METHOD FOR PRODUCING CONDUCTIVE MAYENITE TYPE COMPOUND

Abstract

An object of the present invention is to provide a method for producing conductive mayenite, with which a reaction is completed in a short time, an operation can be simplified, the reaction is easily controlled, and the cost of energy can be reduced. The present invention is a method for producing conductive mayenite, characterized by mixing a mayenite type compound with a carbon component, placing the resulting mixture in an airtight container, and irradiating the mixture with a microwave in an inert gas atmosphere or in a vacuum atmosphere to heat the mixture.

Claims

1. A method for producing a conductive mayenite type compound, characterized by mixing a mayenite type compound with a carbon component, placing the resulting mixture in an airtight container, and irradiating the mixture with a microwave in an inert gas atmosphere or in a vacuum atmosphere to heat the mixture.

2. The method for producing a conductive mayenite type compound according to claim 1, characterized in that the mayenite type compound is a compound having a representative composition of (Ca.sub.12Al.sub.14O.sub.33) and also having a crystal structure constituted by three-dimensionally connected voids (cages).

3. The method for producing a conductive mayenite type compound according to claim 1, characterized in that the carbon component is at least one selected from the group consisting of silicon carbide, active carbon, graphite, carbon black, Ru/carbon, and graphene.

4. The method for producing a conductive mayenite type compound according to claim 1, characterized in that the airtight container is made of quartz glass.

5. The method for producing a conductive mayenite type compound according to claim 1, characterized in that the heating conditions of the mixture by the irradiation with the microwave are at 600 to 1200 C. for 5 to 60 minutes.

6. The method for producing a conductive mayenite type compound according to claim 2, characterized in that the carbon component is at least one selected from the group consisting of silicon carbide, active carbon, graphite, carbon black, Ru/carbon, and graphene.

7. The method for producing a conductive mayenite type compound according to claim 2, characterized in that the airtight container is made of quartz glass.

8. The method for producing a conductive mayenite type compound according to claim 3, characterized in that the airtight container is made of quartz glass.

9. The method for producing a conductive mayenite type compound according to claim 6, characterized in that the airtight container is made of quartz glass.

10. The method for producing a conductive mayenite type compound according to claim 2, characterized in that the heating conditions of the mixture by the irradiation with the microwave are at 600 to 1200 C. for 5 to 60 minutes.

11. The method for producing a conductive mayenite type compound according to claim 3, characterized in that the heating conditions of the mixture by the irradiation with the microwave are at 600 to 1200 C. for 5 to 60 minutes.

12. The method for producing a conductive mayenite type compound according to claim 4, characterized in that the heating conditions of the mixture by the irradiation with the microwave are at 600 to 1200 C. for 5 to 60 minutes.

13. The method for producing a conductive mayenite type compound according to claim 6, characterized in that the heating conditions of the mixture by the irradiation with the microwave are at 600 to 1200 C. for 5 to 60 minutes.

14. The method for producing a conductive mayenite type compound according to claim 7, characterized in that the heating conditions of the mixture by the irradiation with the microwave are at 600 to 1200 C. for 5 to 60 minutes.

15. The method for producing a conductive mayenite type compound according to claim 8, characterized in that the heating conditions of the mixture by the irradiation with the microwave are at 600 to 1200 C. for 5 to 60 minutes.

16. The method for producing a conductive mayenite type compound according to claim 9, characterized in that the heating conditions of the mixture by the irradiation with the microwave are at 600 to 1200 C. for 5 to 60 minutes.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] FIG. 1 is a vertical cross-sectional view of a microwave generator schematically showing a state of irradiation by the microwave generator.

[0024] FIG. 2 shows Raman analysis spectra.

[0025] FIG. 3 is a graph showing the D/G values of the Raman analysis spectra.

[0026] FIG. 4 shows ESR analysis spectra.

[0027] FIG. 5 shows ESR analysis spectra.

[0028] FIG. 6 is a view showing XRD analysis results.

DESCRIPTION OF EMBODIMENTS

[0029] Next, Examples of the present invention will be described along with Comparative Examples, however, the present invention is not limited to these Examples.

[0030] A method for producing a mayenite type compound (C12A7) used in the present invention is not particularly limited. For example, in this Example, a mayenite type compound was produced by adding aluminum oxide to calcium oxide as described below.

[0031] Other than this, the same compound can be produced also by a production process including a step of producing katoite using an aluminum powder and calcium hydroxide as raw materials and a step of converting the katoite into a mayenite type compound.

<Method for Producing Mayenite Type Compound in this Example>

[0032] A powder of CaCO.sub.3 (Kishida Chemical Co., Ltd., 99.5%) (4.00 g) and a powder of -Al.sub.2O.sub.3(Alfa Aesar, 99.9%) (2.38 g) were weighed by an electronic balance and mixed well using a mortar. The mixed powder was transferred to an alumina crucible, and melted at 1300 C. for 12 hours in an air atmosphere using an electric furnace (Koyo Thermo Systems Co., Ltd., KBF314N), followed by natural cooling, whereby a mayenite type compound (C12A7) was produced.

Example 1 (Use of Glassy Carbon as Carbon Component and Irradiation with Microwave in Nitrogen Atmosphere)

[0033] The mayenite type compound (0.22 g) and glassy carbon (Aldrich Co., Ltd.) (0.035 g) were mixed, and the resulting mixture was placed in an ampoule tube (diameter: 2.5 cm, length: 15 cm). Subsequently, nitrogen gas replacement in the ampoule tube was performed so that the oxygen concentration in the tube was decreased to less than 1% (v/v), and the tube was sealed. Subsequently, this ampoule tube was disposed in a reaction vessel of a microwave generator, and by a magnetron of the microwave generator, the mixture in the ampoule tube was irradiated with a microwave with a frequency of 2.45 GHz at a temperature of 800 to 900 C. for 20 minutes.

Example 2 (Use of Glassy Carbon as Carbon Component and Irradiation with Microwave in Argon Atmosphere)

[0034] The same procedure as in Example 1 was performed except that argon gas replacement was performed in place of nitrogen gas replacement.

Example 3 (Use of Acetylene Black as Carbon Component and Irradiation with Microwave in Nitrogen Atmosphere)

[0035] The same procedure as in Example 1 was performed except that acetylene black (Strem Chemicals, Inc.) (0.029 g) was used in place of glassy carbon.

Example 4 (Use of Graphene as Carbon Component and Irradiation with Microwave in Nitrogen Atmosphere)

[0036] The same procedure as in Example 1 was performed except that graphene (Strem Chemicals, Inc.) (0.0251 g) was used in place of glassy carbon.

Example 5 (Use of Glassy Carbon as Carbon Component and Irradiation with Microwave in Vacuum Atmosphere)

[0037] The mayenite type compound (C12A7) (0.22 g) and glassy carbon (Aldrich Co., Ltd.) (0.035 g) were mixed, and the resulting mixture was placed in an ampoule tube (diameter: 2.5 cm, length: 15 cm). Subsequently, the ampoule tube was sealed, and then, the pressure in the tube was decreased to 10 to 3 torr using a vacuum pump. Subsequently, this ampoule tube was disposed in a reaction vessel of a microwave generator, and by a magnetron of the microwave generator, the mixture in the ampoule tube was irradiated with a microwave with a frequency of 2.45 GHz at a temperature of 800 to 900 C. for 20 minutes.

Comparative Example 1 (Conductive Mayenite of Prior Art)

[0038] A conductive mayenite type compound was prepared according to the method described in JP-A-2014-136661.

Comparative Example 2 (Use of Glassy Carbon as Carbon Component and Irradiation with Microwave in Air Atmosphere)

[0039] The same procedure as in Example 1 was performed except that the air atmosphere was left as it is without performing nitrogen replacement in the ampoule tube.

Comparative Example 3 (Use of Glassy Carbon as Carbon Component, in Air Atmosphere, and No Irradiation with Microwave)

[0040] The same procedure as in Example 1 was performed except that the air atmosphere was left as it is without performing nitrogen replacement in the ampoule tube, and irradiation with a microwave was not performed.

Analysis of Product

(1) Raman Spectroscopy

[0041] With respect to the products obtained in the above-mentioned Examples and Comparative Examples, Raman spectroscopy was performed under the following conditions.

[0042] Analyzer: NRS-3100 manufactured by JASCO Corporation (Analytical Conditions) [0043] excitation wavelength: 532 nm [0044] exposure time: 30 sec [0045] cumulative number: 2 [0046] objective lens: 100 [0047] laser power: about 1 mW

[0048] The measurement was performed at 5 points in each sample, and an average of the obtained measurements was calculated.

[0049] The Raman analysis spectra of graphene before and after irradiation with the microwave in Example 4 are shown in FIG. 2.

[0050] The D/G values obtained from the Raman analysis spectra of the carbon component before and after irradiation with the microwave in Example 1 and Example 4 are shown in FIG. 3.

[0051] In FIG. 3, a higher D/G value indicates that carbon defects in the measurement sample increased.

[0052] From FIG. 3, it was confirmed that carbon in the sample irradiated with the microwave in Example 1 (using glassy carbon) and Example 4 (using graphene) has a high D/G value, and therefore, crystal defects increased, and themayenite type compound was partially reduced.

(2) Electron Spin Resonance (ESR) Analysis

[0053] With respect to the products obtained in the above-mentioned Examples and Comparative Examples, an electron spin resonance analysis was performed under the following conditions. The ESR analysis is a method used for detection of an unpaired electron.

[0054] Analyzer: JES-RE3X (JES-PX1000) manufactured by JEOL Ltd.

(Analytical Conditions)

[0055] measurement temperature: room temperature [0056] microwave frequency: 9.2 GHz [0057] microwave power: 1 mW [0058] magnetic field modulation width: 0.1 mT [0059] standard reference material: Mn.sup.2+/MnO.sub.2

[0060] The electron spin resonance analysis results for the samples of the products obtained in Examples 1 to 4 and Comparative Examples 1 to 3 are shown in FIG. 4 and FIG. 5.

[0061] As shown in FIG. 4 and FIG. 5, in the products of Examples 1 to 4 irradiated with the microwave, a peak at around 324 mT is attributed to e as compared with the product of Comparative Example 3 without irradiation with a microwave, and it is found that the products of Examples 1 to 4 and Comparative Example 1 are each a conductive mayenite type compound. In the product of Comparative Example 2 (in the air atmosphere), a peak of O.sup.2 is detected at around 322 mT, and it is found that a conductive mayenite type compound is not formed.

(3) X-Ray Diffraction (XRD) Analysis

[0062] With respect to the products obtained in the above-mentioned Examples and Comparative Examples, an X-ray diffraction (XRD) analysis was performed under the following conditions.

[0063] X-ray diffractometer: RINT 2500HF+/PC-FA manufactured by Rigaku Corporation (Analytical Conditions) [0064] Cu/40 kV/40 mA [0065] scan speed: 10/min [0066] scanning range: 10 to 70.0

[0067] The X-ray diffraction analysis results for the samples of the products obtained in Examples 1, 2, and 5 and Comparative Examples 1 and 2 are shown in FIG. 6.

[0068] From these X-ray diffraction analysis results, it was confirmed that the products obtained in the above-mentioned Examples maintain a mayenite type compound structure.

[0069] Incidentally, it is known that by calcining a raw material of a mayenite type compound at about 500 C. or higher, the raw material is converted into the mayenite type compound. Therefore, in the present invention, by irradiating a raw material of a mayenite type compound with a microwave to heat the raw material, the raw material is converted into the mayenite type compound, and therefore, the mayenite type compound utilized in the present invention may be, for example, katoite which is a precursor of the mayenite type compound, or may be aluminum oxide and calcium oxide, or aluminum oxide and calcium hydroxide.