JP2001248024A - Hollow ceramic fiber product and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply a functional ceramic to catalyst carriers, catalysts, photocatalysts, sensors, oxide conductors, etc., and improve efficiency by increasing a specific surface area and enhance the degree of freedom of the shape of a product. SOLUTION: This method for producing a ceramic hollow fiber product is to soak an organic fiber such as raw cotton, raw wool, woven fabric, knit fabric, synthetic fiber paper, nonwoven fabric or the like in a solution containing a metal compound to be a precursor, form a metal oxide film having >=0.1 μm thickness around a hydrophilic peripheral surface of the organic fiber by hydrolysis, etc., subsequently, remove the organic fiber by baking, etc., and obtain the ceramic hollow fiber product in which hollow holes corresponding to the shape of the organic fiber are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic fiber product, in particular, a ceramic hollow fiber product or a ceramic porous material having a hollow fiber skeleton useful as a photocatalyst, a sensor, an oxide conductor or the like, and a method for producing the same.

[0002]

2. Description of the Related Art Ceramics are excellent in heat resistance, abrasion resistance, chemical resistance and the like, and are used for various functional applications such as catalyst carriers, catalysts, photocatalysts, and sensors. In these applications, they are usually used in the form of a film or in the form of a powder in order to increase the specific surface area. In addition, ceramics generally have disadvantages such as brittleness and poor workability.

[0003] Therefore, ceramic fibers are used in applications requiring flexibility and flexibility. As ceramic fibers, glass fibers such as silica fibers, silicon carbide fibers, boron fibers, and alumina fibers have been known for a long time.

[0004] Recently, titanium oxide has attracted attention as a catalyst for the photolysis reaction, and has been widely used in various fields such as decomposition and sterilization of harmful substances and odorous substances in water and air, and prevention of surface contamination of various articles. It is used in the form of titanium oxide powder or coating.

[0005] It is known that titanium oxide is used as a filter in the form of a porous material such as a felt, cotton, or woven fabric. However, a porous material in which fibers are entangled usually involves particles such as a catalyst. It is applied to the surface of an inorganic fiber or an organic fiber together with a binder to be carried, and is formed into a filter or the like (Japanese Patent Application Laid-Open No. 11-47558).

[0006] Fibers of titanium oxide itself have also been developed. For example, Japanese Patent Application Laid-Open No. 9-276705 discloses that
A titania fiber having a crystal form of anatase having a BET specific surface area of 10 m ² / g or more is disclosed. As a method for producing the titania fiber, a method of spinning using a spinning solution containing a polymetalloxane and firing, and a sol-gel method are disclosed.

[0007] Further, tin oxide, which is electrically conductive and is used as a transparent electrode for a liquid crystal element or a gas sensor, is also made of a polycrystalline or amorphous fiber by a spinning method.
There is known a method for producing (for example,
349326).

[0008]

The titanium oxide is a powder,
Various forms such as a plate-like powder, a nanotube, a thin film, a porous body, and a long fiber are known. However, powder coating has a small degree of freedom in shape and cannot be used as a filter. Spraying the titanium oxide powder on the fibers reduces the specific surface area and degrades the fibers. When an organic substance is used as a carrier, the organic substance is decomposed by ultraviolet irradiation, so that the photocatalytic effect cannot be sufficiently exhibited. When used as a thin film, only the surface of the film functions as a photocatalyst, and the efficiency is poor.

[0009] Tin oxide is known to be used as a thin film and in the form of powder or acicular powder to be contained in a conductive paint. Powder coatings and powder-mixed polymers using these are known. Has high resistance.

As described above, ceramics have a small specific surface area in the case of a thin film, and powder is difficult and difficult to handle.
Further, ceramic fibers generally employ a method in which a raw material is melted and formed into fibers by a spinning method or the like, which is expensive and difficult to apply to a material system having a high melting point. Further, in the case of producing a fiber molded body having a complicated structure, a method of processing the fiber into a felt shape or the like is also known, but it involves many steps such as spinning, cutting, and molding, resulting in high cost.

These functional ceramics are used as catalyst carriers,
In order to improve the efficiency by applying it to catalysts, photocatalysts, sensors, etc., it is necessary to improve the degree of freedom of the product shape. For this reason, for example, as a method for producing a flexible ceramic structure having a complex fine skeleton, a natural or synthetic polymer porous material, such as paper, sponge, polypropylene foam, a substrate made of a porous polymer, etc. There is known a method in which a metal alkoxide solution is impregnated, a base material impregnated with the metal alkoxide solution is fired, and the base material is burned off by firing (JP-A-7-187846, JP-A-8-34680). However, it is very difficult to impregnate the micropores with the alkoxide, and it is also difficult to obtain a desired shape due to shrinkage during firing.

[0012]

Means for Solving the Problems The present inventors have intensively researched and developed a low-temperature synthesis of ceramics and a production method of ceramics capable of controlling micro to macro morphology. No, titanium oxide, 2
The present inventors have found a method capable of producing a hollow ceramic fiber having a remarkably large specific surface area composed of tin oxide, silicon oxide or the like and having flexibility at low temperature, and a ceramic porous body having a hollow fiber skeleton.

That is, the present invention comprises a metal oxide having a thickness of 0.1 μm or more deposited from a solution containing a metal compound as a precursor on the outer peripheral surface of an organic fiber, and the organic fiber is removed. This is a ceramic hollow fiber product in which pores corresponding to the shape of the organic fiber are formed inside, thereby increasing the specific surface area.

The present invention also relates to a hollow fiber in which the organic fibers are raw cotton, raw wool, woven fabric, knitted fabric, synthetic fiber paper, or nonwoven fabric, and in which continuous pores corresponding to the shape of these organic fibers are formed. The ceramic hollow fiber product described above, which is a ceramic porous body having a skeleton.

Further, the present invention is a ceramic hollow fiber product obtained by crushing the above-mentioned ceramic hollow fiber product into a short hollow fiber to form a paste.

The present invention also relates to a metal oxide having a thickness of 0.1 μm or more of a precursor compound on a hydrophilic outer peripheral surface of an organic fiber by immersing the organic fiber in a solution containing a metal compound to be a precursor. This is a method for producing a ceramic hollow fiber product in which pores corresponding to the shape of the organic fiber are formed inside by removing the organic fiber after forming the film.

Further, according to the present invention, the metal compound serving as a precursor is a halide, alkoxide, sulfate, oxysulfate, nitrate, acetate, oxalate or titanium oxide of Ti, Sn, Zr, Al or Si. And a fiber product is titania, tin oxide, zirconia, alumina, or silica.

Further, according to the present invention, the solution containing the metal compound serving as the precursor may be a TiF solution having a pH of 1 to 3 and 25 to 70 ° C.
_The method for producing a ceramic hollow fiber product according to claim 4, wherein the aqueous solution contains ₄ and the fiber product is titania.

Further, the present invention is characterized in that after forming the metal oxide film, the crystallinity of the metal oxide film is increased by heating and the organic fibers are burned off to form pores. This is a method for producing fiber products.

[0020] The present invention also provides a method for producing an organic fiber, comprising: raw cotton;
Using raw wool, woven, knitted, synthetic fiber paper, or non-woven fabric,
A method for producing a ceramic hollow fiber product as described above, which comprises producing a ceramic porous body having a skeleton of hollow fibers having continuous pores corresponding to the shape of these organic fibers.

Further, the present invention is a method for producing a hollow ceramic fiber product, which comprises crushing the hollow ceramic fiber product obtained by each of the above methods into a short fiber to obtain a paste state.

The method of the present invention uses means for forming a metal oxide film on the outer peripheral surface of an organic fiber by using a method called a chemical solution deposition method. Conventionally, as a method of forming a thin film such as titanium oxide on a substrate surface, CVD,
Although ion plating, a sputtering method, a sol-gel method, and the like are known, all of these methods are synthesis methods at a high temperature and are not suitable for forming a uniform film on an outer peripheral surface of an organic fiber.

Since the method of the present invention utilizes precipitation by hydrolysis or the like from an aqueous solution, it is necessary that the surface of natural organic fibers such as cotton and wool and synthetic fibers be hydrophilic. When the fiber itself does not have hydrophilicity, a hydrophilic treatment may be performed by a known means.

The film thickness formed on the outer peripheral surface of the organic fiber is 0.1 mm.
If the thickness is less than 1 μm, the metal oxide film shrinks and twists when the organic fibers are removed by firing, and the shape cannot be maintained. The thickness of the film increases in proportion to the immersion time.
About μ is preferable. When a sol coating method is used as the film formation method, the film contains an organic substance or moisture, and the metal oxide film shrinks and adheres, so that a desired form cannot be obtained. Solution that easily dissolves organic fibers in a short time instead of firing method, for example, alkaline solution,
A method of immersing in an organic solvent to dissolve and remove the organic fibers can also be employed.

After forming the metal oxide film on the organic fiber,
It is taken out from the aqueous solution, dried appropriately, and fired to burn off the organic fibers. The metal oxide film does not rupture or swell, and the organic fibers are not covered with the micropores or metal oxide film present in the metal oxide film formed on the outer peripheral surface. Gasifies from the part and disappears.

Therefore, micrometer-scale holes corresponding to the shape of the organic fibers and communicating with the outside air are formed in a short period of time inside the obtained ceramic fibers. The inner surface of the hollow continuous hole becomes a transcript of the outer surface of the organic fiber constituting the woven or knitted fabric.If the surface of the fiber is rough, the surface becomes a rough surface. Since the surface becomes a smooth surface, the surface roughness of the hollow continuous hole can be arbitrarily adjusted.

In the method of the present invention, as the organic fiber,
When raw cotton, raw wool, woven fabric, knitted fabric, synthetic fiber paper, or non-woven fabric is used, a porous ceramic body having these organic fibers as a mold and hollow fibers having continuous pores corresponding to the shape as a skeleton is formed. As a result, a surface that communicates with the outside air is formed not only on the outer surface but also on the inside of the fiber skeleton, so that the specific surface area can be significantly increased.

Therefore, for example, a titanium oxide porous body in the form of felt, lace, cotton, or the like can be directly produced from the raw material without passing through the step of spinning the raw material into fiber. In the case of titanium oxide, for example, an aqueous solution containing a metal fluoride salt is used to form a metal oxide film at a low temperature of room temperature to about 70 ° C., and the metal oxide film is simply immersed in the aqueous solution and left for a required time. Thus, the required film thickness is formed, so that the working efficiency is excellent and the cost is advantageous.
Further, when the content of anatase type titanium oxide in the titanium oxide prepared by the liquid phase deposition method is small, it is heated to about 300 to 500 ° C. Although heating is performed, the organic fibers may be burned out by these heat treatments.

The ceramic hollow fiber product and the ceramic porous body having the hollow fiber as a skeleton are crushed by crushing or crushing into short fibers in the form of a paste. However, in the case of tin dioxide, when this is used as a component of the conductive paint, the contact area becomes larger than that of powdered tin dioxide even with the same weight, so that the conductivity can be improved.

When the ceramic hollow fiber product and the ceramic porous body having a hollow fiber skeleton of the present invention are titania, the efficiency as a photocatalyst can be increased, and the catalyst is useful as a catalyst for decomposing dioxin and NOx. In the case of silica, it is useful as a catalyst carrier having a high specific surface area and a low pressure loss.

[0031]

DETAILED DESCRIPTION OF THE INVENTION Gold used for deposition from low temperature aqueous solution
TiF as the genus halide_Four, SnF _Two, SiF
₆Use such as. Hydrolysis reaction in aqueous solution is an example
For example, TiF_Four, SnF_TwoIs represented by the following equation.

TiF ₄ + H ₂ O → Ti (OH) ₄ → TiO ₂ SnF ₂ + H ₂ O + O ₂ → Sn (OH) ₄ → Sn
When SbF ₃ is added when forming SnO ₂ using O ₂ and SnF ₂ , Sb-doped SnO ₂ hollow fibers can be obtained.

As an example, TiF is used as a metal halide.
₄ will be described in more detail.
Alternatively, add ammonia water to deionized water to adjust the pH to 1
3 to which TiF ₄ was added in an amount of 0.005 to 0.1 mol.
Dissolve to a concentration of 1 / l. If these conditions are not satisfied, a good film will not be deposited. This is stirred for about 1 hour. The organic fibers are washed with dilute nitric acid, ethanol, deionized water or the like, if necessary, and the solution is heated at 25 to 70 ° C.
Immersion for 0.5 to 260 hours. The organic fiber having the metal oxide film formed thereon is preferably washed with deionized water at room temperature for about 10 minutes while applying ultrasonic waves.
Then, it is dried in an electric furnace at 60 ° C. for about 30 minutes in air.

After drying, when heated to about 400 to 600 ° C. in the same electric furnace or another electric furnace, the organic fibers burn and gasify and disappear. Thereby, a ceramic hollow fiber product and a ceramic porous body having a hollow fiber as a skeleton are obtained. Even when a TiF ₆ aqueous solution having poor crystallinity is used, the heating improves the crystallinity.

[0035]

EXAMPLES Example 1 TiF ₄ was dissolved in water to which ammonia was added to adjust the pH to a concentration of 0.04M and stirred for 1 hour. Lace was immersed in this solution as a kind of woven fabric and kept at 60 ° C. for 24 hours to deposit an anatase-type titania film. The sample on which titania was precipitated was dried, and then dried in air.
The organics were removed by burning at ℃. The produced titania was evaluated by an optical microscope, SEM, X-ray diffraction and the like.

As shown in the optical micrograph of the outer surface of the produced titania in FIG. 1, the obtained titania retains the stitch shape of the lace even after removing the organic fibers, and corresponds to the shape of the lace. A porous body consisting only of anatase having a skeleton of hollow fibers in which pores communicating with the outside air were formed was obtained.

After removing the fibers, the titania had an outer diameter of about 10 μm as shown in FIG. 2, and the inside of the membrane having a thickness of about 1 μm was hollow, indicating that a titania hollow fiber was produced. . This titania has elasticity, and its shape was restored even if it was lightly pressed by hand.

Example 2 Example 1 except that natural cotton was used instead of lace.
As above, titania was precipitated. When the natural cotton was burned, about 6 mg / cc (porosity of about 99.8%) of cotton-like titania was obtained. This titania has elasticity, and its shape was restored even if it was lightly pressed by hand.

[0039]

According to the present invention, ceramic fibers having an extremely large specific surface area can be obtained, and a high-performance ceramic porous body can be freely designed by controlling the form of the organic fiber used as a mold. In addition, it can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is an optical micrograph as a substitute for a drawing of the outer surface of titania having the form of a lace produced according to Example 1.

FIG. 2 is an optical microscope photograph instead of a drawing showing a hollow shape of the titania fiber after removing the organic fiber.

Claims (9)

[Claims] 1. A metal oxide having a thickness of 0.1 μm or more deposited from a solution containing a metal compound serving as a precursor on the outer peripheral surface of an organic fiber. A ceramic hollow fiber product in which pores corresponding to the shape of the organic fiber are formed to increase the specific surface area. 2. The method according to claim 1, wherein the organic fibers are raw cotton, raw wool, woven fabric, knitted fabric,
The ceramic hollow fiber according to claim 1, wherein the ceramic hollow fiber is a synthetic fiber paper or a nonwoven fabric, and is a ceramic porous body having a skeleton of a hollow fiber having continuous pores corresponding to the shape of the organic fiber. Product. 3. A ceramic hollow fiber product, wherein the ceramic hollow fiber product according to claim 1 or 2 is crushed into a hollow short fiber to form a paste. 4. A metal oxide film having a thickness of 0.1 μm or more of the precursor compound is formed on the hydrophilic outer peripheral surface of the organic fiber by immersing the organic fiber in a solution containing a metal compound to be a precursor. Then, a method for producing a ceramic hollow fiber product in which pores corresponding to the shape of the organic fiber are formed inside by removing the organic fiber. 5. The precursor metal compound is Ti, Sn,
A halide, alkoxide, sulfate, oxysulfate, nitrate, acetate, oxalate, or titanate, stannate, aluminate, or silicate of Zr, Al, or Si; 5. The method for producing a ceramic hollow fiber product according to claim 4, wherein the ceramic hollow fiber product is tin oxide, zirconia, alumina, or silica. 6. The ceramic according to claim ₄ , wherein the solution containing the metal compound serving as a precursor is an aqueous solution containing TiF _{4 at} a pH of 1 to 25 and 25 to 70 ° C., and the textile is titania. A method for producing hollow fiber products. 7. The method according to claim 4, wherein after forming the metal oxide film, the crystallinity of the metal oxide film is increased by heating, and the organic fibers are burned off to form pores.
The method for producing a ceramic hollow fiber product according to any one of the above. 8. Ceramics using raw cotton, raw wool, woven fabric, knitted fabric, synthetic fiber paper or non-woven fabric as organic fibers, and having a skeleton of hollow fibers having continuous pores corresponding to the shape of these organic fibers. The method for producing a ceramic hollow fiber product according to any one of claims 4 to 7, wherein a porous body is produced. 9. A method for producing a hollow ceramic fiber product, wherein the hollow ceramic fiber product obtained by the method according to any one of claims 1 to 8 is crushed into a short fiber into a paste. .