JP2018197700A - Gas sensor - Google Patents

Abstract

To provide a gas sensor having a high gas responsiveness and recoverability while keeping the adsorptivity of siloxane compounds.SOLUTION: A gas sensor 10 includes a case body 20, a gas detection element 30, and a filter 40. The case body 20 includes a case body cylinder part 21, a first metal gauze 22, and an encapsulation member 23. The gas detection element 30 includes a gas sensing body 31, a heater electrode 32, and a center electrode 33. The filter 40 includes a plurality of silica gels 41. A siloxane removal agent is added to the silica gel 41. Preferably, the grain size of the silica gel 41 is 850 μm to 1700 μm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gas sensor, and more particularly to a gas sensor including a filter for removing miscellaneous gases.

  2. Description of the Related Art Conventionally, a gas sensor is known in which a gas detection element is accommodated in a case and a gas to be detected flows into the case to detect a specific gas. In these gas sensors, the gas sensing element of the gas sensing element is poisoned by the siloxane compounds contained in the gas to be detected, and there is a risk of generating false alarms. Therefore, by providing a filter containing a porous substance such as activated carbon or silica gel, the inflow of siloxane compounds into the gas detection element is prevented.

  In particular, in the case of a gas sensor that detects LP gas components with a home gas alarm device or the like, since isobutane contained in LP gas is adsorbed on the activated carbon, the activated carbon cannot be used as a filter material. Therefore, silica gel is used for the filter of the gas sensor that detects the LP gas component. However, since silica gel is inferior in the adsorption performance of the siloxane compound compared to other porous materials, it is used by adding a siloxane removal component to the silica gel. It has been proposed.

JP2012-241037

  However, if a filter using silica gel with a small particle size is installed in order to increase the surface area of silica gel and adsorb more siloxane compounds, it will be difficult for gas to pass through the filter, resulting in slow gas responsiveness and recovery. There was a problem.

  An object of the present invention is to provide a gas sensor having good gas responsiveness and recoverability while maintaining adsorption performance of siloxane compounds.

  In order to achieve the above object, a first invention provides a case body having a gas inlet, a gas detection element disposed inside the case body, and the gas inlet and the gas detection. The gas sensor includes a filter through which a gas to be detected passes, which is disposed between the element and the filter. The filter includes silica gel to which a siloxane removing agent is added, and the particle size of the silica gel is 850 μm to 1700 μm.

  A second invention is a gas sensor according to the first invention, further comprising a partition member that forms a space above or below the gas inlet, and the filter is configured such that silica gel is filled in the space.

  A third invention is a gas sensor according to the first invention, wherein the filter is a plate-like body in which silica gel is sandwiched between sheet bodies.

  In this way, a gap is formed between the filled silica gels, and the gas easily passes through the filter, so that the gas responsiveness and recoverability can be improved while maintaining the adsorption performance of the siloxane compounds. it can.

  ADVANTAGE OF THE INVENTION According to this invention, the gas sensor with favorable gas responsiveness and recoverability can be provided, maintaining the adsorption performance of siloxane compounds.

It is sectional drawing of the gas sensor by embodiment of this invention. It is sectional drawing of the gas sensor by the modification of embodiment of this invention. It is sectional drawing of the gas sensor by another modification of embodiment of this invention. It is sectional drawing of the gas sensor by another modification of embodiment of this invention. In the Example of this invention, it is the graph showing the relationship between time when the gas containing isobutane was inject | poured, and gas sensor resistance value. It is the graph which expanded the gas injection start and the exhaust gas start vicinity among the graphs of FIG.

  Next, embodiments of the invention will be described with reference to the drawings.

  With reference to FIG. 1, a gas sensor 10 according to an embodiment of the present invention includes a case body 20, a gas detection element 30, and a filter 40. The case body 20 includes a case body cylinder portion 20 a, a case body upper plate portion 20 b, a gas inflow port 21, a first wire mesh 22, and a sealing member 23. The gas detection element 30 includes a gas sensitive body 31, a heater electrode 32, and a center electrode 33. The filter 40 includes a plurality of silica gel particles 41. Silica gel particles 41 are added with a siloxane remover.

  Referring to FIG. 1, a case body 20 includes a cylindrical case body cylinder portion 20a, and a case body upper plate portion 20b integrally formed so as to stick inward from an upper end portion of the case body cylinder portion 20a. Consists of. A gas inlet 21 for taking in the detection target gas is formed in the center of the case body upper plate portion 20b. A first wire mesh 22 is attached to the inside of the case body upper plate portion 20 b so as to cover the gas inlet 21. The sealing member 23 is a disk-shaped member and is fitted into the lower end portion of the case body cylinder portion 20a. A lead terminal described later protrudes from the sealing member 23.

  Although case body 20 will not be restrict | limited especially if it is a material which can protect a gas detection element, For example, it forms with a synthetic resin or a metal. The first wire mesh 22 is preferably made of stainless steel. The sealing member 23 may be an insulating material and is preferably a urethane resin.

  When the gas detection element 30 is exposed to the detection target gas, the gas detection element 30 changes the electric resistance value according to the concentration of the target gas. The gas detection element 30 includes a gas sensitive body 31, a heater electrode 32, a center electrode 33, and lead terminals 34a, 34b, and 34c. The heater electrode 32 and the center electrode 33 are embedded in the gas sensitive body 31.

  The gas sensitive body 31 is formed so as to fill a gap between the heater electrode 32 and the center electrode 33 and further cover the heater electrode 32. The gas sensitive body 31 includes a metal oxide semiconductor and has, for example, a spherical shape, a rugby ball shape, a spheroid shape, or a bead shape. This metal oxide semiconductor contains, for example, a metal oxide selected from tin oxide, tungsten oxide, indium oxide, zinc oxide, titanium oxide, strontium titanate, barium titanate, and barium stannate. The gas sensitive body 4 is formed, for example, by firing a molding material containing a metal oxide semiconductor powder. The metal oxide semiconductor preferably supports a catalyst that reduces sensitivity to various gases. Such catalysts include palladium, tungsten, platinum, rhodium, cerium, molybdenum, vanadium, and the like. One of these catalysts may be used alone, or two or more of them may be used in combination.

  The heater electrode 32 is formed by winding a noble metal wire in a coil shape. The heater electrode 32 is energized to generate heat, thereby heating the gas sensitive body 31 to a predetermined temperature. The heater electrode 32 is made of, for example, a wire made of a noble metal wire such as platinum or a platinum alloy having a wire diameter of 10 to 25 μm (preferably 15 to 20 μm, more preferably 15 μm). Lead wires are provided at both ends of the heater electrode 32, respectively. The lead wire is provided so as to be drawn from the inside of the gas sensitive body 31 to the outside of the gas sensitive body 31. The lead wire is electrically connected to the lead terminals 34a and 34b. Thereby, the gas sensor 1 is fixed to the lead terminals 34a and 34b. Note that the lead terminals 34a and 34b and the heater electrode 32 may be separate bodies, but in the present embodiment, the lead terminals 34a and 34b and the heater electrode 32 are formed of a single wire and are integrally formed.

  The center electrode 33 is passed through the heater electrode 32 along the central axis of the heater electrode 32. The center electrode 33 is disposed away from the heater electrode 32 so as not to contact the heater electrode 32. The center electrode 33 is formed in a straight line and is embedded in the gas sensitive body 31. The center electrode 3 is made of, for example, a wire made of a noble metal wire such as platinum or a platinum alloy having a wire diameter of 10 to 25 μm (preferably 15 to 20 μm, more preferably 15 μm). In addition, although the center electrode 33 of this embodiment is comprised with the same wire diameter and the same material with respect to the heater electrode 32, you may mutually differ. At least one end of the center electrode 33 is provided with a lead wire. The lead wire is provided so as to be drawn out from the inside of the gas sensitive body 4 to the outside of the gas sensitive body 4. In the center electrode 33, the part pulled out from the gas sensitive body 31 of the edge part on the opposite side to the side connected to the lead terminal 34c does not need to be provided.

  In the present embodiment, the gas detection element 30 is housed in the inner case body 50. The inner case body 50 includes an inner case body cylinder portion 50a, an inner case body upper plate portion 50b integrally formed so as to stick inward from the upper end portion of the inner case body cylinder portion 50a, a base 51, 2 wire mesh 52. The inner case body 50 has a shape similar to that of the case body 20, but the height of the inner case body cylinder portion 50a is lower than that of the case body cylinder portion 20a. It is about 2 heights. The outer diameter of the inner case body cylinder part 50a is formed slightly smaller than the inner diameter of the case body cylinder part 20a.

  The filter 40 is provided between the first wire mesh 22 and the second wire mesh 52. The filter 40 is provided between the gas inlet 21 and the gas detection element 30 so as to cover the gas inlet 21. The detection target gas enters from the gas inlet 21, passes through the filter 40, and reaches the gas detection element 30. The filter 40 includes a plurality of silica gels 41 and can be formed by filling the silica gel 41 between the first metal mesh 22 and the second metal mesh 52. The plurality of silica gels 41 are sandwiched between the first metal mesh 22 and the second metal mesh 52. Silica gel 41 carries a siloxane remover. The particle size of the silica gel 41 is preferably 850 μm to 1700 μm. When the particle size is 850 μm or less, the gap between the silica gel particles is reduced and the detection target gas is difficult to pass through, so that the gas response time and recovery time become longer. On the other hand, when the particle size is 1700 μm or more, handling when the silica gel is filled becomes difficult. In addition, when the particle size is 1700 μm or more, only about two stages of silica gel enter between the first wire mesh 22 and the second wire mesh 52, making it difficult to remove siloxane. When the distance between the first wire mesh 22 and the second wire mesh 52 is H1, and the diameter of the gas inlet 21 is D1, the particle size of the silica gel is preferably H1 / 3 or less, or D1 / 3 or less.

  As the siloxane remover, it is preferable to use an acid compound having an acid dissociation index (pKa) of 10 or more and 2.2 or less and a molecular weight of 1000 or less. The molecular weight of the acidic compound is 1000 or less, preferably 500 or less, and more preferably 400 or less. Examples of acidic compounds include carboxylic acids such as oxalic acid, maleic acid, benzenehexacarboxylic acid, benzenepentacarboxylic acid, pyromellitic acid, and inorganic acids such as sulfurous acid, sulfuric acid, phosphoric acid, phosphorous acid, and hypophosphorous acid. Preferred are phosphoric esters such as methyl phosphate, dimethyl phosphate and inosinic acid, amino acids such as cysteine and histidine, sulfonic acids such as p-toluenesulfonic acid and benzenesulfonic acid, and mixtures containing these. The amount of the acidic compound supported on the silica gel is preferably 0.1 to 20% by weight, more preferably 0.5 to 15% by weight, and further preferably 1 to 10% by weight.

In the gas sensor 10 according to the first embodiment, since the particle diameter of the silica gel contained in the filter is 850 μm to 1700 μm, a gap is formed between the silica gel particles, and the gas easily passes therethrough. Further, since the silica gel carries a siloxane remover, the siloxane can be removed efficiently. Therefore, it is possible to provide a gas sensor with a short gas response time and recovery time while removing siloxane.
<Modification A>

  In the above embodiment, the filter is provided between the first wire mesh attached to the case body and the second wire mesh attached to the inner case body. However, the second wire mesh is attached to the case body without providing the inner case body. It may be attached. Referring to FIG. 2, gas sensor 10A includes a case body 20A, a gas detection element 30A, and a filter 40A. The case body 20A includes a case body cylinder portion 20Aa, a case body upper plate portion 20Ab, a first wire mesh 22A, and a sealing member 23A. The case body further includes a second wire mesh 24A and a fixing member 25A.

The second wire mesh 24A is attached to the fixing member 25A. The fixing member 25A is provided at a height of about 1/3 to 1/2 from the upper end of the case body cylinder portion 20Aa. The fixing member 25A may be formed in the case body 20A in advance, or may be fitted later. The filter 40A is provided between the first wire mesh 22A and the second wire mesh 24A. The filter 40A is provided between the gas inlet 21A and the gas detection element 30A.
<Modification B>

  In the above embodiment, the filter is provided below the gas inlet, but the filter may be provided above the gas inlet. Referring to FIG. 3, gas sensor 10B includes a case body 20B, a gas detection element 30B, and a filter 40B. The case body 20B includes a case body cylinder portion 20Ba, a case body upper plate portion 20Bb, a first wire mesh 22B, and a sealing member 23B. The filter 40B is filled with silica gel carrying a siloxane remover between the partition member 60B and the first wire mesh 22B.

The partition member 60B is not particularly limited as long as it can take in the detection target gas. The partition member 60 </ b> B may be a stainless steel wire mesh, or may have a side surface made of metal or resin, with an opening provided on the upper surface, and a wire mesh attached.
<Modification C>

  In the above-described embodiment, the filter is configured by filling the space sandwiched between the metal meshes with silica gel, but a plate-like body sandwiched between the silica gels with a sheet body may be attached. Referring to FIG. 4, gas sensor 10C includes a case body 20C, a gas detection element 30C, and a filter 40C. The filter 40C is a plate-like body in which silica gel is filled between the sheet bodies 71C and 72C. The fixing member 73C is a member for fixing the filter 40C to the gas inlet side of the case body 20C.

  The sheet bodies 71C and 72C are not particularly limited as long as they allow the detection target gas to pass therethrough, and examples thereof include a wire net and a porous film. A waterproof porous membrane is particularly preferable because moisture in the atmosphere can be prevented from reaching the gas detection element.

  In the above embodiment, the case body is cylindrical, but other shapes may be used. For example, the case body may be a rectangular parallelepiped. The gas inlet is not limited to a circular shape in plan view, and may be a rectangular shape.

  Furthermore, although the gas detection element has been described as a semiconductor type gas detection element in the above embodiment, a catalytic combustion type or electrochemical gas detection element may be used.

Examples will be described below.
When silica gel loaded with a siloxane remover was used in a filter, the response time and recovery time for isobutane were verified for each silica gel particle size.

  The gas sensor has the same structure as that in FIG. 1, the height of the filter (distance from the second wire mesh to the first wire mesh) is 7.7 mm, and the diameter of the filter (inner diameter of the case body) is 5.1 mm. A siloxane remover was supported on silica gel (Carriert Q-15 manufactured by Fuji Silysia Co., Ltd.), and filled between the first wire mesh and the second wire mesh. A gas containing 3000 ppm of isobutane at a temperature of 20 ° C. and a humidity of 65% RII was injected into this gas sensor. The gas was injected for 0 second, and after 300 seconds, the gas was exhausted. There are four types of silica gel particle sizes: 180 to 500 μm, 500 to 1000 μm, 850 to 1000 μm, and 1180 to 1700 μm. It should be noted that silica gel having a particle size of 1700 μm or more could not be used because only a few silica gel particles could be filled and handling during filling was difficult.

  The above verification results will be described with reference to FIGS. FIG. 5 is a graph showing the relationship between the time when gas containing isobutane is injected and the resistance value of the gas sensor. FIG. 6 is an enlarged view of the vicinity of the start of gas injection and the start of exhaust gas in the graph of FIG. Simultaneously with the start of gas injection, the resistance value decreases and stabilizes after a certain period of time. When gas exhaust is started, the resistance value gradually increases, and after a certain time has elapsed, the resistance value becomes stable again.

Further, _{R 100} a resistance value of 180 second time point after the start of gas injection and _{R 100,} the time to reach 90% of the resistance value _{R 100} from the injection of gas and response time _{t 90,} since the exhaust gas as recovery time t ₁₀ the time to reach 10% of the resistance value, the result of calculating the response time and recovery time for each particle size, expressed in Table 1.

  It can be seen that as the particle size increases, both the response time and the recovery time become shorter. The shorter the response time / recovery time, the better. Specifically, it is desirable that the response time is 55 seconds or less and the recovery time is 95 seconds or less. Therefore, the particle size is preferably 850 μm or more.

10, 10A, 10B, 10C Gas sensor 20, 20A, 20B, 20C Case body 30, 30A, 30B, 30C Gas detection element 40, 40A, 40B, 40C Filter

Claims (3)

A case body having a gas inlet;
A gas detection element disposed inside the case body;
A filter that is disposed on the gas inlet or between the gas inlet and the gas detection element and through which the detection target gas passes;
The filter includes silica gel carrying a siloxane remover,
The gas sensor has a particle diameter of 850 μm to 1700 μm. A partition member that forms a space above or below the gas inlet;
The gas sensor according to claim 1, wherein the filter has a configuration in which the silica gel is filled in the space.   The gas sensor according to claim 1, wherein the filter is a plate-like body in which the silica gel is sandwiched between sheet bodies.

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