JP3155687B2 - Method for producing silicon nitride fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity and high-strength silicon nitride fiber having a Si--N skeleton.

[0002]

2. Description of the Related Art Spun polycarbosilane fibers have a thickness of 0.5%.
The polycarbosilane fiber that has been infusibilized by irradiating it with ionizing radiation such as an electron beam at a dose of about 90 MGy is heated to 800 to 1700 ° C. in a nitrogen gas atmosphere such as ammonia to nitride the polycarbosilane fiber. A method for producing a silicon nitride fiber having a -N skeleton has been proposed.

[0003]

However, in the conventional method for producing silicon nitride fibers using polycarbosilane fibers as a starting material, a large amount of oxygen is taken in as impurities or the fibers are decomposed and become brittle. Is coming. The tensile strength of the fiber containing a large amount of oxygen is about 1 GPa, and there is a problem that the mechanical strength is low.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a manufacturing method capable of realizing high strength and high strength silicon nitride fibers.

[0005]

In order to achieve the above object, the present invention provides a polycarbosilane fiber which has been subjected to infusibilization treatment by irradiating with ionizing radiation, by nitriding in an ammonia atmosphere at 500 ° C. or higher. Followed by 1200-1400 ° C
Baking in an inert gas atmosphere with an oxygen content of 1
It is characterized in that high-purity silicon nitride having a weight of 0% by weight or less and a tensile strength of 1.4 GPa or more is obtained.

[0006]

DETAILED DESCRIPTION OF THE INVENTION Polycarbosilane fibers after nitriding in an ammonia atmosphere are fired in an inert gas atmosphere at 1200 to 1400 ° C. to obtain an oxygen content of 10% by weight or less and a tensile strength of 1%. A high-strength silicon nitride fiber of .4 GPa or more can be realized.

The ionizing radiation to be irradiated to make the polycarbosilane fiber after spinning infusible includes an electron beam, α
Radiation, γ-ray, X-ray, etc., and the irradiation dose is 0.5 to 90.
Desirably MGy. The irradiation dose is 0.5MGy
In the following, infusibilization is insufficient and the fibers may melt during firing. Gel fraction is 100% at 90MGy or more
It becomes meaningless to irradiate a higher dose.

The temperature at which the polycarbosilane fibers are nitrided in an ammonia atmosphere is 500 ° C. or more,
Below, no nitriding reaction occurs. Although the upper limit is not particularly defined, 1400 ° C. is desirable, and when it exceeds 1400 ° C., crystallization of silicon nitride fibers starts to occur, and strength is reduced.

It is desirable to feed ammonia preheated to 500 to 1000 ° C. If a non-preheated ammonia gas stream is fed, the temperature of the fiber surface is lowered, causing oxygen to be mixed and the strength is likely to be reduced.

After the nitriding treatment, the temperature for continuous firing in an inert gas atmosphere is 1200 to 1400 ° C., and 1200 ° C.
In the following, unreacted residual radicals are present in the silicon nitride fibers, which are taken out into the room temperature atmosphere and combined with oxygen and hydrogen in the atmosphere to increase the oxygen content and decrease the strength. At 1400 ° C. or higher, crystallization of silicon nitride fibers starts to occur, and the strength decreases. When the heating rate is 200 ° C./hour or more, the oxygen content in the silicon nitride fiber can be reduced.

It is desirable to feed an inert gas preheated to 1200 to 1400 ° C. If a gas that is not preheated is sent, it causes oxygen contamination and the strength tends to decrease.
Examples of the inert gas include a nitrogen gas and an argon gas.

[0012] After the nitriding treatment in an ammonia atmosphere, the sintering treatment is performed continuously in an inert gas atmosphere without exposure to the air, so that the oxygen content in the silicon nitride fiber can be reduced.

[0013]

Hereinafter, an embodiment of the present invention will be described in comparison with a comparative example.

Example 1 A polycarbosilane fiber having a diameter of 18 μm obtained by using a spinning device was irradiated with a 10 MGy electron beam in a helium gas atmosphere to make it infusible. The infusibilized fiber after irradiation is heated from room temperature to 800 ° C. in an ammonia gas atmosphere under no tension.
After the temperature was increased at a rate of 300 ° C./hour, the temperature was increased to 1300 ° C. in an argon gas stream. Thereafter, the mixture was gradually cooled to room temperature to obtain a colorless and transparent fiber.

[0015] The obtained fiber was put into agate milk loaf, pulverized, and subjected to elemental analysis by fluorescent X-ray analysis. As a result, the oxygen content was 5.8% by weight. When a single fiber was evaluated at room temperature using a tensile tester, the tensile strength was 2.5 G
Pa.

Example 2 A polycarbosilane fiber having a diameter of 20 μm obtained by using a spinning apparatus was irradiated with 15 MGy γ rays in an argon gas atmosphere to make it infusible. The infusibilized fiber after irradiation is heated from room temperature to 1100 ° C. in an ammonia gas atmosphere under no tension and then heated in a nitrogen gas stream preheated to 1200 ° C.
The temperature was raised to 0 ° C. Thereafter, the mixture was gradually cooled to room temperature to obtain a colorless and transparent fiber.

The obtained fiber was put into agate milk loaf and pulverized, and subjected to elemental analysis by fluorescent X-ray analysis. As a result, the oxygen content was 6.0% by weight. When a single fiber at room temperature was evaluated using a tensile tester, the tensile strength was 2.8 G
Pa.

Comparative Example 1 A polycarbosilane fiber having a diameter of 17 μm obtained by using a spinning apparatus was irradiated with 20 MGy α rays in an argon gas atmosphere to make it infusible. Irradiated infusibilized fiber is heated from room temperature to 700 ° C. in an ammonia gas atmosphere under tension without tension.
After the temperature was raised at a rate of ° C / hour,
The temperature was raised to 000 ° C. Then, when gradually cooled to room temperature, white fibers mixed with black were obtained.

The obtained fiber was put into agate milk plum and pulverized, and subjected to elemental analysis by fluorescent X-ray analysis. As a result, the oxygen content was 15% by weight. When a single fiber was evaluated at room temperature using a tensile tester, the tensile strength was 1.2 G.
Pa.

Comparative Example 2 A polycarbosilane fiber having a diameter of 19 μm obtained by using a spinning device was irradiated with a 3MGy electron beam in a helium gas atmosphere to make it infusible. The infusibilized fiber after irradiation is 300 ° C. from room temperature to 1400 ° C. in an ammonia atmosphere under no tension.
/ Hour after heating at a rate of 1500 hours in a nitrogen gas stream.
The temperature was raised to ° C.

The obtained fiber is very brittle, and it is presumed that crystallization has started.

Example 3 A polycarbosilane fiber having a diameter of 18 μm obtained by using a spinning device was irradiated with an electron beam of 15 MGy in a helium gas atmosphere to make it infusible. Irradiated infusibilized fiber under ambient temperature in an ammonia atmosphere at 300 ° C. from room temperature to 800 ° C.
/ Hour and maintained for 1 hour, then continuously switched to nitrogen gas atmosphere without touching the air, 800
The temperature was increased from 300 ° C. to 1200 ° C. at a rate of 300 ° C./hour and maintained for 1 hour. Thereafter, the mixture was gradually cooled to room temperature to obtain a colorless and transparent fiber.

The obtained fiber was put in agate milk powder and pulverized, and subjected to elemental analysis by fluorescent X-ray analysis. As a result, the oxygen content was 6.0% by weight. When a single fiber at room temperature was evaluated using a tensile tester, the tensile strength was 2.1 GP.
a.

Example 4 A polycarbosilane fiber having a diameter of 18 μm infusibilized in the same manner as in Example 3 was blown from a room temperature to 800 ° C. while blowing an ammonia stream preheated to 800 ° C. under no tension.
The temperature is raised at a rate of 00 ° C./hour and maintained for 1 hour, and then raised from 800 ° C. to 1200 ° C. at a rate of 300 ° C./hour while continuously blowing a nitrogen gas stream preheated to 1200 ° C. without contacting the atmosphere. Warmed and held for 1 hour. Thereafter, the mixture was gradually cooled to room temperature to obtain a colorless and transparent fiber.

The obtained fiber was put in agate milk powder and pulverized, and subjected to elemental analysis by fluorescent X-ray analysis. As a result, the oxygen content was 2.8% by weight. When a single fiber at room temperature was evaluated using a tensile tester, the tensile strength was 3.2 GP.
a.

Example 5 A polycarbosilane fiber having a diameter of 18 μm, which was made infusible in the same manner as in Example 3, was heated from room temperature to 800 ° C. at a rate of 100 ° C./hour in an ammonia atmosphere without tension.
Hold for a period of time, then switch to nitrogen gas atmosphere continuously without exposure to air,
The temperature was raised at a rate of 00 ° C./hour and maintained for 1 hour. Thereafter, the mixture was gradually cooled to room temperature to obtain a golden white fiber.

The obtained fiber was put in agate milk powder and pulverized, and subjected to elemental analysis by fluorescent X-ray analysis. As a result, the oxygen content was 9% by weight. When a single fiber at normal temperature was evaluated using a tensile tester, the tensile strength was 1.5 GPa.

Comparative Example 3 A polycarbosilane fiber having a diameter of 18 μm, which was made infusible in the same manner as in Example 3, was heated from room temperature to 400 ° C. at a rate of 300 ° C./hour in an ammonia atmosphere under no tension.
Hold for a while, then switch to nitrogen gas atmosphere continuously without touching the air,
The temperature was raised at a rate of 0 ° C./hour and maintained for 1 hour. afterwards,
The mixture was gradually cooled to room temperature to obtain a white fiber mixed with black.

The obtained fiber was put into agate milk loaf, pulverized, and subjected to elemental analysis by fluorescent X-ray analysis. As a result, the carbon content was 50% by weight and silicon carbide was obtained.

[0030]

As described above, according to the present invention, a polycarbosilane fiber which has been infusibilized by irradiation with ionizing radiation is subjected to a nitriding treatment in an ammonia atmosphere at 500 ° C. or higher, and then to 1200 The baking treatment is performed in an inert gas atmosphere at 1400 ° C., and high-purity and high-strength silicon nitride fibers having an oxygen content of 10% by weight or less and a tensile strength of 1.5 GPa or more can be obtained.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Ishigami 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside Power System Research Laboratories, Hitachi, Ltd. (72) Inventor Seiji Kamimura Hidaka-cho, Hitachi City, Ibaraki Prefecture 5-1-1, Nippon Electric Wire & Cable Co., Ltd. Power System Research Laboratory (72) Inventor Kiyoshi Watanabe 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Pref. Nippon Electric Wire & Cable Co., Ltd. Power System Research Laboratory (72) Inventor Yagyu Hideki 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside the Power System Research Laboratories, Hitachi, Ltd. (56) References JP-A-2-258611 (JP, A) JP-A-2-258612 (JP, A) JP-A-1-139819 (JP, A) JP-A-63-235526 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D01F 9/10

Claims (4)

(57) [Claims] 1. A polycarbosilane fiber which has been infusibilized by irradiation with ionizing radiation is nitrided in an ammonia atmosphere at 500 ° C. or higher, followed by 1200 to 1400
A method for producing a silicon nitride fiber, comprising: performing a baking treatment in an inert gas atmosphere at a temperature of 10 ° C. to obtain high-purity silicon nitride having an oxygen content of 10% by weight or less and a tensile strength of 1.4 GPa or more. 2. The sintering temperature in the ammonia atmosphere is as follows:
The method for producing a silicon nitride fiber according to claim 1, wherein the temperature is 500 to 1400C. 3. The temperature rising rate in the ammonia atmosphere and the temperature rising rate in the inert gas atmosphere are both 200 ° C.
3. The method for producing a silicon nitride fiber according to claim 1 or 2, wherein 4. The method for producing silicon nitride fibers according to claim 1, wherein after the nitriding treatment in an ammonia atmosphere, the sintering treatment is carried out continuously in an inert gas atmosphere without being exposed to the air.