JP2009139106A - Hydrogen detection element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen detection element capable of accurately detecting hydrogen concentration even if the pressure of gas including hydrogen gas changes. <P>SOLUTION: The hydrogen detection element comprises: a sensitive section 9 made of a metal alloy; an electrical resistance detection section 18 for detecting a change in electrical resistance generated by the dissolution of hydrogen by the metal alloy of the sensitive section 9; a pressure detection section 19 for detecting the pressure of gas near the sensitive section 9; and a correction section 17 for correcting the detection signal of a change in electrical resistance detected by the electrical resistance detection section 18 by a pressure change detection signal detected by the pressure detection section 19. Even if the pressure of gas including hydrogen gas changes and a change in electrical resistance detected by the electrical resistance detection section 18 varies, the variation of the change in the electrical resistance can be corrected by the correction section 17 based on the detection of the change in the pressure of gas by the pressure detection section 19, thus accurately measuring hydrogen concentration. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hydrogen detection element based on the basic principle of detecting hydrogen by reacting with hydrogen gas and changing its electrical resistance.

Due to fossil fuel depletion and environmental problems such as global warming prevention, research and development related to the use of hydrogen energy centered on fuel cells has been actively conducted in recent years. A device required for utilizing this fuel cell in an automobile is a hydrogen detection element, and its use is roughly classified into two types: hydrogen gas leak detection and fuel cell hydrogen gas concentration detection. Of these, for the latter concentration detection, it is necessary to detect the concentration of hydrogen gas containing various gases that degrade the performance of the detection elements such as H ₂ O, CO, CH ₄ , and CO ₂ , so Development of a hydrogen detector with excellent toxicity is awaited. At the same time, since it is used for detection of the hydrogen concentration in the hydrogen gas pipe, detection under an oxygen-free atmosphere is an essential condition.

  As described above, hydrogen detection elements used for detecting the concentration of hydrogen gas for fuel cells are required to be resistant to other gases and to be detected in an oxygen-free atmosphere. The current situation is that none of these requirements is met.

In other words, there are two types of existing hydrogen detection elements, the semiconductor type and the catalytic combustion type, but any type of detection element can detect accurately in an atmosphere without oxygen because of its detection principle. Have difficulty. In addition, regarding the resistance to toxic gases such as H ₂ O, CO, CH ₄ , and CO ₂ , in the case of a semiconductor type, metal oxide semiconductor particles represented by SnO ₂ are used, so that the metal oxide semiconductor particles themselves are oxidized. However, it does not receive poisoning such as reduction, but the detection principle changes between the air depletion layer formed on the surface of the metal oxide semiconductor particles and in a reducing gas such as H ₂ or CO. As a result, a change in conductivity of the sensing element occurs, thereby enabling gas detection. When gases such as H ₂ O, CO, CH ₄ , and CO ₂ are present in hydrogen, these gases are adsorbed. Since the electron depletion layer changes, accurate hydrogen concentration measurement becomes difficult.

  In the case of the catalytic combustion type, ceramics such as alumina or alumina silica, which carries a noble metal catalyst such as Pt or Pd, is used. However, this noble metal catalyst is poisoned by a gas such as CO and has catalytic activity. It disappears and the hydrogen detection function disappears.

  On the other hand, in addition to these semiconductor and catalytic combustion types, hydrogen detection using the principle that the electrical resistance changes as the metal alloy dissolves hydrogen as a hydrogen detection element capable of detection in an oxygen-free atmosphere. An element has been proposed (see Patent Document 1) and is marketed by “H2scan” in the United States (see Non-Patent Document 1).

For example, a hydrogen sensing element marketed by “H2scan” in the United States is a Pd—Ni crystalline alloy in which a sensitive part is formed, and hydrogen in the measurement gas is dissolved in this metal alloy. By detecting the change in electric resistance that occurs, the hydrogen concentration can be measured.
JP 2004-125513 A Ross C. Thomas and Robert C. Hughes, J. Electrochem. Soc., Vol. 144, No. 9, September, 3245 (1997)

  However, in the hydrogen detection element based on the principle of detecting the electrical resistance change caused by the dissolution of hydrogen in the metal alloy as described above, the measured value may vary depending on the gas to be measured and the measurement conditions. There is a problem that it is difficult to accurately measure the hydrogen concentration.

The present invention has been made in view of the above points, and has an object to provide a hydrogen detection element capable of accurately measuring the hydrogen concentration, and is capable of detection in an oxygen-free atmosphere. An object of the present invention is to provide a hydrogen detection element that is capable of being deteriorated without repeated deterioration of hydrogen detection and having excellent resistance to toxic gases such as H ₂ O, CO, CH ₄ , and CO ₂ .

  The present inventor has found that the rate of change in electrical resistance when a metal alloy dissolves hydrogen has pressure dependence, and has completed the present invention. In other words, even if the hydrogen concentration in the measurement gas is the same, the higher the measurement gas pressure, that is, the hydrogen gas pressure, the greater the amount of hydrogen dissolved in the metal alloy, and the greater the rate of change in electrical resistance. For example, it has been found that the rate of change in electrical resistance differs between a 90% concentration hydrogen gas having a pressure of 100 kPa and a 90% concentration hydrogen gas having a pressure of 200 kPa. Accordingly, the present invention is configured to detect the pressure fluctuation and accurately measure the hydrogen concentration when the pressure of the gas containing hydrogen gas fluctuates.

  That is, a hydrogen sensing element according to claim 1 of the present invention includes a sensitive part made of a metal alloy, an electrical resistance detecting part for detecting a change in electrical resistance caused by the metal alloy of the sensitive part dissolving hydrogen, and the vicinity of the sensitive part. A pressure detection unit for detecting the pressure of the gas, and a correction unit for correcting the detection signal of the electrical resistance change detected by the electrical resistance detection unit with the detection signal of the pressure change detected by the pressure detection unit. It is what.

  According to this invention, even if the pressure of the gas containing hydrogen gas changes and the electrical resistance change detected by the electrical resistance detector varies, based on the detection of the change in the gas pressure by the pressure detector, The correction unit can correct the variation in the electric resistance change, and can accurately measure the hydrogen concentration even when the pressure of the gas containing hydrogen gas changes.

  According to a second aspect of the present invention, the sensitive part is made of a metal alloy in which the hydrogen dissolution amount and the square root of the hydrogen pressure are in a proportional relationship at a constant temperature.

  According to the present invention, the sensitive part can be formed of a metal alloy having a clear correlation between the hydrogen dissolution amount and the hydrogen pressure, and the fluctuation of the electric resistance change can be accurately performed based on the detection of the change in the gas pressure. The hydrogen concentration can be accurately measured even when the pressure of the gas containing hydrogen gas changes.

  The invention of claim 3 is characterized in that the metal alloy is made of an amorphous alloy containing Pd and Si.

An amorphous alloy containing Pd and Si can detect hydrogen in an atmosphere free of oxygen, and has excellent resistance even in an atmosphere containing H ₂ O, CO, CH ₄ , CO ₂ , and the like. The volume expansion at the time of hydrogen dissolution is small, and no delamination or the like occurs in the sensitive part formed of the metal alloy film, so that it is possible to produce a hydrogen detecting element with excellent durability.

  The invention according to claim 4 is characterized in that the metal alloy is made of an amorphous alloy containing Pd and P.

The amorphous alloy containing Pd and P can detect hydrogen in an atmosphere without oxygen, and has excellent resistance even in an atmosphere containing H ₂ O, CO, CH ₄ , CO ₂ , and the like. The volume expansion at the time of hydrogen dissolution is small, and no delamination or the like occurs in the sensitive part formed of the metal alloy film, so that it is possible to produce a hydrogen detecting element with excellent durability.

  The invention of claim 5 is characterized in that Pd or Pt is laminated in a thin film as a hydrogen dissociation catalyst layer on the sensitive part made of the metal alloy.

  According to this invention, the hydrogen dissociation catalyst layer made of Pd or Pt promotes the dissociation of hydrogen molecules, promotes the diffusion of hydrogen atoms into the metal alloy, and changes the electrical resistance of the sensitive part made of the metal alloy. The rate becomes higher and the response speed becomes faster, and a highly sensitive hydrogen sensing element can be produced.

  The invention according to claim 6 is characterized by comprising a heating means for heating the sensitive part.

  According to the present invention, the sensitive part can be heated and maintained at a constant temperature, and the hydrogen detection sensitivity is not affected by the ambient temperature, and hydrogen detection can be performed stably.

  According to the present invention, even if the pressure of the gas containing hydrogen gas changes and the electrical resistance change detected by the electrical resistance detector varies, based on the detection of the change in the pressure of the gas by the pressure detector, The correction unit can correct the change in the electric resistance change, and the hydrogen concentration can be accurately measured even when the pressure of the gas containing hydrogen gas changes.

  Hereinafter, the best mode for carrying out the present invention will be described.

  The hydrogen detecting element according to the present invention includes a sensitive part made of a metal alloy, an electric resistance detecting part that detects a change in electric resistance caused by the metal alloy of the sensitive part dissolving hydrogen, and a gas pressure for measuring the hydrogen concentration. And a correction unit that corrects the detection signal of the electrical resistance change detected by the electrical resistance detection unit with the detection signal of the pressure change detected by the pressure detection unit. .

  Pd alloys, La alloys, Zr alloys, Ni alloys, Ti alloys, Mg alloys, and the like are known as metal alloys that cause a change in electrical resistance when hydrogen dissolves. PdSi, PdNi, PdCuSi, PdNiSi, PdCuNiP, LaNi, ZrNi, ZrPd, TiNi, TiMn, NiNbZr, MgPd, and the like. A sensitive part can be formed of these metal alloys.

  When a gas containing hydrogen gas comes into contact with these metal alloys forming the sensitive part and the hydrogen in the gas dissolves in the metal alloy, the electrical resistance of the metal alloy increases and the electrical resistance according to the amount of dissolved hydrogen. Change occurs. And this electrical resistance change of a sensitive part is detected by an electrical resistance detection part, the change of an electrical resistance value is output as a signal, and the hydrogen concentration in gas can be detected.

  Here, the amount of hydrogen dissolved in the metal alloy has pressure dependence. That is, when the pressure of the measurement gas in the atmosphere is increased and the hydrogen pressure is increased, the amount of hydrogen dissolved in the metal alloy is increased, and thus the amount of hydrogen dissolved in the metal alloy is increased. This means that the change in electrical resistance also increases. Therefore, even when hydrogen gas of the same concentration is detected, if the pressure of the gas in the atmosphere containing hydrogen gas changes and the hydrogen pressure changes, the amount of hydrogen dissolved in the metal alloy varies, so the electrical resistance of the metal alloy As a result, the hydrogen concentration cannot be detected accurately.

  Therefore, in the present invention, a pressure detection unit for detecting the pressure of gas to be measured in the vicinity of the sensitive part is provided together with an electrical resistance detection part for detecting a change in electrical resistance of the sensitive part made of a metal alloy. The pressure detection unit is formed of a pressure detection element that detects a pressure change as a change in an electrical signal. As described above, the electrical resistance change detection signal output from the electrical resistance detection unit and the pressure change detection signal output from the pressure detection unit are input to the correction unit. The correction unit is formed with a CPU, a memory, and the like. From the relationship between the rate of change in electrical resistance due to hydrogen dissolution in the metal alloy forming the sensitive unit and the pressure of the gas containing hydrogen, the hydrogen concentration The correction formula for correcting the measured value is stored in memory.

  Then, when the detection signal of the electrical resistance change output from the electrical resistance detection unit and the detection signal of the pressure change output from the pressure detection unit are input to the correction unit, based on the above correction formula, A calculation in which the detection signal is corrected by the detection signal of the pressure change is performed by the CPU, and the fluctuation of the electric resistance change due to the pressure change can be corrected. In this way, even if the pressure of the measurement gas changes and the amount of hydrogen dissolved in the metal alloy fluctuates and the electric resistance change detected by the electric resistance detector changes, this fluctuation due to the pressure change is corrected. Thus, the hydrogen concentration can be accurately detected.

  As described above, when detecting changes in atmospheric gas pressure and correcting fluctuations in the electrical resistance change of the metal alloy due to the pressure change, the amount of hydrogen dissolved in the metal alloy forming the sensitive part and the hydrogen gas are It is necessary that there is a correlation between the pressure of the containing gas, that is, the hydrogen pressure. Therefore, in the present invention, it is preferable to use a metal alloy having such a characteristic that the amount of hydrogen dissolved in the metal alloy and the square root of the hydrogen pressure are in a proportional relationship at the same constant temperature. This relationship is called Sieverts' law, and the relational expression is shown in Equation (1).

√ (P _H2 ) = K _S × (H / M) (1)
P _H2 : Hydrogen pressure K _S : Sieverts constant H / M: Hydrogen dissolution amount in metal alloy The metal alloy having characteristics satisfying such Sieverts law is not particularly limited, but PdSi, PdCuSi, PdNiSi, PdCuNiP, etc. can be illustrated.

As the metal alloy for forming the sensitive part, the above-described various alloys can be used, and among them, an amorphous alloy containing Pd and Si and an amorphous alloy containing Pd and P are preferable. These not only have characteristics satisfying the Sieverts law that enables pressure correction as described above, but also have excellent resistance in an atmosphere containing H ₂ O, CO, CH ₄ , CO _2, etc., and hydrogen Since the volume expansion at the time of dissolution is small, it is possible to provide a hydrogen detecting element having excellent durability.

  Here, an amorphous alloy is a metal element in which metal elements are randomly arranged and the nearest interatomic distance, coordination number, and relative position between atoms have a non-constant form such as crystalline. . This amorphous alloy includes so-called metallic glass alloys, which are characterized by exhibiting a glass transition and a wide supercooled liquid region in the previous stage of crystallization when heated. It is also called various expressions such as glass, glass alloy, and glass metal.

Amorphous alloys have the following advantages over crystalline ones. (1) Excellent chemical and physical stability compared to crystalline. (2) Compared to crystalline materials, the volume expansion due to hydrogen dissolution is small, so it is difficult to deteriorate. (3) Since a uniform layer can be obtained in a wide composition range, the amount of dissolved hydrogen can be easily controlled continuously. (4) Since the electric resistance is larger than that of the crystalline material, it is suitable for reading the electric resistance change accompanying hydrogen dissolution. (5) Amorphous alloys easily form a passive film on the surface, and therefore have excellent resistance to poisoning gases such as H ₂ O, CO, CH ₄ , and CO ₂ .

  When hydrogen penetrates into the sensitive part formed of such an amorphous alloy thin film, the electrical resistance of the alloy thin film changes due to the penetration of hydrogen, and this phenomenon can be used to detect hydrogen. It can be done. Further, when hydrogen dissolves in the metal alloy, volume expansion occurs, but this volume expansion is much smaller in the amorphous alloy than in the crystalline alloy. This is because, in the case of a crystalline alloy, dissolved hydrogen atoms penetrate into the crystal lattice constituting the crystal and are regularly arranged at predetermined positions, so that the crystal lattice is expanded and exhibits a large volume expansion. In the case of the alloy, the dissolved hydrogen atoms enter the gaps between the metal atoms arranged in a distant manner, and thus do not exhibit a large volume expansion unlike the crystalline alloy. For this reason, by forming the sensitive part using an amorphous alloy, it is possible to prevent problems such as a decrease in life due to embrittlement of the metal alloy and peeling of the sensitive part when used in a thin film shape. is there.

  Pd has a strong affinity with hydrogen, has the ability to absorb 900 times or more volume of hydrogen at room temperature, and has the property of increasing electrical resistance due to the absorption of hydrogen, and bringing hydrogen molecules into an atomic state. Since it has a catalytic ability to dissociate, it has characteristics suitable as a material for a hydrogen detection element that facilitates absorption of hydrogen.

  The amorphous alloy containing Pd and Si or the amorphous alloy containing Pd and P may contain other metal elements or metalloid elements. For example, in an amorphous alloy containing Pd and Si, examples of other metals and semimetals include Cu, Cr, Co, Ni, Mn, Fe, Ag, Au, Ge, B, and C. It is preferable to contain one or more elements selected from these. Moreover, in the amorphous alloy containing Pd and P, Ni, Cu, Fe, etc. can be mentioned as other metals and semimetals, and one or more elements selected from these can be contained. Is preferred.

  As a form of the metal alloy forming the sensitive part, a thin film, foil, powder, or the like can be used. Moreover, it is preferable to set the shape of the sensitive part formed of the metal alloy so that the resistance change amount at the time of hydrogen detection becomes large.

  In forming the sensitive portion with a metal alloy thin film, the thin film production method is preferably, for example, sputtering, vacuum vapor deposition, electron beam vapor deposition, chemical vapor deposition (CVD), or plating. Of course, the present invention is not limited to these methods and means, and appropriate methods and means can be used. The film thickness of the metal alloy forming the sensitive part is preferably set to about 10 to 10,000 nm. The metal alloy thin film may be formed directly on the surface of the substrate, or a metal thin film such as Ti or Cr may be formed on the underlayer in order to enhance the adhesion of the metal alloy. The material of the base material that forms the sensitive part is not particularly limited, and various types of materials can be used, from hard materials such as glass and plastic to soft materials such as vinyl sheets and wraps. is there. Further, the form of the substrate is not particularly limited, but for example, a substrate is preferable.

  When the sensitive part is formed using a metal alloy foil, the sensitive part may be formed by winding a foil around a cylindrical base material made of ceramics or the like. When the sensitive part is formed of a powdered metal alloy, the metal alloy powder is kneaded together with an organic binder, organic solvent, etc., pasted into an oxide film on the surface, such as silicon substrate, ceramic substrate, glass substrate, etc. A sensitive part can be formed on the paste by screen printing. In this case, since the electrical resistance is higher than that of a thin film or foil, it is preferable to form an electrode on a substrate in advance with a metal such as gold and to form a film thereon.

  Moreover, in this invention, you may make it form the catalyst layer excellent in the hydrogen dissociation catalytic action on the surface of the sensitive part which consists of a metal alloy formed as mentioned above on a base material. The catalyst layer is preferably formed of a thin film of Pd or Pt, but is not limited thereto, and any catalyst layer having the same effect can be used. This catalyst layer can be formed, for example, by coating and laminating Pd or Pt having a thickness of 1 to 100 nm on the exposed surface of the metal alloy thin film forming the sensitive part. Is particularly preferably about 5 nm. Of course, the formation method, thickness and form of the catalyst layer are not particularly limited. This catalyst layer can be suitably produced by, for example, sputtering, vacuum deposition, electron beam deposition, chemical vapor deposition (CVD), plating, etc., but is limited to these methods and means. Rather, any method and means can be used.

  By providing a catalyst layer having a hydrogen dissociation catalytic action on the surface of the sensitive part made of a metal alloy in this way, the dissociation of hydrogen molecules is promoted and the diffusion of hydrogen atoms into the metal alloy is promoted. The rate of change in electrical resistance of the sensitive part is increased and the response speed is increased, so that a highly sensitive hydrogen detecting element can be produced.

  Here, as described above, the amount of hydrogen dissolved in the metal alloy has pressure dependency, but the amount of hydrogen dissolved in the metal alloy also has temperature dependency. That is, the amount of hydrogen dissolved in the alloy increases as the temperature of the measurement gas in the atmosphere decreases, and the change in electrical resistance increases as the amount of hydrogen dissolved in the metal alloy increases. Therefore, even when detecting hydrogen gas at the same concentration, if the detection temperature of the hydrogen detector changes, the amount of hydrogen dissolved in the metal alloy will change, and the electrical resistance will also change. It cannot be detected.

  Therefore, in the present invention, a heating means is provided to heat the sensitive part. If the heating means is set to heat the sensitive part to a constant temperature higher than the maximum value of the changing ambient temperature, the hydrogen concentration can be detected under a constant temperature condition, and the temperature change The hydrogen concentration can be accurately detected without being affected by the above.

  As the heating means, for example, a heater that generates heat when energized can be used. A heater is formed on the back side of the substrate provided with a sensitive part made of a metal alloy on the surface, and the sensitive part is heated by the heater. Can be. In addition, a heater may be provided on the back side of the sensitive part made of a metal alloy via an insulating layer. In the case of a structure in which a sensitive part is formed by winding a metal alloy foil around a cylindrical base material, It is also possible to wind a heater wire or the like through an insulating layer below. Any material such as Pt, Ta, or nichrome can be used as the material of the heater.

  An example of a specific structure of the hydrogen detection element is shown in FIG. In FIG. 1A, reference numeral 1 denotes a metal stem serving as a body of the element, and the metal stem 1 is formed by providing a frame-shaped cylindrical portion 3 on the upper surface of a substrate 2. A pressure sensor chip 4 is provided on the upper surface of the substrate 2 of the metal stem 1 in the cylindrical portion 3. The pressure sensor chip 4 is formed of, for example, a silicon substrate having a diaphragm structure having a piezoresistive gauge provided on the upper surface, and the lower surface communicates with the surrounding atmosphere through a through hole 5 provided in the substrate 2 of the metal stem 1. It is supposed to be. In addition, a stainless steel diaphragm 6 is attached to the opening on the upper surface of the cylindrical portion 3 so as to close the opening. Silicone oil 7 is placed in the space in the cylindrical portion 3 that is sealed by the diaphragm 6. Is filled in a sealed state. Further, a polyimide insulating film 8 is provided on the outer surface of the diaphragm 6, and a sensitive portion 9 made of a metal alloy thin film is provided on the outer surface of the insulating film 8. In addition to the sensitive portion 9, a thin film of the heater 20 is provided on the outer surface of the insulating film 8. Lead pins 11 and 12 are attached to the substrate 2 of the metal stem 1 without being in contact with the substrate 2 by the insulating layer 10. The lead pins 11 are attached to the sensitive portion 9 via the wires 13, and the lead pins 12 are pressurized via the wires 14. Each sensor chip 4 is electrically connected. A resistance measuring instrument 15 is connected to the lead pin 11, and a sensor circuit 16 having a bridge circuit or the like is connected to the lead pin 12. Further, the resistance measuring instrument 15 and the sensor circuit 16 are electrically connected to a correction unit 17 formed with a CPU, a memory and the like. In FIG. 1A, an electric resistance detector 18 is formed by the resistance value measuring instrument 15 and the like, and a pressure detector 19 is formed by the pressure sensor chip 4, the diaphragm 6, the sensor circuit 16, and the like. It is what is done.

  In the hydrogen detection element formed as described above, when hydrogen gas in the measurement gas comes into contact with the sensitive part 9, hydrogen dissolves in the metal alloy forming the sensitive part 9, and hydrogen dissolves in the metal alloy. As a result, the electric resistance value of the sensitive portion 9 formed of a metal alloy changes. This change in electrical resistance is detected by the resistance measuring instrument 15, and a detection signal of change in electrical resistance due to dissolution of hydrogen is input to the correction unit 17. Further, the diaphragm 6 bends according to the pressure of the measurement gas, the pressure is transmitted to the pressure sensor chip 4 through the silicone oil 7 sealed inside the diaphragm 6, and the pressure sensor chip 4 is deformed according to the pressure, The electrical resistance changes according to the deformation. This change in electrical resistance is detected by the sensor circuit 16, and a detection signal for change in electrical resistance due to a change in pressure is input to the correction unit 17. In the correction unit 17, the amount of hydrogen dissolved in the metal alloy forming the sensitive unit 9, that is, the hydrogen concentration is determined based on the detection signal of the electrical resistance change detected by the resistance measuring device 15 (electrical resistance detection unit 18). Calculated. Further, the pressure of the measurement gas is calculated based on the detection signal of the electric resistance change detected by the sensor circuit 16 (pressure detection unit 19), and further, the calculation for correcting the hydrogen concentration is performed according to the pressure of the measurement gas. The accurate hydrogen concentration of the measurement gas can be detected. Further, the sensitive portion 9 made of an amorphous alloy thin film is heated to a constant temperature by the heater 20, and the temperature of the sensitive portion 9 is kept constant so that it is not affected by changes in the ambient temperature. FIG. 1 shows an example of the hydrogen detection element of the present invention, and the present invention is not limited to this structure, and may have another structure.

  Next, the present invention will be specifically described with reference to examples.

  A 50 μm-thick stainless steel plate having a 5 μm-thick polyimide insulating film 8 on one side is punched out into a circle having a diameter of 10 mm to produce a diaphragm 6. A 100 nm-thick amorphous film is formed on the polyimide insulating film 8 using a sputtering apparatus. The sensitive part 9 was produced by sputtering an alloy thin film. At this time, the sensitive portion 9 was formed in a meandering pattern as shown in FIG. 1B using a stainless steel mask.

  The composition of the amorphous alloy thin film forming the sensitive part is Pd—Si (Example 1), Pd—Cu—Si (Example 2), Pd—Ni—Si (Example 3), Pd—. Four types of Cu-Ni-P (Example 4) were used. The respective elemental composition ratios are shown in “Table 1”. In addition, a sample in which a catalyst layer composed of a Pd thin film having a thickness of 5 nm was formed on a Pd—Cu—Si based amorphous alloy thin film was also produced (Example 5). As a result of phase identification of each of these alloy thin films by X-ray diffraction, each alloy thin film was formed as an amorphous single phase except for the catalyst layer of the Pd thin film. Further, Pt is sputtered on the polyimide insulating film 8 using a sputtering apparatus and a stainless steel mask in the same manner as described above, and the heater 20 is formed in a meandering pattern along the sensitive portion 9 as shown in FIG. Formed.

  In order to measure the relationship between the amount of hydrogen dissolved in the sensitive part made of the amorphous alloy thin film and gas pressure produced as described above, a sample was placed in a sealed chamber and the flow rate was controlled by a mass flow controller. The electric resistance of the sensitive part made of an amorphous alloy thin film was measured while flowing. First, nitrogen gas is introduced into the chamber, and after confirming that the electric resistance of the sensitive part is stable, the gas adjusted to have a hydrogen concentration of 1 to 100% with nitrogen gas is used as the pressure inside the chamber. Was introduced so as to be 100 kPa, 200 kPa, and 300 kPa.

Then, let R _{0 be} the electric resistance of the sensitive part when nitrogen gas is introduced, and R be the stable electric resistance after introducing hydrogen gas, and change ΔR = R−R ₀ and change ΔR / R ₀ (%) It calculated | required for every hydrogen concentration and each pressure in a chamber. Since the amount of dissolved hydrogen (H / M: see equation (1)) is proportional to the rate of change in electrical resistance (ΔR / R ₀ (%)), the relationship between the amount of dissolved hydrogen and the hydrogen pressure is It can be replaced with the relationship between the rate of change (ΔR / R ₀ (%)) and the hydrogen pressure. All measurements were performed at room temperature (25 ° C.).

As described above, when the rate of change in electrical resistance (ΔR / R ₀ (%)) and the hydrogen pressure data obtained in each of Examples 1 to 5 were plotted on a log-log graph, Example 1 A linear relationship was obtained for all of ~ 5. As an example, FIG. 2 shows the relationship between the rate of change in electrical resistance (ΔR / R ₀ (%)) obtained in Example 1 and the hydrogen pressure (P _H2 ). This means that the alloy metal of each example has the characteristic that, at a certain temperature, the amount of hydrogen dissolved in the sensitive part made of the metal alloy and the square root of the hydrogen pressure are proportional. is there.

And in the case of the sensitive part which consists of a metal alloy of Example 1, Formula (2) of an approximate expression can be derived from the graph of FIG. By developing the equation (2) to derive an equation (3) for obtaining the hydrogen pressure (P _H2 ), and finally substituting the result of the equation (3) into the equation (4), the hydrogen gas concentration ( C _H2 ) can be obtained. These formulas (3) and (4) are correction formulas for hydrogen concentration due to pressure change.

(ΔR / R ₀ ) × 100 = 0.1323 × P _H2 ^0.4292 Formula (2)
P _H2 = ((ΔR / R ₀ ) × 100) ^{1 / 0.4292 /} 0.1323 ^{1 / 0.4292} Formula (3)
C _H2 = P _H2 / (P _GAS / 100) Formula (4)
R: Electrical resistance of the sensitive part in hydrogen / hydrogen and nitrogen mixed gas (Ω)
R ₀ : electric resistance (Ω) of the sensitive part in nitrogen gas
ΔR = R−R ₀
C _H2 : Hydrogen gas concentration (%)
P _GAS : Gas pressure (kPa)
Next, the hydrogen detection element shown in FIG. 1 was assembled using the diaphragm 6 provided with the sensitive part 9 made of an amorphous alloy thin film, produced as described above. Then, this hydrogen detection element was mounted in a sealed chamber, and a test was performed in which a change in electrical resistance of the sensitive portion 9 was detected by the resistance measuring instrument 15 and a change in pressure was detected by the sensor circuit 16. First, nitrogen gas is introduced into the chamber, and after confirming that the electrical resistance of the sensitive portion 9 is stable, hydrogen gas is introduced into the chamber in the order of steps 1 to 9 shown in “Table 2”. The concentration and gas pressure were switched, and a signal of electrical resistance change (ΔR / R ₀ (%)) due to the hydrogen gas concentration and a gas pressure (P _GAS ) signal at each step were detected.

FIG. 3 shows a graph of data detected for the hydrogen detection element using the sensitive unit 9 of Example 1. FIG. In FIG. 3, the electric resistance change (ΔR / R ₀ (%)) obtained from the hydrogen gas detection signal is displayed on the upper graph, and the gas pressure (P _GAS ) is displayed on the lower graph. As seen in Steps 2 to 4, Steps 5 to 6, and Steps 7 to 8 in FIG. 3, even if the hydrogen gas concentration is the same, the change in electrical pressure (ΔR / R ₀ (%)) is caused by the change in pressure. As the pressure changes, the hydrogen gas concentration cannot be detected correctly.

Then, a signal of electrical resistance change (ΔR / R ₀ (%)) and a signal of gas pressure (P _GAS ) are input to the correction unit 17, and the electrical resistance change ( ΔR / R ₀ (%)) was corrected with the gas pressure (P _GAS ) to determine the hydrogen gas concentration. The corrected hydrogen gas concentration is shown in the graph of FIG. In FIG. 4, the hydrogen gas concentration (%) is displayed on the upper graph, and the gas pressure (P _GAS ) is displayed on the lower graph. As shown in steps 2-4, steps 5-6, and steps 7-8 in FIG. 4, it is confirmed that the hydrogen concentration in the gas introduced into the chamber is correctly detected even if the pressure changes. Is done.

  As described above, when the gas pressure is constant, the gas concentration can be measured by detecting a change in the electrical resistance of the sensitive part. It is impossible to measure the gas concentration as shown in the graph of FIG. 3 only by detecting the change in resistance. On the other hand, as in the present invention, even when the gas pressure changes by detecting and correcting the change in the gas pressure at the same time as detecting the change in the electrical resistance of the sensitive part, the graph of FIG. Thus, the gas concentration can be measured.

  In addition, in the hydrogen detection element manufactured by providing the sensitive part of the above Examples 1 to 5, the metal alloy of the sensitive part for detecting hydrogen is Pd and Si or an amorphous alloy containing Pd and P. It was confirmed that the volume expansion of the alloy at the time of hydrogen dissolution was small, the sensitive part was not peeled off from the stainless steel diaphragm (with polyimide thin film) even after the above test, and the durability was also excellent.

An example of the hydrogen detection element which concerns on this invention is shown, (a) is the sectional drawing, (b) is a figure which shows the pattern of a sensitive part and a heater. It is a graph which shows the relationship between the change rate ((DELTA) R / _R0 (%)) of an electrical resistance of the sensitive part in Example 1, and hydrogen pressure ( _PH2 ). It is a graph which shows the electrical resistance change ((DELTA) R / _R0 (%)) by hydrogen gas density | concentration in Example 1, and the change of a gas pressure ( _PGAS ). 2 is a graph showing changes in hydrogen gas concentration and gas pressure (P _GAS ) in Example 1.

Explanation of symbols

9 Sensing section 17 Correction section 18 Electrical resistance detection section 19 Pressure detection section

Claims (6)

  A sensitive part made of a metal alloy, an electrical resistance detecting part for detecting a change in electrical resistance caused by the metal alloy of the sensitive part dissolving hydrogen, a pressure detecting part for detecting the pressure of gas in the vicinity of the sensitive part, and an electrical resistance A hydrogen sensing element comprising: a correction unit that corrects a detection signal of a change in electrical resistance detected by the detection unit with a detection signal of a pressure change detected by the pressure detection unit.   The hydrogen sensing element according to claim 1, wherein the sensitive part is made of a metal alloy in which the hydrogen dissolution amount and the square root of the hydrogen pressure are in a proportional relationship at a constant temperature.   The hydrogen detecting element according to claim 1, wherein the metal alloy is made of an amorphous alloy containing Pd and Si.   4. The hydrogen detecting element according to claim 1, wherein the metal alloy is an amorphous alloy containing Pd and P. 5.   5. The hydrogen detection element according to claim 1, wherein Pd or Pt is laminated as a hydrogen dissociation catalyst layer in a thin film shape on the sensitive portion made of the metal alloy.   The hydrogen detection element according to claim 1, further comprising a heating unit that heats the sensitive part.

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