JPS61194348A - Co gas defection element - Google Patents

Abstract

PURPOSE:To reduce power consumption and to stabilize the temp. of an element by efficiently and uniformly heating the element, by connecting a substrate comprising an oxygen ion conductive solid electrolyte and an electric insulating substrate having a heater circuit printed thereon. CONSTITUTION:A Au-paste is applied to a solid electrolyte 1 formed by the press molding of a stabilized ZrO2 powder by a thick film printing and backed to form electric signal take-out parts 2, 2' and Pt-electrodes 3, 3' are subsequently formed by electron beam vapor deposition. A CO-containing combustible gas oxidizing catalyst layer is formed by thick film printing so as to perfectly cover one Pt-electrode 3 while a catalyst layer 5 oxidizing combustible gas other than CO-gas is formed by thick film printing so as to perfectly cover the other Pt-electrode 3'. Next, the surfaces, to which any printing is not applied, of the solid electrolyte substrate 1 and an electric insulating alumina substrate 6 having a heater circuit 8 formed thereto are mutually adhered by an inorg. adhesive to obtain a CO-gas detection element.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a CO gas sensing element.

(Prior Art) If flammable gases including CO gas exist in the atmosphere, there is a danger of toxicity to living things and explosion, and therefore various gas detection elements capable of detecting these gases have been proposed.

Among these, a gas detection element using an oxygen ion conductive solid electrolyte that utilizes an electrochemical reaction has been developed, for example, in Japanese Patent Application Laid-open No. 5
As shown in Japanese Patent No. 5-39005, one side of the electrode is covered with a combustible gas oxidation catalyst, and in particular, in order to selectively detect CO gas, as shown in Japanese Patent Application Laid-Open No. 59-37456, There is one in which two types of catalyst layers having different oxidizing abilities for CO gas are provided on each electrode. When these elements are maintained at 300° C. to 400° C. and placed in air containing flammable gas or CO gas, an electromotive force is generated depending on the concentration of the flammable gas or CO gas. The presence of gas can be detected by detecting this electromotive force, but if the temperature of the test atmosphere is room temperature, the element is heated externally to 200°C to 40°C.
It is necessary to maintain the temperature at 00°C. As this method, JP-A-59-
As shown in Japanese Patent No. 109857, there is a method of heating from the outside with a wire-wound heater.

(Problems to be Solved by the Invention) However, in the above method, the oxygen ion conductive solid electrolyte and the catalyst layer are heated via the cylindrical member that holds them, so the heating efficiency is poor and the heater power is increased. The drawback was that it had to be done.

It is an object of the present invention to solve these drawbacks and provide a CO gas sensing element that is stable in temperature and requires low heater power.

(Means for Solving the Problems) The present invention forms a pair of electrodes on one side of which a lead wire can be attached, and one of the electrodes is connected to a layer of a catalyst for oxidizing combustible gas including CO gas, and the other is The other side of the substrate is made of oxygen ion conductive solid electrolyte whose electrodes are covered with a layer of catalyst that oxidizes combustible gases other than CO gas, and the other side is an electrically insulating substrate with a heater circuit printed on which lead wires can be attached. The present invention relates to a CO gas detection element formed by bonding the other surface with the other surface.

In the present invention, the oxygen ion conductive solid electrolyte substrate (hereinafter referred to as solid electrolyte substrate) is YzO
A solid electrolyte substrate of zirconia (stabilized Zr0z) stabilized with s) or the like is preferred. The electrodes are formed using platinum (Pt
), gold (Au), etc., are preferably deposited in pairs on the solid electrolyte substrate by, for example, electron beam evaporation so as to face each other.

Electrodes are coated with a layer of catalyst that oxidizes combustible gases including CO gas by printing a paste of alumina powder supporting Pt, palladium (Pd), etc. on the solid electrolyte substrate on which the electrodes are attached. is preferable. To coat an electrode with a layer of a catalyst that oxidizes combustible gases other than CO gas, powders such as tin oxide, chromium oxide, titanium oxide, etc. are made into a paste and printed on the solid electrolyte substrate on which the electrode is attached. is preferable. What is the material of the electrically insulating board?

There are no particular limitations as long as it can withstand the temperature of the heater used for printing to maintain the temperature of the solid electrolyte substrate to be bonded and fixed at about 400°C. Usually alumina, steatite, mullite, etc. are used. It is preferable to print the heater circuit with Pt paste from the viewpoint of heat resistance. Although there are no particular restrictions on the method of bonding the solid electrolyte substrate and the electrically insulating substrate, it is preferable to bond them using a heat-resistant inorganic adhesive.

(Function) When the CO gas detection element configured as described above is placed in a test gas atmosphere by energizing the i-heater circuit so that the temperature of the solid electrolyte substrate becomes, for example, 400°C, the combustible gas is selectively oxidized. This is because an electromotive force proportional to the KCO gas concentration between both electrodes is generated.

This electromotive force is measured by an external instrument connected to lead wires from the electrodes, and the concentration of CO gas is measured.

(Example) Next, the present invention will be explained in detail by way of examples.

Example 1 FIG. is used as a solid electrolyte substrate.Stabilized ZrO
The two powders were granulated using a spray dryer, press-molded, and sintered at 1650°C to obtain a solid electrolyte substrate 1 of 4 x 8 x 0, 8 mm. As shown in FIG. 1(b), Au paste (Dupont Co., Ltd.) is placed on the substrate 1.

≠9791) was printed in a double-sided pattern with a thickness of 10 μm, and then heat-treated and baked at 900° C. for 10 minutes to form the electrical signal extraction portions 2, 2'. Most of the solid electrolyte substrate 1 overlaps a part of each electric signal extraction section 2, 2'.
As shown above, P with a size of 2 x 2 mm and a film thickness of 0.1 μm
T-electrodes 3.3' were formed by electron beam evaporation. 3 parts 3M, film thickness 20 μm so as to completely cover one side 3 of the Pt electrode.
A combustible gas oxidation catalyst layer 4 containing CO is formed by thick film printing. The combustible gas oxidation catalyst layer 4 has a specific surface area of 340
m”/g alumina powder (KHD alumina manufactured by Sumitomo Aluminum is ground to a size of 350 mesh or less)
To.

The raw material was a powder impregnated with an aqueous solution of chloroplatinic acid to contain 2 wt% of Pi and then heat-treated at 800°C for 10 hours, based on 100 parts by weight of the raw material powder.

A sialumina-supported Pt catalyst layer was formed by printing 3 parts of baset, which was kneaded with 10 parts by weight of ethyl cellulose as a binder and 60 to 70 parts by weight of carpitol acetate as a solvent, to a thickness of 30 μm.

Also, add 3 layers to completely cover the other Pt electrode 3'.
A catalyst layer 5 that oxidizes combustible gas other than CO gas is formed by thick film printing to have a thickness of 3 mm and a film thickness of 20 μm. The catalyst layer for oxidizing combustible gases other than CO gas is prepared by neutralizing an aqueous solution of stannous chloride with an aqueous potassium carbonate solution and removing the precipitate by 600%
5 parts by weight of ethyl cellulose as a binder per 10 parts by weight of tin oxide powder obtained by heat treatment at ℃ for 10 hours,
A paste prepared by adding 35 to 40 parts by weight of carpitol acetate and kneading is printed to a size of 3×31 mm and a film thickness of 30 ttm.

As a result, a tin oxide catalyst layer was formed. In order to solidify these two types of catalyst layers, heat treatment was performed at 500° C. for 1 hour. The electrical signal extraction part 2.2' has an Au wire (
+11 diameter 0.2 mm) were connected by thermocompression bonding as lead wires 9 and 9' as shown in FIG. on the other hand.

A heater circuit 8 is printed on the surface of an alumina electrically insulating substrate 6 (4 x 8 x 0.8 cm) using PT paste (Shoei Chemical Pt-4005) as shown in Figure 1 (C).
It was formed by baking at 0°C for 60 minutes. The resistance of the heater was 12Ω. A heater voltage applying section (1x1mm) 7 is connected to both ends of this heater circuit using Au paste (
DuPontna 9791) and baked at 900°C for 20 minutes. The heater voltage application section 7 includes an Au wire (wire diameter 0).
．． 2 wn ) were connected by thermocompression bonding to form heater power supply leads 10 and 10' as shown in FIG. Next, a stabilized ZrO2 solid electrolyte substrate 1 and an electrically insulating substrate 6
The non-printed surfaces of the were bonded together with an inorganic adhesive (Sumitomo Electric Sumiceram S-18C) to form the CO gas detection element shown in Figure 1 (al).Lead wires 9, 9 shown in Figure 2
' to the electric signal take-out bottle 11.11' of the mount 13, spot weld the heater power supply lead 10.10' to the bottle 12.12', and attach a double-walled wire mesh (stainless steel! R) to the mount. It was covered with a CO gas detection sensor.

FIG. 3 shows the relationship between the heater voltage and temperature characteristics of the CO gas detection element (hereinafter referred to as element) according to this example. Moreover, in FIG. 4, CO gas is 200 ppm.

H+ H2 gas 1.0001) pm, fi gas 1,000
The relationship between element electromotive force and heater voltage with respect to pI)m is shown.

From Figures 3 and 4, when the heater voltage is low and the element temperature (solid electrolyte substrate temperature) is low, the activity of the catalyst 5 that oxidizes combustible gases other than CO gas is low, so +H2
The element electromotive force for gas is large.

However, if the heater voltage is increased and the element temperature is increased, the activity of the catalyst increases.
By setting the temperature to 0°C, discrimination between b, co gas and H2 gas becomes possible. The voltage applied to the heater required to bring the element temperature to 350° C. to 450° C. is 4 to 5 μm, and the power consumption at this time is about 1.3 to 2 OW. With conventional heating using a wire-wound heater (Japanese Patent Application Laid-Open No. 109859/1985), it takes about 2.5 to raise the element temperature to 350°C to 450°C.
~3.5W is required, so the power consumption is reduced by this embodiment.

FIG. 5 shows the heater voltages of the CO gas detection elements of the two embodiments: 4. OV and 5t! The results of examining the responsiveness to Co, H2, and CH4 gases in the test box are shown below. In Figure 5, CO gas 200 pp
For nl, saturation electromotive force is reached within 1 minute. Recovery after gas purge was also within 1 minute, indicating good response characteristics.

Examples 2 to 4 Elements were manufactured using an alumina-supported Pd catalyst instead of the alumina-supported Pt catalyst in Example 1.

In addition, in place of the tin oxide catalyst, chromium acetate was heated to 500°C.
Chromium oxide obtained by thermal decomposition for 10 hours.

An element was manufactured using titanium oxide obtained by thermally decomposing titanium oxide at 500° C. for 10 hours. 200 ppm of CO gas, 1,000 ppm of H2 gas and CH4 of these elements
Gas 2. Table 1 shows the element electromotive force versus oooppm.

From Table 1 in the margin below, it can be seen that CO gas can be clearly distinguished from H2 gas and CH4 gas.

Example 5 As shown in FIG. 6, the catalyst layer 5 for oxidizing combustible gases other than CO gas in Example 1 was spread out to cover the Pt electrode 3 and the combustible gas oxidation catalyst layer 4. Discrimination between CO gas, H2 gas and CH4 gas.

It was the same as Example 1.

(Effect of the invention) According to the present invention, the element can be efficiently and uniformly heated.

Since the power consumption is small and the element temperature is stable, an energy-saving and highly reliable CO gas detection element can be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the structure of a CO gas detection element according to an embodiment of the present invention, in which (a) is a cross-sectional view, (b) is a top view, (C) is a bottom view, and Figure 2 is a CO gas detection sensor. Fig. 3 is a graph showing the relationship between heater applied voltage and element temperature, Fig. 4 is a graph showing the relationship between heater applied voltage and element electromotive force, and Fig. 5 shows CO for various gases. A graph showing the response characteristics of the gas sensing element, and FIG. 6 is a sectional view showing the structure of a CO sensing element according to another embodiment of the present invention. Explanation of symbols l...Solid electrolyte substrate 2--Electrical signal extraction section 3-
... Ptt electrode 4 ... Combustible gas oxidation catalyst layer 5
... Catalyst layer 6 that oxidizes combustible gas other than CO gas.
...Electrical insulating substrate 7...Heater voltage application section 8.
...Heater circuit 9..., lead wire 10...lead for heater power supply 11...electrical signal extraction bin 12...pin for heater power supply 13...mount;:Eye body electric P4Y 2nd round Heater 3 Heater (p energized (7) ≠ Figure closed (#) 5th port 1 Ro

Claims (1)

[Claims] 1. A pair of electrodes to which lead wires can be attached are formed on one surface, one of the electrodes is a catalyst layer for oxidizing combustible gas including CO gas, and the other electrode is for oxidizing combustible gases other than CO gas. A CO gas detection element formed by bonding the other side of a substrate made of an oxygen ion conductive solid electrolyte coated with a catalyst layer and the other side of an electrically insulating substrate on which a heater circuit to which lead wires can be attached is printed on one side.