JP2010145295A - Gas sensing element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensing element being hardly influenced by environment temperature. <P>SOLUTION: The gas detecting element 1, capable of self-heating, includes a gas sensing part 12 set so as to freely contact with a detection gas. The gas sensing part 12 is covered with a heat-insulating member 13 with gas diffusion property and heat resistance at least at the temperature where the gas sensing part 12 reaches. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas detection element that includes a gas sensitive part provided so as to be in contact with a gas to be detected and is capable of self-heating.

In general, as a so-called self-heating type gas detection element capable of self-heating, a catalytic combustion type gas detection element, a semiconductor type gas detection element, a solid electrolyte type gas detection element, and the like are known.
For example, a catalytic combustion type gas detection element is provided with a combustion catalyst part as a gas sensitive part in which a noble metal catalyst such as platinum is supported on a metal oxide sintered body such as alumina provided on a noble metal wire such as platinum. The detected gas to be detected in the unit is brought into contact with the noble metal catalyst and burned, so that a temperature change that occurs during combustion is detected as a change in the resistance value of the noble metal wire. Since the combustion heat of the gas to be detected is proportional to the concentration of the gas to be detected and the resistance value of the noble metal wire is proportional to the heat of combustion, the gas to be detected is measured by measuring the change in resistance of the noble metal wire due to the combustion of the gas to be detected. Concentration can be measured.

  Such a catalytic combustion type gas detection element is employed in a hydrogen fuel cell vehicle (FCV) as a hydrogen gas sensor for detecting leakage of hydrogen from a fuel cell, for example. When the user operates the FCV to start the fuel cell system, the hydrogen gas sensor is first started to detect the hydrogen concentration, and after confirming that there is no hydrogen leakage, the fuel cell system is started. For this reason, in FCV, there is a time lag between when the user operates to start the fuel cell system and when it is actually started. To reduce this time lag, the hydrogen gas sensor is It is required to shorten the time until it becomes possible to detect. In recent years, FCV can be used even in a low temperature environment such as −30 ° C., and accordingly, a hydrogen gas sensor can also be used at −30 ° C., and particularly hydrogen can be detected in that environment. A short time is required.

  In addition, since the self-heating type gas detection element such as the catalytic combustion type gas detection element, which is a conventional technique in the present invention, is a general technique, prior art documents such as patent documents are not shown.

However, since the conventional catalytic combustion type gas detection element detects a temperature change accompanying combustion of the gas to be detected as described above, it is easily affected by the environmental temperature. Usually, in a gas sensor using a catalytic combustion type gas detection element, a temperature compensation element is provided to reduce the influence of the environmental temperature. However, at a low temperature such as −20 ° C. to −30 ° C., the gas detection element There was a problem that the temperature became unstable and the detection accuracy was affected.
In addition, other self-heating type gas detection elements have the same problem because the temperature of the gas detection element is affected by the environmental temperature.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a gas detection element that is hardly affected by environmental temperature.

  The characteristic configuration of the gas detection element according to the present invention for achieving the above object is a gas detection element that includes a gas sensitive part that is provided so as to be in contact with a gas to be detected, and is capable of self-heating. The gas sensitive part is covered with a heat retaining member having at least heat resistance to the temperature reached by the gas sensitive part.

By covering the gas sensitive part with a heat retaining member as in this configuration, the influence of the temperature of the environment where the gas detection element is installed on the gas sensitive part can be reduced, and the temperature due to self-heating is maintained. be able to.
Further, since the heat retaining member has gas diffusibility and the gas to be detected can reach the gas sensitive part via the heat retaining member, the heat retaining member can be provided in the vicinity of the gas sensitive part, and the heat retaining effect is enhanced.
Furthermore, since the heat retaining member has heat resistance to at least the temperature reached by the gas sensitive part, even if it is provided in the vicinity of the gas sensitive part, there is no adverse effect due to thermal decomposition or the like.
Therefore, according to this structure, the detection accuracy with respect to the gas to be detected can be maintained regardless of the environmental temperature.

In the gas detection element according to the present invention, the gas sensitive part is preferably provided on a noble metal wire.
The effect is particularly enhanced by covering the so-called bead type, in which the gas sensitive part is provided on the noble metal wire as in this configuration, by covering the heat retaining member.

In the gas detection element according to the present invention, the heat retaining member is preferably a nonwoven fabric made of inorganic fibers.
According to this configuration, a heat retaining member having good heat resistance and gas diffusibility can be realized.

The gas detection element according to the present invention is preferably one that detects a temperature change accompanying the combustion by burning the detected gas in the gas sensitive part.
The effect of the heat retaining member is particularly high for the contact combustion type gas detection element that detects the temperature change by burning the detection target gas in the gas sensitive part as in this configuration.

  Hereinafter, an embodiment of a gas sensor using a gas detection element according to the present invention will be described with reference to the drawings. Here, a catalytic combustion type gas detection element is exemplified as the gas detection element, but the present invention is not limited to this. Other gas detection elements include conventionally known self-heating type gas detection elements such as a hot-wire semiconductor gas detection element and a solid electrolyte gas detection element.

  As shown in FIG. 3, the gas sensor according to the present embodiment is based on a contact combustion type gas detection element 1 that detects and detects a gas to be detected, and a temperature change other than the combustion of the gas to be detected, such as an environmental change. A temperature compensation element 10 for correcting a change in resistance value of the catalytic combustion type gas detection element 1 and fixed resistances R1 and R2 are incorporated in a bridge circuit. The bridge circuit constantly supplies a current of about 90 to 120 mA by the power source E, and maintains the contact gas detection element 1 at a temperature at which the detected gas is easy to contact and burn.

  The catalytic combustion type gas detection element 1 and the temperature compensation element 10 are set to have the same resistance value. For this reason, when there is no gas to be detected, the bridge circuit is in an equilibrium state, and the sensor output V is not generated. On the other hand, if the gas to be detected exists, the temperature of the catalytic combustion type gas detection element 1 rises due to the combustion and the resistance value increases, so that the balance of the bridge circuit is lost and the sensor output V is generated. Since the sensor output V is proportional to the concentration of the gas to be detected, the concentration of the gas to be detected in the air can be measured by this gas sensor.

  As shown in FIG. 2, the catalytic combustion type gas detection element 1 is provided in a coiled noble metal wire 11 so that a combustion catalyst unit 12 for combusting the detected gas can be brought into contact with the detected gas as a gas sensitive unit. As shown in FIG. 1, both ends of the noble metal wire 11 are attached to the sensor base 3 by being connected to the respective nickel pins 2, and the resistance value of the noble metal wire can be measured via the nickel pins. . A cylindrical housing 4 having a vent 41 through which gas can flow is attached to the sensor base 3. The inside of the housing 4 is filled with a heat retaining member 13, and the combustion catalyst portion 12 is covered with the heat retaining member 13.

  The combustion catalyst unit 12 carries a noble metal catalyst on a catalyst carrier. As the noble metal catalyst, platinum, palladium, platinum and palladium and the like can be used, and are not particularly limited. The catalyst carrier is not particularly limited, and for example, a sintered body in which a rare earth metal oxide such as ceria or lanthanum is supported on a metal oxide such as alumina or silica alumina can be preferably applied. When at least one of alumina and alumina silica is used as the metal oxide, the pore diameter of the catalyst carrier to be produced can be reduced and the specific surface area can be increased, so that the noble metal catalyst can be highly dispersed in the catalyst carrier. It is possible and preferable. Of course, the catalyst carrier can also contain a rare earth metal oxide sintered body such as ceria as a main component.

  The combustion catalyst unit 12 is preferably substantially spherical. If the combustion catalyst portion 12 is substantially spherical, the temperature change on the surface of the combustion catalyst portion 12 is evenly transmitted to the noble metal wire 11, so that the resistance value of the noble metal wire 11 is easy to stabilize and the initial stabilization time can be shortened. it can.

The combustion catalyst unit 12 is not particularly limited, but is provided so that the apparent volume is 0.014 mm ³ or less, for example. The apparent volume is a volume including the inner noble metal wire 11 and the pores of the combustion catalyst portion 12. In the catalytic combustion type gas detection element 1 including the combustion catalyst portion 12 having a small apparent volume, the temperature in the vicinity of the combustion catalyst portion 12 is easily transmitted to the noble metal wire 11, and the temperature of the combustion catalyst portion 12 as a whole is also increased. Since it becomes easy to stabilize, it is preferable.

  The noble metal wire 11 is not particularly limited in material, wire diameter, coil diameter, number of coil turns, and the like used in the conventional catalytic combustion type gas detection element, but in this embodiment, the noble metal wire 11 In order to reduce the apparent volume, it is preferable to reduce the wire diameter and the coil diameter. For example, a wire diameter of 10 μm, a coil inner diameter of 50 μm, and a coil winding number of about 6 turns is used. Platinum or the like can be used as the material for the noble metal wire 11 and is not particularly limited. For example, platinum rhodium containing 8 to 10% rhodium in platinum is preferable because it is hard and can be easily processed into a coil shape with a small coil inner diameter.

The heat retaining member 13 is formed of a nonwoven fabric made of inorganic fibers. The inorganic fiber is not particularly limited. For example, ceramic fibers such as alumina and silica, glass fibers, carbon fibers, metal fibers, and the like can be used. Depending on the temperature that the combustion catalyst unit 12 can reach, at least with respect to the temperature. And having heat resistance may be selected as appropriate. Of course, it is not limited to inorganic fibers, and other materials can be preferably used as long as they have heat resistance. Non-woven fabric has a heat retaining function to retain sufficient air inside, and has a gas diffusibility that diffuses gas approaching from one side to the other side because the internal space communicates from one side to the other side. The heat insulating material 13 in the present invention can be preferably applied. The density of the nonwoven fabric can be set to be, for example, 0.01 to 0.5 g / cm ³ , but is not particularly limited. That is, the density of the nonwoven fabric may be appropriately set so that at least the detected gas and the oxygen gas for burning the detected gas can diffuse and reach the combustion catalyst unit 12. By providing such a heat retaining member 13 in the combustion catalyst unit 12, it is possible to reduce the influence on the combustion catalyst unit 12 due to fluctuations in environmental temperature, and to maintain the temperature due to self-heating of the combustion catalyst unit 12. For this reason, it becomes easy to detect the temperature change by combustion of to-be-detected gas, and the detection precision with respect to to-be-detected gas can be maintained. In this embodiment, the case where the heat retaining member 13 covers the combustion catalyst portion 12 and fills the entire inside of the housing 4 is illustrated, but is not particularly limited. For example, only in the vicinity of the combustion catalyst portion 12. It can also be provided. Further, the fact that the heat retaining member 13 covers the combustion catalyst portion 12 means that the heat retaining member 13 exists around the combustion catalyst portion 12 regardless of whether or not the combustion catalyst portion 12 and the heat retaining member 13 are in contact with each other. . The heat retaining member 13 is not limited to a non-woven fabric form as long as it has heat retaining properties and gas diffusibility. For example, a laminated material of woven fabric, knitted fabric, etc. It can be preferably applied. As the porous material having communication holes, for example, a porous material made of an inorganic material having heat resistance such as ceramics can be preferably applied.

  Since the temperature compensation element 10 corrects the change in resistance of the catalytic combustion type gas detection element 1, it is preferable that the temperature characteristic of the temperature compensation element 10 is the same as that of the catalytic combustion type gas detection element 1. For this reason, in the present embodiment, the same noble metal wire as that of the catalytic combustion type gas detection element 1 is provided with a carrier having the same apparent volume except that no noble metal catalyst is supported, and is similarly covered with a heat retaining member. It is.

  In addition, about the structure and function of the gas sensor provided with the other contact combustion type gas detection element 1, it is the same as that of a conventionally well-known gas sensor.

  In the following, an embodiment using the catalytic combustion type gas detection element 1 shown in FIGS. 1 and 2 as a gas detection element according to the present invention will be shown, and the present invention will be described in more detail. However, the present invention is not limited to these examples.

Example 1
By a conventionally known method, 2 mol% of ceria is added to alumina in a coiled platinum rhodium wire (wire diameter: 10 μm, coil inner diameter: 50 μm, coil winding number: 6 turns) containing 10 wt% rhodium in platinum as the noble metal wire 11. A combustion catalyst part 12 carrying a platinum catalyst of 10 wt% as a noble metal catalyst on a supported catalyst carrier is provided so as to have a substantially spherical shape with an element diameter of about 0.3 mm, and both ends of the platinum rhodium wire are connected to nickel pins 2 respectively. did. Next, as shown in FIG. 4, the combustion catalyst portion 12 was covered with a heat retaining member 13 made of an alumina fiber non-woven fabric, and the housing 4 was attached thereon to produce the catalytic combustion type gas detection element 1 according to the present invention. At this time, the packing density of the heat retaining member 13 was set to 0.14 g / cm ³ .
By a similar method, a temperature compensation element 10 which is different from the catalytic combustion type gas detection element 1 only in that a noble metal catalyst is not provided is manufactured, and the gas sensor is incorporated into the bridge circuit shown in FIG. 3 together with the catalytic combustion type gas detection element 1. Was made.
In addition, as a comparative example, a gas sensor different from the catalytic combustion type gas detection element 1 and the temperature compensation element 10 of Example 1 only in that the heat retaining member 13 is not provided is manufactured.

  The gas sensitivity characteristics of the gas sensor thus produced with respect to the gas concentration of hydrogen when the applied voltage was 1.6 V and the ambient temperature was −30 ° C. to 100 ° C. were examined. As a result, in the gas sensor provided with the heat retaining member 13, as shown in FIG. 5, it has been found that the hydrogen sensitivity can be maintained at −30 ° C. to 100 ° C. without being affected by the ambient environmental temperature. On the other hand, in the gas sensor not provided with the heat retaining member 13, as shown in FIG. 6, it was found that when hydrogen is 25% LEL or more, the sensitivity decreases when the temperature is 0 ° C. or less.

(Example 2)
In addition to the gas sensors used in Example 1 and the comparative example, as shown in FIG. 7, the gas sensor (thermal insulation) differs from the catalytic combustion type gas detection element 1 and the temperature compensation element 10 of Example 1 only in the filling density of the thermal insulation member 13. The packing density of the member 13 was 0.01 g / cm ³ ), and the responsiveness to hydrogen at 20 ° C. and −30 ° C. was examined for each gas sensor. As a result, in the gas sensor not provided with the heat retaining member 13, the sensor output at −30 ° C. was lowered as shown in FIG. 10, whereas the heat retaining member 13 (filling density: 0.14 g / cm ³ ) was provided. In the gas sensor, as shown in FIG. 8, there was almost no change in the sensor output between 20 ° C. and −30 ° C. Moreover, even if it is a gas sensor (packing density: 0.01 g / cm < ³ >) which made the filling density of the heat retention member 13 low, as shown in FIG. 9, compared with the case where the heat insulation member 13 is not provided, in -30 degreeC. It was found that the influence on the sensor output can be reduced.

  Since the gas sensor provided with the heat retaining member 13 in the combustion catalyst unit 12 can maintain good hydrogen sensitivity even at −30 ° C., for example, it can be preferably applied as a gas sensor for detecting hydrogen leakage of FCV.

  Moreover, about the gas sensor which the hydrogen sensitivity fell at -30 degreeC and which did not provide the heat retention member 13, when the housing 4 of the contact combustion type gas detection element was removed and the combustion catalyst part 12 was investigated, as shown in FIG. It was found that ice was generated around the combustion catalyst section 12. This is considered to be because the water vapor generated by the combustion of hydrogen in the combustion catalyst unit 12 was cooled and frozen by the surrounding environment. For this reason, it has been found that the gas detection element according to the present invention is particularly effective when water (water vapor) is generated during gas detection, for example, when combustible gas is detected by combustion.

[Another embodiment]
In the above-described embodiment, the present invention has been described with reference to an example in which the present invention is applied to a catalytic combustion type gas detection element. However, the present invention is not limited thereto. It can be applied to a sensing element. Even in this case, it is possible to reduce the influence due to the fluctuation of the environmental temperature, and it is possible to maintain the self-heated temperature.

  The gas detection element according to the present invention can be applied to various gas sensors that detect gas, such as a hydrogen gas sensor that detects hydrogen leakage in a fuel cell vehicle.

Schematic of the catalytic combustion type gas detection element according to the present embodiment Schematic of the combustion catalyst part of the catalytic combustion type gas detection element according to the present embodiment Configuration diagram of gas sensor according to this embodiment Photo showing the configuration of the catalytic combustion gas detector The graph which shows the gas sensitivity characteristic with respect to hydrogen in -30 degreeC-100 degreeC The graph which shows the gas sensitivity characteristic with respect to hydrogen in -30 degreeC-100 degreeC Photo showing the configuration of the catalytic combustion gas detector Graph showing responsiveness to hydrogen at -30 ° C and 20 ° C Graph showing responsiveness to hydrogen at -30 ° C and 20 ° C Graph showing responsiveness to hydrogen at -30 ° C and 20 ° C Photo after a responsiveness test of a catalytic combustion type gas detector without a thermal insulation member

Explanation of symbols

1 Contact combustion type gas detector (gas detector)
10 Temperature compensation element 11 Precious metal wire 12 Combustion catalyst part (gas sensitive part)
13 Thermal insulation material

Claims (4)

A gas sensing element having a gas sensitive part provided so as to be in contact with the gas to be sensed and capable of self-heating,
A gas detection element having a gas diffusibility and at least a heat-resisting member having heat resistance with respect to a temperature reached by the gas sensitive part, the gas sensitive part being covered.   The gas detection element according to claim 1, wherein the gas sensitive part is provided on a noble metal wire.   The gas detection element according to claim 1, wherein the heat retaining member is a nonwoven fabric made of inorganic fibers.   The gas detection element according to any one of claims 1 to 3, wherein a temperature change caused by the combustion is detected by burning the detected gas in the gas sensitive part.