JPS6082953A - Carbon monoxide sensing element - Google Patents

Abstract

PURPOSE:To improve sensitivity for carbon monoxide of a gas sensing element comprising a metal oxide semiconductor inserted between upper and lower two electrodes by using ruthenium oxide for the electrode material. CONSTITUTION:A lower electrode 3 is printed on the surface of an alumina substrate 2 with ruthenium oxide paste which is calcined to complete the lower electrode 3. A gas sensing layer 4 comprising a metal oxide semiconductor is formed on the electrode 3, further, an upper electrode 5 is formed with the same paste to prepare thus a gas sensing element. The gas sensing element prepd. by this process has improved sensitivity for gaseous CO, but low sensitivity for gaseous hydrogen, and ethanol vapor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a -carbon oxide gas detection element with improved sensitivity characteristics for -carbon oxide.

[Background of the invention]

Carbon monoxide gas detection elements are used for fire alarms in hotels, etc., carbon monoxide poisoning prevention alarms in general homes, etc.

The carbon monoxide gas detection element used for these alarms must be able to detect only -carbon oxide gas without being disturbed by other gases, and must not cause false alarms.

On the other hand, if a false alarm is caused by other gas disturbances,
This has become a common practice, and even when carbon monoxide gas is being generated and a warning is issued, people do not pay attention to it, leading to a major accident.

As a conventional carbon monoxide gas detection element, a tin oxide (SaO2) ceramic sintered body using a platinum electrode has been mainly used.

For this carbon oxide gas detection element, various additives that are highly sensitive only to carbon oxide have been studied, but the sensitivity to hydrogen gas and ethanol gas is higher than to carbon oxide gas. The reality is that false alarms are inevitable, and there is an urgent need to develop a detection element that is highly sensitive to carbon oxide gas.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a carbon monoxide gas detection element that exhibits high sensitivity to p, -carbon oxide gas.

[Summary of the invention]

That is, the present invention is characterized in that by using ruthenium oxide for the upper electrode and the lower electrode, the sensitivity to carbon oxide gas is improved, while the sensitivity to hydrogen gas and ethanol gas is greatly reduced. shall be.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below.

First, the inventors developed various oxide conductor materials and additives to improve the sensitivity of carbon oxide gas.

and electrode materials were investigated.

As a result, it was found that when ruthenium oxide was used as an electrode material, the sensitivity to -carbon oxide gas was improved, and the sensitivity to hydrogen gas and ethanol gas was significantly reduced.

We have also discovered that in order to make the most of the effects of this electrode material, a sandwich structure is optimal because it allows gas to easily come into contact with the electrode.

Furthermore, the oxide semiconductor is tin oxide (Sn02).

Tungsten oxide (WO,), chromium oxide (Cr2
0).

Zinc oxide (ZnO), indium oxide (In20)
It has been found that the above-mentioned effects of using ruthenium oxide as an electrode are high in this case.

An example will be shown below and its details will be explained.

Two types of test elements were prepared and compared: an element using a conventional platinum electrode and an electrode using ruthenium oxide of this example.

This element was made in the shape of a sandwich, as shown in the figure, using a square alumina substrate with -5 sides. The procedure for creating it is as follows.

First, a zigzag-shaped platinum heater 1 is printed on the back surface of an alumina substrate 2 using platinum paste.

After drying this, the heater was baked at 1200° C. for 2 hours using an electric heater.

Next, a lower electrode 3 was printed on the surface of the alumina substrate 2 using platinum paste or ruthenium oxide paste, and after drying, it was held at a maximum of 900° C. for 10 minutes using a belt furnace to bake the lower electrode 3. .

On this lower electrode 3, a gas-sensitive layer 4 was printed using a paste prepared by adding 10% wt of zinc borosilicate binder glass to a predetermined oxide semiconductor powder. After drying this gas-sensitive layer 4, an upper electrode 5 was printed on it using the same paste as the lower electrode 3, and after drying, it was held at a maximum temperature of 900° C. for 10 minutes using a belt furnace to produce an element. .

In this way, the characteristics of two types of elements having platinum electrodes and ruthenium oxide electrodes were measured, and the results are summarized in Table-1.

The element temperature was 400°C. The gas concentration is 10
00 ppm. Sensitivity is the value obtained by dividing the resistance value of the element immediately before contact with gas by the resistance value of the element after contact with gas. From Table-1, oxide semiconductor Cr203 (A5
, 6), when comparing a platinum (pt) electrode and a ruthenium (Ru02) electrode, the ruthenium electrode has better sensitivity to -carbon oxide gas and better sensitivity to hydrogen gas and ethanol gas. It can be seen that there has been a significant decrease in contrast.

For example, when looking at the oxide semiconductor SnSn02 (, 2), it is reduced to 1/2.4 for hydrogen gas and 1/7.7 for ethanol gas.

Furthermore, it is clear from Table 1 that the sensitivity characteristics of the ruthenium electrode are influenced by the type of oxide semiconductor.

It can be seen that 5n02 is the best oxide semiconductor, followed by WO3, ZnO, In2O5, and Cr2O5 in that order.

Although this embodiment has been described with respect to an element created using a printing method, similar effects can be obtained with a thin film using a vapor deposition method or the like.

Furthermore, even if several wt % of additives are added to the oxide semiconductor, the above effects are not affected.

〔Effect of the invention〕

According to the present invention as described in detail above, ruthenium is used for the upper and lower electrodes, and an oxide semiconductor is sandwiched between the electrodes, so that the sensitivity to carbon oxide gas is improved and the sensitivity to hydrogen gas is improved. The sensitivity to gas and ethanol gas could be greatly reduced.

As a result, - there are no false alarms for carbon oxide gas9;
-We were able to greatly improve the accuracy and reliability of carbon oxide gas detection.

[Brief explanation of the drawing]

The attached drawing is a perspective view of an FC element prepared for testing a carbon oxide gas detection element. DESCRIPTION OF SYMBOLS 1... Heater, 2... Narumina substrate, 3... Lower electrode, 4... Gas-sensitive layer, 5... Upper electrode. Agent Patent Attorney Masami Akimoto

Claims (1)

[Scope of Claims] 1. In a carbon monoxide gas detection element having a sandwich-like gas-sensitive layer interposed between an upper electrode and a lower electrode, ruthenium oxide is used for the upper electrode and the lower electrode. A carbon monoxide gas detection element featuring: 2. In the gas-sensitive layer according to claim 1, tin oxide (Sn02) + tungsten oxide (WO5). Rimu oxide (Cr205) *Zinc oxide (ZnO)
, or indium oxide (In203).