JP2712698B2 - Method for producing C / C composite material by composite gas phase impregnation method - Google Patents

Description

The present invention relates to a method for producing a C / C composite material having excellent strength and toughness.

[Prior art] Carbon fiber has high tensile strength, and utilizing this property, carbon fiber reinforced carbon (hereinafter abbreviated as C / C) in which carbon fiber is combined with another carbonaceous material. There are composites. Such C / C composites have several times the strength of conventional carbon materials and change the image of carbon materials as brittle and weak materials, and their high strength, heat resistance and abrasion resistance It is a material that is expected to be widely used in fields such as the electronics industry, nuclear power industry, and aerospace industry, taking advantage of such physical properties.

As a method for producing this type of composite material, for example, a carbon fiber tow, a woven fabric, a nonwoven fabric, or the like obtained by carbonizing cellulose or polyacrylonitrile-based fibers is formed into a required shape with a thermosetting resin, and then formed. There is known a method in which a resin is carbonized by heat treatment in an active gas atmosphere, and if necessary, after cooling, the same process is repeated again (for example, carbon No. 115, pages 196 to 208, (1983)). .

The C / C composite material obtained by this method is excellent in impact resistance, and is practically used because it is relatively inexpensive. However, since the volume shrinkage is extremely large in the carbonization step by the heat treatment of the resin, it is impossible to completely remove the fibers from falling out or cracking and the residual pores depending on the conditions. Insufficient toughness. As another method, as shown in FIG. 4, a carbon fiber tow, knitted woven fabric, non-woven fabric, etc. obtained by carbonizing cellulose or polyacrylonitrile fiber is easily formed into a preform (13). Into a furnace (15) equipped with a heater (14) and heated to 800 to 2000 ° C., where hydrocarbon gas is introduced from an inlet (16) to be decomposed and carbonized on the carbon fiber surface, and the carbon is removed. There is known a method of depositing and hardening on a fiber surface (hereinafter, this method is referred to as a CVD method). (1
7) is a gas outlet.

The C / C composite material obtained by the CVD method is C / C obtained by the above method.
Although it has better mechanical properties than the C composite material, the reactive gas cannot be sufficiently impregnated into the preform (13), that is, the inside of the preform, and there are many residual pores in the inside of the preform and the strength properties are low. It was not enough. The following can be considered as a cause of this. Hydrocarbon gas is continuously supplied into the reaction vessel, the gas initially supplied into the vessel is impregnated into the preform (13), and carbonaceous material is deposited by thermal decomposition. However, since the gas generated after the reaction stays in place, impregnation of the new reactable hydrocarbon gas into the preform (13) is hindered, so that the inside of the preform (13) and the surrounding containers And a concentration gradient having a large difference is generated. In addition, the gas inlet (1
Since there is always a pressure gradient between the 6) side and the discharge port (17) side, the gas flow is constant according to this gradient, and is not the inside of the preform (13) but the discharge port (17).
It will flow toward the side. These two gradients prevent sufficient infiltration of the hydrocarbon gas into the preform (13), and the carbonaceous deposition concentrates from the inside of the preform (13) to the outside, resulting in heterogeneous decomposition and deposition. This is because there are many residual pores inside the molded product, and only a molded product having low strength characteristics can be obtained. In addition, it takes a long time to form a composite, and it is difficult to efficiently produce a molded article having a complicated shape. Further, as an improved method, a process is known in which a carbon fiber mat is impregnated with pitches, heated and carbonized, and the porous portion is filled with pyrolytic carbon to obtain a composite material. However, these methods still suffer from strength problems due to non-uniform matrix carbonaceous material,
There is a need for better manufacturing methods.

[Problems to be Solved by the Invention] In a conventional method for producing a C / C composite material, a carbon-based fiber is used as a starting material, and impregnation with a resin is performed on a molded article formed into a desired shape such as a woven fabric. Filling of carbonaceous material by sintering, single heating method, or CVD by source gas supply method, resulting in insufficient mechanical properties due to residual pores, low efficiency during production, and the shape of the compact However, there was a problem that constraints such as size were inevitable.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to almost completely eliminate the residual pores of the molded body, improve the strength, and achieve high-speed molding by the composite-type gas-phase impregnation. It is intended to make it possible.

[Means for Solving the Problems] A method for producing a C / C composite material by a composite gas-phase impregnation method according to the present invention is a method for producing a carbon-based fiber as a reinforcing material, using a hydrocarbon gas and a hydrocarbon gas containing a halogen element. In producing a C / C composite material by pyrolyzing at least one raw material gas and depositing and filling the generated carbonaceous material, it is excited by light or electromagnetic waves to accelerate the reaction, and intermittently supplies the gas. At least one of the methods is further added.

[Action] In the method for producing a C / C composite material by the composite gas-phase impregnation method in the present invention, a tow of carbon-based fiber or a preform mainly composed of carbon-based fiber is introduced into a reaction vessel and heated. At the same time, a hydrocarbon raw material gas is introduced to cause a decomposition reaction, and further, for example, microwaves are superimposed to efficiently realize decomposition, and deposition and filling of carbonaceous material.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing a manufacturing method of the present invention.

Carbon fiber tow made from rayon, polyacrylonitrile, petroleum or coal pitch (1) (10 fibers
A bundle of 0 to 20,000 fibers) is introduced into the reaction vessel (3), and a hydrocarbon gas such as methane, ethane, propane, or benzene is supplied from the inlet (6) as a raw material gas. First, an electric current is applied to the fiber tow (1) through the electrode (4) to heat the fiber tow itself. (5)
Is a seal portion, and (7) is a gas outlet. At this stage, the thermal decomposition of the raw material gas proceeds to decompose and deposit carbonaceous material in the space of the fiber tow, but the filling efficiency is not sufficient.
Therefore, the microwave of 2000 to 3000 MHz generated by the magnetron (8) is further superimposed through the waveguide (9). At this time, it was effective to generate hydrogen plasma. At this stage, decomposition and deposition of the raw material gas are remarkably promoted, and complete densification and high-speed production of the composite material become possible. In this example, the partial pressure of methane was set to 20 to 200 Torr and the fiber temperature was set to 700 to 1400 ° C. However, the effect of the superimposed microwave enabled a good filling of carbonaceous material at a relatively low temperature, ie, 700 to 1000 ° C. Particularly good results were obtained when the methane partial pressure was in the range of 40 to 80 Torr. Similar results have been obtained with other hydrocarbons as the raw material gas, but similar results have been obtained with dichloroethylene and the like at lower temperatures (700 ° C. or lower). When manufactured only by pyrolysis in a conventional method, even a composite material having a small volume such as a fiber tow requires a high temperature and a long time. Fig. 2 shows the combined method of pyrolysis and microwave
It is the result which compared the change with respect to the reaction time of the carbonaceous filling amount at the time of producing a C / C composite material with the change with respect to the reaction time of the carbonaceous filling at the time of the conventional C / C composite material production by thermal decomposition alone. The vertical axis represents the carbonaceous content (arbitrary scale), and the horizontal axis represents the reaction time (arbitrary scale). The curve (a) in the figure shows a graph of a method for producing a C / C composite material by the composite gas-phase impregnation method according to the present invention, and the curve (b) shows the result of a conventional production method. In the conventional method, when decomposition and deposition progress to some extent, closed pores are formed, and the filling does not proceed. On the other hand, in the composite method, carbonaceous filling is performed until the residual pores reach almost zero. As a result, the bending strength of the obtained C / C composite material was 450 MPa or more when the volume ratio of the carbon fiber was about 50%. This combination scheme is also possible with other combinations,
For example, heating by high frequency from outside the reaction vessel,
Further, there is a method of exciting the fiber portion with light or electromagnetic waves to promote the reaction. The filling of the carbonaceous material into the fiber tow was possible by any of the methods. In particular, the method of direct energization to the fiber and the combined method of microwaves were simple and efficient. FIG. 3 shows another embodiment of the present invention, in which the supply of the raw material gas is performed intermittently (in a pulsed manner) instead of the continuous and steady supply generally performed in the ordinary gas phase impregnation method. In the form). That is, the fiber tow (1) is introduced into the reaction vessel (3), and the raw material gas is introduced into the reaction vessel (3).
The gas pressure is increased (controlled) by, for example, accumulating gas in the reactor, and the reaction vessel (3) is depressurized by an exhaust system. In this state, the valve (10) of the gas introduction line (6) is opened to release the gas accumulated in the reservoir tank (11) at a stretch, thereby increasing the gas pressure in the reaction vessel at a stretch. After the gas has been supplied in this manner, the supply is temporarily stopped, and when the pressure in the reaction vessel is reduced, the gas is released into the reaction vessel at once, and the gas pressure is increased at a stretch. By repeating this and supplying the gas intermittently (in a pulsed manner), it is possible to prevent a pressure gradient and a concentration gradient of the raw material gas from being generated in the reaction vessel.
Since the deposition of carbonaceous material inside is sufficiently and efficiently performed, the decomposition and deposition of carbonaceous material can be uniformly performed on the entire tow (1) without being concentrated outside the tow (1). In addition, when the inside of the reaction vessel is depressurized during the gas supply suspension period, the reacted gas remaining inside and near the tow (1) is sufficiently exhausted, so that new gas is discharged from the tow (1). ) Fully impregnated inside. Since the gas is sufficiently impregnated into the inside of the preform, the carbonaceous material can be decomposed and deposited with uniform pores in the inside of the preform. Further, the gas is activated by microwaves generated by the magnetron (8) to promote decomposition and precipitation. In FIG. 3, (12) is a raw material gas cylinder,
(9) shows a waveguide, (7) shows a gas outlet, and (2) shows the obtained C / C composite material. The resulting C / C composite material has good carbonaceous texture uniformity and has an effect of preventing the occurrence of defects that cause strength deterioration. In addition, the product quality of C / C composite material is kept constant and the yield is improved.

In this example, the production of the rod-shaped C / C composite material was described using a carbon fiber tow as a starting material.However, for example, the rod-shaped C / C composite material obtained here was used as a starting material. A preform molded into the shape of the above, that is, a molded product formed into a woven or knitted material can be similarly carried out in a manufacturing process of filling carbonaceous material with a single heating method or an excitation method, a gas supply method. The performance was improved as compared with the case of manufacturing by the method described above.

As the raw material gas, a hydrocarbon gas containing a halogen element such as chlorine in addition to the above-mentioned hydrocarbon gas is used alone or in combination.

[Effects of the Invention] As described above, according to the present invention, a carbon-based fiber is used as a reinforcing material, and a raw material gas composed of at least one of a hydrocarbon gas and a hydrocarbon gas containing a halogen element is thermally decomposed.
When depositing and filling the generated carbonaceous material to produce a C / C composite, it is excited by light or electromagnetic waves to accelerate the reaction,
By additionally adding at least one of a method of intermittently supplying gas and carbon, the carbonaceous material can be completely tightly packed to produce a high-performance C / C composite material. Also,
By adopting this manufacturing method, C /
There is an effect that a C composite material can be obtained stably.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the production method of the present invention, FIG. 2 is a graph showing the measurement results of the filling rate of carbonaceous material, FIG. 3 is an explanatory view showing another embodiment of the present invention, and FIG. It is explanatory drawing which shows the conventional manufacturing method. In the figure, (1) is a carbon fiber tow, (2) is a C / C composite material, (3) is a reaction vessel, (4) is an electrode, (5) is a seal, (6) is a raw material gas inlet, (7) is a gas outlet,
(8) is a magnetron, (9) is a waveguide, (10) is a valve, (8) is a magnetron, (9) is a waveguide, (10) is a valve, (11) is a reservoir tank, (12) Is a raw material gas cylinder, (13) is a preform, (14) is a heater, (15)
Is a furnace, (16) is a gas inlet, and (17) is a gas outlet. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] C / C for thermally decomposing a raw material gas comprising at least one of a hydrocarbon gas and a hydrocarbon gas containing a halogen element using carbon-based fibers as a reinforcing material, and depositing and filling the generated carbonaceous material. In the method for producing a composite material, when the raw material gas is thermally decomposed to deposit and fill carbonaceous material, the reaction is excited by light or electromagnetic waves to accelerate the reaction, and at least one of intermittent gas supply methods is applied. A method for producing a C / C composite material by a composite gas-phase impregnation method, characterized in that: