JPH06100564B2 - Gas detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas detector for detecting a gas component or its concentration.

[Prior Art] Conventionally, an oxygen gas detector, a flammable gas detector, a humidity detector, and the like have been put into practical use as gas detectors for detecting the presence or concentration of gas in the atmosphere.

Many of these use a metal oxide sensitizer having a characteristic that its electric resistance changes when it comes into contact with gas.

In this type of gas detector, a hybrid technique is often used in which a metal oxide sensor, its electrode and its lead wire are thick-film printed on a substrate made of an insulating material.

[Problems to be Solved by the Invention] However, as described above, in the gas detector formed by thick film printing, the metal oxide sensor is exposed to the gas to be measured or is covered with a thin protective layer. Only there. for that reason,
The temperature of the metal oxide sensitive body itself changes depending on the temperature of the gas to be measured.

By the way, the metal oxide sensitive material has temperature dependence. Therefore, the output of the gas detector also changes due to the temperature change of the measured gas. For example, when measuring O _{2 in} the exhaust gas of an internal combustion engine, stable measurement is difficult because the exhaust gas temperature changes drastically.

Further, there is a problem that it takes time to manufacture the above-described conventional gas detector, and further, there are problems of thermal shock resistance and durability.

[Means for Solving Problems] The present invention employs the following means in order to solve the above problems.

That is, the gist of the present invention is to provide a gas detector using a metal oxide sensitizer whose electric resistance changes depending on the ambient gas component and / or its concentration, in a heat-resistant space having a sealed space from the surroundings. An electrically insulating ceramic box body, a pair of heat-resistant metal electrodes provided in the box body by coating one end side thereof on the wall surface of the box body forming the space, and provided in the box body A gas for communicating the space with the surroundings, and the metal oxide sensitizer that is injected into the space from the communication hole and is then fired to come into contact with the pair of electrodes. On the detector.

Here, as the metal oxide sensitive material, various materials conventionally used as metal oxide sensitive materials can be used. For example, in the case of an oxygen gas detector, SnO ₂ , TiO ₂ , Nb ₂ O ₅ , V ₂
Oxides of transition metal elements such as O ₅ , Cr ₂ O ₃ , CoO, and NiO can be used. ZnO, Fe ₂ O ₃ or the like can be used as a combustible gas detector. If it is a humidity detector, Cr ₂ O ₃ , Fe ₂ O ₃ , Mg
_{Cr 2 O 4, Fe 2 O} 3 -K 2 O or the like can be used.

In addition, for the purpose of reducing the temperature fluctuation of the metal oxide sensor at the time of measurement, or for the purpose of activating the metal oxide sensor by evaporating the water on the surface of the metal oxide sensor in the humidity detector. The body may be provided near the metal oxide sensitive body. That is, it is possible to employ a heating element which is arranged near the metal oxide sensitive body and which is embedded entirely or largely in the box body.

Further, a part of this heating element and one electrode of the metal oxide sensitive body may be connected to serve as a power source for the metal oxide sensitive body, thereby simplifying the measuring circuit.

[Operation] In the gas detector of the present invention, a box sealed from the surroundings is used as a container for housing the metal oxide sensitive body.
Moreover, this box is made of heat-resistant electrically insulating ceramic. Therefore, the boxes are firmly joined together without any gap, and have excellent thermal shock resistance and durability.

In addition, since the metal oxide sensitive body of the present invention is fired after being injected into the space of such a ceramic box through the communication hole, the material of the metal oxide sensitive body is not leaked during manufacturing. Since the metal oxide sensitizer can be surely arranged at a desired place without adhesion or adhesion, the manufacturing thereof is simplified.

Further, the communication hole of the box is not only used for injecting the metal oxide sensitive body, but also plays a role of bringing the metal oxide sensitive body into contact with the surrounding gas to be measured at the time of measurement.

Further, the metal oxide sensitizer is fired after being injected into the space hermetically sealed from the surroundings, but the walls forming this space are dense and thick, and thus have a disconnection effect. Further, since the metal oxide sensitive body is in contact with the surrounding measured gas only through the continuous holes, the area of the metal oxide sensitive body exposed to the surrounding measured gas is smaller than that of the conventional gas metal oxide sensitive body. . Therefore, the output of the gas detector of the present invention is unlikely to be affected by the temperature change of the ambient measured gas.

[Embodiment] A first embodiment of the present invention will be described with reference to the perspective view of FIG. 1 and the exploded perspective view of FIG. Note that the scale of each drawing is different for the sake of explanation.

The present embodiment is an oxygen gas detector 20 using TiO ₂ as the metal oxide sensitive body 10.

As shown in FIG. 1, the oxygen gas detector 20 is a box body 30 made of alumina as a main component and having a width of 4 mm, a length of 35 mm, and a thickness of 1.5 mm.
And width 2 mm × length 5 mm × thickness 50 μ provided inside the box 30
m space 40 and two holes 50a that communicate the space 40 with the surroundings,
50b, and a metal oxide sensitizer 10 made of TiO ₂ which is baked after being injected into the space through the holes 50a and 50b.

Further, as shown in FIG. 2, the oxygen gas detector 20 has a heating element 60 around the metal oxide sensitive body 10 and the inner electrodes of the pair of electrodes 70a, 70b of the metal oxide sensitive body 10. 70a is connected in the middle of the heating element 60.

For convenience of explanation, in FIG. 1, the heating element 60 and the electrodes 70a, 70b are shown.
And terminals 80a connected to these through through holes,
80b and 80c are omitted.

The oxygen gas detector 20 is manufactured as follows.

92 wt% alumina, 3 wt% magnesia, and 5 wt% sintering aid (silica, calcia, etc.) were mixed in a pot mill for 20 hours. Then, the mixture was mixed with polyvinyl butyral 12 wt% and dibutyl phthalate 4 wt% as an organic binder.
Was added, and methyl ethyl ketone, toluene and the like were added as a solvent. Further, the mixture was mixed in a pot mill for 15 hours, and a doctor blade method was used to prepare an alumina sheet having a thickness of 0.8 mm for forming the box body 30 of the oxygen gas detector 20.

Next, platinum black and sponge-like platinum were blended in a ratio of 2: 1 and 10% by weight of the raw material mixture of the alumina sheet used above was added, and a solvent such as butylcarbidol and Ethocel was added, It was used as an electrode paste.

The alumina sheet was cut into an appropriate size to form box body forming members 90a and 90b.

22μ of the electrode paste on the box forming member 90a
Screen printing with a thickness of m, heating element 60, electrodes 70a, 70
b formed.

The space 40 is formed on the box-forming member 90a on which the electrodes and the like are printed by screen-printing the material mixture of the alumina sheet prepared above to about 70 μm.
Spacer 100 was formed.

Next, 1.0 mmφ through holes 50a and 50b were opened in the box body forming member 90b at positions corresponding to the spaces 40, and then the box body forming member 90b was laminated and pressure-bonded to the spacer 100.

After drying the laminate, it was heated to 300 ° C. to remove the organic binder and the like. Further, it was baked at 1520 ° C. for 2 hours to form a box body 30.

Next, impregnate titania with chloroplatinic acid (about 0.7 mol
%), Dried at 200 ° C., and then calcined in a nitrogen atmosphere at 1300 ° C. To this titania, 2 mol% of platinum black and 5 wt% of an organic binder such as polyvinyl butyral were added, and butyl carbidol and the like as a solvent were mixed in a pot mill to obtain a titania paste.

The titania paste was poured from one hole 50a of the box body 30 through the other hole 50b until the titania paste came out. The box 30 filled with this titania paste is 1200 ° C.
An oxygen gas detector 20 was obtained by firing in the atmosphere. By this firing, the titania paste became a porous sintered body.

In order to investigate the effect of the oxygen gas detector 20 of this embodiment,
An oxygen gas detector in which the metal oxide sensor is directly exposed to the gas to be measured was manufactured as a comparative example. This comparative example was manufactured by directly applying the titania paste on the above-mentioned box body forming member 90a.

Experiment 1 Regarding the relationship between the measured gas temperature and the output of the gas detector,
Examined.

In this example and the comparative example, 12 V is applied between the heating element terminals.
Next, a load resistance was provided between the metal oxide sensitive body terminal and the earth side terminal of the heating element terminal, and the voltage generated in the load resistance was used as the output of the oxygen gas detector. The load resistance was 50 KΩ in this example and 20 KΩ in the comparative example. The gas to be measured is the exhaust gas of the internal combustion engine, and the air-fuel ratios λ≈0.9 and λ≈1.1
It was measured at.

Results are shown in FIG. In the figure, the circles and the solid lines represent the present embodiment, and the circles and the broken lines represent the comparative example.

As is apparent from FIG. 3, the output of this example is not affected by the exhaust gas temperature as compared with the comparative example. Especially in the rich range (λ
.Apprxeq.0.9), this example shows an excellent effect.

It is considered that this is because the wall of the box body 30 is thick and dense, so that the heat insulating effect is large.

Experiment 2 The power consumption of the heating element required to keep the metal oxide sensitive body at a constant temperature was examined.

In this example and the comparative example, a voltage is applied between the heating element terminals.
Then, the temperature of the metal oxide sensitive body and the current flowing between the terminals of the heating element are measured. The power consumption of the heating element was calculated from the above voltage and current. The gas to be measured is the exhaust gas of the propane gas burner. The measured gas temperature was measured at 350 ° C and 900 ° C.

Results are shown in FIG. In the figure, the circles and the solid lines represent the present embodiment, and the circles and the broken lines represent the comparative example. In addition, in the measurement, both the present example and the comparative example are installed in the housing. Therefore, even if the electric power of the heating element is 0, the temperature of the metal oxide sensitive body does not become the same as the temperature of the gas to be measured.

As is clear from FIG. 4, the temperature of the metal oxide sensitizer of this example reaches a predetermined temperature with less power consumption than that of the comparative example. Particularly, in the low temperature range (the measured gas temperature is 350 ° C.), the present example shows an excellent effect.

This is probably because the box 30 has a large heat insulating effect as in Experiment 1.

A second embodiment of the present invention will be described with reference to the perspective view of FIG. 5 and the exploded perspective view of FIG. Note that the scale of each drawing is different for the sake of explanation.

The present embodiment is an oxygen gas detector 120 that uses TiO ₂ as the metal oxide sensor 110.

As shown in FIG. 5, the oxygen gas detector 120 is a box body 13 made of alumina as a main component and having a width of 4 mm, a length of 35 mm, and a thickness of 1.5 mm.
0, a T-shaped space 140 provided inside the box 130, and three holes 150a, 150b, 150c that communicate the space 140 with the surroundings,
And a metal oxide sensitizer body 110 made of TiO ₂ which is fired after being injected into the space.

In addition, the oxygen gas detector 120, as shown in FIG.
A pair of electrodes 170a, 170 of the heating element 160 and the metal oxide sensitive element 110.
have b.

For convenience of explanation, in FIG. 5, the heating element 160, the electrodes 170a, 17
0b is omitted.

The oxygen gas detector 120 is manufactured as follows.

An alumina sheet forming the box body 130 of the oxygen gas detector 120 was manufactured by the same method as in the first embodiment.

Next, the electrode paste was prepared in the same manner as in the first embodiment.

The alumina sheet was cut into an appropriate size to form box forming members 190a and 190b.

22μ of the electrode paste on the box-forming member 190a
screen printing with a thickness of m to form the heating element 160,
Similarly, the electrode paste is applied to the box forming member 190b.
The electrodes 70a and 70b were formed by screen printing with a thickness of μm.

In the same manner as in the first embodiment, three spacers 200a of about 70 μm that form the space 140 are formed on the box forming member 190a,
200b and 200c were formed.

Next, the box forming member 190b was laminated and pressure-bonded to the spacer 200.

Hereinafter, in the same manner as in the first embodiment, the titania paste was prepared, and the titania paste was injected into the space 140 of the box 130 and fired in the atmosphere at 1200 ° C. to obtain an oxygen gas detector.
Got 120.

This example also had the same effect as the first example.

[Advantages of the Invention] As described in detail above, in the gas detector of the present invention, a box sealed from the surroundings is used as a container for housing the metal oxide responsive body. It is composed of a heat-resistant electrically insulating ceramic. Therefore, the boxes are firmly joined together without any gaps, and have excellent thermal shock resistance and durability, so that failure or the like does not easily occur even when used in a harsh environment.

Further, the metal oxide sensitive body of the present invention is fired after being injected into the space of such a ceramic box through the communication hole. Therefore, at the time of manufacturing, the material of the metal oxide sensitizer does not leak or adhere to other parts, and moreover, the metal oxide sensitizer can be surely arranged at a desired position, so that the manufacturing is easy.

Moreover, the communication hole of the box is not only used for injecting the metal oxide sensitive body, but also plays a role of bringing the metal oxide sensitive body and the surrounding gas to be measured into contact during measurement.

Further, the metal oxide sensitive body of the present invention is baked after being injected into the space hermetically sealed from the surroundings, and is in contact with the surrounding measured gas only through the communication holes. Therefore, the output of the gas detector of the present invention is unlikely to be affected by the temperature change of the ambient measured gas.

Therefore, even in a place where the temperature of the surrounding measured gas changes greatly, the gas component and concentration of the surrounding measured gas can be correctly measured.

Further, when the heating element is provided, the temperature of the metal oxide sensitive element can be maintained at a predetermined temperature with less power consumption, which contributes to energy saving and also extends the life of the heating element.

[Brief description of drawings]

FIG. 1 is a perspective view of a first embodiment of the present invention, FIG. 2 is an exploded perspective view for explaining its manufacture, and FIG. 3 is a diagram showing the relationship between the measured gas temperature and the output of a gas detector. FIG. 4 is a diagram showing the relationship between the power consumption of the heating element required to keep the metal oxide sensitive body at a constant temperature and the temperature of the gas to be measured, and FIG. 5 is a diagram showing the second embodiment of the present invention. FIG. 6 is an exploded perspective view for explaining the manufacture thereof. 10, 110 …… Metal oxide sensitizer 20, 120 …… Oxygen gas detector 30, 130 …… Box 40, 140 …… Space 50a, 50b, 50c, 150a, 150b, 150c …… Hole 60, 160… ... Heating elements 70a, 70b, 170a, 170b ... Electrodes 90a, 90b, 190a, 190b ... Box body forming members 100, 200a, 200b, 200c ... Spacers

Claims (2)

[Claims] 1. A gas detector using a metal oxide sensitizer whose electric resistance changes according to the ambient gas component and / or its concentration, in a heat-resistant electrical insulating property having a space sealed from the surroundings. A ceramic box body, a pair of heat-resistant metal electrodes provided in the box body by coating one end side thereof on a wall surface of the box body forming the space, and a pair of heat-resistant metal electrodes provided in the box body. A gas detector comprising: a communication hole that communicates the space with the surroundings; and the metal oxide sensitizer that is injected into the space from the communication hole and then baked to contact the pair of electrodes. 2. The gas detector according to claim 1, further comprising a heating element which is disposed in the vicinity of the metal oxide sensitizer and which is entirely or largely embedded in the box body.