JPS5999242A - Production of gas sensitive element - Google Patents

Abstract

PURPOSE:To obtain a gas sensitive element having excellent responsiveness by forming a film consisting of an org. compd. contg. Pt, etc. and Al, etc. on the surface of a gas sensitive body, then heating the same to decompose the org. compd. thereby forming a catalyst layer consisting of a catalyst metal such as Pd or the like and a carrier such as Al2O3 or the like. CONSTITUTION:A pair of electrodes 2 consisting of Au, etc. are provided on the surface of a cylindrical substrate consisting of Al2O3 as an insulating substrate 1. An n-butanol soln. contg. tin octylate is coated on the surface of the substrate 1 and the electrodes 2 and is dried to evaporate n-butanol. The substrate is then subjected to a heat treatment to decompose the tin octylate and to oxidize the same to form a thin SnO2 film as a gas sensitive body 3. A raw material soln. formed by mixing an org. soln. prepd. by dissolving Pd resinate in n-butanol and an org. soln. prepd. by dissolving Al naphthenate in toluene is coated on the surface of the body 3 and is then dried to evaporate the org. solvent. The sensitive body is then subjected to a heat treatment to decompose the Pd sesinate and Al naphthenate and to oxidize Al thereby forming a catalyst layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a gas-sensitive element, and particularly to a method for manufacturing a gas-sensitive element having a catalyst layer.

[Technical background of the invention and its problems]

Conventionally, various studies have been conducted on gas-sensitive elements using gas-sensitive materials such as 5N02-based oxide semiconductors whose resistance changes upon contact with various gases. A catalyst is used for the purpose of increasing detection sensitivity for dregs, etc., and one structure of a gas-sensitive element using this catalyst is one in which two catalyst layers are provided on a gas-sensitive member.

Such a catalyst layer is generally made of a carrier C such as A120s.
A thick film mixed with a catalytic metal such as 2pt is used.

However, since the thick film is formed through a process of applying and sintering a paste-like raw material, there is a problem in that the reproducibility is very poor and the characteristics of the gas-sensitive element vary widely. Furthermore, since the thickness of this thick film is on the order of 102 μm, there is a drawback that the response speed during gas detection is slow. In addition, gas-sensitive elements are usually equipped with a heater, and gas detection is performed while heating the gas-sensitive element. However, when the film thickness is large, a temperature gradient occurs within the catalyst layer, which tends to generate thermal stress. In addition, if the thickness of the catalyst layer is large, it is difficult to accurately set the temperature of the gas-sensitive element, which may cause variations in the characteristics of the gas-sensitive element. There were also problems.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and has responsiveness (
Second, the present invention aims to provide an excellent method for manufacturing a gas-sensitive element.

[Key points of invention]

The present invention relates to a substrate, a gas sensitive body provided on the substrate, a gas sensitive body whose resistance changes upon contact with the gas sensitive body, a pair of electrodes provided on the gas sensitive body, and a gas sensitive body provided on the substrate. In the method for manufacturing a gas-sensitive element comprising a body surface (-a catalyst layer provided), the gas-sensor bottom surface (2, Pd, P
After forming a film made of a metal organic compound containing at least one of Pd, Rh and at least one of Al, Zr+Si, heating is performed to decompose this organic compound, and Pd,
at least one catalyst metal among Pt and Rh; and A4
This is a method for manufacturing a gas-sensitive element in which a catalyst layer is formed of at least one type of carrier among 03 HZrO2+5i02.

In addition, the present invention (the substrates in the two cases are A40s and 5i)
Heat-resistant insulating ceramic substrates such as sN++BN and 5i02 are used, and 5nOz series r Z is used as the gas sensitive body.
nO yarn.

Gas to be measured such as Fe2Os (an oxide semiconductor whose resistance value changes upon contact with the other is used).The gas to be measured is C
These are reducing scum such as O and hydrocarbons such as methane.

The 5nu2-based, ZnO-based, and Fe2O-based oxide semiconductors each contain 20 g of 5n02+ ZnO+ Fe as a main component, and optionally contain additives such as Sb and Nb.

This gas sensitive material can be produced using vapor deposition or sputtering methods.

Thermal decomposition of organic compounds of metals, etc. (Thin films formed in two layers, thick films formed by coating, sintering, etc. are used, but
In particular, a thin film of about 2100 nm to 1000 mm is preferable.

A pair of electrodes are provided to detect the resistance value of this gas sensitive body (2), but these electrodes may be placed on an insulating substrate (2 provided, and above this (2) a gas sensitive body may be provided, or on top of the gas sensitive body (
- May be provided. The electrode is Pt.

Au or the like is used, and it is formed by a vapor deposition method, a sputtering method, a screen printing method, etc.

Next, the catalyst layer will be described.

The catalyst layer contains at least one catalyst metal among Pt, Pd, and Rh, and AA! This catalyst layer is formed using a thermal decomposition method of an organic compound of a metal and at least one kind of carrier among 20s + Zr0215ift. This catalytic metal is used to improve gas-sensitive characteristics such as gas responsiveness and gas selectivity. In order to prevent deterioration of characteristics (-).

The present invention (2) The organic compound of the metal used is Pt
s Pd, Rh, A7. Metal alcoholides, metal soaps, resin salts, and other organic compounds of Zrs St that are commonly used (= generally decomposed to produce metals or metal oxides) by heating are used.

The organic compound of this metal is, for example, lavender oil*, hexane, toluene, and other organic solvents (-).A mixed solution is applied to the bottom of the gas sensor to form a film.The composition ratio of the catalyst layer is determined by the amount of metal in this solution. The amount of the organic compound of the metal can be changed (easier to control).After the film is formed, drying treatment is performed for about 1 hour at room temperature and from 100 to 150 mm for about 1 hour to evaporate the organic solvent and remove the metal organic compound. is preferably fixed on the gas sensitive member.

The organic compound of this metal can be heated (from -, simple C
Decomposes bithermally to form metals or metal oxides. At this time, AZ
At least one of + Zr + Sl is oxidized by reacting with an oxygen atom in an organic compound or by heating in an atmosphere in the presence of nitrogen, resulting in A120B.

ZrO□2! It becomes 102. In this way (hydrolysis of bimetallic organic compounds (2!17. Pt,
At least one catalytic metal selected from Pd and Rh, and A
40a w ZrO2.

A catalyst layer consisting of at least one type of carrier among 5102 can be formed.

In this way, the gas-sensitive element (2) using a catalyst layer formed by the thermal decomposition method of a bimetallic organic compound has very high responsiveness to the gas to be measured. This is considered to be because a porous state is well realized in the catalyst layer formed by such a method.

In other words, the catalyst layer is required to be in a porous state so as not to interfere with the contact between the gas sensitive body and the gas to be measured, but according to this method of thermal decomposition of organic compounds, organic matter is removed from a state in which metals are dispersed in advance. This is thought to be due to the formation of one vacancy in this part.

Further, according to this thermal decomposition method of organic compounds, a catalyst layer having a desired composition ratio can be easily obtained by adjusting the amount of the metal organic compound in the organic bath medium. In addition, the organic compound of the metal is uniformly dispersed in the organic solvent (=), and a uniform composition is achieved with good reproducibility even in the formed catalyst layer, so it is highly reliable when mass-producing gas-sensitive elements. Gender (1
It's dredged.

Furthermore, a homogeneous film can be formed in any case (- regardless of the shape of the insulating substrate, such as a flat plate, 9, a cylinder, etc.).

The weight ratio of this catalyst metal in the catalyst layer is preferably about 1 to 90% by weight. If it is less than 1% by weight, the catalyst layer will not have sufficient catalytic ability (2), and if it exceeds 90% by weight, the catalyst layer may not be able to maintain sufficient insulation properties. Gas detection is performed by measuring the change in resistance of the gas sensitive body, but the insulation properties of the catalyst layer provided on the gas sensitive body (-) may be damaged. If not, the resistance value of the gas sensitive body and the catalyst layer will be measured, not just the resistance value of the gas sensitive body itself. When the resistance value of the gas sensitive body becomes smaller, it becomes difficult to measure the resistance value of the gas sensitive body, and gas detection becomes virtually impossible.

In the uninvented gas-sensitive element provided with such a catalyst layer, since the catalyst layer and the gas-sensitive element are manufactured separately, it is possible to set the optimum manufacturing conditions for each (-), and the process of manufacturing the gas-sensitive element is The degree of freedom increases.Also, if a catalyst metal is mixed into the gas-sensitive element, its dispersion state will change as the gas-sensitive element is used, and there is a risk that the resistance value and other characteristics of the gas-sensitive element may change. However, in the case of the present invention in which a catalyst layer containing a carrier (two catalyst metals) is provided, this fear does not exist.

The thickness of the catalyst layer is preferably about 50 to 1000 nm.

If the film thickness is less than 50 nm, the catalytic ability of the catalyst layer will not be fully demonstrated, and if it exceeds 1000 nm, the response speed to the gas to be measured may become slow. There is a rising speed when it comes into contact with the target gas, and a recovery speed when the target gas is removed, but both become slower (-) when the film thickness exceeds 1000 nm.

In particular, when using a device (-) to notify a danger that measures CO2, if the response speed is slow, gas detection will be delayed and it is very dangerous (2').

〔Effect of the invention〕

As explained above, according to the present invention, a gas-sensitive element with excellent responsiveness can be obtained.

[Embodiments of the invention]

The present invention will be explained in detail below.

FIGS. 1 and 2 are views showing a gas-sensitive element according to the present invention. FIG. 1 is a perspective view, and FIG. 2 is a sectional view.

A pair of electrodes (2) made of Au are provided on the surface of a cylindrical substrate made of A4O3 as an insulating substrate (1). Octyl tin is coated on the surface of this insulating substrate (1) and this electrode (2). After applying an n-butanol bath solution containing 102 ft% and drying in the air for about 30 minutes,
Dry for 0.30 minutes and evaporate the n-butanol. followed by 4
00~700°CT: Heat treatment in air for 30 minutes to decompose and oxidize tin octylate to form a thin film of gas sensitive material (SnO as 3J).・Rapid cooling is preferable, and a film thickness of about 100 nm to 1000 nm is preferable in terms of sensitivity, gas response, etc. The film thickness can be determined by changing the concentration of tin octylate or by repeating coating and heat treatment several times. It can be controlled by

Subsequently, two catalyst layers (4) are formed on the surface of the gas sensitive body (3).

Pd resin salts such as palladium resinate (ENG
ELIiARD Co.: A raw material solution prepared by mixing an organic solution containing glyph in n-butanol (1% dissolved) and an organic solution containing aluminum naphthenate dissolved in toluene (2%) in the desired ratio was coated on the gas sensitive member (3). , after sleeping in the air for about 30 minutes,
Dry recording for about 120"030 minutes to evaporate the organic solvents n-butanol and toluene.
Heat-treated in air for about 0 minutes to form a Pd1l fat salt.

Aluminum naphthenate is decomposed and AA is oxidized to form a catalyst layer (4) consisting of Pd and A120B. As in the case of the gas sensitive member (3) ('-This heat treatment is preferably carried out by rapid heating and cooling in order to prevent the occurrence of cracks, etc., and from the viewpoint of catalytic efficacy, gas response, etc.
A film thickness of approximately nm is preferable. The film thickness can be controlled by repeating the coating and heat treatment process of the raw material hot liquid, and by changing the thickness of the Pd resin salt and aluminum sulfate. Approximately 4 times is preferable, and if repeated too many times, cracks etc. may occur.

The insulating substrate (1) on which the electrode (2), the gas sensitive body (3), and the catalyst layer (4) were formed as described above was transferred to the electrode (2).
The lead wire connected to the stem (5) is suspended by fixing the pin (6) (2) to the stem (5).
1) (2 is a heater (7) for heating the gas sensitive body (3)
).

Although a cylindrical substrate was used in this embodiment, the same effect can be achieved by using a flat substrate, and the heater may also be formed on the substrate (using 2 Ru 02 paste, etc.). - For example, the casing may be fixed directly to the casing.

The response and recovery characteristics of the gas-sensitive element (2) according to the present invention constructed as described above were investigated. The results are shown in Table 1. In addition to the layer, as a comparative example, A40g was used as a carrier, and the catalyst layer was coated and sintered with a paste of a mixture of A40g and catalyst metal (a thick film with a diagonal was provided). -Recovery characteristics were investigated.

The response and recovery characteristics were measured in a 200 ppm CO gas atmosphere (response time), and the resistance value in the atmosphere after exhausting the CO gas. Until it returns to (1 time required (
The recovery time) was measured. Note that the response time is the time from the time of CO gas injection. υCO gas concentration is 200 pp.
The time required to reach m (about 5 seconds) and the recovery time are CO
The time from when the gas is exhausted, including the time required for it to be replaced with fresh air (approximately 15 seconds).

As is clear from Table 1, in the embodiment of the present invention, the response time is about 3 o sec, and the recovery time is about 1 minute ('
''-In comparison, in the case of the comparative example, the response time for each case is around 100 seconds, which takes a long time,
It is around 0 seconds, and it can be seen that the present invention is superior in response and recovery characteristics, especially (second recovery characteristics).

Examples of the present invention using a Pd A4Os based catalyst layer (solid line) and comparative example using a thick film catalyst layer (broken line) by coating and sintering a Pd-A7203 based paste in Table 1
The response and recovery characteristics are compared in Figure 3.

In the example of the present invention, the resistance value is saturated immediately after CO gas injection fal (=2), and the resistance value returns quickly after CO gas exhaust tbJ (=2), whereas in the comparative example, both are gradual (1
You can see that things are changing.

Furthermore, Table 2 shows the difference in sensitivity due to the difference in collector temperature. The gas-sensitive elements were the same as the examples shown in Table 1 (1).Co, H2, CaHa, CH4, C2H50H
(I investigated the sensitivity using two. Below is the second margin.
As is clear from the table (the gas selectivity differs depending on the element temperature), the CO gas sensitivity is even higher at low temperatures (100°C), and the sensitivity for CH4 increases at low temperatures (100°C). By changing the temperature, various target gases can be measured using the same gas-sensitive element.

In the embodiments described above, Aa2os was used as the carrier, but the same effect can be obtained by using 5ins + 1ro2.

In this case, for example, silicon, zirconium alkoxide, zirconium naphthenate, etc. can be used as the organic compound.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a gas-sensitive element according to the present invention, FIG. 2 is a sectional view of a gas-sensitive element according to the present invention, and FIG. 3 is a response/return characteristic of the gas-sensitive element 1... Substrate 2. ...Electrode 3...Gas sensitive body 4...Catalyst layer representative Patent attorney Noriyuki Chika (and one other person) Figure 3 Haruma (1)

Claims (1)

[Claims] A substrate, a gas sensitive member provided on the substrate whose resistance value changes upon contact with a gas to be measured, and this gas sensitive member (=
In the method for manufacturing a gas-sensitive element comprising a pair of electrodes provided on the surface of the gas-sensitive member and a catalyst layer provided on the surface of the gas-sensitive member, the surface of the gas-sensitive member (=, Pd , Pt , Rh
At least one of the following and Al. After forming a film made of a metal organic compound containing at least one of Zr + St, this organic compound is thermally decomposed to produce at least one catalytic metal of Pd, Pt, and Rh, and at least one of A40a l ZrO2+ 5i02. 1. A method for producing a gas-sensitive element, comprising forming a catalyst layer comprising at least one type of carrier.