JP2008007374A - Method for manufacturing electroconductive ceramics material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a 12CaO 7Al<SB>2</SB>O<SB>3</SB>polycrystalline substance having higher electrical conductivity with high productivity. <P>SOLUTION: A 12CaO 7Al<SB>2</SB>O<SB>3</SB>powder is arranged in a carbon crucible wherein carbon sheets are sheeted, a carbon lid is put on the opening of the crucible, the crucible with the lid is introduced into a melting furnace. 12CaO 7Al<SB>2</SB>O<SB>3</SB>polycrystalline substance having higher electrical conductivity can be manufactured by melting the powder in the crucible in a dried nitrogen atmosphere, cooling and solidifying. In the present method, a melting and solidifying treatment is required only once, while a conventional method has required twice-repeated such treatments, and the resultant solid does not stick to the crucible. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a conductive ceramic material.

In recent years, a powder of oxide 12CaO · 7Al ₂ O ₃ (hereinafter referred to as C12A7) having a cage-like crystal structure is pressed and then held and melted at about 1600 [° C.] in a reducing atmosphere. It is said that C12A7 polycrystal having a conductivity of 5 [S / cm] can be produced by repeating the steps of slow cooling and solidification twice or by crystallizing glass melted in a reducing atmosphere in a vacuum atmosphere. A report was made (see Non-Patent Documents 1 and 2).
Kim et al., J. Am. Chem. Soc., 127, 1370-1371 (2005) Kim et al., Chem. Mater., 18, 1938-1944 (2006)

  However, according to the above manufacturing method, the melt-solidification process must be performed twice. In addition, when C12A7 is melted and solidified, the solidified body adheres to the crucible, so that the crucible must be destroyed when the solidified body is taken out. For this reason, according to the said manufacturing method, manufacturing cost can be reduced and the C12A7 polycrystal which has electroconductivity cannot be manufactured with high productivity. In addition, the C12A7 polycrystal has a conductivity at room temperature of 5 [S / cm] or less, and does not have sufficient conductivity.

The present invention has been made to solve the above-described problems, and its object is to produce a conductive ceramic material capable of producing a 12CaO.7Al ₂ O ₃ polycrystal having higher productivity and higher conductivity. It is to provide a method.

As a result of intensive research, the inventors of the present invention have arranged 12CaO · 7Al ₂ O ₃ powder in a carbon crucible with a carbon sheet spread on the inner surface, and made carbon in the opening of the crucible. 12CaO.7Al having higher conductivity by introducing the crucible with the lid into the melting furnace, melting the powder in the crucible in a dry nitrogen atmosphere, and then cooling and solidifying it. _{It was found that 2} O ₃ polycrystals can be produced. Further, in this case, it was found that the melt-solidification process that was required twice was sufficient and the solidified body was not fixed to the crucible.

The conductive 12CaO · 7Al ₂ O ₃ polycrystal can be expected to be used as a reducing agent. Moreover, since the material is composed of an element having a large Clarke number, it can be expected as an inexpensive conductive material. Also, application as a field emission electron emitter can be expected. In addition, it can be expected to be applied as an electrode that requires special bonding characteristics, such as an electrode material of an electrochemical device accompanied by oxidation-reduction or a charge injection material in an organic EL device.

According to the method for producing a conductive ceramic material of the present invention, the melt and solidification process is performed only once, and the solidified body does not adhere to the crucible, so that 12CaO · 7Al ₂ O ₃ polycrystal having higher productivity and higher conductivity. The body can be manufactured.

  Hereinafter, the best mode for carrying out the present invention will be described.

[Example 1]
In Example 1, first, a commercially available calcium carbonate powder (specific surface area 5.5 [m ² / g]) and a commercially available aluminum oxide powder (specific surface area 141 [m ² / g]) were mixed at a molar ratio of 12: 7. These powders were wet-mixed with an aqueous medium, dried, and then passed through a sieve to obtain a mixed powder. Next, the mixed powder was heat-treated in an air atmosphere at 1200 [° C.] for 4 hours to cause a solid phase reaction, thereby synthesizing C12A7 powder. Whether or not it was C12A7 was confirmed by an X-ray diffraction pattern of the powder after solid-phase synthesis (see FIG. 1).

  Next, after filling a carbon crucible (inner surface size φ24 × H45 [mm]) with a commercially available carbon sheet (trade name: Grafoil) on the inner surface with pellets obtained by uniaxial pressing of C12A7 powder, and then opening the carbon crucible A carbon lid was placed on the part. At this time, the air permeability between the inside and outside of the carbon crucible was ensured by the gap between the crucible and the lid. Next, the crucible is put in a carbon crucible with a cover similar to the above, and the double crucible is placed in a commercial electric furnace whose inner surface is covered with refractory bricks in a dry nitrogen atmosphere at 1600 [° C.]. , After 1 hour of melting treatment, cooled to room temperature. The cooling rate of the electric furnace was 300 [° C./h].

  Next, the molten solidified body was taken out from the carbon crucible. At this time, the molten solidified body and the carbon crucible were not fixed, and the molten solidified body could be easily taken out. However, the carbon sheet adhered to the curved surface that was in contact with the carbon crucible on the surface of the molten solidified body. Next, after removing the carbon sheet on the surface of the melt-solidified body by machining, the sample was crushed, and a part of the sample was further pulverized and powdered, and then the phase was identified by X-ray diffraction. C12A7 A phase was confirmed (see FIG. 2). The powder had a dark green color. Furthermore, when the continuity of the fractured surface of the crushed sample was examined with a commercially available tester or a commercially available insulation resistance meter, continuity was confirmed.

  Therefore, an attempt was made to measure the room temperature conductivity. That is, a rectangular parallelepiped of about 2 × 2 × 17 [mm] is cut out as a sample from a melt-solidified body similarly produced by machining, and using a normal DC four-terminal method (see FIG. 3, reference numeral 1 indicates the sample). An attempt was made to measure the room temperature conductivity of the sample at a current of 0.1 [A]. However, the room temperature conductivity of the sample could not be measured because the detection voltage was not stable.

  When the surface of the sample was observed, it was found that an altered layer (hydroxide) having high electrical resistance was present. From this, it can be inferred that the reason why the detected voltage is not stable is that the potential of the current source and the ground side of the voltmeter (terminals T1 and T3 shown in FIG. 3) differs depending on the altered layer.

  C12A7 is also known as a cement material, and it is well known that its powder reacts with moisture in the air. From this fact, it is inferred that even a bulk body having a very small surface area compared to the powder reacted with moisture in the air to generate hydroxide on the surface.

  Thus, the room temperature conductivity of the sample was measured by using the differential direct current four-terminal method as shown in FIG. 4 and equalizing the potentials of the current source and the ground side of the voltmeter (terminal T1 shown in FIG. 4). As a result, the IV characteristics were ohmic and the room temperature conductivity was as high as 120 [S / cm]. Moreover, when the electrical conductivity at a temperature of 100 [° C.] was measured in the same manner, the electrical conductivity was almost the same as that at room temperature. That is, in this temperature range, the temperature dependence of the conductivity was not observed or was extremely small.

[Example 2]
In Example 2, first, a molten and solidified body was obtained by performing the same treatment as in Example 1 except that a commercially available carbon furnace was used as the electric furnace for performing melting and solidification. Next, after cooling to room temperature, the molten solidified body was taken out from the carbon crucible. At this time, the molten solidified body and the carbon crucible were not fixed, and the molten solidified body could be easily taken out. However, the carbon sheet adhered to the curved surface that was in contact with the carbon crucible on the surface of the molten solidified body. Next, after removing the carbon sheet on the surface of the melt-solidified body by machining, the sample was crushed, and a part of the sample was further pulverized and powdered, and then the phase was identified by X-ray diffraction. C12A7 Phase was confirmed. The powder had a dark green color. Furthermore, when the continuity of the fractured surface of the crushed sample was examined with a commercially available tester or a commercially available insulation resistance meter, the continuity was confirmed, and the room temperature conductivity measured by the differential DC 4-terminal method was 80 [S / cm. ]Met.

Example 3
In Example 3, first, a molten solidified body was obtained by performing the same treatment as in Example 1 except that the carbon sheet was not spread on the inner surface of the carbon crucible. At this time, the molten solidified body and the carbon crucible were fixed, and the molten solidified body could not be taken out unless the carbon crucible was broken. Next, the taken-out molten solidified body was crushed, and some samples were further pulverized to form a powder, and then the phase was identified by X-ray diffraction. As a result, C12A7 phase was confirmed. The powder had a dark green color. Furthermore, when the continuity of the fractured surface of the crushed sample was examined with a commercially available tester or a commercially available insulation resistance meter, the continuity was confirmed, and the room temperature conductivity measured by the differential DC 4-terminal method was 100 [S / cm. ]Met.

[Comparative Example 1]
In Comparative Example 1, first, a molten solidified body was obtained by performing the same treatment as in Example 1 except that the atmosphere during the melting treatment for 1 hour was changed to a dry argon atmosphere at 1600 [° C.]. Next, after cooling to room temperature, the molten solidified body was taken out from the carbon crucible. At this time, the molten solidified body and the carbon crucible were not fixed, and the molten solidified body could be easily taken out. However, the carbon sheet adhered to the curved surface that was in contact with the carbon crucible on the surface of the molten solidified body. Next, after removing the carbon sheet on the surface of the melted solidified body taken out by machining, the sample was crushed, and some samples were further pulverized and powdered, and then the phases were identified by X-ray diffraction. A 3CaO.Al ₂ O ₃ (C3A) phase and a CaO · Al ₂ O ₃ (CA) phase were confirmed (see FIG. 5). Moreover, the powder was gray. Furthermore, when continuity was investigated with the commercially available tester or the commercially available insulation resistance meter with respect to the fracture surface of the crushed sample, continuity was not confirmed.

  Next, melt solidification is performed again in the same manner as in Example 1 except that the pulverized powder (mixture of the C3A phase and the CA phase) is 1600 [° C.] and the atmosphere during the melting process for 1 hour is a dry argon atmosphere. A solidified body was obtained. After cooling to room temperature, the molten solidified body was taken out from the carbon crucible. At this time, the molten solidified body and the carbon crucible were not fixed, and the molten solidified body was easily taken out. However, the carbon sheet adhered to the curved surface that was in contact with the carbon crucible on the surface of the molten solidified body.

  Next, after removing the carbon sheet on the surface of the melt-solidified body by machining, the sample was crushed, and some samples were further pulverized and powdered, and then the phase was identified by X-ray diffraction. C12A7 A phase was confirmed (see FIG. 6). The powder had a dark green color. Furthermore, when the continuity of the fractured surface of the crushed sample was examined with a commercially available tester or a commercially available insulation resistance meter, the continuity was confirmed, and the room temperature conductivity measured by the differential DC 4-terminal method was 5 [S / cm. ]Met. Moreover, when the temperature of the measurement system was raised and the conductivity was measured in the same manner at several temperatures up to 200 ° C., the value showed a semiconducting behavior that gradually increased. Moreover, the activation energy was estimated to be 0.12 [eV] by the Arrhenius plot.

[Comparative Example 2]
The molten solidified body was obtained by performing the same treatment as in Example 1 except that the carbon sheet was not spread on the inner surface of the carbon crucible and that the atmosphere during the melting treatment for 1 hour was changed to a dry argon atmosphere. Obtained. At this time, the molten solidified body and the carbon crucible were fixed, and the molten solidified body could not be taken out unless the carbon crucible was broken. Next, the molten solidified body was crushed, and some samples were further pulverized to form a powder, and then the phases were identified by X-ray diffraction. As a result, the C3A phase and the CA phase were confirmed. Moreover, the powder was gray. Furthermore, when continuity was investigated with the commercially available tester or the commercially available insulation resistance meter with respect to the fracture surface of the crushed sample, continuity was not confirmed.

Next, except that the pulverized powder (mixture of C3A phase and CA phase) was not spread with a carbon sheet on the inner surface of the carbon crucible, and that the atmosphere during the melting treatment at 1600 [° C.] for 1 hour was a dry argon atmosphere. Was melt-solidified again in the same manner as in Example 1 to obtain a melt-solidified body. At this time, the molten solidified body and the carbon crucible are fixed, and the molten solidified body cannot be taken out unless the carbon crucible is broken. Next, the molten solidified body is crushed, and a part of the sample is further pulverized. After the phase was identified by X-ray diffraction, C12A7 phase was confirmed. The powder had a dark green color. Furthermore, when the continuity of the fractured surface of the crushed sample was examined with a commercially available tester or a commercially available insulation resistance meter, the continuity was confirmed, and the room temperature conductivity measured by the differential DC 4-terminal method was 5 [S / cm. ]Met.

[Comparative Example 3]
In Comparative Example 3, first, a molten solidified body was obtained by performing the same treatment as in Example 2 except that the atmosphere at 1600 [° C.] for 1 hour was changed to a dry argon atmosphere. Next, after cooling to room temperature, the molten solidified body was taken out from the carbon crucible. At this time, the molten solidified body and the carbon crucible were not fixed, and the molten solidified body could be easily taken out. However, the carbon sheet adhered to the curved surface that was in contact with the carbon crucible on the surface of the molten solidified body. Next, after removing the carbon sheet on the surface of the melted solidified body taken out by machining, the sample was crushed, and some samples were further pulverized and powdered, and then the phases were identified by X-ray diffraction. A 5CaO.3Al ₂ O ₃ (hereinafter referred to as C5A3) phase and a C3A phase were confirmed. Moreover, the powder was gray. Furthermore, when continuity was investigated with the commercially available tester or the commercially available insulation resistance meter with respect to the fracture surface of the crushed sample, continuity was not confirmed.

  Next, by performing pulverization and solidification again in the same manner as in Example 2 except that the pulverized powder (mixture of the C5A3 phase and the C3A phase) was 1600 [° C.] and the atmosphere during the melting treatment for 1 hour was a dry argon atmosphere A melt-solidified body was obtained. Next, after cooling to room temperature, the molten solidified body was taken out from the carbon crucible. At this time, the molten solidified body and the carbon crucible were not fixed, and the molten solidified body could be easily taken out. However, the carbon sheet adhered to the curved surface that was in contact with the carbon crucible on the surface of the molten solidified body.

  Next, after removing the carbon sheet on the surface of the melt-solidified body by machining, the sample was crushed, and a part of the sample was further pulverized and powdered, and then the phase was identified by X-ray diffraction. C12A7 Phase was confirmed. The powder had a dark green color. Furthermore, when the continuity of the fractured surface of the crushed sample was examined with a commercially available tester or a commercially available insulation resistance meter, the continuity was confirmed, and the conductivity measured by the differential DC 4-terminal method was 5 [S / cm]. Met.

The results are summarized in Table 1.

As is clear from Table 1, 12CaO · 7Al ₂ O ₃ powder was placed in a carbon crucible with a carbon sheet laid on the inner surface, and a carbon lid was placed on the opening of the crucible, and the lid was placed. The introduced crucible is introduced into a melting furnace, and the powder in the crucible is melted in a dry nitrogen atmosphere and then cooled and solidified, so that the solidified body does not stick to the crucible and has higher conductivity. _It can be seen that a ₂ O ₃ polycrystal can be produced.

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the scope of the present invention.

The X-ray diffraction pattern obtained from the powder of Example 1 after solid-phase synthesis is shown. It is an X-ray diffraction pattern obtained from the powder of Example 1 after one melt-solidification treatment. The wiring diagram at the time of measuring electrical conductivity by the direct current 4 terminal method is shown. The wiring diagram at the time of measuring electrical conductivity by the differential direct current 4 terminal method is shown. The X-ray-diffraction figure obtained from the powder of the comparative example 1 after the 1st melt-solidification process is shown. It is an X-ray diffraction pattern obtained from the powder of Comparative Example 1 after the second melt solidification treatment.

Claims (2)

A step of placing a raw material powder having a composition of approximately 12CaO · 7Al ₂ O ₃ in terms of an oxide in a carbon crucible;
Placing a carbon lid on the crucible opening;
Introducing the crucible on which the lid is placed into a melting furnace, melting the powder in the crucible in a dry nitrogen atmosphere, and cooling and solidifying the powder. A method for producing a conductive ceramic material according to claim 1, made of carbon before placing the raw material powder having a composition of general 12CaO · 7Al ₂ O ₃ in terms of the oxide in a carbon crucible A method for producing a conductive ceramic material comprising a step of spreading a carbon sheet on the inner surface of the crucible.

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