JPH0742095B2 - Graphite manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing highly oriented block-shaped graphite used as a radiation optical element such as an X-ray monochromator, a neutron monochromator and a neutron filter.

[0002]

2. Description of the Related Art Graphite occupies an important position as an industrial material due to its outstanding heat resistance, chemical resistance, high electrical conductivity, etc., and is widely used as a gasket, an electrode, a heating element and a structural material. Among them, highly oriented graphite is widely used as a monochromator for X-rays and neutron rays, or a filter because it has excellent spectral and reflection characteristics for X-rays and neutron rays.

One of the methods used for this purpose is to use naturally occurring graphite, but high-quality graphite has a very limited production amount, and it is difficult to handle in the form of powder or graphite. Artificial production of graphite is performed because of the flaky shape. As a method for producing such artificial graphite, there is a method by high temperature decomposition deposition of hydrocarbon gas in a gas phase and hot working thereof. This is a method of forming by a process of re-annealing at 3400 ° C. for a long time while applying pressure. The graphite produced in this manner is called highly oriented graphite (HOPG) and has excellent properties comparable to natural single crystal graphite. However, this method has an extremely complicated manufacturing process and a significantly low yield, and as a result, HOPG has been extremely expensive.

In order to solve the above-mentioned drawbacks of the conventional method for producing high-quality graphite and to make the production method easy and inexpensive, a method for producing high-quality graphite by firing a polymer film at high temperature has been developed. Was done. Polymer materials generally belong to difficult graphite materials.
Even if it is heated to a high temperature of 0 ° C., it is not converted into good quality graphite. However, recent studies have shown that some of the polymeric materials are converted to good quality graphite by appropriate heat treatment. Examples of such polymers include polyoxadiazole, aromatic polyimide, aromatic polyamide, polybenzimidazole, polybenzobisthiazole, polybenzoxazole, polythiazole, and polyparaphenylene vinylene. Based on these findings, the inventors of the present invention have filed patent applications, which are disclosed in JP-A-61-275114 and JP-A-61-275114.
-275115, JP-A-61-275117, and the like.

On the basis of these inventions, studies were made to laminate polymer films and fire them under pressure to produce block-shaped graphite. Examples of these are Japanese Patent Laid-Open No. 1-1.
No. 05199 and Japanese Patent Laid-Open No. 235218/1988.

[0006]

However, in order to form a highly oriented block by laminating a plurality of polymer films, it is necessary to devise many means, and simply pressurizing and firing can achieve a high purpose. Oriented graphite cannot be obtained. In order to obtain highly oriented graphite, it is important that each film is properly oriented inside the block, that the graphite crystals are arranged neatly inside the film, and that the films adhere to each other. However, for example, the above-mentioned polymer films all undergo thermal decomposition in the temperature range of 300 to 600 ° C., and the films rapidly shrink. Further, these polymers are in a hard carbon state which is hard and brittle in a temperature range around 1000 ° C to 2000 ° C.
Therefore, even if these polymer films are laminated and heat-treated while applying pressure, wrinkles and internal structure distortion are usually generated due to shrinkage deformation of the films, and in extreme cases, destruction occurs. Therefore, the key point of the technology to create a highly oriented graphite block from multiple polymer films is to determine the strain that occurs during the process of thermal decomposition, carbonization, and graphitization due to expansion and contraction of the polymer film. The point is to leave it in the final graphite block.

Therefore, for example, no pressure is applied essentially in the thermal decomposition temperature range, and the decomposition temperature is not lower than 2000 ° C.
Apply a pressure between 2 and 50 kg / cm ² in the temperature range of
At 600 ° C or higher, a method of applying a pressure of 50 kg / cm ² or higher is used. The pressure cannot be applied in the thermal decomposition temperature region because when the pressure is applied in this region, the films are fused to each other, preventing the smooth release of the decomposition gas generated from the inside, and finally the carbon dioxide is generated by the generated gas. Because it leads to destruction. The pressure operation between the decomposition temperature and 2000 ° C. is a step of removing the internal strain generated in the decomposition temperature region by firing so as not to destroy the carbonized product (in the state of hard carbon). Further, the pressure operation at 2600 ° C. or higher is a step of adhering the films together while promoting the graphitization.

The above method is a method for producing highly oriented graphite by controlling the steps of pyrolysis, carbonization, graphitization, and adhesion, and the value of the mosaic spread is 1.0 °. Thus, a highly oriented graphite block having a characteristic of about 0.7 ° can be obtained. However, in order to realize a block having better orientation, it is important to reduce the strain generated in the thermal decomposition process. To do so, in the pyrolysis process,
It is desirable to prevent the polymer films from adhering to each other and pressurize while smoothly releasing the decomposition gas. However, since the pressure in the thermal decomposition process usually causes the films to adhere to each other as described above, the pressure cannot be applied.

The present invention solves the disadvantage that the conventional manufacturing process is extremely complicated and the yield is extremely low, and as a result, highly oriented graphite is extremely expensive, and the manufacturing method is easy and the cost is high. It is an object of the present invention to realize a method for producing high quality graphite by firing a molecular film at a high temperature.

[0010]

In order to achieve this object, the present invention relates to a method in which a plurality of polymer films are laminated, and an inorganic powder is present between the polymer films to apply pressure and heat treatment. Is composed of.

[0011]

According to the present invention, the polymer films are prevented from adhering to each other in the thermal decomposition step due to the above constitution.
The decomposed gas can pass smoothly between the polymer films and diffuse to the outside. That is, since the polymer films do not fuse with each other, it is possible to apply a certain amount of pressure, and it is possible for the polymer films to slip with each other, thereby introducing wrinkles and strains in the polymer films. Can be prevented.

Since the carbonized block thus produced has a small amount of strain initially introduced, each polymer film is properly oriented inside the block, and highly oriented graphite in which crystals are arranged neatly inside the film. Becomes

[0013]

EXAMPLE An example of the present invention will be described below, but before that, an outline of the present invention will be described.

As a result of studies to solve the above-mentioned problems, the applicant of the present invention has found that a polymer film is thermally decomposed by allowing an inorganic powder having a particle size of a certain size or less to be present between the polymer films and heat-treated. The present invention has been completed by discovering that the films do not adhere to each other in the process and the decomposed gas can smoothly diffuse to the outside through the spaces between the films. In this method, the films are not fused to each other, so that it is possible to apply a certain amount of pressure, it is possible to slip between the films, thereby preventing the introduction of wrinkles and strains in the film .

The carbonized block thus prepared is subjected to high temperature treatment according to the above-mentioned method to be graphitized. However, since the strain introduced in the initial stage is small, a graphite block having an excellent orientation as compared with the conventional method is obtained. You can The amount of the inorganic powder used at this time is selected within a range that prevents fusion of the polymer film and does not adversely affect the properties of graphite.

Materials and methods of the present invention will be described below. In the present invention, various polyphenylene oxadiazole (POD), polybenzothiazole (PBT), polybenzobisthiazole (PBBT), polybenzoxazole (PBO), polybenzobisoxazole (PBB)
O), various aromatic polyimides (PI), various aromatic polyamides (PA), poly (phenylene benzimidazole) (PBI), poly (phenylene benzobisimidazole) (PPBI), polythiazole (PT), At least one polymer film selected from poly (paraphenylene vinylene) (PPV) is used.

Here, various polyoxadiazoles mean polyparaphenylene-1.3.4-oxadiazole and isomers thereof. The various aromatic polyimides are polyimides represented by the following general formula.

[0018]

[Chemical 1]

The aromatic polyamide is a polyamide represented by the following general formula.

[0020]

[Chemical 2]

However, the present invention is not limited to these polyimides and polyamides.

The raw polymer film in the present invention is the above-mentioned POD, PBT, PBBT, PBO, PBBO, P.
It is selected from among I, PA, PBI, PBBI, PT, PPV, etc., but the method of the present invention can be similarly applied to a polymer film that produces good quality graphite by heat treatment at high temperature. Is.

In the method of the present invention, the starting material is 400
It is desirable to use a film having a thickness of less than μm. This is because when a raw material having a thickness of 400 μm or more is used, it is difficult to obtain a highly oriented graphite block because the internal structure of the film is destroyed by the gas generated from the inside of the film even by the method of the present invention. This is because

As the inorganic powder according to the present invention, silica,
Calcium oxide, magnesium oxide, aluminum oxide, iron oxide, carbon, graphite, titanium oxide, calcium carbonate, magnesium silicate, calcium silicate, barium carbonate, barium sulfate, lead oxide,
Representative examples include chromium oxide, silicon carbide, calcium carbide, and the like, and mixtures thereof. Examples of mixtures include kaolin, clay, acid clay, talc,
Examples include Benton and white carbon.
These inorganic powders can be used as they are,
It may be dispersed in water or an organic solvent. It is also possible to use it in the form of a derivative such as a stearic acid derivative.

The role of these inorganic powders is to prevent fusion between the films and to enable pressure firing in the thermal decomposition process. However, on the other hand, if the amount of the inorganic powder is too large, the inorganic powder itself disturbs the orientation of the completed graphite block and prevents the adhesion in the film bonding process at 2600 ° C. or higher. Therefore, it is desirable that the amount of the inorganic powder is the minimum amount necessary to achieve the purpose of preventing fusion.

From this point of view, various inorganic powders and their particle sizes were examined to determine the optimum amount. As a result, the particle size should be 20 μm or less, and more preferably 1 μm.
It turned out to be m. Further, when the particle size is 20 μm or less, the amount required to prevent fusion is 1 of the film weight.
% Or less, more preferably 0.1% or less. Inorganic powders that satisfy these conditions have almost no adverse effect on the properties of graphite, and conversely, a positive effect is obtained by removing the strain by applying pressure during the thermal decomposition process. As a result, the characteristics of the obtained graphite are remarkably improved as compared with the production method using no inorganic powder.

In addition to the method of the present invention, a method of adding an inorganic powder to the polymer film in advance can be considered. However, such a method is not suitable for the purpose of the invention of preventing film fusion. This is because the internal addition method requires a much larger amount of addition in order to prevent fusion, as compared with the method of the present invention, and they adversely affect the properties of the final graphite. In the case of polyimide, the minimum amount required to prevent fusion between films was 5% of the film weight when using silica powder having an average particle size of 10 μm. Therefore, naturally, such an inorganic powder adversely affects the final orientation properties of graphite.

On the other hand, in the conventional process in which no inorganic powder is used at all, it is necessary to apply essentially no pressure in the temperature range where the film expands and contracts in order to carbonize while preventing the films from fusing. Become. Here, the meaning of essentially not applying pressure means that a minute pressure such as the weight of a jig for pressurization may be applied.
The allowable pressure at this time is generally 2 kg / cm ²
It is below, preferably below 1 kg / cm ² . On the other hand, when an inorganic powder such as that of the present invention is used, it becomes difficult for the films to adhere to each other, so a maximum of 10 kg / c
Pressurization of m ² is possible. Therefore, the obtained carbonized product had far fewer wrinkles than the case where no inorganic powder was used. When graphitization was carried out using the carbonized material thus obtained, an improvement in rocking characteristics of 0.2 ° on average could be realized.

The present invention will be described in detail below by taking an aromatic polyimide as an example. FIG. 1 shows the measurement results of the elongation and contraction of polyimide (Kapton, 25 μm, manufactured by DuPont) in the plane direction. Polyimide as shown here is 450 to 5
It stretches slightly at 00 ° C and shrinks sharply to 75% of its original length in the region of 500 to 700 ° C. This temperature range corresponds to the thermal decomposition range of the polymer. Applying a pressure of 10 kg / cm ² using polyimide (Kapton H film) and applying 1000 ℃
When the temperature was raised to 0, the minimum amount required to prevent fusion between films was 0.01% of the film weight when silica powder having an average particle size of 0.02 μm was used. Further, the film thus obtained was subjected to 3000 kg under a pressure of 200 kg / cm ^2.
As a result of the ° C treatment, the films adhered well to each other, and the measured rocking characteristic was 0.56 °.

On the other hand, when silica powder having an average particle size of 30 μm was used, the minimum amount necessary to prevent fusion between films was 2% of the film weight. In this case, the film thus obtained was treated at 3000 ° C. under a pressure of 200 kg / cm ² , but the films did not adhere to each other, and the rocking characteristic measured on one film was 1.8 °.

The above-mentioned manufacturing method of pressurization and heat treatment is not necessarily limited to polyimide, and generally applicable to polymers which are converted into excellent graphite by heat treatment.

(First Embodiment) The first embodiment of the present invention will be described below.

Polyparaphenylene having a thickness of 50 μm-1.
3.4-Average particle size 1 on the oxadiazole film surface
The talc powder of μm was evenly sprinkled, and then excess talc powder was removed while applying vibration to adjust the powder amount to 0.05% of the polymer film.

100 films (2 ×
3 cm ² ) was set on a jig made of graphite, and the temperature was raised to 1200 ° C. at a rate of 10 ° C./min in an argon gas atmosphere. During this period, a pressure of 5 kg / cm ² was applied to the sample. Next, after reaching 1200 ° C., pressure was applied while maintaining the same temperature rising rate. Applied pressure is 20 kg / cm
² and pressure was applied until the temperature reached 1400 ° C. After that, the pressure was reduced so that only the pressure corresponding to the weight of the jig was applied until the temperature was raised to 2600 ° C. After the temperature reached 2600 ° C, pressure was applied again. The applied pressure is 200 kg / cm ² . While maintaining this pressure, the temperature was raised to 3000 ° C. to complete the heat treatment. The resulting graphite block had a uniform surface with almost no wrinkles.

The characteristics of the obtained graphite were measured using a rotor flex RU-200B type X-ray diffractometer manufactured by Rigaku Denki Co., Ltd. The half value width of the diffraction line obtained as a result of the rocking characteristic measurement at the peak position of the graphite (002) diffraction line was evaluated. As a result of the measurement, it was found that the rocking characteristic was 0.56 °, which was excellent as an X-ray or neutron beam monochromator.

The same treatment was carried out on the film without using talc, but during the temperature rising process up to 1200 ° C., the films fused to each other and were destroyed by the gas generated from the inside. Next, in order to prevent destruction, the pressure during the firing process up to 1200 ° C was limited to the pressure due to the weight of the jig, 100 g / cm
^The process was performed in the number ² , and the subsequent processes were the same. The locking characteristic of the obtained block was 0.8 °. From this, it was found that the method of the present invention is very effective in improving the locking characteristic.

(Second Embodiment) The second embodiment of the present invention will be described below.

An average particle size of 0.02 μ was formed on the surface of polyimide (Kapton H film, DuPont) having a thickness of 25 μm.
The silica powder of m 3 was evenly sprinkled, and then excess silica powder was removed while applying vibration so that the powder amount became 0.02% of the polymer film.

200 films (3 ×
3 cm ² ) are stacked, set in a graphite jig in the same manner as in the first embodiment, and placed in an argon gas atmosphere for 10 minutes.
The temperature was raised to 1400 ° C at a rate of ° C / min. During this period, a pressure of 4 kg / cm ² was applied to the sample. Next 1
After reaching 400 ℃, 30 while maintaining the same rate of temperature rise
It was applied while applying a pressure of kg / cm ² until the temperature reached 1600 ° C. Then the pressure is reduced and the temperature rises to 2700
Only the pressure corresponding to the weight of the jig (100 g / cm ² ) was applied until the temperature was raised to ℃. After the temperature reached 2700 ° C., pressure was applied again. The applied pressure is 300 kg / cm ² . 30 keeping this pressure
The temperature was raised to 00 ° C. to complete the heat treatment. The resulting graphite block had a uniform surface with almost no wrinkles.

The characteristics of the obtained graphite were measured using a rotor flex RU-200B type X-ray diffractometer manufactured by Rigaku Denki Co., Ltd. The half value width of the diffraction line obtained as a result of the rocking characteristic measurement at the peak position of the graphite (002) diffraction line was evaluated. As a result of the measurement, it was found that the rocking characteristic was 0.48 °, which had excellent characteristics as an X-ray or neutron beam monochromator.

The same treatment was carried out using a film which was not treated with silica powder, but during the temperature rising process up to 1400 ° C., the films were fused and destroyed due to the gas generated from the inside. Next, to prevent destruction, 1400 ℃
The pressure was 100 g / cm ² which is the pressure due to the weight of the jig, and the subsequent treatment was the same. The locking characteristic of the obtained block is 0.7.
It was 0 °. From this, it was found that the method of the present invention is very effective on a lake having rocking characteristics.

(Embodiment 3) The third embodiment of the present invention will be described below.

The same silica treatment as in the second embodiment described above was carried out by applying PBT, PBBT, PBO, PB having a thickness of 50 μm.
The BO, PA, PBI, PBBI, PT and PPV films were used. Next, 100 sheets of each film were laminated, each set in a jig made of graphite, and heated to 1500 ° C. at a rate of 10 ° C./min in an argon gas atmosphere. During this period, a pressure of 4 kg / cm ² was applied to the sample. Next, after reaching 1500 ° C., pressure was applied while maintaining the same temperature rising rate. Applied pressure is 30 k
It was g / cm ² and was applied until the temperature reached 1800 ° C.
After that, the pressure was reduced so that only the pressure corresponding to the weight of the jig was applied until the temperature was raised to 2800 ° C. After the temperature reached 2800 ° C, pressure was applied again. The applied pressure is 300 kg / cm ² . While maintaining this pressure, the temperature was raised to 3000 ° C. to complete the heat treatment. The resulting graphite block had a uniform surface with almost no wrinkles.

For comparison, using a film not subjected to oxidation treatment, the pressure in the heat treatment process up to 1500 ° C. was set to 100 g / cm ² corresponding to the weight of the graphite jig, and the same treatment was performed thereafter to prepare a graphite block. .

The properties of the obtained graphite were measured by using a rotor flex RU-200B type X-ray diffractometer manufactured by Rigaku Denki Co., Ltd. The half value width of the diffraction line obtained as a result of the rocking characteristic measurement at the peak position of the graphite (002) diffraction line was evaluated. The measurement results (Table 1)
Shown in.

[0046]

[Table 1]

From these results, it is clear that the graphite blocks obtained from these polymers all have excellent characteristics as an X-ray or neutron beam monochromator.

(Fourth Embodiment) The fourth embodiment of the present invention will be described below.

The same treatment as in the second embodiment described above was carried out on the surface of a 25 μm-thick polyimide (Kapton H film from DuPont) silica (average particle size 2 μm,
0.2 μm, 0.02 μm) calcium oxide (average particle size 1 μm), magnesium oxide (average particle size 5 μm),
Using aluminum oxide (average particle size 2 μm), carbon (average particle size 2 μm), graphite (average particle size 2 μm), titanium oxide (average particle size 0.5 μm), calcium carbonate (average particle size 0.4 μm) It was

200 films (3 ×
3 cm ² ) are stacked, set in a graphite jig in the same manner as in the first embodiment, and placed in an argon gas atmosphere for 10 minutes.
The temperature was raised to 1400 ° C at a rate of ° C / min. During this period, a pressure of 4 kg / cm ² was applied to the sample. Next 1
After reaching 400 ℃, 30 while maintaining the same rate of temperature rise
It was applied while applying a pressure of kg / cm ² until the temperature reached 1600 ° C. Then the pressure is reduced and the temperature rises to 2700
Only the pressure corresponding to the weight of the jig (100 g / cm ² ) was applied until the temperature was raised to ℃. After the temperature reached 2700 ° C., pressure was applied again. The applied pressure is 300 kg / cm ² . 30 keeping this pressure
The temperature was raised to 00 ° C. to complete the heat treatment. The resulting graphite block had a uniform surface with almost no wrinkles.

The characteristics of the obtained graphite were measured by using a rotor flex RU-200B type X-ray diffractometer manufactured by Rigaku Denki Co., Ltd. The half value width of the diffraction line obtained as a result of the rocking characteristic measurement at the peak position of the graphite (002) diffraction line was evaluated. The measurement results (Table 2)
Shown in.

[0052]

[Table 2]

As is clear from these results, it was found that the graphite blocks obtained from these polymers all have excellent characteristics as an X-ray or neutron beam monochromator.

[0054]

As described above, according to the present invention, a plurality of polymer films are laminated, and an inorganic powder is present between the polymer films to apply pressure and heat treatment.
The polymer films do not adhere to each other during the thermal decomposition process, and the decomposed gas can pass smoothly between the polymer films and diffuse to the outside.

That is, since the polymer films are not fused to each other, it is possible to apply a certain amount of pressure, and it is possible for the polymer films to slide with each other, thereby introducing wrinkles and strains in the polymer films. Can be prevented.

This makes it possible to obtain a graphite block having high orientation. This block is a high quality graphite made by a very simple method compared to the conventional graphite block making method, and can be widely used as an X-ray or neutron beam monochromator and as a neutron filter. I can.

[Brief description of drawings]

FIG. 1 is a polyimide used as an example of the present invention (Kapton H film manufactured by DuPont, thickness 25 μm)
Characteristic diagram showing expansion and contraction of film

Claims (4)

[Claims] 1. A method for producing graphite, which comprises laminating a plurality of polymer films, making an inorganic powder present between the polymer films, and applying pressure and heat treatment. 2. The method for producing graphite according to claim 1, wherein the weight of the inorganic powder is less than 1% based on the polymer. 3. The method for producing graphite according to claim 1, wherein the average particle size of the inorganic powder is 20 microns or less. 4. The polymer film is at least one selected from polyoxadiazole, aromatic polyimide, aromatic polyamide, polybenzimidazole, polybenzobisthiazole, polybenzoxazole, polythiazole, and polyparaphenylene vinylene. The method for producing graphite according to claim 1, wherein the graphite is of a type.