JPS59142445A - Durably stable gas detecting element - Google Patents

Abstract

PURPOSE:To improve the durable stability and to reduce the change of electric conductivity especially in a high-humidity atmosphere in a sintered SnO2 type combustible gas detecting element by incorporating an oxide of lanthanoid and an oxide of a group IV-a element in the periodic table into SnO2 in a specified ratio. CONSTITUTION:Oxides of lanthanoid such as La2O3, CeO2 or Sm2O3 and oxides of Ti, Hf, Zr and Th are incorporated into SnO2 respectively within the range of 0.01-20mol%. The paste crushed and mixed in the presence of water is coated between a couple of platinum electrodes provided on the surface of an Al2O3 substrate or the like provided with a platinum heating body on the rear surface. Afte drying, the paste is sintered at 800 deg.C for 2hr. Otherwise, the hydroxides coprecipitated from a mixed soln. contg. water-soluble compds. of tin, lanthanoid, Ti and Zr in a respective specified ratio are prepared and said hydroxides are made into paste after drying, and the paste is sintered in the same way as the above-mentioned method. In this way, the durable gas detecting element to be heated always at 300-450 deg.C even in a high-humidity atmosphere can be obtained, since changes in the minute structure of the sintered semiconductor surface are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a time-stable gas sensing element that is an improved Sn 02 sintered gas sensing element and has improved stability over time.

Conventionally, CH4, LPG, city gas, H2.

As elements for detecting combustible gases such as CO, catalytic combustion type detection elements or semiconductor type detection elements using metal oxides such as 5n02 and Fe702 are used. Generally, a 5n02 semiconductor type sensing element has a pair of electrodes and 5n02 as a main component between the pair of electrodes, and a conductivity improver such as 5nC12.

Insulating heat-resistant materials such as 5t02, Al2O3, 5i02-A1203, and Pt as a catalyst in some cases.

A sintered body containing noble metals such as Pd and Rh is provided. Now, when the gas sensing element comes into contact with a flammable gas and the sintered semiconductor adsorbs the gas, its electrical conductivity increases rapidly. When the flammable gas is removed, the sintered semiconductor desorbs the gas and restores its electrical conductivity to its initial value. In order to quickly adsorb and desorb this gas, the sintered semiconductor that is the gas sensitive material is heated directly or indirectly, generally at 300°.
The temperature is constantly maintained between ℃ and 450℃.

As mentioned above, gas detection elements are used by heating the sintered semiconductor part to 300 to 450°C by constantly energizing it, so the heat history changes over time, especially in high humidity environments such as kitchens. Thermal history changes the surface microstructure of the sintered semiconductor, increasing its electrical conductivity. therefore,
Even if you initially set the alarm to sound at the appropriate gas concentration depending on the type of gas, depending on the date and time of use and the usage environment, the alarm may sound even if the gas is in a dilute state below the set concentration. This was a big problem as a police weapon.

This invention was made in view of the above points, and
02 contains lanthanide oxide and Ti.

Zr, Hf, and Th oxides are 0 and 01 to 20, respectively.
By containing the gas in the range of 1% by mo, it is possible to maintain an appropriate conductivity, reduce changes in conductivity even during long-term use or use in a high-humidity atmosphere, and significantly improve stability over time. This is what we provide. This invention will be explained below.

(Example 1) A predetermined amount of Sn02 was weighed out, a rank-made oxide and oxides of Ti, Zr, Hf, and Th were added to it in predetermined ratios, and water was added, crushed, and mixed. Make a paste.

Next, the paste described in "2" was applied between a pair of platinum electrodes provided on the surface of an alumina substrate with a platinum heating element provided on the back surface, and
Dry at 800″C for 2 hours, then dry at 800″C for 2 hours.
(hereinafter this method will be referred to as the mixing method).

(Example 2) Sn02 was dispersed and mixed in water to make a paste, and the same was applied between platinum electrodes on an alumina substrate, dried, and
℃ for 1 hour, impregnated with a mixed aqueous solution of Ti, Zr, Hf, and Th compounds and a lanthanoid compound that becomes an oxide by thermal decomposition to a predetermined content, and dried at 800℃.
It was baked at °C for 2 hours (hereinafter this method will be referred to as the impregnation method).

(Example 3) When adding a predetermined amount of the mixed aqueous solution of the lanthanoid compound shown in Example 2 and Ti, Zr, Hf, and Th compounds to the aqueous solution of the Sn compound, and adjusting the pH to precipitate Sn as a hydroxide, These additives are also coprecipitated at the same time. Next, separate the precipitate.

After drying, it was made into a uniform paste as in Example 1, and applied between the electrodes of an alumina substrate. After drying, it was fired at 8000C for 2 hours (hereinafter, this method will be referred to as coprecipitation method).

Next, Example 1 (mixed method), Example? (impregnation method) and Example 3 (co-precipitation method) After the gas sensing element having the sintered semiconductor was energized for 200 hours and kept in a working state,
H2: 11000pp.

CH4: 11000pP, C2Hs OH: 11
000 pp of each gas, the electrical resistance was measured, and this was taken as the initial resistance. Thereafter, the device was kept in use and its gas sensitivity characteristics were measured over time.

Table 1 shows the measurement results for the various gas detection elements.
The characteristics of (initial value ratio) are shown in the drawing.

As can be seen from Table 1 or the drawings, the case without additives,
Compared to the case of addition according to this invention, the one according to this invention has improved stability over time.

In addition, lanthanide oxide and IV for SnO□
It has been experimentally confirmed that mo1% of group a oxide is effective in the range of 0.01 to 20.

As explained above, the present invention uses lanthanoid ti1. l
At least one type of malt oxide is o, oi ~ 20 mo1%,
and at least one type of group IVa metal oxide.
The 5N02 sintered type contains ~20 mo1%, so it maintains appropriate conductivity, reduces changes in conductivity even when used for long periods of time or in high humidity environments, and has excellent stability over time. This has the advantage that a gas sensing element can be obtained.

[Brief explanation of drawings]

The drawing shows 5n02 and La2030.5mo1%. It is a characteristic diagram of H2 sensitivity (initial value ratio) with respect to time when Hf021mo1% is added. One-hour procedural amendment (spontaneous) March 13, 1980 Dear Commissioner of the Japan Patent Office 1, Indication of the case Patent application 1982-0154E! No. 4 No. 2, Title of the invention Time-stable gas detection element 3, Relationship to the case of the person making the amendment Patent applicant address 2-5-4 Mitsuya Naka, Yodogawa-ku, Osaka-shi, Osaka Name Shin-Cosmos Electric Co., Ltd. Representative Kasahara Department of Science 4, Agent: Kobayashi Patent Office, 6th floor, Okunomatsu Building, 31-16 Sakuragaoka-cho, Shibuya-ku, Tokyo 150, Japan Telephone: 03 (496) 1256-5, Detailed explanation of the invention in the specification subject to amendment Column 6, Contents of amendment (1) “Initial gas” on page 2, line 17 of the specification has been changed to “initially,
"Gas" is corrected. (2) Similarly, "Change in conductivity" on page 3, line 8 is corrected to "Change in conductivity and gas sensitivity." (3) Also, change “sensitivity” on page 5, line 12 to “sensitivity change”.
and correct it. that's all

Claims (1)

[Claims] In the tin oxide sintered gas sensing element, at least one type of rank-made oxide is added to tin oxide in an amount of 0.01 to 20 mo1%.
, and at least one type of group IVa metal oxide at 0.0
A time-stable gas detection element characterized by containing 1 to 20 mo1%.