JPH0470252B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing an alumina-based ceramic precursor sol that is useful for obtaining alumina-based ceramics, and particularly relates to a method for producing an alumina-based ceramic precursor sol that is useful for producing silica-alumina fibers. The present invention relates to a method for producing a silica alumina precursor sol.

[Prior Art] Ceramic fibers are widely used in industry, such as heat insulating materials, vibration isolating materials, adsorbents, filtration materials,
It is used as a reinforcing material for composite materials, and its use as a reinforcing material for composite materials will be particularly important in the future.

Conventionally, reinforcing materials for the composite materials include metal fibers, carbon fibers, surface-treated composite fibers, polycrystalline fibers such as alumina and zirconia, whiskers, and the like. Among these, polycrystalline fibers are superior to other fiber materials in that they can be used in high-temperature oxidizing atmospheres where carbon fibers and metal fibers cannot be used, and they do not lose their excellent mechanical properties even at high temperatures. This makes it possible to achieve both heat resistance and brittleness mitigation, which are most expected of ceramic materials.

Methods for producing silica-alumina fibers having such characteristics include melt-spinning silica-alumina minerals, or spinning from a solution containing an aluminum compound or a silicon compound, and firing the filament to produce silica-alumina fibers. There are ways to get it.

[Problems to be solved by the invention] However, conventional manufacturing methods have problems such as limitations on the content of silicon compounds, only short fibers can be obtained, and the need for special equipment for manufacturing. Has a point. Therefore, it is desired to develop a manufacturing method for easily obtaining silica-alumina fibers, which are long fibers.

The present invention uses aluminum alkoxide and silicon alkoxide as starting materials, takes full advantage of their advantages, and aims to obtain a silica-alumina precursor sol that can be spun and produce long fibers when fired. This is the purpose.

[Means to solve the problem]

The present inventors conducted research in order to solve the above problems, and reacted aluminum alkoxide with a compound having active hydrogen, mixed the reaction product with silicon alkoxide and/or its derivative, It was discovered that when the mixture is hydrolyzed, a silica-alumina precursor sol exhibiting sufficient spinnability can be obtained by adjusting the ratio of the compound having active hydrogen to the aluminum alkoxide and the ratio of water to a specific ratio, The invention has been completed.

That is, the present invention uses a reaction mixture in which a compound having active hydrogen is reacted with 0.6 to 2.7 moles of active hydrogen per mole of aluminum alkoxide, and a ceramic having a silica content of 40% by weight after firing. A method for producing a silica alumina precursor sol, which comprises mixing the following amounts of silicon alkoxide and/or its derivatives, and hydrolyzing the mixture with 0.5 to 1.5 moles of water per mole of total alkoxide. be.

The present invention will be explained in detail below.

The aluminum alkoxide used in the present invention is represented by the general formula (RO) ₃ Al (R: alkyl group), and specifically R is methyl, ethyl, n-propyl, iso-propyl, n-butyl. ,
There are iso-butyl, sec-butyl, tert-butyl, etc.

In addition, compounds with active hydrogen that are reacted with aluminum alkoxide generally have a hydrogen atom in the compound that is bonded to a heteroatom other than a carbon atom such as oxygen, nitrogen, or sulfur, and the latter is more reactive than the former. It is characterized by its strong sexuality. The compound having active hydrogen as referred to in the present invention is:
It satisfies the above-mentioned conditions and is reactive with aluminum alkoxide, which is the starting material.
Compounds listed in "Metal Alkoxides" by Gaur, pages 149-298 correspond.

Specifically, monomethanolamine, monoethanolamine, mono n-propanolamine, monoiso-propanolamine, dimethanolamine, diethanolamine, di-n-propanolamine, diiso-propanolamine, trimethanolamine, triethanolamine. , tri-n-propanolamine, and tri-iso-propanolamine; β-alkanolamine compounds represented by acetylacetone and ethyl acetoacetate.
- Diketone compounds; glycol compounds represented by ethylene glycol and diethylene glycol;
Other examples include organic acids, phenols, thiols, amines, etc., but alkanolamine compounds and β-diketone compounds are particularly preferred from the viewpoint of adjusting the hydrolysis rate. Further, among these, triethanolamine is particularly preferred as the alkanolamine compound, and ethyl acetoacetate is particularly preferred as the β-diketone compound.

The amount of the compound having active hydrogen to be used is in the range of 0.6 to 2.7 moles of active hydrogen per mole of aluminum alkoxide. Since β-diketone compounds such as acetylacetone and ethyl acetoacetate participate in the reaction in the enol form, the number of active hydrogens is counted as one per molecule. Since the hydrogen atom of the hydroxyl group of alkanolamines participates in the reaction with aluminum alkoxide, the number of active hydrogens in one molecule is 1 for monoalkanolamines, 2 for dialkanolamines, and 3 for trialkanolamines. count. When the amount of the compound having active hydrogen is within the above range, the hydrolysis rate of aluminum alkoxide can be sufficiently adjusted during hydrolysis, and a sol having a viscosity suitable for spinning operations can be obtained.

If the amount of the compound having active hydrogen used is less than 0.6 moles of active hydrogen, the hydrolysis rate of aluminum alkoxide will not be sufficiently adjusted, and the reaction will proceed rapidly during hydrolysis.
A powdery precipitate is deposited, making it impossible to synthesize a sol with a viscosity suitable for spinning operations. On the other hand, if the amount used is more than 2.7 mol, a viscous sol will be obtained after removing the hydrolyzed alcohol and organic solvent from the system, but the gelation rate will be low because it is stable against hydrolysis even after the spinning operation. It is extremely slow and difficult to maintain the shape of the gel fiber, making it impractical.

The reaction between aluminum alkoxide and a compound having active hydrogen can be carried out by mixing the two at room temperature or under heating, but the reaction is preferably carried out in the presence of an organic solvent from the viewpoint of miscibility and uniformity of the reaction. It is preferable to do so. However, the reaction is possible even in the absence of an organic solvent. The organic solvent used here is preferably one that dissolves aluminum alkoxide, specifically alcohols such as iso-propanol and sec-butanol, aromatic hydrocarbons such as toluene, benzene, xylene, etc. , tetrahydrofuran, dimethylformamide, carbon tetrachloride, etc., but alcohols are preferred from the viewpoint of solubility.

On the other hand, the silicon alkoxide to be mixed with the above 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 not more than 4 times the mole of silicon alkoxide, and oligomers which have undergone a polycondensation reaction in advance.

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

The amount of water used when hydrolyzing a mixture of a reaction mixture of aluminum alkoxide and a compound having active hydrogen mixed with silicon alkoxide and/or its derivatives is 0.5 to 1.5 mol per mol of total alkoxide. Use within range. If the amount of water used is less than 0.5 mol, a viscous sol is obtained after the removal of the hydrolyzed alcohol and, if an organic solvent is used in the system, but after the spinning operation It becomes difficult to maintain the shape of the gel fiber, making it impractical. On the other hand, if the amount of water used is more than 1.5 mol,
During hydrolysis, the reaction progresses rapidly and a powdery precipitate is deposited or a viscous sol is obtained. However, the gelation is rapid, and the spinnable state and time are extremely short, making it suitable for spinning operations. It is not suitable for the synthesis of viscous sols.

Methods for hydrolyzing the mixture include hydrolysis by adding a mixture of water and an organic solvent that has an appropriate solubility in water or dissolves water, hydrolysis using moisture in the air, Examples include hydrolysis using blowing gas containing water vapor. When monoethanolamine and acetylacetone are used as compounds with active hydrogen, hydrolysis using moisture in the air,
Alternatively, it is preferable to use a hydrolysis method that utilizes blowing gas containing water vapor. In this case, when hydrolysis is performed by adding a mixture of water and an organic solvent that has a suitable solubility in water or dissolves water, the concentration of water must be kept at an extremely low concentration. A precipitate forms, making it unsuitable for industrial synthesis of a sol with a viscosity suitable for spinning operations. When triethanolamine or ethyl acetoacetate is used as a compound having active hydrogen, there are no particular limitations on the hydrolysis method. From this point of view, these two compounds can be said to be particularly preferable compounds.

Further, this hydrolysis is preferably carried out in the presence of an organic solvent for the same reason as described in the reaction of aluminum alkoxide and a compound having active hydrogen. The organic solvent for this purpose may be added in this hydrolysis step, but aluminum alkoxide and a compound having active hydrogen have already been mixed and reacted in the presence of an organic solvent, or silicon alkoxide can be partially hydrated. When decomposition is carried out in the presence of an organic solvent, a mixture of silicon alkoxide and/or its derivatives containing the organic solvent may be directly subjected to the hydrolysis reaction.

The order of mixing aluminum alkoxide, a compound having active hydrogen, silicon alkoxide and/or its derivative, and water used in the present invention is that the aluminum alkoxide and the compound having active hydrogen react before adding water, There are no particular restrictions as long as silicon alkoxide and/or its derivatives coexist in the reaction mixture.

A silica alumina precursor sol is obtained by the above hydrolysis. This sol has a certain degree of viscosity and spinnability, but its concentration is low and insufficient for spinning, so a viscous sol that can be spun can be obtained by performing an appropriate concentration operation. This concentration operation may be either normal pressure distillation or reduced pressure distillation. This concentrated viscous sol can be used for spinning.

According to the present invention, a spinnable sol having a viscosity suitable for spinning can be efficiently and easily obtained. Then, by appropriately drying and firing the gel fiber after spinning, continuous long fibers of silica alumina can be obtained.

In addition, the silica-alumina fibers obtained in this way are treated with B ₂ O ₃ , MgO,
P ₂ O ₅ , CaO, Cr ₂ O ₃ , CuO, Fe ₂ O ₃ , TiO ₂ ,
Additives of ZrO ₂ can be added. These compounds can be added as oxides, inorganic salts, organic salts, metal alkoxides, etc. before or after the production of the silica-alumina precursor sol and before spinning. By adding one or more of these additives, it becomes possible to obtain continuous long fibers of silica alumina with high strength after firing.

[Effect]

In the present invention, aluminum alkoxide is reacted with a compound having active hydrogen, the reaction product is mixed with silicon alkoxide and/or a derivative thereof, and the mixture is hydrolyzed. When the proportion of the compound having active hydrogen and the proportion of water are set to the above-described specific ratios, a silica-alumina precursor sol exhibiting sufficient stringiness can be obtained.

〔Example〕

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

Example 1 For 1 mole of aluminum sec-butoxide
sec-butanol 6.6 moles, triethanolamine
0.33 mol was mixed at room temperature for 2 hours to obtain a reaction product. Silicon methoxide is added to the resulting reaction product.
0.04 mol of the total alkoxide was mixed, and a mixture of 1.0 mol of water and 3.3 mol of sec-butanol was added to the total alkoxide, stirred for 12 hours, and distilled under reduced pressure at 60°C and 100 mmHg to obtain sec-butanol. After removal, a spinnable sol was obtained which could be spun, and a transparent gel fiber was obtained by performing a spinning operation.

The obtained gel fiber was dried at 50°C for 24 hours and then fired at 1100°C to produce Al-Si spinel (γ-Al _{2 )} with a silica content of 5% by weight.
A silica-alumina fiber consisting of an O ₃ ) phase was obtained.

Example 2 For 1 mole of aluminum sec-butoxide
sec-butanol 6.6 moles, triethanolamine
0.8 mol was mixed at room temperature for 2 hours to obtain a reaction product. 0.36 mol of silicon methoxide, 0.72 mol of sec-butoxide, and 0.36 mol of water were mixed at 50°C for 2 hours to obtain a silicon alkoxide derivative. The above reactant and silicon alkoxide derivative were mixed, and a mixed solution of 1.0 mole of water and 3.3 mole of sec-butanol was added to the total alkoxide to perform a hydrolysis operation. After addition, stir for 12 hours and heat at 60℃100
After removing sec-butanol by vacuum distillation at mmHg, a spinnable sol was obtained, and a transparent gel fiber was obtained by performing a spinning operation. The obtained gel fiber was dried at 50°C for 24 hours and then fired at 1300°C to form an Al-Si spinel (γ-Al ₂ O ₃ ) phase with a silica content of 30% by weight.
Silica-alumina fibers consisting of a mullite phase were obtained.

Example 3 For 1 mole of aluminum sec-butoxide
sec-butanol 6.6 moles, triethanolamine
0.6 mol was mixed at room temperature for 2 hours to obtain a reaction product. The resulting reaction product contains methyl silicate 51
(Average degree of polymerization 3) 0.05 mol was mixed, and then 1.0 mol of water and 3.3 mol of water were added to the total alkoxide.
Stir for 12 hours after adding the sec-butanol mixture,
After distilling under reduced pressure at 60° C. and 100 mmHg to remove sec-butanol, a spinnable sol that could be spun was obtained, and a transparent gel fiber was obtained by performing a spinning operation. After drying this gel fiber at 50°C for 24 hours, it was treated at 200°C in a steam atmosphere.
Silica-alumina fibers having a silica content of 15% by weight and consisting of an Al-Si spinel (γ-Al ₂ O ₃ ) phase and a mullite phase were obtained by firing at 1300°C.

Example 4 For 1 mole of aluminum sec-butoxide
sec-butanol 6.6 moles, triethanolamine
0.4 mol was mixed at room temperature for 2 hours to obtain a reaction product. Add silicon methoxide to the resulting reaction mixture
Mix 0.33 mol and 1.2 to total alkoxide
After adding a mixture of 3.3 moles of water and 3.3 moles of sec-butanol, the mixture was stirred for 12 hours, distilled under reduced pressure at 60°C and 100 mmHg to remove the sec-butanol, and a spinnable sol was obtained. A transparent gel fiber was obtained by performing the operation. This gel fiber was dried and then fired at 1300°C to obtain silica-alumina (mullite) fibers having a mullite phase with a silica content of 28% by weight.

Comparative Example 1 The same operation as in Example 2 was carried out using 0.2 mol of triethanolamine. A precipitate was deposited with the addition of the water/sec-butanol mixture, and a spinnable sol having a viscosity capable of spinning was not obtained.

Comparative Example 2 Triethanolamine was not used in Example 1,
I performed the same operation. A precipitate was deposited with the addition of water, and a spinnable sol having a viscosity suitable for spinning could not be obtained.

Comparative Example 3 The same operation as in Example 1 was carried out using 1.2 mol of triethanolamine. After the sec-butanol was removed from the system, the viscosity increased and spinning operations became possible, but the transition from sol to gel fiber was slow and shape retention was difficult, and gel fiber could not be obtained.

〔Effect of the invention〕

According to the present invention, a silica-alumina precursor sol that is chemically stable and has a viscosity that allows spinning can be efficiently obtained in a short time. Then, by spinning this silica-alumina precursor sol and performing appropriate drying and firing, long-fiber silica-alumina fibers can be easily and efficiently produced.

Claims (1)

[Claims] 1. For 1 mole of aluminum alkoxide,
Compounds with active hydrogen expressed in moles of active hydrogen
Mix 0.6 to 2.7 mol of the reacted reaction mixture with silicon alkoxide and/or its derivatives in an amount such that the silica content in the ceramics after firing is 40% by weight or less, and add the mixture to 1 mol of total alkoxide. A method for producing a silica alumina precursor sol, which comprises hydrolyzing with 0.5 to 1.5 moles of water. 2. The method for producing a silica alumina precursor sol according to claim 1, wherein the compound having active hydrogen is an alkanolamine or a β-diketone compound.