JPH0251412A - Production of graphite crystal having high orientation characteristic - Google Patents

Abstract

PURPOSE:To obtain quickly and inexpensively a graphite crystal having high orientation characteristic being suitable as a host material for an intercalated compd. of graphite by calcining previously a molded body of a thermosetting resin, and subjecting the molded thermosetting resin to hot hydrostatic pressing after completing the previous calcination while leaving H2. CONSTITUTION:A molded body of a thermosetting resin (e.g., phenolformaldehyde resin) is calcined previously and the previous calcination is completed while H2 remains. Suitable H2 concn. to be left is 50-5000ppm. A graphite crystal having high orientation characteristic is obtd. by subjecting the obtained previously calcined product to hot hydrostatic pressure treatment, suitably at 2000-3000 deg.C, 1000-3000atm. It is preferred to elevate the pressure to a specified pressure at a temp. <= the previous calcination temp., then elevating the temp. to a specified temp. Thus, a large sized graphite crystal is obtd. stably, and novel field of use of graphite wafer for epitaxial growth can be developed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing highly oriented graphite crystals suitable as host materials for X-ray or neutron beam monochromators and graphite intercalation compounds.

[Prior Art] Artificial graphite is usually obtained as an aggregate of fine crystal grains, and it is difficult to obtain a single crystal. Furthermore, even in the case of natural graphite, although it has been confirmed as a single crystal, the crystal grains are as small as 2 to 3 crystals.

This is because graphite does not melt at normal pressure, and its vapor pressure is 2500°.
This is because the atmospheric pressure is extremely low at approximately 10-6 atmospheres, making it extremely difficult to grow single crystals.

Academically, it is used to elucidate the basic physical properties and crystal growth mechanism of graphite, and industrially, it is used as a host material for X-ray or neutron beam monomers, chromators, and graphite intercalation compounds on a macroscopic scale. Obtaining a material having graphite crystals or growing a large graphite single crystal is an extremely important issue, and has traditionally been a cause for concern.

Against this background, a few techniques for growing single crystals of graphite have been proposed in recent years, but these single crystal growing techniques depend on the method of preparation: recrystallization from a metal melt; It is classified into ■decomposition of metal carbides, and ■pressure heat treatment of pyrolytic carbon.

In the method (2) of obtaining single crystal graphite by recrystallization from a metal melt, graphite crystals are precipitated from carbon-molten Ni, carbon-molten titanium boride, or carbon-molten iron. Industrially, graphite precipitated from magnetic iron in steel plants is produced as quiche graphite.

On the other hand, methods for obtaining single-crystal graphite by decomposing metal carbides in (2) include a method in which tantalum carbide and aluminum carbide are heat-treated to precipitate crystals, and a method in which crystals are obtained by decomposing silicon carbide using halogen gas. .

Furthermore, since the pressurized heat treatment method of pyrolytic carbon (2) was announced by Moore et al. in 1964, it has been widely used in basic research on graphite, and its unique properties have been used to put it into practical use for special purposes. has been done.

In this method for producing highly oriented pyrolytic graphite, first, a stress of 250 kg/cn (250 kg/cn) is applied to pyrolytic carbon in a uniaxial direction at 3000°C, and then uniaxial pressure and heating are performed.
Reheat treatment by heating to 500°C or higher. In this method, graphite creeps by pressurized heat treatment at 3000° C., and the pebble and conical structures peculiar to pyrolytic carbon disappear. HOP G obtained in this way exhibits single-crystal-like physical properties and is used in practical applications such as X-ray or neutron beam monochromators, while it is also used in research on graphite layer compounds, which are expected to have high conductivity. ing.

[Problems to be Solved by the Invention] However, although the above-mentioned methods (1) and (2) yield a single crystal with an ideal crystal structure, in both methods, the layer plane is precipitated in the form of flakes with a spread of several mm at most. The problem is that large shapes cannot be obtained. Furthermore, since the single crystals produced by these methods come into contact with a metal melt, it is difficult to obtain a single crystal with high purity. Therefore, there are significant limitations on its usefulness as a graphite material.

On the other hand, the method (2) described above requires processing at an ultra-high temperature of over 3000° C. Due to the difficulty of achieving this ultra-high temperature, mass production is extremely difficult and there is concern about the supply of materials.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a method for manufacturing highly oriented graphite crystals, which allows highly oriented graphite crystals to be manufactured quickly and at low cost.

[Means for Solving the Problems] The method for producing highly oriented graphite crystals according to the present invention includes a step of pre-calcining a thermosetting resin molded body and finishing it in a state in which hydrogen remains, The method is characterized by comprising a step of subjecting the product to hot isostatic pressure treatment.

[Function] As a result of intensive research aimed at developing a method for rapidly producing large-sized highly oriented graphite crystals, the inventors of the present application have developed a method for rapidly producing large-sized highly oriented graphite crystals. It has been found that highly oriented graphite crystals can be precipitated inside the shaped carbon compact by pre-firing the shaped carbon compact and then subjecting it to hot isostatic pressing (HIP) under predetermined conditions. The present invention has been made based on this knowledge.

In the present invention, after a thermosetting resin such as phenol formaldehyde resin or furfuryl alcohol is molded, it is heated to a predetermined temperature and pre-baked. These thermosetting resins generate H2O, Co□ during the heated pyrolysis process.
, CO, CH4, and H2 gases are generated during carbonization. When the carbon-carbon bond is finally fired to a temperature at which hydrogen gas generation ends, cyclization of the carbon-carbon bond progresses, resulting in so-called glassy carbon.

Therefore, when heat-treating these thermosetting resin molded bodies,
Preliminary firing is stopped at a temperature at which hydrogen generation is still possible, in other words, at a temperature below the temperature at which low-molecular hydrocarbons remain, and then an ultra-high temperature hot isostatic pressing device (ultra-high temperature HIP) is used. By performing the HIP treatment, highly oriented graphite crystals are precipitated inside the molded body.

The heating temperature in this HIP treatment is 2000 to 300℃.
The applied pressure at 0° C. is preferably 1,000 to 3,000 atm. As a result, large highly oriented graphite crystals are precipitated inside the compact while being surrounded by glassy carbon.

Although many aspects of the mechanism of crystal phase generation are not clear,
In the ultra-high temperature HIP treatment after pre-firing, the low-molecular hydrocarbons or easily blackened components generated from the glass-like carbon molded body are compressed inside the molded body under high pressure (isotropically) without being released to the outside. It is presumed that the crystals precipitated and grew as graphite crystals.

Conventionally, it was thought that isotropic pressure as in HIP inhibits the growth of graphite crystals, but when isotropic pressure is applied after pre-firing as in the present invention, It is thought that hydrogen gas is generated inside the molded body surrounded by the glassy carbon phase, and this gas pressure increases anisotropy and promotes the growth of graphite crystals.

The pre-firing temperature needs to be below 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 ultra-high temperature HIP is required in the next step.
Graphite crystals do not precipitate even after treatment.

On the other hand, if the pre-calcination temperature is too low, the glassy carbon phase surrounding the graphite crystal phase will be fragile, making it impossible to produce large-sized graphite crystals.

For this reason, the pre-firing temperature is set at a residual hydrogen concentration of 50 to 50.
It is preferable that the amount is within the range of 00 ppm.

[Example code] Examples of the present invention will be described in more detail below.

In the present invention, a single crystal of graphite is deposited inside the molded body in a state where the entire surface is surrounded by glassy carbon. Therefore,
It is necessary to make the surface of the compact into glassy carbon by pre-firing, but thermosetting resins that become glassy carbon after pre-firing include phenolic resins, furan-based resins, etc., which can be obtained in powder form. resin, xylene resin,
There are melamine resins, aniline resins, etc. Those obtained in aqueous or oily form include resol and novolac type phenol formaldehyde resins, furan resins,
There are xylene resins, melamine resins, aniline resins, etc.

First, these thermosetting resins are molded into a predetermined shape by a known method. Examples of this molding method include, for example, pouring liquid thermosetting resin into a frame to form a mold, or pressing powdered thermosetting resin using a mold in cold and hot conditions. There is a way.

Next, this thermosetting resin molded body is heated in an inert gas atmosphere such as N2 or Ar gas until the residual hydrogen concentration of the molded body is 50~50.
Preliminary firing is performed by heating to a concentration of 5000 ppm.

After that, the pre-fired sample was subjected to ultra-high temperature HIP,
HIP treatment is performed under conditions of 2000 to 3000°C and 1000 to 3000 atm. At this time, it is effective to carry out the treatment in a pressure-first pattern in which the pressure is increased to a predetermined pressure while the treatment temperature is maintained below the pre-firing temperature, and then the temperature is increased to a predetermined temperature. If the temperature and pressure are increased at the same time, the material will be heated to a temperature range where hydrogen, etc. will be generated even though the pressure is insufficient, and as a result, components that will graphitize from the low-molecular hydrocarbons will be released. , precipitation of graphite crystals is less likely to occur.

In addition to the method of manufacturing from a single thermosetting resin, it is also possible to mold a graphitizable carbon precursor such as petroleum coke or mesoface pitch surrounded by a non-graphitizable carbon precursor such as a thermosetting resin. After that, there is also a method of similarly performing preliminary firing and ultra-high temperature HIP.

Next, the results of actually producing graphite crystals using the method of the present invention will be explained.

A powdered phenol formaldehyde resin was molded into a shape with a diameter of 80 mm and a thickness of 6 mm using a hot press. Then, the residual hydrogen concentration in nitrogen gas is (1)
5100ppm (2) 200ppm (3) 25p
After pre-firing the three compacts to a temperature of 255θ using ultra-high temperature HIP,
℃ and 2000 atm. As a result, various characteristics such as presence or absence of precipitation of graphite phase are shown in Table 1 below. If the pre-calcination temperature is lower than the temperature at which the residual hydrogen concentration is 5000 ppm, the glassy carbon phase will be brittle and a dense graphite crystal phase will not be obtained. In addition, precipitation of graphite phase does not occur at such high temperatures that the residual hydrogen concentration is lower than 50 ppm.

Example 2 - A molded body molded in the same manner as in Example 1 was molded with a residual hydrogen concentration of 20
After pre-calcining to 0 ppm, treatment was performed at 2550° C. and 2000 atm using HIP.

At this time, the temperature increase rate is 500℃/hr (1) Pressure increase to 2000 atm at pre-firing temperature (pressure advance) (2) 1800℃
HIP treatment was performed under various conditions of 2000 atm (simultaneous temperature and pressure increase). The results are shown in Table 2 below.

Table 1 Table 2 Table 2
A molded body with a diameter of 40 mm and a thickness of 4 mm was obtained. After pre-firing this molded body, it is heated to 2500℃ using ultra-high temperature HIP.
and 2,000 atmospheres of pressure, with a diameter of 35 mff1.
The thickness is 2.3111! A graphite crystal with a bulk density of 2.15 was obtained.

Example 4 Phenol formaldehyde resin powder was hot-pressed into (1) an outer diameter of 80mm, an inner diameter of 60mm, and a height of 1mm.
50 mm pipe shape, (2) width 50 mm, 13 rows 50III+, height 150 mm (thickness N 5 m
m ) box shape, (3) diameter 200mm, thickness 6mI
Three types of I+ discs were formed, pre-fired, and then subjected to ultra-high temperature HIP treatment. The shape of the obtained graphite crystal is as follows.

(1) When formed into a pipe shape, the outer diameter is 651 mm, the inner diameter is 60 mm, and the height is 115 mm. (2) When formed into a box shape, the width is 35 mm, the depth is 35 m + n, and the height is 115 mm (
3) When molded into a disk shape, the diameter was 1551 m and the thickness was 2.3 + I1 m. In this way, an extremely large graphite crystal was obtained.

[Effects of the Invention] According to the present invention, since hot isostatic pressure treatment is performed after preliminary firing, highly oriented graphite crystals used in X-ray or neutron beam monochromators and as a host material for graphite intercalation compounds can be rapidly produced. and can be manufactured at low cost.

Therefore, according to the present invention, it is possible to stably supply large-sized graphite crystals, and it is possible to supply sputtering targeters 1 to 1 for electronic materials, graphite wafers for epitaxial growth, and substrates with excellent thermal and electrical conductivity. It has become possible to develop new applications such as materials, artificial heart valves with low thrombogenicity, and sliding members such as magnetic head base materials.

Furthermore, it becomes possible to manufacture graphite crystals in shapes such as pipes, boxes, etc., and it is possible to supply extremely useful materials for applications that were previously impossible.

Claims (5)

[Claims] (1) A method comprising the steps of pre-calcining a thermosetting resin molded body and finishing the process with hydrogen remaining, and subjecting the pre-calcined 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 the preliminary firing step is completed when the residual hydrogen concentration of the compact is 50 to 5000 ppm. (3) The hot isostatic pressure treatment is carried out at 2000 to 300
The method for producing highly oriented graphite crystals according to claim 1 or 2, characterized in that the treatment is carried out at 0° C. and at 1,000 to 3,000 atmospheres. (4) The hot isostatic pressing treatment is characterized in that the pressure is increased to a predetermined pressure at a temperature below the pre-firing temperature, and then the temperature is raised to a predetermined temperature. A method for producing highly oriented graphite crystals. (5) A thermosetting resin molded body is used, in which the graphitizable carbon precursor is surrounded by a thermosetting resin carbon precursor. A method for producing highly oriented graphite crystals as described in .