JPH08170955A - Aldehyde gas detection element - Google Patents

Abstract

PURPOSE: To obtain a detection element with a high sensitivity for aldehyde by adding molybdenum of molybdenum compound to a catalyst sensitization type semiconductor gas detection element consisting of a gas--sensitive body which mainly consists of tin oxide or indium oxide and platinum catalyst. CONSTITUTION: Molybdenum or molybdenum compound is added to a catalyst sensitization type semiconductor gas detection element consisting of a gas- sensitive body which mainly consists of tin oxide or indium oxide and platinum catalyst. When actually manufacturing a detection element, for example alumina substrate 1 is prepared as an insulation substrate and comb-shaped gold electrode 2 is formed on the substrate 1 by the vacuum deposition method. Then, after forming thin tin film on the upper surfaces, heat treatment is performed in air, thus obtaining a thin-film gas sensor 3 consisting of tin oxide. Further, after molybdenum trioxide 4 is subjected to vacuum deposition on the gas sensor 3, platinum catalyst 5 is formed by the vacuum deposition method. Finally, aging treatment is performed to stabilize the element resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detecting element having high sensitivity to aldehyde gas.

[0002]

2. Description of the Related Art Aldehyde gas has various forms such as acetaldehyde and formaldehyde. Among them, for example, acetaldehyde generated when smoking cigarettes or when edible oil is overheated during cooking is , Is a typical substance of odor pollution component, and is a highly toxic gas that causes serious damage to human body and living organisms by itself.

Therefore, various studies have been made on an apparatus for detecting this kind of aldehyde gas. For example, JP-A-6-160283 discloses an apparatus for detecting formaldehyde by using a chemiluminescence method. It is disclosed. The aldehyde gas detection device disclosed in this publication is
A composition in which an aldehyde gas is dissolved by atomizing an aldehyde-soluble liquid solvent, the liquid solvent is mixed with a liquid reaction reagent, and the chemiluminescence amount generated by the chemical reaction of these two liquids is detected by an optical sensor. Is.

Another example is a semiconductor gas sensing element using a metal oxide semiconductor such as tin oxide or indium oxide as a gas sensor. For example, JP-A-3-44
Japanese Patent No. 546 discloses a configuration in which an element in which a sintered body of tin oxide or zinc oxide is formed on a platinum wire coil is used as a sensor for detecting a malodorous substance such as acetaldehyde or methyl mercaptan. . Further, Japanese Patent Application Laid-Open No. 4-155132 discloses a structure in which acetaldehyde generated by overheating of edible oil is detected by a semiconductor gas detecting element, thereby preventing a tempura fire.

[0005]

However, the conventional aldehyde gas detection device has the following problems. First, the structure disclosed in Japanese Patent Laid-Open No. 6-160283 uses a chemiluminescence method, and therefore has a drawback that the device becomes large and maintenance is very difficult. On the other hand, JP-A-3-44546.
Although the semiconductor gas detecting elements disclosed in Japanese Patent Laid-Open No. 4-155132 and Japanese Patent Laid-Open No. 4-155132 are small in size and easy to maintain and have a long life, their sensitivity to aldehyde gas is not sufficient.

In a semiconductor gas detecting element, in order to improve the sensitivity to a target gas,
Although catalytic substances such as gold, platinum and palladium are added,
So far, no catalytic substance has been found that exhibits an excellent sensitizing effect on aldehyde gas.

The present invention has been made based on such a point, and an object of the present invention is to provide a gas detection element having high sensitivity to aldehyde gases such as acetaldehyde and formaldehyde.

[0008]

As a result of various studies to achieve the above-mentioned object, the present inventor has found that, surprisingly, among the conventionally known catalyst-sensitized semiconductor gas detecting elements, It has been found that the sensitivity to aldehyde gas is remarkably improved by adding molybdenum or a molybdenum compound as a third component to an element composed of a gas sensitive material containing tin oxide or indium oxide as a main component and a platinum catalyst. The present inventor has completed the present invention based on this finding.

That is, in the gas detecting element according to the present invention, molybdenum or a molybdenum compound is added to a catalyst-sensitized semiconductor gas detecting element composed of a gas sensor containing tin oxide or indium oxide as a main component and a platinum catalyst. It is characterized by. At that time, it is considered that the catalyst-sensitized semiconductor gas detection element is composed of a thin film gas sensor containing tin oxide or indium oxide as a main component and a platinum catalyst. Further, the catalyst-sensitized semiconductor gas detecting element may be composed of a thin film gas sensor having tin oxide or indium oxide as a main component and having a mass film thickness of 5000 Å or less, and a platinum catalyst having a mass film thickness of 100 Å or less. Conceivable.

The catalyst-sensitized semiconductor gas detecting element applicable to the present invention is not particularly limited as long as it is composed of a gas sensitive material containing tin oxide or indium oxide as a main component and a platinum catalyst. Various configurations are known,
You can apply them. For example, a structure in which a sintered body of tin oxide is used as a gas sensitive body and a platinum catalyst is added to the gas sensitive body (Japanese Utility Model Laid-Open No. Sho 60-9551, device name "carbon monoxide gas detector", etc.), tin oxide And a structure in which a platinum catalyst is added to the thin film of the above (1) or the thin film of indium oxide (Japanese Patent Application Laid-Open No. 2-263148, the title of the invention is "carbon monoxide gas detecting element") and the like.

Of these, a tin oxide thin film or an indium oxide thin film as a gas-sensing body, to which a platinum catalyst is added, is particularly preferable because the sensitizing effect for aldehyde gas is remarkably exhibited.

As a method for forming the gas sensitive body, the conventionally known means described in the above-mentioned publications and other publicly known publications may be used as they are without any particular limitation. For example, when forming a thin film gas sensor, a vacuum deposition method,
A method such as a sputtering method can be used. At this time, the film thickness of the tin oxide thin film or the indium oxide thin film is
It is formed so that the mass film thickness is 5000 Å or less. If the mass film thickness exceeds 5000 Å, the element resistance value becomes low and the sensitivity is lowered.

The method of adding the platinum catalyst is not particularly limited, and the conventionally known means described in the above-mentioned publications and other known publications may be used as they are. For example, when this catalyst is added to the thin film gas sensor, a method such as a vacuum vapor deposition method or a sputtering method can be used. At this time, the added amount is such that the mass film thickness is 100Å
It is formed as follows. If the mass film thickness exceeds 100Å, the gas sensitive body itself cannot maintain the properties of a semiconductor and the detection characteristics deteriorate.

In the present invention, it is indispensable to add molybdenum or a molybdenum compound to the catalyst-sensitized semiconductor gas detecting element having the above structure. By adding these, a sensitizing effect on aldehyde gas is exhibited. As the molybdenum compound, an oxide (MoO ₃ Mo
O ₂ etc.), halides, sulfides (Mo ₂ S ₃ , MoS
₂ etc.), nitride, silicide (Mo ₅ Si ₃ , MoS
i ₂ , Mo ₃ Si, etc.) and the like. The method of adding these is not particularly limited, but for example, when the gas sensitizer constituting the catalyst-sensitized semiconductor gas detecting element is a thin film, a method such as a vacuum deposition method or a sputtering method can be used. At this time, the addition amount of molybdenum or a molybdenum compound is arbitrary as long as it does not affect the expression of the sensitizing effect to the aldehyde gas, but the mass film thickness is preferably 10,000 Å or less, and more preferably 200 mass.
It is desirable to keep it below 0Å. When the mass film thickness exceeds 10,000 Å, the responsiveness to aldehyde gas is lowered, and the material cost and the addition time are lengthened to increase the manufacturing cost. If the mass film thickness exceeds 2000Å, the manufacturing cost will increase.

[0015]

The gas detecting element of the present invention having the above structure can detect an aldehyde gas with high sensitivity due to the effect of adding molybdenum or a molybdenum compound.

[0016]

EXAMPLES The following examples show examples in which the present invention is applied to a thin film type element.

Example 1 A gas detecting element having a structure as shown in FIG. 1 was produced by the following procedure. First, an alumina substrate having a length, width and thickness of 8 × 7 × 0.635 mm is prepared as an insulating substrate 1, and a comb-shaped metal electrode 2 having a mass film thickness of 1000 Å as shown in FIG. 2 is prepared on the substrate 1. It was formed by a vacuum evaporation method. Then, after forming a tin thin film with a mass thickness of 150Å on their upper surface,
A heat treatment was carried out in air at 500 ° C. for 10 minutes to obtain a thin film gas sensitive body 3 made of tin oxide. Further, molybdenum trioxide 4 was vacuum-deposited on the thin-film gas sensor 3 so as to have a mass film thickness of 200Å, and then a platinum catalyst 5 having a mass film thickness of 20Å was formed by a vacuum evaporation method. Finally, in order to stabilize the resistance value of the element, aging treatment was performed at 220 ° C. for about 20 hours. In FIG. 1, reference numeral 6 is a heating element for controlling the element temperature. A PTC heater was used in this example.

Comparative Example 1 An element was produced by using the same material and the same construction method as in Example 1 except that molybdenum trioxide was not added.

Example 2 This example shows an example in which the structure of the gas sensitive body is changed. An element was manufactured by using the same material and the same construction method as in Example 1 except that an indium thin film having a mass film thickness of 150 Å was used as the gas responsive body.

Comparative Example 2 An element was manufactured by using the same material as in Example 2 except that molybdenum trioxide was not added, and by the same method as in Example 1.

Here, the sensitivities of the above four types of elements to aldehyde gas were measured under the following conditions. First, each element was fixed in a closed container while being kept at 220 ° C. Next, the concentration in the container is 200 to 2000 pp
m of acetaldehyde was injected with a syringe and sufficiently stirred by a fan, and the electric resistance value of each element was measured. The sensitivity to acetaldehyde [resistance value in air / resistance value in acetaldehyde] was calculated based on the obtained electric resistance value, and the results are shown in Table 1.

[0022]

[Table 1]

According to Table 1, the element of this example to which molybdenum trioxide was added showed about 2 to 7 times the sensitivity as compared with the element of the comparative example to which molybdenum trioxide was not added. It is understood that there is. That is, it can be said that the element of this example is extremely sensitive to acetaldehyde.

In the above embodiment, an example in which the present invention is applied to a thin film type element in which a tin oxide thin film or an indium oxide thin film is used as a gas sensitive material is shown. It can also be applied to a sintered element whose body is a gas sensitive body.

[0025]

As described in detail above, according to the present invention, among the conventionally known catalyst-sensitized semiconductor gas detection elements, particularly, a gas sensor containing tin oxide or indium oxide as a main component and a platinum catalyst are used. By adding molybdenum or a molybdenum compound as a third component to the constructed element, an element having high sensitivity to aldehyde gas could be obtained. As a result, it can be applied to a wide range of applications such as air purifiers used in general homes and various offices, air conditioners such as ventilation fans, and cookers. Therefore,
It can greatly contribute to the creation of a safe and comfortable living environment.

[Brief description of drawings]

FIG. 1 is a cross-sectional view (conceptual diagram) showing a configuration of a gas detection element (Example 1 and Example 2) according to the present invention.

FIG. 2 is a plan view showing an example of a comb-shaped gold electrode used in the present invention.

[Explanation of symbols]

 1 Insulating substrate 2 Comb type gold electrode 3 Thin film gas sensor 4 Molybdenum trioxide 5 Platinum catalyst 6 Heating element

Claims (3)

[Claims] 1. Aldehyde gas detection, characterized in that molybdenum or a molybdenum compound is added to a catalyst-sensitized semiconductor gas detection element consisting of a gas sensor containing tin oxide or indium oxide as a main component and a platinum catalyst. element. 2. An aldehyde characterized by adding molybdenum or a molybdenum compound to a catalyst-sensitized semiconductor gas sensing element comprising a thin film gas sensor containing tin oxide or indium oxide as a main component and a platinum catalyst. Gas detection element. 3. A catalyst-sensitized semiconductor gas detection element comprising a thin film gas sensor containing tin oxide or indium oxide as a main component and having a mass film thickness of 5000 Å or less and a platinum catalyst having a mass film thickness of 100 Å or less. Alternatively, an aldehyde gas detection element characterized by adding a molybdenum compound.