JPS6165151A - gas detection element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas detection element for detecting combustion exhaust gas, gas leakage, and the like.

[Conventional technology]

Although various gas detection elements have been proposed in the past, they generally do not have selectivity for miscellaneous gases such as alcohol, and therefore miscellaneous gases from alcohol cans are determined to be gas leaks. Moreover, the sensitivity tends to increase over time, making it especially effective against miscellaneous gases/liJ! Due to the high sensitivity rate, it causes false alarms for household gas leak alarms.

[Problem that the invention seeks to solve]

As a countermeasure against such miscellaneous gases, a mixture of Mn2O3 and alumina, or Co3o, -α-A120. It has been proposed to coat the surface of the gas detection element as a filter, but these tend to become more sensitive to alcohol over time when energized in high temperature, high humidity, or long-term energization. This is thought to be due to the fact that the Mn2O3'PCo304 powder is easy to sink, so its activity as an oxidation catalyst gradually decreases, and the filter effect for oxidizing and removing alcohol decreases.

This invention suppresses the sensitivity to miscellaneous gases such as alcohol mentioned above, and improves its characteristics in high humidity and reducing atmospheres.
The purpose is to maintain stability for a long period of time even under harsh conditions such as toxic atmospheres.

[Means for solving problems]

This invention uses copper full S as a removal layer for miscellaneous gases.
When full ξ such as nickel fulminate, U with other metals
The outer layer of the 14-metal oxide gas detection element is coated with the oxide as a single porous layer.

The composite oxide of this invention includes activated alumina and Cu.

When impregnated with a dilute aqueous solution of salts such as Co, Mn + Ni + Fe, and fired, alumina and these metal ions combine to form heat-resistant and durable composite oxides such as Cu 1□04. easy to form, α-A I 20 B
This is based on the finding that such a combination does not occur in the case of . For example, CLIO, Co3O4゜N
iO is a black oxide, but it is a composite oxide formed by combining with activated alumina, such as CuAl□04゜Co.
Al2O41NiAhO, has a spinel crystal structure and exhibits a pale blue color.

Previous attempts have been made to mix M n 203 and alumina to coat devices. In addition, α-AI 203 was impregnated with an aqueous solution of cobalt nitrate and fired to form Co304-α~Al
ρ.

It has also been proposed to obtain and use α-A120s, but in this case, α-A120s has the most chemically stable structure among aluminas and does not react with CO, and cobalt and aluminum are As a matter of fact, it is mixed, and it is only in the west. In this case, it exhibits a black color as Co3O4.

In addition, in conventional examples, the content of Cu, Go, etc. is 5 to 5% by weight as oxides of these metals relative to alumina.
However, in this invention, only metal ions adsorbed on the surface of activated alumina are used, and in terms of conventional methods, the concentration of 7 is effective even at 5% or less, which is contrary to conventional wisdom. It focuses on the area.

[Effect]

Fulminate, which is a composite oxide with alumina, is very thermally stable and can be used within the operating temperature range of gas sensing elements (150
~500°C), there is no reduction in activity due to sinks, etc., such as those caused by single positional compounds of copper or cobalt. Furthermore, even when placed in a reducing atmosphere, it is much more stable and less likely to be reduced than a single oxide. Moreover, it was found that it has moderate oxidation activity. That is, (1) The combustion activity for miscellaneous gases such as alcohol is very high, but the combustion activity for methane and butane is small.

By coating the outer layer of the metal oxide semiconductor gas-sparing element with these composite oxides as a porous layer, the miscellaneous gases can be burned off and the sensitivity of the element to miscellaneous gases can be suppressed.

(it) Fulminate was extremely stable both thermally and chemically, and provided durability that could not be obtained with single oxides. In other words, in the case of a single oxide, the activity of the oxide particles tends to decrease due to the presence of water vapor in a high-temperature, high-humidity atmosphere.
First, in a reducing atmosphere such as hydrogen, the properties change and sinks are likely to occur as the oxide is reduced, but in these respects, this composite oxide is an order of magnitude more stable than a single oxide. .

(i+il) Because a composite oxide is formed on the inner surface of the pores of activated alumina and exhibits activity as an oxidation catalyst, toxic substances such as organic silicone and 802 are durable even when exposed to an atmosphere where the pore-toxic gas coexists. I'm very particular about my gender.

〔Example〕

Active gamma alumina (specific surface area 1 o m”/g)
into a copper nitrate aqueous solution with a concentration of 0.1 mol/l, -
After being allowed to stand day and night for impregnation and adsorption, the excess liquid is filtered, dried and then baked at 900°C for 2 hours. Although the content of steel in this case depends on the adsorption capacity of gamma alumina, it was 5% or less of gamma alumina in terms of copper oxide. Other metal salts are prepared in the same manner.

This powder was soaked in water with a small amount of alumina binder and spread on the outer layer of a metal oxide semiconductor gas sensing element.
Sintered at °C for 1 hour. The gas produced in this way
The first figure shows the total pressure of the sensing element.

In Figure 1, 1 is Alumina Motoki (3X1.5X0.4 questions)
A platinum film heater 2 is provided on the lower surface, and a heater protective film 3 is placed on top of the platinum film heater 2 . A platinum film electrode 4 is provided on the upper surface of the alumina base 1, and is covered with a SnO□ sintered layer 5 to constitute a thick film type metal oxide semiconductor gas sensing element. Then, a porous layer 6 of copper fulminate, which is a composite oxide, formed by the above-mentioned procedure is provided on the outer layer of this gold:% t'& compound half-quadruple gas sensing element, and the gas sensing element of the present invention is obtained. configured.

Figure 2 shows an example when applied to a hot wire type semiconductor device.
T is a fill-shaped platinum electrode/heater 5. The coil part of the platinum electrode/heater T is covered with a sintered layer of S.sub.nO. This 5n02! A porous layer 6 of aluminate was applied to the outside of the eyebrows 5 using the above-mentioned procedure and pressure.

Note that, as a method for producing a composite oxide of Cu, Co+Mn, N+, Fe and alumina, it goes without saying that ordinary catalyst production methods such as coprecipitation method and competitive adsorption method can be applied.

FIG. 3 shows the once-dependent characteristic of the gas sensitivity of a thick film type gas sensing element in which the copper fluorite coating according to the present invention is applied. It can be seen that the ethanol sensitivity is significantly suppressed when compared with the conventional uncoated element shown in FIG. Note that the vertical axis in this figure represents the conductance change rate indicated by the gas sensitivity of the gas detection element, where Go is the contactance of the element in the atmosphere and Gg is the contactance in the gas.

Table 1 shows the durability of the element when placed in a high-temperature, high-humidity atmosphere, with 0.1% H and 50°C.

After 30 days of hearing-impaired samples were sealed in 95% high humidity, the humidity was returned to normal, and the alarm concentration as a W binding device was measured. Compared to the initial value, M n203 *Cub
In an example in which a mixture of a single oxide of , Co5t, and alumina is coated, it becomes extremely sensitive to ethanol dihydrogen, leading to false alarms. The German fulminate of this invention has good durability. Table 2 shows SO2
These are the results of a 10-day encapsulation test in a 0.5 ppm toxic atmosphere. Similarly, each of the residual aluminates did not change much compared to the initial value, indicating good toxicity resistance.

〔Effect of the invention〕

As explained above, this invention includes Cu r Cor Mn + N in the outer layer of a metal oxide semiconductor gas sensing element.
Since it is coated with a porous negative layer made of at least -11 of the composite oxide of +rFe and alumina, it is possible to suppress the sensitivity to miscellaneous gases such as alcohol, and furthermore, its characteristics can be reduced to high temperature and high humidity. It has the effect of being able to be stably maintained for a long period of time even under harsh conditions such as in a toxic atmosphere.

[Brief explanation of drawings]

Figure 1 shows the advantage of this invention: 2i! ! Figure 2 is a sectional view of a hot-wire type gas detection element showing another embodiment of the present invention, and Figure 3 is a cross-sectional view of a gas sensing element according to the present invention. Gas concentration dependence characteristic diagram of the sensing element, 4th
The figure is a diagram showing the gas a degree 1 temperature characteristic of a conventional gas detection element. In the figure, 1 is an alumina substrate, 2 is a platinum film heater, 3 is a heater protective film, 4 is a platinum film electrode, and 5 is S n O! sintered layer,
6 is a porous oxide layer, and 7 is a coiled platinum + single pole/heater.

Claims (1)

[Claims] The outer layer of the metal oxide semiconductor gas sensing element contains Cu, Co,
A gas sensing element coated with a porous layer made of at least one of composite oxides of Mn, Ni, and Fe with alumina.