JPH0465662A - Sensor for oxidative gas - Google Patents

Abstract

PURPOSE:To obtain the gas sensor which has a high sensitivity to oxidative gases of NOx, O3, etc., and is slightly disturbed by combustible gases by providing a WO3 film connected with a pair of electrodes and a heater for heating the WO3 film on a heat resistant insulating substrate. CONSTITUTION:This sensor consists of the heat resistant insulating substrate 2 consisting of alumina, etc., the thin film 4 of WO3, the electrodes 6, 8, 10, the heater 12 of an RuO2 film, etc. The WO3 has the exceptionally high sensitivity to the oxidative gases of NOx, O3, etc., and has the lower sensitivity to other gases and, therefore, the gas sensor having the high sensitivity to the NOx is usable for controlling the introduction of the outdoor air to an automobile. Not the combustible gases, such as CO and H2, in the exhaust gases are detected but the NOx in the exhaust gases is detected by the gas sensor having the high sensitivity to the NOx. The NOx is contained in a large amt. in diesel exhaust gases and the sensor having the high sensitivity to the diesel exhaust gases is obtd. The NOx is included in gasoline exhaust gases as well. The detection of the gasoline exhaust gases is possible therefrom as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a sensor for oxidizing gases such as NOx and Os. The invention also relates to obtaining a gas sensor for controlling the introduction of outside air into a motor vehicle through the detection of NOx.

[Prior Art] Japanese Patent Publication No. 45-17.038 discloses a gas sensor in which PL is added to a WO3 thin film. The detection targets shown here are H2 and NHs, NOx and 01
Detection is not mentioned.

Separately, Japanese Patent Publication No. 59-50.528 proposes controlling the introduction of outside air into an automobile using a metal oxide semiconductor gas sensor. This technology uses a gas sensor to detect pollution in the outside air, especially bad odors caused by exhaust gases from the surrounding air, and then shuts off the outside air from entering the cabin.

The problem here is that the sensor's sensitivity to exhaust gas from a diesel engine is lower than its sensitivity to exhaust gas from a gasoline engine. Gas sensors typically detect flammable gases. Gasoline exhaust gas contains large amounts of CO and H3.
It is easy to obtain high sensitivity. NOx in exhaust gas acts to cancel the sensitivity to combustible gases, but the amount of NOx in gasoline exhaust gas is small. The CO and H5 concentrations in diesel exhaust gas are low, and the sensitivity obtained from the sensor is negligible. Diesel exhaust gas contains a large amount of N.
The inclusion of Ox further reduces the sensitivity of the sensor.

Gas sensors for controlling outside air intake in automobiles are required to detect contamination of outside air according to the senses of passengers. Diesel exhaust gas is smellier than gasoline exhaust gas, and detection of diesel exhaust gas must be prioritized over detection of gasoline exhaust gas.

However, known gas sensors have low sensitivity to diesel exhaust gas and can only detect gasoline exhaust gas.

[Aoi Akira's problem] The inventor discovered that the WO1 film has an exceptionally high sensitivity to oxidizing gases such as NOx and 0'1, and low sensitivity to other gases. Gas sensors that are highly sensitive to NOx can be used to control the outside air intake of automobiles. A sensor that is highly sensitive to NOx 9 detects NOx in the exhaust gas, rather than detecting combustible gases such as CO and H2 in the exhaust gas. NOx is contained in large amounts in diesel exhaust gas, and a highly sensitive sensor can be obtained for diesel exhaust gas.NOx is also contained in gasoline exhaust gas, and gasoline exhaust gas can also be detected from this.

An object of this invention is to obtain a sensor that is highly sensitive to oxidizing gases such as NOx and Ol. Other problems of this invention are:
An object of the present invention is to obtain a gas sensor for controlling outside air intake for automobiles that is highly sensitive to diesel exhaust gas.

[Configuration of the invention 1 In this invention, the WO1 film is used as the gas detection material.

Compared to other metal oxide semiconductors, WO1 film has lower NOx and 03
It has high sensitivity to combustible gases such as CO and H3, and almost no sensitivity to combustible gases such as CO and H3. This fact can also be used to detect diesel exhaust gas and the like. Since NOx decomposes during the process of diffusing inside Wo, it is preferable to use WOj as a thin film.

[Example] Fig. 9 shows the structure of a gas sensor. In the figure, 2 is a heat-resistant insulating substrate such as alumina, 4 is a thin film of WOl, 6, 8 .
10 is an electrode, and 12 is a heater such as a Ru01 film. W
The Os thin film 4 was formed by oxidizing a vacuum-deposited W film (thickness: 0.3 μm). However, it is not limited to thin films, and film thicknesses of 10 to 20
A thick film on the order of μm can also be used. Although the WO3 membrane 4 used is simple, a sensitizer such as a noble metal catalyst may be added thereto. As a comparative example, 5n02 film, In, '6. A film (both 0.3 μm thick and formed by vacuum evaporation) was used.

FIGS. 1 to 3 show the characteristics of a gas sensor using WO3 Thumed 4. The sensor temperature is 300° C., and the vertical axis of each figure represents the sensor resistance Rs. tIglrM is 03, NOx%H
8. This shows the sensitivity of ethanol. WO3 membrane 4
is 0. It is highly sensitive to H2 and NOx, has no sensitivity to H2 or CO, and has only a slight sensitivity to ethanol.

Figures 2 and 3 show the sensitivity to exhaust gas from an automobile engine. In these measurements, exhaust gases from diesel and gasoline engines were all collected with sampling bags, diluted to 5000 ppm, and used. The sensor is more sensitive to diesel exhaust gas than gasoline exhaust gas, and both become highly resistant upon contact with exhaust gas. This is because the sensor is primarily sensitive to NOx in the exhaust gas.

Figures 4 and 5 show the results when In, O, and thin films were used instead of WO and thin films. J, SnO in Figure 7.

The results when using a thin film are shown. The exhaust gas sensitivity of the WO1 thin film 4 is In, 0. and SnO. These differences in sensitivity are due to differences in NOx sensitivity and differences in combustible gas sensitivity.

Figure 8 shows a commercially available SnO thick film general-purpose sensor (TGS8).
22. "TGS822" (trade name) indicates its sensitivity to gasoline exhaust gas and diesel exhaust gas.

There is almost no sensitivity to diesel exhaust gas, and the resistance value decreases with gasoline exhaust gas. This is SnO.

This is because the membrane is more sensitive to combustible gases in gasoline exhaust gas than to NOx.

[Effects of the Invention] According to the present invention, a gas sensor can be obtained that is highly sensitive to oxidizing gases such as NOx and 03, and is minimally interfered with by combustible gases.

Such a gas sensor can be used to control outside air introduction into an automobile by detecting NOx in exhaust gas.

[Brief explanation of the drawing]

Figures 1 to 3 are characteristic diagrams of the embodiment, Figures 4 to 8 are characteristic diagrams of conventional examples; FIG. 9 is a plan view of the embodiment. In the figure, 2 board 4 WO3 membrane, 12 heater.

Claims (4)

[Claims] (1) WO with a pair of electrodes connected on a heat-resistant insulating substrate
An oxidizing gas sensor equipped with a WO_3 film and a heater for heating the WO_3 film. (2) The oxidizing gas sensor according to claim 1, wherein the oxidizing gas to be detected is O_3. (3) The oxidizing gas sensor according to claim 1, wherein the oxidizing gas to be detected is NOx. (4) The oxidizing gas sensor according to claim 3, wherein the NOx to be detected is NOx in automobile exhaust gas.