JP3707053B2 - Method for manufacturing a film for a gas sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes an element having a film composed of a mixed layer of a catalytic metal that dissociates and adsorbs a reducing gas such as hydrogen or a hydrogen-containing compound gas and a solid compound semiconductor reduced by hydrogen atoms, and the solid compound semiconductor by reduction The present invention relates to a method for manufacturing a film for a gas sensor comprising an optical means for detecting a change in light absorption of the gas.
[0002]
[Prior art]
Various methods are known as a gas sensor for detecting a reducing gas, for example, hydrogen such as hydrogen gas, ammonia gas, silane gas, and hydrogen sulfide gas, or a hydrogen-containing compound gas.
[0003]
Conventional gas sensors are mainly of catalytic combustion type or semiconductor type. The catalytic combustion type gas sensor is a device in which a catalytic metal such as platinum (Pt) or palladium (Pd) is heated by a heater to electrically detect a change in conductivity caused by combustion due to gas contact. A semiconductor gas sensor detects changes in electrical characteristics of a semiconductor due to gas adsorption. At that time, the semiconductor is used in a heated state for various reasons such as gas selectivity, responsiveness, and element characteristics. The
[0004]
As described above, in the conventional gas sensors, the gas to be detected is almost always accompanied by heating and combustion regardless of flammability and explosiveness, and there is a problem in terms of safety. Since the element is heated, the deterioration of the element is quick, the characteristics are liable to become unstable, and there is a problem in reliability and element life.
[0005]
As a gas sensor that solves the above problems, when the hydrogen atom is reduced by the catalyst metal that dissociates and adsorbs hydrogen or a hydrogen-containing compound gas and the hydrogen atom generated by the dissociative adsorption in the catalyst metal, and the hydrogen atom no longer exists There has been proposed a gas sensor including an element having a laminated structure of a solid compound semiconductor that returns to a state before being reduced to an oxygen, and an optical means for detecting a change in light absorption of the solid compound semiconductor due to the reduction (special feature). No. 3-67218).
[0006]
In the above Japanese Patent Publication No. 3-67218, as a gas sensor, an element having the laminated structure is formed by vapor deposition on a glass substrate, or the laminated structure is formed on an outer peripheral portion of an optical fiber core. The structure of a so-called optical fiber type gas sensor used as a clad, and the solid compound semiconductor having the above-mentioned laminated structure as a thin film optical waveguide, the substrate and the catalyst metal as a clad layer, and optical fibers at both ends of the solid compound semiconductor. An optical fiber type gas sensor having a different configuration formed by combining the two is disclosed.
[0007]
[Problems to be solved by the invention]
By the way, the gas sensor provided with the laminated structure of the catalytic metal and the solid compound semiconductor has poor detection sensitivity, and particularly at a low temperature of 0 ° C. or less, the response speed is very slow with the decrease in hydrogen adsorption activity. There was a problem.
[0008]
In recent years, a gas detection method and apparatus using a film in which a sol-gel solution in which chloroplatinic acid or palladium chloride is uniformly dispersed at a molecular level in an aqueous solution of H ₂ WO ₄ is applied to a substrate and dried and then sintered is reported. Yes.
(See S. Sekimoto, H. Nakagawa, S. Okazaki, K. fukuda, S. Asakura, T. Shigemori, S. Takahashi, Sensors and Actuators B66 (2000) 142-145)
According to the above, there is an advantage that an optical fiber type gas sensor can be easily produced by coating and baking, but there is a problem that detection sensitivity necessary for practical use cannot be obtained at a low temperature of 0 ° C. or lower.
[0009]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to have sufficient sensitivity for practical use even at a low temperature of 0 ° C. or lower, and to prevent the sensing element from being heated and energized. Another object of the present invention is to provide a method for manufacturing a film for a gas sensor having high reliability and element lifetime.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention reduces a catalyst metal that dissociates and adsorbs hydrogen or a hydrogen-containing compound gas, and a hydrogen atom generated by the dissociative adsorption in the catalyst metal, and the hydrogen atom exists. For a gas sensor comprising: an element having a film composed of a mixed layer with a solid compound semiconductor that returns to a state before being reduced when no longer occurs; and optical means for detecting a change in light absorption of the solid compound semiconductor due to reduction In the method for producing a film, in the sol-gel solution of the solid compound semiconductor, a sol-gel solution in which a catalytic metal compound is uniformly dispersed at a molecular level is applied to a substrate and baked to form a film, and then in dry air Then, heat treatment is performed at 30 to 100 ° C. for a predetermined time (the invention of claim 1).
[0011]
Heat treatment (aging) at a temperature of 30 to 100 ° C., preferably about 50 ° C. in dry air, for example, for 1 hour increases the catalytic activity and provides sufficient sensitivity characteristics. The exact reason for this factor is unknown, but to guess, the following can be considered. That is, when adsorbed water or the like, which is a component other than the catalyst metal, evaporates, for example, when WO ₃ is used as the solid compound semiconductor, the portion that has been evaporated and desorbed becomes pores in the metal catalyst / WO ₃ film, The area of the catalyst metal, the solid compound semiconductor WO _{3 of} the support, and the three-phase interface of the gas is expanded. Thereby, it is considered that even at a low temperature of 0 ° C. or lower, the catalytic activity is increased and sufficient sensitivity characteristics can be obtained.
[0012]
In the first aspect of the invention, the embodiments of the catalytic metal and the catalytic metal compound are preferably the inventions of the following second to fourth aspects. That is, in the method for producing a film according to claim 1, the catalyst metal is any one of platinum (Pt), palladium (Pd), nickel (Ni), ruthenium (Ru), and iridium (Ir), or A mixture is obtained (the invention of claim 2). In the film manufacturing method according to claim 1, the catalytic metal compound is chloroplatinic acid or palladium chloride (invention of claim 3).
[0013]
Furthermore, in the film manufacturing method according to claim 1, the catalytic metal compound is a dinitrodiammine compound of the catalytic metal, and an aqueous nitrate solution thereof is mixed into the sol-gel solution of the solid compound semiconductor (the invention of claim 4). ). In this case, instead of chloroplatinic acid or palladium chloride in the invention of claim 3, a membrane is formed using a nitrate aqueous solution of a catalytic metal dinitrodiammine compound, but the aging is applied to other types of membranes. In this case, the same effect can be obtained, and the invention of claim 4 is an embodiment in this aspect.
[0014]
The film using the dinitrodiammine compound is a novel film, and the same applicant as the present application has filed an application for Japanese Patent Application No. 2001-370062 regarding this novel film and its manufacturing method. Dinitrodiammine compounds have a decomposition temperature of 200 ° C. to 235 ° C. and a relatively low temperature. By applying this compound and calcining at a low temperature, components other than the catalyst metal are evaporated to improve sensitivity characteristics. Can be planned. The effect of applying this dinitrodiammine compound is the effect of improving the sensitivity characteristics in the firing process, unlike the above aging, and by applying both the new film and the aging, a double sensitivity improvement effect is obtained. It is done.
[0015]
In the inventions of the first to fourth aspects, the inventions of the following fifth to ninth aspects are preferable as embodiments of the firing temperature, the solid compound semiconductor, the substrate and the like. That is, in the method for producing a film according to any one of claims 1 to 4, a firing temperature when the film is formed by applying to the substrate and firing is set to a range of 300 to 700 ° C. Invention). The preferred range of the firing temperature varies depending on the type of film to be formed, but the above range is preferred from the viewpoint of sensitivity characteristics. In addition, when using chloroplatinic acid or palladium chloride, the range of 500-670 degreeC is more preferable.
[0016]
6. The method for producing a film according to claim 1, wherein the solid compound semiconductor is tungsten trioxide (WO ₃ ), molybdenum trioxide (MoO ₃ ), titanium dioxide (TiO ₂ ), hydroxide. Any one of iridium (Ir (OH) _n ), vanadium pentoxide (V ₂ O ₅ ), and rhodium oxide (Rh ₂ O ₃ .xH ₂ O) is used.
[0017]
Furthermore, in the manufacturing method of the film | membrane in any one of Claim 1 thru | or 6, the said board | substrate is made into a glass substrate (invention of Claim 7).
[0018]
In the case of a film of an optical fiber type gas sensor, the inventions of the following claims 8 to 9 are preferable. That is, in the film manufacturing method according to claim 7, the substrate is an optical fiber core instead of the glass substrate, and the film is a clad formed on an outer peripheral portion of the core. Invention). Furthermore, in the film manufacturing method according to claim 8, a plurality of films serving as the cladding are formed at predetermined intervals in the axial direction of the optical fiber (invention of claim 9).
[0019]
According to the ninth aspect of the present invention, as described in detail later, hydrogen leakage is detected with high sensitivity by using a pulsed light source, projecting light onto a plurality of gas sensors via an optical fiber, and detecting backscattered light. A sensor capable of detecting the position of the point is obtained.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below based on the drawings.
[0021]
FIG. 1 is a schematic cross-sectional view showing a basic structure of a gas sensor element according to the present invention. Based on this, a method for producing a film for a gas sensor of the present invention will be described below.
[0022]
In FIG. 1, an element 1 has a reducing gas, ie, hydrogen gas H ₂ , ammonia gas NH ₃ , and silane gas SiH, as a gas to be detected on a substrate 2 such as a glass substrate, SiO ₂ substrate, or optical fiber core. ₄ , a catalytic metal 3 that generates hydrogen atoms from these gas molecules when hydrogen sulfide gas H ₂ S comes into contact with the solid compound semiconductor 4 whose light absorption changes due to the hydrogen atoms generated in the catalytic metal 3, Has a structure in which a film 34 is uniformly dispersed at the molecular level.
[0023]
As described above, any one of platinum (Pt), palladium (Pd), nickel (Ni), ruthenium (Ru), and iridium (Ir) is used as the catalytic metal 3 having a function of dissociating and adsorbing hydrogen. In addition, the solid compound semiconductor 4 includes tungsten trioxide (WO ₃ ), molybdenum trioxide (MoO ₃ ), titanium dioxide (TiO ₂ ), iridium hydroxide (Ir (OH) _n ), vanadium pentoxide. Either (V ₂ O ₅ ) or rhodium oxide (Rh ₂ O ₃ .xH ₂ O) can be used.
[0024]
Next, a basic manufacturing method of the element 1 including the film 34 will be described below, for example, when platinum (Pt) is used for the catalyst metal 3 and WO ₃ (tungsten trioxide) is used for the solid compound semiconductor 4.
[0025]
First, an aqueous solution of sodium tungstate (manufactured by Wako Pure Chemical Industries) dissolved in pure water is used to create a sol-gel solution in which sodium and hydrogen atoms are exchanged using a cation exchange resin (SKN-1: manufactured by Mitsubishi Chemical). To do.
[0026]
Then, as chloroplatinic acid, for example, 1/10 mol amount of a solution (1 mol / L) in which hexachloroplatinic (IV) acid (H ₂ PtCl ₆ · 6H ₂ O) is dissolved in pure water is added and uniformly dispersed and mixed. Then, for example, a washed glass substrate is immersed in the mixed sol-gel solution, and the sol-gel solution is applied to the substrate by a dip coating method in which the glass substrate is slowly pulled up.
[0027]
Subsequently, after the film applied to the substrate is sufficiently dried at room temperature, the film is temporarily baked at 200 ° C. for 1 hour in an electric furnace, and then baked at 400 ° C. for 1 hour, for example. In this element, light absorption changes as follows.
[0028]
Hydrogen in which hydrogen gas is dissociated and adsorbed on platinum of the catalytic metal 3 in the sol-gel film spills over from platinum and is injected into WO ₃ (tungsten trioxide) of the solid compound semiconductor 4. WO ₃ (tungsten trioxide) of the solid compound semiconductor 4 that has been injected with H ⁺ (proton) from platinum of the catalytic metal 3 is reduced, and a photochromism phenomenon called tungsten bronze in which the density of lattice defects changes is generated. Light absorption in the near-infrared wavelength region around μm increases. When hydrogen gas runs out, H ⁺ (proton) is desorbed and light absorption is also reduced.
[0029]
By injecting H ⁺ (proton), the light absorption of such an element occurs in the case of contact with a reducing gas such as ammonia gas NH ₃ , silane gas SiH ₄ , and hydrogen sulfide gas H ₂ S as well as hydrogen gas. Is done in the same way. If the element is heated by a heater, the response speed can be further increased.
[0030]
Next, FIG. 2 is a conceptual explanatory view showing an embodiment of the gas sensor according to the present invention using the element 1 of FIG.
[0031]
The gas sensor shown in FIG. 2 includes a light source 5 using a light emitting diode and a light receiving element 6 using a photodiode with an element 1 interposed therebetween, and light emitted from the light source 5 enters the light receiving element 6 via the element 1. To be configured. An external power source 7 is connected to the light source 5 to cause the light source 5 to emit light continuously or pulsed. The light receiving element 6 is connected to the detection circuit 8 and is configured to electrically detect a light receiving output corresponding to a change in the amount of transmitted light obtained by the light receiving element 6 and to issue an alarm with a buzzer or a lamp as necessary. .
[0032]
In FIG. 2, gas detection is performed as follows. When the gas to be detected flows into the gas sensor, hydrogen atoms generated by the dissociation of hydrogen in the catalytic metal 3 in the element 1 reduce the solid compound semiconductor 4, and light absorption occurs when WO ₃ is used as the solid compound semiconductor 4. It increases and the amount of transmitted light decreases corresponding to the gas concentration. For this reason, when the signal intensity of the light receiving element in the detection circuit 8 decreases and becomes a predetermined numerical value or less, a gas alarm is given.
[0033]
When the element 1 using WO ₃ is used as the solid compound semiconductor 4, light is absorbed in a wavelength region centered on 1.4 μm by reduction, and thus the light source 5 has a large absorption amount of the element 1. It is desirable to use a light source that emits light having a wavelength in the near infrared region.
[0034]
Next, FIG. 3 is a conceptual explanatory view showing an embodiment different from FIG. 2 of the gas sensor according to the present invention. The gas sensor of FIG. 3 corresponds to the optical fiber type gas sensor, and is characterized in that the film 34 of the element 1 shown in FIG. 1 is used as a clad of an optical fiber. That is, a sol-gel film in which catalytic metal palladium is dispersed in a solid compound semiconductor WO ₃ is applied and fired on the outer periphery of a quartz optical fiber core 9 disposed in the center, and emitted from a light source in the optical fiber core 9. The light is allowed to pass through and enter the light receiving element. The element having the above configuration is referred to as a fiber-type element, whereas an element using a glass substrate is hereinafter referred to as a thin film-type element.
[0035]
In the gas sensor of FIG. 3, in the state where there is no contact with the gas to be detected, the light absorption of the film (solid compound semiconductor 4 and catalyst metal 3) forming the cladding of the optical fiber is small, so that the optical fiber core emitted from the light source The light that travels reflecting inside the light 9 is transmitted efficiently, and a sufficient amount of light reaches the light receiving element. On the other hand, when the gas to be detected comes into contact, hydrogen atoms generated in the catalytic metal 3 reduce the solid compound semiconductor 4, and when WO ₃ is used as the solid compound semiconductor 4, light absorption increases, corresponding to the gas concentration. The amount of light transmitted through the optical fiber is reduced. Gas detection is performed by detecting a decrease in the amount of light transmitted through the optical fiber with a light receiving element.
[0036]
Next, FIG. 4 will be described. FIG. 4 is a conceptual explanatory view showing an embodiment of an optical fiber type gas sensor different from FIG. The gas sensor of FIG. 4 is a multipoint hydrogen gas sensor in which a hydrogen sensitive film is formed on an optical fiber at a plurality of locations (three locations in FIG. 4) at predetermined intervals, and the membrane of the present invention is applied. Thus, a multipoint hydrogen gas sensor excellent in sensitivity can be obtained. In FIG. 4, three elements 1 are provided on measurement points A, B, and C of the optical fiber 10, light is emitted from the light source 5, and light reflected from the reflection mirror 14 is received via the branch 3. The device 6 is configured to receive light. According to this gas sensor, using OTDR (Optical Time Domain Reflection; a method of detecting backscattered light using a pulsed light source) technology, the positions of measurement points A, B, and C are specified by the time difference of reflected light, By measuring the change in the amount of light received due to the light absorption of the film, the position of the hydrogen leak point can be detected.
[0037]
【Example】
(Example 1)
(1) Preparation of sol-gel solution (using chloroplatinic acid)
Take 13.24 g of Na ₂ WO ₄ · 2H ₂ O (manufactured by Wako Pure Chemical Industries, Ltd.) in a measuring flask and add pure water to adjust to 200 ml. An ultrasonic wave was irradiated for 20 minutes to dissolve, and a colorless and transparent Na ₂ WO ₄ aqueous solution (0.2 mol / L) was obtained. Cation exchange resin (SKN-1: manufactured by Mitsubishi Chemical) to 276.27G: a (= exchange mol weight of about 0.6 mol) was filled in a column tower, passed through Na ₂ WO ₄ solution, to exchange Na ⁺ to H ^+, A light brown H ₂ WO ₄ clear aqueous solution was obtained. To this was added 1/10 molar amount of hexachloroplatinic (IV) acid (H ₂ PtCl ₆ .6H ₂ O), 1 mol / L aqueous solution to prepare a sol-gel solution.
(2) Fabrication of thin-film gas sensor element (using chloroplatinic acid) After rinsing with alkali, immersing the glass substrate after replacement with pure water and drying with a rinser drier in the above sol-gel solution, pulling up at a constant speed and dip coating did. At this time, one surface was protected with a masking tape and peeled off after coating.
[0038]
After drying at room temperature for 1 hour, pre-baking at 200 ° C. for 1 hour in an electric furnace, baking at 400 ° C. for 1 hour and then cooling to room temperature. Thereafter, heat treatment was performed at 50 ° C. in dry air, and aging was performed for 3 hours to obtain the element 1 shown in FIG.
[0039]
As shown in FIG. 2, the element 1 is placed in a container capable of inflowing outside air, a predetermined gas to be detected is introduced into the container, and a change due to light absorption extracted by the fiber is detected using a photodiode. did.
[0040]
(Example 2)
(Production of fiber type gas sensor element (using chloroplatinic acid))
A step index type plastic clad fiber (PCF; quartz core / polyfluoroacrylate clad) with a core diameter of 200μm and a clad diameter of 230μm is immersed in 2-aminoethanol to degrade the clad, and mechanically peels and removes the clad. To do. The quartz core fiber from which the cladding was removed was immersed in the sol-gel solution described in Example 1, and then pulled up at a constant speed and dip-coated. After drying at room temperature for 1 hour, it was temporarily fired at 200 ° C. for 1 hour in an electric furnace, then fired at 400 ° C. for 1 hour, and then cooled to room temperature to obtain a fiber-type device. Thereafter, heat treatment was performed at 50 ° C. in dry air, and aging was performed for 3 hours to obtain a fiber element 1.
[0041]
In the obtained fiber, both ends of the detection unit were fused and connected to another fiber for bonding with the optical system. As shown in FIG. 3, the fiber type sensor is placed in a chamber 11 in which outside air can flow in, a predetermined gas to be detected is introduced into the chamber 11, and changes due to light absorption taken out by the optical fiber 10 are changed. Detection was performed using a photodiode. In addition, in FIG. 3, 12 is a thermostat.
[0042]
(Example 3)
(1) Preparation of sol-gel solution (using dinitrodiammine palladium nitrate)
Take 13.24 g of Na ₂ WO ₄ · 2H ₂ O (manufactured by Wako Pure Chemical Industries, Ltd.) in a measuring flask and add pure water to adjust to 200 ml. An ultrasonic wave was irradiated for 20 minutes to dissolve, and a colorless and transparent Na ₂ WO ₄ aqueous solution (0.2 mol / L) was obtained. Cation exchange resin (SKN-1: manufactured by Mitsubishi Chemical) to 276.27G: a (= exchange mol weight of about 0.6 mol) was filled in a column tower, passed through Na ₂ WO ₄ solution, to exchange Na ⁺ to H ^+, A light brown H ₂ WO ₄ clear aqueous solution was obtained. To this was added 0.1 g (approximately 0.026 mol / L) of a dinitrodiammine palladium nitrate aqueous solution (8.4466 wt%, Tanaka Kikinzoku) to prepare a sol-gel solution.
(2) Production of thin-film gas sensor element (using dinitrodiammine palladium nitrate) A thin-film gas sensor element was produced in the same manner as in Example 1 using the sol-gel solution described above.
[0043]
(Example 4)
(Production of fiber type gas sensor element (using dinitrodiammine palladium nitrate))
Using the sol-gel solution described in Example 3, a fiber type sensor was prepared in the same manner as in Example 2.
[0044]
(Comparative Example 1)
(Production of thin-film gas sensor element (using chloroplatinic acid))
The device of Example 1 was fabricated in the same manner except that aging at 50 ° C. was performed after firing.
[0045]
(Comparative Example 2)
(Production of fiber type gas sensor element (using chloroplatinic acid))
In the fiber-type element of Example 2, an element was produced in the same manner except that aging at 50 ° C. was performed after firing.
[0046]
Next, FIG. 5 and FIG. 6 related to the evaluation results of the above-described embodiment will be described. FIG. 5 shows the evaluation results of the temperature-dependent characteristics of the transmitted light amount decrease rate in Examples 1 and 3 and Comparative Example 1 relating to the thin film type gas sensor. Moreover, the same result of Example 2, 4 and the comparative example 2 regarding a fiber type gas sensor is shown in FIG.
[0047]
5 and 6, the gas concentration of the injected hydrogen was 0.5% (volume concentration), and a 1310 nm semiconductor laser was used as the light source. The initial detection output of incident light from the light source was 48.7 to 48.4 μW. The transmitted light amount decrease rate is expressed as a decrease rate of the transmitted light amount when the initial light amount is 100% and 5 minutes have passed after the introduction of hydrogen gas.
[0048]
The practical lower limit of the rate of decrease in the amount of transmitted light is 0.2 to 0.3%, and as is apparent from the results of FIGS. 5 and 6, the rate of change in any of the examples compared to the comparative example. The effect of aging was confirmed. In addition, in the case of the examples according to the present invention, it was revealed that the present invention can be sufficiently put into practical use even at a low temperature of −20 ° C. at 0 ° C. or lower.
[0049]
In addition, compared with the thin film type gas sensor shown in FIG. 5, the fiber type gas sensor shown in FIG. 6 generally shows a higher change rate. That is, the change in absorbance is large. The reason is as follows. That is, in the case of a thin film type gas sensor, the absorbance only changes by the film thickness of the sensor film, but in the case of an optical fiber type gas sensor, the entire periphery of the fiber is covered with the sensor film. This is because light called hevanescent light oozes out and is absorbed, so that the change in absorbance increases by the optical path length of the coated portion.
[0050]
【The invention's effect】
As described above, according to the present invention, the hydrogen atom is reduced by the catalyst metal that dissociates and adsorbs hydrogen or a hydrogen-containing compound gas, and the hydrogen atom generated by the dissociative adsorption in the catalyst metal, and the hydrogen atom does not exist. A gas sensor film comprising: an element having a film composed of a mixed layer of a solid compound semiconductor that returns to a state before being reduced; and optical means for detecting a change in light absorption of the solid compound semiconductor due to the reduction. In the manufacturing method,
In the sol-gel solution of the solid compound semiconductor, a catalyst metal compound, for example, a sol-gel solution in which chloroplatinic acid or palladium chloride is uniformly dispersed at a molecular level, or in place of the chloroplatinic acid or palladium chloride, the catalyst After the aqueous solution of nitrate of metal dinitrodiammine compound is mixed in the sol-gel solution of the solid compound semiconductor, the sol-gel solution uniformly dispersed at the molecular level is applied to the substrate and baked to form a film, and then dried air Because it was decided to heat treatment at 30-100 ℃ for a predetermined time in
To provide a method for producing a film for a gas sensor that has sufficient sensitivity in practical use even at a low temperature of 0 ° C. or less, is safe without heating and energizing a sensing element, and has high reliability and element life. Can do.
[0051]
In recent years, hydrogen has attracted attention as a next-generation clean energy due to global warming and environmental problems. In particular, in a hydrogen station for a fuel cell vehicle, there is a high demand for an area-type sensor that is safe and highly reliable and has a wide sensor area. According to the present invention, all the hydrogen gas can be detected with light sensitivity, so that all the advantages of light such as downsizing, high reliability, heat resistance, durability, fire resistance, explosion proof, etc. can be utilized and the above requirements can be satisfied. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a basic structure of a gas sensor element according to the present invention. FIG. 2 is a conceptual explanatory view showing an embodiment of a gas sensor according to the present invention. FIG. 4 is a conceptual explanatory diagram showing an embodiment of an optical fiber type gas sensor different from FIG. 3. FIG. 5 is a graph showing a temperature dependent characteristic of a transmitted light amount reduction rate related to a thin film type gas sensor. Fig. 6 shows the results of evaluation. Fig. 6 shows the results of evaluating the temperature dependence of the rate of decrease in transmitted light related to the fiber type gas sensor.
1: Element, 2: Substrate, 3: Catalyst metal, 4: Solid compound semiconductor, 5: Light source, 6: Light receiving element, 7: Power supply, 8: Detection circuit, 9: Fiber core, 10: Optical fiber, 13: Branch 14: reflection mirror, 34: membrane.

Claims (9)

It is reduced by the catalytic metal that dissociates and adsorbs hydrogen or a hydrogen-containing compound gas, and the hydrogen atom generated by the dissociative adsorption in the catalytic metal, and returns to the state before the reduction when the hydrogen atom does not exist. In a method for producing a film for a gas sensor, comprising: an element having a film composed of a mixed layer with a solid compound semiconductor; and an optical means for detecting a change in light absorption of the solid compound semiconductor due to reduction.
A sol-gel solution in which a catalytic metal compound is uniformly dispersed at a molecular level in the sol-gel solution of the solid compound semiconductor is applied to a substrate and baked to form a film, and then predetermined at 30 to 100 ° C. in dry air. A method for producing a film for a gas sensor, characterized by performing a time heating treatment. 2. The method of manufacturing a membrane according to claim 1, wherein the catalyst metal is any one of platinum (Pt), palladium (Pd), nickel (Ni), ruthenium (Ru), iridium (Ir), or a mixture thereof. A method for producing a film for a gas sensor. The method for producing a film for a gas sensor according to claim 1, wherein the catalytic metal compound is chloroplatinic acid or palladium chloride. 2. The method for producing a film according to claim 1, wherein the catalytic metal compound is a dinitrodiammine compound of the catalytic metal, and an aqueous nitrate solution thereof is mixed into a sol-gel solution of the solid compound semiconductor. A method for producing a membrane. 5. The gas sensor according to claim 1, wherein a baking temperature when the film is formed by applying to the substrate and baking is set to a range of 300 to 700 ° C. 5. For producing a film for use. 6. The method of manufacturing a film according to claim 1, wherein the solid compound semiconductor is tungsten trioxide (WO ₃ ), molybdenum trioxide (MoO ₃ ), titanium dioxide (TiO ₂ ), iridium hydroxide ( Ir (OH) _n ), vanadium pentoxide (V ₂ O ₅ ), or rhodium oxide (Rh ₂ O ₃ .xH ₂ O), a method for producing a film for a gas sensor. 7. The method for producing a film for a gas sensor according to claim 1, wherein the substrate is a glass substrate. 8. The gas sensor according to claim 7, wherein the substrate is an optical fiber core instead of the glass substrate, and the film is a clad formed on an outer peripheral portion of the core. For producing a film for use. 9. The method of manufacturing a film for a gas sensor according to claim 8, wherein a plurality of films serving as the cladding are formed at predetermined intervals in the axial direction of the optical fiber.

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