JPH076091B2 - Method for producing silica-alumina fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silica-alumina fiber, more specifically, it is obtained by chemically modifying an aluminum alkoxide to obtain a silicon alkoxide or a derivative thereof. In the method for obtaining a silica-alumina fiber by firing the gel fiber to be obtained, the gel fiber is heat-treated before firing,
And a method for producing a silica-alumina fiber which is steam-treated and has no residual carbon and is excellent in strength uniformity.

[Conventional technology]

Ceramic fibers are widely used in industry and are used, for example, as heat insulating materials, vibration damping materials, adsorbents, filtration materials, and reinforcing materials for composite materials. Especially, applications as reinforcing materials for composite materials will be considered important from now on. .

Conventionally, examples of the reinforcing material for the composite material include metal fibers, carbon fibers, surface-treated composite fibers, polycrystalline fibers such as alumina and zirconia, and whiskers. Among them, polycrystalline fiber is superior to other fiber materials in that it can be used in a high temperature oxidizing atmosphere where carbon fiber or metal fiber cannot be used, and that it does not lose excellent mechanical properties even at high temperature. Thus, it becomes possible to achieve both the heat resistance and the brittleness relaxation that are most expected of ceramic materials.

As a method for producing silica-alumina fibers having such characteristics, a method of melt-spinning silica-alumina-based minerals, or a spinning operation from a solution containing an aluminum compound and a silicon compound, and firing the filaments to produce silica-alumina fibers. There are ways to get it.

However, the conventional manufacturing methods have problems that the content ratio of the silicon compound is limited, that only short fibers can be obtained, and that a special device is required for manufacturing. Therefore, it is desired to develop a manufacturing method for easily obtaining long-length silica-alumina fibers.

In order to solve this problem, the present inventors have used aluminum alkoxide and silicon alkoxide as starting materials, make the best use of their advantages, are spinnable, and obtain long fibers when they are fired. A method for producing a silica-alumina precursor gel that can be used was proposed (Japanese Patent Application No. 63-254).
783).

This method involves reacting an aluminum alkoxide with a compound having active hydrogen, mixing the reaction product with a silicon alkoxide and / or a derivative thereof, and hydrolyzing the mixture to obtain a compound having active hydrogen for the aluminum alkoxide. It was proposed that a silica-alumina precursor gel exhibiting sufficient spinnability can be obtained at a specific ratio of the ratio of 1 and the ratio of water.

[Problems to be Solved by the Invention]

According to the above invention, good spinnability is exhibited, and a precursor of continuous silica-alumina fiber can be easily obtained with good reproducibility. However, especially when the silica content is increased, carbon remains in the fiber after firing, resulting in a blackish fiber, uneven strength, and the presence of air bubbles in the fiber depending on the firing conditions. There is also
Control of firing conditions and control of atmosphere were often complicated.

An object of the present invention is to solve these problems and to produce a silica-alumina fiber which is easy to reproduce with good reproducibility and has excellent uniformity of strength without residual carbon and bubbles.

[Means for Solving the Problems]

The present invention comprises a step of forming a reaction mixture by mixing an aluminum alkoxide with an alkanolamine compound and / or a β-diketone compound to form a reaction mixture, and the silica content in the ceramic after firing of the reaction mixture is 40% by weight. A step of mixing the following amounts of silicon alkoxide and / or its derivative, and hydrolyzing the mixture to form a sol, the precursor gel fiber obtained by spinning the sol at a temperature of 100 to 250 ° C. A method for producing a silica-alumina fiber, which comprises a step of heat-treating, a step of steam-treating the gel fiber after the heat-treatment, and a step of firing the steam-treated gel fiber. Can solve problems.

Aluminum alkoxide used in the present invention is represented by the general formula (RO) ₃ Al (R: alkyl group),
Specifically, R is methyl, ethyl, n-propyl, iso-
Propyl, n-butyl, iso-butyl, sec-butyl, te
rt-butyl and the like.

Further, a compound having active hydrogen to be reacted with an aluminum alkoxide generally means that a hydrogen atom in an organic compound is bonded to a heteroatom such as oxygen, nitrogen, or sulfur, and has higher reactivity than a normal hydrogen-carbon bond. It has characteristics. The compound having active hydrogen referred to in the present invention is one which satisfies the above-mentioned conditions and has reactivity with an aluminum alkoxide as a starting material,
DC Bradley, RC Mehrotra and DP Gaur “Matal Alk
The compounds listed in oxides "p149-298 correspond.

In the present invention, as compounds having active hydrogen, monoethanolamine, mono-n-propanolamine, monoiso
-Propanolamine, diethanolamine, diiso-
Propanolamine, triethanolamine, tri-iso
-Alkanolamine compounds represented by propanolamine; β-diketone compounds represented by acetylacetone and ethyl acetoacetate are used, and these are particularly preferable from the viewpoint of adjusting the hydrolysis rate. Further, among these, triethanolamine is particularly preferable as the alkanolamine compound, and β-ketone acid esters such as ethyl acetoacetate are particularly preferable as the β-diketone compound.

With respect to the amount of the compound having active hydrogen, other than the β-diketone compound, it is used within a range of 0.6 to 2.7 mol in terms of the number of mols of active hydrogen with respect to 1 mol of aluminum alkoxide. Β-, such as acetylacetone and ethyl acetoacetate
Since the diketone compound is an enol type and participates in the reaction, the number of active hydrogen is counted as 1 in 1 molecule, but in the case of β-diketone compounds, especially β-ketone ester such as ethyl acetoacetate, aluminum alkoxide is stabilized. It has an excellent ability to be converted into
A use amount in the range of 0.2 to 1.5 mol is sufficiently effective.

In alkanolamines, the hydrogen atom of the hydroxyl group participates in the reaction with aluminum alkoxide, so the number of active hydrogens in one molecule is 1 for monoalkanolamine, 2 for dialkanolamine, and 3 for trialkanolamine. count. When the amount of the compound having active hydrogen used is within the above range, the hydrolysis rate of the aluminum alkoxide during the hydrolysis is sufficiently adjusted to obtain a sol having a viscosity suitable for the spinning operation.

When the amount of the compound having active hydrogen used is less than the above range, the hydrolysis rate of the aluminum alkoxide is not sufficiently adjusted, the reaction rapidly progresses during the hydrolysis, and a powdery precipitate is deposited, resulting in spinning. It is not possible to synthesize a sol with a viscosity suitable for operation. On the other hand, if the amount used is more than the above range, after the hydrolysis alcohol and organic solvent are removed from the system, a viscous sol is obtained, but the gelation rate is stable because it is stable against hydrolysis even after the spinning operation. It is extremely slow, and it becomes difficult to maintain the shape of the gel fiber, making it impractical.

The reaction between the aluminum alkoxide and the compound having active hydrogen can be carried out by mixing both at room temperature or under heating, but the reaction is carried out in the presence of an organic solvent from the viewpoint of miscibility and uniformity of the reaction. It is preferable to carry out.
However, the reaction is possible without the presence of an organic solvent. The organic solvent used here is preferably one that dissolves aluminum alkoxide, specifically, alcohols represented by iso-propanol, sec-butanol, etc., and aromatic hydrocarbons represented by toluene, benzene, xylene, etc. , Tetrahydrofuran, dimethylformamide, carbon tetrachloride, etc., but alcohols are preferable from the viewpoint of solubility.

On the other hand, the silicon alkoxide mixed with the above-mentioned reaction mixture is represented by the general formula (RO) ₄ Si (R: alkyl group), and specifically R is methyl, ethyl, n-propyl, n-butyl. , Iso-butyl, sec-butyl, tert-
Butyl etc. Derivatives of silicon alkoxide include those obtained by partially hydrolyzing the above-mentioned silicon alkoxide with water in an amount of 4 mol times or less with respect to the silicon alkoxide, and oligomers in which polycondensation reaction has proceeded in advance.

The silicon alkoxide and / or its derivative is used in such an amount that the silica content in the ceramic after firing is 40% by weight or less. If the amount of silica used in the ceramics after firing exceeds 40% by weight, the heat resistance of the resulting silica-alumina fiber will be significantly reduced, and it will be used as a reinforcing material for heat resistance and composite materials. Is significantly limited.

The amount of water used for hydrolyzing a mixture obtained by mixing a reaction mixture of an aluminum alkoxide and a compound having active hydrogen with a silicon alkoxide and / or a derivative thereof is an aluminum alkoxide, a silicon alkoxide, as described later, Including the metal alkoxide of 1), it is used in the range of 0.5 to 2.0 mol per 1 mol of the previous alkoxide. As a derivative of silicon alkoxide,
When using an oligomer that has undergone a polycondensation reaction in advance, water within the above range in which the oligomer is treated as one molecule is used. When a partially hydrolyzed derivative of silicon alkoxide with 4 mole times or less water of silicon alkoxide is used,
The amount of water used for this partial hydrolysis is also taken into account, and water is additionally added so that the amount of hydrolyzed water is within the above range with respect to 1 mol of all alkoxides such as aluminum alkoxide and starting material silicon alkoxide. .

If the amount of water used is less than 0.5 mol, a viscous sol is obtained after removal of the hydrolysis product alcohol and after removal of the organic solvent used in the system, but after spinning operation. It becomes difficult to maintain the shape of the gel fiber, making it impractical. On the other hand, when the amount of water used is more than 2.0 mol, the reaction proceeds rapidly during hydrolysis, and even if a powdery precipitate is deposited or a viscous sol is obtained, gelation is fast and spinning is possible. It is not suitable for synthesizing sols having conditions and times which are extremely short and have a viscosity suitable for the spinning operation.
From the above viewpoint, the more preferable amount of water for hydrolysis is in the range of 0.5 to 1.5 mol based on 1 mol of all alkoxides.

As a method of hydrolyzing the mixture, having a suitable solubility in water, or hydrolysis by the addition of a mixture of water and an organic solvent that dissolves water, hydrolysis utilizing moisture in the air, Hydrolysis using the blowing of a gas containing water vapor may be mentioned. When monoethanolamine or acetylacetone is used as a compound having active hydrogen, hydrolysis utilizing moisture in the air,
Alternatively, it is preferable to use a hydrolysis method utilizing blowing a gas containing water vapor. In this case, in the hydrolysis by adding a mixture of water and an organic solvent that has an appropriate solubility in water or dissolves water, unless the concentration of water is made extremely low, the powdery form during hydrolysis is obtained. Precipitates form and are not suitable for industrial synthesis of sols having a viscosity suitable for spinning operations. When triethanolamine or ethyl acetoacetate is used as the compound having active hydrogen, the hydrolysis method is not particularly limited. From this viewpoint, it can be said that these two compounds are particularly preferable compounds.

In addition, this hydrolysis is preferably carried out in the presence of an organic solvent for the same reason as described in the reaction of the aluminum alkoxide with the compound having active hydrogen. The organic solvent therefor may be added in this hydrolysis step, but it is already mixed with the aluminum alkoxide and the compound having active hydrogen, the reaction is carried out in the presence of the organic solvent, or the partial hydrolysis of the silicon alkoxide. When the decomposition is carried out in the presence of an organic solvent, a mixture containing the organic solvent and containing a silicon alkoxide and / or a derivative thereof may be directly subjected to the hydrolysis reaction.

An aluminum alkoxide used in the present invention,
Compounds having active hydrogen, silicon alkoxide and / or
Or as the order of mixing the derivative and water,
There is no particular limitation as long as the aluminum alkoxide and the compound having active hydrogen react with each other before the addition of water, and the reaction mixture contains the silicon alkoxide and / or its derivative.

A silica alumina precursor sol is obtained by the above hydrolysis. This sol has a certain degree of viscosity and spinnability, but since this is low in concentration and insufficient for spinning, a viscous sol which can be spun can be obtained by an appropriate concentration operation. This concentration operation may be either atmospheric distillation or vacuum distillation. The concentrated viscous sol can be used for spinning by a suitable known method.

The fibrous sol rapidly gels in the presence of a gaseous catalyst that promotes gelation by increasing the amount of water or water vapor in the air, and gel fibers are obtained.

When this gel fiber is fired without any treatment,
In particular, when the silica content becomes high, carbon remains in the fiber after firing, resulting in a blackish fiber, uneven strength, and the presence of air bubbles in the fiber depending on firing conditions. In many cases, the control of firing conditions and the control of atmosphere were complicated.

These problems could be easily solved by subjecting the gel fiber to the following treatments.

The gel fiber obtained is first subjected to heat treatment.

The heat treatment referred to here is to maintain the temperature at or below the decomposition temperature of the remaining organic matter, at 60 ° C or higher, preferably at 100 ° C or higher and 250 ° C or lower.

The treatment time is influenced by the composition, the kind and amount of the compound having active hydrogen used, and the treatment temperature, and cannot be uniquely determined. However, if the treatment temperature is high, about 1 minute of treatment is sufficiently effective.

This processing may be continuous processing or batch processing.

If this treatment time is too short, the densification of the fibers after firing will be insufficient, but there is no particular problem due to being too long, and it is preferable to make it long enough not to cause a problem in the ceramic fiber manufacturing process.

The gel fiber that has been subjected to the above heat treatment is further subjected to steam treatment before firing.

Steam treatment here means a temperature of 40 ° C or higher and a relative humidity of 50%.
It is shown to be placed in the above atmosphere, but in order to shorten the processing time, it is more preferable that the temperature is 60 ° C or higher and the relative humidity is 60%.
The above is better.

The treatment time varies depending on the type and amount of the compound having active hydrogen to be reacted with the aluminum alkoxide.

Further, even if the type and amount of the compound having active hydrogen are different, it is a general tendency that the higher the silica content, the longer the steam treatment time needs to be.

The time cannot be uniquely determined due to the influence of temperature and humidity, but the higher the temperature and the higher the humidity, the shorter the treatment time is, and the treatment for 5 minutes or more is effective.

If this treatment time is too short, carbon remains in the fiber after firing, and there are many variations in strength, but there is no particular problem due to being too long, and it is preferable to make it long enough not to cause a problem in the manufacturing process. .

The above heat treatment and steam treatment may be carried out continuously or in batches on the fibers. In the case where these heat treatments and steam treatments were not performed before firing, there were the above-mentioned problems.

Even when only heat treatment is performed and steam treatment is not performed, carbon remains in the fiber after firing in the same manner, and the strength is often nonuniform, in order to avoid this problem,
Control of firing conditions and control of atmosphere become complicated.

Further, when the gel fiber that has been subjected to only steam treatment without heat treatment is fired, carbon does not remain after firing,
It is possible to obtain colorless and transparent fibers. However, when observing the fiber after firing with an electron microscope, clear pores are not observed, and although it seems that the fibers are sufficiently densified, it has been shown that the specific surface area is high and densification has not progressed, The mechanical properties of the fiber were also unsatisfactory.

As described above, by heat-treating the gel fiber, and subsequently subjecting it to steam treatment and then firing, good reproducibility, residual carbon, and production of silica-alumina fiber excellent in strength uniformity without bubbles are produced. It will be possible.

Further, with respect to the silica-alumina fiber thus obtained, B ₂ O ₃ , MgO, P ₂ O ₅ , CaO, Cr are used for the purpose of controlling crystal transition, suppressing abnormal grain growth, and proceeding with sintering. ₂ O ₃ , CuO, Fe ₂ O ₃ ,
Additives of TiO ₂ and ZrO ₂ can be added. These compounds can be added as oxides, inorganic salts, organic salts, metal alkoxides, etc. before or after the formation of the silica-alumina precursor sol and before spinning. By adding one kind or two or more kinds of these additives, it becomes possible to obtain high-strength continuous silica-alumina fibers after firing.

[Action]

According to the present invention, by subjecting the gel fiber to a heat treatment, followed by a steam treatment followed by firing, good reproducibility, residual carbon, and production of silica-alumina fiber excellent in strength uniformity without bubbles are produced. It will be possible.

Although the clear mechanism is unknown, it is considered as follows.

At the stage of the gel fiber immediately after spinning, the crosslinked structure is not sufficiently developed and it has a somewhat thermoplastic property. Therefore, it is considered that the gel fibers are densified by the heat treatment. Subsequent steam treatment develops an inorganic cross-linking structure and reduces the amount of organic substances that lead to residual carbon after firing, or micropores remain until the temperature range where carbon is oxidatively decomposed, and residual carbon disappears. Conceivable.

Further, only with steam treatment, only the development of the inorganic skeleton proceeds, and the densification does not proceed, so the ceramic content in the gel fiber does not increase, and there are fine pores even after firing,
It is believed that the mechanical properties of the fiber will be inadequate.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

Example 1 1 mol of aluminum sec-butoxide and 6.6 mol of sec-butanol and 0.33 mol of triethanolamine were mixed at room temperature for 2 hours to obtain a reaction product. 0.15 mol of silicon methoxide was mixed with the obtained reaction product, and 1.2 mol times of water and 3.3 mol times of sec- were added to the total alkoxide.
Add the butanol mixture and stir for 12 hours at 60 ° C, 10
After distilling under reduced pressure at 0 mmHg to remove sec-butanol, a spinnable sol capable of being spun was obtained, and a spinning operation was performed to obtain a transparent gel fiber.

The obtained gel fiber was heat-treated at 150 ° C. for 24 hours and then steam-treated at 70 ° C. and a relative humidity of 85% for 24 hours. By firing this fiber at 1100 ° C. for 2 hours, a silica-alumina fiber composed of a mullite having an silica content of 15% by weight and an Al—Si spinel (γ-Al ₂ O ₃ ) phase was obtained.

This fiber was colorless and transparent, and exhibited a breaking strength of 185 Kg / mm ² .

Comparative Example 1 The silica fiber was obtained by firing the gel fiber obtained in Example 1 for 2 hours at 1100 ° C. without any post-treatment. Since this fiber was black and brittle, the breaking strength could not be measured.

Comparative Example 2 The gel fiber obtained in Example 1 was heat-treated at 150 ° C. for 24 hours and then calcined at 1100 ° C. for 2 hours to obtain a silica-alumina fiber. This fiber was black and fragile, so that the breaking strength could not be measured.

Comparative Example 3 The gel fiber obtained in Example 1 was treated at 70 ° C. and relative humidity of 85.
2% at 1100 ° C after steaming for 24 hours under
It was calcined for an hour to obtain silica-alumina fiber. This fiber was colorless and transparent, with no carbon remaining, but a breaking strength of 45.
It had a weak strength of Kg / mm ² .

Example 2 1 mol of aluminum sec-butoxide was mixed with 6.6 mol of sec-butanol and 0.5 mol of ethyl acetoacetate at room temperature for 2 hours to obtain a reaction product. Silicon methoxide 0.36
Mol, sec-butoxide 0.72 mol, and water 0.36 mol were mixed at 50 ° C. for 2 hours to obtain a silicon alkoxide derivative. The reaction product and a silicon alkoxide derivative are mixed, and 1.0 mol times water and 3.3 mol times sec-
A mixed solution of butanol was added and a hydrolysis operation was performed.
After the addition, stir for 12 hours, and distill under reduced pressure at 60 ° C and 100 mmHg for s
After removing ec-butanol, a spinnable spinnable sol was obtained and a spinning operation was performed to obtain a transparent gel fiber. The obtained gel fiber was heat-treated at 180 ° C. for 6 hours and then steam-treated at 90 ° C. and a relative humidity of 90% for 48 hours. By firing this gel fiber at 1000 ° C. for 2 hours, a silica content of 30% by weight is obtained.
A silica-alumina fiber composed of an Al-Si spinel (γ-Al ₂ O ₃ ) phase and a mullite phase was obtained.

This fiber was colorless and transparent, had no residual carbon, and exhibited a breaking strength of 178 kg / mm ² .

Comparative Example 4 The silica fiber was obtained by firing the gel fiber obtained in Example 2 for 2 hours at 1000 ° C. without any post-treatment. Since this fiber was black and brittle, the breaking strength could not be measured.

Comparative Example 5 The gel fiber obtained in Example 2 was heat-treated at 180 ° C. for 6 hours and then calcined at 1000 ° C. for 2 hours to obtain silica-alumina fiber. Since this fiber was black and was brittle, the breaking strength could not be measured.

Comparative Example 6 The gel fiber obtained in Example 2 was treated at 90 ° C. and relative humidity of 90.
2% at 1000 ° C after steaming for 48 hours under
It was calcined for an hour to obtain silica-alumina fiber. This fiber was colorless and transparent, and had no residual carbon, but a breaking strength of 80.
It had a weak strength of Kg / mm ² .

Example 3 1 mol of aluminum sec-butoxide was mixed with 6.6 mol of sec-butanol and 0.6 mol of triethanolamine at room temperature for 1 hour to obtain a reaction product. The obtained reaction product was mixed with 0.015 mol of methyl silicate 51 (average degree of polymerization: 3), and 1.2 mol times of water was added to all alkoxides.
After adding a mixed solution of sec-butanol of 3.3 mol times, stirring for 12 hours, removing sec-butanol by vacuum distillation at 60 ° C and 100 mmHg, a spinnable spinnable sol was obtained, and a spinning operation was performed. A transparent gel fiber was obtained. This gel fiber was heat treated at 170 ° C for 3 hours, then treated at 80 ° C and 70% relative humidity in a steam atmosphere for 3 hours, and calcined at 1100 ° C for 2 hours to obtain a silica content of 5% by weight of Al-Si. A silica-alumina fiber having a spinel (γ-Al ₂ O ₃ ) phase was obtained.

This fiber is colorless and transparent, has no carbon residue, and is 165 kg / mm ²
The breaking strength was shown.

Comparative Example 7 The silica fiber was obtained by firing the gel fiber obtained in Example 3 for 2 hours at 1100 ° C. without any post-treatment. Since this fiber was black and brittle, the breaking strength could not be measured.

Comparative Example 8 The gel fiber obtained in Example 3 was heat-treated at 170 ° C. for 3 hours and then fired at 1100 ° C. for 2 hours to obtain silica-alumina fiber. This fiber was black and fragile, so that the breaking strength could not be measured.

Comparative Example 9 The gel fiber obtained in Example 3 was treated at 80 ° C. and a relative humidity of 70.
% Steam treatment for 3 hours and then firing at 1100 ° C. for 2 hours to obtain silica-alumina fibers. This fiber was colorless and transparent, and no carbon remained, but the breaking strength was
The strength was weak at 35 kg / mm ² .

(Effects of the Invention) According to the present invention, the gel fiber obtained from the chemically modified aluminum alkoxide, silicon alkoxide and / or derivative thereof is subjected to heat treatment, steam treatment and then baked to leave the residue. It is possible to manufacture silica-alumina fibers having no charcoal and excellent strength. This is a very useful production method for producing the same fiber useful as an industrial material with good reproducibility and stability.

Claims (1)

[Claims] 1. A step of mixing an aluminum alkoxide with an alkanolamine compound and / or a β-diketone compound to cause a reaction to form a reaction mixture, wherein the silica content in the reaction mixture and the ceramic after firing is 40% by weight. % Or less of a silicon alkoxide and / or its derivative are mixed, the mixture is hydrolyzed to form a sol, the precursor gel fiber obtained by spinning the sol at 100 to 250 ° C. A method for producing a silica-alumina fiber, comprising a step of heat-treating at a temperature, a step of steam-treating the gel fiber after the heat-treatment, and a step of firing the steam-treated gel fiber.