JPS6259509A - Production of high-density carbon material - Google Patents

Abstract

PURPOSE:To make it possible to produce a high-density carbon material, by blending powder of graphite or coke with a carbonizing organic material as a binder, press molding the blend, putting the molded article in a container made of steel, pressurizing in a high-pressure gas atmosphere into a high-density state, carbonizing further the binder by a hot hydrostatic pressure device and graphitizing a carbonaceous molded article at high temperature. CONSTITUTION:Powder of natural or artificial graphite or coke is sufficiently blended with liquid tar, pitch, resin or powdery mesophase pitch, resin, etc., as a binder. The blend is cold molded or molded at high temperature at about 250 deg.C by a mold or a hydrostatic press. The molded article A is packed into the container 1 made of steel, deaerated from the degassing pipe 4, sealed, compressed by a hot hydrostatic pressure device at 1,000-2,000kg/cm<2> and the binder is carbonized to give a carbonaceous molded article. It is heated in a graphitizing furnace at high temperature, the carbonaceous molded article consisting of coke, natural graphite and the carbonized binder is processed into artificial graphite, to produce a high-density carbon material having improved strength, impermeability to gases and specular gloss finish.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing a high-density carbon material.

Carbon materials have properties not found in other materials, such as excellent heat resistance in an inert atmosphere, chemical stability against chemicals, and light weight, so their field of use has continued to expand in recent years. ing.

Among these, the spread of carbon fiber composite materials has been remarkable, especially due to the appearance of high-strength, high-elastic carbon fibers.

On the other hand, in addition to carbon fiber, carbon materials come in various forms such as amorphous carbon and graphite, and each has unique properties that are not found in other materials. It is.

In recent years, there have been many demands for higher density carbon materials having such characteristics. In other words, improvements in strength, gas impermeability, and mirror finish properties through machining are desired.
For this purpose, the demand for higher density is becoming stronger.

The present invention relates to a suitable method for producing a high-density carbon material that readily meets such demands.

In addition to structural materials, typical applications of such high-density carbon materials include partition plates for fuel cells, susceptors for diffusion heat treatment of semiconductors, and the like.

(Prior Art) By the way, raw materials for carbon materials such as those mentioned above are usually so-called organic substances that carbonize when heated to an elevated temperature. Typical examples thereof include petroleum pitch, tar 2 coke, resin, etc. Generally, carbon materials are manufactured by using these materials as raw materials, mixing them with graphite or the like in some cases, shaping the mixture, and firing the mixture.

However, this calcination, or carbonization, takes advantage of the fact that organic raw materials undergo polymerization and condensation, and functional groups containing hydrogen etc. are separated from the original organic molecules. Since the passages of the gas-permeating molecules based on the group remain as pores, this method usually has the disadvantage that only porous fired products can be obtained.

In addition, when heated rapidly, the functional groups etc. are rapidly removed (thermal decomposition) and cracks occur in the fired product. Therefore, the heating rate must be kept very low, and It took a long time, ranging from several days to several weeks, and was a major bottleneck in industrial production.

(Problems to be Solved by the Invention) The present invention deals with the above-mentioned facts, and in order to improve the conventional manufacturing technology of carbon materials, intensive research has been carried out, particularly focusing on the method of applying pressure during the firing process. As a result of repeated efforts, we have reached this goal.

That is, as a result of firing molded bodies made of carbonizable organic materials such as tar, pitch, and resin under high pressure, the functional groups become more radical under high pressure than when fired near atmospheric pressure. They discovered that the gas produced by this process decomposes into methane and hydrogen with small molecular weights at low temperatures, and that methane decomposes into hydrogen and carbon at temperatures lower than near atmospheric pressure.

This can be inferred from the fact that the yield of carbon increases when fired under high pressure, as shown in FIG.

On the other hand, we have also discovered a phenomenon in which this decomposition reaction is thought to be accelerated when hydrogen is separately stored or sealed in a container that releases i3 in excess to the outside of the system. Furthermore, they discovered a phenomenon in which densified carbon materials also permeate hydrogen at high temperatures, and if they are pressurized at a pressure that is thought to be higher than the pressure of hydrogen, they will not develop cracks.

The present invention is based on the knowledge obtained as a result of these studies, and aims to eliminate the drawbacks of the prior art as described above by applying pressure in the firing process.

(Means for Solving the Problems) Accordingly, the present invention that meets the above objective is firstly encapsulated with a carbonizable organic material in a powdered carbon material or chopped carbon fiber. The second invention is to mix, pressurize in cold or warm, shape, and then hermetically seal in a steel container and pressurize and sinter in a high-pressure gas atmosphere. Subsequently, the obtained fired body is further exposed to a high temperature to graphitize it.

Here, as the raw material used in the present invention, most materials can be used as long as they can be carbonized by heating and firing.
As will be described later, raw materials that generate gas components that cannot be absorbed by the steel container because they are fired while sealed in a steel container may cause the fired product to crack due to the internal pressure of the gas components. I don't like it because it is.

Therefore, when the purpose is to produce a high-density graphite material, it is necessary to use graphite powder or coke powder that graphitizes by heating to a temperature of 1,900°C or higher, which causes shrinkage of the compact during pressure firing. A binder material containing a carbonizable organic material having the property of

Further, when the purpose is to manufacture a high-density carbon fiber/carbon composite material, a carbonizable organic binder material having the above-mentioned characteristics is mixed with a chopped material of PAN-based or tar-pitch-based carbon fiber.

Liquid tar pitch is used as a binder material.

Examples include resin, powdered mesophase pitch, and resin. As the resin, in addition to thermoplastics such as polyethylene, thermosetting phenolic resins and the like can be used.

Then, the above raw materials are thoroughly mixed using a ball mill, a sieve machine, a kneader, etc., and then cooled or heated at 250°C.
The molded product is molded using a mold or isostatic press at a certain temperature.

When manufacturing an isotropic high-density carbon material, it is effective to perform isostatic press molding.

The obtained molded body is hermetically sealed in a steel container.
Pressure molding is performed under a high pressure gas atmosphere.

The container must have an airtight structure to prevent pressure gas from entering during firing in a high-pressure gas atmosphere, which will be described later.The container and lid are usually joined by welding. It is preferable.

In this case, the molded body is heated by the heat during welding, causing thermal decomposition of the binder material, which may result in non-uniformity after firing and poor welding due to gas generated by thermal decomposition. has a structure separated from the molded body,
It is preferable to cool the container portion with water or the like during welding.

Note that the sealing is preferably performed while deaerating the inside of the container, and the most common configuration is to provide the container with a deaeration pipe.

The container containing the compact is then subjected to pressure sintering, and the equipment used in this case is hot isostatic pressing (hot isostatic pressing), which has been used in recent years for pressure sintering of powder in the powder metallurgy field. HIP
) The pressure that the device can generate is 1000 to 2000 kg/
It is industrially advantageous because it has a high diameter of 50 cm and the technology has been established for large-scale equipment with a diameter of 50 cm.

In this pressurized firing, it is important to increase the pressure in advance in order to prevent the pressure of the gas component generated by the decomposition of the carbonizable organic matter from inflating the container and damaging the container.

Further, the generated gas in the container is generally decomposed into carbon and hydrogen, but when the hydrogen in the steel of the container reaches a saturated state, the hydrogen in the steel is released from the container into the pressure gas.

Therefore, in order to suppress the increase in hydrogen in the pressurized gas or to promote the decomposition of methane gas generated by iron, which is the main component of steel, a metal with a large hydrogen storage capacity, such as titanium or steel, is placed inside the container. It is effective to keep it.

Furthermore, it is also effective to interpose a mold release material in the gap between the container and the molded body to facilitate the removal of the fired body from the container after treatment and to prevent reactions between the hydrogen storage material, the fired body, and the container. .

As the mold release material, ceramic powders that do not become densified during processing, such as alumina, BN, or flexible graphite sheets, are suitable.

Through the above-described steps, the molded body becomes a dense fired body of high-density carbon, but this fired body may be further subjected to graphitization treatment if necessary.

By performing the same treatment, it can be used as a material for structural materials and heaters that are used at high temperatures of 2000°C or higher.

Additionally, machining can be made easier.

This graphitization treatment is usually performed using a HIP device for 1000
When carried out under a high pressure of ~2000 kg/cn, it is achieved at around 2000°C, which is lower than atmospheric pressure.

(Example) Hereinafter, specific embodiments of the method of the present invention will be described in detail based on the accompanying drawings.

FIG. 2 shows a molded body (A) of a carbon material as a raw material for a fired body produced by the method of the present invention, that is, a powdered carbon material or chopped carbon fiber is mixed with a carbonizable organic substance as a binder material, and then cold-processed. Alternatively, the molded body (A) formed by warm isostatic pressing using a mold or hydraulic pressure is hermetically sealed in a steel container, and the container is heated under a high pressure gas atmosphere as described below. In order to prevent pressure gas from entering during firing, the structure must be airtight against pressure gas.
It is constructed by joining the container body (11), the bottom part (2), and the lid part (3) by welding.

Of course, the bottom part (2) of the container body (1) can be made integral, and in the above case, the molded body (A) is heated by the heat during welding, and the binder material is thermally decomposed. This can lead to non-uniformity after firing and welding defects due to gas generated by thermal decomposition, so we recommend a structure in which the welded part (5) after inserting the compact is separated from the compact (A) as shown in Figure 3. Alternatively, it is preferable to cool the container portion with water or the like after welding.

In addition, in the container shown in Fig. 2, the thickness of the lid part (3) is thinner than other parts. It is intended that cracking will occur selectively in this area.

It is preferable to seal the container while deaerating the inside of the container, and for this purpose, the container is provided with a deaeration pipe (4) as shown in FIG.

Therefore, in the method of the present invention, first, a carbonizable material is mixed as a binder material into the powdered carbon material or chopped carbon fibers described above, and then the powdered carbon material or the chopped carbon fiber is mixed with a carbonizable material as a binder material, and then the powdered carbon material or the chopped carbon fiber is mixed with a carbonizable material as a binder material. After mixing, cold or warm pressure molding is performed to obtain a molded product, which is then hermetically sealed in the container.

Then, the container containing this molded body is then subjected to a pressure firing process.

As equipment for pressurized firing, the HIP apparatus described above is industrially advantageous and used.

FIG. 4 shows the firing process when such a HIP apparatus is used.

Here, the HIP device main body is a device that has been used for pressure sintering of powder in the powder metallurgy field in recent years, and its configuration is basically a pressure-resistant cylinder (11), as shown in detail in FIG.
Upper M (12) and lower 1i (13) that close the upper and lower openings
The fitting portions are held airtight by sealing materials (14) and (15), respectively, and the pressure acting on the lid portions (12) and (13) is absorbed by the press frame (2).
4) is supported.

The interior of the high-pressure container partitioned as described above surrounds the sample stage (9) on which the object to be processed, that is, the molded object (10) in the container is placed, and the object to be processed (10) is heated and heated. A heating element (18) made of an electrically heated resistance wire supported by a support member (18) to
) The pressure cylinder (11) and upper M (12)
.

A heat insulating layer (17) is incorporated to suppress dissipation of the bottom 1 (13)-5 to define a furnace chamber (16). A water-cooled jacket I-(25) is attached to the high-pressure vessel, and in order to supply pressure medium gas from the introduction hole (22), an inert gas collection device (26) such as nitrogen gas or argon gas, and a compressor i (
28) and pressure reducing regulator (27) and blocking valve (■,)
In addition to being equipped with a 4-person piping system for pressurized gas containing ~(■8),
An electric supply circuit including a heating power source (32) to the heating element and a control device (33) is provided, while a vacuum pump (3
0).

A pressure medium gas discharge piping system including a blocking valve (31) is provided.

Hereinafter, the firing process will be explained in the case where such an HIP apparatus is used.

First, as shown in FIG. 4, after placing the container containing the molded object (A), that is, the object to be processed (10) on the sample stage (9),
By operating the vacuum pump (30), the inside of the HIP device is evacuated and the air inside the device is exhausted.

Further, after performing substitution by introducing a pressure medium gas, such as argon, through the pressure medium gas introduction piping system, the pressure medium gas is
Fill from 0 to 300 kg/cd.

After filling, the temperature is raised to a temperature at which the carbonizable organic matter in the compact (A) is carbonized. In this case, if the temperature is raised in advance, the pressure of the gas component generated by the decomposition of the carbonizable organic matter will inflate the container and damage the container, making it impossible to achieve the intended purpose.

Therefore, it is necessary to apply a pressure higher than this internal pressure to the outer surface of the container. When the pressure on the outer surface of the container is higher, when the carbonizable organic substance softens at 100 to 500° C. during heating, the molded body is compressed and becomes more dense.

When the temperature is low, the gas generated in the container is low in pressure, and contains propane, propylene, ethane, etc., but as the temperature rises, these become lower molecular gas components such as acetylene and methane, and finally decomposes into carbon and hydrogen.

As mentioned above, this tendency is thought to occur at higher pressures and lower temperatures. It is also assumed that iron, which is the main component of the steel used to make the container, acts as a catalyst to promote the decomposition of methane.

Hydrogen, on the other hand, is absorbed by the line of the container material, facilitating the continuation of this decomposition reaction.

When the hydrogen in the network of the vessel reaches a saturated state, the hydrogen in the steel is released from the vessel into the pressure medium gas. Therefore, in order to suppress the increase in hydrogen in the pressure medium gas, it is effective to place a metal with a large hydrogen storage capacity, such as titanium, sponge-like titanium, or steel, inside the container.

FIG. 5 shows an example of such an arrangement in which the hydrogen storage material (7) is embedded in a template (6) interposed on the inner surface of the upper part of the container.

In addition, when the molded body (A) is sealed in a steel container, the mold release material (6) is used in the container body (11, 1! part (3), bottom part (
2) is inserted in the gap between the hydrogen storage material (7) and the fired body to facilitate taking out the fired molded body, that is, the fired body from the container after processing, and at the same time to prevent the reaction between the hydrogen storage material (7), the fired body, and the container. fulfill one's role. Therefore, as the mold release material (6), a ceramic powder that does not become densified during processing, such as alumina, BN, or a flexible graphite sheet, is suitable.

Pressure firing is performed in a ridge-like process procedure to form a molded object (A).
becomes a dense, high-carbon fired body.

This fired body is sufficient for the intended use as it is, but it can be further subjected to graphitization treatment if necessary.

This graphitization treatment is carried out by exposing the obtained fired body to a higher temperature using the HIP apparatus as described above. It can be achieved at a lower temperature of around 2000°C.

By performing this graphitization treatment, it can be used as a material for structural materials and heaters that are used at high temperatures of 2000 degrees Celsius or higher, and machining can be made easier, making it possible to use it in various fields. Expand.

Specific examples will be shown below.

Example 1 20 parts by weight of high viscosity pinch was added to 80 parts by weight of petroleum coke and dry mixed for 4 hours in a ball mill. The obtained raw material was put into a latex bag and 2000 kg/cI
Isostatic press molding was carried out at a pressure of II. Then, the obtained molded body was turned into a cylindrical shape and sealed in a deaerated container shown in FIG. 3.

This container was placed in a HIP device and baked under pressure at the temperature shown in FIG. 6 using a pressure cover turn. After the treatment, the fired body was taken out of the container and its density was measured, and it was found to be 1.73 g/c.
J, no firing cracks were observed.

Comparative Example 1 The same raw materials and molded body as in Example 1 were fired in the HIP apparatus shown in FIG.

As shown in the figure, in addition to the basic configuration described earlier, the device is equipped with a ventilation pipe (19) attached to the bottom of the container, and this pipe (19) is connected to the lower M (13) via a joint (21). It is removably connected to the pressure adjustment hole (20) in the container and connected to the pressure medium gas in the furnace chamber (16) so as to maintain airtightness by means of a sealing material. 16) are provided with through holes (22) and (23) that communicate with each other.

Therefore, the inside of the container of the Kitagi device was in communication with the atmosphere, and was kept at atmospheric pressure. The temperature and pressure cover pattern for firing was almost the same as that shown in FIG. Although the fired body that was taken out had shrunk in size, it had many microcracks and could not be called a healthy fired body. The density determined from the dimensions and weight is 1. ．． 65g/c++! Met.

Example 2 25 parts by weight of PAN-based carbon fibers with a diameter of about 5 μm and a length of 0.7 mm and 75 parts by weight of mesophase pitch powder were mixed and filled into a latex container to produce 20 Q Okg/
Isostatic press molding was performed at a pressure of crA.

The obtained molded body was sealed in a container shown in FIG. 3, and pressure-fired in the same manner as in Example 1.

The density of the obtained fired body was about 1.6 g/cJ.

Example 3 The fired body obtained in Example 1 was vacuum sealed in a quartz glass capsule and heated at 2000°C and 1500 kg/d for 1 hour.
IP processing was performed. The density of the obtained fired body is 2.11
g/cffl, which was extremely densified compared to 93.4% of the true density of natural graphite.

(Effects of the Invention) As described above, according to the method of the present invention, it is possible to produce a high-density carbon material that was impossible with the conventional method, and it is also possible to generate cranks even during firing for an extremely short time compared to the conventional method. It has immeasurable advantages such as economic efficiency in industrial production, and is expected to meet the current demand for higher density carbon materials and have a significant effect on expanding its uses.

[Brief explanation of the drawing]

Fig. 1 is a chart showing the relationship between pressure and carbon yield, Figs. 2 and 3 are cross-sectional views showing each side of the molded body inserted into the container, and Fig. 4 shows the firing process of the present invention. 1 of the devices
A schematic diagram showing an example, FIG. 5 is a sectional view showing another example of how the molded body is inserted into a container, and FIG. 6 is a diagram showing the temperature and
A diagram showing the pressure cover turn, Figure 7 is the HI used in the comparative example.
It is a sectional view showing an outline of PW placement. (1)...Container body, (2)...Bottom part. (3)... Lid part, (4)... Deaeration pipe. (5)...Welding part, (6)...Release material. (7)...Hydrogen storage material. Patent applicant: Kobe Steel, Ltd. Representative Patent attorney: Yasushi Miyagi - Carbon yield (
%)

Claims (1)

[Scope of Claims] 1. Carbonizable organic matter is mixed with a carbon material consisting of powdered carbon material or chopped carbon fiber, and the mixture is pressurized and molded, then hermetically sealed in a steel container and exposed to high pressure gas. A method for producing a high-density carbon material, characterized by pressurized firing in an atmosphere. 2. The method for producing a high-density carbon material according to claim 1, wherein the carbonizable organic substance is liquid tar pitch or resin, or powdered mesophase pitch or resin. 3. Claim 2 in which the resin is a thermoplastic resin such as polyethylene or a thermosetting resin such as a phenolic resin.
A method for producing a high-density carbon material as described in Section 1. 4. The method for producing a high-density carbon material according to claim 1, 2 or 3, wherein the pressure forming means is cold or warm isostatic forming using hydraulic pressure. 5. The method for producing a high-density carbon material according to any one of claims 1 to 4, wherein a mold release material is interposed in the gap when the molded body is hermetically sealed in a steel container. 6. The method for producing a high-density carbon material according to any one of claims 1 to 5, wherein a hydrogen storage material is also enclosed when the molded body is enclosed in a steel container. 7. Claims 1 to 7, in which pressurization by gas pressure precedes temperature increase when pressurized firing in a high-pressure gas atmosphere.
A method for producing a high-density carbon material according to any one of Item 6. 8. Mixing a carbonizable organic substance having a property of causing shrinkage of a molded body during pressure firing of the carbon material into a carbon material consisting of a powdered carbon material or chopped carbon fiber,
After cold or warm pressure forming, the product is hermetically sealed in a steel container and fired under pressure in a high-pressure gas atmosphere, and the resulting fired product is further exposed to high temperatures to graphitize it. A method for producing a high-density carbon material characterized by: 9. The method for producing a high-density carbon material according to claim 8, wherein the carbonizable organic substance is liquid tar pitch or resin, or powdered mesophase pitch or resin. 10. The method for producing a high-density carbon material according to claim 9, wherein the resin is a thermoplastic resin such as polyethylene or a thermosetting resin such as a phenolic resin. 11. The method for producing a high-density carbon material according to claim 8, 9, or 10, wherein the pressure molding means is hydrostatic molding using hydraulic pressure. 12. The method for producing a high-density carbon material according to any one of claims 8 to 11, wherein a mold release material is interposed in the gap when the molded body is hermetically sealed in a steel container. 13. The method for producing a high-density carbon material according to any one of claims 8 to 12, wherein a hydrogen storage material is also enclosed when the molded body is enclosed in a steel container. 14 Claim No. 8 in which pressurization by gas pressure precedes temperature rise when performing pressurized firing in a high-pressure gas atmosphere.
A method for producing a high-density carbon material according to any one of items 1 to 13. 15. The method for producing a high-density carbon material according to any one of claims 8 to 14, wherein the graphitization treatment is performed in a high-pressure inert gas atmosphere.