JP2004045324A - Gas filter and gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas filter that can efficiently suck and eliminate an organic silicone gas being mixed to a detection gas without sucking the detection gas, and to provide a gas sensor that prevents gas detection characteristics from being easily changed by the organic silicone gas. <P>SOLUTION: Powder containing at least one of a silicic acid constituent particle and an aluminosilicate constituent particle and Pt powder is interposed between a pair of porous sheets made of heat-resistant fiber, and a pair of permeable porous sheets is bonded in one piece for forming by using at least one of silica sol and alumina sol. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas filter and a gas sensor.
[0002]
[Prior art]
Conventionally, a gas filter in which a filter layer is directly formed on a gas detection element has been put to practical use as this type of gas filter.
Further, as this type of gas sensor, one in which a filter layer is formed by supporting silica on the outer surface of a gas detection element has been known.
[0003]
[Problems to be solved by the invention]
In recent years, various silicone materials such as silicone putty, silicone rubber, and silicone oil have been frequently used as building materials. Such a silicone material contains an organic silicone having a low polymerization degree and a relatively high volatility, and it has been pointed out that the organic silicone gas has an adverse effect on the gas sensor.
That is, the gas detection sensitivity of the gas detection element may be reduced, or the gas detection sensitivity may be increased with respect to a gas other than the gas to be selectively detected, which may cause malfunction. This is because the organosilicon gas contained in the detection gas reaches the gas detection element, and silicone components such as the organosilicone or a decomposition product thereof are likely to adhere to the gas detection element. This is thought to be due to changing the characteristics.
[0004]
Specifically, for example, in the case of a tin oxide semiconductor type gas detection element for methane, when the silicone component adheres to the gas detection element, the sensitivity to alcohol increases and the methane selectivity to alcohol decreases. Occurs. In the case of a catalytic combustion type gas detection element for hydrocarbon gas, if the silicone component adheres to the gas detection element, there is a problem that the detection sensitivity of the hydrocarbon gas itself is lowered and the hydrocarbon cannot be detected. Arise.
[0005]
Therefore, if silica is supported on the outer surface of the gas detection element to form a filter layer, it is possible to prevent the organosilicon gas from adhering to the filter layer and reaching the inside of the gas detection element. However, when the silicone component adheres to the filter layer, the sensitivity of the gas detection element, gas selection characteristics, and the like tend to change. Therefore, the change in the gas detection characteristic of the gas detection element cannot be suppressed. Further, in order to suppress variation in gas detection characteristics of the gas detection element and to adsorb the organic silicone gas efficiently, it is preferable that the filter layer is formed to have a uniform thickness. However, in order to form the filter layer with a uniform thickness, the filter layer forming material is usually formed in a thick coating so as to eliminate the formation unevenness of the filter layer. Then, the filter layer becomes thick, and the gas detection sensitivity and responsiveness of the gas detection element may be reduced, or the filter layer may be cracked due to heat generation of the gas detection element and may be damaged. There was an inconvenience.
[0006]
Therefore, in order to solve the problems as described above, a gas detection element is provided, a gas guiding path for introducing the detection gas from the external space to the gas detection element is provided, and the silicic acid component particles are provided between the pair of breathable porous bodies In addition, it has been proposed to provide a gas filter including at least one of the aluminosilicate component particles and the gas guide path. (Patent No. 3197455)
[0007]
According to this technique, since the silicic acid component particles or aluminosilicic acid component particles for adsorbing the organosilicon gas are held in the gas filter, the organosilicon gas is adsorbed to the gas filter, and the detection gas The organic silicone gas is removed from the inside and hardly reaches the gas detection element. Therefore, it is possible to suppress the disadvantage that the silicone component adheres to the gas detection element and changes the gas detection characteristics.
Further, as the gas filter, as long as the gas adsorption particles are interposed between a pair of breathable porous sheets, the organic silicone gas adsorption particles are held in a high density and have a surface area. The gas adsorption performance of the gas adsorbing particles can be enhanced because the gas permeability of the detection gas can be maintained high.
[0008]
Furthermore, if the gas filter is formed of a porous sheet made of heat-resistant fibers, even if the gas detection element and the filter that tend to be high in operation are generally provided in close proximity, Therefore, the gas adsorbing particles cannot be retained and the gas adsorbing particles cannot be held. Therefore, both the air permeability and the heat resistance are provided.
Further, if the heat-resistant fibers are integrally bonded using at least one of silica gel and alumina sol, the silica sol or aluminosol serving as a binder also has a function of adsorbing the organic silicone gas, and the detection gas It is difficult to give adverse effects.
[0009]
However, even with such a technique, various effects due to silicone gas could not be completely removed, so there was still room for improvement.
[0010]
Therefore, in view of the above circumstances, an object of the present invention is to provide a gas filter capable of efficiently adsorbing and removing the organosilicon gas mixed in the detection gas without adsorbing the detection gas, and also using the organosilicon gas as a gas detection characteristic. It is to provide a gas sensor that is difficult to change.
[0011]
[Means for Solving the Problems]
As a result of diligent research for the above purpose, the present inventors have found that when the silicon gas is adsorbed and removed using a silicic acid component or aluminosilicate particles, if platinum element (Pt) coexists, high adsorption removal efficiency. Has been found experimentally. The present invention is based on this new finding.
[0012]
In order to achieve the above object, the characteristic configuration of the present invention is:
Between a pair of breathable porous sheets made of heat-resistant fibers, a powder containing at least one of silicate component particles and aluminosilicate component particles and Pt powder, or silicate component particles and aluminosilicate component particles The pair of breathable porous sheets is integrally bonded using at least one of silica sol or alumina sol with at least one of the powders carrying Pt interposed therebetween.
The Pt powder is desirably contained in an amount of 0.2 to 30 wt% with respect to a particle component composed of at least one of silicic acid component particles and aluminosilicate component particles.
The characteristic configuration of the gas sensor of the present invention is as follows:
A gas detection element is provided, a gas guiding path for introducing the detection gas from the external space to the gas detection element is provided, and a powder containing at least one of silicic acid component particles and aluminosilicate component particles and Pt powder, or silicic acid A filter portion containing a powder in which Pt is supported on at least one of component particles and aluminosilicate component particles is provided in the gas induction path.
[0013]
[Function and effect]
In other words, in the gas sensor, a filter unit that can contact the detection gas that reaches the gas detection element from the external space is provided in the gas guide path that guides the detection gas from the external space to the gas detection element. The gas detection element is reached while contacting the part.
At this time, since the filter portion holds the particles of the silicic acid component and the aluminosilicate component for adsorbing the organic silicone gas, even if the detection gas contains an organic silicone gas, the detection gas The organic silicone gas is adsorbed to the filter unit and removed from the detection gas without causing inconvenience such as being adsorbed by the filter unit, and the organosilicon gas reaches the gas detection element. Hateful. Therefore, it is possible to suppress the disadvantage that the silicone component adheres to the gas detection element and changes the gas detection characteristics.
Here, the filter unit includes a powder containing at least one of silicic acid component particles and aluminosilicate component particles and Pt powder, or at least one of silicic acid component particles and aluminosilicate component particles. As a result of interposing the powder carrying the catalyst, the silicone gas adsorption characteristics of the silicic acid component particles and the aluminosilicic acid component particles could be greatly improved, as will be apparent from the experimental examples described later.
[0014]
In addition, when the Pt powder is contained in an amount of 0.2 to 30 wt% with respect to a particle component composed of at least one of silicic acid component particles and aluminosilicate component particles, it is desirable because it exhibits high organosilicon gas adsorption ability.
[0015]
As the gas filter, gas adsorbing particles are interposed between a pair of breathable porous sheets, and the pair of breathable porous sheets are integrally bonded using at least one of silica sol and alumina sol. Since the sol is integrated while being formed into particles, the particles for adsorbing the organic silicone gas can be held in a high density state and in a large surface area, and the breathable porous sheet Since each particle is held, the gas-absorbing performance of the gas-adsorbing particles can be increased because the gas-permeable property of the detection gas can be maintained high. Silica sol and alumina sol also serve as particles for adsorbing organic silicone gas after the gas filter is formed, which is useful for improving the organic silicone gas adsorbing ability of the gas filter after formation.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 2, the gas sensor of the present invention is provided with a gas detection element A, a gas guiding path for introducing a detection gas from the external space B to the gas detection element A, and isolating the gas detection element A from the external space B. The gas filter C is provided in the vent D1 that forms the gas guiding path, and the silica fine particles 2 (13% alumina), which is one of the aluminosilicate component particles, are held in the gas filter C.
The gas detection element A is a so-called hot-wire semiconductor sensor in which a metal oxide semiconductor is coated and sintered on a noble metal coil, and is provided inside a cylindrical housing D. Further, at the top portion of the housing D, there is provided a vent D1 that forms a gas guiding path through which gas can flow between the external space B and the inside of the housing D. And the gas sensor is assembled by inserting the sensor base D2 provided with the gas detection element A into the housing D from below.
Here, the housing D itself is made of an airtight material, and a gas filter C and an explosion-proof wire mesh D3 are provided over the entire surface of the vent hole D1, and an external space is provided via the gas filter C. Gas flows through B and the vicinity of the gas detection element A in the housing.
[0017]
As shown in FIG. 1, the gas filter C is a state in which silica alumina fine particles (13% alumina) and platinum fine particles are dispersed and interposed between a pair of glass fiber nonwoven fabrics 1 as an example of a breathable porous sheet. The glass fiber nonwoven fabrics 1 are formed by impregnating and bonding at a rate of about 0.1 g / cm ² so that the silica alumina fine particles do not flow freely even when vibration is applied using a silica sol binder.
[0018]
Furthermore, the structure of the gas alarm device X which employ | adopts this gas sensor suitably and is arrange | positioned on the wall surface of a kitchen etc. by making a drawing and an up-down direction correspond is demonstrated. As shown in FIG. 3, the alarm box X1 of the gas alarm X is formed in a rectangular box shape, and the inside is a sensor chamber X2 in which a gas sensor is disposed, and a sound generator / transformer / power supply control device. It is partitioned by a partition wall X4 from a device room X3 in which a device Xx is disposed. In the sensor chamber X2, the alarm box X1 is provided with a number of vent holes X5. The vent D1 is disposed toward a vent hole X5 provided in front of the alarm box X1.
[0019]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
(Test Example 1) HMDS (hexamethyldisiloxane) as a silicone gas source is a gas sensor in which a hot-wire semiconductor gas detection element for detecting methane gas, in which a tin oxide semiconductor is coated and sintered on a platinum coil, is disposed in the housing. It was examined how the sensitivity of the gas sensor for detecting methane gas to 1000 ppm of ethanol gas changed when left in a sealed container with 20 ppm for 10 hours.
At this time, the gas filter C is not used for the vent D1 of the housing D (triangle mark), the one gas filter C is used and the vent D1 is covered (circle mark), the gas filter Comparison was made with respect to three types (squares) in which platinum was not added to C. As a result, it became like FIG. The ethanol gas sensitivity was examined by a ratio with the sensor output of the same hot-wire semiconductor sensor for methane detection before the test.
[0020]
The hot-wire semiconductor gas sensor for detecting methane gas should have gas selectivity that selectively detects methane gas separately from the ethanol gas even if ethanol gas and methane gas are mixed. However, as is apparent from FIG. 4, it can be seen that when the gas detection element comes into contact with the HMDS in the sealed container, the gas sensor increases the ethanol gas sensitivity. Therefore, a large gas detection output is exhibited with respect to ethanol which is a mixed gas. Therefore, it cannot be said that the output with respect to methane gas is selectively obtained, and it turns out that selective detection of methane gas becomes increasingly difficult (triangle mark).
However, in the case of using the gas filter containing the silica alumina fine particles, the ethanol gas sensitivity is hardly changed in spite of long-time contact with the silicone gas, and the gas selectivity is hardly lowered. (Square mark). Furthermore, it can be seen that the gas selectivity when using a gas filter containing platinum fine particles in addition to silica alumina fine particles is kept almost constant, and the silicone gas is adsorbed and removed by the gas filter. It is thought that it was done. (Circle)
[0021]
(Test Example 2) After coating and sintering an alumina carrier on a platinum coil, a gas sensor in which a catalytic combustion type gas detection element for detecting methane gas carrying a combustion catalyst is arranged in the housing is used as an HMDS (hexamethyldioxide). It was examined how the sensitivity of 3,000 ppm of methane gas of the gas sensor for detecting methane gas changed when left for 10 hours in a state where 20 ppm of siloxane was contained in a sealed container.
At this time, the gas filter was not used for the vent of the housing (triangle mark), one gas filter was used and the vent was covered (circle mark), and platinum was added to the gas filter. Comparison was made with respect to three types (square marks) that were not. As a result, it became like FIG. The sensitivity of methane gas was examined by comparing it with the sensor output of the same catalytic combustion gas sensor for detecting methane before the test.
[0022]
Originally, it is desirable to keep the output to methane gas constant over time. However, as is apparent from FIG. 5, in the contact combustion type gas sensor for detecting methane gas without using a gas filter (triangle mark), the sensitivity to methane gas decreases due to contact with silicone gas, and the detection of methane gas gradually becomes difficult. I understand that.
However, in the case of using the gas filter containing the silica alumina fine particles (square marks), it is understood that the sensitivity of the methane gas is less likely to be lowered by a short contact with the silicone gas. Furthermore, when a gas filter containing platinum fine particles in addition to silica alumina fine particles is used (circles), the sensitivity of methane gas is kept almost constant over a long period of time. This is considered because the silicone gas was adsorbed and removed by the gas filter.
[0023]
(Test Example 3) The amount of platinum added to the gas filter described above was changed variously, and a 10-hour HMDS exposure test was performed in the same manner as in Test Example 1, and the sensitivity ratio to 3000 ppm of methane gas was determined. became.
From FIG. 6, it can be seen that the sensitivity ratio decreases when the platinum addition amount is too small or too large, and the Pt powder is made up of a particle component composed of at least one of the silicic acid component particles and the aluminosilicate component particles. It can be seen that an extremely high sensitivity ratio is maintained when the content is 0.2 to 30 wt%.
[0024]
[Another embodiment]
Another embodiment will be described below.
From the above-mentioned Examples, it can be seen that the silica gas adsorption / removal ability of the silica alumina is synergistically improved by the platinum component. In addition, according to the above-described prior art, silica as a silicic acid component is known as one that exhibits the same properties as silica alumina as an aluminosilicate component. Therefore, instead of the example using the silica alumina fine particles and the platinum component, silica fine particles and a platinum component may be contained. Therefore, as a form thereof, as in the above-described embodiment, at least one of silica and silica alumina may be included even if the fine particle contains at least one of silica and silica alumina and the fine particle of platinum component. A configuration in which fine particles of platinum component are supported on the fine particles, or a configuration in which at least one fine particle of silica or silica alumina is supported on the fine particles of platinum component may be employed.
[0025]
In addition, examples of the gas sensor to which the gas filter of the present invention is applied include those equipped with a hot-wire semiconductor gas detection element and a catalytic combustion type gas detection element as described above. Any device with elements will function. Therefore, for example, even when the gas filter is not configured as described above, the gas guiding path that guides the detection gas from the external space to the gas detection element is provided with a filter portion that functions in the same manner as the gas filter. However, the silicone gas is adsorbed and removed by the filter portion, and the influence of the silicone gas on the gas detection element can be reduced.
[Brief description of the drawings]
1 is an overall perspective view of a gas filter. FIG. 2 is an exploded view of a gas sensor. FIG. 3 is an exploded perspective view of a gas alarm. FIG. 4 is a graph showing the results of Test Example 1. FIG. [Fig. 6] Graph showing the results of Test Example 3 [Explanation of symbols]
1 Glass fiber nonwoven fabric (breathable porous sheet)
2 At least one of silicic acid component particles and aluminosilicate component particles A Gas detection element B External space C Gas filter

Claims (3)

Powder containing at least one of silicic acid component particles and aluminosilicate component particles and Pt powder between a pair of breathable porous sheets made of heat resistant fibers, or
With at least one of the silicic acid component particles and the aluminosilicic acid component particles interposed with a powder carrying Pt,
A gas filter formed by integrally bonding the pair of breathable porous sheets using at least one of silica sol and alumina sol. 2. The gas filter according to claim 1, wherein the Pt powder is contained in an amount of 0.2 to 30 wt% with respect to a particle component composed of at least one of silicic acid component particles and aluminosilicate component particles. A gas detection element is provided,
A gas guiding path that leads the detection gas from the external space to the gas detection element is provided,
A powder containing at least one of silicate component particles and aluminosilicate component particles and Pt powder, or
The gas sensor which provided the filter part containing the powder which carry | supported Pt in at least any one of a silicic acid component particle | grain and an aluminosilicate component particle | grain in the said gas induction path.

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