JPH0244020A - Production of graphite - Google Patents

Abstract

PURPOSE:To obtain block-shaped graphite having superior blocking characteristics and useful for an X-ray optical element, an X-ray monochromator, a neutron beam diffraction mirror, a filter, etc., by treating arom. polyamide films under specified conditions. CONSTITUTION:Arom. polyamide films are separately heat-treated at >=2,200 deg.C and the resulting carbonaceous films are superposed and bonded at >=2,000 deg.C under >=4kg/cm<2> pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing block graphite used as an X-ray optical element, an X-ray monochromator-neutron beam diffraction mirror, a filter, etc.

Conventional technology Graphite has an important position as an industrial material due to its outstanding heat resistance, chemical resistance, and high conductivity, and is widely used as electrodes, heating elements, and structural materials.

Among them, artificial graphite, which has properties equivalent to single crystal graphite, is widely used as monochromators, filters, and spectroscopic crystals for X-rays and neutrons because of its excellent spectroscopic and reflective properties for Xls and neutron beams.

One way to use such single crystal graphite is to use naturally occurring graphite, but high-quality graphite is produced in very limited quantities and is difficult to handle in the form of powder or small blocks. Unfortunately, graphite is manufactured artificially.

There are two main methods for producing such artificial graphite:
It can be classified into two methods.

The first is Fe, precipitation from Nl/C melt, St, A
This is a method of making carbon by decomposing No. 1 carbide or by cooling a carbon melt under high temperature and high pressure. The graphite thus obtained is called quiche graphite and has the same physical properties as natural graphite. however,
This method only yields graphite in the form of flakes of 1/1 to 1/2, and due to the complexity and high cost of the manufacturing method, it is hardly used industrially.

The second method involves high-temperature decomposition deposition of hydrocarbon gas in a gas phase and hot processing thereof, and is produced by applying a pressure of 10#/- and reannealing at 3400° C. for a long time. The graphite obtained in this way is called highly oriented pyrographite (HOPG), and its properties are almost the same as natural graphite. Unlike quiche graphite, this method allows the production of quite large pieces, but it has the drawbacks of being complicated, having a low yield, and being very expensive.

In contrast, 3,000 different organic or carbonaceous substances
A method of converting graphite by heating at temperatures above ℃ has been considered for a long time.

However, this method did not yield graphite with the same physical properties as natural graphite or Quiche graphite.

For example, the electric conductivity in the a-b plane direction, which is the most typical physical property of graphite, is 1 to 2.5 x 10'S/cm for natural graphite and Quiche graphite, but in this method, it is generally 1 to 2 x 10'S/cm. Only a product of "S/-" conductive dust is obtained. This shows that graphitization generally does not proceed completely in such a method.

In this method, a carbonaceous material such as coke and a binder such as coal tar are usually used as starting materials. Carbon, which is produced by heating coke or charcoal to about 3,000°C, has many different structures, ranging from those relatively close to graphite structures to those that are far from it. In this way, carbon whose structure changes relatively easily into a graphite-like structure by simple heat treatment is called graphitizable carbon, and carbon that does not change is called non-graphitizable carbon. The cause of such structural differences is closely related to the graphitization mechanism and depends on whether the structural defects present in the carbon precursor are easily removed by the subsequent heat treatment. . Therefore, the microstructure of the carbon precursor plays an important role in graphitizability.

In contrast to these methods that use coke as a starting material, several studies have been conducted to create graphite films by using polymeric materials and heat-treating them. This is an attempt to control the fine structure of the carbon precursor while making use of the molecular structure of the polymer material. In this method, a polymer is heat-treated in vacuum or in an inert gas, and a carbonaceous material is formed through decomposition and polycondensation reactions. However, it was known that most polymeric materials could not be used for this purpose. For example, polymers that have been carefully heat-treated for this purpose include phenol formaldehyde resin, polyacrylonitrile,
There are polyamides, polyparaphenylene, polyparaphenylene oxide, polyvinyl chloride, etc., but all of these belong to non-graphitizable materials, and no material with a high graphitization rate has been obtained.

In order to solve these problems, the present inventor has conducted various studies and attempted to graphitize many polymers.

As a result, film-like polyamide (PA) polyoxadiazole (POD), aromatic polyimide (PI), 3
Types of polybenzothiazole (PBT), polybenzobisthiazole (PBBT), polybenzoxazole (
PBO), polybenzobisoxazole (PBBO)
We have obtained new knowledge that when polythiazole (PT) polymers are heat-treated at a specific temperature, they graphitize more easily than any previously known polymer materials. They are JP-A-61-275114 and JP-A-61-27.
5115 and JP-A No. 61-275117.

According to this method, graphite with a high graphitization rate can be easily produced in a short time by heating the above-mentioned polymer at a temperature of 1800° C. or higher, preferably 2500° C. or higher.

To express the degree of graphitization, X-ray diffraction parameters such as the lattice constant and the size of crystallites in the C-axis direction and the graphitization rate calculated therefrom are often used, and electrical conductivity values are also often used. The lattice constant is calculated from the position of the (002) diffraction line of X-rays, and the closer it is to the value of 6708A, which is the lattice constant of natural single crystal graphite, the more developed the graphite structure is. Further, the size of the crystallite in the C-axis direction is calculated from the half-width of the (002) diffraction line, and the larger the value, the better the planar structure of graphite is shown. The crystallite size of natural single crystal graphite is 1oooA or more. The graphitization rate is calculated from the crystal plane spacing (d, .2) from the literature Le Carbons Vol. 1, p. 129, 1965 (Les Carbons Vol. I
I) 129.1965). Of course, it is 100% in natural single crystal graphite. The electrical conductivity value refers to the value in the a-b plane direction of graphite, and is 1 to 2.5 x 10'S/mouth for natural single crystal graphite. The larger the conductive displacement, the closer the structure is to graphite.

Furthermore, one of the X-ray diffraction parameters is a rocking property that indicates how the ab and ab planes overlap. This is called a diffraction intensity curve and is a diffraction intensity curve obtained by rotating the crystal when a monochromatic, parallel X-ray flux is incident. 20 is fixed at the angle at which the (00t) diffraction line appears, and θ is rotated. Measure by thing. This value is evaluated using the absorption half-width, and the rotation angle (
0). The smaller this value is, the more clearly the a-b planes overlap.

Problems to be Solved by the Invention The method of obtaining graphite from the special polymer film mentioned above is easy and very excellent, but as a result of various subsequent studies on this method, the following It has become clear that there are several shortcomings.

The first drawback is that this method cannot produce thick graphite, that is, blocks of graphite.

-The graphitization reaction seems to be unrelated to the thickness of the starting material film, but in reality, the reaction strongly depends on the thickness of the starting material. This is something that was completely unknown until now, but we conducted various experiments to clarify this point. For example, Table 1 shows the results of graphitizing four types of aromatic polyamide films with different thicknesses and evaluating them using the values of the graphite lattice constant, graphitization rate, and electric conductivity in the a-b plane direction. This result clearly shows that the degree of progress of the graphitization reaction varies depending on the thickness of the starting polyamide film. For example, the graphitization rate varies from 99 to 88 inches depending on the thickness. This shows that even if the same polyamide raw material is used, it is possible to obtain graphite in the form of a thin film, but it is difficult to obtain graphite in the form of a thick block.

Margin below Table 1 Margin below The second drawback is that simply heating the polymer raw material does not improve the properties of graphite, such as how neatly the ab-axis plane overlaps the c-axis direction. . This property becomes an important property when trying to use the crystal in an X-ray optical element or the like.

To measure how the ab planes overlap, the rocking method using X-ray diffraction described above is used. X graphite crystal
In order to use it as an optical crystal such as S, it is generally said that a thin graphite film of 50 μm or less requires an angle of 04° or less, and a thick graphite block of 1rrtn or more requires an angle of 3° or less. On the other hand, in the case of the graphitized PA shown in Table 1, the rocking properties were 7.5 mm for samples with starting film thicknesses of 10.25 mm, 100 mm, and 600 mm, respectively. . 9.5:'11'
: It was 16°. This fact shows that in terms of locking properties, it is not possible to create an excellent radiation optical element simply by heating graphite. This is because the thicker the film, the more difficult it is for the ab plane to be oriented due to gas generation from inside the sample during heat treatment.

The present invention improves several drawbacks of the method of producing graphite by heating a polymer film as described above, and has excellent properties as a graphite crystal including rocking properties, and has a thick crystal structure. It was created for the purpose of producing block graphite.

Means for Solving the Problems In order to achieve the above object, the present invention provides a method in which a plurality of carbonaceous films obtained by heat treating an aromatic polyamide film at a temperature of 2200°C or higher are press-bonded at a temperature of 2000°C or higher. This is what I did.

Effect: With the above structure, it is possible to obtain graphite of any thickness and excellent properties in which the ab and ab planes are neatly overlapped.

Examples Examples of the present invention will be described in detail below, but it goes without saying that the present invention is not limited to these examples.

The degree of graphitization was evaluated from the values of the lattice constant, graphitization rate, electrical conductivity rocking property, etc.

Measurement of each physical property of graphite was performed in accordance with the following.

1. Lattice constant (Co) Using a Philips PW-1051 model X-ray diffractometer, the X-ray diffraction line of the sample was measured using 0-section alpha rays. The COO value is determined by Bragg's equation nλ = 2 d s from the (OO2) diffraction line that appears around 2θ = 26~27°.
Calculated using inθ (2ti=co). Here, n=2 and λ is the wavelength of the X-ray.

2. Graphitization rate (%) The graphitization rate was calculated from the value of the interplanar spacing (d) using the following formula.

d,,t = 3.354g + 3.44 (1-g
) Here, g indicates the degree of graphitization; g=1 indicates complete graphite, and g=0 indicates amorphous carbon.

3. Electrical conductivity (S/cm) It was measured by attaching a four-terminal electrode to the sample using silver paste and gold wire, passing a constant current through the outer electrode, and measuring the voltage drop at the inner electrode. The width, length, and thickness of the sample were determined using a microscope to determine the electrical conductivity value.

4. Locking characteristics (0) Rotorflex RU-200B type X manufactured by Rigaku Denki Co., Ltd.
Using a line diffraction device, the rocking characteristics at the peak position of the graphite (002) diffraction line were measured. The half width of the obtained absorption curve was taken as the rocking characteristic.

The present inventors aimed to obtain high quality graphite having excellent properties equivalent to natural graphite.
Polymer films such as OD, PI, PBT, and PBBT were graphitized and hot pressed. the result,
It was discovered that graphite film obtained by heat-treating aromatic polyamide film (PA) can be easily crimped at 2000℃, a temperature of 4#/d or more, and under pressure, and at the same time its locking properties can be significantly improved. Ta. In addition, if the temperature is less than 2000℃ or the pressure is 4'i/-
It was found that the films did not adhere to each other if the temperature was less than that.

For example, 24 μm and 80 μm, respectively, obtained by pressing 4 types of PA films treated at 2600° C. at 2600° C. and a pressure of 20 #/-.
, 320 μm, and 1800 μm thick graphite have rocking properties of 1.2°, 1.4°, respectively.
1.6° and 1.9° amide films were sandwiched between quartz plates, heated at a rate of 20°C per minute in nitrogen, and heated to 1000°C for 1
Heat treated for hours. The heat-treated film thus obtained was sandwiched between graphite substrates, heated at a rate of 10°C per minute from room temperature in an argon stream, treated at the desired temperature Tp for 1 hour, and cooled at a rate of 20°C per minute. Ta. The furnace used was a 46-1 type carbon heater furnace manufactured by Shinsei Denko Co., Ltd.

Next, four of the obtained films were hot pressed using an ultra-high temperature hot press manufactured by Chugai Roko Kogyo ■. The pressing temperature was 2500°C, the pressure was 20 H/- and the pressing time was 1 hour. Table 2 shows the physical property values of the graphite thus obtained before hot pressing and after hot pressing.

As is clear from the results in Table 2, the hot pressing treatment does not have much effect on the lattice constant, graphitization rate, and electrical conductivity properties, but it brings about a significant improvement in the rocking properties. Such excellent locking properties indicate that graphite treated in this manner is optimal for applications such as X-ray optical elements.

Below is a margin Example 2 A PA film was treated at 2800° C. (Tp) in the same manner as in Example 1, and hot pressed under various conditions. The results are shown in Table 3. Pressing time is 1 hour. It can be seen that under hot pressing conditions of less than 2000° C. and less than 4 to 9/CfA, the PA film does not bond and the locking properties are not significantly improved.

On the other hand, if the press temperature and pressure are set to higher than these conditions, it is possible to achieve pressure bonding, and at the same time, a remarkable improvement in the locking properties can be observed. Higher temperature and higher pressure are both effective, and under the press conditions of 2800°C and 100#/-, an excellent locking value of 0.28° could be obtained. This value can be further improved by increasing the pressing time.
After pressing for 2 hours under a pressure of -, the value was 026°.

Margins below Example 3 A PA film treated at 2800°C in the same manner as in Example 2 was hot pressed at 2800°C under a pressure of 40 #/- for 1 hour. The number of films used during pressing was 10, 20, 80, and 200. The thickness of each graphite thus obtained was approximately 33 inches.

110 μm, 380 μm, and 11TIIn, but there was almost no difference in physical properties such as rocking characteristics. In other words, it was found that block-shaped graphite as thick as possible could be obtained using this method.

More than the effects of the invention, in short, the present invention further provides two or more aromatic polyamide films graphitized at 2200°C or higher.
A method for producing graphite characterized by hot pressing at 000°C and a pressure of 4 mm/- or more, which allows the production of almost perfect graphite, which has been difficult to produce in the past, with ease. In particular, it is possible to obtain block-shaped graphite with significantly improved rocking properties compared to conventional methods. Graphite obtained by the method of the present invention can be widely used in X-ray and neutron monochromators.

filter etc.

Claims (1)

[Claims] A plurality of carbonaceous films obtained by heat treating an aromatic polyamide film at a temperature of 2200°C or higher is heated to 2000°C.
A method for producing graphite, characterized by bonding while applying a pressure of 4 kg/cm^2 or more in the above temperature range.