JPH0517119A - Diamond particle and production thereof - Google Patents

Abstract

PURPOSE:To produce good crystalline spherical diamond particles at a high speed in a state free from troubles such as the carbonization and gasification of a thermocouple radiator and a substrate material by growing diamond layers on the surfaces of polycrystalline diamond particles in a specific reaction atmosphere. CONSTITUTION:A carbonaceous (e.g. highly oriented graphite) substrate 7, an inner heater 3 having a cooling pipe 5 for controlling temperature and a carbonaceous thermocouple radiator 2 above the substrate 7 are disposed in a reaction tube 1 equipped with a cooling pipe 4. An inspection hole 6 and lines for charging and discharging mixed gases are further disposed at the upper and lower parts of the reaction tube, respectively. Polycrystalline diamond particles having diameters of 0.25-40mum are placed on the substrate 7, and an inert gas such as argon is charged in the tube. The inert gas is discharged and subsequently a mixture comprising prescribed volumes of a hydrocarbon gas and hydrogen gas is charged in the tube. The pressure of the gas mixture is controlled to 1-10 atmospheric pressure by a sensor 9, mass flow controllers 8 and a valve 10. The radiator 2 and the substrate 7 are maintained at 1800-2200 deg.C and at 700-900 deg.C, respectively, until diamond layers formed on the polycrystalline diamond particles reach a desired thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond particle which has a polycrystalline diamond particle as a nucleus and has diamond grown on its surface by a chemical vapor deposition method and which can be used for polishing, cutting and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Compared to single crystal diamond, polycrystalline diamond synthesized by the impact compression method has fine primary particles constituting the particles that are gradually broken from the surface of the particle.
New micro-grinding points appear as they are missing, and the missing particles and the original particles also have a blocky and rounded shape, so scratches (scratches) on the work piece when used for cutting, etc. Since it is difficult to enter, it is used for ultra-precision machining of magnetic heads and hard disks, but its sharpness makes it unusable in fields that require high cutting and polishing performance. It is limited. In addition, since the synthesis time of polycrystalline diamond obtained by the impact compression method is as short as several microseconds to several tens of microseconds, it is difficult to control the diameter of diamond particles to be synthesized, and the size thereof is comparatively submicron to 50 μm. It is small and has the problem that the particles are too fine to be used for polishing, cutting, etc. Furthermore, because the mechanical strength of polycrystalline diamond is weak, it can be combined with resin, metal and ceramics as it is, It is difficult to use for wheels and cutters. Means such as coating metal on polycrystalline diamond powder have been attempted to cover these drawbacks.

[0003]

The problem to be solved by the present invention is to improve the strength, shape, size, etc. of particles, which are the drawbacks of polycrystalline diamond by the impact compression method, and enhance the polishing property and the cutting property. At the same time, it is to facilitate the compounding with various materials.

[0004]

Means for Solving the Problems As a result of diligent studies on a method for improving the strength of polycrystalline diamond particles, the present inventors have found that a thermoelectron emitting material and a substrate of a specific material are used and a reaction atmosphere under a specific condition is used. It was found that the diamond layer by the chemical vapor deposition method can be grown on the surface of the polycrystalline diamond particles by the treatment with, and the strength and the like can be improved, and the present invention has been completed. That is,
The present invention is directed to surface-modified diamond particles characterized in that a polycrystalline diamond particle synthesized by an impact compression method is coated with a diamond layer grown by a chemical vapor deposition method on the surface thereof, and a pressure of 1 atm to 10 atm. Polycrystalline diamond particles synthesized by the impact compression method placed on a carbonaceous substrate by thermally decomposing a mixed gas consisting of hydrocarbon and hydrogen by a thermoelectron method using a carbonaceous thermoelectron emitting material under a pressure atmosphere. Is a method for producing surface-modified diamond particles, which comprises growing diamond by chemical vapor deposition on the surface of.

As a method for growing diamond by the chemical vapor deposition method, a mixed gas of hydrocarbon and hydrogen is thermally decomposed using a thermoelectron emitting material such as tungsten filament to generate nuclei on a heated substrate. , A method of growing (JP-A-58-91100), and a method of thermally decomposing with discharge energy such as microwave plasma (JP-A-58-58).
No. 110494), and a method of thermally decomposing with high frequency plasma (Japanese Patent Laid-Open No. 58-135117). Among them, the thermoelectron method is simple in equipment and can be synthesized with a large surface area.
It is particularly suitable as the method for producing diamond particles of the present invention. In this case, if tungsten, which is usually used as a thermoelectron emitting material, is used, it is carbonized and deteriorated by the plasma gas generated by the thermal decomposition of the hydrocarbon mixed gas, and stable emission of thermoelectrons and continuous operation of equipment can be performed. It is preferable to use a carbonaceous thermionic emission material as the thermionic emission material because it may disappear. Further, as the substrate for mounting the polycrystalline diamond, it is necessary to use a material that does not directly adhere to the diamond produced by the chemical vapor deposition method. For this purpose, highly oriented graphite, graphite, glassy carbon are used. Although a carbonaceous substrate such as the above is used, highly oriented graphite is preferably used.

As an example of an embodiment of the present invention, a reaction container for growing diamond by a chemical vapor deposition method under a pressurized atmosphere as shown in FIG. 1 is used. This reaction vessel has the following structure. Inside the reaction tube 1 equipped with the external cooling tube 4, a cooling tube 5 for temperature control for placing the carbonaceous substrate 7
An internal heater 3 having a carbonaceous electron emitting material 2 is installed on the upper part of the inner heater 3
It is configured to have an introduction / exhaust line for mixed gas and the like at the bottom. First, polycrystalline diamond particles having a particle size of 0.25 μm to 40 μm synthesized by the impact compression method are placed on a carbonaceous substrate. As a method therefor, a slurry of diamond particles is prepared and dried on the substrate. Etc. may be used. The polycrystalline diamond particles synthesized by the impact compression method used at this time are preferably made uniform in particle size within a desired range in order to make the particle diameters of the particles after surface modification uniform. Further, as the polycrystalline diamond particles by the impact compression method used as a raw material, as a carbonaceous raw material,
Carbide of phenol aldehyde resin, carbide of pitch,
As a metal powder that uses PAN carbide, natural graphite, mesophase carbon, etc. to prevent temperature rise during impact,
Those manufactured using copper (Cu), iron (Fe), cobalt (Co), or the like are preferable. Among them, a polycrystalline diamond produced by combining a carbide of a phenolaldehyde resin and copper (Cu), a carbide of a phenolaldehyde resin and cobalt (Co), a carbide of a pitch and iron (Fe) is a chemical vapor phase. The growth rate of diamond by the method is unprecedented, which is particularly preferable.

After placing the substrate on the inner heater,
Purging with an inert atmosphere such as argon to remove air (particularly oxygen) inside the reaction vessel. After the purged gas is exhausted by a pump, a mixed gas composed of a hydrocarbon gas and a hydrogen gas adjusted to a predetermined amount as a reaction gas is introduced into the reaction vessel. As the hydrocarbon gas, if the number of carbon atoms is large, it is difficult to set conditions such as decomposition by thermoelectrons, so methane, ethane, ethylene, acetylene or the like having a small number of carbon atoms is used, but methane having a simple structure is particularly preferable. . The pressure inside the reaction vessel is monitored by a pressure sensor 9 on the gas discharge line side, and a mass flow controller 8 and a butterfly valve 10 for adjusting the flow rate of the mixed gas.
The pressure may be adjusted to a desired pressure by using. The pressure inside the reaction vessel is 1 to 10 atm. After the inside of the reaction vessel was purged with the mixed gas and the pressure became a steady state, the temperature of the carbonaceous thermionic emission material was changed to 1800 to 2200 ° C.
And the temperature of the carbonaceous substrate is maintained at 700 to 900 ° C.

When the internal pressure exceeds 10 atm, precipitation of non-diamond components such as carbonaceous matter in which Raman spectrum does not show the peak of diamond near 1336 cm ^-1 becomes remarkable, and when it is less than 1 atm. Undesirably slows down the growth rate of. Also,
The reason why the temperature is limited is that the decomposition of methane gas by the thermoelectron emitting material can be efficiently performed and the crystal growth for maintaining the spherical shape of the diamond particles on the substrate can be quickly performed. Such a state is maintained until the thickness of diamond by the chemical vapor deposition method reaches a desired thickness. The holding time varies depending on the quality of the polycrystalline diamond synthesized by the impact compression method used (that is, the difference in the starting materials used in the synthesis), the desired diamond thickness, the reaction conditions such as the pressure and temperature in the container, etc. However, the holding time may be set appropriately depending on the processing conditions. The diamond particles of the present invention have characteristics as a single crystal diamond in which the surface of polycrystalline diamond is coated with a layer of diamond by the chemical vapor deposition method of 1 μm to 300 μm depending on the treatment time, and high cutting performance and polishing performance are obtained. It is a suitable material for required applications such as diamond wheels and cutters.

[0009]

The present invention will be described in more detail with reference to the following examples. FIG. 1 is a sectional view of an embodiment of the device of the present invention. The main reaction vessel is an internal heater-3 having a cooling tube 5 for temperature control inside a reaction tube 1 having a diameter of 100 mm and a height of 300 mm, which is externally cooled by an external cooling tube 4, and a thermoelectron. The radiation material 2 is arranged, and the upper part of the reaction part has a peep window 6 for temperature measurement, and the lower part contains gas mixture or the like.
It has a pressure resistant structure in which a gas line for exhaust is arranged. In practice, after purifying the polycrystalline diamond synthesized by the impact compression method with oxygen plasma, the classified polycrystalline diamond particles having an average particle size of 10 μm are dispersed in an aqueous solution, and dried on a graphite substrate having a diameter of 40 mm to chemically It was used as the nucleus for diamond growth by the vapor phase method. Its weight was 0.2 g. This graphite substrate 7 is placed on the inner heater-3, and the distance between the graphite substrate and thermionic emission material 2 is set to 70.
mm.

First, the pressure inside the reaction vessel was reduced to 0.001 Torr, and then argon gas was introduced until the pressure inside the reaction vessel reached 1.2 atm. This operation was repeated 3 times to purge oxygen in the reaction vessel. Then, a mixed gas of hydrogen gas and methane gas having a methane gas concentration of 4% was introduced into the reaction vessel, and the pressure in the reaction vessel was adjusted to 2 atm. After the inside of the reaction vessel was purged with the mixed gas and the pressure reached a steady state, an electric current was passed through the thermoelectron emitting material 2 to maintain the temperature of the emitting material at 2000 ° C. At this time, the internal heater 3 having the cooling pipe 5
The temperature of the graphite substrate is kept at 800 ° C. This state was maintained for 0.5 hour, and diamond was grown on the surface of the polycrystalline diamond on the graphite substrate by a vapor phase method to modify the surface. Table 1 shows the results of producing diamond particles by using the polycrystalline diamond synthesized by the impact compression method by changing the kind of the carbonaceous raw material and the metal powder having the temperature lowering effect, by the above method and the method in which some conditions are changed. Show. The particle size and shape of the recovered diamond particles were evaluated by electron microscope observation, and the crystal quality was evaluated by microscopic Raman spectrum.

[0011]

[Table 1]

In Examples 1 to 5 shown in Table 1,
In each case, the diamond particles had a good spherical shape. FIG. 2 shows the Raman spectrum of polycrystalline particles synthesized by the impact compression method using the diamond particles obtained by growing diamond by the chemical vapor deposition method on the surface obtained in Example 1 and the synthetic raw material of Example 1. .
It is clear from FIG. 2 that the quality of the diamond crystal is modified by carrying out the method of the present invention. Further, when the polycrystalline diamond synthesized by using the synthetic raw material shown in Example 1 is used as the nucleus, the growth rate of the diamond particles by the chemical vapor deposition method is 20 μm / Hr, which is an unprecedented speed. Further, in Example 6, the growth rate of diamond particles by the chemical vapor deposition method was 23 μ / Hr. In the Raman spectrum of this diamond, although it contained a small amount of diamond-like carbon, it was a diamond single phase in X-ray diffraction.

[0013]

According to the method of the present invention, there is no problem of carbonization and gasification of the thermionic emission material and the substrate material, and spherical diamond having good crystallinity can be obtained at a high speed which has never been seen before. The use of polycrystalline diamond, whose use has been limited, can be expanded, contributing to the development of industry.

[0014]

[Brief description of drawings]

FIG. 1 is a sectional view of a reaction container of an embodiment of the apparatus of the present invention. 1 Reaction Tube 2 Thermionic Emissive Material 3 Internal Heater 4 External Cooling Tube 5 Cooling Tube 6 Viewing Window 7 Substrate 8 Mass Float Roller 9 Pressure Sensor 10 Butterfly Damper

FIG. 2 is a Raman spectrum of polycrystalline diamond synthesized by the impact compression method and the diamond obtained by carrying out the present invention using the polycrystalline diamond. A: Raman spectrum of polycrystalline diamond synthesized by impact compression method B: Raman spectrum of diamond obtained by carrying out the present invention

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masayuki Notoya             1st Kokufucho, Tochigi City, Tochigi Prefecture Mitsui Mining Co., Ltd.             Company Central Research Institute (72) Inventor Katsumitsu Tatsumoto             1st Kokufucho, Tochigi City, Tochigi Prefecture Mitsui Mining Co., Ltd.             Company Central Research Institute

Claims (2)

[Claims] 1. A diamond particle characterized in that the surface of polycrystalline diamond particle synthesized by an impact compression method is coated with a diamond layer grown by a chemical vapor deposition method. 2. A carbonaceous substrate is placed on a carbonaceous substrate by thermally decomposing a mixed gas of hydrocarbon and hydrogen by a thermoelectron method using a carbonaceous thermoelectron emitting material under a pressurized atmosphere of 1 to 10 atmospheres. A method for producing diamond particles, which comprises growing diamond by chemical vapor deposition on the surface of polycrystalline diamond particles synthesized by the impact compression method.