JPH0478732B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing alumina fibers or membranes. Alumina fibers and alumina membranes are useful as heat-resistant materials, heat-insulating materials, reinforcing materials, and the like. BACKGROUND ART Known conventional methods for producing alumina fibers include a precursor polymer method, a slurry method, an inorganic salt method, and a sol-gel method. Representative examples of these methods are as follows. The precursor polymer method is

A viscous solution containing polyaluminoxane, an inorganic polymer having a main chain consisting of the following formula, is mixed with a silicic acid ester, then dry spun and fired. The slurry method _{uses Al2O3} fine powder and a small amount of _MgCl2 .
Al ₂ (OH) ₃ Cl is added as a binder component to 6H ₂ O to form a viscous slurry, which is then dry spun and fired. In the inorganic salt method, a water-soluble organic polymer such as polyethylene oxide or PVA is added to an aqueous solution of aluminum salt, and water-soluble polysiloxane is further mixed to form a viscous liquid, which is then blown out from a nozzle and fired. In the sol-gel method, silica sol and boric acid are added to alumina sol containing ions such as HCOO and CH ₃ COO to form a viscous liquid, which is then spun and fired. However, all of these methods have the following problems. In order to spin fibers using a spinning solution, the spinning dope is important, and the physical properties of the solution such as viscosity, spinnability, uniformity, and stability are important factors, and the spinning dope is easy to manufacture. The important factors are that the spinnability is excellent. From this perspective, although the precursor polymer method has high uniformity, it is difficult to control the manufacturing process for producing the spinning dope. In the sol-gel method, it is difficult to control the concentration because precipitation and turbidity occur during the concentration stage, and the viscosity increases rapidly. Since the inorganic salt method uses a water-soluble organic polymer to provide the viscosity that gives the fiber form, the stock solution may lack stability, such as gelation during the preparation stage. In addition, the slurry method is a so-called heterogeneous system, and there are problems such as the particle size, amount added, dispersion state, etc. of solid particles constituting the spinning dope slightly affect spinnability, making it difficult to control. Purpose of the Invention The present invention aims to eliminate the problems associated with the spinning dope in the conventional method.The purpose of the present invention is to easily adjust the viscosity of the spinning dope and improve spinnability, uniformity, and stability. It is an object of the present invention to provide a method for easily producing alumina fibers or membrane-like products by providing excellent spinnability, good spinnability, and easy production. Structure of the Invention As a result of intensive research to achieve the above object, the present inventors found that 2 to 3 carboxyl groups and 1 to 1 hydroxyl group
A soluble aluminum organic compound is dissolved in an aqueous solution of an organic acid having two carboxyl groups or an organic acid having two carboxyl groups to form a homogeneous solution, and this is heated and concentrated to remove excess water and dissolve. It has been found that by removing the organic residues, a uniform and stable spinning stock solution with viscosity and spinnability suitable for spinning can be easily obtained. In addition, if a viscous liquid is produced in the same manner as above using the aluminum organic compound and an appropriate amount of aluminum inorganic acid salt, and this is used as a spinning stock solution, the fiber obtained by spinning can be fired and sintered. It has been found that during this process, volatile components are reduced, making sintering easier. The present invention was completed based on these findings. The gist of the present invention is as follows: (1) An aluminum organic compound soluble in an organic acid aqueous solution has 2 to 3 carboxyl groups and 1 to 1 hydroxyl group.
2 unique organic acid or carboxyl group
It is characterized by dissolving it in an aqueous solution of its own basic acid, heating and concentrating it to form a viscous liquid, extruding this viscous liquid through a nozzle or slit, forming it into a fibrous or film-like material, and then sintering it. A method for producing alumina fibers or membranes. (2) Both compounds in which the aluminum organic compound soluble in an organic acid aqueous solution is 50 mol% or more in terms of Al ₂ O ₃ and the aluminum inorganic acid salt is less than 50 mol % in terms of Al ₂ O ₃ are A mixed solution is prepared by dissolving an organic acid having 2 to 3 groups and 1 to 2 hydroxyl groups or an organic acid having 2 carboxyl groups in an aqueous solution, and this is heated and concentrated to form a viscous liquid, and this viscous liquid is A method for producing alumina fibers or membranes, which comprises extruding the alumina fibers or membranes through a nozzle or slit, forming them into fibers or membranes, and then sintering them. Examples of the aluminum organic compound dissolved in the organic acid aqueous solution used in the present invention include aluminum alkoxide, aluminum carboxylate, and aluminum acetylacetonate. Examples of the aluminum alkoxide include organic residues such as 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. Further, as the aluminum carboxylate, organic residues include a formyloxy group and an acetyloxy group. Examples of the aluminum inorganic acid salt used in the present invention include aluminum oxychloride, aluminum chloride, aluminum sulfate, and aluminum nitrate. When an aluminum organic compound and an aluminum inorganic acid salt compound are used together, it is necessary that the aluminum organic compound accounts for 50 mol % or more in terms of Al ₂ O ₃ . If it is less than 50 mol%, it will be difficult to solidify it into a fiber-formed product. 2 to 3 carboxyl groups used in the present invention
Examples of organic acids having 1 to 2 hydroxyl groups include etc. In addition, examples of organic acids having two carboxyl groups include: can be mentioned. The spinning stock solution is dissolved in the organic acid aqueous solution containing distilled water in an amount of 20 to 50 times the mole of the amminium organic compound. The amount of organic acid is at least 1 times the mole of the aluminum element in the aluminum organic compound or aluminum inorganic acid salt,
A suitable amount is preferably 1.5 to 2.0 times the molar amount. Dissolution is performed at room temperature or at a temperature up to about 90°C with stirring. In order to improve the physical properties of the alumina fibers or membranes, add small amounts of lithium, beryllium, boron, sodium, calcium, potassium, magnesium, silicon, barylium, chromium, manganese, yttrium, and lanthanum to this solution, as necessary. , tungsten, iron, nickel, copper, zinc, etc., are added as an organic metal compound, carbonate, or inorganic acid salt. The resulting solution is heated to 100°C or higher in an open system and concentrated. This concentration is carried out until a viscous state is obtained. The resulting viscous liquid has fluidity at 70 to 80°C, but when left at room temperature, it gradually increases in viscosity and eventually solidifies. This phenomenon becomes more noticeable in a dry atmosphere. Therefore, continuous fibers can be obtained by extruding this viscous liquid from a nozzle into a dry atmosphere below room temperature while heating it at 70 to 80°C. After removing moisture from the resulting fibers in a dry atmosphere, they are fired in air at 700 to 1000°C to decompose and remove organic components. Alumina long fibers are obtained by sintering this at 1200 to 1400°C. In this case, ultrafine short fibers can be obtained by extruding through a thick diameter nozzle and burning and blowing away with flame. Furthermore, a film-like material can be obtained by using a slit instead of a nozzle. The aluminum organic compound and aluminum inorganic acid salt are used as the aluminum raw material composition.
When used together in an amount of less than 50 mol% in terms of Al ₂ O ₃ , the volatile content decreases during firing and sintering, making sintering easier. In this case, if the aluminum inorganic acid salt is used in an amount greater than the above amount, the viscous liquid becomes difficult to solidify, so the amount needs to be less than 50 mol%. Example 1 2.20 g of aluminum isopropoxide was added to an aqueous solution of 2.88 g of citric acid dissolved in 20 ml of distilled water and stirred to obtain a transparent homogeneous solution. This solution was heated to 100℃.
It was heated and concentrated to a viscosity of 100 poise. This concentrated liquid was extruded through a nozzle at 70 to 80°C into room temperature dry air to obtain colorless and transparent long fibers with a diameter of 5 to 100 μm. The resulting fibers were dried at 100°C overnight, then heat treated at 900°C for 2 hours, and then heated at 1100°C.
It was heated for 2 hours and sintered. As a result, α-alumina long fibers were obtained. Example 2 An aqueous solution of 3.00 g of tartaric acid dissolved in 20 ml of distilled water was
Heat to 90℃ and add basic aluminum acetate to this.
3.78 g of tetrahydrate was added and stirred to obtain a transparent homogeneous solution. This was made into a concentrated solution with a viscosity of 100 poise in the same manner as in Example 1, and used as a spinning dope. Thereafter, α-alumina long fibers were obtained in the same manner as in Example 1. Example 3 1.32 g of aluminum isopropoxide was added to an aqueous solution of 3.84 g of citric acid dissolved in 20 ml of distilled water.
A clear homogeneous solution was obtained by stirring. 0.97 g of aluminum chloride hexahydrate was added to this and stirred to form a transparent homogeneous solution. This solution was heated to 100°C and concentrated to a viscosity of 100 poise. Using this viscous liquid, α-alumina long fibers were obtained in the same manner as in Example 1. Example 4 1.54 g of aluminum isopropoxide was added and dissolved in an aqueous solution of 3.84 g of citric acid dissolved in 20 ml of distilled water to obtain a transparent homogeneous solution. The mixture was then heated to 90° C., 0.51 g of aluminum sulfate was added, and stirred to obtain a clear homogeneous solution. This solution was made into a viscous liquid with a viscosity of 100 poise in the same manner as in Example 1, and used as a spinning dope. Example 1
α-alumina long fibers were obtained in the same manner as above. Note that if a slit is used instead of a nozzle, a film-like product can be obtained, and if it is extruded through a thick diameter nozzle and burned and blown away with flame, ultrafine short fibers can be obtained. Effects of the Invention According to the method of the present invention, it is easy to adjust the viscosity of the spinning dope to an appropriate value, it has excellent spinnability, uniformity, and stability, it has good spinnability, and it is easy to manufacture. be. Moreover, since the aluminum raw material of the spinning dope is an organic compound of aluminum or an inorganic acid aluminum, and the compound that dissolves this is an organic acid aqueous solution, it is easy to remove decomposed components by heating, and it is possible to form pure alumina fibers or membranes. It has excellent effects that can be easily obtained by spinning.

Claims (1)

[Scope of Claims] 1. An aluminum organic compound soluble in an organic acid aqueous solution has 2 to 3 carboxyl groups and 1 to 1 hydroxyl group.
After dissolving in an aqueous solution of an organic acid having two carboxyl groups or an organic acid having two carboxyl groups, it is heated and concentrated to form a viscous liquid, and this viscous liquid is extruded through a nozzle or slit to form a fibrous or film-like product. A method for producing alumina fibers or membrane-like materials, which comprises sintering the alumina fibers or membranes. 2 Both compounds in which the aluminum organic compound soluble in an organic acid aqueous solution is 50 mol% or more in terms of Al ₂ O ₃ and the aluminum inorganic acid salt is less than 50 mol % in terms of Al ₂ O ₃ are combined with carboxyl groups. A mixed solution is prepared by dissolving an organic acid having 2 to 3 carboxyl groups and 1 to 2 hydroxyl groups or an organic acid having 2 carboxyl groups.This is heated and concentrated to form a viscous liquid, and this viscous liquid is passed through a nozzle. Or, a method for producing alumina fibers or membranes, which comprises extruding them through a slit, forming them into fibers or membranes, and then sintering them.