JP2012082081A - Raw material mixture for producing conductive mayenite compound and method of producing conductive mayenite compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve conventional problems in production of an insulating mayenite compound such that baking at 1300°C is needed, melting step must be repeated yet again since a mayenite phase cannot be obtained by just one melting step following the baking, namely, baking step must be performed three times in all, and the conductivity at room temperature of the resulting conductive mayenite compound is not sufficiently high.SOLUTION: The raw material mixture for producing a conductive mayenite compound includes at least a reducing agent, a Ca-containing material, and an Al-containing material, the moisture content of the Al-containing material being less than 4 wt.%. This raw material mixture is used, whereby a polycrystalline mayenite compound with high conductivity can be produced only by baking the raw material mixture once.

Description

  The present invention relates to a raw material mixture for producing a conductive mayenite type compound and a method for producing a conductive mayenite type compound. More specifically, the present invention relates to a raw material mixture for producing a polycrystalline conductive mayenite type compound and a method for producing a polycrystalline conductive mayenite type compound.

As a conductive mayenite type compound (hereinafter may be referred to as mayenite phase), calcium aluminate (hereinafter also referred to as C12A7) represented by a composition of 12CaO · 7Al ₂ O ₃ is various elements and electrons, for example, It is known that O ⁻ , H ⁻ and e ⁻ can be included (Patent Documents 1 and 2). In addition, C12A7 including various elements and electrons as described above is used in fields such as cold electron emitters, conductors, organic EL electron injection electrodes, reducing agents, oxidizing agents, exhaust gas catalysts, thermoelectric conversion materials, and thermoelectric power generation materials. The application of is expected.

In recent years, a mixture of CaCO ₃ and γ-Al ₂ O ₃ is held at 1300 ° C. to produce an insulating mayenite type compound, and the insulating mayenite type compound is held at 1600 ° C. in a reducing atmosphere and melted. It has been reported that a polycrystalline conductive mayenite type compound having an electric conductivity of about 5 S / cm can be produced by repeating the process twice (Non-patent Document 1).

International Publication No. 03/089373 International Publication 05/000741

Kim et al., J. Am. Chem. Soc., Vol. 127, No. 5, 1370-1371 (2005).

  However, in the above production method, 1300 ° C. calcination is necessary for the production of the insulating mayenite type compound which is a precursor of the conductive mayenite type compound, and the mayenite phase can be obtained in the subsequent melting step once. Therefore, it was necessary to repeat the melting step once more, that is, as a result, it was necessary to go through a total of three firing steps. Furthermore, there is a problem that the conductivity at room temperature of the obtained conductive mayenite type compound is not sufficiently high.

  The present invention has been made in order to solve the above-described problems of the prior art, and the object thereof is a raw material mixture capable of producing a highly conductive polycrystalline mayenite type compound in one baking step, and polycrystalline It is to provide a method for producing a conductive mayenite type compound.

The present inventor has intensively studied to solve the above-mentioned problems, and has reached the present invention.
That is, the present invention includes the following <1> to <6>.
<1> A raw material mixture for producing a conductive mayenite type compound, which is a raw material mixture having at least a reducing agent, a Ca-containing substance, and an Al-containing substance, wherein the water content of the Al-containing substance is less than 4% by weight.
<2> The raw material mixture according to <1>, wherein the Al-containing substance is α-Al ₂ O ₃ .
<3> The raw material mixture according to <1> or <2>, wherein the reducing agent is a metal.
<4> The raw material mixture according to <3>, wherein the metal is metal Al.
<5> a step of filling a carbon container with the raw material mixture according to <1> to <4>;
Placing the carbon container in a firing furnace;
A firing step of flowing at least one gas selected from the group consisting of nitrogen and argon into the firing furnace and maintaining the temperature at 1200 to 1600 ° C .;
The manufacturing method of the electroconductive mayenite type compound which has at least.
<6> A conductive mayenite type compound obtained by the production method of <5>.

  If the raw material mixture of this invention is used, a highly conductive polycrystalline mayenite type compound can be manufactured only by baking a raw material mixture once.

2 is an X-ray powder diffraction spectrum of a crystal phase obtained in Examples 1, 2, and 3. FIG. 4 is an X-ray powder diffraction spectrum of a crystal phase obtained in Example 4. 2 is an X-ray powder diffraction spectrum of a crystal phase obtained in Comparative Example 1. 3 is an X-ray powder diffraction spectrum of a crystal phase obtained in Comparative Example 2. 4 is an X-ray powder diffraction spectrum of a crystal phase obtained in Comparative Examples 3 and 4. Is a TG-DTA curve of _α-Al 2 _{O 3} used in Example 1-4. _{3 is} a TG-DTA curve of γ-Al ₂ O ₃ used in Comparative Examples 1 and 2.

  Hereinafter, implementation of the present invention will be described in detail.

<Raw material mixture>
The raw material mixture for producing the conductive mayenite type compound of the present invention is a raw material mixture having at least a reducing agent, a Ca-containing material, and an Al-containing material, and the water content of the Al-containing material is less than 4% by weight. is there.

  The raw material mixture is obtained by mixing a reducing agent, a Ca-containing material, and an Al-containing material. Under the present circumstances, it mix | blends and prepares so that the atomic equivalent ratio of Ca and Al of this mixture may become the range of 1.00: 1.10-1.23.

  The atomic equivalent ratio is preferably 1.00: 1.13 to 1.21, and more preferably 1.00: 1.15 to 1.18.

Within the above range, it is possible to prevent the conductive mayenite type compound obtained to produce a 12CaO · 7Al ₂ O ₃ than the phase of impurities more reliably.

  The raw material mixture may be mixed as long as the reducing agent, the Ca-containing material, and the Al-containing material can be mixed. Examples thereof include a mortar, a ball mill, a sand mill, a planetary mill, a jet mill, and a rocking mill. It is done.

  The mixing method may be either dry or wet, and a dry method is preferable because a drying step is unnecessary after mixing. When wet, an organic solvent such as ethanol can be used.

・ <Reducing agent>
The reducing agent is selected from the group consisting of the Ca-containing substance, the Al-containing substance, a compound obtained by reacting the Ca-containing substance and the Al-containing substance in a redox reaction, and a melt obtained by melting the compound. Any substance may be used as long as it can reduce at least one kind of substance. For example, a metal is preferable. For example, metal K, metal Zn, metal Na, metal Cr, metal V, metal Mn, metal V, metal Si, metal Ti, metal Al, metal Li, metal Mg, and metal Ca are mentioned. In order to obtain a conductive mayenite type compound having high purity or substantially no impurity phase, when metal Al is used as the reducing agent, it also acts as an Al-containing substance, has a strong reducing power, and has 12CaO · 7Al ₂ O. ₃ is preferable because the composition of ₃ is not easily broken.

  The shape of the reducing agent is not particularly limited, but may be in the form of pellets or powder, and may be liquid in the firing step.

Further, when metal Al is used, the atomic equivalent ratio of α-Al ₂ O ₃ can be lowered. The molar ratio of α-Al ₂ O ₃ and metal Al is preferably (6.995: 0.01) to (5.83: 2.33). Within the above range, it is possible to prevent the conductive mayenite type compound obtained to produce a 12CaO · 7Al ₂ O ₃ than the phase of impurities more reliably.

・ <Ca-containing material>
The Ca-containing substance may be any substance that contains a compound containing Ca as a main component, for example, calcium carbonate (CaCO ₃ ), calcium hydroxide (Ca (OH) ₂ ), calcium oxide (CaO), calcium fluoride. (CaF), calcium chloride (CaCl ₂ ) and the like can be mentioned, but calcium carbonate (CaCO ₃ ) is preferable because it is easily available and easy to handle. The shape of the Ca-containing material is not particularly limited, but may be in the form of pellets or powder, and may be liquid in the firing step.

・ <Al-containing material>
As the Al-containing substance, a substance having a moisture content of less than 4% by weight is used. This is to obtain a conductive mayenite type compound having high purity or substantially no impurity phase. When the water content is 4.0% by weight or more, the conductive mayenite type compound obtained contains impurities. The lower the moisture content, the better, preferably less than 3.0% by weight, more preferably less than 2.0% by weight, and even more preferably less than 1.0% by weight.

  In the claims and specification of the present invention, “the water content of the Al-containing substance” is {(weight of Al-containing substance at room temperature before heating the Al-containing substance to be used “about 10 to 20 mg”) − (Weight of Al-containing substance when heating Al-containing substance used to 200 ° C.)} ÷ (Weight of Al-containing substance at room temperature before heating Al-containing substance to be used) × 100 (%).

  The moisture content can be measured by using a differential thermothermal gravimetric simultaneous measurement apparatus (TG / DTA6300, manufactured by SII Nano Technology Co., Ltd.).

Examples of the Al-containing material include α-Al ₂ O ₃ , Al (OH) _3, and AlN. The shape of the Al-containing substance is not particularly limited, but may be in the form of pellets or powder, and may be liquid in the firing step.

[Method for producing conductive mayenite type compound]
The method for producing a conductive mayenite type compound of the present invention comprises a step of filling the raw material mixture in a carbon container, a step of placing the carbon container in a firing furnace, and a firing step. Is the way to get.

・ [Step of filling the raw material mixture into a carbon container]
In the step of filling the raw material mixture into the carbon container, the powder of the raw material mixture may be used as it is, or compressed by hydrostatic pressure press molding or uniaxial press molding of the powder to obtain a green compact. Green compacts may be used. Such a press process can be appropriately performed according to the shape of the desired material.

.. [Carbon container]
The carbon container is preferable in that the charged raw material mixture can be maintained in a reducing atmosphere, and examples thereof include a carbon crucible and a carbon boat. When the raw material mixture is melted, it may be fixed to a carbon crucible or the like, and it may be difficult to take out. Therefore, it is preferable to lay a carbon sheet such as a graphite sheet inside the carbon crucible.

・ [Process of placing the carbon container in the firing furnace]
The step of disposing the carbon container in the firing furnace may be to leave the carbon container filled with the raw material mixture in the soaking area of the firing furnace. In order to maintain a good reducing atmosphere, the carbon container is preferably covered with a member such as an alumina crucible and then left in the soaking area of the firing furnace.

・ [Baking process]
In the firing step, a specific gas is allowed to flow in the firing furnace, and the temperature may be maintained at 1200 to 1600 ° C.

··[gas]
The gas is preferably nitrogen, argon, or a mixed gas of nitrogen and argon.

When nitrogen gas is used, the molar ratio of α-Al ₂ O ₃ and metal Al is preferably (6.995: 0.01) to (5.83: 2.33), and the resulting conductive mayenite is obtained. Generation of an impurity phase other than 12CaO · 7Al ₂ O _{3 in the} mold compound can be prevented more reliably.

When argon gas is used, the molar ratio of α-Al ₂ O ₃ and metal Al is preferably (6.995: 0.01) to (6.50: 1.00), and the obtained conductive mayenite. Generation of an impurity phase other than 12CaO · 7Al ₂ O _{3 in the} mold compound can be prevented more reliably.

.. [Temperature range]
When the temperature range is 1200 to 1415 ° C., the raw material mixture is sintered to obtain a conductive mayenite type compound. In the case of 1415 to 1600 ° C., the raw material mixture is melted to obtain a conductive mayenite type compound.

  On the other hand, when the temperature is lower than 1200 ° C. and higher than 1600 ° C., it is difficult to obtain a conductive mayenite type compound containing C12A7 as a main component.

  Thus, if the manufacturing method of the said raw material mixture and the said electroconductive mayenite type compound is used, a high temperature polycrystalline electroconductive mayenite compound will be obtained by only one temperature raising, temperature holding, and temperature lowering firing steps. .

  The crystal structure of the conductive mayenite type compound was analyzed by a powder X-ray diffraction method (hereinafter sometimes referred to as XRD) using CuKα as a radiation source, using a RINT2500TTR type X-ray diffraction measurement apparatus manufactured by Rigaku Corporation. .

The XRD results in the table are shown based on the following evaluation.
A: A C12A7 single-phase solid was obtained.
Δ: A solid containing the C12A7 phase as the main component and the other phases was obtained.
X: The solid which has C12A7 phase as a main component was not obtained.

  The electrical conductivity of the conductive mayenite type compound is measured by slicing a solid after firing with a diamond cutter or the like, molding, and then bonding Pt wire as a terminal with a conductive paste and evaluating by a DC four-terminal method. did.

  EXAMPLES Next, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited to a following example.

  About the commercially available aluminum oxide powder (purity of 99.99% or more) used in the following examples and comparative examples, the moisture content (% by weight) is measured by a differential thermothermal gravimetric simultaneous measurement apparatus (SII Nanotechnology, Inc. ) “TG / DTA6300” manufactured by the company).

The following is a TG-DTA curve measured to determine the water content of Al ₂ O ₃ used in Examples and Comparative Examples. The measuring method is as described above.

FIG. 6 is a TG-DTA curve of commercially available α-Al ₂ O ₃ (“AKP-50” manufactured by Sumitomo Chemical Co., Ltd.). The water content was 0.35% by weight.

FIG. 7 is a TG-DTA curve of commercially available γ-Al ₂ O ₃ (“AKP-G15” manufactured by Sumitomo Chemical Co., Ltd.). The water content was 5.0% by weight.

  The electrical conductivity of the conductive mayenite type compound used in the following examples and comparative examples is measured by slicing and solidifying the solid after firing with a diamond cutter, and then drying and bonding a Pt wire as a terminal with a conductive paste. The DC four-terminal method was used for evaluation.

[Examples 1 to 3]
Powdered calcium carbonate (CaCO ₃ ) (“CS-3N-A” manufactured by Ube Materials Co., Ltd.) and powdered α-Al ₂ O ₃ (“AKP-50” manufactured by Sumitomo Chemical Co., Ltd.) ) And powdered metal Al (“ALE02PB” manufactured by Kojundo Chemical Co., Ltd.) in a molar ratio of 12: (7−x / 2): x (x = 0.67, x = 1. 33, x = 2.00) and these powders were dry mixed.

  The dry-mixed powder was filled in a graphite sheet (“Graphfoy GTA” manufactured by Graphtec Co., Ltd.) spread in a graphite crucible, covered with a graphite crucible, and further covered with an alumina crucible.

  Next, the alumina crucible was placed in a commercially available electric furnace, and after flowing nitrogen gas and firing at 1500 ° C. for 1 hour, it was cooled to room temperature. The temperature rising rate and cooling rate of the electric furnace were 300 [° C./h].

  Next, a solid sample was taken out from the graphite crucible, cut and molded. The electrical conductivity of the molded sample piece was measured by the DC four-terminal method.

  Further, a part of the molded sample piece was crushed and pulverized, and the phase was identified by powder X-ray diffraction (XRD).

  As a result, a C12A7 single-phase solid was obtained in the region where the amount of metal Al added (mol) x = 0.67 to 2.00, and high electrical conductivity was obtained (see Table 1 and FIG. 1).

  In FIG. 1, (A), (B), and (C) are the amounts of solid metal obtained in the regions where the addition amount (mol) of metal Al is x = 0.67, x = 1.33, and x = 2.00. Powder XRD.

[Example 4]
Example 4 is powdered calcium carbonate (CaCO ₃ ) (“CS 3N-A” manufactured by Ube Materials Co., Ltd.) and powdered α-Al ₂ O ₃ (manufactured by Sumitomo Chemical Co., Ltd.). “AKP-50”) and powdered metal Al (“ALE02PB” manufactured by Kojundo Chemical Co., Ltd.) are weighed at a molar ratio of 12: (7−x / 2): x (x = 0.67). These powders were subjected to the same experimental conditions as [Examples 1 to 3] except that they were dry-mixed, passed argon gas, and fired at 1500 ° C. for 1 hour.

  As a result, a C12A7 single-phase solid was obtained with a metal Al addition amount (mol) x = 0.67 (see Table 2 and FIG. 2).

  FIG. 2 is a solid powder XRD obtained with the addition amount (mol) of metal Al x = 0.67.

[Comparative Example 1]
In Comparative Example 1, powdered calcium carbonate (CaCO ₃ ) (“CS 3N-A” manufactured by Ube Materials Co., Ltd.) and powdered γ-Al ₂ O ₃ (manufactured by Sumitomo Chemical Co., Ltd.) “AKP-G15”) and powdered metal Al (“ALE02PB” manufactured by Kojundo Chemical Co., Ltd.) were weighed in a molar ratio of 12: (7−x / 2): x (x = 0.67). The same experimental conditions as in [Examples 1 to 3] except that these powders were dry mixed.

  As a result, many different phases C3A other than the C12A7 phase were observed (see Table 3 and FIG. 3).

FIG. 3 is a solid powder XRD. In the figure, “□” is a peak indicating that a Ca ₃ Al ₂ O ₆ phase exists.

[Comparative Example 2]
In Comparative Example 2, powdered calcium carbonate (CaCO ₃ ) (“CS 3N-A” manufactured by Ube Materials Co., Ltd.) and powdered γ-Al ₂ O ₃ (Sumitomo Chemical Co., Ltd.) “AKP-G15”) and powdered metal Al (“ALE02PB” manufactured by Kojundo Chemical Co., Ltd.) were weighed in a molar ratio of 12: (7−x / 2): x (x = 0.67). These powders were subjected to the same experimental conditions as [Examples 1 to 3] except that they were dry-mixed, passed argon gas, and fired at 1500 ° C. for 1 hour.

As a result, different phases of the Ca ₃ Al ₂ O ₆ phase and the Ca ₅ Al ₆ O ₁₄ phase were observed, and the C12A7 phase could not be confirmed. (See Table 4, Figure 4).

FIG. 4 shows a solid powder XRD. In the figure, “□” is a peak indicating that a Ca ₃ Al ₂ O ₆ phase is present, and “x” is a peak indicating that a Ca ₅ Al ₆ O ₁₄ phase is present.

[Comparative Examples 3 and 4]
Powdered calcium carbonate (CaCO ₃ ) (“CS-3N-A” manufactured by Ube Materials Co., Ltd.) and powdered α-Al ₂ O ₃ (“AKP-50” manufactured by Sumitomo Chemical Co., Ltd.) ) At a molar ratio of 12: 7, these powders were dry-mixed, and fired in the air at 1200 ° C. for 6 hours to obtain insulating C12A7 polycrystals.

  The obtained insulating C12A7 polycrystal is pulverized and powdered, and this is used as a raw material powder, filled in a graphite sheet (“Graphfoy GTA” manufactured by Graphtec Co., Ltd.) and covered with a graphite crucible. Then, it was further covered with an alumina crucible.

  Next, the alumina crucible was placed in a commercially available electric furnace, nitrogen gas or argon gas was allowed to flow, firing was performed at 1500 ° C. for 1 hour, and then cooled to room temperature. The temperature rising rate and cooling rate of the electric furnace were 300 [° C./h].

  Next, a solid sample was taken out from the graphite crucible, cut and molded. The electrical conductivity of the molded sample piece was measured by the DC four-terminal method.

  A part of the molded sample piece was crushed and pulverized, and the phase was identified by X-ray diffraction (XRD).

  As a result, the C12A7 phase could not be confirmed in any solid produced under any condition. (See Table 5, FIG. 5).

  In FIG. 5, (A) and (B) are solid powder XRD obtained in a nitrogen atmosphere and an argon atmosphere, respectively.

In the figure, “□” is a peak indicating that a Ca ₃ Al ₂ O ₆ phase is present, and “x” is a peak indicating that a Ca ₅ Al ₆ O ₁₄ phase is present.

  In Examples 1 to 4 according to the present invention, a highly pure polycrystalline conductive mayenite compound was obtained. On the other hand, in Comparative Example 1, many different phases were generated in addition to C12A7, and in Comparative Examples 2 to 4, a polycrystalline conductive mayenite compound mainly composed of C12A7 was not obtained.

Claims (6)

  A raw material mixture for producing a conductive mayenite type compound having at least a reducing agent, a Ca-containing substance, and an Al-containing substance, wherein the water content of the Al-containing substance is less than 4% by weight. The raw material mixture according to claim 1, wherein the Al-containing substance is α-Al ₂ O ₃ .   The raw material mixture according to claim 1 or 2, wherein the reducing agent is a metal.   The raw material mixture according to claim 3, wherein the metal is metal Al. Filling the raw material mixture according to claim 1 into a carbon container;
Placing the carbon container in a firing furnace;
A firing step of flowing at least one gas selected from the group consisting of nitrogen and argon into the firing furnace and maintaining the temperature at 1200 to 1600 ° C;
The manufacturing method of the electroconductive mayenite type compound which has at least.   The electroconductive mayenite type compound obtained with the manufacturing method of Claim 5.

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