JP3301144B2 - Carbon monoxide detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide detecting element capable of detecting the concentration of CO charged in a cylinder, for example, even in the presence of oxygen.

[0002]

2. Description of the Related Art Hitherto, a carbon monoxide detecting element for detecting and quantifying CO has been proposed. For example, tin oxide (SnO)
₂₎ carbon monoxide detector element using a thin film can detect the SnO ₂ adsorbed CO by thin, the concentration of CO by using a change of the SnO ₂ thin film resistivity.

It is generally known that a metal composite oxide having an oxygen deficiency structure or a perovskite structure adsorbs and absorbs CO.

[0004]

However, in the prior art, CO cannot be selectively detected, and when oxygen (O ₂ ) is present in the atmosphere, O ₂ is also adsorbed. There was a problem that the concentration of CO could not be obtained.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a carbon monoxide detecting element capable of selectively detecting CO even when O ₂ is present in an atmosphere. .

[0006]

In order to achieve the above object, the present invention provides a piezoelectric substrate, an electrode for exciting an elastic wave formed on the piezoelectric substrate, and an electrode disposed on an elastic wave propagation path. And a metal composite oxide that selectively adsorbs and absorbs CO.

[0007]

According to the present invention, a metal composite oxide capable of selectively adsorbing and absorbing CO in the coexistence of oxygen is formed in a thin film on the piezoelectric substrate, and the CO is adsorbed and absorbed by the metal composite oxide. Further, an elastic wave is excited on the surface of the piezoelectric substrate by applying a high frequency to the electrode. Then, the CO concentration can be detected from the change in the frequency.

[0008]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a pair of comb-shaped electrodes 2 and 3 for exciting elastic waves are formed of gold on both ends of one surface of a piezoelectric substrate 1 formed of lithium niobate into a rectangular shape having a thickness of about 0.5 mm. did. Further, yttrium barium copper oxide (YBa ₂ Cu ₃ O ₇ ) was formed on the elastic wave propagation path of the piezoelectric substrate 1 by a reactive high-frequency magnetron sputtering method as the metal composite oxide 4 having an oxygen defect structure. The film thickness was about 5000 °.

The carbon monoxide sensing element thus obtained was brought into contact with various concentrations of a mixed gas of CO and O 2. Further, the carbon monoxide detecting element was heated by the resistance heater 5 shown in FIG. 2, and the temperature dependence of CO adsorption and absorption was examined. FIG. 3 shows the measurement results of the outlet CO concentration when the inlet concentration is 50 ppm CO and the oxygen concentration is 10%. Approx. 30 from Fig. 3
It is most adsorbed at 0 ° C. and has an inlet CO concentration of about 30
% Is adsorbed.

Next, FIG. 4 shows the measurement results of the outlet CO concentration when the temperature was kept at 300 ° C. and the inlet oxygen concentration was changed. FIG. 4 shows that the CO concentration is constant even when the oxygen concentration changes.

Next, while maintaining the temperature at about 300 ° C., it was brought into contact with various concentrations of CO gas, and a high frequency was applied to the comb-shaped electrodes 2 and 3, and the frequency changed by CO adsorption was examined. FIG. 5 shows a change in frequency at each CO concentration. From FIG. 5, it can be confirmed that the frequency is reduced due to the adsorption of CO. This is considered to be because the yttrium barium copper oxide of the metal composite oxide 4 adsorbs CO, thereby increasing the weight and slowing down the propagation speed, and as a result, the frequency is reduced. That is, the amount of adsorption of CO can be known from the change in frequency, and the concentration of CO can be detected from the change in frequency per unit time. FIG. 6 shows that the frequency change increases with the CO concentration.

In addition to yttrium barium copper oxide, lanthanum barium copper oxide, neodymium barium copper oxide, samarium barium copper oxide and the like are examples of metal composite oxides 4 having an oxygen defect structure or a perovskite structure. Similarly, the concentration of carbon monoxide could be detected.

[0013]

As described above, the carbon monoxide detecting element according to the present invention selectively absorbs and absorbs the piezoelectric substrate, the electrodes for exciting the elastic wave, and the CO disposed on the elastic wave propagation path. It is composed of a metal composite oxide, and the concentration of CO can be detected from a change in frequency due to CO adsorption and absorption.

[Brief description of the drawings]

FIG. 1 is a top view of a carbon monoxide detecting element of the present invention.

FIG. 2 is a bottom view of the carbon monoxide detecting element of the present invention.

FIG. 3 is a diagram showing CO adsorption characteristics of an element at each temperature.

FIG. 4 is a graph showing outlet CO concentration with respect to inlet oxygen concentration change.

FIG. 5 is a diagram showing a change in frequency at each CO concentration.

FIG. 6 is a diagram showing a relationship between a CO concentration and a frequency change amount per unit time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Comb electrode (input side) 3 Comb electrode (output side) 4 Metal composite oxide 5 Resistance heater

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenzo Koji 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-2-35352 (JP, A) JP-A-3 −248057 (JP, A) JP-A-4-307351 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 29/00-29/28 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. A piezoelectric substrate, an electrode for exciting an elastic wave formed on the piezoelectric substrate, and a metal composite oxide disposed on an elastic wave propagation path for adsorbing and absorbing carbon monoxide (CO). A carbon monoxide detection element comprising: 2. The carbon monoxide detecting element according to claim 1, wherein said metal composite oxide has an oxygen deficiency structure or a perovskite structure. 3. An element for detecting carbon monoxide according to claim 1, wherein the operating temperature range of the element is 200 to 300 ° C. 4. A carbon monoxide detecting element according to claim 1, wherein a resistance heating element is formed on the piezoelectric substrate.