JPS61149856A - Gas detecting element - Google Patents

Abstract

PURPOSE:To suppress sensitivity to miescellenous gases by dispersing at least one kind among the pulverous particles of the compound oxide of Cu, Co, Mn, Ni and Fe and alumina into a sintered layer of a metallic oxide semiconductor. CONSTITUTION:An alumina base plate 1 is provided with a platinum film heater 2 on the bottom surface and is coated thereon with a heater protective film 3. A platinum membrane electrode 4 is provided stop the plate 1 and is coated thereon with an SnO2 sintered layer 5. The layer 5 is formed by dispersing the pulverous particles 6 of the copper aluminate which is the compound oxide formed by charging active gamma alumina into an aq. copper nitrate soln. and resting the same overnight to impregnate and adsorb the gamma alumina to the powder of the metallic oxide semiconductor, then filtering the excess liquid and calcining and molding the filtrate after drying to form the paste of said aluminate and molding and sintering the paste.

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]

A variety of gas detection elements have been proposed in the past, but they generally do not have selectivity for miscellaneous gases such as alcohol, so miscellaneous gases from alcohol cans and the like are determined to be gas leaks. Moreover, there is a tendency for the sensitivity to increase over time, and the rate of increase in sensitivity over time is particularly large for miscellaneous gases, which causes false alarms from household gas leak alarm devices.

[Problem that the invention seeks to solve]

As a countermeasure against such miscellaneous gases, it has been proposed to apply a mixture of Mn 10g and alumina or Co304-α-AI, O, to the surface of the gas detection element as a filter, but these are not suitable for high temperature and high humidity. There is a tendency for sensitivity to alcohol to increase over time in a room where electricity is applied for a long period of time or when electricity is applied for a long period of time. This is thought to be due to the fact that Mn103, Co, Go, and powders tend to sink, so that the activity as an oxidation catalyst gradually decreases, and the filter effect for oxidizing and removing furfur decreases.

This invention suppresses the sensitivity to miscellaneous gases such as flucoal mentioned above, and also improves its characteristics in high humidity and reducing atmospheres.
The purpose is to maintain the stability for a long period of time even under severe conditions such as 4N toxic atmosphere.

[Means for solving problems]

In the gas detection element of the present invention, in order to remove miscellaneous gases, the composite oxide of the present invention, such as steel aluminate and nickel aluminate, is made of activated alumina and Cu.

When impregnated with a dilute aqueous solution of salts such as Co, Mn, Ni + Fe, etc. and fired, alumina and these metal ions combine to easily form a heat-resistant and durable adsorption oxidation compound such as CuAl204. , α-A110. This is based on the finding that such a combination does not occur in the case of . For example, Cub, CO3O4+ Ne.

is a black oxide, but it is a composite oxide formed by combining with activated alumina, which is surrounded by CuAl204. CoAl2
O4*NiAl2O, has a spinel crystal structure and exhibits a light evening color.

Traditionally, M n! There have been attempts to coat elements with a mixture of OB and alumina. CoBQ4-α-A was also impregnated with an aqueous solution of α-At, Q, K cobalt nitrate and fired.
I, o.

It has also been proposed to obtain and use α-AI20B, but in this case, α-AI20B has the most chemically stable structure among aluminas and does not react with Co.

Cobalt and aluminum cannot exist in a mixture as their respective oxides. In this case, black Co1
04 color.

In addition, the content of Cu, Go, etc. is 5 to 50 wt% as oxides of these metals, compared to alumina in conventional examples.
However, in this invention, only metal ions adsorbed on the surface of activated alumina are used, and if converted to conventional methods, it is effective even at a concentration of 5% or less, which is outside the realm of conventional wisdom. The focus was on

[Effect]

Aluminate, 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℃), 5
There is no decrease in activity due to K, such as sinks. Also,
Even when placed in a reducing atmosphere, it is much more stable and less susceptible to reduction than single oxides. Moreover, it was found to have moderate oxidation activity. That is, (1) The combustion activity for miscellaneous gases such as alcohol is very high, but that for methane and methane is small.

By dispersing these composite oxides in the sintered layer of metal oxide semiconductor, it is possible to burn off the miscellaneous gases and suppress the sensitivity of the device to miscellaneous gases.

Battered aluminate is extremely stable both thermally and chemically, providing durability that cannot 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 atmosphere, and the oxide is reduced in a reducing atmosphere such as hydrogen. However, in these respects, this composite oxide is far more stable than a single oxide.

O11) Since 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 SO7 cannot penetrate into the pores, and the catalyst inside the pores cannot penetrate. Activity never deteriorates. Therefore, the gas sensing element of the present invention has excellent durability even in an atmosphere where toxic gases coexist.

[Example] Active gamma alumina (specific surface area 100 m”/g
) was put into a [0.1 mol/l nitric acid aqueous solution, -
After being left to soak day and night for 4 hours of impregnation and absorption, the after-cut liquid is filtered, dried, and then fired at 900° C. for 2 hours. In this case, the copper content was 5% or less based on gamma alumina in terms of fermented steel, although it depended on the adsorption capacity of gamma alumina. Other metal salts are prepared in the same manner.

Figure 1 shows a gas sensing element manufactured by dispersing these composite oxidized iron particles in metal oxide semiconductor powder, molding it, and sintering it at 700°C for 1 hour. is alumina base & (3X 1.5 4 is provided, and the top thereof is covered with a 5nOz sintered layer 5, and the SnO □ sintered layer 5 & fIL86 of copper aluminate, which is a sintered resin formed by the above-mentioned procedure on the metal oxide semiconductor powder. is dispersed, made into a paste, molded, and sintered to ferment the thick film type metal oxide semiconductor gas sensing element of the present invention.

Figure 2 shows an example when applied to an M-line semiconductor device.
7 is a coiled platinum electrode/heater, and 5 is a 5N02 sintered layer formed to cover the coil portion of the platinum electrode/heater 1. Fine particles 6 of fulinate were dispersed in this 5n02 sintered layer 5 according to the above-described procedure, and then sintered, molded, and sintered.

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

Figure 3 shows the concentration dependence characteristics of the scum sensitivity of a thick-film type gas sensing element when fine particles 6 of copper aluminate according to the present invention are dispersed in a 5N (Jt-sintered IB layer). It can be seen that the ethanol sensitivity is significantly lower than that of the conventional element. Note that the vertical axis in this figure is the rate of change in contactance indicating the gas sensitivity of the gas detection element, 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 highly humid atmosphere, with 0.1% H and 50°C.

After being sealed in a 95% high humidity environment with poor electrical current for 30 days, the temperature was returned to normal humidity and the degree of resistance as a signal indicator was measured. Compared to the initial value, Mn2 o, IC
In the case of coating with a mixture of a single oxide of ub, Co3O4 and alumina, it is suggested that the coating becomes extremely sensitive to ethanol and hydrogen, leading to false alarms. The aluminate of this invention has good durability. Table 2 is 8
These are the results of an encapsulation test for 10 days in a toxic atmosphere of 0.020.5 ppm. In the same way, each aluminate was compared with the initial value and did not change much, indicating good toxicity resistance.

〔Effect of the invention〕

As explained above, the present invention provides a metal oxide semiconductor gas sensing element in which Cu+ Coo Mn+ N++
Since at least one type of fine particles of composite oxide of Fe and alumina is dispersed within the sintered layer of metal oxide semiconductor, sensitivity to miscellaneous gases such as alcohol can be suppressed, and the characteristics described in 7. Even in a reducing atmosphere with high crystal humidity, a toxic atmosphere, etc., it has the effect of being able to maintain a woman's feet for a long period of time.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a thick film type gas sensing element showing one embodiment of the present invention, Fig. 2 is a sectional view of a hot rope type gas sensing element showing another embodiment of the invention, and Fig. Figure #4, which is a gas acidity dependence characteristic diagram of the gas detection element according to the present invention, is a gas intensity dependence characteristic diagram of a conventional gas detection element. In the figure, 1 is an alumina substrate, 2 is a platinum film heater, 3 is a heater retention film, 4 is a platinum film electrode, 5 is a 5n (J□ sintered layer, 6
1 is a fine particle of composite oxide, 7 is a coiled platinum electrode and heater.

Claims (1)

[Claims] In the metal oxide semiconductor gas sensing element, Cu, Co,
A gas sensing element characterized in that at least one kind of fine particles of a composite oxide of Mn, Ni, Fe, and alumina is dispersed in a sintered layer of a metal oxide semiconductor.