JP2008266105A - Method for producing electrically conductive composite compound - Google Patents

Abstract

An object of the present invention is to impart electrical conductivity to a compound having a composition represented by 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) by a simple method.
A compound having a composition represented by 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) is 700 ° C. or higher and 1500 ° C. or lower in an atmosphere containing nitrogen as a main component together with carbon. And a method for producing an electrically conductive composite compound, comprising heating for 10 minutes to 24 hours to include electrons.
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Description

It is already known that the crystal of an alumina-calcium compound (hereinafter abbreviated as “C12A7” where appropriate) represented by 12CaO · 7Al ₂ O ₃ has high electrical conductivity. This is probably because electrons are included in the formed cage.
C12A7 that encloses electrons in such a cage is obtained by vacuum-sealing C12A7 single crystal together with alkali metal in silica glass, heating, and exposing C12A7 single crystal to alkali metal vapor for tens to hundreds of hours, It is disclosed in Patent Document 1 that it can be manufactured.
However, this method can obtain a compound having high electrical conductivity because electrons can be uniformly clad up to the inside of the crystal. However, it is difficult to control in a process that requires a long time heating in a vacuum process. It has become.

In addition, it is possible to enclose electrons in the cage by placing a C12A7 press body obtained by press-molding C12A7 fine powder at 2000 kg / cm ² in a carbon crucible, covering the carbon and heating and melting at 1550 ° C. or higher. In addition, C12A7 powder is placed in a carbon crucible, heated and melted at 1600 ° C., and then rapidly cooled and solidified into a glass state. Patent Document 2 also discloses that inclusion is possible.
Although these two methods do not go through a vacuum process, the former requires press molding and requires a high temperature of 1550 ° C. or higher for melting by heating, and the latter is heated again after being heated and melted at 1600 ° C. Since it requires complicated operations such as necessity, it cannot be said that the difficulty of control in the process has been solved.

International Publication No. 2005/000741 JP 2005-314196 A

The present invention provides a more complicated operation (vacuum) regardless of the state of the starting material (single crystal, powder, sintered body, press-molded body, thin film, etc.) and the state at the time of reaction (non-molten state, melt state, etc.) The purpose of the present invention is to produce a composite compound having high electrical conductivity without the need for a process, heating several times, etc., and in particular, 12Ca _1-X Sr _X O · 7Al ₂ O ₃ (x = 0 The object is to impart electrical conductivity to the compound having the composition represented by ˜1) by a simple method.

As a result of intensive studies to solve the above problems, the present inventors contacted a compound having a composition represented by 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) with carbon. It was found that a composite compound having high electrical conductivity in which electrons are included can be obtained by heat treatment in nitrogen for several hours, and the present invention has been achieved.
That is, in the present invention, a compound having a composition represented by 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) is 700 ° C. or higher and 1500 ° C. in an atmosphere mainly containing nitrogen together with carbon. It is a method for producing an electrically conductive composite compound, characterized in that it is heated at 10 ° C. or lower and 10 minutes or longer and 24 hours or shorter to enclose electrons.

  The electrically conductive composite compound according to the present invention can be synthesized without requiring a complicated operation regardless of the state of the starting material and the state at the time of reaction. Therefore, the industrial process can be simplified, and the electrically conductive composite compound can be applied to uses such as a cold electron gun, an electrode, an electron injector, and a reducing agent.

The present invention is described in detail below.
A compound having a composition represented by 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1), which is a starting material of the present invention, is a compound having a crystal structure that can be obtained by the following method. .
The compound represented by 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) in the present invention can be produced by using two or more kinds of raw materials mixed so as to correspond to the above composition. .
Specifically, the raw materials include calcium carbonate, calcium hydroxide, strontium carbonate, strontium hydroxide, aluminum oxide, aluminum hydroxide, and the like. From these raw material groups, the amount of calcium (Ca) and the amount of strontium (Sr) What is necessary is just to select so that it may become 12:14 by atomic equivalent ratio of the sum total and the amount of aluminum (Al).

Using the raw materials selected as described above, 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1), which is a starting material, can be produced using a known general method. . For example, although not particularly limited, 12SrO.7Al ₂ O ₃ (hereinafter, abbreviated as “S12A7” as appropriate) is obtained by wet-mixing selected raw materials and then firing at about 700 ° C. to 1400 ° C. for about 3 to 12 hours. Alternatively, C12A7 powder can be obtained. Furthermore, the obtained S12A7 and C12A7 powders are press-molded to form a press-molded body, which is fired at about 700 ° C. to 1400 ° C. for about 3 to 12 hours to obtain a sintered body. In addition, a thin film can be obtained using a sintered body obtained by using a pulsed laser deposition (PLD) method or a sputtering method, which is a general film forming method, as a target. Furthermore, a raw material selected into a platinum crucible or the like is added, and a single crystal can be obtained using the Czochralski method (Cz method) or the floating zone method (FZ method). As described above, a compound having a composition represented by 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1), which is a starting material of the present invention, can be produced.

In order to impart electrical conductivity to 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) obtained as described above, the present invention is characterized by the following treatment. The processing method will be described in detail below.
First, the form of 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) as a starting material is a single crystal, a sintered body, a press-molded body, a powder, a thin film, or a mixed form thereof. Various forms can be used and can be appropriately selected depending on the application.
In the present invention, the above-mentioned 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) and carbon added thereto are added for a specific time under a specific temperature condition in an atmosphere mainly containing nitrogen. Although it is characterized by heating, carbon that can be used here is a material containing carbon as a main component, and as a material containing carbon as a main component, 12Ca _1-X Sr _X O · 7Al _The material, purity, shape, and form are not particularly limited as long as they can contact ₂ O ₃ (x = 0 to 1) and contain carbon.

For example, carbon, graphite, diamond, activated carbon, charcoal-containing carbon and other impurities, coal, organic substances, mixtures thereof, and the like sold as reagents can be used. Here, the organic substance is one that can be used as carbon because it is carbonized by heating in an atmosphere mainly containing nitrogen, which is a requirement of the present invention. Is preferred.
Examples of the form of carbon in the present invention include powder, flat plate / sheet, crucible, boat, and liquid. By processing into a crucible shape or a boat shape into a container, it is possible to serve both as a contact with carbon and at the same time, which is efficient.

The atmosphere containing nitrogen as a main component, which is a heating atmosphere, may be any one as long as it can be heated by introducing a gas containing nitrogen as a main component into a heating furnace. The main component gas is a gas supplied from a nitrogen gas cylinder or nitrogen gas obtained by vaporizing liquid nitrogen, or a mixed gas obtained by diluting these gases with other gases. The mixed gas in the present invention is not particularly limited as long as the main component is nitrogen, and examples thereof include helium, neon, argon, krypton, hydrogen, and chlorine.
In the present invention, nitrogen as a main component means that the content of nitrogen is 70 vol% or more and 100 vol% or less, preferably 80 vol% or more and 100 vol% or less, more preferably 95 vol% or more and 100 vol% or less. is there. A nitrogen content of 70 vol% or less by volume is not preferable because the reaction does not proceed or the reaction rate becomes very slow.

In the present invention, the heat treatment is performed under the above conditions, and the heat treatment temperature in the present invention is preferably 700 ° C. or higher and 1500 ° C. or lower. Below 700 ° C., the reaction does not proceed and electrons are not included. On the other hand, when the temperature is 1500 ° C. or higher, the heating element used in the heating furnace is largely restricted and is not energy efficient.
Further, the heating time in the present invention is preferably 10 minutes to 24 hours, more preferably 30 minutes to 18 hours, further preferably 30 minutes to 12 hours, and most preferably 1 hour to 8 hours. It is. If the heating time is too short, it is difficult to obtain a uniform electric conductor composite compound, and if the heating time is too long, it is not preferable for the process.
As described above, the compound having the composition represented by 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) of the present invention is used as a starting material to produce an electrically conductive composite compound containing electrons. However, the main component of the compound having the composition represented by 12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1), which is the starting material, by the manufacturing method of the present invention is described. Electrons are included in the cage structure, and high electrical conductivity can be obtained.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
Evaluation methods and measurement methods used in the present invention are as follows.
[X-ray analysis (XRD)]
In RINT2000 manufactured by Rigaku Denki Co., Ltd., measurement is performed using Cu Kα rays. The measurement conditions are an acceleration voltage of 50 KV, an acceleration current of 200 mA, a light receiving slit width of 0.15 mm, a scanning speed of 4 ° / min, and a sampling of 0.02 °. The diffraction lines are monochromatic by a graphite monochromator and counted. The structure is identified using JADE made by Materials Data.

[Electrical characteristics]
The electron concentration was calculated from the light absorption spectrum, and the light absorption spectrum obtained by the Kubelka-Munk method from the diffuse reflection spectrum was used for the thin film and the others were used.
The electrical resistance was determined from mobility and electron concentration.
The details of the electron concentration measurement and the electrical resistance measurement were performed using the methods disclosed in Patent Documents 1 and 2 described above.

[Example 1]
A C12A7 single crystal (12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0)) produced by the Cz method was placed on a carbon boat and flowed at 200 cc / min nitrogen gas at 1350 ° C., Heating for 2 hours gave an electrically conductive composite compound.
The obtained electrically conductive composite compound was not melted by heating, and showed high conductivity of 10 S / cm at an electron concentration of 10 ²⁰ / cm ³ .

[Example 2]
2.00 g CaCO ₃ (high purity chemistry) and 2.17 g γ-Al ₂ O ₃ (high purity chemistry) were wet mixed in ethanol (Wako Pure Chemical Industries) to obtain a uniformly mixed sample. . The obtained sample was baked at 1300 ° C. for 6 hours. The obtained compound could be assigned to C12A7 by XRD. The obtained C12A7 powder was placed on a carbon boat and heated at 1480 ° C. for 2 hours in an electric furnace in which 200 cc / min of nitrogen gas was flowed to obtain an electrically conductive composite compound.
The obtained electrically conductive composite compound was in a molten state by heating, and showed a high conductivity of 1 S / cm at an electron concentration of 10 ¹⁹ / cm ³ .

[Example 3]
The C12A7 powder obtained in the same manner as in Example 2 was pressed into a size of 15 mm using a tablet molding machine at 200 kg / cm ² to obtain C12A7 pellets. The C12A7 pellet was fired again at 1300 ° C. for 6 hours to obtain a C12A7 sintered body. The C12A7 sintered body was placed on a PET film having a thickness of 5 mm, and heated at 1350 ° C. for 4 hours in an electric furnace in which 200 cc / min of nitrogen gas was flowed to obtain an electrically conductive composite compound.
The obtained electrically conductive composite compound was not melted by heating, showed high conductivity of 6 S / cm at an electron concentration of 10 ²⁰ / cm ³ .

[Example 4]
2.00 g CaCO ₃ (high purity chemistry) and 2.17 g γ-Al ₂ O ₃ (high purity chemistry) were wet mixed in ethanol (Wako Pure Chemical Industries) to obtain a uniformly mixed sample. . The obtained sample was put in a carbon crucible and heated at 1480 ° C. for 1 hour in an electric furnace in which 200 cc / min of nitrogen gas was flowed to obtain an electrically conductive composite compound. The obtained electrically conductive composite compound was in a molten state by heating, and showed a high conductivity of ³ S / cm at an electron concentration of 10 ¹⁹ / cm ³ .
Under the above conditions, the reaction product when the electric furnace temperature was 950 ° C. was taken out and confirmed by XRD. As a result, it could be attributed to C12A7.

[Example 5]
A sample in which 2.43 g of Sr (OH) ₂ (high purity chemistry) and 2.17 g of γ-Al ₂ O ₃ (high purity chemistry) are wet-mixed in ethanol (Wako Pure Chemical Industries) and mixed uniformly. Got. The obtained mixture was put on a carbon crucible and heated at 900 ° C. for 12 hours in an electric furnace in which 200 cc / min of nitrogen was flowed. The obtained compound could be assigned to S12A7 by XRD, was not melted by heating, and was an electrically conductive composite compound having an electron concentration of 10 ¹⁹ / cm ³ and high conductivity of 2 S / cm.
In addition, when the reaction product at the time when the electric furnace temperature was 700 ° C. was taken out under the above conditions and confirmed by XRD, it could be attributed to S12A7.

[Example 6]
0.74 g Ca (OH) ₂ (high purity chemistry), 1.215 g Sr (OH) ₂ (high purity chemistry) and 2.17 g γ-Al ₂ O ₃ (high purity chemistry) ethanol (Wako Pure) Wet mixing was performed in the medicine to obtain a uniformly mixed sample. The obtained mixture was put on a carbon crucible and heated at 1000 ° C. for 4 hours in an electric furnace in which 200 cc / min of nitrogen was flowed. The obtained compound is an electrically conductive composite compound that can be attributed to a mixed crystal of C12A7 and S12A7 by XRD, is not melted by heating, and has a high conductivity of 1 S / cm at an electron concentration of 10 ¹⁹ / cm ^3. there were.
Under the above conditions, when the reaction product at an electric furnace temperature of 900 ° C. was taken out and confirmed by XRD, it could be attributed to a mixed crystal of C12A7 and S12A7.

[Example 7]
2.00 g of CaCO ₃ (high purity chemistry), 2.17 g of γ-Al ₂ O ₃ (high purity chemistry) and 1.00 g of carbon powder (high purity chemistry) are wet mixed in ethanol (Wako Pure Chemical Industries). Thus, a uniformly mixed sample was obtained. The obtained sample was placed on an alumina boat and heated at 1480 ° C. for 1 hour in an electric furnace in which 200 cc / min of nitrogen gas was flowed to obtain an electrically conductive composite compound.
The obtained electrically conductive composite compound was in a molten state by heating, and showed a high conductivity of 1 S / cm at an electron concentration of 10 ¹⁹ / cm ³ .
Under the above conditions, the reaction product when the electric furnace temperature was 950 ° C. was taken out and confirmed by XRD. As a result, it could be attributed to C12A7 and carbon.

[Example 8]
Using the C12A7 sintered body obtained in the same manner as in Example 3, C12A7 was deposited on the MgO substrate by the pulse laser deposition (PLD) method, and the thin film was fired at 1100 ° C. for 1 hour to obtain a thickness. A 300 nm C12A7 thin film was obtained. The obtained C12A7 thin film was covered with carbon powder (high purity chemistry) and heated at 1350 ° C. for 1 hour in an electric furnace in which 200 cc / min of nitrogen was flowed to obtain an electrically conductive composite compound.
The obtained electrically conductive composite compound was not melted by heating, showed high conductivity of 6 S / cm at an electron concentration of 10 ²⁰ / cm ³ .

[Comparative Example 1]
A composite compound was obtained in the same manner as in Example 1 except that 200 cc / min helium was flowed instead of 200 cc / min nitrogen.
The obtained composite compound was an insulator.
[Comparative Example 2]
A composite compound was obtained in the same manner as in Example 2 except that 200 cc / min argon was flowed instead of 200 cc / min nitrogen.
The obtained composite compound was an insulator.
[Comparative Example 3]
A composite compound was obtained in the same manner as in Example 3 except that a C12A7 sintered body was disposed on an alumina plate instead of a PET film having a thickness of 5 mm.
The obtained composite compound was an insulator.

  Since the electrically conductive composite compound of the present invention has high electrical conductivity and excellent processability, it is suitably used in the fields of cold electron guns, electrodes, electron injectors, reducing agents and the like.

Claims (1)

12Ca _1-X Sr _X O.7Al ₂ O ₃ (x = 0 to 1) of a compound having a composition of carbon and nitrogen as a main component at 700 ° C. to 1500 ° C. for 10 minutes A method for producing an electrically conductive composite compound, comprising heating for 24 hours or less to enclose electrons.