JP2006317196A - Hydrogen gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized inexpensive hydrogen gas sensor of high reliability capable of detecting a hydrogen gas selectively and easily. <P>SOLUTION: In the hydrogen gas sensor 10, an amorphous alloy changed in its physical property value by the occlusion of hydrogen is used as a sensor element 12 and a change in the physical property value of the sensor element 12 and/or the generation of heat in the sensor element 12 is measured to detect the presence of the hydrogen gas and/or the concentration of the hydrogen gas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydrogen gas sensor, and more particularly to a hydrogen gas sensor that utilizes changes in physical property values due to hydrogen storage in a hydrogen storage amorphous alloy.

  Hydrogen gas is one of the most promising clean next-generation energy, and in the automobile industry in particular, research using hydrogen gas as a fuel is actively conducted. Since hydrogen gas is very flammable in the air and there is a risk of explosion even at a relatively low concentration, it is essential to develop a hydrogen gas sensor that can detect leakage of hydrogen gas selectively and with high sensitivity. The hydrogen gas sensor is desirably small and inexpensive.

Hydrogen sensors are used for various purposes mainly due to the following technical requirements.
(1) Detectable hydrogen concentration range (2) Measurement accuracy (resolution)
(3) Response speed (4) Hydrogen selectivity (5) Durability

In recent years, needs for hydrogen sensors for fuel cells are rapidly increasing, and consumer hydrogen sensors for automobiles, homes, and the like are required to be particularly inexpensive and suitable for danger detection. As a detection method of the hydrogen sensor, there are a catalytic combustion method, a semiconductor method, a gas heat conduction method, an electrochemical method, a thermoelectric conversion method, a hydrogen storage alloy method, an optical method, and the like. In general gas analysis, a heat conduction method is employed. However, since this method uses the difference in heat conductivity of gas to measure the gas concentration, hydrogen gas cannot be selectively measured. The catalytic combustion type utilizes the fact that the temperature rises when the catalyst such as Pd or Pt comes into contact with the combustible gas and burns, and the electric resistance value changes. Reactive to flammable gases. Further, the metal oxide semiconductor hydrogen sensor most widely used at present is one that utilizes adsorption of tin oxide (SnO ₂ ) (for example, Patent Document 1). In addition to hydrogen, carbon monoxide such as carbon monoxide and methane is used. Low selectivity due to reaction with hydrogen, high operating temperature of 450 ° C, high energy consumption, and expensive system including signal processing for calibration, securing operating temperature, cleaning, There are problems such as.

Many hydrogen sensors use Group VIIIB metal elements (Ni, Pd, Pt) as sensor elements, and the thermal load is a parameter for hydrogen measurement. Such “hot wire” type sensors have cross-sensitivity to other easily oxidizing materials such as alcohols and hydrocarbons, which can often cause false alarms. Since the current generation of the hot wire sensor operates by an oxidation-reduction reaction, hydrogen cannot be detected when it exists in an inert gas flow or in an oxygen-deficient environment, which is a serious defect of the hot wire sensor.
Further, sensors such as metal insulator semiconductor (MIS) or metal oxide semiconductor (MOS) capacitors, field effect transistors, and platinum gate diodes generally have a low hydrogen detection concentration region. Limited to area.

  Against this background, there has been no satisfactory conventional hydrogen selectivity, and the need for a sensor with high hydrogen selectivity is extremely high. For example, in the case of a fuel cell application, in the case of a sensor around a household fuel cell, the ability to separately detect hydrogen and other flammable gases is not required, but in the case of a fuel cell vehicle hydrogen sensor, hydrogen and other Hydrogen selectivity is an extremely important item because it is necessary to distinguish between hydrocarbons and carbon monoxide contained in the exhaust gas of gasoline vehicles, particularly exhaust gas from gasoline vehicles.

Recently, sensors with improved hydrogen selectivity have been reported one after another. For example, a thermoelectric hydrogen sensor that detects the reaction heat of catalytic metal and hydrogen with a thermoelectric element is characterized by a selectivity that is 20 times or more that of ethanol at 100 ° C. Since this sensor uses the high selectivity of the catalytic action of platinum with respect to hydrogen, the selectivity is higher than the conventional adsorption type. Also, MEMS modules using metal hydride thin film have been commercialized. However, even though the selectivity of hydrogen has increased, other gases other than hydrogen also react with the catalyst metal, which limits the usage environment.
As another hydrogen gas sensor, there is a bimetal type sensor in which a Pd—Ag alloy layer is vapor-deposited on a substrate such as glass and the expansion of the Pd—Ag alloy layer due to hydrogen occlusion is detected as a strain of the substrate (patent) Reference 2). However, Pd and Ag are rare metals, and in the presence of a high concentration of hydrogen, reliability for repeated detection is not sufficient due to hydrogen embrittlement.
Japanese Patent Laid-Open No. 5-288702 2001-296238

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a small, inexpensive, and highly reliable hydrogen gas sensor that can selectively and easily detect hydrogen gas.

As a result of intensive studies by the present inventors to achieve the above object, an amorphous alloy having hydrogen storage properties is used as a sensor element, a change in the physical property value of the sensor element due to hydrogen storage, or a sensor element based on catalytic action It was found that hydrogen gas can be selectively and easily detected by detecting the heat generation at, and the present invention was completed.
That is, the hydrogen gas sensor of the present invention uses, as a sensor element, an amorphous alloy that absorbs hydrogen and changes its physical property value by forming an interstitial compound with hydrogen and / or adsorbing hydrogen, and changes the physical property value of the sensor element. The presence or absence of hydrogen gas and / or the hydrogen gas concentration is detected by measuring heat generation at the sensor element. Further, it is preferable that the amorphous alloy used as the sensor element is a metal glass having oxidation resistance.
Here, “measuring the change in physical property value” is not only the case of directly measuring the value of the physical property value itself, but also a change in phenomenon accompanying the change in the physical property value (for example, a current value due to a change in electrical resistance value, It also means measuring a change in voltage value.

In the above sensor, the presence or absence of hydrogen gas and / or the hydrogen gas concentration can be suitably detected by measuring the change in the electromagnetic property value of the sensor element. Here, the electromagnetic property value means a property value with respect to an electromagnetic phenomenon of the substance, and refers to, for example, an electric resistance value, impedance, dielectric constant, magnetic permeability, and the like. It is particularly preferable to measure changes in electrical resistance and impedance as electromagnetic property values.
In the above sensor, the presence or absence of hydrogen gas and / or the hydrogen gas concentration can be suitably detected by measuring a change in mechanical property value of the sensor element. Here, the mechanical physical property value means a physical property value with respect to a dynamic phenomenon of the substance, and means, for example, length, area, volume, mass, density, elastic modulus, viscosity, and the like.
In the above sensor, the presence or absence of hydrogen gas and / or the hydrogen gas concentration can be suitably detected by measuring the change in the optical property value of the sensor element. Here, the optical physical property value means a physical property value with respect to an optical phenomenon of the substance, and means, for example, light reflectance, absorption rate, refractive index, and the like.
In the above sensor, it is preferable that the sensor element is heated at least when hydrogen gas is detected.

  Moreover, the hydrogen gas detector of the present invention is characterized by comprising sensor means including the hydrogen gas sensor described above and measurement means for measuring a change in physical property value of the sensor element. In the hydrogen gas detector, it is also preferable that the measuring unit measures a plurality of physical property value changes of the sensor element.

  The hydrogen gas sensor of the present invention uses a hydrogen storage amorphous alloy as a sensor element material, and is a small and inexpensive sensor that can detect hydrogen gas selectively and easily by changing physical property values of the sensor element due to hydrogen storage. Therefore, it can be suitably used as a hydrogen gas sensor for concentration measurement or leak detection. In particular, if metallic glass is used as the amorphous alloy, a sensor having low hydrogen embrittlement and high durability and reliability can be obtained.

The hydrogen gas sensor according to the present invention is characterized by using a hydrogen storage amorphous alloy as a sensor element. The presence or absence of hydrogen gas and / or the concentration of hydrogen gas is detected by measuring changes in various physical properties of the sensor element due to hydrogen storage in the amorphous alloy and heat generation in the sensor element. That is, it utilizes changes in the physical properties of the amorphous alloy caused by hydrogen entering the amorphous alloy to form a hydrogen compound or adsorbing hydrogen on the amorphous alloy surface. Since the hydrogen storage amorphous alloy selectively stores only hydrogen, and the equilibrium hydrogen pressure (hydrogen gas concentration) and the hydrogen storage amount show a reversible linear relationship, the hydrogen gas sensor of the present invention is an excellent hydrogen Selectivity and linear characteristics.
The amorphous alloy is preferably a metallic glass. Metallic glass is less prone to embrittlement even with repeated heating and exhibits stable hydrogen storage characteristics over a long period of time. Furthermore, it is desirable that the metal glass has oxidation resistance. The specific composition _{Fe 43 Cr 16 Mo 16 C 10} B x P 15-x ( atomic%: 0 <x <15) can be mentioned. By using a metal glass having oxidation resistance, a sensor with higher durability and reliability can be obtained.

Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a schematic configuration diagram of a hydrogen gas sensor according to an embodiment of the present invention. In this embodiment, hydrogen gas is detected by measuring a change in the electrical property value of the amorphous alloy. That is, the hydrogen gas sensor 10 according to the present embodiment includes a sensor element 12 made of an amorphous alloy plate having hydrogen storage properties, and two electrodes 14a and 14b provided on the same surface of the sensor element 12. Yes. Note that the number of electrodes is not particularly limited, and two or more electrodes may be provided in the sensor element in accordance with a method for measuring electrical property values.

  In FIG. 1, the sensor element 12 is electrically insulated from the back surface of the amorphous alloy plate of the sensor element 12, that is, on the surface opposite to the surface where the sensor electrodes 14a and 14b are disposed. A heater 16 is provided, and heater electrodes 18 a and 18 b are provided connected to both ends of the heater 16. By energizing the heater 16 from the outside, the amorphous alloy plate of the sensor element 12 can be maintained at a constant temperature. The heater 16 may not be integrated with the surface of the sensor element 12 but may be separately installed in the vicinity of the sensor element 12. Further, the heater may be configured not only by external energization as described above, but also by other configurations such as a configuration using catalytic combustion of gas. If the temperature change in the test atmosphere is small and there is no problem in the hydrogen storage capacity of the amorphous alloy constituting the sensor element 12, the heater 16 can be omitted.

The hydrogen gas sensor according to the present embodiment can be configured as described above, and the operation thereof is as follows.
First, the sensor element 12 is exposed to the test atmosphere, and is heated by the heater 16 so that the amorphous alloy plate of the sensor element 12 has a constant temperature. In this case, the amorphous alloy plate is in a hydrogen occlusion state depending on the temperature and the hydrogen gas concentration in the test atmosphere, and the occlusion and release of hydrogen gas from the amorphous alloy are in an equilibrium state.
The amorphous alloy plate generally has a higher electrical resistance value as the hydrogen storage amount, that is, the hydrogen gas concentration in the test atmosphere increases. Accordingly, the hydrogen gas concentration can be detected by energizing the sensor element 12 and detecting a change in the electric resistance value of the sensor element 12. Here, the form of measurement of the electric resistance value change is not particularly limited. For example, the change in the current value flowing through the sensor element is measured with the voltage applied to the sensor element constant, and the current value flowing through the sensor element is made constant. Any form of measuring the change of the voltage value applied to the sensor element, or measuring both the current value and the voltage value, obtaining the electric resistance value from these values, and measuring the change is possible.

As described above, the hydrogen gas sensor of the present invention has a simple structure, can selectively detect only the hydrogen gas in the test atmosphere and easily measure the concentration thereof, and can be manufactured in a small size and at low cost. It is suitable as a hydrogen gas sensor for concentration measurement or leak detection.
As a feature of the hydrogen sensor of this embodiment,
(1) Reacts only with hydrogen.
(2) Wide measurement range.
(3) The linear characteristic between gas concentration and sensor sensitivity is excellent.
(4) The integration with the FET is easy.
Etc. In particular, in terms of responsiveness, a response within a few seconds is possible with a gas heat conduction type and an optical type.

An example of a hydrogen gas detector using the sensor of this embodiment is shown in FIG. The hydrogen gas detector 20 of the embodiment shown in FIG. 2 includes sensor means 22, heating means 24, and measuring means 26. Here, the sensor 10 of FIG. 1 is used as the sensor means 22.
The heating means 24 has a heating power supply 28 for supplying a heating current to the heater 16 provided on the back surface of the amorphous alloy plate of the sensor element 12 via the heater electrodes 18a and 18b, and the amorphous alloy plate of the sensor element 12 is fixed. Maintain temperature. By maintaining the sensor element at a constant temperature, the influence of the test atmosphere temperature can be reduced.
The measuring means 26 is composed of a stabilized power supply 30 and a continuity meter 32 connected in series to the sensor element 12 constituting the sensor means 22 via the sensor electrodes 14a and 14b. A change in resistance value can be detected by the continuity meter 32 as a change in current. With this detection signal, it is possible to take necessary measures such as alarming, lighting notification, circuit protection, circuit interruption, and the like. For example, it can be used for an actuator that activates another system that is normally inactive, or a circuit breaker that shuts off another system that is normally active.

In the above embodiment, an example in which a direct current power source is used as a stabilizing power source and a change in electric resistance value is detected as a change in current has been described. However, the present invention is not limited to this. Other mechanisms for detecting changes in impedance, etc. may also be used. For example, an AC power supply may be used to measure the potential difference and / or current value between the sensor electrodes 14a and 14b and detect the impedance change.
FIG. 3 shows a modification of the hydrogen gas detector of the embodiment of FIG. 2, and the reference numerals 100 are added to members corresponding to those in FIG. In the embodiment shown in FIG. 3, hydrogen gas is detected by measuring the impedance change of the sensor element by the four-terminal method. The measuring means 126 of the present embodiment measures a potential difference between both ends of the sensor element, a power supply unit 130 that applies an alternating voltage of a predetermined frequency to the sensor element of the sensor means 122, an ammeter 132 that measures the current value flowing through the sensor element. And a control / processing unit 136 that controls the power supply unit 130 and processes signals from the ammeter 132 and the voltmeter 134. The control / processing unit 136 controls the power supply unit 130 to change the frequency of the alternating voltage applied to the sensor element, or calculates the impedance of the sensor element based on signals from the voltmeter 134 and the ammeter 132. Since the impedance of the sensor element changes in accordance with the hydrogen storage amount, the hydrogen concentration can be detected from the measured impedance. Here, the application of the voltage to the sensor element may be performed at least when hydrogen gas is detected.

Hereinafter, an embodiment of a hydrogen gas sensor using other physical property value changes of an amorphous alloy will be described. In the following embodiments, it is preferable to keep the temperature of the sensor element constant. By keeping the temperature constant, the influence of the test atmosphere temperature can be reduced.
First, an embodiment in which hydrogen gas is detected by measuring a change in mechanical property value of an amorphous alloy will be described. FIG. 4 shows a schematic configuration of a hydrogen gas detector using a QCM (Quartz Crystal Microbalance) as a hydrogen gas sensor. The hydrogen gas detector 200 shown in FIG. 4 includes a crystal resonator 210 as a hydrogen gas sensor (sensor means) and a measurement means 212 that detects a change in the resonance frequency or impedance of the crystal resonator.
The crystal unit 210 includes a piezoelectric material plate 214 such as quartz, electrodes 216a and 216b formed on both surfaces of the piezoelectric material plate, and sensor element films 218a and 218b formed on the electrodes 216a and 216b. Is done. The sensor element films 218a and 218b are formed of an amorphous alloy that absorbs and releases hydrogen. Here, an example in which the sensor element film is formed on both surfaces of the crystal resonator 210 is shown, but a configuration in which the sensor element film is formed only on one surface may be employed.

The measuring means 212 includes an oscillation circuit that oscillates the crystal resonator 110 by applying a voltage between the electrodes 216a and 216b, or an impedance measurement circuit that measures the impedance of the crystal resonator 210, and the resonance frequency of the crystal resonator 210. Or measure impedance. As the configuration of the measuring means 212, a conventionally known configuration may be used.
The resonance frequency of the crystal unit 210 according to changes in mechanical properties (length change, volume change, mass change, viscoelasticity change, etc.) of the amorphous alloy (sensor element films 218a and 218b) accompanying hydrogen storage and release. Or the impedance changes. By measuring the change in the resonance frequency or impedance of the crystal resonator by the measuring means 212, the presence or absence of hydrogen gas and / or the hydrogen gas concentration can be detected. Moreover, since the frequency change is about 1 Hz with respect to the mass change of nanogram, measurement at a low frequency is useful, and shielding is important.

  FIG. 5 shows an embodiment in which a change in mechanical property value of an amorphous alloy with hydrogen storage and release is detected using a surface acoustic wave (SAW) device. A gas detector 300 in FIG. 5 includes a SAW device 310 (sensor means) as a hydrogen gas sensor, and a measuring means 312 that detects hydrogen gas by measuring a change in velocity of a surface acoustic wave propagating on the SAW device. .

  The SAW device 310 includes a piezoelectric substrate 314 that propagates a surface acoustic wave, a comb-shaped excitation electrode 316 that is provided at one end on the surface of the piezoelectric substrate 314 and excites the surface acoustic wave, and the piezoelectric substrate. A comb-shaped receiving electrode 318 that is provided at the other end on the surface of 314 and receives a surface acoustic wave propagating from the excitation electrode 316 to the surface of the piezoelectric substrate 314, and a piezoelectric element between the excitation electrode 316 and the receiving electrode 318. And an amorphous alloy (sensor element) film 320 provided on at least a part of the surface of the substrate 314.

  The measuring means 312 inputs an electric signal to the excitation electrode 316 side, receives an input unit 322 that excites a surface acoustic wave on the substrate, and an output from the receiving electrode 318, and receives the output of the surface acoustic wave that has propagated on the substrate. And a receiving unit 324 for analyzing the frequency. When an electric signal having a predetermined frequency is input to the excitation electrode 316 by the input unit 322, a surface acoustic wave is excited on the surface of the substrate 314 by the piezoelectric effect. The excited surface wave propagates on the surface of the piezoelectric substrate 314 covered with the sensor element film 320. This surface acoustic wave is received by the receiving electrode 318 and converted into an electric signal by the piezoelectric effect. The receiving unit 324 detects the change in the propagation speed of the surface acoustic wave by analyzing the frequency of the electrical signal.

  When the sensor element 320 is exposed in the test atmosphere, the amorphous alloy constituting the sensor element 320 enters a hydrogen storage state that depends on the temperature and the hydrogen gas concentration in the test atmosphere. Since the mechanical properties (length, volume, mass, elastic modulus, etc.) of the amorphous alloy change according to the hydrogen concentration, the propagation speed of the surface acoustic wave propagating on the surface of the piezoelectric substrate 314 changes. Therefore, by measuring the change in the frequency of the electrical signal received by the receiving unit 324, the presence or absence of hydrogen gas or the change in concentration can be detected.

Next, an embodiment in which a gas is detected by measuring a change in optical properties associated with insertion and extraction of hydrogen in an amorphous alloy will be described. A hydrogen gas detector 400 shown in FIG. 6 irradiates light to the hydrogen gas sensor 410 (sensor means) using an amorphous alloy film as a sensor element, and the amorphous alloy film, and reflects and / or transmits light from the amorphous alloy. And measuring means 412 for detecting. The presence / absence and / or concentration of hydrogen gas is detected by measuring the change in the optical property value of the amorphous alloy by the measuring means 412.
The measurement unit 412 includes a light irradiation unit 414 that irradiates light to the amorphous alloy film of the sensor unit 410 and a light detection unit 416 that detects reflected light from the amorphous alloy film. Light from the light irradiation unit 414 passes through the optical fiber 418 and is irradiated onto the amorphous alloy film of the sensor means 410. The reflected light from the amorphous alloy film is collected at the end of the optical fiber 420 and sent to the light detection unit 416. The light detection unit 416 measures the optical change (reflectance, absorption rate, etc.) of the sensor element by detecting the reflected light.

  The optical characteristics (for example, reflectivity on the surface of the amorphous alloy) change depending on the hydrogen storage state of the amorphous alloy that is the sensor element, so that the presence or absence of hydrogen and / or the hydrogen concentration in the test atmosphere can be detected. it can. In addition, by providing a spectroscope or the like in the light detection unit 416, a configuration in which a change in hue on the surface of the amorphous alloy is measured to detect hydrogen gas is possible.

Next, an embodiment in which hydrogen gas is detected by detecting the reaction heat of hydrogen due to the catalytic action of an amorphous alloy will be described. The gas detector 500 shown in FIG. 7 measures sensor means 510 that converts heat generated by an amorphous alloy (sensor element) into electromotive force by a thermoelectric conversion element, and measures the electromotive force generated by the sensor means 510 to detect gas. Means 512.
Sensor means 510 is provided on thermoelectric conversion material layer 516 formed on substrate 514, electrodes 518 a and 518 b connected to both end positions of thermoelectric conversion material layer 516, and a part on thermoelectric conversion material layer 516. And an amorphous alloy layer 520 (sensor element). The amorphous alloy layer 520 is provided only on the electrode 518a side (left side in the figure) of the thermoelectric conversion material layer 516, and is not provided on the electrode 518b side (right side in the figure) of the thermoelectric conversion material layer 516.
When heat is generated in the amorphous alloy layer 520 due to a hydrogen reaction or the like, a temperature difference is generated between the electrode 518a side and the electrode 518b side of the thermoelectric conversion material layer 516, and an electromotive force is generated between the electrode 518a and the electrode 518b. By measuring the electromotive force by the measuring means 512, hydrogen gas can be detected.

  A configuration in which a plurality of sensor means and measuring means as described above are combined and hydrogen gas is detected by measuring different physical property value changes is also suitable. A gas detector 600 shown in FIG. 8 includes a plurality of sensor units 610-1 to 610-m and a plurality of measurement units 612-1 to 612 that measure changes in physical property values of the sensor units 610-1 to 610-m. Measuring means 612 provided with -n. Here, not only one measurement unit is associated with one sensor unit, but also a plurality of measurement units are associated with one sensor unit, and different physical property values are measured with respect to one sensor unit. Good. In this embodiment, a plurality of changes in physical property values are measured, and the results are combined to detect the presence / absence of hydrogen gas / hydrogen gas concentration, so that more accurate detection of hydrogen gas is possible.

  Although several embodiments have been described above, the physical property values to be measured are not particularly limited as long as the effects of the present invention can be achieved. Even if the physical property values other than those described above are measured, hydrogen gas can be detected. Good. Further, the transducer that changes the change in the physical property value of the sensor element into an electric signal or the like is not limited to the above, and other configurations may be used.

  A characteristic of the present invention is that a hydrogen storage amorphous alloy is used for the sensor element. In other words, reversible changes in physical properties associated with hydrogen storage and release of amorphous alloys are utilized. Hydrogen-absorbing amorphous alloys generally include simple metals (Pd, Zr, Ti, U, other rare earth metals, etc.) that easily absorb (react) hydrogen and generate stable metal hydrides, Fe, Ni, It is formed as an alloy with other metals which hardly absorb (react) such as Co, Al, Mn and Cu. The hydrogen-occlusion amorphous alloy used in the present invention is not particularly limited as long as the object of the present invention can be achieved, but long-term stability, sensitivity, and low temperature are preferable, and the metal glass Those exhibiting properties are particularly preferred.

In crystalline alloys, it is believed that hydrogen penetrates into the voids of tetrahedral or octahedral lattices to create a specific hydride and occludes hydrogen. Therefore, in a crystalline alloy, the hydrogen storage amount at a certain equilibrium hydrogen pressure (corresponding to the test hydrogen gas concentration) is constant in a P (hydrogen equilibrium pressure) -C (hydrogen storage amount) -T (temperature) curve (PCT curve). In other words, a so-called plateau region exists, and a linear relationship may not be obtained between the test hydrogen gas concentration and the hydrogen storage amount (see FIG. 9). In particular, since the lower limit of explosion of hydrogen gas is about 4%, it is desirable that the hydrogen gas concentration in the test atmosphere can be detected in the range of about 0.05 to 1%. A plateau region often appears in the concentration range.
In addition, crystalline alloys are weaker than amorphous alloys, are easily pulverized by hydrogen storage, and are inferior in durability. In contrast, in amorphous alloys, the equilibrium hydrogen pressure (hydrogen gas concentration) and the hydrogen storage amount are continuous. And relatively linear. Furthermore, since amorphous alloys are harder and stronger than crystalline alloys, they have excellent durability.

  In the present invention, it is preferable to use metallic glass (also referred to as glass alloy) among the amorphous alloys as the sensor element. Amorphous alloys are a generic term for alloys that have a macroscopically random atomic structure / configuration and different physical properties from crystalline alloys. Among these, “clear glass transition and wide supercooled liquid region” "Amorphous alloy" is called "metallic glass" and is distinguished from ordinary amorphous alloys. Recently, metallic glass has been regarded as an aggregate of nanocrystals.

One of the features of metallic glass is that it has a glass transition point (Tg) on the lower temperature side than the crystallization temperature (Tx), and the supercooled liquid region represented by ΔTx = Tx−Tg is as large as 10 to 130K. It is stable even in a supercooled liquid state and is in a state where crystallization is suppressed. A normal amorphous alloy has almost no supercooled liquid region.
For this reason, an amorphous phase can be formed only with a rapid cooling of 10 ⁴ to 10 ⁶ K / sec in a normal amorphous alloy, whereas a very slow cooling rate of 10 ⁻² to 10 ³ K / sec in a metal glass. But an amorphous phase can be formed. Therefore, in a normal amorphous alloy, the cooling rate has a great influence on the physical properties of the alloy, but in a metal glass, a very uniform amorphous phase can be obtained regardless of the cooling rate. In the supercooled liquid region, the viscosity is low and processing is easy, and various shapes can be manufactured by a casting method or the like.
Regarding the composition for forming the metallic glass, (1) it is a multi-component system of 3 or more components, (2) the atomic diameters of the 3 main components differ from each other by 12% or more, and (3) the 3 main components. It is known as an empirical rule that the heat of mixing of each other has a negative value (the development history and alloy system of glass alloys: functional materials, vol. 22, No. 6, p. 5-9 ( 2002)). So far, for example, various metallic glass compositions such as Zr—Al— (Ni, Cu) — (Ti, Nb), Zr—Ti—Ni—Cu—Be have been reported.

Although it does not specifically limit as a composition of the metallic glass in this invention, When durability is considered, it is suitable that it is a metallic glass with oxidation resistance. As such a metallic glass, for example, Fe-based metallic glass added with P, and a specific composition is Fe ₄₃ Cr ₁₆ Mo ₁₆ C ₁₀ B _x P _15-x (atomic%: 0 <x <15 ). By using these metallic glasses as sensor elements, it is possible to maintain a stable hydrogen detection capability over a long period of time.
On the other hand, in a conventional hydrogen storage crystal alloy, such as a magnesium / nickel alloy thin film, the film immediately after deposition has a metallic luster and reflects light well. Exposure of this film to hydrogen causes hydrogenation, increasing electrical resistance and optical transmission. Information on the hydrogen concentration can be obtained by measuring the resistance change or transmittance change at this time. However, these alloys have insufficient long-term stability due to oxidation.
On the other hand, when an oxidation-resistant metal glass is used as a sensor element as in the present invention, long-term stability can be improved.

In a hydrogen storage amorphous alloy or metal glass, the storage amount usually decreases as the temperature increases. On the other hand, if the temperature is low, the amount of occlusion increases, but the occlusion speed becomes slow, and the difference in occlusion amount due to the concentration of hydrogen gas in the test atmosphere decreases. Therefore, in order to reduce the influence of the test atmosphere temperature, a heater or the like can be used so that the temperature of the sensor element is constant. The sensor element temperature is preferably from room temperature to 600 ° C., more preferably 400 ° C. or less.
In order to maintain the temperature of the sensor element, there is a configuration in which the sensor element is coupled to a micro hot plate having a MEMS structure. As a result, the sensor can be dramatically improved in terms of response speed, sensitivity, and stability.

The shape of the amorphous alloy or metal glass used as the sensor element is not particularly limited as long as the object of the present invention can be achieved. For example, besides a plate shape, a wire shape, a ribbon shape, a thin film shape, a spring shape, a dumbbell shape, a washer shape and the like can be mentioned. Further, the size of the sensor element can be appropriately determined according to the installation location, detection sensitivity, and the like.
The change in physical properties of metal due to hydrogen is considered to be caused by the hydrogen gas contacting the metal surface becoming atomic due to the catalytic action of the metal surface and being absorbed by the metal. In order to achieve this, it is necessary that the absorbed atomic hydrogen be diffused uniformly and rapidly. For this reason, it is preferable that the thickness of the metal hydrogen atoms in the diffusion direction is thinner. For example, a ribbon or thin film that is exposed to gas on one side only has a thickness of 0.2 mm or less. In this case, 0.4 mm or less is preferable.

  As a method for manufacturing the sensor, when the sensor element is a ribbon, a wire, or the like, for example, there is a method in which a terminal is brazed or fixed with a conductive adhesive. In the case of thin film formation, in addition to the method of fixing the terminal in the same manner as in the case of ribbon or wire after film formation, there is a method of printing an electrode on a ceramic substrate in advance and forming an amorphous alloy thereon by a known method. is there. In this case, for example, thermal spraying may be mentioned as a method for forming the metal glass. In the case of metallic glass, thermal spraying is one of the most effective film forming methods as a method for easily forming a dense film composed of a uniform amorphous phase.

When a metallic glass in an amorphous solid state is heated, it remains in an amorphous solid state at a temperature of Tg or lower, but becomes a supercooled liquid state at Tg to Tx, a crystalline solid state at Tx to Tm, and a liquid at Tm or higher.
In the supercooled liquid region, the metallic glass exhibits viscous flow and has a low viscosity. For this reason, when the metallic glass in the supercooled liquid state collides with the substrate surface, it is crushed instantly and spreads on the substrate surface, and a good splat having a very thin thickness can be formed. A dense film with very few pores can be formed by depositing such splats.

  Further, since the splat is cooled from the supercooled liquid state, a crystalline phase is not generated and only an amorphous phase is obtained. That is, since the amorphous solid state and the supercooled liquid state are reversible, if the metal glass in the supercooled liquid state is cooled, the amorphous solid state metal glass can be obtained regardless of the cooling rate. On the other hand, since the supercooled liquid state and the crystalline solid state are irreversible, even if the metallic glass in the crystalline solid state is cooled to room temperature as it is, it remains in the crystalline solid state and melts at the Tm or higher to be in the liquid state. When the metallic glass is cooled, a crystal phase is generated depending on the cooling rate.

Furthermore, in the case of thermal spraying in the atmosphere, the conventional thermal spraying method in which the material collides in the molten state includes the oxide of the thermal spray material in the coating, which adversely affects the properties of the coating. Even if it is sprayed in the atmosphere, there is almost no influence of oxidation.
Therefore, by causing metal glass particles to collide with the substrate surface in a supercooled state by thermal spraying, a dense metal film consisting of a uniform amorphous solid phase of metal glass and having almost no pores is firmly formed on the substrate. be able to.
As the thermal spraying method, there are atmospheric pressure plasma spraying, low pressure plasma spraying, flame spraying, high-speed flame spraying (HVOF), arc spraying, etc., but high-speed flame spraying is particularly excellent in obtaining a high-density film easily.

  As described above, the change in physical properties of metal due to hydrogen is largely due to the catalytic action of the metal surface. Therefore, in order to supplement the catalytic action of the metal surface, in the present invention, metal fine particles and nano-particles are further added to the amorphous alloy or metal glass surface. It is also possible to carry a particle catalyst or the like.

Hereinafter, the relationship between the hydrogen storage amount (% by mass) and the electric resistance value will be described by taking as an example the case of using Zr ₅₅ Al ₈ Nb ₂ Cu ₃₀ Ni ₅ as the metal glass.
In the test, a sample piece, "Materials Technology 20 amorphous material (University of Tokyo Press) P.71～72, single roll method apparatus" _{Zr 55 Al 8 Nb 2 Cu 30} Ni 5 metal manufactured according to the method described in A glass plate (width about 2 mm, length about 15 mm, thickness about 20 μm) was used.
The sample piece was allowed to occlude hydrogen in the PCT characteristic measuring apparatus PCT-2SD-2 (Suzuki Shokan Co., Ltd.) until equilibrium was reached, and the hydrogen occlusion amount in the sample piece was measured (mass%). The sample piece was taken out from the measuring machine, and its electric resistance value was measured.

Sample pieces having various storage amounts were obtained by changing the conditions of the PCT measuring machine, and the relationship between the hydrogen storage amount and the electrical resistance value was examined. The results are shown in FIG. As can be seen from FIG. 10, the electrical resistance value increased linearly as the hydrogen storage amount increased.
Thus, there is a correlation between the hydrogen storage amount of the metal glass and the electrical resistance value, and it is possible to measure the hydrogen gas concentration using the change in the electrical resistance value accompanying hydrogen storage. .
As sensor materials, Ni ₆₀ Nb ₂₀ Zr ₂₀ (for example, width 0.639 mm × thickness 0.022 mm), Zr ₅₅ Al ₈ Nb ₂ Cu ₃₀ Ni ₅ (for example, width 0.673 mm × thickness 0.018 mm), Fe ₄₃ Cr ₁₆ Mo ₁₆ C ₁₅ B ₁₀ (for example, width 1.807 mm × thickness 0.040 mm) can also be used as a typical metallic glass.

FIG. 11 shows a four-terminal method for measuring a reversible resistance change with respect to the presence or absence of hydrogen in a ribbon-like metallic glass composed of Fe ₄₃ Cr ₁₆ Mo ₁₆ C ₁₅ B ₁₀ and having a width of 2 mm × length of 30 mm × thickness of 30 μm. Is. In the test, a 100% pure _{N 2} gas and a _{N 2} gas and _{H 2} gas containing 1 vol% was switched at 10-minute intervals. The ambient temperature was 400 ° C.
As can be seen from FIG. 11, the time constant is less than 20 seconds, the response speed is relatively fast, and the sensitivity can be further increased by thinning the film. Further, the resistance value is rapidly and reversibly changed by repeating ON / OFF of the H ₂ -containing gas, and the sensing performance hardly changes, and very stable detection can be performed over a long period of time.

Schematic of a hydrogen gas sensor according to an embodiment of the present invention Schematic of a hydrogen gas detector according to an embodiment of the present invention Schematic diagram of a hydrogen gas detector (using impedance change) according to an embodiment of the present invention Schematic of a hydrogen gas sensor and a hydrogen gas detector (using QCM) according to an embodiment of the present invention Schematic of a hydrogen gas sensor and a hydrogen gas detector (using a SAW device) according to an embodiment of the present invention Schematic of a hydrogen gas sensor and a hydrogen gas detector (using changes in optical properties) according to an embodiment of the present invention Schematic diagram of a hydrogen gas sensor and a hydrogen gas detector (detecting heat generation of a sensor element) according to an embodiment of the present invention Schematic of a hydrogen gas detector according to an embodiment of the present invention (which measures changes in a plurality of physical property values) Graph showing the crystal alloy _{(Zr 50 Ni} 50), the PCT curve of the amorphous alloy _{(Zr 50 Ni} 50) Diagram showing the relationship between the hydrogen storage capacity and the electrical resistance of the metallic glass plate _{(Zr 55 Al 8 Nb 2 Cu} 3 0Ni 5) Differences in the atmosphere of the metallic glass _{(Fe 43 Cr 16 Mo 16 C} 15 B 10) (N 2 gas -1% _{H 2} containing _{N 2} gas, 400 ° C.) shows a change in resistance due to

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hydrogen gas sensor 12 Sensor element 14a, 14b Sensor electrode 16 Heater 18a, 18b Heater electrode 20 Hydrogen gas detector 22 Sensor means (hydrogen gas sensor 10)
24 Heating means 26 Measuring means 28 Heating power supply 30 Stabilizing power supply 32 Continuity meter

Claims (9)

  Detecting the presence or absence of hydrogen gas and / or the hydrogen gas concentration by measuring the change in physical properties of the sensor element and / or the heat generation at the sensor element, using an amorphous alloy whose physical property value changes due to hydrogen storage as a sensor element A hydrogen gas sensor. The sensor according to claim 1, wherein
A hydrogen gas sensor, wherein the amorphous alloy is a metal glass having oxidation resistance. The sensor according to claim 1 or 2,
A hydrogen gas sensor, wherein presence or absence of hydrogen gas and / or hydrogen gas concentration is detected by measuring a change in electromagnetic property value of the sensor element. The sensor according to claim 3, wherein
A hydrogen gas sensor, wherein a change in the electromagnetic property value is measured as a change in electric resistance value and / or AC impedance.   3. The hydrogen sensor according to claim 1, wherein presence or absence of hydrogen gas and / or hydrogen gas concentration is detected by measuring a change in mechanical property value of the sensor element.   3. The hydrogen sensor according to claim 1, wherein presence / absence of hydrogen gas and / or hydrogen gas concentration is detected by measuring a change in an optical property value of the sensor element.   7. The hydrogen gas sensor according to claim 1, wherein the sensor element is heated at least when hydrogen gas is detected. Sensor means comprising a hydrogen gas sensor according to claim 1;
Measuring means for measuring a change in physical property value of the sensor element;
A hydrogen gas detector comprising:   9. The hydrogen gas detector according to claim 8, wherein the measuring means measures a plurality of physical property value changes of the sensor element.

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