JP2574179B2 - Method for producing super heat resistant high strength silicon carbide fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a silicon carbide fiber having a high strength, a high elastic modulus and a very high heat resistance, which is made of an organic silicon polymer compound such as polycarbosilane. It relates to a manufacturing method.

(Prior art and its problems) The production process of silicon carbide fiber produced using an organosilicon polymer compound as a precursor can be divided into spinning, infusibilization and firing.

The spinning step is a step in which an organosilicon polymer compound such as polycarbosilane is melt-spun to obtain a thin precursor.

The infusibilization step is a step in which the precursor fiber is heat-treated in an oxidizing atmosphere, generally in the air, to cause a crosslinking reaction to make the fiber insoluble and infusible.

The firing step is a step of obtaining a silicon carbide fiber by subjecting the fiber subjected to the infusibilization treatment to a high temperature treatment at about 1200 ° C. in an oxygen-free atmosphere or under vacuum to make it inorganic.

However, in this conventional method, the organosilicon polymer compound is made infusible by crosslinking with an oxygen, so that the obtained silicon carbide fibers contain 8 to 20% of oxygen. Therefore, the silicon carbide fiber obtained by the conventional method is 1300
At temperatures higher than ℃, the CO removal reaction and the coarsening of silicon carbide crystal particles occur, so that the fiber strength deteriorates remarkably especially at temperatures above 1500 ° C.

In the case of infusibilization by radiation as disclosed in JP-A-53-103025, when irradiation is performed in the presence of oxygen, 7 to 30% of oxygen is released in the same manner as the silicon carbide fiber obtained from the above-mentioned thermal oxidation method. Similar problems arise.

Therefore, when the precursor fibers are irradiated in a non-oxidizing atmosphere or in a vacuum, the introduction of oxygen is relatively small. However, it has been confirmed that a large amount of radicals are present in the body polymer even after the end of the irradiation. When the radicals are taken out into the air, the radicals and oxygen react promptly, and the fiber obtained by sintering eventually has 4 to 12% Will contain a significant amount of oxygen.
Firing after infusibilization without taking it out to the atmosphere is industrially extremely inefficient in operation.

(Object of the Invention) An object of the present invention is to solve the above-mentioned problems and to provide a method for producing a high-strength silicon carbide fiber having extremely high heat resistance.

(Constitution of the Invention) The object of the present invention as described above is to make the precursor fiber obtained by spinning an organosilicon polymer compound infusible by irradiating it under an oxygen-free atmosphere or under vacuum, and then convert the precursor fiber to oxygen. It irradiated with an electron beam under an oxygen-free atmosphere without contacting or under vacuum at 1.1 to 10 ⁷ times the radiation dose rate at the time of the infusible, was deactivated by heating the fibers to 200 ° C. or higher It is achieved by firing in an oxygen-free atmosphere or under vacuum.

The method of the present invention has a great feature in that the precursor fibers are not brought into contact with oxygen from the start of irradiation with radiation until the cooling is completed after the inert treatment.

That the precursor fiber since the crosslinking reaction does not oxygen involvement occurs by irradiation under or under vacuum oxygen-free atmosphere infusibilization is achieved, subsequently during infusibilized radiation dose rate 1.1 to 10 ⁷ times Under an oxygen-free atmosphere or under vacuum to perform an inert treatment to irradiate the fiber to 200 ° C or more by performing electron beam irradiation, the remaining radicals disappear, even if the fiber is cooled and even taken out to the atmosphere Inert with respect to the reaction with oxygen. Therefore, the silicon carbide fiber obtained after firing is 1 to 3 compared to the conventional method.
%, The oxygen content is remarkably small, and even at a high temperature of, for example, 1500 ° C., almost no CO removal reaction and coarsening of silicon carbide crystal particles occur. Thus, high-strength silicon carbide fibers having extremely excellent heat resistance can be efficiently produced.

As a starting material in the method of the present invention, an organosilicon polymer compound having the following structures (a) to (d) containing silicon and carbon as main skeleton components is used. The low-molecular polymer contained therein is removed by solvent extraction or the like, or is heated and polymerized or aged to obtain a molecular weight suitable for spinning.

(D) one containing the skeletal component described in the above (a) to (c) as at least one partial structure among a chain, cyclic and three-dimensional structure, or a mixture of (a) to (c). Of the molecular compounds, polycarbosilane is industrially most preferable because it can be obtained by condensing dichlorodimethylsilane, which is the most common and inexpensive in the silicone industry.

The organosilicon polymer compound is used to obtain precursor fibers having a diameter of, for example, 5 to 50 μm by heat spinning or dry spinning using a solution of benzene, xylene, or the like. In order to obtain a high-strength silicon carbide fiber, a smaller diameter is more preferable.

In order to make the precursor fiber infusible in the method of the present invention, ionizing radiation such as electron beam and gamma ray is used.

When performing electron beam irradiation, the electron beam heating voltage is 20 KV to 10
The MV range is preferred. Irradiation dose rate 1 ~ 10 ⁵ Gy / s,
A dose of 0.1-100 MGy is preferred. If the accelerating voltage is less than 20 KV, the penetration power of the electron beam may be weak and the infusibilization treatment of the fiber may be insufficient, and if it exceeds 10 MV, activation may occur,
In addition, the equipment is expensive and not practical.

When the dose rate is less than 1 Gy / s, the infusibilization process takes too long to be uneconomical, and when it exceeds 10 ⁵ Gy / s, the precursor fiber may generate heat and melt, and the fiber shape may not be retained. Yes and inappropriate.

When the dose is less than 0.1 MGy, the infusibilization is insufficient and it melts at the time of firing and the shape cannot be maintained. On the other hand, when the dose exceeds 100 MGy, the infusibilization is sufficient but the irradiation time is long and uneconomical.

The container for holding the fibers is preferably provided with a metal foil on the irradiation surface and having a structure capable of vacuum replacement.

When performing gamma irradiation, using a ⁶⁰ Co as a radiation source, dose rate 0.1 to 10 ² Gy / s, the dose 0.1~100MGy are preferred. If the dose rate is less than 0.1 Gy / s, the infusibilization process takes too much time and is uneconomical. Conversely, a source exceeding 10 ² Gy / s is not practical.

If the dose is less than 0.1 MGy, it is insufficiently infusibilized and melts at the time of firing, and the shape cannot be maintained. Conversely, if it exceeds 100 MGy, the infusibilization is sufficient but the irradiation time is long and uneconomical.

The container for holding the fibers may have a structure capable of vacuum replacement.

At the time of infusibility, the atmosphere needs to be oxygen-free or vacuum, but heating is not particularly required.

Even after the precursor fiber is made infusible by irradiation with radiation, a large amount of radicals remain, and since it is active, if it is taken out directly into the air, it reacts with oxygen. Therefore, in order to eliminate radicals, the infusibilized fiber is irradiated with an electron beam to rapidly generate heat, thereby performing an inert treatment.

Electron beam irradiation is the radiation dose rate of 1.
Not industrially practical exceeds the upper limit there is no practical effect and suitably smaller than the lower limit of this range is carried out at a dose rate of 1 to 10 ⁷ times. It is important for this inert treatment to raise the temperature of the fiber to 200 ° C. or more by electron beam irradiation, and no other heat source is required.

The temperature of the fiber in the inert treatment may be 200 ° C. or higher, but must not exceed 2200 ° C. Usually 200-1000 ° C is sufficient. If the temperature is lower than 200 ° C, the radical disappearance rate is slow,
On the other hand, when the temperature exceeds 2200 ° C., sublimation of silicon carbide starts and the fibers are decomposed, which is not preferable. Also, 1000
It is not preferable from the viewpoint of energy efficiency to raise the temperature to a temperature higher than the required temperature.

The fiber from which radicals have been eliminated by this inert treatment can, of course, be fired as it is, but if it is taken out to the atmosphere once as usual, it will react with oxygen if it is kept at 100 ° C or higher, so 100 ° C or lower Once cooled, they must be taken out into the air.

Even if the fiber obtained by cooling once to 100 ° C. or less is taken out into the air, it no longer takes in oxygen.

The fibers can then be converted to silicon carbide fibers by firing. The firing temperature is preferably from 800 to 2200 ° C, more preferably from 1000 to 1700 ° C. The firing atmosphere is preferably vacuum, nitrogen, argon or the like. If the firing temperature is lower than 800 ° C., conversion to an inorganic compound is insufficient and the inherent heat resistance of the silicon carbide fiber is not exhibited. On the other hand, when the temperature exceeds 2200 ° C., sublimation of silicon carbide starts and fibers are decomposed, which is not preferable.

(Effects of the Invention) According to the method of the present invention as described above, a high-strength silicon carbide fiber having extremely high heat resistance can be efficiently produced as compared with a conventionally known method, and it can be used for space and aviation. Or, it can be used in the ceramic industry, the steel industry, and other general industrial or consumer use fields which were not previously applicable.

The silicon carbide fiber of the present invention is used as a single fiber, a yarn, a roving cable, a strand, a filament, a chopped filament, and as a woven fabric, a sleeve, a rope by secondary processing because the fiber diameter is small and flexible, and a composite material with metal, ceramics, and the like. For example, when used for fibrous heating elements, fireproof woven fabric, nuclear reactor materials, fusion reactor materials, rocket materials, various refractory materials, etc., they have extremely high strength, high elasticity, light weight, wear resistance, etc. Useful.

(Example) Next, an example of the present invention will be described.

Example 1 Polycarbosilane having a number average molecular weight of about 2,000 was melt-spun as a precursor polymer of silicon carbide fiber, and the average diameter was 12 μm.
m of precursor fibers were obtained.

The precursor fiber was irradiated with an electron beam at a dose rate of 6 × 10 ³ Gy / s and a dose of 9 MGy in a helium stream to make it infusible.

After irradiation, the fibers were not removed into the air, but were continuously heated under a helium stream at a dose rate of 1.5 × 10 ⁴ Gy / s to generate heat at 200 ° C. or higher, thereby performing an inert treatment. The dose at this time is 1MGy
Met. This was allowed to cool to room temperature before being removed.

This infusibilized fiber is heated at a rate of 100 ° C / h in an argon stream at 120
Calcination was performed at 0 ° C. and 1500 ° C. for 1 hour to obtain a silicon carbide fiber.

The characteristics of the silicon carbide fiber after firing Met.

Even after firing at 1500 ° C., there was no significant decrease in fiber strength, and silicon carbide fibers having excellent heat resistance could be produced. Therefore, it can be seen that the silicon carbide fiber obtained in Example 1 has sufficient strength and elastic modulus even when used at 1500 ° C.

Example 2 A precursor fiber was obtained in the same manner as in Example 1, and the precursor fiber was vacuum-sealed in a hard glass tube and irradiated with gamma rays.

The source was irradiated with ⁶⁰ Co at a dose rate of 5.5 Gy / s and a dose of 14 MGy.

The irradiated fiber is irradiated with an electron beam at a dose rate of 9 × 10 ⁴ Gy / s while being encapsulated in a glass tube, and the fiber is heated to 200 ° C. or more to inactivate the fiber, cooled to room temperature, and then cooled. I took out. The dose at this time was 2 MGy.

Subsequently, firing was performed in the same manner as in Example 1 to obtain silicon carbide fibers. The characteristics of the obtained silicon carbide fiber showed excellent heat resistance as in the case of Example 1.

Comparative Example 1 A precursor fiber obtained by the same method as in Example 1 was heat-treated in air at 10 ° C / h at 180 ° C to perform infusibility treatment.

Subsequently, firing was performed in the same manner as in Example 1 to obtain carbon silicon fibers. The obtained silicon carbide fiber showed good strength characteristics when fired at 1200 ° C., but it was too weak to measure the strength when fired at 1500 ° C. and was difficult to handle.

Comparative Example 2 The precursor fiber obtained in the same manner as in Example 1 was similarly irradiated with an electron beam to make it infusible, and the fiber was taken out after cooling to room temperature.

The irradiated fiber was fired in the same manner as in Example 1 to obtain a silicon carbide fiber. The obtained silicon carbide fiber is 1200
The sintering at ℃ C showed good strength characteristics, but the sintering at 1500 ° C showed low strength and poor heat resistance.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Ichikawa 2-5-16 Shodo, Sakae-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Michio Takeda 237 Nishi-Osawa, Osawano-cho, Kamishinkawa-gun, Toyama Prefecture

Claims (4)

(57) [Claims] 1. A precursor fiber obtained by spinning an organosilicon polymer compound is irradiated with radiation in an oxygen-free atmosphere or under vacuum to make it infusible, and then in an oxygen-free atmosphere without contacting with oxygen or the fiber was irradiated with electron beam at 1.1 to 10 ⁷ times the radiation dose rate at the time of the infusible under vacuum
A method for producing a super-heat-resistant high-strength silicon carbide fiber, which comprises performing an inert treatment by generating heat at a temperature of 200 ° C. or higher, and then calcining in an oxygen-free atmosphere or under vacuum. 2. Irradiation at the time of infusibilization uses an electron beam,
Dose rate 1~10 ⁵ Gy / s, the production method of the refractory high-strength silicon carbide fiber of claim 1, wherein the irradiation dose 0.1～100MGy. 3. The ultra-heat-resistant high-strength silicon carbide fiber according to claim 1, wherein the radiation irradiation at the time of infusibility uses gamma rays, and the dose rate is 0.1 to 1.0 × 10 ² Gy / s and the irradiation dose is 0.1 to 100 MGy. Manufacturing method. 4. The method for producing a super-heat-resistant high-strength silicon carbide fiber according to claim 1, wherein the firing temperature is in the range of 800 to 2200 ° C.