JP2843617B2 - Method for producing high-strength silicon carbide ceramic fiber by radiation oxidation - Google Patents

Description

The present invention relates to a method for precisely controlling the degree of oxidation required for infusibilization by radiation oxidation, and a method for selectively infusibilizing precursor fibers from the surface to the inside. It is to provide a method to do.

(Prior art)

The manufacturing process of silicon carbide fiber based on the production of organosilicon-based polymer compounds is divided into spinning, infusibilization, and calcination.The infusibilization process is performed by heat treatment in an oxidizing atmosphere such as air. Going by the way.

[Problems to be solved by the invention]

However, in this conventional method, it is difficult to control the degree of oxidation at a constant level, and the time required for infusibilization is long, thus limiting the overall manufacturing process.

[Means for solving the problem]

In order to infusibilize the organosilicon-based polymer fiber, radiation is used as a method of reacting oxygen.This feature allows oxidation to be carried out at room temperature, the degree of oxidation can be accurately controlled, and The point is that a distribution can be created in the oxidation. Irradiation generates reactive species, such as radicals and ions, in the polymer fiber almost independently of the temperature, and its concentration is proportional to the radiation dose. In conditions where oxygen is present, oxygen reacts preferentially with these reactive species and is oxidized. When the temperature at the time of irradiation is about room temperature, the rate of thermal oxidation is extremely low, so that the amount of oxidation reaction is almost proportional to the dose of radiation. Therefore, by obtaining this proportional coefficient, the degree of oxidation can be accurately controlled by the irradiation dose.

For example, for polycarbosilane which is one of organosilicon-based polymers, the reaction amount of oxygen due to radiation oxidation is 8 × 10 ⁻⁶ mo per 1 g of polycarbosilane for an irradiation dose of 1 kGy.
From the time of l, oxygen of 1.0% can be reacted at 40 kGy and 10% at 400 kGy.

Next, regarding the distribution of radiation oxidation, the reactive species generated by radiation irradiation are uniform inside the precursor resin, whereas oxygen is supplied from the surface of the fiber. Is completely oxidized in the surface layer of the fiber, and the inside thereof is not oxidized at all. The thickness of the oxide layer is determined by the supply rate of oxygen, that is, the transmission rate to the precursor fiber and the dose rate of radiation. When the cross section of the fiber was examined after radiation oxidation, it was found that the surface layer was oxidized as shown in FIG. 1 and the thickness L of the layer was given by the following equation.

Here, L is [cm], D is oxygen diffusion coefficient [cm ² / S],
S is a solubility coefficient [mol / g.atm]. The oxygen permeability coefficient is the product of D and S. Φ is the amount [mol / g.Gy] of the amount of oxygen reacted in the oxide layer by oblique oxidation. Po ₂ is the oxygen partial pressure [atm] of the fiber atmosphere under irradiation, and I is the dose rate.

For example, when the gamma ray is irradiated at a dose rate of 10 KGy / h (2.78 Gy / s) in an atmosphere having an oxygen partial pressure of 300 torr, the oxide layer has a thickness of 5 μm.
m, and at the same oxygen partial pressure, the electron beam is 250KGy / h (69.4Gy
/ s), the thickness of the oxide layer is 1 μm.

As described above, the present invention is a method in which the infusibilized layer due to oxidation can be arbitrarily changed by selecting the oxygen partial pressure and the dose rate. Also, as can be seen from equation (1),
Since the diffusion coefficient and solubility coefficient of oxygen change with temperature, the oxide layer can be changed even when the irradiation temperature is changed. By applying this method in combination under various conditions, it becomes possible to give oxidative infusibility in the fiber in a distribution.

When the fiber oxidized and made infusible by the above method is fired, the characteristics of the obtained silicon carbide-based ceramic fiber depend on the oxygen concentration distribution at the time of making it infusible. This is because most of the oxygen taken in during the infusibilization remains in the ceramic-modified fiber. The ceramic fiber obtained from the infusible one by oxidation of the surface layer alone has a high concentration of oxide distributed in the surface layer, and has an atomic composition different from that of the inside. When it is necessary to modify the surface of the ceramic fiber or the like, the ceramic fiber obtained by oxidizing only such a surface layer is a characteristic material.

〔The invention's effect〕

According to the above-mentioned invention, the step of infusibilization is shortened and uniform infusibilization is possible, and the uniformity of the final product is significantly improved. In addition, by partially infusifying the surface layer of the fiber, the production of ceramic fibers having special characteristics can be expected. Further, only the surface layer is made infusible, and by baking at a high temperature, a portion that is not oxidized inside can be manufactured as a high heat resistant fiber.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

Example 1 As a precursor polymer of a silicon carbide fiber, a fiber of polycarbosilane was irradiated with Co-60 gamma ray at room temperature under an atmosphere of an oxygen pressure of 600 torr at a dose rate of 10 KGy / h (2.78 Gy / s).
After irradiating for 40 and 50 hours, it was baked at 1200 ° C. in an argon stream. In each case, a silicon carbide fiber was obtained and had a strength of 3 to 4 GPa.

The concentration of oxygen in the polycarbosilane fiber after the gamma ray irradiation increased in proportion to the dose, and the weight of oxygen was 0.1 g with respect to 1 g of the unirradiated sample at 400 kGy.

Example 2 Gamma ray dose rate of 10KGy / h (2.78G) was applied to the same polycarbosilane fiber at room temperature under an atmosphere of oxygen pressure of 300 torr.
y / s) for 30,40,50h, then 1200 ℃ in argon stream
Was fired. In each case, a silicon carbide fiber is obtained,
Its intensity was 4 to 5 GPa (maximum value of 5 GPa when infused by 300 kGy irradiation).

When infusibilized under these conditions, the oxide layer is about 4.8 from the surface.
μm, and it was found that the center of the fiber of about 15 μm was not oxidized.

Example 3 The same polycarbosilane fiber was irradiated with an electron beam in an atmosphere at an oxygen pressure of 600 torr. Electron beam acceleration voltage 2MeV, dose rate 1.
After irradiation at 25 MGy / h (350 Gy / s) for 1,000, 2,000 and 3,000 seconds, firing was performed at 1200 ° C. in an argon stream. The strength of the obtained silicon carbide fiber was 3 to 4 GPa. In addition, when irradiation was performed under these conditions, the sample temperature had risen to 50 to 60 ° C. However, the total amount of oxidation was 1/3 of that in Example 1, and the thickness of the oxide layer was estimated to be 1.2 μm. (1) The diffusion coefficient of oxygen is about three times higher than that of gamma-ray irradiation because the temperature of polycarbosilane is increased by electron beam irradiation.
It is larger than the value calculated from the formula.

Comparative Example 1 The same polycarbosilane resin as in Example 1 was thermally oxidized at 180 ° C. to obtain an infusible fiber having an oxidation content of 10%, and then silicon carbide obtained when the same firing as in Example 1 was performed. The fiber strength was 2.5-3.5 GPa.

[Brief description of the drawings]

FIG. 1 is a diagram showing an oxidized cross section of a fiber after radiation oxidation. 1 ... precursor fiber, 2 ... cross section, L ... thickness of oxide layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-106719 (JP, A) JP-A-54-82435 (JP, A) JP-A-53-103025 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) D01F 9/10

Claims (5)

(57) [Claims] A precursor fiber obtained by spinning an organosilicon polymer compound is ionized in a gas atmosphere in which oxygen is mixed with pure oxygen, air, or an inert gas such as helium gas or hydrogen gas. Irradiating a radiation to form an infusibilized layer by oxidation, and then sintering the same in an inert gas atmosphere such as nitrogen gas to produce a high heat-resistant silicon carbide ceramic fiber; When irradiating, by selecting the oxygen partial pressure in the atmosphere and the dose rate of ionizing radiation based on the following formula, the thickness of the oxidized and infusible layer of the precursor fiber is appropriately changed and internally. A highly heat-resistant silicon carbide-based ceramic fiber characterized by having a non-oxidized portion and forming a different atomic composition based on the oxygen concentration inside the fired ceramic fiber. Method. In the above formula, L is the thickness (cm) of the oxidized and infusible layer, D
Is the oxygen diffusion coefficient (cm ² / s), and S is the oxygen solubility coefficient (m
ol / g · atm), DS is the permeability coefficient of oxygen, Φ is the amount of oxygen (mol / g · G) reacting in the oxidized and infusible layer by radiation oxidation.
y), P _O2 is the oxygen partial pressure of the fiber atmosphere under irradiation (at
m) and I indicate the dose rate (Gy / s). 2. The heat-resistant silicon carbide-based material according to claim 1, wherein the radiation for infusibilization is gamma ray or electron beam, and the dose rate is 0.1-100 Gy / s and the irradiation dose is 10 ⁴ -10 ⁷ Gy. A method for producing ceramic fibers. 3. The method according to claim 1, wherein the firing temperature is in the range of 800-1500 ° C. 4. The method of making a precursor fiber infusible by radiation oxidation,
The highly heat-resistant silicon carbide according to any one of claims 1 to 3, wherein the heat treatment is selectively performed inside the fiber, and the thickness of the oxide layer can be arbitrarily adjusted from 0.1 µm to the center of the fiber diameter from the surface layer. A method for producing ceramic fibers. 5. The high heat-resistant silicon carbide according to claim 1, wherein the concentration or amount of oxygen when the precursor fiber is oxidized by radiation can be arbitrarily selected from 0.05 to 30% by weight. A method for producing a ceramic fiber.