JPH0688800A - Carbon dioxide gas sensor element and measuring method for measuring carbon dioxide gas concentration - Google Patents

Abstract

PURPOSE:To obtain a carbon dioxide gas sensor element having a small size, a low cost and high reliability and a method for measuring carbon dioxide gas concentration using the same element. CONSTITUTION:A carbon dioxide gas sensor element comprises an element body 1 made of rare earth element oxide. A variation in an electric resistance due to carbon dioxide gas concentration of the rare earth element oxide is measured by using the element thereby to detect the concentration. It has a small size, a low cost and high reliability, and can measure the concentration with high reproducibility and high aging stability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon dioxide sensor element and a carbon dioxide concentration measuring method.

[0002]

2. Description of the Related Art Conventionally, carbon dioxide sensor elements have been used for environmental hygiene such as living environment control in indoor air conditioning, for agriculture such as carbon dioxide concentration control in greenhouse cultivation, for industrial use such as exhaust gas monitoring, and early detection of fire. It has been used for a wide range of purposes such as disaster prevention. Then, conventionally, as a method for measuring the carbon dioxide concentration in the gas to be measured, a non-dispersive infrared absorption analysis method, a thermal conductivity calculation method, a diaphragm glass electrode method, a solid electrolyte such as NASICON is used. Are known.

For example, in Japanese Patent Laid-Open No. 3-134553, Nasicon (sodium ion conductor ceramic) is used, and the electromotive force due to the cell reaction when it comes into contact with carbon dioxide under a predetermined temperature condition is detected. Accordingly, a carbon dioxide sensor for detecting carbon dioxide is disclosed. Further, JP-A-3-123848 discloses a carbon dioxide concentration sensor of carbon dioxide concentration type using a lithium ion conductive solid electrolyte.

[0004]

However, these conventional measuring devices and methods have problems in that they lack versatility, such as large size and high cost, or poor reproducibility and stability over time.

An object of the present invention is to provide a carbon dioxide gas sensor element and a carbon dioxide gas concentration measuring method capable of solving the above-mentioned problems of the conventional techniques.

[0006]

In the carbon dioxide sensor element according to the present invention, the element body is made of rare earth oxide.

Further, the carbon dioxide concentration measuring method according to the present invention is characterized in that the rare earth oxide is used and the carbon dioxide concentration is detected by measuring the change in electrical resistance of the rare earth oxide depending on the carbon dioxide concentration. And

[0008]

The present invention will now be described in more detail with reference to the accompanying drawings.

In the present invention, a rare earth oxide is used to detect carbon dioxide. The oxide used in the present invention is obtained as follows. That is, first, various materials forming the rare earth oxide are mixed, the raw materials are mixed, and then calcined. Next, a binder is added to the calcined powder to form a compact, and the compact is fired. Further, by providing at least a pair of electrodes on the surface of the obtained rare earth oxide,
A carbon dioxide sensor element can be obtained.

In this sensor element, the electrical resistance value of the sensor element changes due to the chemical interaction between the oxide surface and carbon dioxide molecules in the presence of carbon dioxide.

In the present invention, a sensitizer such as a noble metal may be added when forming a molded body of a rare earth oxide.
Further, as the rare earth oxide, particularly Nd ₂ O ₃ or Ce
When O ₂ is used, it is subjected to heat treatment at a temperature higher than the measurement temperature, and then used, thereby suppressing carbonation and hydroxide formation due to air, which are inevitably generated during storage with other rare earth oxides during storage. , The life can be significantly extended.

On the other hand, according to the carbon dioxide concentration measuring method of the present invention, the rare earth oxide is used, and the change in the electric resistance depending on the carbon dioxide concentration of the rare earth oxide is measured.
The carbon dioxide concentration can be detected.

(Specific Example 1)

One specific embodiment of the carbon dioxide gas sensor element according to the present invention will be described in detail below. In order to manufacture the carbon dioxide sensor element according to the present invention, first,
Nd ₂ O ₃ powder was prepared as a raw material for the rare earth oxide. A predetermined amount was weighed, wet-milled using a ball mill, desolvated and dried.

Further, a binder was added, and the mixture was pressed at a pressure of 1 t / cm ² to form a disc. The compact was fired in air at 1073K for 1 hour.
The obtained fired body had a diameter of 10 mm and a thickness of 1 mm. A silver electrode having an area of 30 mm ² was provided on both surfaces of this fired body to obtain a carbon dioxide gas sensor element. At this time, any raw material may be used as long as the residual product of thermal decomposition is only an oxide. FIG. 1 is a schematic enlarged cross-sectional view of this carbon dioxide sensor element. As shown in FIG. 1, the carbon dioxide sensor element includes an element body 1 made of a rare earth oxide, and electrodes 2 provided on both end surfaces of the element body.

Next, the operation of the carbon dioxide sensor element of this embodiment will be described. For example, when the gas to be measured is introduced into the tube in which the carbon dioxide sensor element is installed, the electrical resistance value of the sensor element changes according to the carbon dioxide concentration. This change in electric resistance value is measured by a measuring device, and excellent reproducibility can be obtained in the relationship between the carbon dioxide partial pressure in the gas to be measured and the electric resistance value. Therefore, by previously obtaining the calibration curve from the measured values of the measured gas whose concentration is known and the reference gas, the carbon dioxide concentration can be stably and accurately determined from the calibration curve even for the measured gas whose concentration is unknown. it can.

In order to examine the sensor characteristics, as shown schematically in FIG. 2, for example, a carbon dioxide of this embodiment is formed by providing silver electrodes 2 on both surfaces of a rare earth oxide element body 1 in a ceramic tube 10. A gas sensor element was arranged, a platinum wire 11 was connected to both electrodes 2, and an AC voltage was applied to the sensor element by an AC power source 12 of 1 V and 50 KHz so that the impedance change of the sensor element could be measured. Carbon dioxide concentration of 2% as a test gas in the ceramic tube 10.
The gas, air, etc. were flowed, and the impedance change was measured at a temperature of 976K. FIG. 3 shows the impedance change measured in this way. As is clear from FIG. 3, the impedance changes according to the carbon dioxide concentration.

(Specific Example 2)

Next, another specific embodiment of the carbon dioxide sensor element according to the present invention will be described. In order to manufacture the carbon dioxide gas sensor element of this example, CeO ₂ powder was prepared as a raw material of rare earth oxide. A predetermined amount was weighed, wet-milled using a ball mill, desolvated and dried.
Further, a binder was added, and the mixture was pressed at a pressure of 1 t / cm ² to form a disc. The compact was fired in air at 973K for 1 hour. The obtained fired body had a diameter of 10 mm and a thickness of 1 mm. A silver electrode having an area of 30 mm ² was provided on both surfaces of this fired body to obtain a carbon dioxide gas sensor element. With respect to this carbon dioxide gas sensor element, an example of measuring the impedance change when the carbon dioxide gas concentration was changed at a temperature of 883 K with the same measuring device as in the case of the carbon dioxide gas sensor element of the specific example 1 described above is shown in FIG. Is shown in. It can be seen from FIG. 4 that the impedance changes according to the carbon dioxide concentration.

(Other specific examples)

FIG. 5 is a table showing another specific embodiment of the present invention. It can be seen that each of the examples has sensitivity to carbon dioxide gas. Expressing these in a relatively broad sense, the present invention is a carbon dioxide gas sensor element characterized by using a rare earth oxide, on the surface of which at least one precious metal element or a conductive oxide, at least a pair of The electrodes are connected. Particularly, as the rare earth oxide, Nd ₂ O ₃ or Ce
When O ₂ is used, the life of the sensor element can be remarkably extended. Further, by measuring the change in resistance of the carbon dioxide sensor element of the present invention, the carbon dioxide concentration can be obtained stably and with good reproducibility.

[0022]

The carbon dioxide sensor element of the present invention is small, inexpensive and highly reliable. If the carbon dioxide sensor element of the present invention is used, the carbon dioxide concentration can be measured with good reproducibility and stability over time. Therefore, the carbon dioxide sensor element of the present invention can be used for indoor air conditioning or greenhouse cultivation, and has a great economic effect.

[Brief description of drawings]

FIG. 1 is a schematic enlarged cross-sectional view of a carbon dioxide sensor element as one embodiment of the present invention.

FIG. 2 is a diagram simply showing a circuit configuration of a carbon dioxide concentration measuring method according to the present invention.

FIG. 3 is a diagram showing carbon dioxide sensitivity by a carbon dioxide sensor element according to an embodiment of the present invention.

FIG. 4 is a diagram showing carbon dioxide sensitivity by a carbon dioxide sensor element as another embodiment of the present invention.

FIG. 5 is a diagram showing a list listing various examples of rare earth oxides constituting the element body of the carbon dioxide sensor element of the present invention.

[Explanation of symbols]

 1 Element body 2 Electrode 10 Ceramic tube 11 Platinum wire 12 Constant voltage AC power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriyoshi Yamauchi 3-36 Noritake Shinmachi, Nishi-ku, Nagoya-shi, Aichi Noritake Company Limited Limited

Claims (4)

[Claims] 1. A carbon dioxide gas sensor element, wherein the element body is made of a rare earth oxide. _2. The carbon dioxide gas sensor element according to claim 1, wherein the rare earth oxide is Nd ₂ O ₃ or CeO ₂ . 3. The carbon dioxide sensor element according to claim 1, wherein at least a pair of electrodes made of at least one noble metal element is formed on the surface of the element body. 4. A carbon dioxide concentration measuring method comprising detecting the carbon dioxide concentration by using a rare earth oxide and measuring a change in electrical resistance of the rare earth oxide depending on the carbon dioxide concentration.