JPH04202056A - Production of graphite - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention relates to a method for producing graphite, for example, as a radiation optical element such as an X-optical element, an X-ray monochromator-1 neutron beam diffraction mirror, or a neutron beam filter. This invention relates to a method for producing graphite that can be used.

(Prior technology) Graphite has outstanding heat resistance, chemical resistance, high electrical conductivity, etc., so it occupies an important position as an industrial material and is widely used as electrodes, heating elements, and structural materials. . Among these, single-crystal graphite has excellent spectroscopic and reflective properties for X-rays and neutron beams, and is therefore used as a monochromator, filter, or spectroscopic crystal for X-rays and neutron beams.

One idea is to use naturally occurring graphite for this radiation optical element, but high-quality natural graphite is produced in very limited quantities and is difficult to handle as it is in the form of powder or flakes. , artificially producing graphite has been carried out.

Conventionally, the following two methods of producing artificial graphite are well known.

The first method is precipitation from Fe, Ni/C melt, 8
There are methods of producing graphite by decomposing carbides such as 1% A1 or by cooling a high-temperature, high-pressure carbon melt. The graphite obtained by this method is
It is called cache graphite and exhibits physical properties similar to natural graphite.

However, the obtained graphite is a fine flake-like substance, and the manufacturing process is extremely complicated, making it difficult to obtain a cost advantage, so it is not used industrially much.

The second method is the high-temperature decomposition deposition of hydrocarbon gas in the gas phase and its hot processing. Graphite is produced through a process of re-annealing at 3400°C for a long time while applying pressure. . The obtained graphite is called highly oriented pyrographite (HOPG), and relatively large pieces have been obtained, and its properties are superior to those of natural graphite. Graphite produced by this method has good rocking properties, which is one of the values representing orientation, and can be used as optical elements for X-rays and neutron beams. However, this manufacturing method has the disadvantages that the process is complicated and the yield is low (therefore, it is very expensive).

A method has been proposed that solves the drawbacks of the conventional methods and allows graphite to be easily obtained at low cost. That is,
This is a method of firing a polymer film. This method heat-treats a polymer compound in a vacuum or inert gas atmosphere, converts it into a carbonaceous material through decomposition and polycondensation reactions, and
This carbonaceous material is further treated at a high temperature to form graphite. Examples of polymer compounds that can be converted into high-quality graphite include 1, aromatic polyamide, polyoxadiazole, aromatic polyimide, polybenzobisthiazole, polybenzoxazole, polybenzobisoxazole, and polythiazole.

Based on these findings, a patent application has already been filed for the invention (Japanese Patent Application Laid-Open No. 61-275114, Japanese Patent Application Laid-open No. 61-27).
5115, JP-A-61-275117, etc.). Furthermore, a patent application has been filed for an invention in which block-shaped graphite is created by laminating polymer films and heating them under pressure (see Japanese Patent Application No. 63-235219).

(Problems to be Solved by the Invention) The already proposed method of laminating and firing polymer films is an extremely excellent method in that a large block-shaped product can be obtained. However, as a result of further investigation, it was found that large block graphite did not have sufficiently uniform properties throughout the crystal.

In view of the above circumstances, an object of the present invention is to provide a method by which large block-shaped graphite having uniform properties throughout can be easily obtained.

(Means for Solving the Problem) In order to achieve the above object, in the method for producing graphite according to claims 1 to 5, a plurality of polymer films are stacked and the temperature range below the polymer thermal decomposition temperature is set. So 20-10
A pressure in the range of 00 g/cm2 is applied, and in a temperature range exceeding the polymer thermal decomposition temperature, a pressure exceeding 1000 g/cm2 is applied to convert the material into graphite.

The pressure in the temperature range below the polymer pyrolysis temperature is 20 to 100
It is 0g/cm2. More preferably 500-800
g/cm2. A pressure exceeding 1000 g/cm2 applied in a temperature range exceeding the polymer thermal decomposition temperature is usually 100 g/cm2.
Selected within the range of kg/cm2 or less. The polymer thermal decomposition temperature is usually about 400 to 600°C. In addition, 1000g/cm2 in the temperature range exceeding the polymer thermal decomposition temperature.
Pressures exceeding 2,000°C are usually applied at temperatures of 2,000°C or higher.

In the firing, it is preferable to first perform the treatment in a vacuum atmosphere in a temperature range below the polymer thermal decomposition temperature, and then to perform the treatment under an inert gas atmosphere.

When increasing the temperature during firing, it is desirable to suppress the temperature increase rate to 10° C./min or less, as described in claim 3.

In addition, when firing a polymer film, a structure consisting mainly of aromatic structures is created during processing near the thermal decomposition temperature, and no major structural changes are observed in the temperature range exceeding the thermal decomposition temperature. Heat treatment is important. That is, as described in claim 5, it is preferable to maintain the temperature at or near the polymer thermal decomposition temperature for a certain period of time.

The polymer film used in the present invention includes polyoxadiazole, aromatic polyamide, and
Examples include films made of at least one of aromatic polyimides, but are not limited thereto, and films of polybenzobisthiazole, polybenzoxazole, polybenzobisoxazole, polythiazole, and the like may be used.

Examples of the aromatic polyimide used in the present invention include the following compounds.

Of course, the starting material film is not limited to these, and it goes without saying that any polymer film that can be converted into high-quality graphite by heat treatment at high temperatures can be used as the starting material film.

II Il Here, R1 is 0R2 The aromatic polyamide used in the present invention is exemplified by the following compounds.

Here, R1 and R2 are exemplified by the following compounds as polyoxadiazoles used in the present invention.

-Polyoxadiazole--N The graphite obtained in the present invention can also be used, for example, in X-ray optical elements, X-ray monochromator-1 neutron beam diffraction mirrors, neutron beam filters, and the like.

It goes without saying that the present invention is not limited to the compounds and treatment conditions exemplified above.

(Function) In the method for producing graphite according to claims 1 to 5, during firing, in the temperature range below the polymer thermal decomposition temperature, 20 to 1
Apply a low pressure of 000g/cm2. For this reason, the polymer film can be neatly oriented without being destroyed before pyrolysis, and at the same time, the gas generated during pyrolysis can be successfully extracted outside the laminated block.
As a result, there are fewer crystal defects, wrinkles and cavities caused by wrinkles are less likely to occur on the surface or inside, a high-quality crystal state appears over a wide range, and overall characteristics can be made uniform.

Also, during production, it is extremely easy to carry out the process without any difficulty, since it is sufficient to laminate polymer films and pay attention to the firing temperature and pressure.

In addition, as claimed in claim 2, the treatment in a vacuum atmosphere at a temperature below the polymer pyrolysis temperature removes air and moisture trapped between the polymer films, as well as gases generated due to pyrolysis. It passes through the laminated block very well, making defects and wrinkles less likely to occur.

As described in claim 3, the temperature increase rate during firing is 10°C/m.
If the temperature is kept below 1.5 in, the film will remain flat without swelling when the air and moisture trapped between the polymer films, or gas during thermal decomposition, escapes, thereby reducing defects. -10-, - becomes more difficult to form and wrinkles.

As described in claim 4, if the temperature is maintained at or near the polymer thermal decomposition temperature for a certain period of time, the residue generated due to thermal decomposition can be removed very effectively, and defects generated in the carbonaceous block can be eliminated. can be minimized.

As described in claim 5, a small amount of polyoxadiazole, aromatic polyamide, and aromatic polyimide (
When using a polymer film consisting of both, it is easy to obtain high quality graphite.

(Example) The present invention will be explained in detail below.

Example 1 - 25 μm thick aromatic polyimide film (Dupon
1,000 sheets (trade name: Kapton Film) were stacked and graphitized as follows.

First, heat treatment was performed from room temperature to 300°C under a vacuum atmosphere (degree of vacuum: =IX10-''Toor) at a pressure of 500 g/cm2 and a temperature increase rate of 5°C/min, and then heat treatment was performed in an argon atmosphere. Thermal decomposition temperature (500°C)
200 kg at a temperature of 3000°C, which is a temperature range exceeding
A pressure of /cm2 was applied and maintained for 1 hour to obtain a block of graphite measuring 6 cm square and 1 cm thick.

Comparative Example 1 - During firing, a pressure of 200 kg/cm2 was applied from room temperature,
Example 1 except that the treatment was carried out in an argon atmosphere
In the same manner as above, a block-shaped graphite having a size of 1.6 cm square and a thickness of 1 cm was obtained.

Example 2 - 25 μm thick aromatic polyimide film (Dupon
1,000 sheets (manufactured by Kapton Film) were stacked and graphitized as follows.

First, heat treatment was performed from room temperature to 300° C. under a vacuum atmosphere (degree of vacuum: =1×10 −3 Torr) at a pressure of 500 g/cm 2 and a temperature increase rate of 5° C./min, and then in an argon atmosphere. Thermal decomposition temperature (500°C)
After holding for 2 hours at a temperature of 3000° C., which is a temperature range exceeding the thermal decomposition temperature, a pressure of 200 kg/cm 2 was applied and held for 1 hour to obtain a block of graphite 1.6 cm square and 1 cm thick.

-Example 3- 500 aromatic polyamide films having a thickness of 50 μm were stacked and graphitized as follows.

First, heat treatment was performed from normal temperature to 300°C under a vacuum atmosphere (degree of vacuum: =IX10-3Toor) at a pressure of 800 g/cm2 and a temperature increase rate of 3°C/min, and then heat treatment was performed in an argon atmosphere. Thermal decomposition temperature (450°C)
After holding for 2 hours at
A pressure of 300 kg/cm 2 was applied and held at a temperature of 00° C. for 1 hour to obtain a block-shaped graphite measuring 16 cm square and 1 cm thick.

Comparative Example 2 - During firing, a pressure of 300 kg/cm2 was applied from room temperature,
Example 3 except that the treatment was carried out in an argon atmosphere
In the same manner as above, a block of graphite having a size of 16 cm square and a thickness of 1 cm was obtained.

Example 4 - 500 polyoxadiazole films with a thickness of 50 μm were stacked and graphitized as follows.

First, heat treatment was performed from room temperature to 250°C under a vacuum atmosphere (degree of vacuum: =IX10-3Toor) at a pressure of 600 g/cm 2 and a temperature increase rate of 2°C/min, and then heat treatment was performed in an argon atmosphere. 400kg/at a temperature of 3000°C, which is a temperature range exceeding the thermal decomposition temperature (450°C).
A pressure of cm2 was applied and held for 2 hours to obtain a block of graphite measuring 16 cm square and 1 cm thick.

Comparative Example 3 - During firing, a pressure of 400 kg/cm2 was applied from room temperature,
Example 4 except that the treatment was carried out in an argon atmosphere.
In the same manner as above, a block of graphite having a size of 16 cm square and a thickness of 1 cm was obtained.

The block-shaped graphite of Examples 1 to 4 and Comparative Examples 1 to 3 was cut into 2 cm square pieces into 64 divided pieces, and the locking properties of each piece were examined and separated. The results are shown in Tables 1 to 4.

Table 2 Table 3 Table 4 Table 1] (i-1 In the case of Example 1, the rocking characteristics are concentrated between 0.9° and 1.1°, whereas in the case of Comparative Example 1 is 0
．． It extends from 9° to 1.4°. On average, the angle in Example 1 is 1.04°, while that in Comparative Example 1 is 1.04°.
．． It is 18°. It is clearly seen that in Example 1, uniform and sufficient characteristics were achieved.

In the case of Example 2, the rocking properties are concentrated around 0.8°, and the average is 085°, which is better than in Example 1, and holding the polymer thermal decomposition temperature for a certain period of time improves the properties. It is clear that it is effective for

In the case of Example 3, the rocking characteristics are concentrated between 0.9° and 1.2°, whereas in the case of Comparative Example 2, the rocking characteristics are concentrated between 0.9° and 1.2°.
．． It extends from 9° to 15°. Even on average, it is 1.09° in Example 3, while it is 1.09° in Comparative Example 2.
It is 34°. It is clearly seen that Example 3 also achieved uniform and sufficient characteristics.

In the case of Example 4, the rocking characteristics are concentrated between 0.9° and 1.4°, whereas in the case of Comparative Example 3, the rocking characteristics are concentrated between 0.9° and 1.4°.
．． It extends from 9° to 15°. On average, the angle is 1.15° in Example 4, while it is 1.15° in Comparative Example 3.
．． It is 26°. It is clearly seen that Example 4 also achieved uniform and sufficient characteristics.

(Effects of the Invention) In the method for producing graphite according to claims 1 to 5, the block body has few defects and there are no wrinkles or cavities caused by the wrinkles on the surface or inside, and a good crystalline state appears over a wide range. In addition to achieving uniformity of overall characteristics,
It is extremely easy to implement as it does not require any particularly sophisticated technology for manufacturing.

In the method for producing graphite according to claim 2, in addition,
Since the process is first performed in a vacuum atmosphere in a temperature range below the polymer thermal decomposition temperature, better quality graphite can be obtained.

In the method for producing graphite according to claim 3, in addition,
Since the temperature increase rate is suppressed to 10° C./min or less, it is possible to obtain a negative layer of high quality graphite.

In the method for producing graphite according to the fourth aspect, since the temperature is maintained at or near the polymer thermal decomposition temperature for a certain period of time, high-quality graphite with very few defects can be obtained.

In the method for producing graphite according to claim 5, since a polymer film made of polyoxadiazole, aromatic polyamide, or aromatic polyimide is used, it is easy to obtain high-quality graphite.

Claims (5)

[Claims] (1) When multiple sheets of polymer films are stacked together, the weight loss is 20 to 1000 g/cm^ in the temperature range below the polymer thermal decomposition temperature.
A method for producing graphite, which is characterized by applying pressure in the range of 2 and converting it into graphite by firing at a pressure exceeding 1000 g/cm^2 in a temperature range exceeding the polymer thermal decomposition temperature. (2) The method for producing graphite according to claim 1, characterized in that the process is first carried out under a vacuum atmosphere in a temperature range below the polymer thermal decomposition temperature, and then the process is carried out under an inert gas atmosphere. (3) The method for producing graphite according to claim 1 or 2, characterized in that in the firing, the temperature is increased at a temperature increase rate of 10° C./min or less. (4) The method for producing graphite according to any one of claims 1 to 3, wherein the graphite is maintained at a temperature at or near the polymer thermal decomposition temperature for a certain period of time. (5) The method for producing graphite according to any one of claims 1 to 4, wherein the polymer film comprises at least one of polyoxadiazole, aromatic polyamide, and aromatic polyimide.