JPH078725B2 - Method for producing mullite fiber or film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is chemically and thermally stable, has a low coefficient of thermal expansion, and is useful as a heat-resistant material, heat insulating material, reinforced reinforcing material, and the like. The present invention relates to a method for producing a fiber or film.

(Prior Art) Conventionally, a method for producing a mullite fiber is a method of hydrolyzing an aluminum alkoxide and a silicon alkoxide in an alcohol solvent containing water and performing a polycondensation reaction to obtain a spinnable solution. Also known is a method of obtaining a solution having spinnability by adding an aluminum salt and polysiliconate to an aqueous solution containing a water-soluble polymer such as polyvinyl alcohol.

(Problems to be Solved by the Invention) However, all of these methods have the following problems.

That is, in the former case, the reaction rates of the aluminum alkoxide and the silicon alkoxide for hydrolysis are different, and the hydrolysis rate of the aluminum alkoxide is generally faster, so that the obtained product is likely to have a non-uniform composition.

In order to solve this problem, for example, an aluminum chelate is used instead of the aluminum alkoxide, or the side chain alkyl group in the aluminum alkoxide is changed to a more bulky group, for example, a tert-butyl group. Attempts have been made to match the hydrolysis rate with the alkoxide, but there are problems such as higher cost than the peculiarities of chemicals.

Further, contrary to the above case, a method of partially hydrolyzing the silicon alkoxide in advance and adding this and an aluminum alkoxide to an alcohol solution containing water has been attempted. It is difficult to accurately control the degree of partial hydrolysis, so that the resulting product is likely to have a non-uniform composition.

Further, in the solution obtained from such a system, the viscosity suddenly increases at a certain point with time of the reaction time and often gels, which makes it difficult to control the spinnability.

On the other hand, the latter case is a so-called non-homogeneous system, and in such a case, there is a problem that a liquid phase is generated at the grain boundary during sintering, which causes a decrease in strength.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method capable of easily producing a mullite fiber or a film-like material having excellent spinnability, uniformity, and stability. .

(Means for Solving the Problem) In order to solve such a problem, the present inventor has conducted earnest research on a method for achieving uniformity of aluminum and silicon and stability of the obtained spinning solution, particularly in the synthesis stage. As a result, the inventors have found a method in which aluminum and silicon are uniformly mixed at the atomic level and a spinning stock solution having stability can be easily obtained, and the present invention has been made here.

That is, the present invention, in an aqueous solution containing aluminum nitrate or aluminum chloride, aluminum alkoxide and silicon alkoxide are added at the same time at room temperature so that the atomic ratio of aluminum and silicon is 3: 1 and dissolved, and then heated and concentrated. What is made into a viscous liquid, the viscous liquid is extruded from a nozzle or a slit to form a fibrous or film-like material, and then sintered, which is characterized by a method for producing a mullite fiber or a film-like material. Is.

Another aspect of the present invention is to add an aluminum alkoxide to an aqueous solution containing aluminum nitrate at room temperature,
After dissolution, silicon alkoxide was added at room temperature so that the atomic ratio of aluminum and silicon was 3: 1 and dissolved, then concentrated by heating to form a viscous liquid, and this viscous liquid was extruded from a nozzle or slit. The present invention provides a method for producing a mullite fiber or a film-like material, which is characterized in that it is formed into a fibrous or film-like material and then sintered.

The present invention will be described in more detail below.

(Operation) In the method for producing a mullite fiber or a film-like product of the present invention,
In short, aluminum alkoxide and silicon alkoxide are simultaneously dissolved in an aqueous solution containing nitric acid alkoxide or aluminum chloride, or, first, aluminum alkoxide and then silicon alkoxide are dissolved in an aqueous solution containing aluminum nitrate, respectively, or, By heating and concentrating the solution obtained in (1), it is possible to easily obtain a spinning dope in which aluminum and silicon are mixed at an atomic level and the viscosity can be appropriately controlled.

Here, whether or not aluminum and silicon are mixed at the atomic level is determined by powder X at each step of the heat treatment.
When observed by line diffraction, it can be easily confirmed that the crystal phase does not appear other than mullite.

The aluminum alkoxide is not particularly limited,
Examples thereof include a methoxy group, an ethoxy group, a normal propoxy group, an isopropoxy group, a normal butoxy group, a secondary butoxy group, and a tertiary butoxy group.

Also, there is no particular limitation as the silicon alkoxide,
For example, a methoxy group, an ethoxy group, etc. can be mentioned.

In the above case, a transparent solution is obtained by simultaneously adding the aluminum alkoxide and the silicon alkoxide to an aqueous solution containing aluminum nitrate or aluminum chloride at room temperature and stirring.

Alternatively, in the above case, the aluminum alkoxide is first added to an aqueous solution containing aluminum nitrate and stirred until it becomes transparent, and then the silicon alkoxide is added to this solution and stirred until it becomes transparent and uniform.

In any of these cases, the amount of aluminum alkoxide with respect to aluminum nitrate or aluminum chloride and the amount of water with respect to the total amount of aluminum and silicon are important, and good spinnability is exhibited when the amount deviates from a certain range. A solution cannot be obtained, and it becomes difficult to form a fiber.

Specifically, in the above case, the molar ratio of aluminum nitrate and aluminum alkoxide is preferably 1: 1 to 1: 6, or the molar ratio of aluminum chloride and aluminum alkoxide is 1: 1 to 1: 1. It is preferable that the molar ratio of water is 3: 3 and the molar ratio of aluminum to silicon is 1:10 to 1:50.

In the above case, the molar ratio of aluminum nitrate and aluminum alkoxide is 1: 1 to 1: 4, and the total molar ratio of aluminum and silicon and the molar ratio of water are 1:10 to 1: 200.
Is preferred.

However, in cases other than the order of addition shown here, that is,
When a silicon alkoxide is first added to an aqueous solution containing aluminum nitrate or aluminum chloride and stirred to form a transparent uniform solution, aluminum alkoxide is added to this solution and stirred to form a transparent uniform solution.
It should be avoided because it gels in the middle of heating and condensing and cannot be formed into a fibrous shape.

Next, the transparent and homogeneous solution thus obtained is heated (eg,
(90 to 100 ° C.) and concentrated to a viscosity of about 1 to 100 poises to give a viscous solution exhibiting spinnability. in this case,
Even if the concentration is too advanced and spinning becomes impossible or the viscosity becomes inconvenient, by adding water again and concentrating,
A solution with a spinnable viscosity can be obtained.

Then, the obtained viscous solution is extruded from a nozzle or a slit. Since this viscous solution easily solidifies in a dry atmosphere of 50 to 60 ° C., it is preferable to carry out spinning in a heated dry atmosphere when spinning. However, it should be noted that if the temperature of the dry air is higher than this, cracks will occur due to rapid evaporation of water from the spun filaments and the resulting precursor fibers will be very brittle.

When a nozzle is used during spinning, a wire such as long fiber can be formed, and when extruded from a slit, a film can be formed.

The obtained fiber or film is further placed in a dryer to sufficiently remove water, and then gradually heated in air to remove excess water, and then by sintering this, Mullite filaments or films are obtained. In this case, the sintering temperature is 60
At 0 ° C., reflection indicating the presence of the mullite phase is already observed by powder X-ray diffraction, but the sintering temperature is preferably 1300 to 1400 ° C. In addition, it is necessary to pay attention to the fact that if the removal of water is insufficient, or if the rate of temperature rise is high, the denseness of the fired product is impaired due to rapid evaporation of water.

The present invention is not limited to the fibers and film-like materials shown here, but can be similarly applied to powders, bulk bodies and the like.

(Examples) Examples of the present invention will be shown below.

Example 1 Aluminum triisopropoxide was selected as the aluminum alkoxide, and tetraethoxysilane (TEOS) was selected as the silicon alkoxide. Further, an aqueous solution of aluminum nitrate was selected as an aqueous solution for dissolving this.

First, 14.1 g of aluminum nitrate nonahydrate was dissolved in 70 ml of distilled water, and aluminum triisopropoxide was added to the solution.
24.4 g and TEOS 10.4 g were added at the same time, and the mixture was stirred at room temperature until the solid matter disappeared and became transparent and uniform.

The solution was heated to 100 ° C and concentrated to a viscosity of 30 poise. This concentrated solution was a colorless, transparent and viscous solution.

Then, this was extruded from a nozzle in a dry air atmosphere at 50 ° C. and molded into a long fiber having a diameter of 10 to 100 μm. The obtained fiber was dried at 100 ° C. for about 1 day, heated from room temperature to 1300 ° C. at a heating rate of 20 ° C./hr, and held at that temperature for 2 hours for sintering. As a result, mullite filaments were obtained.

A mullite film was obtained in the same manner by extrusion using a slit and sintering.

Example 2 Aluminum triisopropoxide was used as the aluminum alkoxide, and TE was used as the silicon alkoxide.
OS is selected. Further, an aqueous solution of aluminum chloride was selected as an aqueous solution for dissolving this.

First, 12.1 g of aluminum chloride hexahydrate was dissolved in 70 ml of distilled water, and aluminum triisopropoxide was added to the solution.
21.7 g and TEOS 10.4 g were added at the same time, and the mixture was stirred at room temperature until the solid matter disappeared and the mixture became transparent and uniform.

This was made into a concentrated solution having a viscosity of 30 poise in the same manner as in Example 1 to prepare a spinning dope. Thereafter, by extrusion and sintering in the same manner as in Example 1, mullite filaments were obtained.

A mullite film was obtained in the same manner by extrusion using a slit and sintering.

Example 3 Aluminum triisopropoxide was used as the aluminum alkoxide, and TE was used as the silicon alkoxide.
OS is selected. Further, an aqueous solution of aluminum nitrate was selected as an aqueous solution for dissolving this.

First, 28.1 g of aluminum nitrate nonahydrate was dissolved in 70 ml of distilled water, and aluminum triisopropoxide was added to the solution.
16.3 g was added, and the mixture was stirred at room temperature until the solid content disappeared and the mixture became transparent and uniform. Further, 10.4 g of TEOS was added to this solution, and the mixture was stirred at room temperature until it became transparent and uniform.

This was made into a concentrated solution having a viscosity of 30 poise in the same manner as in Example 1 to prepare a spinning dope. Thereafter, mullite filaments were obtained by extruding and sintering in the same manner as in Example 1.

A mullite film was obtained in the same manner by extrusion using a slit and sintering.

Needless to say, the present invention is not limited to the above-mentioned examples, and various embodiments are possible in details such as the type of aluminum alkoxide and silicon alkoxide, the viscosity, and the temperature rise.

(Effects of the Invention) As is clear from the above description, according to the present invention, it is easy to mix the composition components extremely uniformly, and it is easy to adjust the viscosity of the spinning dope to an appropriate value, and the spinnability is stable. Since it has excellent properties and is easy to manufacture, it is effective for manufacturing a mullite fiber or a film.

Claims (5)

[Claims] 1. An aluminum alkoxide and a silicon alkoxide are simultaneously added to an aqueous solution containing aluminum nitrate or aluminum chloride at room temperature so that the atomic ratio of aluminum to silicon is 3: 1, and then dissolved, followed by heating and concentration to obtain a viscous solution. A process for producing a mullite fiber or film, which comprises forming a fibrous or film-like product by extruding the viscous liquid through a nozzle or a slit into a viscous liquid and then sintering the fibrous or film-like product. 2. The method according to claim 1, wherein the molar ratio of aluminum nitrate to aluminum alkoxide is 1: 1 to 1: 6. 3. The molar ratio of aluminum chloride to aluminum alkoxide is 1: 1 to 1: 3, and the total molar ratio of aluminum and silicon to water is 1:10 to 1:50. The method of claim 1. 4. An aluminum alkoxide is added to and dissolved in an aqueous solution containing aluminum nitrate at room temperature, and then silicon alkoxide is added and dissolved at room temperature so that the atomic ratio of aluminum to silicon is 3: 1. A method for producing a mullite fiber or a film, which comprises heating and concentrating to form a viscous liquid, extruding the viscous liquid through a nozzle or a slit to form a fibrous or film-like product, and then sintering. 5. The molar ratio of aluminum nitrate to aluminum alkoxide is 1: 1 to 1: 4, and the total molar ratio of aluminum to silicon and water is 1:10 to 1: 200. The method of claim 4.