WO2006090433A1

WO2006090433A1 - Hydrogen gas sensor and process for producing the same

Info

Publication number: WO2006090433A1
Application number: PCT/JP2005/002796
Authority: WO
Inventors: Hiroshi Koda
Original assignee: Fis Inc.
Priority date: 2005-02-22
Filing date: 2005-02-22
Publication date: 2006-08-31
Also published as: JPWO2006090433A1; JP4571665B2

Abstract

A hydrogen gas sensor for detection of hydrogen gas. There is provided a hydrogen gas sensor having heat generation resistor (2) comprising a platinum resistance wire and, superimposed on its surface, a platinum alloy composed of platinum and at least one member selected from among palladium, ruthenium, rhodium, nickel and cobalt. This heat generation resistor (2) is heated at approximately constant temperature, and hydrogen gas is burnt on the surface thereof. The electrical resistance is changed in accordance with any temperature increase brought about by the combustion heat, and thus the change of electrical resistance is outputted as a concentration detection signal for hydrogen gas.

Description

Specification

Hydrogen gas sensor and manufacturing method thereof

Technical field

The present invention relates to a hydrogen gas sensor that detects hydrogen gas.

Background art

Conventionally, a combustible gas is detected by dispersing a catalyst such as platinum or palladium in a bead-shaped porous combustor and detecting the reaction heat generated when the combustible gas is burned using a catalyst. There is provided a contact combustion type gas sensor adapted to detect the above. Fig. 12 shows a conventional gas sensor disclosed in Japanese Patent Publication No. 90210 (hereinafter referred to as “gazette”). The gas sensor 20 includes a combustor 21 that combusts a combustible gas, and a heating resistor 22 that heats the combustor 21 with Joule heat that is generated in response to conduction.

[0003] The combustor 21 is formed of an insulator such as alumina in a bead shape and contains a catalyst such as palladium or platinum. The heating resistor 22 is mainly made of a platinum wire having a high temperature resistance coefficient. The heating resistor 22 is wound in a coil shape, and a portion wound in the coil shape is embedded in the combustion body 21.

In this type of gas sensor 20, a substantially constant current is passed through the heating resistor 22, and the combustor 21 is heated to a constant temperature by Joule heat generated in the heating resistor 22. When combustible gas burns on the surface of the combustor 21, the temperature of the heating resistor 22 rises due to the heat of combustion, and the resistance value of the heating resistor 22 changes. Power to put out S That is, as shown in FIG. 13, the gas sensor 20, the compensation element 23, and the fixed resistors 24 and 25 form a bridge circuit, and the voltage Vc between the output terminals c and d of the bridge circuit is measured to measure the heating resistor 22 The resistance value change is obtained, and combustible degenerate gas is detected from this resistance value change.

[0005] The compensation element 23 is composed of a heating resistor and a bead-like insulator as in the gas sensor 20, and has a temperature characteristic and a humidity characteristic substantially the same as those of the gas sensor 20, and a combustible gas is applied to the force insulator. It does not react with combustible gas because it does not contain a catalyst to be burned. Shown in Figure 13 In the bridge circuit, a series circuit of the gas sensor 20 and the compensation element 23 and a series circuit of the fixed resistors 24 and 25 are connected between the terminals a and b, respectively. In addition, a variable resistor 26 for balance adjustment is connected between terminals a and b, and an intermediate tap of the variable resistor 26 is connected to the midpoint of the fixed resistors 24 and 25. DC power supply E1 is connected between terminals a and b via variable resistor 27 and switch SW, and the voltage applied between terminals a and b is adjusted by adjusting the resistance value of variable resistor 27. is doing.

[0006] Therefore, in this measurement circuit, by adjusting the resistance value of the variable resistor 27, the current flowing through the exothermic resistor 22 changes and the amount of generated heat is adjusted, so that combustible gas is generated in the atmosphere. In the absence, adjust the resistance value of the variable resistor 27 to heat the combustor 21 to about 300 ° C to 500 ° C. In this state, adjust the variable resistor 26 to maintain the equilibrium state of the bridge circuit. Thereafter, when the combustible gas comes into contact with the surface of the combustor 21, the combustible gas is combusted by the action of the catalyst contained in the combustor 21, and the electric resistance of the heating resistor 22 is increased by this combustion heat. On the other hand, since the compensation element 23 does not contain a catalyst, the combustible gas does not burn on the surface of the compensation element 23, and the electrical resistance of the heating resistor does not change. Therefore, a resistance difference occurs in the electric resistance of the metal wire between the gas sensor 20 and the compensation element 23, and a bridge voltage is generated between the output terminals c and d. Since the bridge voltage is output in proportion to the gas concentration of the combustible gas, the gas concentration of the combustible gas can be detected by detecting the bridge voltage. Fig. 14 shows examples of output characteristics for various combustible gases. In the figure, a is methane (CH 2), b in the figure is carbon monoxide (CO),

Four

C in the figure shows the output characteristics for hydrogen (H), and d in the figure shows the output characteristics for isobutane (i-C H).

2 4 10

Show.

[0007] In a general manufacturing method of this type of gas sensor 20, first, a heating resistor 22 is formed by winding a platinum wire having a wire diameter of about 20 50 μm in a coil shape. Next, a ceramic carrier mainly composed of an inorganic insulator such as alumina is made into a sol or paste form, applied to the coil portion of the heating resistor 22 so as to form an elliptical shape, and subjected to heat treatment to bead-like combustion. Form with body 21. Next, the combustor 21 is impregnated with a catalyst such as platinum or palladium and subjected to heat treatment, thereby forming the gas sensor 20 in which the catalyst is supported on the alumina carrier in a highly dispersed state. [0008] By the way, in recent years, hydrogen has attracted attention as an energy source to replace petroleum, and the power of development of automobiles equipped with fuel cells is being promoted. One or more hydrogen gas sensors need to be installed to detect hydrogen leakage, and the use of catalytic combustion gas sensors as the hydrogen gas sensor is being studied.

However, when a gas sensor is mounted on an automobile and used, durability against physical conditions such as vibration is required, and severe conditions such as high-temperature and high-humidity conditions and miscellaneous gases exist. In such an atmosphere, the detection characteristics are not easily affected. In such an atmosphere, durability that does not deteriorate the characteristics over a long period of time is required. In the conventional gas sensor 20 described above, the combustion body 21 provided so as to cover the coil portion of the heating resistor 22 is formed in a bead shape, so that the inertia of the combustion body 21 is relatively large. The heating resistor 22 may be deformed or disconnected by vibration or impact. In addition, when the combustor 21 is heated to a high temperature in order to detect low-concentration hydrogen gas, the rate of loss caused by radiation of the generated heat into the air (so-called gas heat conduction rate) increases. There was a problem that the humidity dependency in the atmosphere increased and the reactivity with poisoning substances increased and long-term reliability was impaired. In addition, the catalytic activity deteriorates in a high-humidity atmosphere, and the agglomeration phenomenon of the catalyst components supported on the combustor 21 in a highly dispersed state occurs. The combustible gas is burned by the catalyst supported on the combustor 21, and the temperature of the combustor 21 having a large heat capacity is increased by the combustion heat, and the temperature rise is transmitted to the heat generating resistor 22. As the electrical resistance of the gas changes, there is a limit to improving the sensitivity and response speed of combustible gases.

[0010] Furthermore, in the method for manufacturing the gas sensor 20 described above, a zone or paste such as alumina manufactured to form the combustor 21 is attached to the coil portion of the heating resistor 22 and dried, followed by firing. However, since the formation is performed by manual work or work close to manual work, it is difficult to finely control the outer dimensions of the combustor 21, and the compensator elements 2 and 3 to be combined are thermally equivalent. Since it was necessary to select, there was a problem that complicated work was required and the number of man-hours increased, resulting in an increase in cost.

[0011] Further, the above-mentioned publication discloses porous insulation on the surface of the heating resistor 22 wound in a coil shape. A catalytic combustion type gas sensor in which a catalyst such as platinum or palladium is dispersed on the surface of this thin film has also been proposed. Due to the weak coupling with the heating element, when mounted on an automobile, the porous insulator with the catalyst dispersed and supported by vibration and impact may peel off the coil-like heating element force, resulting in deterioration of sensitivity.

Disclosure of the invention

[0012] The present invention has been made to solve the above problems, and provides a hydrogen gas sensor excellent in vibration resistance, impact resistance, and stable detection performance over a long period of time, and a method for manufacturing the same. There is to do.

[0013] The hydrogen gas sensor according to the present invention detects hydrogen gas. This hydrogen gas sensor has a heating resistor. The surface composition of the heating resistor is an alloy of platinum and at least one of palladium, ruthenium, rhodium, nickel, or cobalt. The heating resistor is heated to a temperature at which hydrogen gas can be combusted by Joule heat by energization, and hydrogen gas burns on the surface of the heating resistor, and the electrical resistance changes as the temperature rises due to the heat of combustion. Is output as a hydrogen gas concentration detection signal.

According to the present invention, hydrogen gas is burned on the surface of the heating resistor, the electrical resistance of the heating resistor changes according to the temperature rise due to the heat of combustion, and the change in electrical resistance is detected by detecting the concentration of hydrogen gas. It is output as a signal, and the heating resistor can have a function of heating the catalyst, a function of burning hydrogen gas, and a function of generating a change in electrical resistance due to combustion heat. Therefore, unlike the conventional gas sensor, it is not necessary to form a bead-shaped combustion body on the heating resistor, and the possibility that the heating resistor is deformed by vibration or impact can be reduced. As a result, the detection performance is stable over a long period of time. Furthermore, the surface composition of the heating resistor is formed of an alloy of platinum and at least one of palladium, ruthenium, rhodium, nickel, or cobalt, and the catalyst and platinum are alloyed. In this way, the stability of the platinum catalyst, which prevents the catalyst carried on the combustor from peeling off, is increased, the deterioration of sensitivity is reduced, and the detection performance can be stabilized for a long time. [0015] It is also preferable to have a compensation resistor that is made of the same material as the heating resistor and eliminates the combustion activity for hydrogen gas. It is preferable that the surface of the compensation resistor does not burn hydrogen gas, and the resistance value changes due to combustion heat. Therefore, the output signal of the heating resistor can be compensated using the output value of the compensation resistor.

[0016] Further, a case for storing the heating resistor and the compensation resistor is provided, and a vent hole communicating with the outside is formed in the case, and the gas flow path between the vent hole, the heating resistor, and the compensation resistor is poisoned. It is possible to reduce a decrease in sensitivity due to the poisoning substance by providing the filter to adsorb the poisoning substance which is also preferably provided with the substance adsorbing substance.

[0017] Further, in the method for producing a hydrogen gas sensor according to the present invention, a solution obtained by mixing a predetermined concentration of at least one of palladium, ruthenium, rhodium, nickel, and cobalt in a solvent is used as a base material made of platinum. A step of applying, a step of removing the solvent by air drying, and a step of forming a platinum alloy by applying a predetermined voltage to the base material. Since the process of forming the combustor is eliminated, the number of man-hours can be reduced.

[0018] Further, the method for manufacturing a hydrogen gas sensor according to the present invention includes the step of eliminating the combustion activity for hydrogen gas by poisoning a compensation resistor formed of the same material as the heating resistor. By poisoning a compensation resistor made of the same material as the heating resistor, the combustion activity against hydrogen gas is eliminated, so it is easy to produce a compensation resistor with approximately the same temperature and humidity characteristics as the heating resistor. Therefore, the work of combining the heating resistor and the compensation resistor can be easily performed.

Brief Description of Drawings

FIG. 1 is a partially omitted front view showing a hydrogen gas sensor according to a first embodiment.

FIG. 2 is an external perspective view of the hydrogen gas sensor same as above.

FIG. 3 is a sectional view of the hydrogen gas sensor same as above.

FIG. 4 is a partially omitted front view showing another configuration of the hydrogen gas sensor.

FIG. 5 is a partially omitted front view showing another configuration of the hydrogen gas sensor of the above.

FIG. 6 is an external perspective view showing a hydrogen gas sensor of Embodiment 2.

FIG. 7 is an external perspective view showing a hydrogen gas sensor of Embodiment 3. FIG. 8 is a sectional view of the hydrogen gas sensor same as above.

FIG. 9 is an output characteristic diagram of the hydrogen gas sensor same as above.

FIG. 10 is an output characteristic diagram of the hydrogen gas sensor same as above.

FIG. 11 is an output characteristic diagram of the hydrogen gas sensor same as above.

FIG. 12 is an external perspective view of a conventional catalytic combustion type gas sensor partially broken.

FIG. 13 is a circuit diagram of a measurement circuit using the gas sensor same as above.

[Fig.14] Output characteristics of gas sensor same as above 1 "Raw drawing.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] In order to describe the present invention in detail, it will be described with reference to the accompanying drawings.

[0021] (First embodiment)

A first embodiment according to the present invention will be described with reference to the accompanying drawings. In the following explanation, unless otherwise specified, the vertical and horizontal directions are defined in the direction shown in FIG.

FIG. 1 is a diagram schematically showing the structure of a hydrogen gas sensor 1 of the present embodiment, FIG. 2 is an external perspective view, and FIG. 3 is a cross-sectional view. The hydrogen gas sensor 1 includes a heating resistor 2 and a stem. 3a, 3b, base 4 and protective cap 5 are provided.

[0023] The heating resistor 2 has the functions of both the combustion body 21 and the heating resistor 22 in the conventional gas sensor, and the surface composition is at least one of palladium, ruthenium, rhodium, nickel and cobalt. A platinum wire made of an alloy of aluminum and platinum is wound in a coil shape, and both ends thereof are electrically and mechanically connected to the stems 3a and 3b. In this embodiment, the heating resistor 2 having, for example, a wire diameter of about 20 μm is used, and the coil diameter is about 210 β m, the spring is wound about 10 μm, and the total length of the inole is reduced. 360—400 μm. In this embodiment, a material other than pure platinum may be used as long as it is a force-based resistance wire using a platinum wire as the heating resistor 2. For example, zirconia stabilized platinum may be used. In this embodiment, the surface of the platinum-based resistance wire is alloyed with at least one of palladium, ruthenium, rhodium, nickel, and cobalt to form the heating resistor 2. Platinum-based resistance may be used.

[0024] The base 4 is formed in a disc shape from a synthetic resin, and the three stems 3a, 3b, 3c are the base 4 The base 4 is insert-molded so as to penetrate vertically. Of the three stems 3a-3c, the center stem 3c has a shorter protrusion from the top than the other two stems 3a, 3b, and the bases of the two stems 3a, 3b at both ends Both ends 2a and 2b of the heating resistor 2 are fixed to a portion protruding from the upper surface of 4 by a method such as welding. The central stem 3c is used when both the heating resistor 2 and the compensation resistor 8 are attached as described in the second embodiment described later. When only the heating resistor 2 is used, the stem 3c is used. Is not used.

[0025] The protective cap 5 has a substantially cylindrical shape with an open end on the lower surface side, and the base 4 is press-fitted and fixed so that the exothermic antibody 2 is accommodated from the opening. A round hole 6 is formed in the center of the ceiling of the protective cap 5, and a 100 mesh stainless steel wire mesh 7 is attached to the hole 6 for explosion protection. The protective cap 5 may be made of metal or resin.

Here, when measuring hydrogen gas, a heating circuit 2 is heated to a predetermined temperature (for example, about 100 ° C.) by applying a substantially constant voltage between the stems 3a and 3b by a measurement circuit (not shown). . When the hydrogen gas that has entered inside through the vent hole 6 of the protective cap 5 comes into contact with the heating resistor 2, the hydrogen gas burns on the surface of the heating resistor 2 by the catalytic action of platinum on the surface of the heating resistor 2. At this time, the temperature of the heating resistor 2 rises due to the combustion heat of hydrogen gas, and the electrical resistance increases as the temperature rises, so the measurement circuit measures the amount of change in the electrical resistance value of the heating resistor 2. Thus, the gas concentration of hydrogen gas can be measured.

In this embodiment, the heating resistor 2 is formed in a coil shape, and the force S is attached to the stems 3a and 3b so that the axial direction of the coil is substantially parallel to the upward and downward directions, as shown in FIG. It may be attached to the stems 3a and 3b so that the axial direction of the coil is substantially parallel to the horizontal direction. Further, the force S that increases the surface area by forming the heating resistor 2 in a coil shape, and the work of winding in a coil shape that can be formed linearly as shown in FIG. 5, can be eliminated.

Next, a method for manufacturing the heating resistor 2 will be described below. First, a resistance wire (base material) of a platinum series (for example, platinum, dinoleconia stabilized platinum) is wound in a coil shape, and the surface of the resistance wire is made of at least one of palladium, ruthenium, rhodium, nickel, and cobalt. alloy For example, palladium nitrate, ruthenium nitrate, rhodium nitrate, nickel nitrate

After applying an aqueous solution containing a predetermined concentration of at least one of cobalt nitrate to the resistance wire, the solvent is removed by air drying at room temperature for about 1 hour. After that, by applying a voltage of about 1. IV between both ends of the resistance wire for about 10 minutes and heating the surface temperature of the resistance wire to about 900 ° C, the surface of the resistance wire is palladium, ruthenium, rhodium, nickel, cobalt. Alloy with at least one of these. In this way, the heating resistor 2 is formed into an alloy by forming a resistance wire in a desired shape, applying a solution containing a desired catalyst to the surface of the resistance wire, air-drying, and applying a predetermined voltage. Thus, unlike the conventional gas sensor, the process of forming the bead-shaped combustion body on the coil-shaped heating resistor is not required, and the manufacturing process can be simplified. In addition, when forming a bead-shaped combustion body, variations in the shape and dimensions of the combustion body are large. However, in this embodiment, the resistance wire 2 is coiled and the surface is alloyed. Variations in shape and dimensions can be reduced, and variations in sensitivity can be reduced. In addition, the exothermic resistor 2 is composed of a platinum-based resistance wire with an alloy of catalyst and platinum formed on the surface, so that the catalyst carried on the combustor is not peeled off like a conventional gas sensor. Can be stabilized in the long term.

The output characteristics of the gas sensor 1 formed as described above will be described with reference to FIGS. Note that there was no significant difference in characteristics between when the heating resistor 2 was wound in a coil shape and when it was formed in a straight line. Refer to the measurement data when the heating resistor 2 is wound in a coil shape below. And explain.

In the measurement circuit shown in FIG. 13, the gas sensor 1 of this embodiment is connected instead of the gas sensor 20, and a fixed resistor of 10 Ω, for example, is used instead of the compensation element 23, and the voltage applied to the gas sensor 1 is used. Was adjusted using variable resistor 27 so that the voltage was about 0.2 V in a clean atmosphere. Here, when a voltage of about 0.2 V is applied to the gas sensor 1, the temperature of the heating resistor 2 is heated to about 100 ° C. When hydrogen gas enters the protective cap 6 through the metal mesh 7 from the vent hole 6, the hydrogen gas burns on the surface of the heating resistor 2, and the resistance value of the exothermic antibody 2 changes due to the heat of combustion. At this time, since the voltage between the output terminals c and d of the bridge circuit changes, the hydrogen gas concentration can be measured from the change in the output voltage. Figure 9 shows the measurement results of gas sensitivity for various flammable gases. The horizontal axis is the gas concentration (ppm) and the vertical axis is the block. This is the output voltage (mV) of the ridge circuit. In the figure, a is hydrogen, b is carbon monoxide, c is methane, d is isobutane, and e is ethanol. From the measurement results in Fig. 9, flammable gases other than hydrogen gas (C〇, CH, IB, ethano

4) was not combusted, but only hydrogen gas was combusted, so the selectivity of hydrogen gas was very good. In this case, the power consumption of the gas sensor 1 is about 10 mW, and measurement can be performed with very low power consumption. The reason why it can operate with such low power consumption is that it does not have the large combustion capacity 21 like the conventional catalytic combustion type gas sensor, and the combustion heat generated by the combustion of hydrogen gas is efficiently converted into a platinum wire. This is because the resistance value change of the heating resistor 2 can be detected without heating the heating resistor 2 to a high temperature.

[0031] Here, the surface composition of the heating resistor 2 is pure platinum or zirconia stabilized platinum (that is, the surface is not alloyed), platinum-palladium alloy, platinum-ruthenium alloy, platinum-rhodium alloy, platinum For each of the nickel alloy and the platinum-cobalt alloy, the gas sensitivity to hydrogen gas was measured. In either case, the gas sensitivity at the initial stage of use was substantially the same. However, if a voltage of about 0.2 V is applied to the platinum resistance wires of each composition and the operation is continued in a clean atmosphere, the surface composition will be pure platinum or zirconium-stabilized platinum (that is, the surface of the platinum resistance wire). It was found that the sensitivity decreased slightly after 10 days had passed. The cause of the decrease in sensitivity is unknown. Force The burning active sites of platinum on the surface are thought to be deactivated for some reason. On the other hand, when the surface is alloyed, deactivation does not occur for more than 60 days, so it is considered that the durability of active sites increases due to alloying.

[0032] In addition, there is a demand for using the gas sensor 1 of the present embodiment in a fuel cell vehicle to detect leakage of hydrogen gas. A drop test was conducted on the assumption that the gas sensor 1 was attached. In the drop test, the gas sensor 1 is dropped 50 times on concrete with a height of lm force, and the shape of the coil part of the heating resistor 2 is observed before and after the test. The shape of the coil part changes before and after the test. It was confirmed that there were no functional problems. Figure 10 shows the results of sensitivity measurement for hydrogen gas before and after the drop test. B in the figure shows the measured data after the test. From this measurement result, there was no particular change in sensitivity to hydrogen gas. The same test results were obtained with the heating resistor 2 of the gas sensor 1 used in the experiment, even though the force S was a platinum-palladium alloy formed on the surface and a platinum alloy of another composition was formed on the surface. .

[0033] In the conventional gas sensor in which the resistance wire is wound in a coil shape and a bead-shaped alumina support (combustion body) is formed so as to cover the coil portion, the combustion body is heavy, and thus drops several times. However, in this embodiment, the heating resistor 2 has the three functions of the heat generator, the combustion body, and the catalyst. Since the inertia of the heating resistor 2 itself, which does not need to be formed, becomes small, it has been found that it is extremely resistant to impact. Also, with respect to vibration, the vibration resistance could be improved by reducing the inertia of the heating resistor 2.

Next, humidity characteristics of the gas sensor 1 will be described with reference to FIG. Figure 11 shows the measurement results of the hydrogen gas sensitivity when the ambient temperature is approximately constant (21 ° C or 22 ° C) and the humidity in the atmosphere is changed from about 30% to about 80%. Here, a in the figure is measurement data when the temperature is 22 ° C and humidity is 31%, b in the figure is measurement data when the temperature is 21 ° C and humidity is 52%, and c in the figure is Measurement data when temperature is 21 ° C and humidity is 78%. From this test result, it was confirmed that there was almost no change in the output characteristics of the gas sensor 1 in the humidity range from about 30% to about 80%. The same test results were obtained with the heating resistor 2 of the gas sensor 1 used in the experiment, even though the force S was a platinum-palladium alloy formed on the surface and a platinum alloy of another composition was formed on the surface. . The gas sensor 1 of the present embodiment is operated at a relatively low temperature, and most of the heat generated by the heating resistor 2 is released through the stems 3a and 3b, and the ratio of heat radiated into the air (gas heat conduction rate). Therefore, even if the humidity in the atmosphere (that is, gas thermal conductivity) changes, the effect on the output characteristics is considered to be small. In other words, it is considered that the gas sensor 1 of the present embodiment has the property that it is not easily affected by the change in gas thermal conductivity (humidity change) of the atmosphere, and as a result, the output fluctuation due to the humidity change can be reduced.

[0035] The results of measuring the gas characteristics of the gas sensor 1 of the present embodiment under a high humidity atmosphere will be described. The composition of the surface of the heating resistor 2 is pure platinum or dinoleconia stabilized white. For each of gold (that is, the one whose surface is not alloyed), platinum-palladium alloy, platinum-norenium alloy, platinum-rhodium alloy, platinum-nickel alloy, platinum-cobalt alloy, temperature 60 ° C, humidity When a voltage of about 0.2 V is applied to the heating resistor 2 in an 80% Rh atmosphere for a long period of continuous operation, the surface composition of the heating resistor 2 is pure platinum or dinoleconia stabilized platinum (that is, platinum-based). The resistance wire surface was not alloyed, and the sensitivity to hydrogen gas disappeared within 24 hours. On the other hand, when the composition of the surface of the heating resistor 2 is platinum-palladium alloy, platinum-ruthenium alloy, platinum-rhodium alloy, or platinum-nickenore alloy, there is almost no deterioration in sensitivity within 24 hours. The sensitivity gradually decreased over the course of the day, and the sensitivity dropped to about half when about 20 days had passed. After that, the sensitivity was maintained even after about one month. In addition, when the composition of the surface of the heating resistor 2 was a platinum-cobalt alloy, the sensitivity did not decrease for about one month. Based on the above results, those with a platinum alloy composition on the surface of the heating resistor 2 have improved durability in a high-humidity atmosphere, and those with a platinum-cobalt alloy in particular have greatly improved durability against high-humidity atmospheres. Could be improved.

Furthermore, the result of having performed the durability test in the high concentration gas about the gas sensor 1 of this embodiment is demonstrated. The composition of the surface of the heating resistor 2 is pure platinum or dinoleconia stabilized platinum (that is, the one in which the surface is not alloyed), platinum-palladium alloy, platinum-norenium alloy, platinum-rhodium alloy, platinum-deckenore alloy, When a platinum-cobalt alloy was continuously operated for 24 hours by applying a voltage of about 0.2 V to the heating resistor 2 in an atmosphere containing hydrogen gas, methane, isobutane, and ethanol, each of lOOOOppm, No sensitivity degradation was observed for gas sensor 1. The reason that sensitivity degradation does not occur in methane, isobutane, and ethanol is that the gas sensor 1 of the present embodiment operates at a relatively low temperature, so that a combustible gas other than hydrogen gas on the surface of the heating resistor 2 ( This is probably because methane, isobutane, ethanol, etc.) do not burn and are not easily affected by combustion heat. On the other hand, hydrogen gas burns in hydrogen gas, and the surface temperature of the heating resistor 2 rises due to the heat of combustion. Here, in the conventional catalytic combustion sensor, there is a case where the sensitivity reduction phenomenon may be observed due to the sintering of the catalyst supported in a highly dispersed state. However, the gas sensor 1 of the present embodiment is the platinum constituting the heating resistor 2. Or Zirconia stabilized platinum or platinum alloy It is considered that there is no decrease in sensitivity that makes it difficult for the catalyst to agglomerate due to the presence of active sites.

[0037] With respect to the gas sensor 1 of the present embodiment, the results of examining the influence of poisoning by sulfurous acid gas and silicon gas, which are known as poisoning components of the catalyst, will be described below. Here, the composition of the surface of the heating resistor 2 is pure platinum or platinum-stabilized platinum (that is, the alloy whose surface is not alloyed), platinum-palladium alloy, platinum-norretium alloy, platinum-rhodium alloy, platinum A nickel alloy or platinum-cobalt alloy was continuously operated for 24 hours by applying a voltage of about 0.2 V to heating resistor 2 in an atmosphere of 300 ppm sulfurous acid gas and 150 ppm hexamethyldisiloxane. As a result, if the composition of the surface of the heating resistor 2 is pure platinum or zirconia stabilized platinum (that is, alloying the surface of the platinum resistance wire), the sensitivity to hydrogen gas after about 10 minutes. Is gone. On the other hand, when the composition of the surface of the heating resistor 2 is platinum one-renium alloy, platinum-rhodium alloy, or platinum-nickel alloy, the sensitivity starts to decrease after 5 minutes, but the sensitivity remains about half even after one hour. Was. In addition, when the composition of the surface of the heating resistor 2 was a platinum-palladium alloy, there was almost no sensitivity degradation even after 15 minutes, and about half of the sensitivity was maintained even after 24 hours. From the above results, it was found that the durability against poisoning gas was greatly improved when the composition of the surface of the heating resistor 2 was a platinum alloy.

[0038] (Second Embodiment)

A second embodiment according to the present invention will be described with reference to FIG. In this embodiment, the gas sensor 1 described in the first embodiment is provided with a compensation resistor 8 that is made of the same material as the heating resistor 2 and has no activity against hydrogen gas. Since the configuration other than the compensation resistor 8 is the same as that of the first embodiment, common components are denoted by the same reference numerals and description thereof is omitted.

[0039] The compensation resistor 8 is formed by winding a platinum wire in a coil shape, similar to the heating resistor 2 described in the first embodiment, and is formed in substantially the same shape and dimensions as the heating resistor 2. However, a treatment for eliminating the combustion activity against hydrogen gas is performed. The material of the compensation resistor 8 is not limited to the platinum wire, but may be formed of the same platinum resistance wire as the heating resistor 2. [0040] Since the compensation resistor 8 has no combustion activity against hydrogen gas, the hydrogen gas does not burn on the surface of the compensation resistor 8 even if the compensation resistor 8 is heated to the same temperature as the exothermic resistor 2. Therefore, temperature rise due to combustion heat does not occur. The compensation resistor 8 is made of the same material as the heating resistor 2, and therefore has the same temperature-resistance characteristics as the heating resistor 2. Therefore, the ambient temperature is determined using the resistance value of the compensation resistor 8. By correcting the atmospheric conditions such as changes, the resistance value change of the heating resistor 2 due to the heat of combustion can be measured more accurately, and the detection accuracy for hydrogen gas is improved.

[0041] The base 4 is formed in a disc shape from a synthetic resin, and is insert-molded so that the three stems 3a, 3b, 3c penetrate the base 4 in the vertical direction. The three stems 3a, 3b, 3c are arranged in a line in the same plane, and the central stem 3c has a shorter protruding amount from the upper surface than the other two stems 3a, 3b. . Then, both ends of the heating resistor 2 are fixed to the left two stems 3a and 3c by a method such as welding to a portion protruding from the upper surface of the base 4, and the right two stems 3b and 3c are fixed to the two stems 3b and 3c on the right side. The both ends of the compensation resistor 8 are fixed to the portion protruding from the upper surface of the base 4 by a method such as welding. Here, since the three stems 3a-3c are arranged in the same plane, when the heating resistor 2 and the compensation resistor 8 are laser welded to the stem 3a-3c, the welding work can be performed at one time. This has the advantage of improving the performance.

[0042] In manufacturing the gas sensor of the present embodiment, first, a platinum-based (eg, platinum, dinoleconia stabilized platinum) resistance wire (base material) is wound in a coil shape to have the same shape 'dimension. After forming two coils, both ends of one coil are fixed to the stems 3a and 3c insert-molded on the base 4, and both ends of the other coil are fixed to the stems 3b and 3c, respectively. Next, in order to alloy the surface of each coil with at least one of palladium, ruthenium, rhodium, nickel and cobalt, for example, at least one of palladium nitrate, ruthenium nitrate, rhodium nitrate, nickel nitrate and cobalt nitrate. After applying an aqueous solution containing a predetermined concentration of seeds to both coils, the solvent is removed by air drying at room temperature for about 1 hour. Then, a voltage of about 1. IV is applied between stems 3a and 3c and between stems 3b and 3c for about 10 minutes, and the coil surface temperature is heated to about 900 ° C, so that the coil surface is palladium, Alloy with at least one of ruthenium, rhodium, nickelenore and cobalt. After that, In order to heat the coil that becomes compensation resistance 8, a voltage of about 0.8V is applied between stems 3b and 3c to heat the coil to about 700 ° C, and about lOOOOppm sulfurous acid gas or about 100 Oppm in the atmosphere. Hexamethyldisiloxane vapor is introduced and held for about 1 minute to poison the catalyst and deactivate the catalytic activity of the platinum alloy to form compensation resistor 8. The compensation resistor 8 whose catalytic activity has been deactivated by this method has the same size and shape as the heating resistor 2, and the surface of the compensation resistor 8 is not different from the surface of the heating resistor 2 in appearance. In addition, the compensation resistor 8 heats the catalytic activity of the surface after the same platinum-based resistance wire as that of the heating resistor 2 is wound in a coil shape by a winding machine and alloyed on the surface. The same shape and the same dimensions as the resistor 2 can be easily manufactured, the heating resistor 2 has the same temperature-resistance characteristics, and the compensation resistor 8 can be easily combined.

In this embodiment, since the heating resistor 2 and the compensation resistor 8 are housed in the same case, the atmospheric conditions of the heating resistor 2 and the compensation resistor 8 can be made substantially the same. Although it is possible to accurately correct the output of the heating resistor 2 using the resistance value, if the atmospheric conditions of the heating resistor 2 and the compensation resistor 8 can be made almost the same, they should be stored in separate cases. May be.

[0044] (Third embodiment)

A third embodiment according to the present invention will be described with reference to FIG. 7 and FIG. In the present embodiment, in the gas sensor 1 described in the second embodiment, the filter cap 9 holding the filter 12 is put on the upper side of the protective cap 5. Since the configuration other than the filter cap 9 and the filter 12 is the same as that of the second embodiment, common components are denoted by the same reference numerals and description thereof is omitted.

[0045] The filter cap 9 is made of a synthetic resin, and is formed in a substantially cylindrical shape whose end on the upper surface side is closed. A round hole 10 is formed in the upper surface of the filter cap 9, and a 100 mesh stainless steel wire mesh 11 is attached to the hole 10 for explosion protection. Further, a filter 12 that adsorbs poisonous substances in the gas that enters the inside through the vent hole 10 is mounted in the tube of the filter cap 9. The filter 12 is made of an adsorbent porous material such as activated carbon, silica gel, or zeolite, or an adsorbent obtained by impregnating an organic or inorganic porous material with a chemical-capturing liquid component, and is covered with a gas. Poisonous It has the function of adsorbing quality (for example, silicon). Examples of the chemical substance capturing liquid component include KOH, ammonia, and phosphoric acid, which are supported to remove oxidizing gas, to adsorb specific poisonous substances. The organic inorganic porous material may be used by impregnating the liquid with an appropriate component.

Here, the base 4, the protective cap 5, and the filter cap 9 constitute a case in which the heating resistor 2 and the compensation resistor 8 are housed, and the ventilation hole 10 provided in the case (filter cap 9) Since the filter 12 that adsorbs poisonous substances is provided in the gas flow path between the heating resistor 2 and the compensation resistor 8, it can adsorb the poisonous substances in the gas that enters the inside through the vent hole 10. The poisoning of the heating resistor 2 and the compensation resistor 8 due to poisoning substances is suppressed, and the deterioration of sensitivity can be reduced.

Here, with respect to the gas sensor 1 of the present embodiment, the results of examining the influence of poisoning by sulfurous acid gas and silicon gas, which are known as poisoning components of the catalyst, will be described below. Here, the composition of the surface of the heating resistor 2 is pure platinum or zirconia-stabilized platinum (that is, the one in which the surface is not alloyed), platinum-palladium alloy, platinum-ruthenium alloy, platinum-necked zinc alloy, platinum-neckenore alloy. The platinum-cobalt alloy was continuously operated for 24 hours by applying a voltage of about 0.2 V to the heating resistor 2 in an atmosphere containing 30 Oppm of sulfurous acid gas and 150 ppm of hexamethyldisiloxane. However, any gas sensor 1 had the same gas sensitivity as before the test after 24 hours. Thus, the provision of the filter 12 can greatly improve the poisoning durability, and it is possible to maintain stable performance for a long time even when the atmospheric conditions are poor. In the gas sensor 1 described in the first embodiment, it is needless to say that the filter cap 9 holding the filter 12 may be placed on the upper side of the protective cap 5 as in the present embodiment. It is possible to reduce the deterioration of sensitivity by suppressing the poisoning.

[0048] As noted above, it will be apparent that a wide variety of different embodiments can be constructed without departing from the spirit and scope of the invention, so that the invention is not limited to that particular, except as limited in the appended claims. The present invention is not limited to the embodiment.

Claims

The scope of the claims

[1] A hydrogen gas sensor for detecting hydrogen gas, comprising:

A heating resistor, and the surface composition of the heating resistor is an alloy of platinum and at least one of palladium, ruthenium, rhodium, nickel, or cobalt, up to a temperature at which hydrogen gas can be combusted by Joule heat generated by energization. When heated, hydrogen gas is burned on the surface of the heating resistor, and the electrical resistance changes as the temperature rises due to the combustion heat, and the change in electrical resistance is output as a hydrogen gas concentration detection signal.

[2] In the hydrogen gas sensor according to claim 1,

It has the same material force as that of the heating resistor, and has a compensation resistor that eliminates the combustion activity against hydrogen gas.

[3] The hydrogen gas sensor according to claim 2,

The case includes a case for storing the heating resistor and the compensation resistor. The case has a vent hole communicating with the outside, and a gas flow path between the vent hole, the heating resistor, and the compensation resistor is provided. Provide a filter that adsorbs poisonous substances.

[4] The method of manufacturing a hydrogen gas sensor according to claim 1,

Applying a solution in which a predetermined concentration of at least one of palladium, ruthenium, rhodium, nickel, and cobalt is mixed in a solvent to a base material formed of platinum; removing the solvent by air drying;

Forming a platinum alloy by applying a predetermined voltage to the base material.

[5] A method of manufacturing a hydrogen gas sensor according to claim 2,

There is a step of eliminating the combustion activity against hydrogen gas by poisoning a compensation resistor formed of the same material as the heating resistor.