JPH0854363A - Capacitance type carbon dioxide sensor - Google Patents

Abstract

PURPOSE:To obtain a sensor of superior reliability which can quickly detect concentration change of CO2 by increasing reaction speed of forming/ decomposing carbonate and obtain a highly accurate and stable change in electrostatic capacitance, by setting a working temperature of a CO2 detector to be not lower than a specific valve. CONSTITUTION:The capacitance type CO2 sensor 1 is constituted of a disc- shaped conductive CO2 detector formed out of a mixture of a perovskite-type oxide and Cu, and silver electrodes 3 layered at both surfaces of the detector 2. As a material for the CO2 detector 2, BaCO3 and TiO2 of an equal molar composition are weighed, mixed, crushed and baked to obtain BaTiO3. Then, the obtained BaTiO3 and CuO of an equal molar composition are weighed, mixed, molded into a disc shape by a molding press, and baked. Accordingly the CO2 detector 2 is obtained. A working temperature of the CO2 detector is set to be not lower than 560 deg.C, preferably, in a high temperature range of 600-800 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CO ₂ sensor, and more particularly to a capacitance type carbon dioxide gas sensor utilizing the change characteristic of the capacitance of a metal oxide in a CO ₂ atmosphere.

[0002]

2. Description of the Related Art In recent years, a capacitance type carbon dioxide gas sensor has been developed which detects CO ₂ by utilizing the change characteristic of capacitance of metal oxide.

A conventional capacitance type carbon dioxide gas sensor will be described below. As a capacitance type carbon dioxide sensor,
For example, a perovskite metal oxide and a non-composite metal oxide are mixed to form a CO ₂ detector, and the operating temperature is 456.
° C. The reversible carbonate formation and decomposition reaction of the non-composite metallic oxide and CO ₂ in the CO ₂ sensing member in at ～555 ° C., by changing the capacitance of the CO ₂ sensing elements, the capacitance An electrostatic capacitance type carbon dioxide gas sensor for detecting the CO ₂ concentration from the change is disclosed in JP-A-4-24548.

[0004]

However, in the above conventional configuration, the capacitance type carbon dioxide gas sensor has an operating temperature of 5
Since the reaction rate of the carbonate formation / decomposition reaction at a temperature lower than 60 ° C. is slow, it cannot follow the change in the CO ₂ concentration. As a result, C
There are variations in sensitivity with respect to the O ₂ concentration, and even if the CO ₂ concentration becomes zero, the capacitance does not recover to the original value.
There was a problem that reproducibility and stability were lacking when repeatedly measuring the CO ₂ concentration.

The present invention solves the above-mentioned problems of the prior art. By increasing the operating temperature to a high temperature range of 560 ° C. or higher, the reaction rate of the carbonate formation / decomposition reaction is accelerated and the change in CO ₂ concentration is promptly changed. It is an object of the present invention to provide a highly reliable electrostatic capacitance type carbon dioxide gas sensor that can detect and repeatedly obtain a highly accurate and stable change in electrostatic capacitance even when repeatedly measured.

[0006]

In order to achieve this object, the electrostatic capacitance type carbon dioxide gas sensor according to claim 1 of the present invention comprises a CO ₂ detector formed of a mixture of perovskite oxide and CuO. A capacitance type carbon dioxide gas sensor having, wherein the operating temperature of the CO ₂ detector is 560 ° C. or higher,
It preferably has a constitution of 600 ° C to 800 ° C. According to a second aspect of the present invention, in the electrostatic capacitance type carbon dioxide gas sensor according to the first aspect, the perovskite oxide is BaTi.
It has a structure containing O ₃ .

The operating temperature of the CO ₂ detector is 560 ° C. or higher, preferably 600 ° C. to 800 ° C.
The adsorption amount of O ₂ is the largest and the reaction rate of the carbonate formation / decomposition reaction is fast, which is a temperature range suitable for a CO ₂ sensor.

[0008]

With this structure, perovskite oxide and C
By operating the CO ₂ detector of the mixture of uO in the high temperature range of 560 ° C. or higher, the reaction rate of carbonate formation / decomposition reaction is accelerated, and sufficiently good sensitivity, responsiveness and reproducibility are obtained as sensor characteristics. be able to.

[0009]

EXAMPLE An electrostatic capacitance type device according to an example of the present invention will be described below.
The carbon dioxide sensor will be explained with reference to the drawings.
It FIG. 1A shows a capacitance type according to an embodiment of the present invention.
FIG. 1B is a plan view of a carbon dioxide sensor, and FIG.
FIG. 1 is a side view of a capacitance type carbon dioxide gas sensor according to an embodiment.
is there. 1 is a capacitance type CO in one embodiment of the present invention ₂
Sensor, 2 is a mixture of perovskite type oxide and CuO
Disk-shaped conductive CO₂Detector body, 3 is CO₂Inspection
It is a silver electrode laminated on both sides of the knowledge body 2.

The electrostatic capacitance type CO ₂ configured as described above
The method of manufacturing the sensor 1 will be described below.

First, as a raw material for the CO ₂ detector 2, BaC is used.
O ₃ (trade name: barium carbonate, Wako Pure Chemical Industries) and TiO ₂
(Product name: P25, manufactured by Nippon Aerosil Co., Ltd.) is weighed in an equimolar composition, and mixed and pulverized using a mixing raisage machine (Product name: Ishikawa type mixing raisage machine). This mixture is then added to 120
BaTiO ₃ is obtained by firing at 0 ° C. for 12 hours. Next, this BaTiO ₃ and CuO (trade name: copper oxide, manufactured by Wako Pure Chemical Industries, Ltd.) are weighed in equimolar compositions and mixed using the same mixing / raising machine. Then, this mixture was molded with a molding press (hydraulic 25 tons) at a molding pressure of 3 ton / cm ^{2 to} a diameter of 1
Molded into a disc shape with a thickness of 2 mm and a thickness of 0.5 mm
A CO ₂ detector 2 is obtained by firing at 5 ° C. for 5 hours. Next, a silver paste (trade name: SP-5) is formed on both sides of the CO ₂ detector 2.
1, made by Tanaka Kikinzoku Co., Ltd., and dried at 100 ° C. for 2 hours to form a laminated electrode 3 made of silver, and a platinum lead wire (not shown) is added on the electrode 3 to form a capacitance type CO ₂ sensor 1 was obtained.

Using the capacitance type carbon dioxide sensor according to the embodiment of the present invention manufactured as described above, the sensitivity characteristic test was conducted.

Experimental Example Sensitivity characteristics to CO ₂ were measured using the capacitance type CO ₂ sensor 1 in one example of the present invention. The measurement method is ₂ from air containing no CO 2.
% Change in capacitance of the capacitance type CO ₂ sensor 1 when switching to air containing CO ₂ and capacitance when switching from air containing CO ₂ to air not containing CO _2. Change of impedance analyzer (Product name: 41
92A, manufactured by YHP), and the sensitivity was measured under the condition of a frequency of 50 KHz. Here, sensitivity and was the ratio of the capacitance in air containing CO ₂ to the electric capacitance in the air not containing _{CO 2 (Cco 2 / Cair)} .
First, the sensitivity of an air atmosphere containing no CO ₂ (sample 1), then switch the CO ₂ 2% containing the CO ₂ atmosphere after 2 minutes Sensitivity (subject 2), further containing again CO ₂ Sensitivity 2 minutes after switching to the air atmosphere (Sample 3)
Operating temperature 350,450,550,560,70
The measurement was repeated twice at 0 and 800 ° C. The results are shown in (Table 1).

[0014]

[Table 1]

As is clear from this (Table 1), 550
In the temperature range of ℃ or less, although the recovery of the electrostatic capacity after switching from the air containing CO ₂ to the air not containing CO ₂ is poor and there is a problem in repeated use,
The sensitivities in the temperature range of 0 ° C or higher are 1.0 for both Sample 1 and Sample 3 and 2.1 or higher for Sample 2, and the reproducibility is good and the change in the capacitance and its recovery are sufficiently good as sensor characteristics. Was given.

Further, thermal analysis measurement of this capacitance type CO ₂ sensor 1 was performed. The result is shown in FIG. FIG. 2 is a diagram showing a ratio of weight change to temperature change of the capacitance type carbon dioxide sensor in the experimental example. As is clear from FIG. 2, in an air atmosphere, a decrease in weight is recognized from about 300 ° C. to about 600 ° C. as the temperature rises. on the other hand,
In the CO ₂ atmosphere, the weight loss starts from T ₁ ° C and shifts to the high temperature side.
₂ It is considered to represent the amount of adsorption. Therefore, in order to use it as a CO ₂ sensor, it is sufficient to use a temperature range in which the amount of CO ₂ adsorbed is large, and it can be seen from FIG.
It has been found that a temperature of 00 ° C to 800 ° C is suitable.

As described above, according to this embodiment, the CO ₂ detector of the mixture of the perovskite oxide and CuO is 560.
By operating in a high temperature range of ° C or higher, the reaction rate of carbonate formation / decomposition reaction is accelerated to detect CO ₂ concentration change rapidly, and even if repeated measurement is performed, highly accurate and stable electrostatic A change in capacity can be obtained.

[0018]

As described above, according to the present invention, the CO ₂ detector of the mixture of perovskite oxide and CuO is operated in the high temperature range of 560 ° C. or higher, so that the sensor characteristics sufficiently good sensitivity and responsiveness, It is possible to realize a highly reliable electrostatic capacitance type carbon dioxide gas sensor capable of obtaining reproducibility.

[Brief description of drawings]

FIG. 1A is a plan view of an electrostatic capacity type carbon dioxide gas sensor according to an embodiment of the present invention. FIG. 1B is a side view of an electrostatic capacity type carbon dioxide gas sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a ratio of weight change with respect to temperature change of the capacitance-type carbon dioxide sensor in an experimental example.

[Explanation of symbols]

1 Capacitance type CO ₂ sensor 2 CO ₂ detector 3 electrode

Claims (2)

[Claims] 1. A capacitance type carbon dioxide gas sensor having a CO ₂ detector formed of a mixture of perovskite oxide and CuO, wherein the operating temperature of the CO ₂ detector is 560.
A capacitance-type carbon dioxide gas sensor characterized by having a temperature of ℃ or higher. 2. The perovskite oxide is BaTiO ₃
The capacitance-type carbon dioxide gas sensor according to claim 1, which contains: