JP3367106B2 - Method for producing γ-lithium aluminate fiber - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell used in the energy sector for directly converting chemical energy of fuel into electric energy, and more particularly, to an electrolyte plate of a molten carbonate fuel cell in which molten carbonate is impregnated as an electrolyte. The present invention relates to a method for producing γ-lithium aluminate fiber used as a reinforcing material.

[0002]

2. Description of the Related Art In a molten carbonate fuel cell, an electrolyte plate is prepared by impregnating a molten carbonate as an electrolyte into a porous matrix tape, and the electrolyte plate is used as a cathode (oxygen electrode) and an anode (fuel electrode). One cell is sandwiched by both electrodes, and an oxidizing gas is supplied to the cathode side and a fuel gas is supplied to the anode side so that power generation is performed between the cathode and the anode, and each cell is a separator. It is made to be laminated in multiple layers via the to form a stack, and the stack is tightened with an appropriate tightening force.

The electrolyte plate used in the molten carbonate fuel cell has been conventionally manufactured by various methods.

In the case of manufacturing the above electrolyte plate, lithium aluminate (LiAlO ₂ ) is used as a material for holding the electrolyte, and the lithium aluminate powder forms a matrix having a large number of pores, and the matrix is impregnated with the electrolyte. In some cases, an electrolyte plate is formed by holding the electrolyte in the voids of the matrix.

The electrolyte plate obtained by such a method is used by being sandwiched between both electrodes of the cathode and the anode, and the oxidizing gas supplied to the cathode side and the fuel gas supplied to the anode side are completely separated. I have to
The electrolyte plate is subjected to large thermal stress caused by repeated thermal operation between the room temperature and the operating temperature of the fuel cell (about 650 ° C) when the fuel cell is operated or stopped, and the maximum thermal stress at this time is It occurs when the fuel cell is shut off and the electrolyte solidifies. At this time, the volume abruptly changes to generate strain, which is alleviated by cracks in the electrolyte plate. If a crack that penetrates the electrolyte plate in the front and back direction occurs, the electrolyte plate can no longer maintain the ability to separate the oxidizing gas and the fuel gas, and the oxidizing gas and the fuel gas come into direct contact with each other, resulting in a decrease in the battery output. Or there is a problem of causing a risk of explosion.

Therefore, conventionally, when a matrix is made of lithium aluminate powder, a lithium aluminate fiber is produced to prevent the matrix from cracking, and this is used as a reinforcing material for an electrolyte plate. Is proposed.

The lithium aluminate includes α-type, β-type,
There is γ type, but the one that is stable at high temperature is γ type.

Conventionally, as a method for producing the above-mentioned γ-lithium aluminate fiber, among alumina (Al ₂ O ₃ ),
There is a method of producing γ-lithium aluminate fiber by reacting γ-alumina fiber with lithium carbonate or the like to lithiate.

[0009]

However, since the alumina fiber used for producing the above-mentioned γ-lithium aluminate fiber is polycrystal, the γ-lithium aluminate obtained by reacting with lithium carbonate is also polycrystal. There is a problem that mechanical strength does not improve as expected,
Further, since the alumina fiber contains 5% by weight or more of silica, the produced γ-lithium aluminate fiber also contains silica. Since this silica reacts with molten carbonate to destroy the fiber shape, there is a problem that the strength as a structural material is reduced.

Therefore, the present invention is intended to provide a method for producing γ-lithium aluminate fiber which has high purity and is composed of almost a single crystal, and has significantly improved heat resistance, chemical stability and mechanical strength. It is a thing.

[0011]

In order to solve the above-mentioned problems, the present invention provides a compound selected from the group consisting of aluminum salts, aluminum oxides, aluminum hydroxides or hydrates thereof, and organic aluminum hydroxides. A basic compound such as lithium or lithium carbonate is used as a substance selected from the group consisting of lithium hydroxide, a basic compound such as lithium carbonate / aluminum salt, aluminum oxide, aluminum hydroxide or a hydrate thereof and organic aluminum. While mixing at a molar ratio of 0.5 to 5.0, a solvent capable of dissolving the above basic compound is added thereto and mixed, and slurried at a temperature within the range of 25 ° C. to the boiling point of the solvent, and then the slurry. The converted product is gradually dried at a temperature in the range of 50 ° C. to the boiling point to prepare β-lithium aluminate fiber, and then the β-lithium aluminate fiber is prepared. Γ by burning umluminate fiber
To obtain γ-lithium aluminate fiber. In addition, the firing is performed at a temperature within the range of 800 ° C to 1300 ° C.

[0012]

Since a basic compound such as lithium hydroxide or lithium carbonate is dissolved in a solvent, a compound selected from the group consisting of aluminum salt, aluminum oxide, aluminum hydroxide or its hydrate and organic aluminum. Is added and mixed at a temperature within the range of 25 ° C. to the boiling point of the solvent to form a slurry.

By gradually drying the slurried product at a temperature in the range of 50 ° C. to the boiling point, the intermediate β-lithium aluminate fiber can be synthesized at a relatively low temperature, and the single crystal can be easily controlled. While being able to grow, the β-lithium aluminate fiber is fired to be γ-converted into a γ-lithium aluminate fiber, so that the one having significantly improved mechanical strength can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

In the method of the present invention, an aluminum compound and a lithium compound are used as raw materials. The aluminum compound used in the method of the present invention comprises an aluminum salt, aluminum oxide, aluminum hydroxide or its hydrate and organic aluminum. It is one selected from the group.
Similarly, the lithium compound used in the method of the present invention is a basic compound such as lithium hydroxide or lithium carbonate.

FIG. 1 shows a manufacturing process for carrying out the method of the present invention. I is an aluminum compound 1,
What is selected from the group consisting of an aluminum salt, aluminum oxide, aluminum hydroxide or a hydrate thereof and organic aluminum, and as the lithium compound 2, a basic compound such as lithium hydroxide or lithium carbonate is dissolved in the lithium compound 2. A mixing part for mixing and slurrying in the presence of the solvent 3 to be obtained, II is a drying part for drying what is slurried in the mixing part I to carry out a dehydration reaction. Allow the lithium aluminate fiber 4 to be taken out. III is a calcining part for calcining the β-lithium aluminate fiber 4 to make it γ-form, and the γ-lithium aluminate fiber 5 is taken out from the calcining part III.

The solvent 3 used in the method of the present invention refers to water, alcohols or the like, which can dissolve the lithium compound, alone or in a mixture.

In the case of manufacturing by the above manufacturing process, first, in the mixing part I, a basic compound such as lithium hydroxide or lithium carbonate as a lithium compound 2 as a raw material, and an aluminum salt or aluminum oxide as an aluminum compound as a raw material. , Aluminum hydroxide or a hydrate thereof, selected from the group consisting of organoaluminum, and a desirable lithium compound / aluminum compound molar ratio:
The mixture is transferred to a mixing part I at 0.5 to 5.0, and in the mixing part I, a solvent 3 capable of dissolving the lithium compound 2 is added and mixed, and the slurry is slurried at a temperature within the range of 25 ° C. to the boiling point of the solvent 3. Turn into. In this case, since the lithium compound 2 is dissolved in the solvent 3 and the substance selected from the above group as the aluminum compound 1 is mixed therein, it is essentially solid, but the lithium compound 2 is dissolved in the solvent 3 to form a liquid. Therefore, it is slurried. Here, the temperature at the time of mixing and slurrying is set within the range of 25 ° C. to the boiling point of the solvent because the reaction rate is too slow at 25 ° C. or lower and the solvent disappears at the boiling point or higher. Temperatures within the range are preferred.

Next, the above slurry is dried in a drying section II.
At 50 ° C. to a boiling point, a relatively low temperature is gradually dried. When the drying temperature is within the range of 50 ° C. to the boiling point, the evaporation of the solvent is slow at 50 ° C. or lower and it takes a long time to obtain a solid product. This is for drying. Further, to gradually dry in the drying section II means to evaporate the solvent at a drying rate of 3% / hour or less of the total amount of solvent when the amount of solvent becomes 10 times or less of the solid amount. This allows
The single crystal can be grown slowly while being controlled, and the β-lithium aluminate fiber 4 having an aspect ratio of 5 or more can be manufactured. Then, the β-lithium aluminate fiber 4 is fired at a required temperature (800 ° C. to 1300 ° C.) in the firing part III to be converted into γ-form,
The γ-lithium aluminate fiber 5 is manufactured.

Next, an example of a concrete implementation will be shown.

First, 23.5 g of lithium hydroxide (hydrate or anhydride) and 43.7 g of aluminum hydroxide were mixed in the presence of 1600 cc of water as the solvent 3, and mixed at 50 ° C. using a flask. It was slurried to obtain a composite hydroxide _{(LiOH · 2Al (OH) 3} · nH 2 O). This is transferred to a Teflon jar and dried in a dryer at about 105 ° C to evaporate water. When the amount of remaining water reaches about 370 cc, the water is gradually evaporated at an evaporation rate of 48 cc / hour or less to grow β-lithium aluminate crystals.
Then, the β-lithium aluminate fiber grown into a single crystal was washed and fired at 950 ° C. for 30 minutes. As a result, the β-lithium aluminate fiber 4 could be converted into γ-form while maintaining the shape, and γ-lithium aluminate fiber as shown in the photograph of FIG. 2 was obtained.

[0022] In the above manufacturing process, the evaporation rate in the drying unit II is fast, complex hydroxide which is the main component of the slurry _{(LiOH · 2Al (OH) 3} · nH 2 O) is dried as unreacted product solid It was confirmed that a large amount was present in the product, and when the molar ratio of the lithium compound / aluminum compound was 5.0 or more, the obtained β-lithium aluminate fiber was fired in the firing part III to be γ-converted. Even if it does not become a fiber, the firing temperature is below 800 ℃, 1300 ℃
It was also confirmed that β-lithium aluminate does not become γ-ized by the above.

[0023]

As described above, according to the method for producing γ-lithium aluminate fiber of the present invention, it is selected from the group consisting of aluminum salt, aluminum oxide, aluminum hydroxide or its hydrate and organic aluminum. And a basic compound such as lithium hydroxide or lithium carbonate from the group consisting of basic compounds such as lithium hydroxide and lithium carbonate / aluminum salt, aluminum oxide, aluminum hydroxide or a hydrate thereof and organic aluminum. The selected substances are mixed at a molar ratio of 0.5 to 5.0, and a solvent capable of dissolving the above basic compound is added thereto and mixed to form a slurry at a temperature within the range of 25 ° C to the boiling point of the solvent. Then, the slurry is gradually dried at a temperature in the range of 50 ° C. to the boiling point to prepare β-lithium aluminate fiber. After that, the β-lithium aluminate fiber is fired to be γ-converted to obtain γ-lithium aluminate fiber.
Since the process is carried out at a temperature within the range of 0 ° C to 1300 ° C, the intermediate β-lithium aluminate fiber can be synthesized at a relatively low temperature and the fiber control is easy. A single-crystal γ-lithium aluminate fiber is obtained, and by using it as an electrolyte holding material or a reinforcing material of a molten carbonate fuel cell, it is possible to chemically retain the electrolyte for a long period of time to improve the electrolyte holding and mechanical strength, and Also, it can be used as a blanket material for a fusion reactor, and can exhibit excellent effects.

[Brief description of drawings]

FIG. 1 shows steps for carrying out the method of the invention.

FIG. 2 is a photograph showing the structure of γ-lithium aluminate fiber obtained by the production method of the present invention.

[Explanation of symbols]

I mixing section II Drying section III Firing part 1 Aluminum compound 2 Lithium compound 3 solvent 4 β-Lithium aluminate fiber 5 γ-Lithium aluminate fiber

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 63-260812 (JP, A) JP-A 58-176122 (JP, A) JP-A 61-291451 (JP, A) JP-A 53- 140300 (JP, A) JP-A-61-291414 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 8/02 C01F 7/02 D01F 9/08

Claims (2)

(57) [Claims] 1. A compound selected from the group consisting of an aluminum salt, aluminum oxide, aluminum hydroxide or a hydrate thereof and organic aluminum, and a basic compound such as lithium hydroxide or lithium carbonate, lithium hydroxide, A basic compound such as lithium carbonate / aluminum salt, aluminum oxide, aluminum hydroxide or a hydrate thereof, and a substance selected from the group consisting of organoaluminum are mixed at a molar ratio of 0.5 to 5.0. A solvent capable of dissolving the basic compound is added to and mixed with the mixture to form a slurry at a temperature in the range of 25 ° C. to the boiling point of the solvent, and then the slurry is gradually added at a temperature in the range of 50 ° C. to the boiling point. It is dried to produce β-lithium aluminate fiber, and then the β-lithium aluminate fiber is fired to produce γ
A method for producing a γ-lithium aluminate fiber, characterized in that the γ-lithium aluminate fiber is obtained. 2. A compound selected from the group consisting of an aluminum salt, aluminum oxide, aluminum hydroxide or a hydrate thereof and organic aluminum, and a basic compound such as lithium hydroxide or lithium carbonate, lithium hydroxide, A basic compound such as lithium carbonate / aluminum salt, aluminum oxide, aluminum hydroxide or a hydrate thereof, and a substance selected from the group consisting of organoaluminum are mixed at a molar ratio of 0.5 to 5.0. A solvent capable of dissolving the basic compound is added to and mixed with the mixture to form a slurry at a temperature in the range of 25 ° C. to the boiling point of the solvent, and then the slurry is gradually added at a temperature in the range of 50 ° C. to the boiling point. After being dried, β-lithium aluminate fiber is prepared. Thereafter, the β-lithium aluminate fiber is dried at 800 ° C.
To γ-form by firing at a temperature within the range of 1300 ° C.
Γ- characterized by obtaining lithium aluminate fiber
Method for producing lithium aluminate fiber.