JP3497285B2 - Method for producing β-alumina fiber - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention is excellent in alkali resistance,
Further, the present invention relates to a β-alumina fiber rich in ion conductivity and a method for producing the same.

[0002]

2. Description of the Related Art β-Alumina has been conventionally used as an alkali resistant structural material, and has recently been developed as a material for batteries such as sodium-sulfur batteries because of its excellent ionic conductivity. Further, β-alumina is a composite oxide composed of an alkali metal oxide and / or an alkaline earth metal oxide and alumina, and among them, an alkali metal component and / or an alkaline earth metal component are included. Β-alumina containing 5 to 40 mol% and having a crystallographic C-axis lattice constant of 2.1 to 3.5 nm is particularly promising as a battery material because of its excellent ionic conductivity. Thus, β-alumina has excellent performance as various functional materials, but when this β-alumina is used as a molded and processed material, thermal,
Since mechanical strength is insufficient, it is strongly desired to provide fibrous β-alumina as a material that can be reinforced without deteriorating properties such as ionic conductivity.

However, most of the β-alumina provided so far is in the form of powder, and it has been extremely difficult to form β-alumina into fibers, and the method for producing the fibrous β-alumina has been extremely difficult. As for, fibrous from a viscous sol mainly composed of aluminum nitrate and sodium nitrate,
The method of crystallization thereafter is only the level disclosed in JP-A-3-140509.

However, even in such a method for producing β-alumina fibers, if a large amount of sodium salt such as sodium nitrate is added to the spinning dope, the spinnability is deteriorated and the precursor fibers obtained by spinning are There is a problem in physical properties such as strength of the final β-alumina fiber and in production, such that the hygroscopicity is remarkable, the precursor fibers are fused with each other, and it is difficult to maintain the fiber form. That is, in the conventional method for producing β-alumina containing 5 to 40 mol% of sodium component and having physical properties such as a C-axis lattice constant of 2.1 to 3.5 nm in the crystal, β-alumina is used. For example, it was not possible to obtain β-alumina fibers having a tensile strength of 60 kgf / mm ² or more, because physical properties such as the strength of the fibers were deteriorated.

Also, when potassium nitrate is used instead of sodium nitrate, if a large amount of such a potassium salt is added to the spinning dope, the spinnability is deteriorated and spinning is performed as in the case of the sodium salt. The precursor fiber obtained has remarkable hygroscopicity, the precursor fibers are fused with each other, and it is difficult to maintain the fiber morphology, and there is a problem in physical properties such as strength of the final β-alumina fiber and in production. There is. Furthermore, when an alkaline earth metal compound such as a calcium compound, a strontium compound and a barium compound is used instead of or together with sodium nitrate and potassium nitrate, the final β-alumina fiber is as much as when the alkali metal compound is used. There is no problem in the physical properties such as the strength of and the production, but β-
As the alumina fiber, the β-alumina material was not developed by specifying the content of the alkaline earth metal component, the lattice constant of the C axis in the crystal, and the physical properties such as fiber strength. Moreover, in the method for producing the β-alumina fiber described above, an aqueous solution of a water-soluble salt such as sodium nitrate and aluminum nitrate is solized,
Since the spinning solution is prepared from the solized liquid,
In preparing the spinning dope, sol treatment of the aqueous solution,
It takes a long time to perform the filtration treatment of the sol-state liquid and the concentration treatment of the filtrate, and the productivity thereof is extremely low, which is also a problem in production.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the prior art and to produce β-alumina fibers containing a large amount of alkali metal components and / or alkaline earth metal components with high productivity. It is to provide a manufacturing method.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have prepared a spinning dope by adding specific amounts of an alumina powder and a spinning aid, The present invention has been completed by finding that the spinnability and productivity of the spinning dope can be improved, and that various β-alumina fibers having high purity and high strength can be obtained.

That is, the present invention relates to an alkali metal component and / or
Alternatively, in the method for producing β-alumina containing an alkaline earth metal component in an amount of 5 to 40 mol% and having a C-axis lattice constant of 2.1 to 3.5 nm in the crystal, a water-soluble basic aluminum salt and a water-soluble basic aluminum salt are used. Alumina powder is added to a solution prepared by dissolving a water-soluble alkaline earth metal compound and / or a water-soluble alkaline earth metal compound in an aqueous solvent, and a spinning aid is further added to adjust the viscosity to obtain a slurry. A method for producing β-alumina fiber, characterized in that a spinning dope is spun, the spinning dope is spun into a precursor fiber, and the precursor fiber is fired in a range of 1100 to 1600 ° C.
In this preferred embodiment, the alkali metal compound is a sodium compound and / or a potassium compound, a method for producing β-alumina fiber, and an alkaline earth metal compound is a calcium compound, a strontium compound and a barium compound. A method for producing β-alumina fiber, which comprises one or more kinds of alkaline earth metal compounds selected.

The basic aluminum salt used in the present invention is soluble in an aqueous solvent such as basic aluminum lactate, basic aluminum nitrate and basic aluminum acetate, and has an alumina purity of 95% by weight or more after firing. After firing, it is preferable that the composition contains almost no SiO ₂ , Fe ₂ O ₃ or the like.

The alkali metal compound and / or the alkaline earth metal compound is not particularly limited as long as the obtained β-alumina crystal has a C-axis lattice constant of 2.1 to 3.5 nm. As a preferable example, CH ₃ C
00Na, NaNO ₃ , Na ₂ CO ₃ , NaOH, CH ₃ C 00K, KNO ₃ , K ₂ C
O ₃ , KOH, (CH ₃ C00) ₂ Mg, Mg (NO ₃ ) ₂ , MgCO ₃ , Mg (O
H) ₂ , (CH ₃ C00) ₂ Ca, Ca (NO ₃ ) ₂ , CaCO ₃ , Ca (OH) ₂ , (CH
₃ C00) ₂ Sr, Sr (NO ₃ ) ₂ , SrCO ₃ , Sr (OH) ₂ , (CH ₃ C00) ₂ Ba
, Ba (NO ₃ ) ₂ , BaCO ₃ , and Ba (OH) ₂ . These alkali metal compounds and / or alkaline earth metal compounds have a purity of 95% by weight or more of the alkali metal oxides and / or alkaline earth metal oxides after firing,
It is preferable that the composition contains almost no SiO ₂ , Fe ₂ O ₃ or the like after firing.

It should be noted that for alkali metal compounds and / or alkaline earth metal compounds having a low solubility, nitric acid, acetic acid or the like may be used to change the pH to facilitate dissolution. Si in the raw material used in the production method of the present invention
Components such as O ₂ and Fe ₂ O ₃ deteriorate physical properties of the β-alumina fiber, such as deterioration of fiber strength, deterioration of flexibility, and deterioration of ionic conductivity. It is preferably 1% by weight or less. SiO ₂ and Fe ₂ O _{3 in} β-alumina after firing
Is more than 1% by weight, the strength and flexibility of the β-alumina fiber are deteriorated, which is not preferable.

Further, in order to improve the fluidity of the spinning dope and the stability of the precursor, reduce the volatile content during firing, and further improve the fiber strength, a basic aluminum salt, an alkali metal compound and / or Alternatively, the alumina powder is added to a solution in which an alkaline earth metal compound is dissolved in an aqueous solvent, and the mixture is uniformly mixed. The particle size of the alumina powder used is preferably as small as possible from the viewpoint of spinnability or β-alumination reactivity, and the average particle size is 1 μm.
It is preferably m or less, more preferably 0.1 μm or less. As the alumina powder to be added, in addition to high-purity intermediate alumina such as θ-alumina, δ-alumina and γ-alumina and high-purity α-alumina, gibbsite, boehmite, bayerite, diaspore or pseudo-boehmite can be used to increase the Aluminum compounds that provide pure alumina can be used.

Here, the "intermediate alumina" means that when the aluminum compound is heated, volatile components such as water of crystallization are volatilized and changed to alumina, and the X-ray diffraction peak is obtained.
The crystalline form of the crystalline material is from amorphous to thermally stable γ-alumina, δ-alumina, etc., and finally becomes the most stable α-alumina as a crystal. ,
This refers to alumina in the amorphous or thermally unstable crystalline state existing in the process of becoming α-alumina. In the present invention, since these alumina powders are added and used, it is particularly effective to add the organic solvent to the aqueous solvent. That is, the added organic solvent facilitates the mixing and dispersion of the alumina powder, facilitates the uniform penetration of the alkali metal compound and / or the alkaline earth metal compound into the pores on the surface and inside the alumina powder, and calcinates In this case, the β-aluminization reaction of the alumina powder can be uniformly promoted while maintaining the fiber shape. The aqueous solvent in the present invention means water or a mixed solvent of water and a water-soluble solvent such as alcohols.

The method for producing the β-alumina fiber of the present invention will be described below according to the process. First, a basic aluminum salt and an alkali metal compound and / or an alkaline earth metal compound are uniformly dissolved in an aqueous solvent, and alumina powder is added to this solution and mixed to form a uniform slurry. The amount of the alkali metal compound and / or the alkaline earth metal compound used in the β-alumina fiber after firing is
The content of the alkali metal component and / or the alkaline earth metal component is in the range of 5 to 40 mol%, preferably 7 to 20 mol%. When the content of the alkali metal component and / or the alkaline earth metal component is less than 5 mol%,
The β-alumination reaction did not proceed sufficiently and was 40 mol%
If it exceeds, aluminate, alkali metal oxide and /
Alternatively, a large amount of crystals of alkaline earth metal oxides are deposited on the fiber surface, which makes it difficult to obtain a good β-alumina fiber, which is not preferable.

In order to obtain β-alumina fiber having a specific composition with high purity, the content of alkali metal component and / or alkaline earth metal component in the slurry is
It can be achieved by adjusting the amount in the range of 1 to 1.1 times the theoretical molar amount. For example, to obtain β-alumina fiber having a composition of Na ₂ O · 11Al ₂ O ₃ with high purity,
This can be achieved by setting the content of the sodium component in the range of 0.091 to 0.100 (mol / mol) in terms of the molar ratio of Na ₂ O / Al ₂ O ₃ . Further, by adding a magnesium compound and / or a lithium compound in addition to the alkali metal compound and / or the alkaline earth metal compound used in the slurry, β ″ which is one kind of β-alumina.
-Alumina and / or β '''-as alumina, β-
Alumina can be stabilized.

As the alumina powder to be added to the above solution, besides high-purity intermediate alumina such as θ-alumina, δ-alumina and γ-alumina and high-purity α-alumina, gibbsite, boehmite, bayerite, diaspore or pseudo-alumina. Although an aluminum compound which becomes high-purity alumina by firing such as boehmite can be used, high-purity intermediate alumina such as γ-alumina is preferable.
The particle size of these aluminous powders is preferably as small as possible from the viewpoint of spinnability or β-alumination reactivity, and the average particle size is preferably 1 μm or less, more preferably 0.
It is preferably 1 μm or less. The amount of the alumina powder added is preferably 10 to 60% by weight of the total amount of the alumina component,
More preferably, 20 to 40% by weight is desirable.

When no alumina powder is added to the solution, that is, when only a basic aluminum salt is used as an alumina source, it is difficult to maintain the fiber morphology in the spinning step because the hygroscopicity is remarkable, and the yield decreases. When the volatile gas from the inside of the fiber passes through the surface of the fiber during the firing in the subsequent step, large pores of 0.1 to 0.5 μm are sparsely and unevenly generated on the surface of the fiber, and the volatile component is Since the amount of the β-alumina fiber is large, the number of yarn breakages increases due to the large shrinkage during firing, and the strength of the obtained β-alumina fiber tends to be low, so that the target fiber is difficult to obtain. If the amount of the powder added is less than 10% by weight, it is difficult to maintain the fiber morphology due to moisture absorption in the spinning step and shrinkage in the firing step, as in the case of the above-mentioned non-addition. Is not preferable because the strength of
On the other hand, when the amount of the powder added exceeds 60% by weight, yarn breakage is likely to occur during spinning, and the resulting β-alumina fiber surface has large irregularities, resulting in deterioration in fiber strength and other deterioration in quality. Not preferable.

To the slurry thus obtained, 1 to 10% by weight of alumina sol, based on oxide, of 0.1 to
A spinning dope is prepared by adding 10% by weight of a spinning aid. The amount of alumina sol added to the slurry to further improve the fiber strength is preferably 1 to 10% by weight based on the oxide. This alumina sol suppresses pulverization due to abrupt volatilization of volatile components in the basic aluminum salt, and exerts a binder effect on the β-alumina crystals produced, so that the β-alumina fiber obtained is , Its fiber strength is extremely high. When the amount of alumina sol added is less than 1% by weight, this binder effect does not remarkably appear. On the other hand, when it exceeds 10% by weight, there is no particular increase in the effect, and the amount of volatile components increases correspondingly. Not preferable.

Regarding the spinning aid for improving the spinnability of the above spinning dope, ethylene glycol, glycerin,
It is preferable to add an organic compound such as acetic acid, a water-soluble organic polymer compound such as polyvinyl alcohol, polyethylene oxide, polypropylene oxide, or a mixture thereof in an amount of 0.1 to 10% by weight based on the oxide.

The spinning dope thus obtained may be spun by any spinning method such as a centrifugal method, a blow-off method, or an extrusion method, depending on the capability of the spinning apparatus. The kind and amount of additives that also act as a viscosity modifier such as the spinning aid, and the water content and viscosity of the spinning dope may be appropriately determined. For normal conditions of water content and viscosity of spinning dope, the water content is 2
The viscosity is 0 to 45% by weight and the viscosity at 25 ° C. is 300 to 4000 poise, but those conditions are changed depending on the capability of the spinning device and are not limited to these ranges. In the preparation of the spinning dope in the method of the present invention, it is not necessary to perform a treatment operation that requires a long time, such as a sol treatment of an aqueous solution, a filtration treatment of the solized liquid, and a concentration treatment of the filtrate, or the treatment operation is performed. Even if it is carried out, it takes only a short time, and therefore the productivity of the spinning dope is extremely high.

The fiber diameter of the precursor fiber thus obtained by spinning is preferably 2 to 25 μm. In order to obtain fibers having a small fiber diameter, a method of spinning a low-viscosity spinning dope by a centrifugal method or a blow-off method is mainly adopted, but a precursor fiber having a fiber diameter of less than 2 μm is stably produced. Since it is difficult and not practical, it is not preferable to make the fiber diameter less than 2 μm. On the other hand, in order to obtain a fiber having a large fiber diameter, a method of spinning a high-viscosity spinning dope by an extrusion method is mainly adopted, and a fiber diameter of 25 μm is obtained by the method of the present invention.
Although it is possible to obtain a precursor fiber exceeding the above and then to produce β-alumina fiber, long-term firing is required and the production efficiency deteriorates, and the obtained β-alumina fiber maintains the fiber morphology. However, since it becomes hard and brittle and lacks flexibility, it lacks the function as a fiber. Therefore, it is not preferable to use a precursor fiber having a fiber diameter of more than 25 μm. Further, in the method of spinning by the extrusion method, 0.1 to 0.5
By using a spinning nozzle having 100 or more mmφ holes, the productivity can be further improved.

The precursor fiber thus obtained by spinning is heated in a temperature range of 1100 to 1600 ° C. and calcined to obtain an alumina component and an alkali metal compound and / or an alkaline earth metal compound. React to give β-alumina fibers. The firing operation of this precursor fiber may be performed after cutting the precursor fiber into an appropriate length, but a method of continuously passing the spun precursor fiber through a firing furnace is efficient. Precursor fibers in the form of long fibers can be obtained as they are, or by cutting them to an appropriate length and then firing them, β-alumina fibers in the form of long fibers or short fibers of uniform length can be obtained. .

Regarding the calcination temperature, if it is less than 1100 ° C., the β-alumination reaction does not proceed or is very slow,
On the other hand, if the temperature exceeds 1600 ° C., the β-alumina that has been once generated is redissolved, which is not preferable.

When a sodium compound is used as the alkali metal compound and / or the alkaline earth metal compound and the firing temperature is 1275 ° C. or higher, the sublimation of Na ₂ O occurs before the β-alumination reaction proceeds sufficiently. Therefore, it is preferable to bake in a closed box to prevent sublimation of Na ₂ O. The firing time may be appropriately determined according to the properties of the precursor fiber, the type and mixed state of the alkali metal compound and / or alkaline earth metal compound used, the crystal grain size in the desired β-alumina fiber, and the like. The maximum time is about 24 hours.

In the method of the present invention, since the alumina powder and the spinning aid are used in the spinning dope, the spinnability is improved in spite of containing a large amount of the alkali metal compound and / or the alkaline earth metal compound. Good, and also good permeability of the alkali metal compound and / or alkaline earth metal compound into the surface and internal pores of the alumina powder, and the precursor fiber obtained has a high reactivity of β-alumination, A high-strength β-alumina fiber having a long length can be easily manufactured. The fiber raw materials used in the method of the present invention such as the alumina powder and the spinning aid are, especially, SiO ₂ and Fe after firing.
_A high-purity fiber raw material containing almost no impurities such as ₂ O ₃ can be used, and the obtained β-alumina fiber has not only high purity but also higher strength and flexibility.

In the method of the present invention, the precursor fiber is added to 5 to 10
If it is manufactured by a method of cutting it to a length of about 0 mm and firing it, β-alumina fibers of about 3 to 60 mm are mainly obtained. Further, if the precursor fiber is fired as a long fiber as it is, β-alumina fiber in the form of a long fiber can be obtained, and this can be cut into an appropriate length and used as a fiber having a uniform length. You can This β-alumina fiber has excellent performance as an alkali-resistant structural material and a reinforcing material for battery materials such as sodium-sulfur batteries.
By mixing with alumina powder, molding and processing, it is possible to obtain a molding material that has good handleability, does not deteriorate physical properties such as ionic conductivity, does not easily crack due to thermal or mechanical impact, and has high strength. be able to.

[0027]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples.

(Example 1) 2.0 parts by weight of lactic acid, 100.0 parts by weight of basic aluminum lactate (content ratio as Al ₂ O ₃ of 37.0% by weight) and 9.6 parts by weight of sodium nitrate, After being dissolved in 200 parts by weight of water, 24.5 parts by weight of γ-alumina fine powder having an average particle size of 0.02 μm was added, followed by stirring and mixing for 30 minutes [Na ₂ O / (Na ₂ O + Al
₂ O ₃ ) in a molar ratio of 8.6 mol%]. Polyvinyl alcohol (average degree of polymerization: about 3000) was added to this slurry.
Add 0 parts by weight and mix well, and mix this mixture under reduced pressure for 8 hours.
It was concentrated for a period of time to obtain a spinning dope having a viscosity of 2500 poise at 25 ° C. This spinning dope is made into 100 mm holes with a diameter of 0.3 mm.
A fiber having a filament diameter of 1000 filaments is extruded from 0 spinning nozzles into a spinning cylinder for drying, and has a fiber diameter of 1000 filaments.
A precursor fiber of μm was obtained. This precursor fiber is heated at a temperature of 10
Β-alumina fiber in the form of a long fiber consisting of 1000 filaments having a fiber diameter of about 10 μm, which are continuously passed through a firing furnace having a temperature gradient from 0 ° C. to a maximum of 1400 ° C. with a residence time of 7 minutes and fired. Got This β-alumina fiber is
It was a continuous filament having flexibility and a tensile strength of 105 kgf / mm ² . In addition, as a result of identification and analysis by an X-ray diffractometer, a purity of about 96% by weight of Na ₂ O.11Al ₂ O _{3 was obtained.}
(C-axis lattice constant in the crystal: 2.261 nm) and a small amount of Na ₂ O · 7Al ₂ O ₃ (C in the crystal
Axial lattice constant: 2.270 nm) and Na ₂ O · 5Al
₂ O ₃ (C-axis lattice constant in crystal: 3.395 n
m) was a β-alumina fiber. Note that this β
- Results of the SiO ₂ content and Fe ₂ O ₃ content of the alumina fibers was analyzed by high-frequency plasma emission spectrometer (ICP), respectively, 0.05 wt% and 0.06 wt%
And it was a very small amount.

(Example 2) 2.7 parts by weight of lactic acid, 132.0 parts by weight of basic aluminum lactate (content ratio as Al ₂ O ₃ is 37.0% by weight), 33.8 parts by weight of sodium nitrate and magnesium nitrate. 51 parts by weight of hexahydrate, 300 parts of water
After being dissolved in parts by weight, γ-having an average particle size of 0.02 μm
48.8 parts by weight of alumina fine powder was added, and the mixture was stirred and mixed for 30 minutes [(Na ₂ O + MgO) / (Na ₂ O + MgO + A
The molar ratio of 1 ₂ O ₃ ) was 29 mol%]. Polyvinyl alcohol (average degree of polymerization: about 3000) 6.
0 parts by weight was added and mixed well, and the mixture was mixed under reduced pressure to
It was concentrated for a period of time to obtain a spinning dope having a viscosity of 2500 poise at 25 ° C. This spinning dope is made into 100 mm holes with a diameter of 0.3 mm.
A fiber having a filament diameter of 1000 filaments is extruded from 0 spinning nozzles into a spinning cylinder for drying, and has a fiber diameter of 1000 filaments.
A precursor fiber of μm was obtained. About 100 of this precursor fiber
Cut into a length of mm, put in a box made of high-purity alumina, heat up to 1300 ° C. at a heating rate of 100 ° C./hour, hold at the same temperature for 1 hour and bake, fiber diameter about 10 μm, fiber length About 60 mm of β-alumina fiber was obtained. This β-alumina fiber was flexible and had a tensile strength of 85 kgf / mm ² . In addition, as a result of identification and analysis by an X-ray diffractometer, Na ₂ O.MgO.5Al with a purity of about 95% by weight was obtained.
₂ O ₃ (C-axis lattice constant in crystal: 3.348 n
It was the β-alumina fiber of m). In addition, S of this fiber
The iO ₂ content and the Fe ₂ O ₃ content are respectively 0.
It was a very small amount of 05% by weight and 0.07% by weight.

(Example 3) 2.0 parts by weight of lactic acid, 100.0 parts by weight of basic aluminum lactate (content of 37.0% by weight as Al ₂ O ₃ ) and 25.6 parts by weight of potassium nitrate were added to water. After being dissolved in 200 parts by weight, 24.5 parts by weight of γ-alumina fine powder having an average particle diameter of 0.02 μm was added, and mixed by stirring for 30 minutes [K ₂ O / (K ₂ O + Al ₂ O
The molar ratio of ₃ ) was 17 mol%]. To this slurry, 5.0 parts by weight of polyvinyl alcohol (average degree of polymerization: about 3000) was added and mixed well, and the mixture was concentrated under reduced pressure for 8 hours to give a spinning dope having a viscosity of 2500 poise at 25 ° C. did. This spinning dope is extruded from a spinning nozzle having 1000 holes of 0.3 mmφ into a spinning tube for drying to be spun, and a fiber diameter of 1000 filaments of 13 μm.
The precursor fiber of was obtained. About 100 mm of this precursor fiber
Cut to length and put in a box made of high-purity alumina, 1 hourly
At a heating rate of 00 ° C, the temperature is raised to 1200 ° C, and at the same temperature, 1
It was held for a period of time and fired to obtain β-alumina fiber having a fiber length of about 60 mm, which was composed of 1000 filaments having a fiber diameter of about 10 μm. The β-alumina fiber was flexible and had a tensile strength of 100 kgf / mm ² . Also, X
As a result of identification and analysis by a line diffractometer, it was β-alumina fiber having a purity of about 97% by weight in a K ₂ O.5Al ₂ O ₃ crystal and a C-axis lattice constant of 3.423 nm). The SiO ₂ content and Fe ₂ O ₃ content of this fiber were very small amounts of 0.05% by weight and 0.07% by weight, respectively.

(Example 4) 2.0 parts by weight of lactic acid, 100.0 parts by weight of basic aluminum lactate (content ratio as Al ₂ O ₃ of 37.0% by weight) and 16.4 parts by weight of calcium acetate, After being dissolved in 200 parts by weight of water, 24.5 parts by weight of γ-alumina fine powder having an average particle size of 0.02 μm was added, followed by stirring and mixing for 30 minutes [CaO / (CaO + Al ₂ O
The molar ratio of ₃ ) was 15 mol%]. To this slurry, 5.0 parts by weight of polyvinyl alcohol (average degree of polymerization: about 3000) was added and mixed well, and the mixture was concentrated under reduced pressure for 8 hours to give a spinning dope having a viscosity of 2500 poise at 25 ° C. did. This spinning dope is extruded from a spinning nozzle having 1000 holes of 0.3 mmφ into a spinning tube for drying to be spun, and a fiber diameter of 1000 filaments of 13 μm.
The precursor fiber of was obtained. About 100 mm of this precursor fiber
Cut to length and put in a box made of high-purity alumina, 1 hourly
The temperature is raised to 1400 ° C at a heating rate of 00 ° C, and 1
It was held for a time and fired to obtain β-alumina fiber having a fiber diameter of about 10 μm. This β-alumina fiber has flexibility,
The fiber had a tensile strength of 105 kgf / mm ^{2 and} a fiber length of about 60 mm. As a result of identification and analysis by an X-ray diffractometer, it was β-alumina fiber having a purity of about 95% by weight in the CaO.6Al ₂ O ₃ crystal and having a C-axis lattice constant of 2.189 nm. The SiO ₂ content and Fe ₂ O ₃ content of this fiber were 0.06% by weight and 0.08% by weight, respectively, which were very small amounts.

Comparative Example 1 2.0 parts by weight of lactic acid, 100.0 parts by weight of basic aluminum lactate (content ratio as Al ₂ O ₃ of 37.0% by weight) and 5.7 parts by weight of sodium nitrate, After being dissolved in 200 parts by weight of water, 5.0 parts by weight of polyvinyl alcohol (average degree of polymerization of about 3000) was added and sufficiently mixed [Na ₂ O / (Na ₂ O + Al ₂ O ₃ ) at a molar ratio of 8. 5 mol%], and the mixture was concentrated under reduced pressure to give a spinning dope having a viscosity at 25 ° C. of 2500 poise. This concentration under reduced pressure took 15 hours, which required a considerable amount of time as compared with the case where the alumina powder was added to the spinning dope, and the productivity decreased. This spinning dope was mixed with 0.
A precursor nozzle having a fiber diameter of 14 μm consisting of 1000 filaments was obtained by extruding from a spinning nozzle having 1000 holes of 3 mmφ into a spinning cylinder for drying and spinning. However, this precursor fiber was partially fused. The precursor fiber is continuously passed through a firing furnace having a temperature gradient from 100 ° C. to a maximum of 1400 ° C. for a residence time of 7 minutes to be fired to obtain a filament 100 having a fiber diameter of about 10 μm.
A β-alumina fiber in the form of zero filaments was obtained. This β-alumina fiber was a continuous long fiber having a tensile strength of 42 kgf / mm ² , and its fiber strength and flexibility were low as compared with the case where the alumina powder was added to the spinning dope.
As a result of identification and analysis by an X-ray diffractometer, a purity of about 93% by weight of Na ₂ O.11Al ₂ O ₃ (C-axis lattice constant in the crystal: 2.261 nm) and a small amount of N
a ₂ O.7Al ₂ O ₃ (C-axis lattice constant in the crystal:
2.270 nm) and Na ₂ O.5Al ₂ O ₃ (C-axis lattice constant in crystal: 3.395 nm)
It was an alumina fiber. The SiO ₂ content and the Fe ₂ O ₃ content of this β-alumina fiber were analyzed by a high-frequency plasma emission spectroscope (ICP), and as a result, they were 0.03% by weight and 0.06% by weight, respectively, which were very small. Was the amount.

[0033]

In the method of the present invention, since the spinning stock solution contains an alumina powder, a spinning aid, etc., it contains a large amount of an alkali metal compound and / or an alkaline earth metal compound. The spinnability is good, and the reactivity of the obtained precursor fibers for β-alumination is high, so that high-purity β-alumina fibers having a long fiber length can be easily produced. Further, in the preparation of the spinning dope in the method of the present invention, does not require a long-time treatment operation such as sol treatment of an aqueous solution, filtration treatment of the solized liquid and concentration treatment of the filtrate, or the treatment thereof. Since the operation can be completed in a short time, the productivity of the spinning dope is extremely high, and the productivity of the final product β-alumina fiber is also very high. The fiber raw materials used in the method of the present invention, such as the alumina powder and the spinning aid, are especially S after firing.
High-purity fiber raw material containing almost no impurities such as iO ₂ and Fe ₂ O ₃ can be used, and the obtained β-alumina fiber is not only high in purity but also has high strength and flexibility. Become. In the method of the present invention, if the precursor fiber is cut into an appropriate length of about 5 to 100 mm before or after firing, and is produced by the method of firing, it is mainly 3 to 60.
A β-alumina fiber having a size of about mm is obtained. In addition, if the precursor fiber is fired as a long fiber as it is, a β-alumina fiber in the form of a long fiber can be obtained, and by cutting this into an appropriate length, a fiber having a uniform length can be obtained. You can also This β-alumina fiber is an alkali resistant structural material,
Also, it has excellent performance as a reinforcing material for battery materials such as sodium-sulfur batteries, and by mixing with β-alumina powder, molding and processing, the handleability is good, and the ionic conductivity, etc. It is possible to obtain a high-strength molding material in which cracks due to thermal and mechanical impact are unlikely to occur without deteriorating the physical properties.

Further, β-obtained by the method of the present invention
Alumina fibers have excellent characteristics such as high ionic conductivity without deteriorating the strength and flexibility of the fibers, despite containing a large amount of alkali metal components and / or alkaline earth metal components, It is useful as a reinforcement for alkaline structural materials and as an ion conductive member for sodium-sulfur batteries.

Continuation of the front page (56) References JP-A-9-13230 (JP, A) JP-A-3-140509 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) D01F 9 / 08

Claims (3)

(57) [Claims] 1. A method for producing β-alumina containing an alkali metal component and / or an alkaline earth metal component in an amount of 5 to 40 mol% and having a C-axis lattice constant of 2.1 to 3.5 nm in the crystal, A water-soluble basic aluminum salt, and a solution of a water-soluble alkali metal compound and / or a water-soluble alkaline earth metal compound dissolved in an aqueous solvent, an alumina powder is added, and a spinning aid is further added to increase the viscosity. The slurry obtained by adjusting the above is used as a spinning stock solution, and this spinning stock solution is spun into a precursor fiber.
A method for producing β-alumina fiber, which comprises firing in the range of ˜1600 ° C. 2. The β according to claim 1, wherein the alkali metal compound is a sodium compound and / or a potassium compound.
-Alumina fiber manufacturing method. 3. The production of β-alumina fiber according to claim 1 or 2, wherein the alkaline earth metal compound is one or more alkaline earth metal compounds selected from calcium compounds, strontium compounds and barium compounds. Method.