JPH0798682B2 - Method for producing high-density carbon composite material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is a technique for producing a higher density carbon material by impregnating a porous carbon molded body with tar / pitch, resin or the like and carbonizing the same. It is used as a new material for the aerospace industry such as rocket nozzles and aircraft brakes.

(Prior Art) In recent years, a composite material of carbon fiber and a carbon material (C / C composite) is rapidly spreading as a new material in the aerospace industry such as a rocket nozzle and an aircraft brake. In addition, because this C / C composite is lightweight, has high strength, has a small heat capacity, and has excellent impact strength,
It is also being used as a furnace structural material for high temperature furnaces used in an inert atmosphere and as a shelf board material.

Further, the quality of conventional graphite materials has been improved in recent years, and the demand for dense materials having fine crystal powder and few pores is increasing.

The biggest technical challenge in the production of these carbon materials is how to achieve high density. In particular, the establishment of high-density technology on an industrial scale has become a major issue in the industry.

As a technology for increasing the density of these materials, there is a technology of impregnating a porous molded body with a carbonaceous substance such as tar / pitch or a resin, and then carbonizing the same.
A method of firing this under atmospheric pressure is used.

As a technique for impregnating tar / pitch and carbonizing under the pressure of high-pressure gas, for example, as shown in FIG.
The technology of rials Inc (USA) is known. In this case C
The target is the / C composite, and this molded body is mainly composed of carbon fiber.

After vacuum impregnating the molded product with tar and pitch at 200 ° C,
Carbonizes tar pitch at 850 ° C under atmospheric pressure. After rough-processing the outer surface of the obtained molded body, it is put together with tar pitch in an airtight can, vacuum impregnated again, and then the can is sealed. Place the sealed can in a high-temperature, high-pressure furnace and raise the temperature with the pressure of argon gas applied from the outside of the can.
Pressurize and finally carbonize at 650 ° C and 10,000 psi (about 700 kg f / cm ² ) temperature and pressure. After carbonization, the can is removed and graphitization is performed.

(Problems to be Solved by the Invention) With regard to the technique shown in FIG. 7, there is no disclosure of the material and shape of the can shown in the diagram, and further, the method of vacuum sealing, etc. When the present inventors produced a can schematically shown in the figure and actually processed it, the following problems were found.

1) The tar / pitch and the resin used for the main impregnation have a high molecular weight, that is, a solid one at room temperature from the meaning of increasing the carbon yield. However, if solid lumps or powders such as tar / pitch are filled in a container, The bulk density is low, and the container is largely deformed by the compression with the gas pressure during the impregnation operation, and the airtightness is impaired, or the treatment material becomes irritated.

2) Steel container (capsule) used in normal HIP
Has a shape as shown in Fig. 6, and its wall thickness is 1 to 2.5 of the diameter.
%, But when such a capsule is used, the impregnation operation is carried out at a relatively low temperature of 200 to 300 ° C. and several hundred to 2000 kg f /
It does not have sufficient deformability with respect to compression at a gas pressure of cm ² , and the container is deformed or broken, and the desired effect cannot be obtained.

In FIG. 6, 1 is a capsule body (container) having a bottom 1A, 2 is a capsule lid, 3 is a deaeration tube, and 4 is a treated product (carbon material molded body).

In the present invention, high pressure is used for this impregnation to impregnate the impregnating material into even fine pores, and the impregnating material is carbonized in a high pressure gas atmosphere to improve the carbon yield as shown in FIG. The purpose is to efficiently produce a high-density carbon material.

(Means for Solving the Problems) According to the present invention, a porous carbon material compact is impregnated with a carbonaceous substance such as tar / pitch or resin, and the impregnated material is carbonized to produce a high-density carbon composite material. In order to achieve the stated purpose, the following technical measures were taken.

That is, the present invention, in a thin container made of an airtight metal material, the carbon material compact is placed with a gap, and the gap between the container and the carbon material compact is melted under atmospheric pressure or reduced pressure. After filling with an impregnating material such as tar and pitch to cover the entire molded body, a lid made of an airtight metallic material is airtightly connected to the container, and the entire container is mounted in a hot isostatic press. After performing the pressure medium gas replacement operation inside the device, the temperature is raised to a temperature at which the impregnating material such as tar and pitch melts and becomes a liquid, and the pressure medium gas is added to compress the whole container to impregnate. It is characterized in that the material is impregnated into the molded body, and then the temperature is raised to carbonize a part or all of the impregnated material under high pressure.

(Operation) As a method (means) for solving the problem of 1) above,
From the viewpoint of improving the bulk density of the impregnating material, the most preferable method is to heat and melt the impregnating material such as powder or lump tar / pitch or resin to fill the gap between the container and the molded body. In this case, after the solid impregnating material is placed in the container together with the molded body, the entire body may be heated to melt the impregnating material, or the impregnating material may be separately heated and melted to store the molded body in the container. You can pour it gently into the container.

Such an operation may be performed in the atmosphere, but if the molten impregnated material and the molded body are coexistent and the vacuum is applied and the pressure is reduced, the bubbles in the impregnated material can be efficiently removed. Thus, not only the bulk density can be greatly improved, but also a part of the impregnating material is impregnated in the molded body at this point, so that the apparent density of the molded body is increased and the floating of the molded body due to buoyancy can be prevented. In particular, it is effective when the present invention is applied to a molded product having a large amount of pores. In addition, it is preferable to provide a container with a presser for preventing the floating of the molded body against the floating of the molded body which is often experienced during this operation.

In order to solve the problem 2), it is necessary to optimize the material, shape, and thickness of the container. These depend on the manipulation of temperature and pressure within the hot isostatic press. FIG. 4 shows an example of temperature and pressure patterns experimentally conducted by the present inventors.

Here, the temperature of the impregnating step is a temperature at which the impregnating material melts to give a liquid state, and the impregnating material does not decompose or carbonize. In this impregnation step, the pressure outside the container is gradually increased, the entire container is compressed and the molten impregnating material in the container is pushed into the pores of the molded body. Combined with shrinking, in some cases the container shrinks significantly.

Therefore, it is preferable that the container flexibly deforms under the action of such pressure. Aluminum, copper, lead, and metallic materials that flexibly deform at 200-300 ℃
Examples include zinc, but depending on the wall thickness, steel can also be used. The temperature exposed in the carbonization process after the impregnation process is
Aluminum, copper, and steel, which usually have a temperature of 600 ° C. or higher, which does not melt even at 600 ° C., are suitable for the present invention, depending on how much the impregnating material is carbonized.

Although the wall thickness depends on the deformability of the material used, it is preferably thinner than the above-mentioned ordinary capsules, and even in the case of a cylindrical shape, about 0.2 to 1% of the diameter is suitable. The reason why it is better to be thin is that, in addition to the deformability described above, during depressurization after the carbonization step,
This is because it is possible to prevent the capsule from explosively bursting due to ductile fracture when the capsule is swollen due to gas pressure of methane or hydrogen generated by the carbonization reaction filled in the capsule.

Further, regarding the shape of the container, if the body portion is formed into a bellows shape as shown in FIG. 1, it is possible to easily cope with the large shrinkage in the impregnation step. It is particularly suitable for stacking disc-shaped compacts.

In FIG. 1, reference numeral 1 denotes a container, which has a bellows-shaped portion 1A in its body, and a carbon material molded body 4 is accommodated in this container 1 with a gap, and the gap is made of tar. It is filled with a carbonizable substance 5 such as pitch or resin, and is covered with a lid 2 having a degassing pipe 3.

In addition to the above, welding is usually used to connect the container and the lid, so it is necessary to consider measures such as decomposition and alteration of the impregnated material due to heat during welding and prevention of defects in the welded part due to gas generated during decomposition. .

FIG. 2 shows an example of a method of connecting the container and the lid, in which such consideration is taken. After filling the molded body 4 and the impregnating material 5 into the container 1 by the above-mentioned method, the impregnating material may be melted or cooled and solidified, but the lid 2 with the degassing pipe 3 is attached to the container 1. It is attached and the ends are joined by welding 6. In order to prevent the impregnated material 5 from being decomposed by heat during welding, it is preferable to make the distance between the welded portion and the impregnated material longer than that of a normal capsule. After welding, the deaeration tube is pressure-bonded 7 while the inside of the deaeration tube is evacuated. For this crimped part, after cutting and removing excess pipe,
It is also recommended to complete the hermeticity by welding. In this way, it is preferable from the viewpoint of ensuring airtightness that the portion to be finally sealed is a place where the impregnating material inside is not overheated by the heat of welding when welding.

Although not shown, the container prepared in this manner was charged into a hot isostatic press, and after the air in the device was removed by gas replacement with a pressure medium gas, as shown in FIG. Impregnation carbonization is performed at various temperatures and pressure patterns. In the carbonization process, carbonization proceeds due to the decomposition of the impregnated material, but the gas generated at this time decomposes from the hydrocarbon containing the benzene ring into methane and hydrogen as the temperature rises. When all the hydrogen in the impregnated material changes to a substance with a small molecular weight such as H ₂ O or H ₂ , the yield of fixed carbon increases, so such a reaction is recommended and the gas generated in the container is In order to prevent the pressure from becoming higher than the pressure of the pressure medium gas outside the container, it is also recommended to previously set a getter material that absorbs hydrogen in the container.

In the depressurizing step after the carbonization step, since the gas thus generated is accumulated in the container, depending on this pressure, when the pressure of the pressure medium gas outside the container becomes lower than the pressure in the container,
The container swells and finally the weakest part cracks and the gas inside escapes. When this crack is suddenly generated, gas is suddenly released from the container, the molded body inside is cracked, and the heater of the hot isostatic pressing device is damaged. As described above, when a thin container having a large deformability is used, this crack is suitable because a small hole is formed.

(Example) A molded body having 30% by volume of PAN-based carbon fiber and about 35% open porosity containing 30% by volume of carbon was placed in a copper container 1 having a shape as shown in FIG. 3 (a). Then, the space between the container 1 and the molded body 4 is filled with petroleum pitch 5A crushed to an average particle size of about 3 mm.
The temperature was raised to 0 ° C., the petroleum pitch was melted, and the entire molded body 4 was covered with the impregnating material 5. The state at this time is shown in FIG. 3 (b).
Is like. Then titanium foil 8 as a hydrogen getter
After putting in, the lid 2 with the deaeration pipe 3 as shown in FIG. 3 (c)
Was fitted into the container 1 and the ends were joined by welding 6. A vacuum pump was connected to the deaeration pipe 3, and the deaeration pipe 3 was crushed and pressed while vacuuming. The excess deaeration pipe was cut, and the cutting opening was sealed by welding. Although not shown, this container 1 was placed in a hot isostatic press and impregnated and carbonized at the temperature and pressure pattern shown in FIG. After the treatment, the container was taken out from the hot isostatic press, the container was cut, and the molded body inside was collected. The open porosity was about 13%, which proved to be fully carbonized. Specific gravity is about 1.4g / cc to about 1.58g / c
It was confirmed that the density was increased to c and a sufficient density improving effect was obtained.

(Effects of the Invention) The present invention is as described above, and since the production of the high-density carbon composite material by the impregnation carbonization method using high-pressure gas pressure is simple, and the probability that the container is damaged in the impregnation step is reduced, Even if a normal hot isostatic press is used, it can be processed with almost no contamination inside the device, and high pressure impregnation carbonization of 1000 to 2000 kg f / cm ² can be performed without using a special device, resulting in high density. The contribution is extremely large as it gives a new manufacturing method of carbon composite.

[Brief description of drawings]

1 and 2 are sectional views showing a container used in the present invention and a molded body housed therein, and FIG. 3 (a).
(B) and (c) are cross-sectional views showing a part of the process of the embodiment of the present invention, FIG. 4 is a graph showing HIP treatment, and FIG. 5 shows the relationship between carbon yield and pressure. Shows the graph, 6th
FIG. 7 shows a conventional capsule (container), and FIG. 7 is a flowchart of the conventional example. 1 ... container, 2 ... lid, 4 ... molded body, 5 ... impregnated material.

Claims (4)

[Claims] 1. A method for producing a high-density carbon composite material by impregnating a porous carbon material compact with a carbonizing substance such as tar / pitch or resin, and carbonizing the impregnating material to obtain a gas-tight metal. A carbon material compact is placed in a thin container made of material with a gap, and the gap between the container and the carbon material compact is filled with molten impregnating material such as tar and pitch under atmospheric pressure or reduced pressure. After covering the entire molded body by air-tightly, a lid made of an airtight metal material is airtightly coupled to the container, and the entire container is placed in a hot isostatic press.
After performing the pressure medium gas replacement operation inside the apparatus, the temperature is raised to a temperature at which the impregnating material such as tar and pitch is melted and becomes liquid.
A high-density carbon composite material characterized by impregnating a molded body with an impregnating material by adding a pressure medium gas and compressing the whole container, and then heating the temperature to carbonize a part or all of the impregnating material under high pressure. Manufacturing method. 2. The method for producing a high-density carbon composite material according to claim 1, wherein the metal material of the container and the lid is copper, steel, aluminum or an alloy of these metal systems. 3. The method for producing a high-density carbon composite material according to claim 1, wherein the container is formed in a bellows shape. 4. The method for producing a high-density carbon composite material according to claim 1, wherein a getter material that absorbs hydrogen is arranged in the container.