JPS59195148A - Gas detecting element - Google Patents

Abstract

PURPOSE:To obtain a gas detecting element having stable sensitivity and responsiveness without any variation, etc. in output due to the combustion heat in a gas to be detected, by depositing specified elements such as Bi, P on the surface of a sintered body of metal oxide semiconductor to suppress the combustion activity of the surface layer. CONSTITUTION:The parts of metal oxide such as SnO2, ZnO is screen-printed on the surface of an alumina substrate 1 provided with a platinium heater electrode 2 at the rear surface and a platinum electrode 3 at the surface respectively, dried and sintered to form the metal oxide semiconductor 4. Next, 0.01mol% aqueous solution of H3PO4, Pb(NO3)2, TiCl3, Bi(NO3)3.5H2O is impregnated into the sintered body, and said body is dried, then thermally decomposed for 1hr at 600 deg.C to deposit the material for obstructing the combustion of the detecting gas at the surface of the semiconductor 4. Thus, the output variation due to the combustion heat of the combustible gas to be tested such as H2, C2H5O and the error generation due to the decrease of the concn. of the gas attaining to the inner part of the sintered layer 4 due to the combustion are prevented and the stable sensitivity and the responsiveness are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas sensing element in which the combustion activity of a metal oxide semiconductor is suppressed.

Figure 1 is a side sectional view showing an example of a conventional waste detection element.
1 is an alumina substrate, 2 is a PT film heater 3 is a PT electrode,
4 is 5no2. It is a metal oxide semiconductor such as Fe2O3+ ZnO.

This gas detection element using 5VC1 gold IA' (II compound semiconductor 4) is capable of reacting to combustible gases by using metal oxide semiconductors such as 5n02r Fe2O3, ZnO, etc., which themselves have activity as oxidation catalysts. When in contact, a combustion reaction occurs on the surface of the gas sensing element.For this reason, at the gas sensing element pressure, the response characteristics of the element sensitivity will be abnormal in the gas at a certain concentration. In a thick-film sintered gas sensing element using ZnO, as shown in Figure 2, the temperature T = 400 in a constant concentration of 0.1% ethanol.
When operated at 'C;, the output in this case attenuates over time and is not stable.

Moreover, as shown in FIG. 3, metal oxide semiconductor 4VcSn
When a gas sensing element having a thick film element mainly composed of O□ is operated at approximately 350°C, H2(#!.

Overshoot appears in the response characteristics to detected gases such as 0.1%) and ethanol. Such a characteristic has disadvantages such as being unfavorable in terms of circuit design such as alarm level setting of a waste alarm device.

The present invention is intended to solve the above-mentioned drawbacks, and the abnormality in the response characteristics of the detected gas is caused by the combustion consumption of the liquid detected gas on the surface layer of the sintered body made of metal oxide semiconductor.
It was discovered that the actual gas concentration reaching the inside of the sintered layer decreased from C, and that this was caused by the fact that the temperature of the scum-sensitive area increased due to the heat of combustion reaction, and the gas sensitivity changed over time. , which suppresses the combustion activity of the sintered layer and reduces the stabilization of gas sensitivity, and it is possible to suppress combustion in the surface layer by crushing the active points by attaching a combustion-inactive substance to the surface. This is what I found. This invention will be explained below.

In an embodiment of the present invention, a sintered body of a metal oxide semiconductor is impregnated with a dilute aqueous solution of at least one salt among VcBi, p, pb, 'ri, si, AI, etc., and then heat-treated after drying or A combustion inhibiting substance is supported on the surface of a metal oxide semiconductor by chemical vapor deposition using an organometallic compound of metal.

Next, as a specific example of the above, 99.99 '3'o
of tin metal is dissolved in nitric acid, and aqueous ammonia is added dropwise to obtain a 67" LL precipitate, which is washed with water, dried, and calcined to obtain tin oxide powder. This powder is crushed, and 1 liter of water is added. The paste was screen-printed on an alumina substrate with a heater electrode on the PT film (2), and after drying, it was sintered at 800°C for 2 hours. H3P 04 , P b (NO3)2 , T i
C13B i (NO3)3.5 H20 etc. 0.0
1mo1% aqueous solution! After impregnation and drying, thermal decomposition is performed at 600°C for 1 hour.

FIG. 4 shows the gas-sensitive response characteristics of the gas sensing element thus fabricated. In this figure, the gas sensing element is H2
It takes about 1 minute for the output to stabilize in 01% gas, but after that it becomes very stable.

As explained above, 1. Thus, the present invention (a provision for suppressing combustion activity in a sintered body of a metal oxide semiconductor of a soil, gas detection element,
Since at least one of Bi+P, Pb+Ti+Sit AI is supported on the surface, the combustion efficiency in the surface layer is improved.
This has the advantage of providing a gas sensing probe that can be used to reduce the temperature of the gas, has no change in output in the gas to be detected, and has stable sensitivity response characteristics.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view showing an example of a conventional gas detection element, Figs. 2 and 3 are characteristic diagrams of the conventional gas detection element when operated in a gas to be detected, and Fig. 4 is the invention according to the present invention. This is a characteristic diagram when the gas detection element of the embodiment is operated in a gas to be detected. In the figure, 1 is an alumina substrate, 2 is a PT film, and a heater 3 is a Pt film.
The electrode 4 is a metal oxide semiconductor. ) Figure 1 Figure 2 9 hours (min) Figure 3 Figure 4 1 hour (min) Procedural amendment (voluntary) 113+1 Mr. Commissioner of the Japan Patent Office 1, Indication of the case Patent application 1982 -0883'913 No. 2,
Title of the invention Gas detection element 3, relationship to the case of the person making the amendment Patent applicant address 2-5-4 Mitsuya Naka, Yodoyo-ku, Osaka, Osaka Name Shin-Cosmos Electric Co., Ltd. Representative Osamu Kasahara 4th generation Mr. Kobayashi Chigon'1 Office, 6th floor, Matsu Building, 31-16 Sakurato-cho, Shibuya-ku, Tokyo, 150 Japan Telephone: 03 (496) 1256-5, Detailed explanation of the invention in the specification to be amended Column 6, Contents of amendment (1) Changed “in itself” from line 19 on page 1 of the specification to “in itself”
and correct it. (2) Similarly, on page 3, line 13, change “combustion inhibitors” to “
Corrected to ``trace amounts of combustion inhibitors''. that's all

Claims (1)

[Claims] In a gas sensing element using a sintered body of a metal oxide semiconductor, at least one of Bi, P, Pb, Ti, Si, and AI is added to the sintered body to suppress combustion activity of the metal oxide semiconductor. A gas detection element characterized in that it is carried on the surface of the body.