JPH06129973A - Nitrogen oxide detector - Google Patents

Abstract

PURPOSE:To enable selectively detecting NO even when O2 is present in the atmosphere by providing the element with an electrode, on a piezoelectric substrate, that excites elastic wave and a catalyzer that adsorbs NO. CONSTITUTION:On bath ends of one surface of a piezoelectric substrate 1, formed in rectangular of LiNbO3, and having its thickness about 0.5mm, a pair of comb-like electrodes 2 and 3, made of Au, that excites elastic wave is formed. Electrodes 2 and 3 are connected to load wires 4 and 5 with Au paste. Further, a YBa2Cu3O7 thin film, a composite oxide containing Cu, is formed as a catalyser 6 that selectively adsorbs NO and excellent in heat resistance, on an elastic wave propagation path of the substrate 1 by thickness of about 5000Angstrom . This composite oxide is excellent in heat resistance, its structure does not change even at 500 deg.C. By making the nitrogen oxide detecting element contact to the mixture gas of NO, O2 of various concentrations, and heating it, accurate NO concentration is detected even when the atmosphere contains O2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nitrogen oxides (N) contained in exhaust gas of various combustion processes such as internal combustion engines.
The present invention relates to a nitrogen oxide detecting element capable of detecting the concentration of Ox), particularly nitric oxide (NO) contained in a large amount in the source of combustion process.

[0002]

2. Description of the Related Art Conventionally, a nitrogen oxide detecting element for detecting and quantifying NOx has been proposed. For example, JP-A-61-1
No. 93945 discloses tin oxide (Sn) containing iron (Fe).
A nitrogen oxide detection element using an O ₂ ) thin film has been proposed. It said nitrogen oxide sensing element can detect the SnO ₂ adsorbs NO by thin, the concentration of NO using a change in the SnO ₂ thin film resistivity. In addition, JP-A 1-1
Japanese Patent No. 48953 describes that a nitrogen oxide detection element using a phthalocyanine-lead complex thin film can similarly detect the concentration of NO.

[0003]

However, according to the conventional technique, NO cannot be selectively detected, and when oxygen (O ₂ ) is present in the atmosphere, O ₂ is also adsorbed, so that it is accurate. There was a problem that the concentration of NO could not be obtained. Further, in the phthalocyanine-lead complex, about 15
There was a problem that the structure was destroyed at 0 ° C and sufficient heat resistance could not be obtained.

The present invention solves the above problems, and an object of the present invention is to provide a nitrogen oxide detection element which selectively detects NO even when O ₂ exists in the atmosphere and has sufficient heat resistance. It is what

[0005]

In order to achieve the above object, the present invention provides a piezoelectric substrate, electrodes for exciting elastic waves formed on the piezoelectric substrate, and an elastic wave propagation path. It is a nitrogen oxide detection element including a catalyst that selectively adsorbs NO.

[0006]

According to the present invention, with the above structure, NO is selectively adsorbed even when O ₂ is present in the atmosphere on the piezoelectric substrate, and a catalyst having excellent heat resistance is formed in a thin film. Adsorb. Further, by applying a high frequency to the electrodes, elastic waves are excited on the surface of the piezoelectric substrate. Then, the NO concentration can be detected from the change in frequency.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

(Embodiment 1) In FIG. 1, in order to excite elastic waves at both ends of one surface of a piezoelectric substrate 1 formed in a rectangular shape with a thickness of about 0.5 mm from lithium niobate (LiNbO ₃ ). A pair of comb-shaped electrodes 2 and 3 of gold (Au)
And the lead wires 4 and 5 were connected to the comb-shaped electrodes 2 and 3 by Au paste. In addition, the comb-shaped electrode 2,
3 may be formed of a metal other than Au, but when a metal that is easily oxidized is used, it is preferable to coat it with alumina in order to prevent oxidation by NO which is a corrosive gas.

Further, a yttrium barium copper oxide (YBa ₂ Cu ₃ O ₇ ) thin film, which is a complex oxide containing Cu as a catalyst 6 which selectively adsorbs NO and has excellent heat resistance, is formed by reactive high frequency magnetron sputtering. The piezoelectric substrate 1 was formed on the elastic wave propagation path with a thickness of about 5000 Å.
The composite oxide such as YBa ₂ Cu ₃ O ₇ has excellent heat resistance, and its structure does not change even at a high temperature of 500 ° C.

The nitrogen oxide detecting element thus obtained was brought into contact with a mixed gas of NO and O ₂ having various concentrations and heated to examine the selectivity and temperature dependence of NO adsorption. The results obtained when NO: 50 ppm and O ₂ : 8% were supplied are shown in FIG. From FIG. 3, it can be seen that the NO concentration at the outlet decreases with temperature up to 300 ° C. At about 300 ° C., the NO concentration was reduced by about 30%, which shows that the NO is most adsorbed. It can be seen that when the temperature is further increased, the adsorbed NO is discharged, and about 90% of the adsorbed NO is discharged up to 500 ° C. Also N
Almost the same results were obtained when O: 50 ppm and O ₂ : 0%, and it was confirmed that NO was selectively adsorbed regardless of O ₂ in the atmosphere.

FIG. 4 shows the results when the concentration of NO supplied is changed. It can be seen from FIG. 4 that the ratio of the outlet NO concentration to the supplied NO concentration is constant even if the NO concentration changes.

Therefore, while maintaining the temperature at about 300 ° C., the mixture was brought into contact with a mixed gas of NO and O _{2 having} various concentrations, a high frequency was applied to the comb electrodes 2 and 3, and the frequency changed by NO adsorption was examined. The change in frequency due to NO adsorption is shown in FIG. It can be seen from FIG. 5 that the frequency decreases linearly because NO is adsorbed. It is considered that the catalyst 6 adsorbs NO to increase the weight, and the increase in the weight decreases the propagation speed, resulting in a decrease in the frequency. Therefore, the NO concentration can be detected from the frequency change per unit time, that is, the slope of the straight line in FIG. FIG. 6 shows a plot of the slope. It can be seen from FIG. 6 that the frequency change increases as the NO concentration increases.

In FIG. 2, the piezoelectric substrate 1 is used to keep the nitrogen oxide detecting element of the present invention at a uniform temperature.
It is preferable to form the resistance heating body 7 on the surface of the side where the electrodes 2 and 3 are not formed. Further, in order to prevent the resistance heating body 7 from being oxidized by NO, it is preferable to coat it with alumina or the like.

[0014]

As described above, the nitrogen oxide detecting element of the present invention comprises the piezoelectric substrate, the electrode for exciting the elastic wave, and the catalyst for selectively adsorbing NO arranged on the elastic wave propagation path. From the change in frequency due to NO adsorption
Can be detected. By using YBa ₂ Cu ₃ O ₇ which is a complex oxide containing copper with excellent heat resistance as a catalyst, it is possible to detect a stable NO concentration even at high temperature and to selectively adsorb NO. An accurate NO concentration can be detected even if O ₂ is present.

[Brief description of drawings]

FIG. 1 is a top view of a nitrogen oxide detection element of the present invention.

FIG. 2 is a bottom view of the nitrogen oxide detection element of the present invention.

FIG. 3 is a characteristic diagram showing the temperature dependence of NO adsorption characteristics.

FIG. 4 is a characteristic diagram showing the relationship between NO concentration and NO adsorption amount.

FIG. 5 is a characteristic diagram showing a frequency change due to NO adsorption.

FIG. 6 is a characteristic diagram showing the relationship between the NO concentration and the frequency that changes per unit time.

[Explanation of symbols]

 1 piezoelectric substrate 2 comb-shaped electrode (input side) 3 comb-shaped electrode (output side) 6 catalyst 7 resistance heating element

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kunihiro Tsuruta 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kenzo Ochi, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A nitrogen oxide detection element comprising a piezoelectric substrate, an electrode for exciting an elastic wave formed on the piezoelectric substrate, and a catalyst for adsorbing nitrogen oxide arranged on an elastic wave propagation path. . 2. The nitrogen oxide detection element according to claim 1, wherein the catalyst is a complex oxide containing copper (Cu). 3. The nitrogen oxide detection element according to claim 1, wherein the operating temperature range is 200 to 400 ° C. 4. The nitrogen oxide detecting element according to claim 1, wherein a resistance heating body is formed on the piezoelectric substrate. 5. The nitrogen oxide detecting element according to claim 1, wherein the electrode and the resistance heating body are coated with ceramics.