JPH05247727A - Production of silicon carbide fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber useful as a heat-resistant material, reinforcing fiber, electrically conductive material, radiation-resistant material, etc., in large quantities at a low cost by supporting silica on a cellulose fiber and baking the fiber at a specific temperature in vacuum or in argon gas atmosphere. CONSTITUTION:Viscose rayon staple is immersed in 4N sodium hydroxide solution at room temperature for 12hr, centrifuged to remove the liquid and immersed in an aqueous solution of sodium silicate at room temperature for 3hr. The fiber impregnated with sodium silicate is centrifuged to remove the liquid and brought into contact with carbon dioxide gas of 1kg/cm<2> pressure in a pressure vessel to effect the deposition of silica in the fiber. The obtained silica- supporting cellulose fiber is subjected to the primary baking in nitrogen atmosphere at a heating rate of 10 deg.C/hr between room temperature and 400 deg.C and 100 deg.C/hr between 400 deg.C and 900 deg.C, and then to the secondary baking in vacuum or in argon atmosphere at a heating rate of 3000 deg.C/hr between room temperature and 1000 deg.C and 1000 deg.C/hr between 1000 deg.C and 1500 deg.C to obtain the objective silicon carbide fiber.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel method for producing silicon carbide fibers. More specifically, the present invention relates to the production of silicon carbide fibers useful as heat resistant materials, reinforced fibers, conductive materials, radiation resistant materials and the like.

[0002]

2. Description of the Related Art It has long been known that silicon carbide is produced when silica and carbon are reacted at a high temperature in an inert gas atmosphere. It is also well known that when organic substances such as cellulose are baked in an inert atmosphere, carbon remains.

Japanese Unexamined Patent Publication (Kokai) No. 52-63427 discloses a method of obtaining a silicon carbide fiber by spinning a silicon-containing organic polymer and firing it in an inert gas atmosphere. This method is characterized in that a polymer fiber containing silicon in the molecule has already been used as a raw material.

Japanese Patent Publication No. 44-18574 discloses a method for obtaining silicon carbide fibers by bringing carbon fibers into contact with steam such as silicon or a melt. The silicon carbide fiber obtained by this method has a defect that coarse crystals are aggregated and have poor mechanical strength.

French Patent No. 1,560,688 describes S
A method for obtaining fine fibrous silicon carbide by reacting iO gas with CO gas at high temperature is disclosed. Further, JP-A-49-9500 discloses a method of reacting carbon and silicon tetrachloride in the presence of a nickel catalyst to obtain fine fibrous silicon carbide. The whisker-like silicon carbide fibers obtained by these methods are generally very small in size (the diameter is about 1 micron and the length is often less than 1 mm), and therefore they are difficult to handle and exhibit sufficient performance. In addition, it is difficult to obtain a homogeneous product inexpensively and in large quantities.

US Patent Application No. 541,188 (198)
4) discloses a method in which colloidal silica and rayon fibers are suspended in water, dried, and fired in an argon atmosphere to obtain silicon carbide fibers. However, there is a drawback that the silicon carbide fiber cannot be manufactured at low cost by any other method including this method.

[0007]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a method for producing a large amount of silicon carbide fibers excellent in strength and heat resistance at low cost by a simple process from easily available and inexpensive raw materials. It is a thing.

[0008]

The method for producing a silicon carbide fiber according to the present invention comprises a silica fiber-supported cellulose fiber in a vacuum or in an argon atmosphere in the range of 1100 to 2: 1.
It is characterized by firing at 300 ° C.

[0009]

The cellulose fiber used in the present invention may be any one as long as it contains cellulose as a main component, and can be selected from, for example, natural lignocellulose fiber and regenerated cellulose fiber. Examples of natural lignocellulosic fibers include wood pulp fibers manufactured from wood, non-wood pulp fibers manufactured from herbs, and cotton fibers. As the regenerated cellulose fiber, viscose rayon, cuprammonium rayon, nitrifying silk, saponified acetate, etc. can be used.

The regenerated cellulose fibers may be in the form of long fibers or short fibers obtained by cutting them. The diameter (fineness) of the cellulose fiber is not particularly limited. Regenerated cellulose fibers are, in addition to fibers made of only cellulose,
It may be a fiber containing an additive such as titanium dioxide.

In the method of the present invention, in order to support silica on the cellulose fiber, for example, the cellulose fiber is immersed in an aqueous solution of a water-soluble silicic acid compound such as sodium silicate, and after removing the liquid, carbon dioxide gas or an acid aqueous solution is used. It is possible to use a method in which the water-soluble silicic acid compound impregnated in the cellulose fiber is neutralized and precipitated to support silica (silicon dioxide) inside the fiber.

According to this method, the silica-supporting ratio of the silica-supported cellulose fibers (weight of silica / weight of silica-supporting fiber) can be arbitrarily adjusted to about 0 to 60% by weight. The suitable silica loading rate for the method is
It is 5 to 50% by weight based on the total weight of the silica-supported cellulose fibers.

The atmosphere at the time of firing the cellulose fiber supporting silica needs to be substantially vacuum or argon atmosphere. When firing the silica-supported cellulose fibers, it is possible to raise the temperature to the maximum temperature in a single firing operation and fire this, but in the process of the cellulose pyrolyzing and changing to carbonaceous material. Since volatile substances and tar are generated, it is desirable to perform firing in two steps. That is, the first firing (first firing) is 1
Firing in a stream of an inert gas (argon gas, nitrogen gas, etc.) at a temperature of 000 ° C. or lower to remove volatile components and tar, once cooling, the fiber is transferred to a high-temperature furnace, and second firing ( A method of firing to a predetermined maximum temperature in the secondary firing) is practically desirable.

Any firing furnace can be used as long as it can perform firing at a predetermined temperature in an atmosphere of an inert gas (argon gas) or substantially in vacuum. For firing at 1500 ° C. or higher, it is desirable to use a carbon resistance furnace. The rate of temperature rise during the primary firing is
A temperature rising rate of 10 to 100 ° C / hr is desirable from room temperature to around 500 ° C, and 5 from 500 ° C to around 1000 ° C.
A heating rate of 0 to 200 ° C./hr is desirable.

There is no particular limitation on the rate of temperature rise during the secondary firing. The maximum temperature during the secondary firing is 1100 to 2300 ° C.
Is preferred. When the secondary firing temperature is less than 1100 ° C., the formation of silicon carbide is insufficient, and
If the temperature is higher than 2300 ° C, the decomposition of the silicon carbide produced will be significant. There is no particular limitation on the time for holding the maximum temperature in the firing step, and it can be appropriately selected from 0 hours (cooling immediately without holding) to about 24 hours. When raising the temperature, a predetermined holding time may be provided at an appropriate temperature until the maximum temperature is reached. For example, hold at 1500 ℃ for 1 hour, then 20
A firing schedule may be taken such that the temperature is raised to 00 ° C. and the temperature is kept at 2000 ° C. for 1 hour. The cooling rate is not particularly limited.

[0016]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 (1) Preparation of silica-supporting cellulose fiber Viscose rayon staple (1.5 denier, 3 mm
Long) 100 g of absolute dryness was dipped in 4N sodium hydroxide solution at room temperature for 12 hours, and it was dried at 1500 G (gravitational acceleration) for 3
The solution was centrifugally deliquored and then immersed in a No. 3 sodium silicate aqueous solution at room temperature for 3 hours. The sodium silicate-impregnated fiber was centrifugally deliquored at 1500 G for 3 minutes, and then contacted with carbon dioxide gas at a pressure of 1 kg / cm ^{2 in} a pressure vessel to deposit silica in the fiber. The silica-supported fiber was defibrated in water, washed, and dried. In order to measure the ash content of this silica-supported fiber, it was calcined in air at 900 ° C,
When the ash content was calculated, the silica content of the dry fiber was 30%.
Met.

(2) Firing The above-mentioned silica-supported cellulose fibers were treated in a nitrogen atmosphere.
Firing was performed from room temperature to 400 ° C. at a heating rate of 10 ° C./hr, and from 400 ° C. to 900 ° C. at a heating rate of 100 ° C./hr (primary firing). The firing yield of this primary firing is 50.
%Met. The fiber that has been subjected to primary firing is heated in an argon atmosphere from room temperature to 1000 ° C. at a heating rate of 3000 ° C./hr, and from 1000 ° C. to 1500 ° C. at 1000 ° C.
The temperature was raised at a temperature rising rate of ° C / hr, the temperature was maintained at 1500 ° C for 3 hours (secondary firing), and then cooled. The firing yield of this secondary firing was 63%.

As a result of X-ray diffraction analysis of the fired fiber, it was confirmed that the fiber was silicon carbide fiber containing 90% or more of beta-type silicon carbide. 1 fired fiber
It had a diameter of 0 micron and a length of 1.5 mm. When this fiber was heated to 900 ° C. in air, no weight loss was observed.

Example 2 The silica-supported cellulose fiber prepared in Example 1 was heated from room temperature to 400 ° C. at a temperature rising rate of 10 ° C./hr and at 400 ° C.
Firing was performed at a temperature rising rate of 100 ° C./hr from 1 ° C. to 900 ° C. (primary firing). The firing yield of this primary firing was 50%. Next, the primary fired fiber was heated in an argon atmosphere from room temperature to 1000 ° C at a heating rate of 3000 ° C / hr, and from 1000 ° C to 1950 ° C at 1000 ° C.
The temperature was raised at a heating rate of / hr, the temperature was maintained at 1950 ° C. for 1 hour (secondary firing), and then cooled. The firing yield of this secondary firing was 51%.

When the fired fiber was analyzed by an X-ray diffraction method, it was confirmed to be a silicon carbide fiber containing 90% or more of alpha-type silicon carbide. When this fiber was heated to 900 ° C. in air, no weight loss was observed. The fired fiber has a diameter of 10 microns and a
It had a length of mm.

[0022]

According to the method of the present invention, a silicon carbide fiber excellent in heat resistance and mechanical strength can be obtained by a simple process.
And it is possible to mass-produce at low cost.

Claims (1)

[Claims] 1. A cellulosic fiber supporting silica,
110 in a substantially vacuum or argon gas atmosphere
A method for producing a silicon carbide fiber, which comprises firing at 0 to 2300 ° C.