JPS622145A - Gas detection element - Google Patents

Abstract

PURPOSE:To enable the detection of hydrogen, ethanol and nitrogen oxide at a low concentration with a high sensitivity and a high selecting property, by providing an SnO2 based thin film supporting Ag so as to cover a pair of electrodes arranged on the surface of an insulation substrate. CONSTITUTION:A specified amount of a metallic soap of Sn is dissolved by a solvent such as toluene to adjust a desired concentration of a material solution for forming a thin film, the mixture is applied on the circumferential surface of an insulation substrate 1 having a pair of electrodes 2 and 2 and then, after allowed to stand in the aid for a specified time, it is heated to vaporize the solvent. Thereafter, the element thus obtained is baked entirely in the air to form an SnO2 based thin film. This process is repeated to attain a desired thickness. Then, the element with a thin film formed is immersed into a solution containing silver nitrate or the like and baked to form an element supporing Ag. A gas is brought into contact with the element thus obtained and the electric resistance value varied is read out with the electrodes 2 and 2 thereby enabling a highly sensitive detection of ethanol, hydrogen and nitrogen oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a gas detection element, and particularly to a gas detection element that detects hydrogen, ethanol, and nitrogen monoxide gases with high sensitivity and good selectivity.

[Technical background of the invention and its problems]

Conventionally, t S n O2, Z r+ 0 , which exhibits N-type semiconductor characteristics, has been used as an element for detecting reducing gases in the atmosphere.

Gas sensing elements using sintered bodies of metal oxide semiconductors such as Fe2O2 are known. In this gas detection element, the electrical conductivity increases when the total i-ide semiconductor comes into contact with a reducing gas, and the conductivity decreases when it comes into contact with an oxidizing gas, so that the electrical resistance value changes at that time. Gas is detected by measuring .

Furthermore, in recent years, thin film type elements have been developed in place of the sintered type gas sensing elements as described above in order to reduce the size and increase the functionality of elements. This thin film type gas sensing element uses a metal oxide semiconductor, which determines its gas sensitivity, by sputtering, vapor deposition, or CVD.
Law etc ill! A thin film structure was obtained by depositing using the J-forming method.

In both the sintered type and thin film type gas sensing elements mentioned above, metal oxide semiconductor alone has low sensitivity and insufficient selectivity as a gas sensing element.
Usually, a noble metal such as platinum (Pt) or palladium (Pd) is used as a catalyst to increase the sensitivity of the device. To achieve this, measures have been taken, for example, to directly add pt or pd to the metal oxide semiconductor, or to form a catalyst layer supporting Pt or Pd on the gold monoride semiconductor.

When such a treatment is performed, the detection sensitivity is improved compared to the case without a catalyst, but there is a problem in that it still does not exhibit sufficient sensitivity to low-concentration reducing gases. Moreover, when various gases are mixed, it is difficult to selectively detect only one specific gas with high sensitivity. ,W
This poses a problem in that it is extremely difficult because it induces malfunction of the element.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a gas detection element that can detect low concentrations of hydrogen, ethanol, and nitrogen monoxide, which is an oxidizing gas, with high sensitivity and selectivity. This is the purpose.

[Summary of the invention]

In order to achieve the above object, the gas sensing element according to the present invention has a pair of electrodes provided on the surface of an insulating substrate, and a metal compound containing 3n that is thermally decomposed and immersed in a solution containing Δq. A SnO2-based thin film supporting Ag was prepared and provided to cover the electrode, and the Ag acts as a catalyst.

[Detailed description of the invention]

Hereinafter, the present invention will be explained in more detail with reference to FIGS. 1 and 2.

Since FIG. 1b shows a specific example of the present invention, a pair of electrodes 2.2 are disposed on the outer peripheral surface of a cylindrical insulating base 1 made of an insulating material such as alumina yamlite. Further, on the outer peripheral side of the body 1, the base body 1 and the electrodes 2,
A 5no2 type 7a film 3 is provided to cover the 5no2 type 7a film 2. The film thickness of this film 3 is preferably in the range of 1,000 to 1 μm; if the film thickness is 1 μm or more, the sensitivity to the reducing gas decreases, and even if it is less than 1,000 Å, sufficient sensitivity can be achieved. This is because they cannot be obtained.

The thin film 3 is formed by thermally decomposing an organometallic compound containing Sn, and specifically, the thin film 3 is created by the following method.

First, a predetermined portion of Sn metal soap (for example, tin octylate) or a resin salt or alkoxide containing 3N is added to the
A raw material solution for forming a thin film having a desired concentration is prepared by dissolving it using a solvent such as toluene, benzene, or n-butyl alcohol. Next, this solution is applied to the outer peripheral surface of the insulating substrate 1 having a pair of electrodes 2.2, and the solution is applied to the outer peripheral surface of the insulating substrate 1 having a pair of electrodes 2.2.
0 minutes to 1 hour), then heat to an appropriate temperature (usually about 120°C).
) to vaporize the solvent. Thereafter, when the entire device is fired in air for 30 minutes to 1 hour at a concentration of 400 to 700°C, the organic compound containing Sn is thermally decomposed and the S
An nO2-based thin film is formed. This coating-firing process is 1
By repeating this process up to 4 times (depending on the temperature of the raw material solution), the desired film thickness can be obtained.

Next, the element on which the thin film was formed as described above, for example,
The element is made by supporting Ag by immersing it in a solution containing A'G such as silver nitrate or silver carbonate, or by impregnating the element with the solution and firing at a temperature of 400 to SnO°C. is formed.

As shown in FIG. 2, the element configured in this way is held above a circular insulating plate 4 in a state where it does not come into contact with other parts. bottle 5
, 5 . . . are supported by electrode lead wires 6 , 6 . Furthermore, a heater 7 for adjusting the surface temperature (operating temperature) of the element is provided inside the element, and both ends of the heater 7 are connected to the bottle 5.

In the case of the present invention, when gas comes into contact with the element, its electrical conductivity changes, and by reading the change in electrical resistance value at that time with the electrode 2.2, it is possible to detect the presence of ethanol, hydrogen, -M nitrogen, etc. can be detected with high sensitivity.

Therefore, for example, if this device is applied to an alcohol detector and used to check for drunk driving, it will operate with extremely high accuracy and prevent malfunctions.

[Embodiments of the invention]

Example 1 3N tin octylate was used as a raw material for SnO2-based ill.
A sample solution was prepared by adding n-butyl alcohol so that the content was 1.0 to 10 wt% and stirring thoroughly.

Next, the above solution was applied to the outer surface of the insulating substrate 1 provided with the electrode 2 as shown in FIG. vaporized.

Next, the whole was baked in the air at SnO<0>C for 1 hour, and this coating-baking process was repeated three times to form a thin film with a thickness of about 3000.

Furthermore, the insulating substrate on which the thin film was formed as described above was coated with 0.
Impregnation was carried out for about 1 hour while immersed in a 0.05N silver nitrate solution. After the impregnation, the device was assembled and heat-treated at about SnO° C. using a heater 7, as shown in FIG.

Table 1 shows the sensitivity characteristics of the device prepared as described above and the sensitivity characteristics of the device supported with the 〇 catalyst.

Table 1 The above sensitivity is R'air (in-air resistance value) and Rgas
(resistance value in gas), and the operating temperature is approximately 400℃.
In addition, the gas m degree is C2H50)1 is 100
p111II, No is 1 oppm.

1” 2, C01CH, i So c4H10 is 110
The case of 00pp is shown in each case.

As is clear from Table 1, this element has an extremely high sensitivity to ethanol, followed by a high sensitivity to hydrogen, and even compared to elements that do not support Ag, the sensitivity to ethanol and hydrogen is higher than that to other gases. It can be seen that the increase is greater than that of drunkenness. Also, - for nitrogen oxide,
Contrary to the reducing gas, the resistance value is higher, indicating that the sensitivity is also sufficiently high.Furthermore, these sensitivity characteristics can be obtained by either impregnation or immersion, with almost the same effect.

Example 2 Nb and sb as additives when creating SnO2-based thin film
was added at an atomic ratio of 1.0%, and further, S n O2N
Table 2 shows the sensitivity characteristics of the elements impregnated with different silver nitrate solution concentrations for the b series. The element fabrication process and measurement conditions are the same as in Example 1.

Table 2 It is clear from Table 2 that Sb as an additive,
It can be seen that no matter which Nb is used, the sensitivity is high for ethanol, hydrogen, and nitrogen monoxide. Also, when changing the concentration of silver nitrate solution, there is no large change in sensitivity, but it is higher when using a low concentration solution for ethanol and nitric oxide, and using a high concentration solution for hydrogen. It can be seen that there is a tendency to show sensitivity.

〔Effect of the invention〕

As described above, the gas detection element according to the present invention has a low II
Shows extremely high sensitivity to Maro's ethanol, and
It also shows high sensitivity to hydrogen and nitric oxide,
If applied to a device that selectively detects these gases, such as an alcohol detector, it will be possible to detect these gases with extremely high accuracy and sensitivity, resulting in high usefulness.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing a gas detection element according to the present invention, and FIG. 2 is a perspective view of a sensor to which the element of FIG. 1 is applied. DESCRIPTION OF SYMBOLS 1... Insulating base, 2... Electric bridge, 3... Thin film, 4...
...Insulating plate, 5...Bin, 6...Lead wire, 7...
·heater. Applicant's representative Inomata Seishu F Zuho 2 indents

Claims (1)

[Claims] A pair of electrodes provided on the surface of an insulating substrate, and Ag provided to cover the electrodes created by thermally decomposing an organometallic compound containing Sn and immersing it in a solution containing Ag. A gas sensing element characterized by having a supporting SnO_2-based thin film.