JP2633638B2 - Method for producing highly oriented graphite crystal - Google Patents

Description

The present invention relates to a method for producing highly oriented graphite crystals suitable as a host material for an X-ray or neutron beam monochromator and a graphite intercalation compound.

[Prior Art] Artificial graphite is usually obtained as an aggregate of fine crystal grains, and it is difficult to obtain a single crystal. Also, even in the case of natural graphite, the crystal grains are confirmed to be a single crystal but at most 2 grains.
It is as small as ~ 3mm.

This is because graphite does not melt at normal pressure and the vapor pressure is 2500K
This is because it is extremely difficult to grow a single crystal since the pressure is about 10 ⁻⁶ atm.

Thus, academically, it is necessary to elucidate the basic physical properties and crystal growth mechanism of graphite, and industrially, as a host material of X-ray or neutron monochromator and graphite intercalation compound, on a macroscopic scale. Obtaining a material having a graphite crystal or growing a large graphite single crystal is a very important task, and has been given great interest in the past.

Against this background, there have recently been proposed a few techniques for growing graphite single crystals. It is classified into the decomposition of carbides and the heat treatment under pressure of pyrolytic carbon.

The method for obtaining single-crystal graphite by recrystallization from a metal melt is to precipitate graphite crystals from carbon-molten Ni, carbon-molten titanium boride or carbon-molten iron. Industrially, graphite precipitated from molten iron in an iron making plant is manufactured as quiche graphite.

On the other hand, as a method of obtaining single-crystal graphite by decomposition of the metal compound, there are a method of heat-treating tantalum carbide and aluminum carbide to precipitate crystals, and a method of obtaining crystals by decomposition using silicon carbide halogen gas.

Furthermore, the pressurized heat treatment method of pyrolytic carbon was introduced in 1964.
Since it was announced by Moore et al., It has been widely used for basic research on graphite and has been put to practical use for special applications by utilizing its unique properties. In this method for producing highly oriented pyrolytic graphite, first, pyrolytic carbon is subjected to 250k at 3000 ° C.
g / cm ² stress in uniaxial direction, uniaxial pressurization and heating,
Then, it is heated to 3500 ° C. or more and heat-treated again. In this method, graphite is creeped by the heat treatment under pressure at 3000 ° C., and the pebble and the cone structure peculiar to pyrolytic carbon disappear.
The HOPG thus obtained shows single crystal physical properties, and X
The wires are used in neutron monochromators and the like, and are also used for research on graphite layer compounds, which are expected to have high electrical conductivity.

[Problems to be Solved by the Invention] However, in the above-mentioned method and method, although a single crystal having an ideal crystal structure is obtained, in each case, flakes having a layer surface spread of at most several mm are deposited and a large shape is formed. There is a drawback that you can not get things. In addition, since the single crystal produced by these methods is in contact with the molten metal, it is difficult to obtain a single crystal having high purity. Therefore, the usefulness as a graphite material is significantly restricted.

On the other hand, the above-mentioned method requires processing at an ultra-high temperature exceeding 3000 ° C., and since it is difficult to obtain this ultra-high temperature, mass production is extremely difficult, and there is concern about material supply.

The present invention has been made in view of the above problems, and has as its object to provide a method for producing a highly oriented graphite crystal, which can produce a highly oriented graphite crystal quickly and at low cost. .

[Means for Solving the Problems] A method for producing a highly oriented graphite crystal according to the present invention comprises a step of pre-firing a molded article of a thermosetting resin and terminating the same in a state in which hydrogen remains, and a step of pre-firing. And subjecting the article to hot isostatic pressing.

[Action] The inventors of the present application have conducted intensive studies to develop a method for rapidly producing large-sized highly-oriented graphite crystals, and as a result, a glass containing a low-molecular hydrocarbon that can grow into graphite crystals by heat treatment. After pre-firing the shaped carbon compact, it was found that highly oriented graphite crystals could be precipitated inside the compact by performing hot isostatic pressing (HIP) treatment under predetermined conditions. The present invention has been made based on such findings.

In the present invention, a thermosetting resin such as phenol formaldehyde resin or furfuryl alcohol is molded, and then heated to a predetermined temperature and pre-fired. These thermosetting resins in the course of pyrolysis, which is _{heated, H 2 O, CO 2,} C
O, CH ₄ and H ₂ gas are generated while carbonizing.
Then, when firing is performed to a temperature at which hydrogen gas generation is finally completed, cyclization of the carbon-carbon bond proceeds, and so-called glassy carbon is formed.

Thus, when heat-treating these thermosetting resin molded bodies, pre-firing is stopped at a temperature at which hydrogen can still be generated, in other words, at a temperature equal to or lower than the temperature at which low-molecular hydrocarbons remain,
Subsequently, by performing HIP treatment using an ultra-high-temperature hot isostatic press (ultra-high-temperature HIP) or the like, highly oriented graphite crystals are precipitated inside the molded body.

The heating temperature in this HIP treatment is preferably 2000 to 3000 ° C., and the pressure is preferably 1000 to 3000 atm. As a result, large, highly oriented graphite crystals are precipitated inside the molded body while being surrounded by the glassy carbon.

Although there are many unclear points about the mechanism of crystal phase generation, in ultra-high temperature HIP treatment after pre-firing, low molecular hydrocarbons or graphitizable components generated from the glassy carbon compact are subjected to high pressure (isotropic). It is presumed that they were not released to the outside of the compact but were compressed inside, and precipitated and grown as graphite crystals.

Conventionally, under isotropic pressure such as HIP, it was thought to inhibit the growth of graphite crystals, but after pre-baking as in the present invention, when isotropic pressing is performed, It is considered that the generation of hydrogen gas inside the molded body surrounded by the glassy carbon phase causes anisotropy to increase due to this gas pressure, thereby promoting the growth of graphite crystals.

The pre-firing temperature must be lower than the temperature at which the generation of hydrogen gas ends. If the pre-firing temperature exceeds this temperature, the residual hydrogen concentration is too low and
Even if the treatment is performed, no precipitation of graphite crystals occurs.

On the other hand, if the pre-firing temperature is too low, the glassy carbon phase surrounding the graphite crystal phase is fragile, and large-size graphite crystals cannot be produced.

For this reason, the pre-firing temperature is such that the residual hydrogen concentration is 50 to 5000
It is preferable to be in the range of ppm.

EXAMPLES Hereinafter, examples of the present invention will be described more specifically. In the present invention, a single crystal of graphite is deposited inside the molded body while the entire surface is surrounded by glassy carbon. Therefore, it is necessary to make the surface of the molded body vitreous carbon by pre-firing. As the thermosetting resin that becomes vitreous carbon after pre-firing, a phenolic resin, There are furan-based resins, xylene-based resins, melamine-based resins and aniline-based resins, and those obtained as aqueous or oily, such as resole and novolak phenol formaldehyde-based resins, furan-based resins, xylene-based resins, melamine-based resins and There are aniline-based resins and the like.

First, these thermosetting resins are formed into a predetermined shape by a known method. As a molding method, for example, a method of pouring a liquid thermosetting resin into a frame and embedding it,
There is a method in which a powdery thermosetting resin is pressed cold and hot using a mold.

Then, the thermosetting resin molded body in an inert gas atmosphere such as N ₂ or Ar gas, residual hydrogen concentration of the molded body 50 to 5000
Pre-bake by heating to ppm.

Then, the sample after pre-baking was processed using ultra-high temperature HIP,
The HIP process is performed under the conditions of 000 to 3000 ° C. and 1000 to 3000 atm. At this time, it is effective to increase the pressure to a predetermined pressure while maintaining the processing temperature at the pre-firing temperature or lower, and then perform the processing in a pressure leading pattern in which the temperature is raised to the predetermined temperature. If the temperature is raised and the pressure is increased at the same time, it is heated to a temperature range in which hydrogen and the like are generated in spite of insufficient pressurization, thereby releasing a component which is graphitized from low molecular hydrocarbons. In addition, precipitation of graphite crystals does not easily occur.

In addition, other than the method of manufacturing from a thermosetting resin alone, petroleum coke, after molding a graphitizable carbon precursor such as mesophase pitch in a form surrounded by a non-graphitizable carbon precursor such as a thermosetting resin Similarly, there is a method of performing pre-baking and ultra-high temperature HIP.

Next, the results of actually producing graphite crystals by the method of the present invention will be described.

Example 1 A powdery phenol formaldehyde resin was formed into a shape having a diameter of 80 mm and a thickness of 6 mm by hot pressing. Next, the residual hydrogen concentration in nitrogen gas was (1) 5100ppm respectively.
(2) 200 ppm (3) After pre-firing the three molded bodies to 25 ppm, these pre-fired products were subjected to ultra-high temperature HIP.
Was used at 2550 ° C. and 2000 atm. As a result, various characteristics such as the presence or absence of the graphite phase are shown in Table 1 below. If the pre-firing temperature is lower than the temperature at which the residual hydrogen concentration becomes 5000 ppm, the vitreous carbon phase is brittle and a dense graphite crystal phase cannot be obtained. At a high temperature at which the residual hydrogen concentration is lower than 50 ppm, no graphite phase precipitates.

Example 2 A molded article molded in the same manner as in Example 1 was produced with a residual hydrogen concentration of 20.
After pre-firing to 0 ppm, 2550 using HIP
C. and 2,000 atm. At this time, the heating rate is 50
The HIP treatment was performed at 0 ° C./hr under the following conditions: (1) increased pressure to 2000 atm at the pre-firing temperature (pressure precedent); The results are shown in Table 2 below.

Example 3 Mesocarbon microbeads from which a mesophase component in a pitch was extracted were hot-pressed while being surrounded by a phenol formaldehyde resin, and had a diameter of 50 mm and a thickness of 6 m.
Thus, a m-shaped molded body was obtained (the portion of the mesocarbon microbeads was 40 mm in diameter and 4 mm in thickness). After preliminarily firing this compact, it was treated at 2500 ° C. and 2,000 atm using ultra-high temperature HIP to obtain graphite crystal having a diameter of 35 mm, a thickness of 2.3 mm and a bulk density of 2.15.

Example 4 A phenol formaldehyde resin powder was hot-pressed. (1) Pipe shape having an outer diameter of 80 mm, an inner diameter of 60 mm and a height of 150 mm, (2) a width of 50 mm, a depth of 50 mm and a height of 150 mm
(3) 200mm diameter, 6mm thick disk-shaped, 3mm shaped, pre-fired, ultra high temperature HIP
Processing was performed. The shape of the obtained graphite crystal is as follows.

(1) When formed into a pipe shape Outer diameter 65 mm, Inner diameter 60 mm, Height 115 mm (2) When formed into a box shape Width 35 mm, Depth 35 mm, Height 115 mm (3) When formed into a disk shape Thus, a very large graphite crystal was obtained with a diameter of 155 mm and a thickness of 2.3 mm.

[Effects of the Invention] According to the present invention, since hot isostatic pressure treatment is performed after pre-firing, a highly oriented graphite crystal used as a monochromator for X-rays or neutrons and a host material for a graphite intercalation compound can be rapidly produced. And at low cost.

For this reason, according to the present invention, it is possible to stably supply a large-sized graphite crystal, a sputtering target relating to electronic materials, a graphite wafer for epitaxial growth, a substrate material having excellent heat and electric conductivity, and a thrombus. New applications such as sliding members such as artificial heart valves and magnetic head base materials having low formability have become possible.

Further, it becomes possible to produce graphite crystals having a pipe shape, a box shape or the like or a different shape, and it is possible to supply a material that is extremely useful for applications that have not been possible in the past.

Claims (5)

(57) [Claims] 1. A method comprising the steps of: preliminarily firing a molded article of a thermosetting resin and terminating it in a state in which hydrogen remains; and subjecting the prefired product to hot isostatic pressing. A method for producing highly oriented graphite crystals. 2. The method for producing highly oriented graphite crystals according to claim 1, wherein said pre-firing step is completed when the residual hydrogen concentration of said compact is 50 to 5000 ppm. 3. The method of claim 2, wherein the hot isostatic pressing is performed in a range of 2,000 to 3,000.
The method for producing highly oriented graphite crystals according to claim 1 or 2, wherein the treatment is performed at a temperature of 1000C and at a pressure of 1000 to 3000 atmospheres. 4. The method according to claim 1, wherein in the hot isostatic pressing, the pressure is increased to a predetermined pressure at a high temperature equal to or lower than a pre-firing temperature, and then the temperature is increased to the predetermined temperature.
The method for producing a highly oriented graphite crystal according to the above item. 5. A thermosetting resin molded body obtained by molding the precursor to be graphitizable carbon in a form surrounded by a thermosetting resin carbon precursor. Or 1
The method for producing a highly oriented graphite crystal according to the above item.