JP2007093240A - Contact combustion type gas sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance gas sensitivity and a response speed with respect to a gas to be sensed without damaging impact resistance in a contact combustion type gas sensor element. <P>SOLUTION: The contact combustion type gas sensor element includes a cylindrical hollow porous ceramic body, the heater coil spirally wound around the surface of the porous ceramic body, a heat conductive layer which covers a part of the heater coil while enclosing the porous ceramic body and a sintered body having a catalyst layer and has a hollow structure. Since the flow of the gas to be sensed is enhanced and a contact combustible area becomes large in this contact combustion type gas sensor element, the response time to the gas to be sensed becomes short, the gas sensitivity of the gas to be sensed becomes high and the impact resistance of the contact combustion type gas sensor element is excellent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a catalytic combustion type gas sensor element.

Combustible gas sensors that detect hydrogen gas, methane gas, or the like include contact combustion type gas sensors, semiconductor type gas sensors, and the like, all of which incorporate a heat source that is used for detection of combustible gases.
For example, the catalytic combustion type gas sensor element has a heater coil, and the resistance value change of the heater coil due to the catalytic combustion heat of the combustible gas generated on the combustion catalyst equipped in the heater coil is outputted as a voltage change, so that the combustibility is achieved. It detects the presence of gas.
In addition, for example, a semiconductor gas sensor element has a heater coil, and a change in electric conductivity of the semiconductor layer generated by the adsorption phenomenon of the flammable gas in the semiconductor layer equipped in the heater coil is output as a voltage change to output the flammable gas. It detects existence.

  Conventionally, a catalytic combustion type gas sensor element includes a catalyst layer having a catalyst for burning the detection target gas, a sintered body having a heat conduction layer for efficiently transmitting the combustion heat of the gas to the heater coil, and the combustion heat of the gas. It consists of a heater coil whose electrical characteristic value changes, and has a structure in which the coiled portion of the heater coil is embedded in the sintered body. Both ends of the heater coil are connected to and supported by electrode pins for external connection.

  In addition to these existing gas sensors, for example, in a contact combustion type gas sensor having a hollow structure, a coiled resistance wire is wound around a core wire of molybdenum wire or white wire, and after coating the surface with an alumina insulating material, the core wire is There is known a production method for dissolving and removing with a strong acid (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 52-116289 (FIG. 4)

  In the contact combustion type gas sensor element, if the gas concentration is the same, it is better that the amount of change in the voltage output from the detection element is large. This large amount of change in output voltage means high gas sensitivity. For this reason, the gas to be detected causes catalytic combustion on the catalyst surface, and the combustion heat must be efficiently transmitted to the heater coil while suppressing loss as much as possible.

  Further, in the contact combustion type gas sensor, it is preferable that the voltage output from the detection element is stabilized in the shortest possible time if the gas concentration is the same. The short time required to stabilize the output voltage means that the response speed is fast. In order to increase the response speed, the heater coil as a heat source in the sintered body can efficiently receive the combustion heat so that the resistance value can be changed efficiently.

  Therefore, an efficient heat conduction means is indispensable for a high-sensitivity, high-speed contact combustion type gas sensor. The hollow catalytic combustion type gas sensor element does not have a heat conductive material inside, and it can be expected that the heat capacity is lowered and the heat conductivity is improved. In addition, since the detection target gas may flow not only to the sensor surface but also to the hollow portion, an effect of increasing the response speed can be expected.

  In addition, a porous ceramic body is used as the core inside the sensor, which is resistant to external impacts.

  However, when a hollow catalytic combustion gas sensor element is fabricated by the method disclosed in Patent Document 1, the core wire itself around which the heater coil is wound is removed by strong acid. It is exposed and cannot accurately transfer the combustion heat of the detection target gas.

  In addition, when a hollow catalytic combustion gas sensor element is manufactured by the method disclosed in Patent Document 1, the core wire itself around which the heater coil is wound is removed by strong acid, so that an impact from the outside is not affected. It is weaker than existing catalytic combustion type gas sensor elements, and there is a possibility that the electrodeposited alumina insulating material may collapse.

  In order to solve the above problems, a catalytic combustion gas sensor element according to the present invention includes a porous ceramic body, a heater coil spirally wound on the surface of the porous ceramic body, and a porous ceramic body. It has a sintered body with a heat conduction layer and a catalyst layer that covers a part of the heater coil, and the electrical characteristic value of the heater coil changes due to the combustion heat generated by the combustion of the gas in contact. It is characterized by detecting the presence of combustible gas based on a change in value.

  The porous ceramic body in the catalytic combustion type gas sensor element according to the present invention preferably has a cylindrical shape and a hollow structure.

  In the contact combustion type gas sensor element according to the present invention, it is preferable that the heater coil is spirally wound while being in contact with the surface of the porous ceramic body to form a constituent body.

  In the catalytic combustion type gas sensor element according to the present invention, it is preferable that a heat conduction layer and a catalyst layer are formed on the surface of the structure.

  According to the catalytic combustion type gas sensor element related to the present invention, a porous ceramic body, a heater coil spirally wound on the surface of the porous ceramic body, and a part of the heater coil while enclosing the porous ceramic body. And a sintered body having a heat conductive layer and a catalyst layer, and the porous ceramic body has a cylindrical shape and a hollow structure. The heat capacity of the entire heat conductive layer is small, and the thermal conductivity, gas sensitivity, and response speed are improved. Moreover, the porous ceramic body is used as a core, and the strength of the entire catalytic combustion type gas sensor element is improved.

  Hereinafter, preferred embodiments of a catalytic combustion type gas sensor element of the present invention will be described in detail with reference to the drawings.

    FIG. 5 shows a configuration diagram of a conventional catalytic combustion type gas sensor element. The conventional element has a configuration in which the heater coil 1 is covered with a heat conductive layer material 2 and the surface of the heat conductive layer material 2 is covered with a combustion catalyst material 3.

The block diagram of the contact combustion type gas sensor element concerning embodiment of this invention is demonstrated. As shown in FIG. 2, the porous ceramic body 4 has a cylindrical shape and a hollow structure, and the material is preferably the same as that of the heat conduction layer material 2 or the combustion catalyst material 3. The heater coil 1 has a non-coiled lead portion and a single-winding center portion, or a single-winding coil lead portion and a double-winding heater coil 5 as shown in FIG. What is comprised by these is preferable.

    As shown in FIG. 4, the heater coil 1 is spirally wound in contact with the surface of the porous ceramic body 4 to form the structure 6. Next, as shown in FIG. 1, for example, the surface of the structure 6 is impregnated with a heat conductive layer material 2 in which alumina (aluminum oxide) and a glass material are mixed with a solvent. Next, when the heater coil 1 is energized and the solvent is blown and fired, a heat conductive layer is formed. Moreover, it is preferable that the helically wound portion of the heater coil 1 is covered with the porous ceramic body 4 and the heat conductive layer and is not exposed.

    Next, after the heat conductive layer is formed, the combustion catalyst material 3 is applied. Thereafter, similarly, the heater coil 1 is energized and fired to form a catalyst layer. Here, a sintered body 7 composed of a heat conductive layer and a catalyst layer is formed.

    The porous ceramic body 4 has a cylindrical shape, and preferably has an inner diameter of 10 μm to 5 mm and an outer diameter of 20 μm to 10 mm. When the shape of the porous ceramic body falls within these ranges, the catalytic combustion type gas sensor according to the embodiment of the present invention has a gas sensitivity, response speed, and impact resistance when compared with the catalytic combustion type gas sensor having an existing structure. Improves.

    Next, using the catalytic combustion type gas sensor element having the structure of the present invention, the gas sensitivity and response time for the detection target gas were evaluated.

  As an example, a heater coil (construction body) having a total length of 1 mm is formed by spirally winding a platinum alloy wire having a wire diameter of 20 μm around the surface of a porous ceramic body made of cylindrical alumina having a shape as shown in Table 3. did.

  The surface of the above-described structure was impregnated with a heat conductive layer material composed of a glass material, an alumina material, and ethylene glycol, and the heater coil was energized and baked.

  As a comparative example, as shown in FIG. 6, with reference to the manufacturing method of Patent Document 1, a part of a platinum alloy wire having a wire diameter of 20 μm is shown in Table 3, and a molybdenum core wire having a diameter of 5 μm or 100 μm. A heat conductive layer material composed of a glass material and an alumina material was electrodeposited on a 1 mm long heater coil wound in a single winding, and then the molybdenum core wire was dissolved with a strong acid.

  In all of the above examples and comparative examples, after forming a heat conductive layer on the surface of the heater coil, a slurry-like combustion catalyst material mainly composed of tin oxide and platinum is applied to the surface of the heat conductive layer, and the heater The coil was energized and fired to evaluate as a catalytic combustion type gas sensor element.

  Assembling as a catalytic combustion type gas sensor element with the above configuration, the time to reach a 90% stable value of the output signal of the gas sensor with respect to 4000 ppm of methane gas and hydrogen as detection target gases (hereinafter referred to as response time) was evaluated. The evaluation results are shown in Table 1.

  As a result of the response time evaluation, the response time of Example 2 was short for hydrogen and methane as detection target gases, 3 seconds for hydrogen, and 5 seconds for methane. This is because the cavity part of Example 2 is larger than Example 1, and the area which can be contact-combusted is larger. Moreover, since the comparative example 1 and the comparative example 2 have the part which the heater coil has exposed in the cavity part, transmission of a combustion heat is delayed and responsiveness is bad.

  Next, voltage values (hereinafter referred to as gas sensitivity) of output signals in Examples and Comparative Examples with respect to hydrogen as detection target gases and 4000 and 8000 ppm of methane gas were evaluated. The evaluation results are shown in FIG.

    Regardless of hydrogen and methane gas, the gas sensitivity was highest in Example 2. As in Example 1 or Comparative Example 1, when the cavity is small, the heat capacity of the entire element is large, so the heat conduction efficiency to the heater coil is poor. Even if the cavity is larger than Comparative Example 1 as in Comparative Example 2, if there is a portion where the heater coil is exposed in the cavity as described above, the heat conduction efficiency will deteriorate, and as a result gas sensitivity will be reduced. Deteriorate.

  In Example 1 and Example 2, the material of the porous ceramic body is the same alumina as the heat conductive layer material, but this may contain tin oxide or platinum used for the catalyst. By using the combustion catalyst material as the porous ceramic body, the gas to be detected flowing into the cavity of the element can be burned, so that the gas sensitivity is further improved.

  Next, impact resistance evaluation was performed. Each catalytic combustion type gas sensor element was assembled as a catalytic combustion type gas sensor, and a 300 g weight was attached to the gas sensor casing and dropped from a height of 1 m three times. Thereafter, the gas sensor was energized in the absence of the detection target gas, and the voltage value change (zero point fluctuation) before and after the impact test was measured. The results are shown in Table 2.

  As a result of the impact resistance evaluation, the voltage value change after the test was 1.2 mV in Example 1 and 1.5 mV in Example 2. In each example, the voltage value change was small. Next, Comparative Example 1 was 30 mV, and Comparative Example 2 was 85 mV. The voltage value change in each comparative example was larger than that in the example. Since the change in voltage value is large, in the comparative example, there is a possibility that the sintered body portion collapsed due to impact. This can be said that the hollow-type embodiment including the porous ceramic body has higher impact resistance than the comparative example. This porous ceramic body has the function of lowering the heat capacity due to the hollow structure and the function of not impairing the impact resistance as a core material.

  From the above results, a cylindrical hollow ceramic body, a heater coil spirally wound around the surface of the porous ceramic body, and a portion of the heater coil that covers the porous ceramic body while enclosing the porous ceramic body. A catalytic combustion type gas sensor element including a conductive layer and a sintered body having a catalyst layer has a short response time to a detection target gas, high gas sensitivity, and excellent impact resistance.

  In the above, the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the inner and outer diameters of the porous ceramic body, the total length of the porous ceramic body, the number of turns of the heater coil, and the like can be changed as appropriate.

    As described above, the catalytic combustion type gas sensor element according to the present invention is useful for a gas leak detection device for home or industry, and is particularly suitable for a device for detecting a combustible gas used in a fuel cell.

It is sectional drawing of the contact combustion type gas sensor element concerning embodiment of this invention. It is sectional drawing of the porous ceramic body used for the catalytic combustion type gas sensor element concerning embodiment of this invention. It is the elements on larger scale of the double winding heater coil used for the catalytic combustion type gas sensor element concerning embodiment of this invention. It is sectional drawing of the structure by the single winding heater coil and porous ceramic body which are used for the catalytic combustion type gas sensor element concerning embodiment of this invention. It is sectional drawing of the conventional catalytic combustion type gas sensor element. It is sectional drawing of the conventional gas detection element. It is a graph showing the gas sensitivity of the contact combustion type gas sensor element concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single winding heater coil 2 Heat conductive layer material 3 Combustion catalyst material 4 Porous ceramic body 5 Double winding heater coil 6 Structure 7 Sintered body

Claims (3)

This is a contact combustion type gas sensor element that detects the presence of combustible gas based on the change in the electrical characteristic value of the heater coil due to the combustion heat generated by the combustion of the gas in contact with the sintered body. And
A cylindrical ceramic body having a hollow structure and having a hollow structure,
The heater coil is spirally wound on the surface of the porous ceramic body;
A catalytic combustion type gas sensor element having a heat conductive layer and a catalyst layer, wherein the sintered body encloses the porous ceramic body and covers a part of the heater coil.   The contact combustion gas sensor element according to claim 1, wherein the heater coil is wound in a spiral shape while being in contact with the surface of the porous ceramic body to form a constituent body.   The catalytic combustion type gas sensor element according to claim 2, wherein the heat conductive layer and the catalyst layer are formed on a surface of the structure.

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