JPS60170759A - Combustible gas detecting element - Google Patents

Abstract

PURPOSE:To decrease only the gas sensitivity to CO while maintaining the sensitivities to other combustible gases as they are by composing a compensating element by incorporating prescribed quantities of Sn, Pt into alpha-Fe2O3. CONSTITUTION:Ferric chloride and ferrous sulfate are dissolved into water, and stannic chloride is added so that a 0.1-50mol% composition expressed in terms of SnO2 is obtained. Ammonium hydroxide solution is dropped into the solution to adjust its pH to 7. After finishing the dropping, the coprecipitate is filtered by sucking, and the obtained powder is dried. The dried material is added to an aqueous solution of platinum chloride acid, and mixed in dry state. A pair of electrodes 3, 4 are embedded into the obtained powder, and said body is ignited to obtain a sintered body 1. This body is attached to a header 13 for the detecting element to obtain the gas detecting element for compensation. Since the sensitivity of said element is small only against CO, the sensor responding only to CO can be composed by the combination with the gas detecting element sensitive to CO.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a gas detection element using a nuclear alloy metal oxide semiconductor used to detect combustible gases.

Structures of conventional examples and their problems In recent years, various (
JF research and development is becoming more active. This is largely due to the frequent occurrence of explosions and poisoning accidents caused by flammable gases, mainly in households and in German factories, which has become a major social problem. Among these, in particular, those that detect propane gas or city gas have been developed and put into practical use with considerably high levels of sensitivity and reliability. These are widely applied, for example, to various gas leak alarm devices.

On the other hand, as another social need for gas disaster prevention, CO
detection has become a hot topic. This is largely due to the spread of various gas appliances and the airtightness of housing structures.

That is, there is a problem of incomplete combustion of gas appliances or poisoning due to Co generated from new building materials in the early stages of a fire.

In particular, the latter is an extremely important social problem because it accounts for the majority of deaths caused by fire. However, at present, there is no inexpensive and simple gas sensor that can accurately detect CO, and the above-mentioned social needs are not fully met.

The reason for this is that while the purpose of sensors for other combustible gases is to prevent gas explosions, the main purpose of sensors for CO is to prevent C○ poisoning. The amount is pitiful compared to the lower explosive limit, and detection of a minute amount must be considered as a counterattack. For this reason, CO sensors are not sensitive to various other gases even if they are present, while they must be sensitive to Co even in the presence of extremely small amounts. . That is, (1) the sensor is required to be selective to CO and to have commercial reliability.

In low-cost, highly reliable combustible gas sensors, oxide semiconductors that are maintained at high temperatures are often used to detect changes in their resistance. Some substances have been found in this oxide semiconductor that are highly sensitive to Co (C), but unfortunately, sufficient senna has not yet been obtained in terms of selectivity and reliability. It is.

Under these circumstances, various methods have been tried to improve gas selectivity, such as adding noble metal additives to the gas sensitive body and changing the operating temperature. There seems to be a limit to what can be done with this element. For this reason, a method using a plurality of elements can be considered. That is, a combination of an element sensitive to combustible gases including CO and a blue element (hereinafter referred to as a compensation element) sensitive to flammable gases other than CO,
The aim is to detect only Co by processing these signals. However, this requires a compensation element as well as a CO sensitive element, and also requires control of its gas sensitivity. The difficulty here is that some types of gas (
In this case, it is necessary to create an element (compensation element) that is not sensitive only to Co), and the current situation is that the development of elements that are highly selective is delayed.

Purpose of the Invention The present invention was made in view of the above situation, and it
This realizes a compensating element necessary for selectively detecting.

Structure of the Invention The gas sensing element of the present invention is a gas sensitive material made of a-Fe203 containing Sn in an amount of 0.1 to 50 mo 1% in terms of SnO2, to which 0.1 to 10% by weight of pt is added. By adding pt to α-Fe203 containing SnO, which is the base material of the gas sensitive material, only the gas sensitivity to CO is reduced, while the sensitivity to other combustible gases remains the same. This was achieved by discovering that the value can be maintained.

Description of actual case The present invention will be explained in detail below.

First, in Example 1, the effect of adding pt when the amount of pt added is varied in the matrix phase in which the amount of E+ n O2 contained in a-Fe203 is varied will be described.

[Actual sister example 1] Commercially available ferric chloride (FeCff13-eR20) 3o
y and (iRM ferrous (Fe3O3・7H2o) 6oy) were bathed in 12 liters of water and stirred while maintaining the temperature at 50C. Commercially available stannic chloride (5n (j2゜・6M 20 ) B was added so that the composition was as shown in the table (amount of Sn02).While keeping the temperature of M solution at 60C, B was added to this solution.
Specified ammonium hydroxide (NH2OH) bath solution at 60C
The hydrogen ions in the solution were added dropwise at a rate of 7 C,/min until the number of hydrogen ions in the solution reached 7. Immediately after the dropwise addition was completed, the coprecipitate was suction-filtered. The powder thus obtained was heated at 110C in air.
It was dried. This dried material was heated to 400C in air for 1
This heat-treated powder was heated with commercially available chloroplatinic acid (H4F tcff6.
61'120) in water and the concentration is 1007%/
A solution adjusted to reach rni was added. Then, the respective powders were dry-mixed using a mill for 3 hours.

Two platinum wires were embedded in this powder, which was pressure-molded into a cylinder shape with a diameter of 2 and a diameter of 3 mm, and fired at 760C for 1 hour in air. The obtained sintered body with the porous chamber was attached to a sensing element bracket, a coil-shaped heater was placed around the sintered body, and a tin-proof stainless steel net was covered to form a 4-inch sensing element.

FIG. 1 shows the structure of a gas detection element. In the figure, 1 is a sintered body, and 2 electrodes 3 made of platinum and urine.
．． 4 is embedded. Reference numeral 2 denotes a heater for heating the sintered body 1, and power is supplied to the heater through heater pins 11 and 12 through heater frames 7 and 8. The resistance Q of the sintered body 1 is configured to be measured between the pins 9, 10 from the electrodes 3, 4 through the frame 6.6. Heater pin 11. '+2 and pin 9.10 are header 1
3, and a stainless copper wire mesh 14 is attached to the header.

The gas sensitivity characteristics (' 350 C) of the device obtained as described above were investigated.

The method for measuring gas sensitivity characteristics is to apply a current to the heater part of the sensing element in advance, adjust the temperature of the sensing element to 350C, and then insert it into a measurement box with a known volume. , test gas 2 (CO gas (CO5) with a syringe)
-0% and N295.0% mixed gas),) gas (99
% or more), and i C4~. :/jsu (99% or more)
) was injected into the measurement box, and Co, N2. %rui/r! 1-
C4H1o birthday. , the resistance value of the sintered sensitive body was measured when α capacity % (1 ooppm) was reached. The gas concentration to be measured was chosen to be 1100 ppm because the permissible concentration of Co in terms of industrial hygiene is 100 ppm, so it was necessary to be sensitive at least below this concentration.

The gas sensitivity characteristic is (1 gas sensitivity (resistance value in air (R
a) Evaluation was made using the resistance value (Rcr) in 7 gases.

Table 1 shows the gas lfv degree (Ra/)Icy).

Below Margin Table 1 ■ Comparative Table 1 From Table 1, Lr containing 0.1 to 50 mol% of S n O2
By adding pt to α-F' e 203, C
A remarkable decrease in sensitivity was observed only for Co, indicating that it can be realized as a complementary element for Co.

In this sister example 1, the sensitive body was a sintered body, but
In Example 2 shown below, the effect of adding PT when the sensitive body is a sintered film will be described.

[Sister Example 2] The starting material is commercially available ferric chloride (keCls・6H
20) 309 and ferrous sulfate (F@1804-7H20)
eoyK chloride 2>3 (5nCF!4-5820) was added so that the composition was as shown in Table 2 (Sn○2 amount), and a coprecipitate was obtained using the same method as in Example 1. . Dry this.

After heat treatment, commercially available chloroplatinic acid (N2PtC1
26・e M 20 ) is bathed in water and its hardness is 10.
A solution adjusted to 0 j3f/ml was added, and each powder was dry mixed for 3 hours using a miller.

This powder was sized to a size of 60 to 100 microns, and triethanolamine was added to form a paste. The structure of a sintered film type gas sensing element created using this is shown in Figures 2a and 2b as a front view and a back view, respectively, as a substrate of the gas sensing element.

Width: 5111m, respectively Thickness: Q, 5111111
A pair of comb-shaped gold electrodes 16 were formed on the surface m1 of the alumina substrate 15 at an interval of 0.5 ntm. A gold electrode 17 for the resistor is also formed on the back side at the same time, and a glaze resistor J is formed at the same time.
'jr type 18 was printed, exposed and used as a heater.

Next, it was printed on the surface of the above-mentioned Pasteke substrate with a thickness of about 70 μm, and after air drying at room temperature, it was gradually heated to a temperature of 750 C and held at this temperature for 1 hour. At this stage, the paste was released and became a sintered film 19. The thickness of this gas-reactive body was approximately 56. The gas sensitivity characteristics of each sensing element were measured in the same manner as in Example 1.
It is shown in Table 2.

As is clear from Table 2, almost the same characteristics as those obtained in Example 1 are obtained even when the sensitive body is a sintered film.

From Ushita No. 1 and Table 2, if the amount of S n O2 is less than 0.1 mol or more than 50 mol φ, the sensitivity to combustible gases other than Co is low, so it cannot be used, and as the amount of Pt added. is 0.1! There is no effect below the amount, and 1
If it exceeds 0%, it becomes impractical due to the stability of the characteristics.Sn contained in the gas detection element of the present invention
The O2 and Pt amounts were limited (d) for the reasons mentioned above.

By the way, in Examples 1 and 2, ferrous sulfate and ferric chloride were used as the iron salts, and chloride was used as the tin salt as the starting materials for the base materials. Regarding PT, we have described the one using chloroplatinic acid, but in the present invention, the final composition of the susceptor only needs to be within the above-mentioned range, and the starting materials and manufacturing process are not limited. do not have.

As described in detail, the gas sensing element of the present invention uses a sintered body or a sintered film obtained by adding pt to α-Fe203 containing Sn○2 as an additive as a sensitive body. , thereby creating a compensation element that can realize a multi-sensor system (a signal processing system using a combination of an element that is also sensitive to Co and an element that is not sensitive to CO) for CO gas, which has been said to be able to selectively detect trace amounts of Iil+L. It provides:

Here, an example of selective CO detection using a multiple sensor method using the product of the present invention will be described.

a Fe 203 containing 10 mol of b n O2 as an element sensitive to CO (Sample No. A-9 in Table ')
) and the compensation element is a combination of the above composition with 1.0% PT added (sample No. A-4 in Table 1), the gas tag tx of each element,
When this pixel element comes into contact with a flammable gas (for example, C09H2 at a concentration of 1100pp, or 1-C4H1° gas), the switch will operate when the drop in resistance value falls below a preset resistance value. Table 3 shows the results for both cases.

Table 3-1-' From this result, it can be seen that the signal of the pixel element is different only when Co is used, and it can be distinguished from other combustible gases.

This is an accurate response to the growing social needs of CO sensors that can prevent CO poisoning accidents that occur in incomplete combustion of gas appliances or in the early stages of fires, as accidents tend to occur frequently these days. Yes, and the effects are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the structure of a gas sensing element according to the present invention, and FIGS. 2a and 2b are a front view and a back view of the element. 1... Sintered body, 2... Heater, 3, 4
... Electrode, 5.6 ... Frame, 7. ．． 8
・・・・・・Heater frame, 9, 10...
Bottle, 11. 12 ... Hi~ri JIJ Pino, 12
....-＼Tutter 114 ... Stainless brocade] wire mesh, 15 ... Alumina substrate, 16 ... Distribution j+i1K, 17 ... Gold electrode for resistor, 18 ...・
Clase nail 1 no'+. Body, 19...?) L conjunctiva. Name of agent: Patent attorney Nakao 1ka (male and 1 other person)

Claims (2)

[Claims] (1) Convert eijA(S”) to S n O2 and convert it to 0.
Alpha-type ferric iron (aF' e
203) to which 0.1 to 10% by weight of platinum (pt) was added was used as a gas sensitive material, and a pair of electrodes for measuring electrical resistance and a heater for heating were applied to it to make it flammable. A combustible gas detection element characterized in that a combustible gas is detected by using a change in electrical resistance 116 of the gas sensitive body due to a single change in gas. (2) A sintered body obtained by pressure molding and firing a gas sensitive body, or a sintered body obtained by printing a paste and firing it.