JPH07294473A - Carbon monoxide gas detector - Google Patents

Abstract

PURPOSE:To provide a carbon monoxide gas detector which does not give a false report by ethyl alcohol vapor. CONSTITUTION:A gas detecting element M where a carrier 2 composed of composite oxide of iron oxide and titanium oxide is fixed to a platinum filament 1 and a gold catalyst 3 is carried on the carrier 2 and a compensating element K where a carrier 5 composed of composite oxide of iron oxide and titanium oxide is fixed to a platinum filament and an oxidation catalyst 6 of copper oxide, nickel oxide or manganese oxide is carried on the carrier 5, are incorporated into a bridge circuit B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide gas detecting device capable of detecting toxic carbon monoxide gas generated by incomplete combustion of combustible gas, and more particularly to a compensating element of the detecting device. Regarding configuration.

[0002]

2. Description of the Related Art A gas detecting element in which palladium, which is an oxidation catalyst for combustible gas, is supported on an alumina carrier adhered to a platinum filament, and similarly, an alumina carrier adhered to a platinum filament is not exposed to combustible gas. A catalytic combustion type gas detection device which forms a bridge circuit from a compensating element carrying active lead oxide and detects a combustible gas is disclosed in Japanese Patent Publication No. 57-52986 and widely used. Further, a semiconductor gas sensor utilizing that electric resistance changes when a metal oxide such as tin oxide comes into contact with a flammable gas is also used to detect the flammable gas.

On the other hand, unlike the above-mentioned method, a combustible gas detection material using a ternary complex oxide containing iron oxide as a main component and gold and titanium oxide contained therein has a low concentration of carbon monoxide. It has a high gas sensitivity to gas.
-195340 gazette.

[0004]

However, the gas sensor using this ternary complex oxide as a gas sensing material has the following: (1) When used at low temperature (up to 150 ° C), the gas sensitivity to carbon monoxide gas is Fall to. (2) When used at a high temperature (150 ° C. to 250 ° C.), the gas sensitivity to ethyl alcohol vapor becomes higher than the gas sensitivity to carbon monoxide gas, and when used in a carbon monoxide gas alarm device, there is a possibility that false alarm may occur. I have

An object of the present invention is to provide a gas sensor which uses iron oxide as a main component and uses a ternary compound oxide containing gold and titanium oxide, and has high sensitivity to ethyl alcohol vapor at a temperature of 150 to 250 ° C. An object of the present invention is to provide a carbon monoxide gas detection device that solves the above problem and can selectively detect a low concentration of carbon monoxide gas.

[0006]

According to the present invention, there is provided a gas detection element having a carrier attached to a platinum filament and a first oxidation catalyst carried on the carrier, and a carrier attached to the platinum filament. Comprising a compensating element carrying a second oxidation catalyst, wherein these gas detecting element and compensating element are respectively incorporated in the branches of a bridge circuit, wherein the carrier is a composite oxide of titanium oxide and iron oxide. Yes, the first oxidation catalyst is gold, and the second oxidation catalyst is copper oxide, nickel oxide, or manganese oxide.

[0007]

[Function] A gas detection element in which gold is supported on a composite oxide composed of iron oxide and titanium oxide, the electric resistance of the composite oxide decreases when contacted with carbon monoxide gas or ethyl alcohol vapor, and the electric power of the gas detection element decreases. The resistance decreases. on the other hand,
The compensating element in which copper oxide, nickel oxide or manganese oxide is supported on a composite oxide composed of iron oxide and titanium oxide has little change in electric resistance even when contacted with carbon monoxide gas, but when contacted with ethyl alcohol vapor The electric resistance of the complex oxide is lowered, and the electric resistance of the compensating element is lowered. When the platinum wire is energized, the gas detecting element and the compensating element are heated to a predetermined temperature. The decrease in the electric resistance of the gas detection element or the compensating element due to the ethyl alcohol vapor or the carbon monoxide gas occurs when the electric resistance of the composite oxide of iron oxide and titanium oxide becomes smaller than the resistance of the platinum wire.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. Embodiment 1 FIG. 1 is an electrical connection diagram showing a bridge circuit of a carbon monoxide gas detection device according to an embodiment of the present invention.

FIG. 2 is a fragmentary perspective view showing a carbon monoxide gas detecting element according to an embodiment of the present invention. FIG. 3 is a fragmentary perspective view showing a compensating element of a carbon monoxide gas detection device according to an embodiment of the present invention carrying copper oxide. The carbon monoxide gas detection device according to the present invention includes fixed resistors R ₁ , R ₂ ,
A resistance bridge circuit B including a gas detection element M and a compensation element K, a power source E for supplying power to the bridge circuit B, and a load V connected to the output side of the bridge circuit B.

As shown in FIG. 2, the gas detecting element M includes a platinum wire 1 and a composite oxide 2 composed of iron oxide and titanium oxide 6
After baking at 00 ° C., it is immersed in an aqueous solution of chloroauric acid, dried and pyrolyzed at 400 ° C. in air to give 10 parts of gold catalyst 3.
Wt% loading, heated to about 250 ℃,
When carbon monoxide gas or ethyl alcohol vapor comes into contact, the electric resistance of the composite oxide 2 decreases, and the electric resistance of the gas detection element M decreases.

As shown in FIG. 3, the compensating element K was prepared by baking a platinum oxide filament 4 on a composite oxide 5 consisting of iron oxide and titanium oxide at 600.degree. It is soaked, dried and pyrolyzed in air at 550 ° C. to carry 1% by weight of a copper oxide oxidation catalyst 6, heated to about 250 ° C., and contacted with carbon monoxide gas. Although it does not change, the electrical resistance of the complex oxide 5 decreases when it comes into contact with the ethyl alcohol vapor, and the electrical resistance of the compensating element K also decreases.

Copper oxide oxidation catalyst 6 for composite oxide 5
The supported amount of is preferably 0.1 to 5% by weight. If the supported amount is small, even if it contacts with ethyl alcohol vapor, the electrical resistance will not decrease and it will not be effective. Further, when the amount supported is large, the electrical resistance is likely to decrease when coming into contact with carbon monoxide gas, and the output of the bridge circuit decreases. The method for producing the composite oxides 2 and 5 composed of iron oxide and titanium oxide may be a generally known method. For example, an aqueous iron nitrate solution may be mixed with titanium oxide obtained by oxidizing titanium chloride with hydrogen peroxide. , Neutralize with sodium carbonate to precipitate and wash with water, then in air 40
Water is added to the crushed product after firing at 0 ° C to form a paste, which is applied to the platinum filaments 1 and 4 and 600 ° C in air.
Bake with. As for the mixing ratio of iron oxide and titanium oxide, titanium oxide 2 is suitable for 100 parts by weight of iron oxide.

FIG. 4 is a diagram showing the gas concentration dependence of the bridge output in the carbon monoxide gas detection device according to the embodiment of the present invention in which the compensating element carries a copper oxide catalyst. The characteristic line (a) is the output voltage characteristic of the bridge circuit B when the carbon monoxide gas is brought into contact therewith, and the characteristic line (b) is the output voltage characteristic when brought into contact with the ethyl alcohol vapor. It can be seen that the gas sensitivity of ethyl alcohol vapor is significantly lower than that of carbon monoxide gas.

FIG. 6 is a diagram showing the dependence of the bridge output on the amount of copper oxide carried in the carbon monoxide gas detection apparatus according to the embodiment of the present invention in which the compensating element carries a copper oxide catalyst. The amount of gold supported on the composite oxide composed of iron oxide and titanium oxide in the gas detection element was 10% by weight. The bridge output was examined by changing the amount of copper oxide supported on the compensating element. The characteristic line (e) is for 1000 ppm concentration of carbon monoxide gas, and the characteristic line (f) is for 1000 ppm concentration of ethyl alcohol vapor. When the amount of copper oxide supported increases, the sensitivity of the compensating element to carbon monoxide gas gradually increases, and the bridge output of carbon monoxide gas decreases. Further, the sensitivity of the compensating element to ethyl alcohol vapor rapidly increases when the amount of copper oxide supported is 0 to 1% by weight, and the bridge output to ethyl alcohol vapor decreases. Thus, it is found that the supported amount of copper oxide is appropriately in the range of 0.1 to 5% by weight. Comparative Example 1 For comparison, the same gas detection element as in Example 1 was used, and the compensating element was baked by adhering only a composite oxide composed of iron oxide and titanium oxide that does not support copper oxide to a platinum filament. A carbon monoxide gas detector was produced using the above.

FIG. 5 is a diagram showing the gas concentration dependence of the bridge output in the carbon monoxide gas detection apparatus according to Comparative Example 1. Characteristic line (C) is one in contact with carbon monoxide gas, and characteristic line (D) is one in contact with ethyl alcohol vapor. When a compensating element that does not support copper oxide is used, the gas sensitivity to ethyl alcohol vapor is about twice that of carbon monoxide gas, and there is a risk of false alarms due to ethyl alcohol vapor. On the other hand, when a compensating element having a composition composed of iron oxide carrying copper oxide and titanium oxide attached thereto is used as in the present invention, the gas sensitivity of carbon monoxide gas is slightly reduced, but the gas of ethyl alcohol vapor is reduced. Since the sensitivity is greatly reduced, a carbon monoxide gas alarm can be obtained in which false alarms due to ethyl alcohol vapor do not occur. Example 2 The same as Example 1 except that a nickel oxide oxidation catalyst was used as the compensating element. This compensating element K is shown in FIG.
As shown in Fig. 4, after the composite oxide 5 consisting of iron oxide and titanium oxide was baked on the platinum wire 4 at 600 ° C, it was immersed in an aqueous solution of nickel nitrate, dried, and thermally decomposed in air at 550 ° C. , 1% by weight of nickel oxide oxidation catalyst 6 was carried, and it did not change when heated to about 250 ° C. and contacted with carbon monoxide gas. The resistance decreases, and the electric resistance of the compensation element K decreases. The amount of the nickel oxide oxidation catalyst 6 supported on the composite oxide 5 is preferably 0.1 to 5% by weight.

FIG. 7 is a diagram showing the gas concentration dependence of the bridge output in the carbon monoxide gas detection device according to the embodiment of the present invention in which the compensating element carries nickel oxide. A characteristic line (g) is an output voltage characteristic of the bridge circuit B when the carbon monoxide gas is brought into contact with it. A characteristic line (h) is an output voltage characteristic when it comes into contact with ethyl alcohol vapor. It can be seen that the gas sensitivity of ethyl alcohol vapor is significantly lower than that of carbon monoxide gas. Example 3 The same as Example 1 except that a manganese oxide oxidation catalyst was used as the compensating element. As shown in FIG. 3, this compensating element K was prepared by baking a platinum filament 4 on a composite oxide 5 composed of iron oxide and titanium oxide at 600 ° C., immersing it in an aqueous solution of manganese nitrate, and drying it in air. It is thermally decomposed at 550 ° C. and carries 1% by weight of an oxidation catalyst 6 of manganese oxide. It is heated to about 250 ° C. and does not change even if it contacts carbon monoxide gas, but it contacts ethyl alcohol vapor. Then, the electric resistance of the composite oxide 5 is lowered, and the compensating element K
Has a low electrical resistance. The amount of the manganese oxide oxidation catalyst 6 supported on the composite oxide 5 is preferably 0.1 to 5% by weight.

FIG. 8 is a diagram showing the gas concentration dependence of the bridge output for the carbon monoxide gas detection device according to the embodiment of the present invention in which manganese oxide is carried on the compensating element. A characteristic line (i) is an output voltage characteristic of the bridge circuit B when the carbon monoxide gas is brought into contact with it. The characteristic line (nu) is the output voltage characteristic when it contacts with ethyl alcohol vapor. It can be seen that the gas sensitivity of ethyl alcohol vapor is significantly lower than that of carbon monoxide gas.

[0018]

According to the present invention, a gas detection element having a complex oxide of iron oxide and titanium oxide supporting a gold catalyst attached to a platinum filament and copper oxide, nickel oxide or manganese oxide are supported. Since a compensating element in which a complex oxide of iron oxide and titanium oxide is adhered to a platinum wire is used at the side of the bridge circuit, the gas detecting element changes its electrical resistance by both carbon monoxide gas and ethyl alcohol vapor. . On the other hand, the electric resistance of the compensating element changes due to the ethyl alcohol vapor, but only a minute electric resistance change occurs with respect to the carbon monoxide gas. In this way, a carbon monoxide gas detection device can be obtained in which the output of the bridge circuit gives an alarm for carbon monoxide gas but does not give a false alarm due to ethyl alcohol vapor.

[Brief description of drawings]

FIG. 1 is an electrical connection diagram showing a bridge circuit of a carbon monoxide gas detection device according to an embodiment of the present invention.

FIG. 2 is a fragmentary perspective view showing a gas detection element of a carbon monoxide gas detection device according to an embodiment of the present invention.

FIG. 3 is a fragmentary perspective view showing a compensating element of a carbon monoxide gas detector according to an embodiment of the present invention supporting copper oxide.

FIG. 4 is a diagram showing a gas concentration dependence of a bridge output in a carbon monoxide gas detection device according to an embodiment of the present invention in which a compensating element carries copper oxide.

5 is a diagram showing the gas concentration dependence of the bridge output in the carbon monoxide gas detection apparatus according to Comparative Example 1. FIG.

FIG. 6 is a diagram showing the dependence of the bridge output on the amount of copper oxide carried in the carbon monoxide gas detection apparatus according to the embodiment of the present invention in which the compensating element carries copper oxide.

FIG. 7 is a diagram showing a gas concentration dependency of a bridge output in a carbon monoxide detection device according to an embodiment of the present invention in which a compensating element carries nickel oxide.

FIG. 8 is a diagram showing the gas concentration dependence of the bridge output in the carbon monoxide detection device according to the embodiment of the present invention in which manganese oxide is supported on the compensating element.

[Explanation of symbols]

 1 Platinum Wire 2 Iron Oxide-Titanium Oxide Carrier 3 Gold Catalyst 4 Platinum Wire 5 Iron Oxide-Titanium Oxide Carrier 6 Oxidation Catalyst M Gas Detection Element K Compensation Element B Bridge Circuit

Claims (1)

[Claims] 1. A gas detection element in which a carrier attached to a platinum filament carries a first oxidation catalyst, and a compensation element in which a carrier attached to a platinum filament carries a second oxidation catalyst. Prepare,
In the device in which the gas detecting element and the compensating element are respectively incorporated in the branch sides of the bridge circuit, the carrier is a composite oxide of titanium oxide and iron oxide, the first oxidation catalyst is gold, and A carbon monoxide gas detection device, wherein the second oxidation catalyst is copper oxide, nickel oxide or manganese oxide.