JPS587941B2 - Tokutei Ino Kangensei Gaso Sentaku Techini Kenshiyutsu Sultame no Fukugogata Gas Kenchisoshi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite gas detection element for selectively detecting a specific type of reducing gas.

In conventional gas detection elements and devices using them,
Since various reducing gases were detected indiscriminately, in actual use, the gases originally targeted for detection were gases for alcohol gas detection, propane gas detection, and CO2 gas detection.
Although it is limited depending on each application such as gas detection, it can be used for detection even if unnecessary reducing gases other than the gas to be detected are mixed in the atmosphere used. Because of the influence of such unnecessary gases, the equipment often malfunctions in a way that is not intended for its intended purpose, making it extremely unreliable in terms of accuracy.

The present invention overcomes the above-mentioned conventional drawbacks by forming a composite pair of gas sensing sections into which gas is selectively introduced through filters, and in which the pair of gas sensing sections is connected to a desired specific sensor in an appropriate circuit. It exhibits the effect of selectively detecting only different types of reducing gases, allowing it to detect only the target reducing gases depending on the application and eliminating errors caused by the effects of reducing gases that are not the target of detection. This makes it possible to significantly improve the accuracy and reliability of the detection device, and furthermore, such a pair of gas sensing sections can be integrated into a very compact structure, and each gas sensing section can be An object of the present invention is to provide a composite gas detection element for selectively detecting a specific type of reducing gas, which is easy to take out a terminal from an electrode and connect to a circuit, and is extremely useful for incorporating into a device. The structure is as follows.

The present invention provides a partition made of a filter material using an oxidation catalyst or an air-impermeable material in the center of a cylindrical container made of an airtight material and open at both ends, and both sides of the partition A gas sensing part made of a gas-sensitive metal oxide semiconductor is installed in the container, and a filter with selective gas permeability made of an oxidation catalyst is installed in the openings at both ends of the container.
In addition to making the above-mentioned two filters have different oxidizing abilities, an insulating electrode carrier is passed through the central axis of the entire filter, and a range from both ends to the vicinity of the center is formed on the circumferential surface of the electrode carrier. This is a composite gas sensing element for selectively detecting a specific type of reducing gas, which is formed by forming a pair of electrodes for each of the two gas sensing sections divided in the longitudinal direction.

In explaining the present invention in detail, first, the transmittance of the filter incorporated in the element of the present invention will be explained.

The materials for this filter include Nip, Co203,
Coo, ZnO, Sn02, Fe203, V205, A
g20, various metal oxide catalysts such as CuO, or metal oxides added with one or several kinds of noble metal oxidation catalysts such as Pd, Pt, Rh, Ir, Ru, Ag, Au, etc.
Alternatively, any material that functions as an oxidation catalyst may be used, such as a noble metal oxidation catalyst mixed with or supported on a base material such as asbestos, alumina, or silica.

Depending on its ability as an oxidation catalyst, filters made of such oxidation catalysts can be used to treat one or several types of reducing gases that are easily oxidized.
It has selective permeability in that it reacts with the gas and converts it into an inert gas, thereby blocking its permeation as a reducing gas, while allowing other reducing gases that are less likely to be oxidized to pass through as is. The type of gas that is permeated depends on the degree of oxidizing ability of the filter, and the relationship is as shown in the graph of FIG.

In other words, the graph in Figure 1 shows the relationship between the oxidation ability of a filter made from an oxidation catalyst and its permeability to various reducing gases. In the graph, the vertical axis represents the gas permeability in percentage; The horizontal axis represents the oxidation ability of the filter, that is, the activity as an oxidation catalyst. Curves A to E in the same graph are A for CO gas, B for H2 gas, C for ethanol, D for inbutane, and E for methane. The relationship between filter oxidation ability and transmittance is shown.

As shown in the same graph, among these gases, CO gas is the most likely to be blocked from permeation, and if the filter has a relatively low oxidizing ability as indicated by the symbol F1 on the horizontal axis of the same graph, only CO gas will be blocked. Permeation is blocked and most other gases are allowed to permeate.

This means that with this level of oxidation ability, CO gas, which is the most easily oxidized of the above gases, is oxidized by 02 in the atmosphere through the catalytic action of the filter and becomes inactive CO2, resulting in the permeation of CO gas itself. This is because the gases are blocked, while other gases that are less easily oxidized pass through without being oxidized.

In addition, if the oxidizing ability of the filter is a little higher than this, as shown by the symbol F2 in the same graph, in addition to CO gas, H2 gas, which is the next most easily oxidized gas, will also be oxidized and converted to H20. The permeation of certain gases is blocked, while other gases are allowed to permeate.

Similarly, as the oxidizing ability of the filter increases, the types of gases that are blocked from permeation increase in the order of oxidizability, and for the gases illustrated in the same graph,
In the oxidizing ability shown by the symbol F3 in the same graph, C
O, H2, and alcohol are blocked from permeating, and isobutane and methane are permeated, and at an oxidizing ability of F4, only methane is permeated.

In this way, a filter formed using an oxidation catalyst has a selective gas permeation effect, and the type of gas that can be selectively permeated depends on the oxidation ability of the filter, that is, the activity as an oxidation catalyst. Therefore,

Note that when the oxidizing ability of the filter is lowered to the level indicated by F0, all of the gases indicated by A-E in the same graph are transmitted.

Specific examples of filters having these various oxidizing abilities are shown in the following (Table 1).

The symbols indicating the oxidizing ability in the same table correspond to the symbols shown in the graph of FIG.

The device of the present invention is constructed by utilizing the characteristics of a filter using such an oxidation catalyst, and examples of the present invention will be described in detail below with reference to the drawings.

In Figure 2, 1 is a cylindrical container that is open at both ends and is made of an insulating material such as ceramic or glass, or a metal pipe coated with an insulating material. It is formed to have a density and thickness of .

Inside the container 1, there are two gas sensing units 2 arranged on the left and right sides.
a, 2b, a filter 3 as a central partition interposed between the sensing parts 2a, 2b, and filters 4a, 4b disposed at the openings at both ends, respectively.
In addition, an elongated rod-shaped electrode carrier 5 formed of an insulating material is passed through the central portion of these, and both ends of the electrode carrier 5 protrude to the sides of the container 1 .

Pairs of electrodes 6 a , 6 a ′ and 6 b , 6 b ′ divided along the longitudinal direction are formed on the circumferential surface of the electrode carrier 5 on both sides excluding the central portion. .

That is, each pair of electrodes 6a and 6a' and 6b and 6b
' are in a state where they face each other in the circumferential direction, and their center portions are in contact with the respective gas sensing parts 4a and 4b, and the ends of each electrode 5a, 5a' and 6b, 6b' are exposed to the outside of the container 1. configured to be exposed.

These electrodes 5a, 5a' and 6b, 6b' are
Au, Pt, and P are applied to each predetermined portion of the circumferential surface of the electrode supporting body 20.
The materials for the gas portions 2a and 2b include Sn02, Sn02,
A single substance of various metal oxide semiconductors such as In203, TiO2, ZnO, NiO, Cr203, etc., or a mixture of multiple types of metal oxide semiconductors, or using such a metal oxide semiconductor as the main material and adding Pd, Pt, Rh,
Adopt any material that has a gas sensing effect based on metal oxide semiconductors, such as those with added catalysts such as Ir, Ru, Ag, Au, etc., or those containing alumina, silica, etc. to increase mechanical strength. It is possible.

Further, as described above, each of the filters 3, 4a, and 4b is made of an oxidation catalyst and has selective gas permeability depending on its oxidation ability.

The oxidizing ability of each filter 3, 4a, 4b is such that the oxidizing ability of the filter 4b at the other end is higher than that of the filter 4a located at one end, and the filter 3 at the center has a higher oxidizing ability than the filter 4b located at the other end. Under the condition that it has an oxidizing ability of the same level or higher than that,
As will be described in detail later, it is set appropriately depending on the type of gas to be detected.

As the partition provided in the center of the container, an air-impermeable material may be used instead of the filter 3 described above.

That is, the partition section is connected to the filter 4b at the other end.
This is to prevent the gas whose permeation is prevented from entering the gas sensing section 2b from the filter 4a at the one end (lower oxidizing ability) through the gas sensing section 2a.

Therefore, even if the partition is made of an air-impermeable material, by blocking gas there, the necessary function of the partition can be obtained.

However, if the partition part is formed by the filter 3 using an oxidation catalyst as in this embodiment and the oxidation capacity is set as described above, the necessary function as a partition part will be satisfied and the ventilation will be good. It is more preferable because it is maintained at

In addition, in this case, each filter 3, 4a, 4b
In order for the material to have an appropriate oxidizing ability, it is sufficient to select the material, temperature conditions, etc.

In other words, when forming a filter by adding a noble metal oxidation catalyst to a base material such as metal oxide, asbestos, alumina, or silica, increasing the amount of the noble metal oxidation catalyst will increase the catalytic action, that is, the oxidation ability. It gets expensive.

In addition, since the oxidation ability also depends on the heating temperature, each of the filters 3 and 4 mentioned above depends on the relationship between the material and the heating temperature.
Make sure that a, 4 and b have appropriate abilities that satisfy the above conditions.

Reference numeral 7 denotes a membrane-shaped heater attached to the outer peripheral surface of the container 1, which heats each of the filters 3, 4a, 4b and both gas sensing sections 2a, 2b.

In this way, the element S of the present invention is constructed, and this element S
are a pair of conductive supports 8a, which also serve as leads, each of which has both end portions of the electrode carrier 5 attached to, for example, a base plate, etc.;
If the electrodes 8a', 8b, and 8b' are clamped and fixed, each of the electrodes 6a, 6a' and 6b, 6b'
It is convenient for taking out terminals from the terminal and incorporating them into circuits.

This element S is usually incorporated into a circuit as shown in FIG. 4 and used.

That is, in this circuit, both the sensing parts 2a and 2b integrally equipped in the element S of the present invention are connected in parallel to a power supply 9, and the sensing parts 2a and 2b are connected with resistors 10a and 2b, respectively. 10b are connected in series and the electric actuator 11 is connected between them, so that a voltage corresponding to the difference between the respective outputs obtained from the two gas sensing elements 2a and 2b is applied to the electric actuator 11. .

As the electric actuator 11, a meter, an alarm, a ventilation fan, a solenoid valve, and various other control devices may be arbitrarily employed.

Next, to explain the operation of the element of the present invention when incorporated into the above circuit, for example, each of the above filters 3, 4a
, 4b, the oxidizing ability of the filter 4a at one end is shown as F2 in the same graph, and the oxidizing ability of the filter 4b at the other end and the filter 3 in the center is shown as F3 in the same graph. As can be seen from the same graph, among the reducing gases shown in the same graph, CO gas and H2 gas are both blocked from permeation by the filters 4a and 4b at both ends, so both the sensing parts 3a and 3b are can be almost reached, and isobutane and methane are
Since the light transmits almost freely through all of a, 4a and 3, it is sensed to the same extent by both sensing sections 2a and 2b.

Since alcohol can pass through the filter 4a at one end, it can be sensed by one sensing part 2a but not by the other sensing part 2b.

Therefore, when the oxidizing ability of each filter 4a, 4b, and 3 is determined in this way, the difference between the outputs of the two sensing sections 2a, 2b is extracted as the final output, as shown in the circuit of FIG. If this is done, only alcohol will be sufficiently detected, and the output of other reducing gases will be almost negated.

However, in reality, even under these setting conditions, some amount of H2 gas, etc., which is more easily oxidized than alcohol, will pass through, depending on the oxidation ability of each filter 4a, 4b, 3, and some amount of isobutane, etc., which is less oxidized than alcohol. Since the permeation of these gases is blocked, some final output is produced in the above circuit for these gases, but these outputs are very small compared to the output for alcohol, so
There is no doubt that an excellent selective detection effect for alcohol can be obtained.

Similarly, for each of the other reducing gases, by adjusting the oxidizing abilities of the filters 4a, 4b, and 3 accordingly, the desired specific single type of reducing gas can be selectively selected. Can be detected.

Further, by increasing the difference in oxidizing ability between the filter 4a and the filters 4b and 3, it is possible to selectively detect several types of reducing gases whose transmittances change between them.

The following (Table 2) shows the results of an experiment conducted by the present inventor regarding the selective detection effect for a specific type of gas when using the element of the present invention.

In this experiment, isobutane was selectively detected, and in the element having the shape shown in FIG.
A filter corresponding to the oxidation capacity F4 as shown in Table 1 above was used for both the other end side and the central filters 4b and 3.

The heating temperature is 370°C. In addition, the gas sensing parts 2a, 2
A simple substance of SnO2 was used as the metal oxide semiconductor of b.

Then, it is incorporated into the circuit shown in FIG. 4, and the voltage of the power supply 9 is set to 1
0V, the resistance value of the resistor 10a is 6KΩ, and the resistance value of the resistor 10b is 9KΩ, and the resistance values of the gas sensing parts 2a and 2b in each gas shown in (Table 2) and the electrically actuated member 11 are 5.
The output voltage was measured.

Measurements were performed using the natural flow method.

From this table, it can be seen that under the above experimental conditions, the output voltage changes greatly in 1000 ppm of isobutane compared to in air, and the change in output voltage is small in other gases, indicating that isobutane is selective. It can be seen that it is detected.

FIG. 5 shows another embodiment of the element S of the present invention, in which an electrode carrier 5' is formed in the shape of a pipe and can be penetrated through the central axis of the cylindrical container 1. A heater 7' is inserted inside.

Each pair of electrodes 6a provided on the circumferential surface of the electrode carrier 5'
, 6a', 6b, 6b', both gas sensing bodies 2a, 2b disposed between the electrode carrier 5' and the container 1, and the respective filters 3, 4a, 4b have the same structure as in the previous embodiment. The same is true.

In addition, in the configuration shown in each of the above embodiments, each pair of electrodes 6a, 6a' and 6 for both gas sensing parts 2a and 2b is
b and 6b' are shown as straight strips along the longitudinal direction in the illustrated example, but in addition to this structure, for example, each pair of electrodes may be twisted in the circumferential direction with a constant interval maintained between them. It is also possible to arbitrarily adopt a structure in which the electrodes have a spiral shape, or the opposing sides of a pair of electrodes have a saw blade shape or other uneven shape in which the concave portions and convex portions face each other. In this way, the opposing area of each pair of electrodes becomes larger, and the resistance value between the electrodes can be lowered.

Alternatively, one electrode 6a and 6b for each of the gas sensing sections 2a and 2b may be connected in the longitudinal direction to form an electrode common to both the gas sensing sections 2a and 2b.

However, in this case, it is necessary that the electrode common to both the gas sensing sections 2a and 2b be connected to the power source 9 in order to incorporate it into a circuit as shown in FIG.

It goes without saying that the structure of the other parts may be modified as desired without departing from the gist of the present invention.

As described above, the gas sensing element of the present invention includes a pair of gas sensing sections, and a filter having selective gas permeability depending on the oxidizing ability is provided for each of the two gas sensing sections. This allows both sensing parts to selectively sense only the reducing gas that passes through their respective filters.
In addition, by making the oxidizing ability of each filter different for each sensing part, the type of reducing gas that can pass through each filter, that is, the type of gas that can be sensed in each sensing part, is made different. Since the sensitivity of both sensing parts is made to be significantly different only for the specific type of reducing gas corresponding to the difference, by being incorporated into a bridge circuit etc. that extracts the difference in the output of the two sensing parts, it is possible to detect the specific type of reducing gas. By selectively detecting only the reducing gases, the influence of other reducing gases can be greatly reduced.

As can be seen from the graph in Figure 1, a desired specific reducing gas can be selectively detected as described above by selecting the oxidizing capacity of each filter. By selectively detecting only the specific reducing gas that is the object of detection, it is possible to prevent malfunction of the device due to unnecessary reducing gases that are not the object of detection, and the detection accuracy can be significantly improved.

Furthermore, since both of the gas sensing sections and the filters for each sensing section are arranged and equipped in a cylindrical container to form a composite and integrated structure, the structure is streamlined and extremely compact.

Further, a pair of electrodes for each of the above-mentioned elements is formed on the circumferential surface of an electrode supporting body which is penetrated through the central portion of these, and each electrode is led out to the outside while being supported by the electrode supporting body. Because of this, it is easy to take out the terminals from each electrode, connect them to the circuit, attach them, etc., and it is extremely convenient to incorporate them into a device, which brings about many practical effects.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the oxidizing ability of the filter used in the element of the present invention and the transmittance for various reducing gases, FIG. 2 is a cross-sectional view showing an example of the present invention, and FIG.
4 is a circuit diagram showing an example of the circuit configuration of a gas detection device using the element of the present invention, and FIG. 5 is a sectional view showing another embodiment of the present invention. . DESCRIPTION OF SYMBOLS 1... Container, 2a, 2b... Gas sensing part, 3... Central partition part, 4a, 4b... Filter, 5, 5'... Electrode carrier, 6a, 6a', 6b, 6b'... Above Each pair of electrodes for both gas sensing parts.

Claims (1)

[Claims] 1 A partition made of a filter material using an oxidation catalyst or a non-porous material is provided in the center of a cylindrical container made of an airtight material and open at both ends, and a gas-sensitive material is provided on both sides of the partition. A gas sensing section made of a chemical metal oxide semiconductor is provided, and a filter with selective gas permeability made of an oxidation catalyst is provided at the openings at both ends of the container. an insulating electrode carrier is passed through the central axis portion of the electrode carrier, and the gas sensing portions are divided along the longitudinal direction from both ends of the electrode carrier to the respective central portions on the peripheral surface of the electrode carrier. A composite gas detection element for selectively detecting a specific type of reducing gas, which is formed by forming a pair of electrodes for each of the two electrodes.