JPS60170760A - Combustible gas detecting element - Google Patents

Abstract

PURPOSE:To obtain a compensating element used for detecting CO selectively by composing a detecting element by adding TiO2 to alpha-Fe2O3, further adding a prescribed quantity of Pt or Pd. CONSTITUTION:Ferric chloride and ferrous sulfate are dissolved into water, and titanic sulfide solution is added thereto up to 0.1-50mol% expressed in terme of TiO2. Ammonium hydroxide solution is dropped to the solution to adjust pH to 7. After finishing the dropping, the coprecipitate is filtered and dried to obtain the powder material. Said powder is added to an aqueous solution of platinum chloride acid or paradium chloride powder by 0.1-10wt% Pt or Pd, and mixed in dry state. A pair of electrodes 3, 4 are embedded into the powder material, and said body is sintered to obtain a sintered body 1. The body 1 is attached to a element header 13 to obtain the detecting element. Since the sensitivity of said element is low only against CO, the CO sensor can be composed by combining with the gas detecting element having sensitivity against CO.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention (-i) relates to a gas detection element using a composite total bending oxide semiconductor used for detecting combustible gases.

Conventional configurations and their problems A variety of research and development efforts have been intensified regarding materials for detection elements for delayed generation and combustible gases. This is strongly attributable to the fact that explosive IJ accidents caused by flammable gas and small and medium-sized RB accidents occur frequently in households and various factories, which has become a major social problem. Particularly among these, those that detect propane gas or city gas have been developed and put into practical use with considerably high levels of both sensitivity and reliability. These are widely applied, for example, to various gas leak alarms.

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.

Particularly in the latter case, since most of the causes of death due to fire belong to this category, it has become a common committee issue. In fact, at present, there is no inexpensive, 1g1 gas sensor that can accurately detect Co, and the situation is such that the social needs described in J are not fully met.

The reason for this is that in the case of Ike's EJ combustible gas sensor, t;L
While the purpose is to prevent gas explosions, in the case of CO sensors, the main purpose is to prevent CO poisoning;
This is because fi;l- must be detected in the vagina, where LiF is extremely small compared to the lower explosive limit. For this reason, the CO sensor is not sensitive to various other gases even if they exist;
-1: It is necessary to be sensitive to the existence of extremely small fans. In other words, a CO sensor is required to have a selectivity for CO (poor selectivity) and a reliability as high as 11j1.

CIJ combustible gas sensors, which are inexpensive and highly reliable, often use oxide semiconductors that are kept at high temperatures, and detect changes in their resistance values. Several types of substances have been found in this oxide semiconductor that have a high sensitivity to C6 and have a monotonous response, but unfortunately, sensors with sufficient selectivity and monotony dependence have not yet been obtained. 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. For this reason, a method using a plurality of elements has been considered. That is, Co
An element sensitive to combustible gases containing hB and an element sensitive to combustible gases other than CO groups (hereinafter referred to as a compensation element) are combined, and the aim is to detect only CO through the signal processing. However, this requires a compensation element as well as a CO sensitive element, and also requires control of its gas sensitivity. The difficult thing here is to create an element (compensation element) that is not sensitive only to a certain type of gas (in this case, Co), and the reason for the current delay in the development of such elements with excellent selectivity is that This is the reality.

Purpose of the inventionKihatsu1. ! lj was developed in view of this situation, and is intended to realize a compensation element necessary for selectively detecting CO.

Configuration of Origin 1 The gas detection element of the present invention has Ti converted to TlO2 of 0.
．． At least one of pt and Pd is added to αFe 203 containing 1-50 mol %, with a total of 1 Q addition j71,
0.1 to 10% of the compound was used as a gas sensitive material, and this is α-Fe203 containing gas 11 and TlO2, which is the matrix material for the reacting material, and pt or Pd.
Attach /! This was achieved by discovering that by reducing the gas sensitivity to CO, it was possible to maintain a value of 1 degree compared to that of other combustible gases.

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

First, in Example 1, the effect of adding PT or Pd to a 42-size matrix in which the matrix of TlO2 contained in α-Fe203 is changed will be described.

[Example 1] 30 g of commercially available ferric chloride (FeCQ, 6H20) and 60 g of ferrous sulfate (FeS04.7H20). ! 9 to 1a
of water and stirred while keeping the temperature at 50°C.

Add to this a commercially available titanium sulfate solution (Ti(SC2)2).
were added so that the composition was as shown in Table 1 (TlO2 amount). While keeping the temperature of the solution at 60°C, add 8
60c of specified ammonium hydroxide (NH40H) solution
The solution was added dropwise at a ratio of c/l+ until the hydrogen ion concentration of the solution reached 7. Immediately after the dropwise addition was completed, the coprecipitate was filtered by 1 strain. The powder thus obtained was heated to 110% in air.
Lightly baked at ℃. This drying),・■ place the object in the air for 40
Heat treatment at 0° C. for 1 hour resulted in 11 days.

Table 1 (additives Pt, Pd) is added to this heat-treated powder.
Commercially available chloroplatinic acid (H2
When Pt (j26・6H20) is dissolved in water, the concentration is 100 m9/m+! For palladium, commercially available palladium chloride powder (PdCα2
), singly or in combination, f
Added 7%. Then, each powder was mixed for about 3 hours using a mixer.

Two platinum wires were embedded in this powder to create an inner diameter of 2mm.

Pressure molded into a cylindrical shape with a tube length of 3 mm and placed in air for 75 minutes.
Firing was performed at 0°C for 1 hour. The obtained porous sintered body was attached to a sensing element header, a coil-shaped heater was placed around the sintered body, and an explosion-proof stainless steel net was covered to obtain a sensing element.

FIG. 1 shows the structure of a gas detection element. In the figure, 1 is a sintered body, 2 is an electrode 3 made of platinum wire,
4 is embedded. 2 is l:tl+, a heater for heating the body 1, and power is supplied to the heater from the heater pin ratio 12 through the heater frame 7.8. The resistance of the sintered body 1 is arranged to be measured between the pins 9,100 from the electrode 3.4 through the frame 6.6. Heater pins 11, 12 and pins 9, 10 are fixed to header 13 and attached to a stainless steel wire mesh 14 header.

Regarding the sensing element obtained as follows, gas I
J & O 4, I + I (3s o ℃) 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 350°C, and then insert it into a measurement box with a known volume. , test gas (CO gas (COs) with a syringe
, o% and N296.0%), H2 gas (9
9 or more), and 1-C4H1° gas (99% or more)
2) into the measurement box, CO2H2 or 1-C4
The resistance end of the sintered sensitive body was measured when the H1° concentration reached 001 volume, 1% (10ppm) K. The gas concentration to be measured was chosen to be 100 ppm because the permissible concentration of CO for industrial hygiene is 1100 ppm, so at least 11 people would be required to respond at this concentration or lower.

Gas 1-tooth response characteristics are: (1) gas sensitivity (resistance value in air (
Evaluation was made using resistance value in gas (Rq).

Table 1 shows the gas density (Ra/Rq).The margin below is Table 1.
By adding pt or Pd to -Fe 203 , a remarkable decrease in sensitivity was observed for CO, which made it difficult to realize it as a compensation element for CO.

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

[Example 2] Departure 11ij' PI is 1 old slope of ferric chloride (FeCR)
3-6H20) 30.9 and 114L ferrous acid (FeSO
4,7H20) Er o
K was added so as to have the composition shown, and a coprecipitate was obtained using the same knob method as in Example 1. After drying this and performing image processing, platinum chloride solution and salt (hybaradium) were added to it so that it had the composition shown in Table 2 (additives Pt, Pd), and each powder was washed. The mixture was mixed for about 3 hours using a machine.

This powder was sized to 60 to 1Q○μ, and triethanolamine was added to form a paste. This was used to create a sintered model gas sensing element as shown in Figure 2 (a) and (bl
These are shown as a front view and a back view, respectively. In the figure, the substrate of the gas sensing element is vertical.

Alumina substrate 15 each 5mm wide and 0.6mm thick
A pair of comb-shaped Imaichi JVj1 with a spacing of 0.6 mm on the 0 surface.
6 was formed. A gold electrode 1 for a resistor was also formed on the back surface at the same time, and during this time a glaze resistor 18 was baked at marks 11i11 to serve as a heater.

Next, the above paste was printed on the surface of the substrate to a thickness of about 70/1, allowed to air dry at room temperature, and then gradually heated to a temperature of 750°C. The paste was held at 11°C for 1 hour. At this stage, the paste became an evaporated heel sintered film 19. The thickness of this gas sensitive member was about 56μ. In this way, a gas sensing element-r- was obtained.

The following is a blank space in Table 2.The gas sensitivity characteristics of the sensing elements of each comparative example were measured in the same manner as in Example 1, and are shown in Table 2.

As is clear from Table 2, almost the same characteristics as those obtained in Example 1 were obtained even when the sensitive body was a sintered film. When the T IO2 value is less than 0.1 molar and greater than 60 molar, it is not used because the sensitivity to +'iJ' combustible gases other than CO is low. The addition of Pt or [Pd as the old J1 is 0.1 jf, and if it is less than 10 times, it has no effect, and if it exceeds 10 times, it becomes impractical due to the stability of the characteristics. . TlO2 and pt or Pcj contained in the gas detection element of the developed uJl
The reason lfi was limited was due to two reasons.

By the way, in Examples 1 and 2, ferrous sulfate and salt 1-II were used as the iron salt, and a titanium sulfate solution was used as the titanium as the starting materials for the HJ ignition material. Regarding pt and Pd, the salt f arsenic acid and the salt r hivaladium have been described, but in the present invention, the final composition of the reactor only needs to be within the range mentioned above, and no starting materials are used. It does not limit the manufacturing process.

Release l-! As explained in January, the gas sensing element of the present invention further incorporates p-Fe203 containing T102 as an additive.
A sintered body or a sintered film doped with t or Pd is used as a sensitive body, which allows selection of ++'-
To provide a compensation element that can realize a multi-sensor system (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 considered difficult to detect. It is.

Here, we will present an example of Co selection (+< target detection) using a multi-sensor method using a wooden invention.

As a sensor sensitive to CO, α-Fe203 (sample z+6A-12 in Table 1) containing 10 mol of TlO2 was used, and as a sleeve tn element, the above compositions Kpt and Pd were each added with a 1.0 mol ratio. (Sample tttxA in Table 1
-1s), and the resistance value when a combustible gas (for example, 1100pp concentration of CO, H2, or t/'1i-C4H1゜bl gas) comes into contact with this pixel element. Table 3 shows the results when the switch is activated when the resistance value decreases to less than the preset resistance value.

Table 3 From the results, it can be seen that the signals of the CQ pixel elements are different and can be distinguished from the 73i3J combustible gas.

This is due to the incomplete combustion of gas appliances or the beginning of a fire) In recent years, there has been a tendency for accidents to occur frequently due to CO generated at It corresponds to this, and its effects are extremely human.

[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. 2(a) and 2(b) are a front view and a back view of the element. 1... Sintered body, 2... Heater, 3, 4
... Electrode, 5.6 ... Frame, 7,
8... Frame for heater, 9.10...
・Pin, 11.12...Heater pin, 13.
...Header, 14...Stainless steel wire mesh, 16...Alumina substrate, 16...
・Gold electrode, 17...Gold electrode for resistor, 18...
...Glaze resistor, 19...Sintered film.

Claims (2)

[Claims] (1) Titanium y (Ti) is converted to TiO2 and is 0.1-6
Alpha-type ferric oxide (α-F e 2
0s), at least one of platinum (PT) and palladium (Pd) in a total additive amount of 0.1 to 10%
The added material is used as a gas sensitive body, and a pair of electrodes for measuring electrical resistance and a heater for heating are attached to it. A combustible gas detection element characterized by detecting a combustible gas using change. (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.