JP2877424B2 - Method for producing ceramic fiber and coating material by radiation oxidation infusibilization of precursor polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention uses a radiation oxidation method to infusibilize a precursor of a ceramic fiber, a ceramic paint, and a coating material, and to significantly reduce the strength of the precursor. Since it can be improved, the step of ceramicization can be simplified. Also,
Since the ceramic can be formed under tension, a high-strength ceramic material can be manufactured.

[Conventional technology]

The process of producing ceramic fibers such as silicon carbide produced using polymer fibers as a precursor, which is performed as a conventional technique, is performed by infusibilizing the fibers by thermal oxidation or crosslinking by irradiation, and then in an inert gas. Firing,
This is a method of making a ceramic.

[Problems to be solved by the invention]

However, in the method of the prior art, in the case of thermal oxidation, infusibility can be achieved, but the strength of the precursor fiber does not increase, and the fiber is cut in the subsequent firing step. In addition, the radiation infusibility increased the strength of the precursor fiber by about 10 times, but was not yet strong enough to apply tension to the fiber. In the case of paints and coating materials, cracks occurred in the initial stage of firing, and a uniform film could not be obtained.

[Means for solving the problem]

The infusibilization of the ceramic fiber and the precursor polymer of the paint is performed at room temperature by radiation oxidation, and as a method of improving the strength of the infusibilized one, radiation-oxidized one is used.
By performing heat treatment in the range of 0 ° C. to 500 ° C. and performing cross-linking by a thermal decomposition reaction of an oxidation product, the strength of the precursor can be remarkably improved before the ceramic formation.

[Action]

When the precursor polymer is irradiated in an oxygen atmosphere, radicals or ions induced by the polymer easily react with oxygen, and most of the oxygen is taken into the polymer, and part of the oxygen is converted to carbon dioxide or water. It is released as decomposition gas. At this time, cleavage of the polymer is caused. As a result, the molecular weight of the polymer will generally decrease,
Mechanical properties tend to decrease. Therefore, the precursor polymer is dissolved when immersed in a good solvent for the polymer after radiation oxidation of the polymer.

When the radiation-oxidized precursor polymer is heated, oxygen bonded to the polymer chain is decomposed, causing cross-linking between the polymers.

Radiation oxidation generates radicals or ions uniformly in the polymer, so in the oxidized region,
Compared to thermal oxidation, oxygen is more uniformly dispersed and bonded to the polymer, so if this is thermally decomposed and causes crosslinking, the distribution will be similar to that of crosslinking by irradiation in vacuum, As macromolecules increase in density. Therefore, when the molecular weight of the precursor polymer is relatively small and the tensile strength is low, it is considered that the strength is increased by converting to a macromolecule. This is confirmed by the fact that the radiation-oxidized polycarbosilane is gelled when thermally decomposed and crosslinked.

It is also possible to make the infusibilization by radiation oxidation non-uniform macroscopically. That is, only the surface layer of the fiber can be made infusible. Applying this principle, the infusibilized fiber is heat-treated to gel the infusibilized part, and then immersed in a good solvent to remove the infusibilized part (in the case of fiber, Core part) can be extracted. Thereafter, by firing with an inert gas, a cylindrical ceramic fiber is obtained. The principle is shown in FIG.

First, the precursor polymer fiber 1 is radiation-oxidized to form a radiation-oxidized region 2 on the surface. By subjecting the fibers to heat treatment, oxidative crosslinking occurs in the region 2 to form an oxidative crosslinked region 3.

Thereafter, the fibers are subjected to a solvent extraction treatment to dissolve and remove portions other than the crosslinked region to form hollow fibers to obtain a cylindrical shape. This is further baked and turned into a ceramic to obtain a cylindrical ceramic fiber 5.

Note that this cannot be performed at all by the thermal oxidation infusibilization. That is, the strength of the polymer does not increase even after the heat treatment, and the oxidized region cannot be controlled.

〔The invention's effect〕

According to the present invention, the infusibilization and subsequent sintering become extremely easy because the strength of the precursor is increased, and ceramic fibers having uniform properties can be obtained.

In addition, a ceramic fiber having a complicated structure such as a cylindrical shape can be manufactured, and functionality can be imparted.

Example 1 As a precursor of a silicon carbide fiber, a polycarbosilane fiber having a diameter of 10 μm was irradiated with Go-60 gamma ray at room temperature in an atmosphere of 600 torr oxygen at a dose rate of 2.78 Gy / s for 30, 40, 50 hours ( h) After irradiating, hold in air at 300 ° C. for 30 minutes in air, take out at room temperature, and measure the strength of the fibers. All the fibers have strength of 20-50 MPa,
It increased 100 to 500 times compared to before heat treatment. The heat-treated fiber was immersed in tetrahydrofuran for 1 hour at room temperature, and the amount of extraction was measured. As a result, it was 3% or less, and the fiber strength was hardly displaced by the extraction. The strength of the silicon carbide fiber obtained by calcining (1200 ° C.) with this in an argon stream was 3 to 4 GPa.

[Example 2] The same polycarbosilane fiber as in Example 1 was replaced with 600 torr of oxygen.
In an atmosphere of, the electron beam was irradiated at an acceleration voltage of 2 MeV and a dose rate of 350 Gy / s at 0.6 and 0.81.0 MGy. This was heat treated at 300 ° C. for 30 minutes in argon. The strength when taken out into the air at room temperature was 20 to 40 MPa. It was 100-400 times higher than before heat treatment. When extracted with tetrahydrofuran, the gelation ratio was 30 to 60%, and the higher the dose, the higher the value. The silicon carbide fiber obtained by firing this sample in an argon stream (1200 ° C.) had a strength of 2 to 3 GPa.

[Brief description of the drawings]

FIG. 1 is a process chart for producing a cylindrical ceramic fiber by carrying out the method of the present invention. 1 ... precursor polymer fiber, 2 ... radiation oxidation region, 3 ... crosslinking (gelling) region by oxidation, 4 ... hollowed portion, 5 ... cylindrical ceramic fiber.

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Claims (4)

(57) [Claims] An ionizing radiation is irradiated in an oxygen atmosphere obtained by diluting a silicon-based polymer fiber or a film with pure oxygen gas or nitrogen gas, and then heat-treated in air or an inert gas. A method for producing a high-strength ceramic fiber and a heat-resistant coating material using the polymer as a precursor, characterized by firing in a gas. 2. The silicon-based polymer fiber is irradiated with ionizing radiation in a pure oxygen or diluted oxygen gas atmosphere, heat-treated in air or an inert gas, and then a soluble portion is extracted with a silicon-based polymer solvent. And baking in an inert gas to produce a porous or pipe-shaped ceramic fiber using the polymer fiber as a precursor. 3. Irradiation with ionizing radiation (X-ray, γ-ray, electron beam, high-energy ion, etc.) is carried out at -78 ° C. at a dose rate of 0.1 to 100 Gy / S and an integrated dose of 10 ⁴ to 10 ⁷ Gy. The oxidation method according to claim 1 or 2, wherein radiation is induced by performing the treatment at a temperature of from + 200 ° C. 4. A method for producing a high-strength ceramic fiber and a heat-resistant coating material, wherein the strength of a fiber or the like is improved by irradiating a precursor fiber such as a silicon-based polymer fiber with ionizing radiation.