JP2522836B2 - Carbon dioxide detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a carbon dioxide detecting element. More specifically, the present invention relates to powdered chlorine apatite, which has a high reactivity with carbon dioxide gas and is suitable as a carbon dioxide gas detection element material, and its use.

(B) Conventional technology Apatite (apatite) is a calcium phosphate containing fluorine, chlorine, and a hydroxyl group, and one rich in chlorine is called chlorine apatite.

Regarding the synthesis of chlorapatite [theoretical formula: Ca ₁₀ (PO ₄ ) ₆ (Cl) ₂ ], dry method, hydrothermal method, melting method, etc. have been conventionally known. Although it was said that the compound could not be synthesized below, it has been found by the inventors of the present invention that by reacting hydroxyapatite with ammonium chloride in an aqueous medium, almost pure chlorapatite close to the theoretical formula can be obtained. (JP-A-64-28212).

On the other hand, as an application of apatite, hydroxyapatite [Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ] has the property that its electrical resistance fluctuates when it comes into contact with carbon dioxide at high temperature, and therefore it is The use of carbon gas, which is a composite material with calcium, as a sensing element material has been proposed (Japanese Patent Laid-Open No. 2000-242242).
62-242847).

Further, the inventors have further found that a single phase of chlorapatite or a solution of chlorapatite in solid solution with hydroxyapatite may change its electric resistance when it comes into contact with carbon dioxide gas without being combined with other materials. Found (Japanese Patent Laid-Open No. 64-28)
No. 212).

(C) Problems to be Solved by the Invention When chlorine apatite is used as a sensing element material for the above-mentioned carbon gas, etc., it is required to have a form of powdered chlorine apatite composed of uniform fine particles. The powdered chlorapatite used is in the form of an agglomerate, and is in a non-uniform granular state. Therefore, the detection element material obtained by using this powder has problems such as cracking, uniform coating, and thin film cannot be obtained, and sensitivity, durability, response characteristics, etc. At present, no practical carbon dioxide sensor has been obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a carbon dioxide detecting element using powdered chlorine apatite in a uniform granular state.

(D) Means for Solving the Problems Thus, according to the present invention, a freeze-dried product of a chlorine apatite precipitate obtained by directly or indirectly treating hydroxyapatite with ammonium chloride is provided between a pair of electrodes. ,
Provided is a carbon dioxide gas detection device in which a detection element material made of powdered chlorine apatite having a particle size of 0.1 μm or less is electrically interposed.

The powdered chlorine apatite of the present invention comprises a freeze-dried body of chlorine apatite. The above-mentioned chlorine apatite is obtained by directly or indirectly treating hydroxyapatite with ammonium chloride, and high-purity chlorine apatite having a high degree of chlorine substitution is preferable. As the above-mentioned “direct treatment with ammonium chloride”, for example, a method known as a wet method in the art, in which hydroxyapatite is reacted with ammonium chloride in an alkaline aqueous medium, can be mentioned as a preferable example. On the other hand, as a method of "indirectly treating with ammonium chloride", for example, after burning hydroxyapatite, it is mixed with calcium chloride in an ethanol medium, and after burning the mixture, excess calcium is eluted with ammonium chloride. Suitable methods include those known in the art as dry methods. The conditions for synthesizing chlorapatite by the wet method and the dry method are described in detail in the prior application filed by the present inventors (Japanese Patent Application Laid-Open No. 64-28212), and thus the description is referred to.

The powdered chlorine apatite used in the present invention is obtained by freeze-drying the above chlorine apatite. The conditions for this freeze-drying include, for example, pre-freezing with liquid nitrogen or the like and then freeze-drying under reduced pressure of 100 μHg or less. The freeze-dried product obtained by this freeze-drying has a particle size of 0.
It becomes a homogeneous powder body of 1 μm or less.

The present invention comprises a freeze-dried product of a chlorine apatite precipitate obtained by directly or indirectly treating hydroxyapatite with ammonium chloride between a pair of electrodes, and comprises a powdered chlorine apatite having a particle size of 0.1 μm or less. The present invention provides a carbon dioxide gas detecting element in which the following detecting element material is electrically interposed.

In the carbon dioxide gas detecting element, powdered chlorine apatite, which is a freeze-dried product of chlorine apatite obtained by the wet method or the dry method, is used as the detecting element material. In this case, the freeze-dried product may be a mixture of a wet method, a dry method and a mixture. The form of the element material formed may be any one known in the art, such as a pellet type or a thin film type. In the case of the pellet type, the above-mentioned powdered chlorine apatite is pressure-molded into a desired shape (see FIG. 3). Further, in the case of a thin film type, the above-mentioned powdered chlorine apatite is mixed with an appropriate binder and a plasticizer in an appropriate solvent, and after further viscosity adjustment, it is applied and molded to a predetermined thickness to form a thin film detection element material. To be done. As a form of the element applied in this case, as shown in FIG. 4, a pair of electrodes may be formed on both sides of a thin film element material and provided on an insulating substrate.
As shown in FIG. 5, a thin film element material (b) is provided on an insulating substrate (a), and a pair of comb-shaped electrodes (c) and (c) are formed on the surface of the element material. Good. Specifically, reference is made to the description of Examples below.

(E) Action According to the present invention, the chlorine apatite precipitate obtained by directly or indirectly treating hydroxyapatite with ammonium chloride is formed between the pair of electrodes by a freeze-dried product, and is 0.1 μm.
The detection element material made of powdered chlorine apatite having the following particle size is electrically interposed.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

(F) Example Example 1 Synthesis of powdered chlorine apatite by wet method As a starting material, 500 g of calcium carbonate for alkali analysis (manufactured by Wako Pure Chemical Industries, Ltd.) was calcined at 1000 ° C. for 3 hours to decarboxylate, and then 20
When it was 0 ° C., it was taken out of the electric furnace and steam hydrated.
This was aged for 1 day and then suspended in distilled pure water of 5.
This was stirred with a stirring motor, and during this period, phosphoric acid (Wako Pure Chemical Industries, special grade reagent) diluted 3-fold into the suspension was continuously added dropwise, and the addition was completed at pH 9.0 to 10.0. It was confirmed by powder X-ray diffraction that the product obtained here was hydroxyapatite (hydroxyapatite: hereinafter abbreviated as HAp).

After that, ammonium chloride (manufactured by Showa Kagaku Co., Ltd., special grade reagent) dissolved in 10 times distilled pure water was added dropwise so that the water of crystallization of HAp was replaced with almost the same amount of chlorine ions, and pH was adjusted to 8 with a 3N-ammonia solution. It was adjusted to 0 to 10.0 and stirred overnight.
Then, the reaction mixture is allowed to stand at room temperature, and when the formed precipitate is settled, the reaction mixture is filtered, and the obtained precipitate is preliminarily frozen in liquid nitrogen, and then freeze-dried under reduced pressure of 25 μHg. Then, about 800 g of chlorine apatite fine particles having a particle diameter of 0.1 μm or less was obtained. A flow chart of the synthesis up to the above chlorine apatite is shown in FIG.

Example 2 Synthesis of Chlorapatite by Dry Method About 60 g of the calcined powder of HAp obtained in the above Example 1 was weighed, and about 10 g of calcium chloride (Showa Kagaku Co., Ltd., first-class reagent) was added to this, and the mixture was added to ethanol. And mixed for 8 hours.
This was calcined at 800 ° C for 24 hours to obtain chlorinated apatite with excess calcium.
Shown in the figure).

Then, add excess calcium from this chlorine apatite to about 10 ammonium chloride (Showa Chemical Co., Ltd. special grade reagent).
Elution was carried out in an aqueous solution prepared by dissolving 0 g of 5 in distilled water. After that, the product is washed with distilled water (2), filtered, and the obtained filtered material is collected.
It was dried at 120 ° C.

This was freeze-dried under the same conditions as above, and the particle size was 0.1.
About 65 g of fine particles of chlorine apatite having a size of less than μm were obtained.

Example 3 Production of Carbon Dioxide Gas Detector i) FIG. 3 shows the powdered chlorine apatite obtained by the wet method in Example 1 and the chlorine apatite produced by the dry method in Example 2 respectively. A pallet type carbon dioxide detecting element was produced.

That is, first, add each powdered chlorine apatite to 15 x 10 x 2 mm.
Was uniaxially pressure-molded at 200 kg / cm ² and baked at 800 ° C. for 2 hours to prepare a detection element pellet (2). Then, the electrode paste (Pt) is applied as shown in the figure so that the surface of this pellet is divided into two, and platinum lead wires (4) (4) are applied to this.
Then, the electrodes (3) and (3) were baked at 800 ° C. for 15 minutes to prepare a carbon dioxide detection element (1).

ii) Further, as shown in FIG. 4, a pair of front and back electrodes are formed by using each of the powdered chlorine apatite obtained by the wet method obtained in Example 1 and the powdered chlorine apatite obtained by the dry method obtained in Example 2. A thin film type carbon dioxide gas detection element having an element material interposed therebetween was produced.

That is, first, take 100 g of each powdered chlorine apatite,
20-30% by weight of polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd .; BL-1, BM-2, BH-3 etc.) as a binder is added to each, and a mixture of diethyl phthalate and dibutyl phthalate as a plasticizer is 20-30% by weight. In addition, 50% by weight of a mixed solution of solvents (toluene, methanol, ethanol) was added, and an antifoaming agent (manufactured by Sanyo Kasei Co., Ltd .; Ionet S-85)
0.1 wt% was added and mixed in a ball mill for 15 hours.
Then, defoam with a rotary evaporator to reduce the viscosity to 1000.
The device film having a film thickness of 100 μm or less was formed by the doctor blade method while adjusting so as to be cps.

Then, this is cut into a 1 × 1 cm element film piece, and first, the element film piece (13) is attached onto an alumina substrate (11) via a lower electrode layer (12), and then the upper surface of the element film. An upper electrode layer (12) is formed on each of the electrodes, and platinum lead wires (14) and (14) are further provided on the respective electrode layers (12) and (12) to form a fourth electrode layer.
A carbon dioxide detection element (10) shown in the figure was produced.

Electrical Measurement Using the measurement system shown in FIG. 6, the carbon dioxide detection element (1) is measured by the measurement sequence shown in (a) below, and the carbon dioxide detection element (10) is measured in (a) below. Each was measured in a sequence. In the measurement system, (21) is a gas cylinder and (2
2) gas mixer, (23) dryer, (24) humidifier, (25) thermocouple, (26) temperature controller, (2)
7) is an impedance analyzer, (28) is a ceramic heater, (29) is a gas chromatograph, and (30) is a carbon dioxide detection element to be detected.

That is, each carbon dioxide gas detection element is heated to 300 to 400 ° C by a heater or an electric furnace, and air, carbon dioxide gas (CO ² / air
= 0.1 to 10%) at 200 ml / min alternately, and the impedance change at that time is measured by the impedance analyzer (YHP
Impedance and admittance were measured at 4192A manufactured by the same company. The relative humidity of the carrier gas is 0-100%
I changed it to.

The results for the carbon dioxide detection element (1) are shown in FIG.
The results of the carbon dioxide detecting element (10) are shown in FIG.

Results-In the carbon dioxide detection element (1), the initial impedance value was 16.6 MΩ at a frequency of 1 KHz and 21.7 MΩ at a frequency of 500 Hz, and the rate of change was 132% at a frequency of 1 KHz and 155% at 500 Hz. This device showed the characteristics of the detecting element without the catalyst.

-In the carbon dioxide detector (10), the initial impedance value was 21.1 MΩ at a frequency of 1 KHz, 38.0 MΩ at 500 Hz, and the rate of change was 104% at a frequency of 1 KHz and 105% at 500 Hz. This element also showed the detection element characteristics without a catalyst. Moreover, the impedance did not change with time, and the reaction became constant for a few seconds.

(G) Effect of the Invention According to the present invention, uniform fine-powdered chlorine apatite can be obtained by freeze-drying high-purity chlorine apatite synthesized by the wet method or the dry method. Further, when a carbon dioxide gas detecting element is manufactured using powdered chlorine apatite, it is possible to provide a carbon dioxide gas detecting element having improved sensitivity, durability, etc., with respect to the change in impedance over time.

[Brief description of drawings]

FIG. 1 is a flow chart diagram of the synthesis of chlorine apatite by the wet method, FIG. 2 is a partial flow chart diagram of the synthesis of chlorine apatite by the dry method, and FIG. 3 is a perspective view of a carbon dioxide detecting element of one example of the present invention. FIG. 5 and FIG. 5 respectively correspond to FIG. 3 of another example of the present invention, FIG. 6 is a structural explanatory view of a measuring system for electrical measurement of a carbon dioxide detecting element of the present invention, and FIG. FIG. 8 is a diagram showing the result of measuring the carbon dioxide detecting element by the measuring system of FIG. 6 in a specific measuring sequence, and FIG. 8 is the measuring system of the carbon dioxide detecting element of FIG. 4 in the measuring system of FIG. It is a figure showing the result. 2 ... Pellet type element material, 3, 12, c ... 1 pair of electrodes, 4, 14 ... Lead, 13, b ... Thin film element material, 11, a ... Insulating substrate.

Claims (3)

(57) [Claims] 1. A powdered chlorine apatite having a particle size of 0.1 μm or less, which is composed of a freeze-dried product of a chlorine apatite precipitate obtained by directly or indirectly treating hydroxyapatite with ammonium chloride between a pair of electrodes. A carbon dioxide gas detection element in which a detection element material made of is electrically interposed. 2. The carbon dioxide detecting element according to claim 1, wherein the chlorine apatite precipitate is obtained by reacting hydroxyapatite with ammonium chloride in an alkaline aqueous medium. 3. A chlorapatite precipitate is obtained by calcining hydroxyapatite, mixing it with calcimu chloride in an ethanol medium, calcining the mixture to prepare calcium-excessive chlorapatite, and mixing this chlorapatite with ammonium chloride. The carbon dioxide detecting element according to claim 1, which is obtained by reacting.