JP2007071866A - Film for gas sensor, element for gas sensor and method for manufacturing the element for gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film for gas sensor which has high responsiveness with respect to an object gas to be sensed and can be used repeatedly, and to provide an element for gas sensor and a method for manufacturing them. <P>SOLUTION: The film is made up by dispersing minute particles of a group VIII metal into a thin film-shaped substrate made of tungsten trioxide, and at least a portion of the tungsten trioxide composing the thin film-shaped substrate is in an amorphous state. It is preferable that the state is one in which all the minute particles of the group VIII metal are made embedded inside the thin film-shaped substrate. Furthermore, the tungsten trioxide composing the thin film-shaped substrate is preferably in a porous state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas sensor thin film, a gas sensor element body, and a method for manufacturing a gas sensor element body.

In recent years, development of a new energy system using, for example, a hydrogen gas fuel such as a fuel cell has attracted attention because of the advantages of preventing environmental pollution such as air pollution inhibiting effect and warming inhibiting effect.
However, hydrogen gas ignites when present in the atmosphere in an amount of 4% by volume or more, and has a dangerous property of exploding because of its high combustion speed. This has led to the widespread use of energy systems using hydrogen fuel as described above. Accordingly, for example, there is an increasing need for development of a highly accurate gas sensor capable of reliably detecting gas leakage in a short time so that hydrogen gas can be transported and stored safely.

Currently, for example, there are catalytic combustion type and semiconductor type gas sensors for detecting flammable gas such as hydrogen gas, but these are long for about 1 minute for detecting hydrogen gas, for example. A response time is required, and there is a possibility that an explosion may occur when the hydrogen gas concentration reaches 4% by volume or more in the detection target space within this response time, which is very dangerous.
In the case of the catalytic combustion type, a change in current-voltage characteristics and temperature characteristics due to adhesion of hydrogen gas molecules to the functional thin film of metal oxide is electrically detected. Adhesion of other gas molecules may change the current-voltage characteristics and temperature characteristics, which may prevent accurate detection of the hydrogen gas that is the detection target gas. Since the sensitivity deteriorates due to deterioration, there is a problem that the hydrogen gas concentration cannot be stably detected over a long period of time.

  In order to solve the problem of deterioration of the functional thin film as described above, an optical gas sensor that optically measures the degree of gas desorption to a specific functional thin film using, for example, an optical sensor has been proposed (for example, , See Patent Document 1).

However, even in such an optical gas sensor, since a long response time is required for gas detection, it cannot be said that an optical gas sensor having high response has been realized.
JP 2003-329592 A

The present invention has been made in view of the above circumstances, and a first object thereof is to provide a thin film for a gas sensor that can obtain high responsiveness to a detection target gas and can be repeatedly used. There is.
A second object of the present invention is to provide a gas sensor element body having the gas sensor thin film.
A third object of the present invention is to provide a method for manufacturing a gas sensor element body that can provide the gas sensor element body described above.

The thin film for a gas sensor of the present invention is a thin film for a gas sensor in which Group VIII metal fine particles are dispersed in a thin film substrate made of tungsten trioxide,
At least a part of tungsten trioxide constituting the thin film base material is in an amorphous state.

  In the thin film for a gas sensor of the present invention, it is preferable that 90% by volume or more of the Group VIII metal fine particles are embedded in the thin film-like base material. It is preferable that all of the group metal fine particles are buried in the thin-film substrate.

  Moreover, in the thin film for gas sensors of this invention, it is preferable that the tungsten trioxide which comprises the said thin-film-like base material is a porous state.

  The element body for gas sensor of the present invention is characterized in that the gas sensor thin film is formed on the surface of a plate-like light-transmitting substrate.

In the gas sensor element body of the present invention, it is preferable that the translucent substrate is made of an amorphous material.
In the gas sensor element body of the present invention, the translucent substrate is made of a crystalline material, and an amorphous intermediate layer made of an amorphous material is interposed between the translucent substrate and the gas sensor thin film. It is preferable to intervene.

The method for producing an element body for a gas sensor according to the present invention includes: a gas sensor thin film in which a group VIII metal fine particle is dispersed in a thin film substrate made of tungsten trioxide on a translucent substrate; A method of manufacturing an element body,
Thin film formation obtained by mixing tungsten alkoxide solution obtained by dissolving tungsten hexachloride in alcohol solvent and Group VIII metal ion-containing alcohol solution obtained by dissolving group VIII metal salt in alcohol solvent It is characterized by including the process of apply | coating the solution for light on a translucent base | substrate, drying, and baking after that.

  According to the gas sensor thin film of the present invention, since the group VIII metal fine particles are contained in a matrix made of tungsten trioxide in an amorphous state at least partially, the group VIII metal fine particles By introducing a detection target gas such as hydrogen gas into the matrix in a short time by the catalytic action, the light transmittance of the gas sensor thin film changes in a very short time. In addition, since the light transmittance of the gas sensor thin film reversibly changes depending on whether the atmosphere gas to be contacted is the detection target gas or the atmosphere, a characteristic of high reproducibility can be obtained.

  According to the method for manufacturing an element body for a gas sensor of the present invention, a state in which Group VIII metal fine particles are contained in a specific state in a matrix made of tungsten trioxide in an amorphous state at least partially is realized. A thin film for a gas sensor can be obtained, and accordingly, an element body for a gas sensor including a thin film for a gas sensor that achieves the characteristics of high responsiveness to a detection target gas and high repeatability can be obtained.

  Since the gas sensor element body obtained by the manufacturing method described above includes the gas sensor thin film, the gas sensor element body has high responsiveness to the detection target gas, and the contacted atmospheric gas is the detection target gas. Since the light transmittance of the gas sensor thin film reversibly changes depending on the case and the case of the atmosphere, and has high repetitive reproducibility, it is particularly useful as a gas sensor element constituting an optical gas sensor.

  Hereinafter, the present invention will be specifically described.

<Thin film for gas sensor>
FIG. 1 is an explanatory sectional view schematically showing an example of the configuration of a thin film for a gas sensor of the present invention.
In the gas sensor thin film 10, group VIII metal fine particles (hereinafter also referred to as “catalyst metal fine particles”) P are dispersed in a thin film substrate (hereinafter also referred to as “matrix”) 12 made of tungsten trioxide. It has been done.

In such a gas sensor thin film 10, the matrix 12 is colored by contact with a reducing gas such as hydrogen gas in a normal state where the atmosphere is in contact with the gas sensor thin film 10. On the other hand, it has a so-called electrochromic property in which the matrix 12 is decolored and returned to the normal state when the atmosphere comes into contact with the colored state.
Here, “electrochromic characteristics” refers to a phenomenon in which optical characteristics reversibly change due to an electrochemical redox reaction.

The reducing gas that can bring the gas sensor thin film 10 into a colored state by being brought into contact with the gas sensor thin film 10 is catalyzed by the catalytic metal fine particles P to generate protons (H ⁺ ). Such a reducing gas includes hydrogen gas (H ₂ ), ammonia gas (NH ₃ ), silane gas (SiH ₄ ), hydrogen sulfide gas (H ₂ S), and chlorine gas (Cl ₂ ). Etc. In the optical gas sensor described later, these reducing gases are used as detection target gases.
In the following, hydrogen gas will be described as an example of the reducing gas.

In the gas sensor thin film 10, when hydrogen gas is brought into contact with the surface thereof, protons (H ⁺ ) and electrons (e ⁻ ) are generated from the hydrogen atoms constituting the hydrogen gas by the catalytic metal fine particles P, and the protons. (H ⁺ ) and electrons (e ⁻ ) are supplied into the matrix 12 by a so-called spillover effect by the catalytic metal fine particles P, and the tungsten trioxide constituting the matrix 12 is changed from a hexavalent state in a normal state to a proton (H It changes to a pentavalent state called a so-called tungsten bronze structure in which ⁺ ) is inserted.
The gas sensor thin film 10 has a specific low light transmittance that absorbs visible light in a wavelength region of 600 to 800 nm due to absorption transfer between valences by electrons that transition between the hexavalent state and the pentavalent state. It changes to the colored state it has. At this time, the matrix 12 which was colorless and transparent in the normal state is in a state of exhibiting blue (tungsten bronze).
On the other hand, when the introduction of hydrogen gas is stopped and, for example, the gas sensor thin film 10 is exposed to the atmosphere, protons (H ⁺ ) are desorbed from tungsten trioxide having a tungsten bronze structure in the matrix 12. 10 returns from the colored state to the normal state. At this time, the matrix 12 recovers from blue to a colorless and transparent state.

In the gas sensor thin film 10 of the present invention, at least a part of tungsten trioxide constituting the matrix 12 is in an amorphous state.
Such amorphous tungsten trioxide (hereinafter also referred to as “amorphous tungsten trioxide”) can stably hold the catalytic metal fine particles P, and the matrix 12 has the catalyst metal fine particles P It is assumed that it contributes to exhibiting sufficient catalytic activity.

The ratio of amorphous tungsten trioxide to the entire tungsten trioxide constituting the matrix 12 is preferably 30 to 100% by volume, more preferably 30 to 99% by volume, and particularly preferably 80 to 99% by volume. .
If the ratio of amorphous tungsten trioxide constituting the matrix 12 is too small, the entire tungsten trioxide constituting the matrix 12 has a high crystallinity, so that the structure of tungsten trioxide is very tight as a whole. As a result, the flow rate of the hydrogen gas is reduced, so that the contact probability between the tungsten trioxide constituting the matrix 12 and the hydrogen gas is reduced, and the catalyst metal fine particles P are not stably maintained. As a result, sufficient catalytic activity cannot be obtained, and adsorption or desorption of protons by hydrogen gas cannot be performed in a short time, so that the obtained gas sensor thin film 10 has a long response time to hydrogen gas, that is, responsiveness. May be low.

Moreover, it is preferable that the tungsten trioxide which comprises the matrix 12 is a porous state.
Since the tungsten trioxide constituting the matrix 12 is in a porous state, the solid phase by the matrix 12 made of tungsten trioxide in the porous state, the solid phase by the catalytic metal fine particles P, and the gas phase by hydrogen gas. Are brought into contact with each other with a large surface area, and the adsorption or desorption of hydrogen gas to tungsten trioxide is sufficiently promoted, so that the gas sensor thin film 10 can be changed to the colored state or the normal state in a very short time. It is inferred that

Such a porous state is obtained, for example, when pores are formed in a portion where alcohol molecules are desorbed by the alcohol solvent when the alcohol solvent is volatilized in the production method described later. .
The size of the pores constituting the tungsten trioxide in the porous state is, for example, preferably 1.0 μm or less in diameter, and more preferably 0.5 μm or less in diameter.

The Group VIII metal constituting the catalytic metal fine particles P of the thin film 10 for gas sensor of the present invention is a so-called platinum group metal belonging to Group VIII in the periodic table.
Examples of such a group VIII metal include platinum (Pt), palladium (Pd), nickel (Ni), ruthenium (Ru), iridium (Ir), etc., and these may be one or more kinds. Can be used in combination.
In particular, it is preferable to use platinum as the Group VIII metal constituting the catalytic metal fine particles P of the thin film for gas sensor 10.

The catalyst metal fine particles P preferably have a particle size of 1 to 50 nm, more preferably 5 to 30 nm.
If the particle diameter of the catalytic metal fine particles P is too small, sufficient catalytic action cannot be obtained, and a sufficiently large change in light transmittance, that is, high sensitivity cannot be obtained in the obtained gas sensor thin film. On the other hand, if the particle size of the catalyst metal fine particles P is excessive, a sufficient surface area cannot be obtained for the catalyst metal fine particles and the catalytic activity is reduced. As a result, a sufficiently large change in light transmittance is obtained. I can't.

The content ratio of the catalyst metal fine particles P in the gas sensor thin film 10 is, for example, an atomic ratio (W: M) of tungsten atoms (W) in the matrix 12 of the gas sensor thin film 10 to catalyst metal atoms (M) in the catalyst metal fine particles P. 13: 0.5 to 13: 5, and more preferably 13: 1.0 to 13: 2.0.
If the ratio (M / W) of catalyst metal atoms (M) to tungsten atoms (W) in the gas sensor thin film 10 is too small, a sufficiently large change in light transmittance cannot be obtained in the obtained gas sensor thin film. . On the other hand, if the ratio (M / W) of the catalyst metal atoms (M) to the tungsten atoms (W) in the gas sensor thin film 10 is excessive, excessive aggregation of the catalyst metal fine particles precipitated in the thermal firing treatment step described later. In the gas sensor thin film obtained by the generation of the catalyst, the catalyst metal fine particles have a large particle size, and the overall catalytic activity is reduced by reducing the proportion of the catalyst metal fine particles that can contact the hydrogen gas that contributes to the catalytic action. Therefore, a sufficiently large change in light transmittance cannot be obtained.

In the gas sensor thin film 10, 90% by volume or more of all the catalytic metal fine particles P are preferably embedded in the matrix 12, and 100% by volume of all the catalytic metal fine particles P are in the matrix 12. It is particularly preferred that it is configured to be buried.
The reason for this is not clear, but the retention stability of the catalyst metal fine particles P buried in the matrix 12 is high, and compared to the catalyst metal fine particles P exposed on the surface of the gas sensor thin film 10. Therefore, the gas sensor thin film 10 obtained by the catalytic metal fine particles P having a high retention stability that is equal to or higher than a desired ratio exhibits a sufficient catalytic action as a whole. This is because high responsiveness can be achieved.

  The film thickness of such a gas sensor thin film 10 varies depending on the type and content ratio of the group VIII metal constituting the catalytic metal fine particles P contained in the gas sensor thin film 10, for example, the group VIII metal is platinum, When the ratio (W: Pt) of tungsten atoms (W) to platinum atoms (Pt) in the gas sensor thin film 10 is 13: 1.5, it is preferably, for example, 70 to 1000 nm, more preferably 70. ˜500 nm, particularly preferably 150 nm.

  If the thickness of the gas sensor thin film 10 is too small, a sufficiently large change in light transmittance may not be obtained. On the other hand, if the film thickness of the gas sensor thin film 10 is excessive, there is a possibility that the alcoholic solvent remains without being sufficiently removed in the thermal baking treatment step of the manufacturing method described later. The electrochromic characteristics may not be obtained.

<Element body for gas sensor>
FIG. 2 is an explanatory diagram showing an example of a configuration of a gas sensor element body on which the gas sensor thin film of FIG. 1 is formed.
The gas sensor element body 20 of the present invention is formed by forming the gas sensor thin film 10 on the surface of a translucent substrate 22.

The translucent substrate 22 constituting the gas sensor element body 20 is in an amorphous state.
Since the translucent substrate 22 is in an amorphous state, the crystallization of the matrix is prevented from being promoted for structural reasons in the thermal baking process of the manufacturing method to be described later. The formation of the amorphous tungsten trioxide constituting the matrix 12 is not hindered, and the matrix 12 in the obtained gas sensor element body 20 contains the desired proportion of amorphous tungsten trioxide.

  As such a translucent substrate 22 in an amorphous state, for example, a substrate made of alkali-free glass, quartz glass, borosilicate glass, soda lime glass, translucent synthetic resin, or the like can be used.

  The shape of the translucent substrate 22 can be appropriately determined depending on the shape of the target optical gas sensor. For example, when the target is a thin plate type optical gas sensor, it can be a thin plate. In the case of an optical fiber type gas sensor, the translucent substrate 22 is a cylindrical one constituting the core of the optical fiber, and the gas sensor thin film 10 is formed as a clad of the optical fiber on the outer peripheral surface. It can be.

<Method for producing element body for gas sensor>
In the present invention, the gas sensor element body 20 is obtained through the following steps.

(1) Preparation process of tungsten alkoxide solution First, as shown in the following reaction formula (1), a tungsten alkoxide solution called a sol-gel solution is prepared by dissolving a tungsten halide compound in an alcohol solvent. Prepare. However, in Reaction Formula (1), R represents an alkyl group, X represents a halogen atom, and n represents an integer of 1 or more.
Reaction formula _{(1): WX n + nROH} → W (OR) n + nHX

The tungsten concentration in the tungsten alkoxide solution is preferably such that the concentration of tungsten atoms in the tungsten alkoxide solution is 1 × 10 ⁻⁴ mol / L to ¹ × 10 ⁻¹ mol / L, for example.

  As the alcohol solvent, for example, monovalent alcohol compounds such as ethanol, methanol, and propanol, and various compounds such as polyhydric alcohols can be used. Moreover, you may use these 1 type or in mixture of 2 or more types.

  By preparing tungsten alkoxide solution by dissolving tungsten in an alcohol-based solvent, tungsten alkoxide is formed in the solution, and this is not clear, but is exposed on the surface of the obtained gas sensor thin film 10. It is possible to realize a state in which the volume of the catalyst metal fine particles P embedded in the interior thereof is larger than that of the catalyst metal fine particles P in the fresh state.

(2) Preparation of Group VIII Metal Ion-Containing Alcohol Solution On the other hand, by adding a Group VIII metal raw material compound (Group VIII metal salt) providing Group VIII metal constituting the catalyst metal fine particles P to the alcohol solvent, catalyst metal A group VIII metal ion-containing alcohol solution in which metal ions to form the fine particles P are dissolved in the alcohol solvent with high uniformity is prepared.
When the group VIII metal constituting the catalyst metal fine particles P is, for example, platinum, examples of the group VIII metal raw material compound include hexachloroplatinic (IV) acid (H ₂ PtCl ₆ .6H ₂ O), tetrachloroplatinic acid (HPtCl). ₄ ), chloroplatinic acid such as hexachloroplatinic acid (HPtCl ₆ ) can be used.
Moreover, as an alcohol compound which comprises an alcohol-type solvent, the thing similar to the alcohol compound which comprises said tungsten alkoxide solution can be mentioned.
Here, the alcohol compound for preparing the tungsten alkoxide solution and the alcohol compound for preparing the Group VIII metal ion-containing alcohol solution may be the same or different, but they must be the same. preferable.

The concentration of the Group VIII metal raw material compound in the Group VIII metal ion-containing alcohol solution is preferably, for example, 1 × 10 ⁻⁵ mol / L to 1 × 10 ⁻² mol / L, and more preferably 9 × 10 ^−4. Mol / L.

(3) Step of preparing thin film forming solution Furthermore, the step of preparing the tungsten alkoxide solution obtained in the step of preparing the (1) tungsten alkoxide solution and the step of preparing the (2) group VIII metal ion-containing alcohol solution. The solution for forming a thin film is prepared by mixing and stirring the Group VIII metal ion-containing alcohol solution. The mixing and stirring time of the tungsten alkoxide solution and the group VIII metal ion-containing alcohol solution is, for example, 5 to 30 minutes.

(4) Application / Drying Step The thin film-forming solution obtained in (3) above is applied onto the surface of the translucent substrate 22. As a coating method, for example, a spin coating method, a dip coating method, or the like can be used.
Subsequently, it is dried at 50 to 100 ° C. for 1 to 10 minutes, for example.

(5) Thermal calcination treatment step And, with respect to the element precursor for a gas sensor coated with a thin film forming solution on one surface and dried, the calcination temperature is preferably 320 to 430 ° C, more preferably 320 to 400 ° C. A thermal firing process is performed in The catalytic metal fine particles P are dispersed and precipitated in the matrix 12 by this thermal firing treatment.
When the firing temperature is less than 320 ° C., the gas sensor element body obtained does not have sufficient adhesion between the gas sensor thin film and the translucent substrate, and the alcoholic solvent remains without being reliably removed. However, there is a risk that sufficient sensitivity to hydrogen gas cannot be obtained. On the other hand, when the heat treatment temperature exceeds 430 ° C., tungsten trioxide constituting the matrix 12 of the obtained gas sensor element body has a high crystallinity as a whole, and a sufficiently high response to hydrogen gas may not be obtained. There is.

(6) Post-heat treatment step in a hydrogen atmosphere It is preferable to perform a heat treatment in a hydrogen atmosphere after the thermal firing treatment step. By performing a heat treatment step thereafter, the gas sensor thin film 10 obtained can be further improved in response to hydrogen gas, sensitivity due to changes in light transmittance, and repeatability.
The reason for this is not clear, but it is presumed that the catalytic activity of the catalytic metal fine particles P is increased because the tungsten bronze structure is easily formed.

<Optical gas sensor>
The gas sensor element body 20 of the present invention can be used, for example, as a gas sensor element in an optical gas sensor.
This optical gas sensor is provided with, for example, a light transmittance detector (not shown), and the light transmittance detector changes the light transmittance from the light transmittance of the gas sensor thin film 10 in a normal state. It is possible to detect that the gas concentration of the hydrogen gas in the detection target space has changed based on the change in the light transmittance.
Further, the optical gas sensor is returned to a normal state by being exposed to the atmosphere, for example, and becomes a state where hydrogen gas can be detected again.
In this optical gas sensor, for example, when hydrogen gas having a concentration of 100% by volume is introduced, the light transmittance at a measurement wavelength of 633 nm becomes 50% or less of the normal state within 1.0 second, and hydrogen gas is introduced. When the atmosphere is introduced in the colored state, it is preferable that the light transmittance at the measurement wavelength of 633 nm returns to 50% of the normal state in a short time. By having such a performance, it is possible to detect in a short time that, for example, the concentration of hydrogen gas in the detection target space is 4% by volume or more.

  Although the embodiments of the present invention have been specifically described above, the embodiments of the present invention are not limited to the above examples, and various modifications can be made.

For example, as shown in FIG. 3, the gas sensor element body is made of a crystalline material as the translucent base 22A, and is made of an amorphous material on the translucent base 22A made of the crystalline material. An amorphous intermediate layer 24 may be provided.
As a result, as in the case where the above-described translucent substrate is made of an amorphous material, the generation of amorphous tungsten trioxide constituting the matrix 12 of the gas sensor thin film 10 is inhibited in the thermal firing process. Instead, the matrix 12 in the obtained gas sensor element body 20A contains amorphous tungsten trioxide at a desired ratio.

  Examples of the amorphous material constituting the amorphous intermediate layer 24 include non-alkali glass, quartz glass, borosilicate glass, soda lime glass, and translucent synthetic resin.

  According to the gas sensor thin film 10 as described above, since the catalytic metal fine particles P are contained in the matrix 12 made of amorphous tungsten trioxide at least partially, the catalytic metal fine particles P are included. Since the detection target gas such as hydrogen gas is introduced into the matrix 12 in a short time by the catalytic action of the above, the light transmittance of the gas sensor thin film 10 changes in a very short time. Since the light transmittance of the gas sensor thin film 10 reversibly changes depending on whether the atmospheric gas being contacted is the detection target gas or the atmosphere, the responsiveness is high, and the reproducibility is high. Is obtained.

  In addition, according to the above method for manufacturing a gas sensor element body, the gas sensor thin film 10 in which a state in which the catalytic metal fine particles P are contained in the matrix 12 made of at least a part of the amorphous tungsten trioxide is realized. Therefore, it is possible to obtain the gas sensor element body 20 including the gas sensor thin film 10 that achieves the characteristics of high responsiveness to the detection target gas and high repeatability.

  Since the gas sensor element body 20 obtained by the above manufacturing method includes the gas sensor thin film 10, the gas sensor element body 20 has a characteristic of high responsiveness to the detection target gas, and the contacted atmospheric gas is the detection target gas. Since the light transmittance of the gas sensor thin film 10 reversibly changes depending on the case and the case of the atmosphere, and has high repeatability, it is particularly useful as a gas sensor element constituting an optical gas sensor.

<Example 1>
A tungsten alkoxide solution [1] was prepared by dissolving 3 g of tungsten hexachloride (WCl ₆ ) in 42 ml of ethanol (C ₂ H ₅ OH) in an argon atmosphere and stirring for 1 hour. On the other hand, 1 g of hexachloroplatinic acid (H ₂ PtCl ₆ .6H ₂ O) was dissolved in 100 ml of ethanol at room temperature to prepare a platinum ion-containing alcohol solution [1]. These were mixed so that the molar ratio of tungsten atoms: platinum atoms (W: Pt) was 13: 1.2 and stirred for 10 minutes to obtain a thin film forming solution [1] for gas sensors. The forming solution [1] was applied to a non-alkali glass substrate having an area of 50 mm ² and a thickness of 1 mm by spin coating and dried at 100 ° C. for 5 minutes, and then thermally baked in the atmosphere. The element body sample [a] for gas sensor was obtained by performing a heat baking process for 10 minutes at the process temperature of 350 degreeC on the conditions of the temperature increase rate of 100 degreeC / h, and the temperature decrease rate of 100 degreeC / h.
This gas sensor element body sample [a] was 250 nm when the film thickness was measured with a scanning electron microscope (SEM). Further, when the crystal phase of the gas sensor element sample [a] was identified by X-ray diffraction analysis (XRD), it was confirmed that at least a part of the tungsten trioxide as a matrix was in an amorphous state. . Furthermore, when the surface state was observed using an atomic force microscope (AFM), it was confirmed that the matrix was in a porous state in any sample.

<Example 2>
A gas sensor element sample [b] was obtained in the same manner as in Example 1 except that the thermal firing temperature was 400 ° C.
When the film thickness of this gas sensor element sample [b] was measured with a scanning electron microscope (SEM), it was 230 nm. Further, when the crystal phase of the gas sensor element sample [b] was identified by X-ray diffraction analysis (XRD), it was confirmed that at least a part of the tungsten trioxide as a matrix was in an amorphous state. . Furthermore, when the surface state was observed using an atomic force microscope (AFM), it was confirmed that the matrix was in a porous state in any sample.

Evaluation of response and recovery of the gas sensor element samples [a] and [b] to hydrogen gas having a concentration of 100% by volume (hereinafter also referred to as “100% H ₂ gas”) is as follows. went.

[Evaluation of responsiveness and recoverability to 100% H ₂ gas]
The sample was placed in a glass cell installed in a spectrophotometer at room temperature, the atmosphere in the glass cell was replaced with argon gas, 100% H ₂ gas was introduced, and the change in light transmittance with respect to elapsed time was measured. . From the introduction of 100% H ₂ gas after 400 seconds to stop the introduction of 100% H ₂ gas was introduced air into the glass cell. The measurement wavelength for measuring the light transmittance was 633 nm.
The results are shown in FIG. 4 and FIG. However, the light transmittance measured in an argon gas atmosphere before the introduction of 100% H ₂ gas was 100%.

In Examples 1 and 2 above, as shown in the graphs of FIGS. 4 and 5, the response times required until the light transmittance reaches 50% were 1.1 seconds and 3.6 seconds, respectively. It was confirmed that hydrogen gas can be detected in an extremely short time. It was also confirmed that the light transmittance was recovered when the introduced gas was switched from 100% H ₂ gas to the atmosphere.

<Example 3>
A tungsten alkoxide solution [2] was prepared by dissolving 3 g of tungsten hexachloride (WCl ₆ ) in 42 ml of ethanol (C ₂ H ₅ OH) in a dry nitrogen atmosphere and stirring for 1 hour. On the other hand, 1 g of hexachloroplatinic acid (H ₂ PtCl ₆ .6H ₂ O) is dissolved in 100 ml of ethanol at room temperature to prepare a platinum ion-containing alcohol solution [2], which is made of tungsten atom: platinum atom (W: Pt) Is mixed at a molar ratio of 13: 1.5 and stirred for 10 minutes to obtain a thin film forming solution for gas sensor [2]. This thin film forming solution for gas sensor [2] is 3.0 cm × 3 An operation of applying to a non-alkali glass substrate having a size of 0.0 cm by spin coating and then drying at 100 ° C. for 5 minutes is performed five times, and then the temperature is raised in the atmosphere at 400 ° C. for 10 minutes. Gas sensor element body sample [c] was obtained by performing a thermal firing process under conditions of a rate of 100 ° C./h and a temperature drop rate of 100 ° C./h.
When the film thickness of this gas sensor element body sample [c] was measured with a scanning electron microscope (SEM), it was 300 nm. Further, when the crystal phase of the gas sensor element sample [c] was identified by X-ray diffraction analysis (XRD), it was confirmed that at least a part of the tungsten trioxide as a matrix was in an amorphous state. . Furthermore, when the surface state was observed using an atomic force microscope (AFM), it was confirmed that the matrix was in a porous state.

The gas sensor element sample [c] is evaluated for responsiveness to 100% H ₂ gas, and the gas sensor element sample [c] is placed in a glass cell installed in a spectrophotometer at room temperature. After the atmosphere in the cell was replaced with argon gas, 100% H ₂ gas was introduced, and the change in light transmittance with respect to elapsed time was measured. The measurement wavelength for measuring the light transmittance was 633 nm.
The results are shown in FIG. However, the light transmittance measured in an argon gas atmosphere before the introduction of 100% H ₂ gas was 100%.

  In Example 3, as shown in the graph of FIG. 6, the response time required until the light transmittance reaches 50% is as very short as 0.8 seconds, and the hydrogen gas is reduced in a short time. It was confirmed that it could be detected.

<Comparative Example 1>
A comparative gas sensor element sample [d] was obtained in the same manner as in Example 3 except that the temperature of the thermal firing treatment was 500 ° C.
This gas sensor element sample [d] was 280 nm in thickness measured with a scanning electron microscope (SEM). Further, from the X-ray diffraction spectrum of the gas sensor element sample [d] by X-ray diffraction analysis (XRD), it was confirmed that crystallization of tungsten trioxide as a matrix was promoted.

For the comparative gas sensor element sample [d], the responsiveness and recoverability to 100% H ₂ gas were evaluated in the same manner as in Example 1.
The results are shown in FIG. However, the light transmittance measured in an argon gas atmosphere before the introduction of 100% H ₂ gas was 100%.

  In the comparative example 1 described above, as shown in the graph of FIG. 7, the response time required for the light transmittance to reach 50% was 2.0 seconds, which was a relatively short time. It was confirmed that it took a long time for the rate of change to recover to 50%.

<Example 4>
In the same manner as in Example 1, a gas sensor element body sample [e] was obtained.
When the film thickness of the gas sensor element sample [e] was measured with a scanning electron microscope (SEM), it was 250 nm. Further, when the crystal phase of the gas sensor element sample [e] was identified by X-ray diffraction analysis (XRD), it was confirmed that at least a part of the tungsten trioxide as a matrix was in an amorphous state. . Furthermore, when the surface state was observed using an atomic force microscope (AFM), it was confirmed that the matrix was in a porous state in any sample.

The gas sensor element body sample [e] is mixed with hydrogen gas having a hydrogen gas concentration of 2 to 20% by volume and dry air (hereinafter also referred to as “H ₂ mixed gas”), and 100% H. _The response to _two gases was evaluated as follows. That is, the gas sensor element sample [e] is placed in a glass cell installed in a spectrophotometer at room temperature, and the atmosphere in the glass cell is replaced with argon gas, and then the hydrogen gas concentration is 2 vol%, 5 vol. Either 20% by volume or 20% by volume of H ₂ mixed gas or 100% H ₂ gas was introduced as a detection target gas, and the change in light transmittance with respect to elapsed time was measured. The introduction of the detection target gas was stopped 400 seconds after the introduction of the detection target gas, and the atmosphere was introduced into the glass cell. The measurement wavelength for measuring the light transmittance was 633 nm.
The results are shown in FIG. However, the light transmittance measured in an argon gas atmosphere before introduction of the H ₂ mixed gas or 100% H ₂ gas was 100%. In FIG. 8, 100% H ₂ gas (i), hydrogen gas concentration of 20% by volume (ii), hydrogen gas concentration of 5% by volume (iii), hydrogen A gas concentration of 2% by volume is indicated by (iv).

  In the above Example 4, as shown in the graph of FIG. 8, it is confirmed that the change rate of the light transmittance with respect to gas is so high that the hydrogen gas density | concentration is high about the detection object gas introduced. For example, it is considered that the concentration of hydrogen gas in the detection target gas can be detected from the value of the change rate of the light transmission rate of the detection target gas such as the response time required until the light transmission reaches 50%. Further, it was confirmed that the light transmittance was restored when the introduced gas was switched to the atmosphere.

<Example 5>
A tungsten alkoxide solution [3] was prepared by dissolving 3 g of tungsten hexachloride (WCl ₆ ) in 42 ml of 2-butanol (C ₄ H ₉ OH) in a dry argon atmosphere and stirring for 1 hour. On the other hand, 1 g of hexachloroplatinic acid (H ₂ PtCl ₆ .6H ₂ O) is dissolved in 50 ml of 2-butanol at room temperature to prepare a platinum ion-containing alcohol solution [3], and palladium acetate ((CH ₃ COO) ₂ Pd) 0.0157 g of cooling was dissolved in 19 ml of 2-butanol to prepare a palladium ion-containing alcohol solution [1], and these were converted to tungsten atoms: (platinum atoms + palladium atoms) (W: (Pt + Pd)). Mixing so that the molar ratio is 13: 1.2 and the platinum atom: palladium atom (Pt: Pd) is 9: 1 in the molar ratio, and the platinum ion-containing alcohol solution is added for 10 minutes when the platinum ion-containing alcohol solution is added. When the alcohol solution is added, each solution is stirred for 1 minute to obtain a thin film forming solution [3] for gas sensor. The gas sensor thin film forming solution [3], on an alkali-free glass substrate of the area 50 nm ² thickness 1 mm, for 10 times the operation of drying the coating and then 5 minutes 100 ° C. by a spin coating method, then, the atmosphere Was subjected to a thermal firing treatment at a thermal firing temperature of 350 ° C. for 10 minutes under the conditions of a rate of temperature increase of 100 ° C./h and a rate of temperature decrease of 100 ° C./h to obtain a gas sensor element body sample [f].
The gas sensor element body sample [f] was 244.6 nm in thickness measured by a scanning electron microscope (SEM). Further, when the crystal phase of the gas sensor element sample [f] was identified by X-ray diffraction analysis (XRD), it was confirmed that at least a part of the tungsten trioxide as a matrix was in an amorphous state. . Furthermore, when the surface state was observed using an atomic force microscope (AFM), it was confirmed that the matrix was in a porous state.

The responsiveness to 100% H ₂ gas and the recoverability of the gas sensor element body sample [f] were evaluated as follows. That is, the gas sensor element sample [f] is placed in a glass cell installed in a spectrophotometer at room temperature, and the atmosphere in the glass cell is replaced with argon gas, and then 100% H ₂ gas is introduced. The change in light transmittance with respect to time was measured. From the introduction of 100% H ₂ gas after 400 seconds to stop the introduction of 100% H ₂ gas was introduced air into the glass cell. The measurement wavelength for measuring the light transmittance was 633 nm.
The results are shown in FIG. However, the light transmittance measured in an argon gas atmosphere before the introduction of 100% H ₂ gas was 100%.

In Example 5, as shown in the graph of FIG. 9, the response time required until the light transmittance reaches 50% is 0.6 seconds, and hydrogen gas can be detected in a very short time. It was confirmed that it was possible. Further, it was confirmed that the transmittance was recovered in a very short time when the introduced gas was switched from 100% H ₂ gas to the atmosphere.

It is sectional drawing for description which shows an example of a structure of the thin film for gas sensors of this invention typically. It is explanatory drawing which shows typically an example of a structure of the element body for gas sensors provided with the thin film for gas sensors of FIG. It is explanatory drawing which shows typically another example of a structure of the element body for gas sensors provided with the thin film for gas sensors of FIG. 3 is a graph showing the results of Example 1. 10 is a graph showing the results of Example 2. 10 is a graph showing the results of Example 3. 6 is a graph showing the results of Comparative Example 1. It is a graph which shows the result of Example 4. 10 is a graph showing the results of Example 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Gas sensor thin film 12 Matrix P Catalytic metal fine particles 20, 20A Gas sensor element body 22, 22A Translucent base 24 Amorphous intermediate layer

Claims (8)

A thin film for a gas sensor in which Group VIII metal fine particles are dispersed in a thin film substrate made of tungsten trioxide,
A thin film for a gas sensor, wherein at least a part of tungsten trioxide constituting the thin film substrate is in an amorphous state.   2. The thin film for a gas sensor according to claim 1, wherein 90% by volume or more of the Group VIII metal fine particles are embedded in the thin film base material. 3.   2. The thin film for a gas sensor according to claim 1, wherein all of the Group VIII metal fine particles are embedded in the thin film base material. 3.   The thin film for a gas sensor according to any one of claims 1 to 3, wherein the tungsten trioxide constituting the thin-film substrate is in a porous state.   A gas sensor element body, wherein the thin film for a gas sensor according to any one of claims 1 to 4 is formed on a surface of a plate-like translucent substrate.   6. The gas sensor element body according to claim 5, wherein the translucent substrate is made of an amorphous material.   6. The translucent substrate is made of a crystalline material, and an amorphous intermediate layer made of an amorphous material is interposed between the translucent substrate and the gas sensor thin film. 2. An element body for a gas sensor according to 1. A method for producing a gas sensor element body in which a thin film for a gas sensor in which a group VIII metal fine particle is dispersed in a thin film substrate made of tungsten trioxide is formed on a translucent substrate, comprising tungsten hexachloride A solution for forming a thin film obtained by mixing a tungsten alkoxide solution obtained by dissolving an alcohol solvent with a group VIII metal ion-containing alcohol solution obtained by dissolving a group VIII metal salt in an alcohol solvent. A method for producing an element body for a gas sensor, comprising the steps of coating on a light-transmitting substrate, drying, and then firing.