sensor was changed.In this case, even though the catalyst layer material was the same, it was found that He didn't show any respect.

From this test result, -% sensitivity to carbon oxide (
It has become clear that what is shown in can be obtained by using WO3 as a base sensor and forming a catalyst layer containing a mixture of Cr203 and CO2O3 on the base sensor, and only carbon monoxide is present between other gases. It has been confirmed that the selection can be detected.

The mixing ratio of the catalyst layer material at this time is 370 parts of Cr2O and CO.
It is 2O330 parts.

Table 3 shows the results of investigating the sensitivity of each 41e compound catalyst to hydrogen gas.

In Table 3, the test marked positive 1 is a test in which the gas detection sensitivity of the WO3 host sensor was investigated without forming 1 m of catalyst. As a result, the sensitivity to each gas is shown in Table 1.
The results were the same as in Table 2.

Tests Nn2 to Nn6 used WO3 as the base sensor and varied the catalyst layer material, and as a result, it was found that the mixture of MnO2 and Cr2O5 as the catalyst layer material exhibited a unique sensitivity to hydrogen gas. found.

Tests 7 and 8 were used to investigate the gas detection sensitivity when the base sensor was changed using the above catalyst material (a mixture of C02 and Cr2O3); in this case, the catalyst layer material was the same. However, from the test results, the one that showed a specific sensitivity to hydrogen gas was found by using WO3 as the base sensor and placing it on the base sensor. It has become clear that this can be obtained by forming a catalyst layer in which MnO2 and Cr2O3 are mixed, and it has been confirmed that only hydrogen gas can be selectively detected between other dregs. The mixing ratio of the catalyst layer material at this time was 10,250 parts of Mr and 20,350 parts of Cr.

Table 4 shows the results of investigating the sensitivity of various oxide catalysts to alcohol, which is a typical interfering gas.

In Table 4, the tests C and 1 show the gas detection sensitivity of the WO3 matrix sensor without forming a catalyst layer. As a result, the sensitivity to valley gas is m 1
The results were the same as in Tables 3 and 3.

In tests Nn2 to Nn6, the base sensor was vvO3 and the catalyst layer material was varied in various ways. As a result, the mixture of ZnO and 5n02 as the catalyst material showed a unique sensitivity to alcohol. There was found.

Tests Na7 and 8 used the above catalyst material 9 (a mixture of ZnO and 5n02) to examine the sensitivity to detection of debris when the base sensor was replaced.In this case, the catalyst layer material was Although they were the same, they did not show the specific sensitivity to alcohol.

From this test result, it is clear that a specific sensitivity to alcohol can be obtained by using WO3 as the base sensor and forming a catalyst layer containing a mixture of ZnO and 8nU2 on the base sensor. It was confirmed that only alcohol can be selectively detected among other scum. The mixing ratio of the catalyst layer material at this time is Zn070
Part 5n0230 part.

For the above four types of scum: hydrogen gas, carbon oxide, methane scum, and alcohol, the base sensor is made of the same material,
The relationship between this base sensor and the catalyst layer selected according to the gas component was explained.

Next, the production of this catalyst layer will be explained using a catalyst layer for alcohol as an example.

In the production of other catalyst layers, the only difference is the catalyst layer material and its mixing ratio, and the other steps are the same, so the explanation will be omitted.

First, ZnO (commercially available 99.9"CH and 5n02 (commercially available, manufactured by Rare Metallic) and 5n02 (99.9%, manufactured by Rare Metallic).

Weigh the mixture so that the mixing ratio is 30 parts and 70 parts. To 100 parts of these two types of acetides, 10 parts of glass frit material was further weighed out and mixed for 2 hours in a trough machine equipped with an agate bowl. 10. Powder mixed in this way. F
To this, 3 ml of a vehicle consisting of α-terpineol-nitrocellulose was added and kneaded well to prepare a thick film printing paste for alcohol.

Make thick film printing paste+ for other gases in the same way.

WOa prepared in advance with the paste made in this way
Print a thick film of 50 μm on the base sensor.

FIG. 2 shows its appearance. In the diagram, for example, if 12 is a methane gas sensor, 3 is a carbon monoxide sensor, 14 is a hydrogen gas sensor, and 15 is an alcohol sensor, 12 is a methane catalyst Zn030 +5
Catalyst layer of n0270, 13 has carbon monoxide catalyst Cr2
0a70 + CO20330 catalyst layer, 14 a catalyst layer for hydrogen gas Mn0250 + Cr20350, and 15 a catalyst layer for alcohol Zn070 + 5n
A catalyst layer of 0230° is coated on the upper electrode of the W0303 part sensor to obtain a gas detection waste sensor in which four types of sensor elements are integrated.

[Effects of the Invention] As detailed above, according to the gas sensor for extracting various kinds of scum of the present invention, the same base sensor is used, and a metal oxidation catalyst layer selected depending on the scum component is formed on the base sensor. As a result, the manufacturing process of the base sensor can be made using only one type, and the quantification can be improved, and there is no variation in the sensor resistance value, and the reliability can be greatly improved.Also, as is clear from the test results, It has become possible to separate methane gas and alcohol, which were considered impossible to separate, and hydrogen gas and carbon monoxide, greatly improving sensitivity.

For these reasons, it can be made low in price, eliminates false alarms, facilitates its widespread use in general households, and fully demonstrates its function as a gas leak alarm, and has a great social effect.

[Brief explanation of the drawing]

Figures 1 and 2 show an embodiment of the present invention, with Figure 1 being an external view for explaining a gas sensor for detecting multiple gases, and Figure 2 being a four-element integrated sensor coated with a catalyst layer. FIG. 1... Insulating substrate 2... Lower electrodes 3, 4, 6. , 7... Maternal sensor 8 , 9.10
．． 11... Upper electrode 12.13, 14.15... Oxide catalyst coating layer agent Patent attorney: Daiichi Takahashi Yun Continuation of No. 10 ■k Inventor: Akira Ikegami Yoshida, Totsuka-ku, Yokohama City Town 29 Akiji Hitachi, Ltd. Production Technology Laboratory

Claims (1)

[Claims] In an integrated waste sensor formed by forming a plurality of sensors on an insulating substrate, a plurality of base sensors made of the same material are formed on the insulating substrate, and on the base sensors, a carbon dioxide having a catalytic activity depending on the type of waste is formed. A gas sensor for detecting various gases, characterized by forming a proboscis catalyst coating layer.