JPS61147145A - Gas detecting element - Google Patents

Abstract

PURPOSE:To obtain a detecting element which obviates the need for operation at a high temp. and has excellent selectivity to various gases by making use of the change of a conductive high polymer in the electrical conductivity or absorption spectrum thereof when said polymer contacts with gas. CONSTITUTION:Electrodes 2a, 2b are formed to both terminals of the electrically conductive high-polymer molding 1 and lead wires 3a, 3b are connected thereto. Any materials including metal such as platinum, gold or aluminum, carbon black, electrodac and silver paste are usable for the material to constitute the electrodes 2a, 2b. Any forms including film and block forms are possible for the molding 1. The electrodes 2a, 2b may be positioned to any position, i.e., any face of the molding 1. The electrodes 2a, 2b may be formed into any shape including such as, for example, comb-tooth electrodes. The installation of the electrodes on the front and rear surfaces of the molding is also possible if the molding is a film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a gas sensing element using a conductive polymer for monitoring the presence of a specific gas or measuring the current date.

[Background Art] In recent years, as information processing capabilities have dramatically improved due to advances in electronics, sensors, which are means for extracting information, have become increasingly important. Among various sensors, gas sensors in particular are widely used as gas leak alarms, exhaust gas monitors, and various industrial sensors. Conventional gas sensors are mainly made of ZnO or F
It was made of semiconductors or ceramics, such as e201. Gas sensors using these materials utilize resistance changes when they come into contact with gas at high temperatures. Also, catalytic combustion type gas sensors using platinum wires, etc. are also used, but they utilize the change in resistance of the platinum wires due to the temperature rise caused by combustion when the heated platinum wires come into contact with flammable gas. there were.

[Problems to be Solved by the Invention] However, many of the various conventional gas sensors described above have a drawback in that they need to be operated at high temperatures. Furthermore, there was also the drawback of poor selectivity for various gases. Therefore, there is a desire for a gas detection element that can selectively detect various gases including household city gas, automobile exhaust gas, industrial gas, and the like.

Therefore, an object of the present invention is to provide a gas sensing element that satisfies the above-mentioned needs, does not require operation at high temperatures, and has excellent selectivity to various gases.

Means for Solving the Problems] The present invention was made as a result of intensive studies to solve the above problems, and its gist is to provide a gas sensing element made of a conductive polymer. This is a gas sensing element that utilizes the fact that the conductivity or absorption spectrum changes when the conductive polymer comes into contact with gas.

Examples of the [8B electroconductive valve] used in the present invention include polyacetylene, polypyrrole, polythiophene, polyparaphenylene, polyaniline, polyphenylene vinylene, polyselenophene, polyfuran, and derivatives thereof. These conductive polymers are highly developed conjugated systems (Yamakawa and Yamabe, "Synthetic Metals," published by Kagaku Dojin), and have relatively high conductivity, and doping with various substances increases the conductivity. It changes. The present invention actively utilizes the change in properties of conductive polymers caused by doping.

Although the present invention is a gas sensing element made of a conductive polymer, either a change in conductivity or a change in absorption spectrum can be utilized. Next, specific structural examples in each case will be explained.

FIG. 1 shows an example of a structure in which a change in conductivity is utilized.
, 2b are formed, and lead wires 3a, 3b are connected to the electrodes 2a, 2b. Electrodes 2a, 2
As the material constituting b, any material including metals such as platinum, gold, or aluminum, carbon black, electrodac, and silver paste can be used. In addition, conductive polymer molded body 1
can be in any form including film and block shapes. The electrodes 2a and 2b may be formed on either side of the conductive polymer molded body 1. Also,
Regarding the shape of the electrodes 2a and 2b, for example, the shape of the comb l1m
It can be configured into any shape like an electrode. Furthermore, when the molded body is a film, it is also possible to install electrodes on the front and back surfaces of the molded body.

FIG. 2 is a perspective view showing an example of a structure in which a change in absorption spectrum is utilized. Here, a conductive polymer thin film 5' is formed on a substrate 4 made of a material such as glass or plastic. There is. When utilizing changes in the absorption spectrum, it is not necessarily necessary to fix the conductive polymer to the substrate 4 as shown in FIG. 2, and it is possible to use the molded body of the conductive polymer (for example, a film) itself. Needless to say. Furthermore, it is also possible for light to pass through the conductive polymer thin film 5 in a direction parallel to the plane of the thin film 5. It is also possible to combine optical fibers and use light from the optical fibers.

[Example] Hereinafter, specific examples of the present invention will be described.

叉' L I. 22: Thickness 201mm produced by electrolytic polymerization method (for example, described in Takashi Kaneto-1 Katsumi Furuno: Functional Materials Vol. 4 (1984) 8).
tl, electrodes were formed on a polythiophene film with a width of 5 mm (the distance between the electrodes was 31111), and a gas sensing element was fabricated. Co, N20, and NO gases were brought into contact with this sensing element, and changes in electrical conductivity over time were measured. The results are shown in Figure 3. Further, when the pressure dependence of these gases was tested, the results shown in FIG. 4 were obtained.

It can be seen from FIGS. 3 and 4 that the conductivity of the gas sensing element of this example increases by several orders of magnitude, especially with No gas, and therefore has excellent selectivity to No and the like. Therefore, it can be used to determine whether or not No exists in the gas to be detected, and can also be used to determine whether or not No exists in the gas to be detected.
It can be seen that the O content can be easily measured.

m: A polythiophene film with a thickness of about 1 μm was polymerized on a 40×1011111 Nesa glass (rTo transparent conductive glass) plate by an electrolytic polymerization method to prepare a gas sensing element.

No color change was observed when exposed to gases such as N2, Co and N20 for about 1 hour. However, No gas (100IIIIIIH!It) k
: When exposed, after about 10 minutes, the absorption spectrum changed as shown in Figure 5, changing from red to brown or an intermediate color between blue and brown. Therefore, if the gas detection element of this embodiment is used, N.

It can be seen that the presence of gas can be easily confirmed visually.

A polypyrrole film having a thickness of 20 μm was prepared using the electrolytic polymerization method in Example 11, and a gas detection element was prepared. With Co, N, 0, and N2 gases, no change occurred in the electrical conductivity, but when exposed to No gas (200 lIIHg), an increase in electrical conductivity of about one order of magnitude was observed.

Winter LLi22 100 μm thick polyacetylene (synthesis method: T,
E to, M, 3hirakawa and 3.1k
eda:J.

Po1y, Sci, Chem, E
d 12 <1974> 11) was used to create a gas sensing element. The size is 10m11 in width,
The distance between the electrodes was 41III.

The gas detection element of this example is as shown in FIG.
No reaction was shown at all to N20 gas, but the conductivity increased by more than one digit with No gas. Therefore, it can be seen that the gas sensing element of this example is effective as a No-selective gas sensing element.

B: Chemical synthesis method (K,
)<anazawa, A, F, [)iaz and M, Krounbi: J+polym, 3ci,
Poly, 1ett, Ed, 20 (1982) 1
87) to produce a gas detection element. The gas detection element of this example is as shown in FIG.
．． Co shows no change in conductivity at all, but No.
An increase in conductivity of more than one digit was observed depending on the gas. Therefore, it was confirmed that the gas sensing element of this example was a gas sensing element with No selectivity.

[Effects of the Invention] As described above, the gas detection element of the present invention utilizes the fact that the conductivity or absorption spectrum of a conductive polymer changes upon contact with a specific gas. Since it has excellent selectivity, it is possible to easily and reliably identify the presence of the gas to be detected.

Therefore, for example, it is possible to identify whether the gas to be detected is a so-called No, c, which includes No to be detected. Furthermore, when the gas to be detected is a mixed gas, the presence of NO contained in the mixed gas can be detected, and in particular, the partial pressure of NO, and therefore the content of No gas, can be determined from the rate of change in conductivity. becomes possible.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the structure of a gas sensing element of the present invention in which a change in conductivity is utilized. FIG. 2 is a perspective view showing an example of the structure of the gas sensing element of the present invention in which a change in absorption spectrum is utilized. FIG. 3 is a diagram showing the change in electrical conductivity over time of the gas sensing element of Example 1. FIG. 4 is a diagram showing the gas pressure dependence of the electrical conductivity of the gas sensing element of Example 1 (when polythiophene is used). FIG. 5 is a diagram showing changes in the absorption spectrum of the gas sensing element of Example 2 (when polythiophene is used). FIG. 6 is a diagram showing the gas pressure dependence of the electrical conductivity of the gas sensing element of Example 4 (when polyacetylene is used). Figure 7 shows Example 5 (when using polypyrrole film)
FIG. 3 is a diagram showing changes in electrical conductivity over time of a gas sensing element in FIG. In the figure, 1 is a conductive polymer molded body, and 2a is a conductive polymer molded body. 2bG, electrode, 3a, 3b Hal, l-t'l!
, 4 is a substrate, and 5 is a conductive polymer thin film. Figure 1 Conductivity (S/cm) Figure 6 Force (mmHg) Tokiyami (Intermediate) Procedural Correction C (Method) January 2'7, 1986.45

Claims (3)

[Claims] (1) A gas sensing element made of a conductive polymer, which utilizes the fact that the conductive polymer changes its conductivity or absorption spectrum when it comes into contact with a gas. (2) The gas detection element according to claim 1, wherein the gas is nitrogen oxide gas (NOx). (3) The gas detection element according to claim 2, wherein the nitrogen oxide gas (NOx) is nitrogen monoxide gas (NO).